US20120019850A1 - Method for calibrating color image forming apparatus - Google Patents
Method for calibrating color image forming apparatus Download PDFInfo
- Publication number
- US20120019850A1 US20120019850A1 US13/244,171 US201113244171A US2012019850A1 US 20120019850 A1 US20120019850 A1 US 20120019850A1 US 201113244171 A US201113244171 A US 201113244171A US 2012019850 A1 US2012019850 A1 US 2012019850A1
- Authority
- US
- United States
- Prior art keywords
- color
- patches
- recording medium
- image forming
- patch
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Images
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/46—Colour picture communication systems
- H04N1/56—Processing of colour picture signals
- H04N1/60—Colour correction or control
- H04N1/603—Colour correction or control controlled by characteristics of the picture signal generator or the picture reproducer
- H04N1/6033—Colour correction or control controlled by characteristics of the picture signal generator or the picture reproducer using test pattern analysis
Definitions
- the present invention relates to a method for calibrating a color image forming apparatus such as a color printer or a color copier, and more particularly to a color signal conversion method for measuring a test chart outputted to improve the color stability of a color image forming apparatus using a chromaticity detecting means, and converting a color signal in a first color specification system that is the detection result of the chromaticity detecting means into a color signal in a second color specification system.
- the color image forming apparatus having a sensor for detecting the chromaticity of a patch on the recording medium after the forming and fixing of a monochromatic gradation patch of cyan (C), magenta (M), yellow (Y) or black (K) or a mixed color patch in which CMY are mixed on the recording medium (hereafter referred to as a color sensor) is well known (e.g., refer to U.S. Patent Application Publication No. 2003/049040).
- the color stability of a final output image formed on the recording medium is controlled by feeding back the detected result to a calibration table for correcting the exposure amount, the process conditions and the color gradation characteristics of an image forming portion.
- the output image of the color image forming apparatus may be detected by an external image reading apparatus or a chromaticity meter to make the same control.
- This color sensor uses a light emitting element having three or more kinds of light sources with different emission spectra of red (R), green (G) and blue (B), respectively, and a light receiving element with sensitivity in the visible region, or a light emitting element having a light source that emits light of white color (W) and a light receiving element formed with three or more filters of different spectral transmittances. Thereby, three or more kinds of outputs such as the RGB outputs are obtained.
- the color matching functions for the spectral sensitivity of RGB outputs of the color sensor and the XYZ chromaticity values as defined by the International Commission on Illumination do not have completely linear relations. Therefore, there is a problem that some differences may occur between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination.
- the XYZ chromaticity values calculated from the RGB output signals of the sensor for a certain patch and the XYZ chromacity values calculated from the spectral reflectance for the patch as defined by the International Commission on Illumination may be different in some cases. And this difference between the chromaticity values may vary in magnitude, depending on the color material or substratum color of the patch used in forming the patch.
- This invention has been achieved in the light of the above-mentioned problems, and it is an object of the invention to provide a color signal conversion method for reducing the differences occurring between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination in a simple manner when measuring a test chart outputted by the color image forming apparatus.
- the invention provides a color image calibration method as defined in the claims.
- FIG. 1 is a flowchart for converting the RGB outputs into XYZ chromaticity values according to an embodiment 1;
- FIG. 2 is a diagram showing the overall configuration of a color image forming apparatus according to embodiment 1;
- FIG. 3 is a view showing the electrophotographic color image forming apparatus in cross section according to embodiment 1;
- FIG. 4 is a block diagram showing the configuration of a color sensor and its peripheral devices according to embodiment 1;
- FIG. 5 is a view showing the color sensor in cross section according to embodiment 1;
- FIG. 6 is a diagram showing one example of the test chart in embodiment 1;
- FIG. 7 is a diagram ( 1 ) showing a connection method between color image forming apparatus and color image reading apparatus according to an embodiment 2;
- FIG. 8 is a diagram ( 2 ) showing a connection method between color image forming apparatus and color image reading apparatus according to embodiment 2;
- FIG. 9 is a view showing one example of a color image reading apparatus according to embodiment 2.
- FIG. 10 is a view showing one example of the test chart according to embodiment 2.
- FIG. 11 is a flowchart for converting the RGB outputs to XYZ chromaticity values according to an embodiment 3.
- FIG. 2 is a diagram showing the overall configuration of an electrophotographic color image forming apparatus according to embodiment 1.
- This color image forming apparatus comprises an image processing portion and an image forming portion.
- a process in the image processing portion will be described below.
- the RGB signals representing the colors of an image sent from a personal computer are converted into device RGB signals (hereafter referred to as “DevRGB”) in conformance with a color reproduction range of the color image forming apparatus.
- the converted DevRGB signals are converted into the CMYK signals indicating the colors of toner color materials for the color image forming apparatus, using a color separation table 112 .
- a calibration table 113 is a table for correcting the density-gradation characteristics intrinsic to the color image forming apparatus and employed to convert the CMYK signals into the C′M′Y′K′ signals in which the density-gradation characteristics are corrected.
- the C′M′Y′K′ signals are converted into the exposure times Tc, Tm, Ty and Tk of corresponding scanner portions 24 C, 24 M, 24 Y and 24 K (see FIG. 3 ).
- Main means involved in the image formation include charging means 122 , exposing means 123 , developing means 124 , transferring means 125 and fixing means 126 , which are controlled by a CPU 121 . Moreover, a color sensor 42 is connected to the CPU.
- FIG. 3 is a cross-sectional view of the color image forming apparatus.
- This apparatus is the color image forming apparatus of tandem type employing an intermediate transfer member 28 , which is one example of the electrophotographic color image forming apparatus, as shown in FIG. 3 .
- the operation of the image forming portion in the electrophotographic color image forming apparatus will be described below.
- the image forming portion forms an electrostatic latent image with exposing light applied based on an exposure time converted by the image processing portion, forming the monochromatic toner images by developing this electrostatic latent image, forming a multi-color toner image by superposing the monochromatic toner images, transferring this multi-color toner image onto a recording medium 11 , and fixing the multi-color toner image on the recording medium.
- the charging means 122 comprises four injection charge devices 23 Y, 23 M, 23 C and 23 K for charging the photosensitive members 22 Y, 22 M, 22 C and 22 K at the stations of yellow (Y), magenta (M), cyan (C) and black (K), the injection charge devices having respective sleeves 23 YS, 23 MS, 23 CS and 23 KS.
- the photosensitive members 22 Y, 22 M, 22 C and 22 K have an organic photoconductive layer applied on the outer periphery of an aluminum cylinder, and are rotated by a driving force of a drive motor, not shown.
- the photosensitive members 22 Y, 22 M, 22 C and 22 K are rotated in a counterclockwise direction along with an image forming operation by the drive motor.
- the exposing means 123 applies exposing light from the scanner portions 24 Y, 24 M, 24 C and 24 K onto the photosensitive members 22 Y, 22 M, 22 C and 22 K, selectively exposing the surfaces of the photosensitive members 22 Y, 22 M, 22 C and 22 K to form the electrostatic latent images.
- the developing means 124 comprises four developing devices 26 Y, 26 M, 26 C and 26 K for developing the images of yellow (Y), magenta (M), cyan (C) and black (K) at respective stations to visualize the electrostatic latent images, in which the developing devices are provided with the sleeves 26 YS, 26 MS, 26 CS and 26 KS. Each developing device 26 can be detachably attached.
- the transferring means 125 transfers the monochrome toner images, along with the rotation of the photosensitive members 22 Y, 22 M, 22 C and 22 K and the primary transfer rollers 27 Y, 27 M, 27 C and 27 K located oppositely, by rotating the intermediate transfer member 28 in a clockwise direction to transfer the monochrome toner images from the photosensitive members 22 to the intermediate transfer member 28 .
- the monochrome toner images are transferred onto the intermediate transfer member 28 efficiently. This operation is called a primary transfer.
- the transferring means 125 superposes the monochrome toner images on the intermediate transfer member 28 at respective stations, conveys the superposed multi-color toner image up to a secondary transfer roller 29 along with the rotation of the intermediate transfer member 28 , picks up and conveys a recording medium 11 from a sheet feeding tray 21 to the secondary transfer roller 29 , and transfers the multi-color toner image on the intermediate transfer member 28 onto the recording medium 11 .
- the toner image is electrostatically transferred by applying an appropriate bias voltage to the secondary transfer roller 29 . This operation is called a secondary transfer.
- the secondary transfer roller 29 contacts the recording medium 11 at a position 29 a, while transferring the multi-color toner image onto the recording medium 11 , and is spaced to a position 29 b after the printing process.
- the fixing means 126 comprises a fixing roller 32 for heating the recording medium 11 and a pressure roller 33 for pressing the recording medium 11 onto the fixing roller 32 to fuse and fix the transferred multi-color toner image on the recording medium 11 .
- the fixing roller 32 and the pressure roller 33 are hollow and internally comprise heaters 34 and 35 , respectively.
- a fixing apparatus 31 conveys the recording medium 11 holding the multi-color toner image onto the fixing roller 32 and the pressure roller 33 , and fixes the toner on the recording medium by applying heat and pressure.
- the recording medium 11 after the fixing of the toner is then discharged to a sheet discharge tray, not shown, by a sheet discharge roller, not shown, whereby the image forming operation is ended.
- Cleaning means 30 cleans the toner remaining on the intermediate transfer member 28 , in which after the transfer of the multi-color toner image of four colors formed on the intermediate transfer member 28 onto the recording medium 11 , waste toner is stored in a cleaner container.
- a color sensor 42 is disposed downstream of the fixing apparatus 31 on a conveying path of the recording medium, opposed to an image forming face of the recording medium 11 , detecting the color of a mixed color patch that, after fixing, is formed on the recording medium 11 . This detection process is for the purpose of outputting the RGB values. Disposed inside the color image forming apparatus, the color sensor can automatically detect the color before the sheet with image fixed is discharged to a sheet discharging portion.
- FIG. 4 is a block diagram showing the configuration of the color sensor 42 and its peripheral devices.
- the color sensor and its peripheral devices are a light emitting element 101 , a light receiving element 102 , an A/D converter 104 and a CPU 121 .
- the light emitting element 101 is a light source of the color sensor that emits light to a measurement object 103 .
- irregular light is reflected, as the reflection factor depends on a body color of the measurement object.
- the irregular reflected light enters the light receiving element 102 that converts light into an electric signal.
- an analog electric signal is converted into a digital electric signal by the A/D converter 104 .
- the digital electric signal is taken into the CPU 121 , and the XYZ chromaticity values are outputted through a linear conversion process as shown in formula (1).
- FIG. 5 is a cross-sectional view of the color sensor 42 .
- the color sensor 42 employs a white color LED 53 as the light emitting element 101 and a charge storage type sensor 54 a with on-chip filters for three or more colors, such as RGB, as the light receiving element 102 .
- Light from the white color LED 53 is made incident obliquely at an angle of 45° upon the recording medium 11 on which is formed the patch after fixing, and the intensity of irregular reflected light in a direction of 0° is detected by the charge storage type sensor 54 a with the RGB on-chip filters.
- a light receiving portion of the charge storage type sensor 54 a with RGB on-chip filters has independent pixels of RGB like 54 b.
- the light receiving element 102 may be a photodiode.
- a set of three pixels of RGB may be arranged multiply. Also, instead of the mentioned arrangement, the angle of incidence may be 0° and the angle of reflection may be 45°. Moreover, an LED for emitting light of three or more colors such as RGB and a sensor without filter may be combined.
- FIG. 6 is a diagram showing one example of a test chart detected by the color sensor 42 .
- a color stabilization control test chart 60 is a gradation patch pattern of gray that is the most important color in making the color balance, and composed of a gray gradation patch 61 of only black (K) and a process gray gradation patch 62 in which yellow (Y), magenta (M) and cyan (C) are mixed.
- the gray gradation patch 61 of only black (K) and the process gray gradation patch 62 which have the same chromaticity in the image processing portion of the image forming apparatus, are paired, such as 61 a and 62 a, 61 b and 62 b, 61 c and 62 c.
- the chromaticity of this patch is detected by the color sensor 42 , and is fed back to a calibration table so that there may be no color difference between the gray gradation patch 61 of only black (K) and the process gray gradation patch 62 which are paired.
- XYZ are XYZ chromaticity values calculated by converting the RGB outputs of the sensor
- r, g and b are sensor outputs
- A is a conversion matrix
- a is a matrix element.
- This method involves changing the matrix A in formula (1) for every attribute of patch.
- a gray gradation patch matrix A 1 of only black (K) and a process gray gradation patch matrix A 2 are set up.
- the matrices A 1 and A 2 are optimized to convert the RGB outputs of the sensor detecting the patch of each attribute into the XYZ chromaticity values.
- FIG. 1 is a flowchart for converting the RGB outputs of the sensor into the XYZ chromaticity values.
- step 211 it is determined whether or not the detected patch is gray gradation patch 61 of only black (K) or process gray gradation patch 62 . Since the patch format of the color stabilization control test chart 60 is fixed in the image forming apparatus, the determination may be made in the sequence of detecting the patch.
- step 211 If it is determined in step 211 that the detected patch is a gray gradation patch 61 of only black (K) because the patch is detected at an odd number in the color stabilization control test chart 60 , the RGB outputs of the sensor are converted into the XYZ chromaticity values, using the gray gradation patch matrix A 1 of only black (K), in accordance with formula (1), in step 212 .
- step 211 If it is determined in step 211 that the detected patch is the process gray gradation patch 62 , because the patch is detected at an even number in the color stabilization control test chart 60 , the RGB outputs of the sensor are converted into the XYZ chromaticity values, using the process gray gradation patch matrix A 2 , in accordance with formula (1), in step 213 .
- the number of measured patches is about 250 for the gray gradation patch of only black, and about 500 for the process gray gradation patch.
- the results are shown in Table 1:
- the numerical values as listed in the table are average values of chromaticity value differences occurring between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination. Both the XYZ values are converted into L*a*b* as defined by the International Commission on Illumination and then calculated as the color difference ( ⁇ E).
- This method is based on the premise that the attribute of a patch can be determined when detecting the patch.
- the attribute of a patch detected by the color sensor can be judged, and thus this method is applicable.
- the methods for converting the RGB outputs of the sensor into XYZ chromaticity values include a linear conversion method by matrix, a neural network method and a method using a look-up table.
- a linear conversion method by matrix e.g., a linear conversion method by matrix
- a neural network method e.g., a neural network method
- a method using a look-up table e.g., a linear conversion method by matrix
- a neural network method e.g., a method using a look-up table.
- an image forming apparatus not having a color sensor like color sensor 42 above implements color stabilization control equivalent to that described in embodiment 1, employing an external image reading apparatus, instead of color sensor 42 , and using a color conversion method that reduces the differences between the XYZ chromaticity values obtained by converting the RGB outputs of the external image reading apparatus and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination.
- FIG. 7 and FIG. 8 are diagrams showing a connection method between color image forming apparatus and color image reading apparatus.
- the color image forming apparatus and color image reading apparatus are directly connected, but in FIG. 8 , they are connected via a network.
- the color image reading apparatus like the color sensor, mounts a white color source and a sensor with the filters of three or more colors such as RGB, or light sources of three or more colors such as RGB and a sensor having sensitivity in the visible region, and outputs the RGB sensor signals.
- FIG. 9 is a view showing a flat bed image scanner as seen from above as one example of the color image reading apparatus. The of this apparatus operation will be described below.
- the user of the image reading apparatus sets a medium formed with the image on a platen 402 . Once the medium is set, the sensor 401 is moved in a direction as indicated by the arrow. The sensor proceeds in step operation, and reads the image one line at each step. By integrating these images of one line each, the entire image formed on one medium can be read.
- a monochrome gradation patch of cyan (C), magenta (M), yellow (Y) and black (K) or a patch in which CMY are mixed is formed on the recording medium, and the outputted recording medium formed with the patch is set on the color image reading apparatus to detect the chromaticity of the patch.
- FIG. 10 is a view showing one example of the test chart detected by the color image reading apparatus.
- a color stabilization control test chart 63 is a gradation patch pattern of gray, which is the most important color in making the color balance, and is composed of a gray gradation patch of only black (K) 61 and a process gray gradation patch 62 in which yellow (Y), magenta (M) and cyan (C) are mixed.
- the gray gradation patch 61 of only black (K) and the process gray gradation patch 62 which have the same chromaticity in the image processing portion of the image forming apparatus, are paired, such as 61 a and 62 a, 61 b and 62 b, 61 c and 62 c.
- a different point from the color sensor test chart as shown in FIG. 6 in embodiment 1 is that the patches 61 , 62 are arranged over the entire face of the recording medium 1 , since the color image reading apparatus can read the images on the overall face of the recording medium at one time.
- the color conversion method for reducing the differences between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination is identical to the method shown in FIG. 1 in embodiment 1.
- step 211 in FIG. 1 it is determined whether the detected patch is a gray gradation patch of only black (K) like patch 61 or a process gray gradation patch like patch 62 .
- the image reading apparatus can selectively detect the gray gradation patch of only black (K) 61 or process gray gradation patch 62 using patch position coordinate information of the color stabilization control test chart 63 .
- the image reading apparatus is connected to the image forming apparatus, and notifies the image reading apparatus of the patch position coordinate information of the color stabilization control test chart 63 . In this way the determination in step 211 in FIG. 1 is made.
- the methods for converting the RGB outputs of the sensor into XYZ chromaticity values include a linear conversion method using a matrix, a neural network method and a method using a look-up table.
- a linear conversion method using a matrix e.g., a linear conversion method using a matrix
- a neural network method e.g., a neural network method
- a look-up table e.g., a look-up table.
- the color image forming apparatus having no color sensor is connected to the color image reading apparatus, and by changing various parameters for use in converting the RGB outputs of the color image reading apparatus into XYZ chromaticity values for every attribute of patch, it is possible to reduce the differences between the XYZ chromaticity values obtained by converting the RGB outputs of the color reading apparatus and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination, whereby the precision of color stabilization control using the XYZ chromaticity values can be improved.
- the method for changing the matrix for use in converting the RGB outputs into XYZ chromaticity values as described in embodiments 1 and 2 is shown, in which the matrix is changed depending on the attribute of the patch, i.e., whether the patch is a gray gradation patch of only black (K) or a process gray gradation patch, and by detecting the substratum color of patch, namely, the color of the recording medium, to judge the color area.
- FIG. 11 is a flowchart for converting the RGB outputs into XYZ chromaticity values in embodiment 3.
- step 221 the recording medium 11 in an area where the patch is not formed as the substratum color of patch is detected, and it is judged into which of (1) to (6) the sizes of the RGB outputs are classified: (1) R>G>B, (2) R>B>G, (3) B>R>G, (4) B>G>R, (5) G>R>B and (6) G>B>R.
- step 222 it is determined whether the detected patch is a gray gradation patch of only black (K) like patch 61 or a process gray gradation patch like patch 62 .
- the patch format of color stabilization control test charts 60 , 63 is fixed in the image forming apparatus, whereby the determination is made based on the sequence or position of detecting the patch.
- step 222 If it is determined in step 222 that the detected patch is a gray gradation patch of only black (K) like patch 61 , the RGB outputs of the sensor are converted into XYZ chromaticity values in accordance with formula (1), employing matrix A 1 for gray gradation patch of only black (K) in step 223 .
- step 222 If it is determined in step 222 that the detected patch is a process gray gradation patch like patch 62 , the RGB outputs of the sensor are converted into XYZ chromaticity values in accordance with formula (1), employing matrix A 2 for process gray gradation patch in step 224 .
- the procedure goes respectively tone of flows F 302 to F 306 .
- the matrix for gray gradation patch of only black (K) is A 3
- the matrix for process gray gradation patch is A 4 , these matrixes differing from A 1 and A 2 in F 301 , and the others being the same.
- the matrix for gray gradation patch of only black (K) is A 5
- the matrix for process gray gradation patch is A 6
- the matrix for gray gradation patch of only black (K) is A 7
- the matrix for process gray gradation patch is A 8
- the matrix for gray gradation patch of only black (K) is A 9
- the matrix for process gray gradation patch is A 10
- the matrix for gray gradation patch of only black (K) is A 11
- the matrix for process gray gradation patch is A 12 .
- the color of patch formed on the recording medium 11 is affected by the substratum color of patch, namely, the color of the recording medium 11 , without regard to the color material used for the gray gradation patch of only black (K) or process gray gradation patch.
- the color of patch formed on a red recording medium is redder than the color of the same patch formed on a white recording medium. That is, even when the color image forming apparatus forms the same patch, the spectral reflectance of the patch may differ according to the color of the recording medium on which the patch is formed.
- the color areas of substratum color of patch are classified into six attributes, but the classification method for attributes is not limited to the method shown herein.
- the methods for converting the RGB outputs of the sensor into XYZ chromaticity values include a linear conversion method by means of a matrix, a neural network method and a method using a look-up table.
- a linear conversion method by means of a matrix
- a neural network method and a method using a look-up table.
- any method if the color area of the recording medium and the attribute of the patch are judged, it is possible to reduce the differences between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination by changing the weight of connection between neurons for use in the neural network for every color area of the recording medium and every attribute of patch, or using the look-up table.
Abstract
A calibration method for calibrating a color image forming apparatus includes detecting the color of a patch formed on a recording medium by the color image forming apparatus using a color sensor, converting a detected color signal in a first color specification system into a color signal in a second color specification system, and adjusting at least one of the image forming conditions for the color image forming apparatus, based on the color signal converted in the conversion step, where the conversion conditions in the color signal conversion are different depending on the attributes of the patch.
Description
- 1. Field of the Invention
- The present invention relates to a method for calibrating a color image forming apparatus such as a color printer or a color copier, and more particularly to a color signal conversion method for measuring a test chart outputted to improve the color stability of a color image forming apparatus using a chromaticity detecting means, and converting a color signal in a first color specification system that is the detection result of the chromaticity detecting means into a color signal in a second color specification system.
- 2. Background of the Related Art
- Recently, there has been increasing demand for a color image forming apparatus of the electrophotography type or the inkjet type, such as a color printer or a color copier, having high color stability of its output image.
- Thus, the color image forming apparatus having a sensor for detecting the chromaticity of a patch on the recording medium after the forming and fixing of a monochromatic gradation patch of cyan (C), magenta (M), yellow (Y) or black (K) or a mixed color patch in which CMY are mixed on the recording medium (hereafter referred to as a color sensor) is well known (e.g., refer to U.S. Patent Application Publication No. 2003/049040).
- In this color image forming apparatus, the color stability of a final output image formed on the recording medium is controlled by feeding back the detected result to a calibration table for correcting the exposure amount, the process conditions and the color gradation characteristics of an image forming portion. Also, the output image of the color image forming apparatus may be detected by an external image reading apparatus or a chromaticity meter to make the same control.
- This color sensor uses a light emitting element having three or more kinds of light sources with different emission spectra of red (R), green (G) and blue (B), respectively, and a light receiving element with sensitivity in the visible region, or a light emitting element having a light source that emits light of white color (W) and a light receiving element formed with three or more filters of different spectral transmittances. Thereby, three or more kinds of outputs such as the RGB outputs are obtained.
- In the color image forming apparatus of the ink jet type, since the color balance changes depending on a change in the ink discharge amount with the lapse of time, an environmental difference from one place or time of use to another, or the individual differences among ink cartridges, the color gradation characteristics cannot be kept constant. Thus, some color image forming apparatuses effect color stabilization control by substituting a color sensor for the ink head and detecting the chromaticity of a patch on the recording medium.
- In the above color stabilization control, there is a process of converting the sensor outputs, which are RGB values, into XYZ chromaticity values as defined by the International Commission on Illumination (CIE). For this conversion, the prior art has used a method employing a matrix, as well as a method using a look-up table.
- However, the above prior art had the following problems.
- Generally, the color matching functions for the spectral sensitivity of RGB outputs of the color sensor and the XYZ chromaticity values as defined by the International Commission on Illumination do not have completely linear relations. Therefore, there is a problem that some differences may occur between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination.
- That is, the XYZ chromaticity values calculated from the RGB output signals of the sensor for a certain patch and the XYZ chromacity values calculated from the spectral reflectance for the patch as defined by the International Commission on Illumination may be different in some cases. And this difference between the chromaticity values may vary in magnitude, depending on the color material or substratum color of the patch used in forming the patch.
- This invention has been achieved in the light of the above-mentioned problems, and it is an object of the invention to provide a color signal conversion method for reducing the differences occurring between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination in a simple manner when measuring a test chart outputted by the color image forming apparatus.
- In order to accomplish the above object, the invention provides a color image calibration method as defined in the claims.
- With this invention, it is possible to reduce the differences occurring between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination by changing various kinds of parameters used in converting the RGB outputs of the sensor into the XYZ chromaticity values depending on the attribute of patch. And the precision of color stability control using the XYZ chromaticity values can be improved.
- Other objects, constitutions and effects of the invention will be apparent from the following detailed description of the invention and the drawings.
-
FIG. 1 is a flowchart for converting the RGB outputs into XYZ chromaticity values according to anembodiment 1; -
FIG. 2 is a diagram showing the overall configuration of a color image forming apparatus according toembodiment 1; -
FIG. 3 is a view showing the electrophotographic color image forming apparatus in cross section according toembodiment 1; -
FIG. 4 is a block diagram showing the configuration of a color sensor and its peripheral devices according toembodiment 1; -
FIG. 5 is a view showing the color sensor in cross section according toembodiment 1; -
FIG. 6 is a diagram showing one example of the test chart inembodiment 1; -
FIG. 7 is a diagram (1) showing a connection method between color image forming apparatus and color image reading apparatus according to anembodiment 2; -
FIG. 8 is a diagram (2) showing a connection method between color image forming apparatus and color image reading apparatus according toembodiment 2; -
FIG. 9 is a view showing one example of a color image reading apparatus according toembodiment 2; -
FIG. 10 is a view showing one example of the test chart according toembodiment 2; and -
FIG. 11 is a flowchart for converting the RGB outputs to XYZ chromaticity values according to anembodiment 3. - The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.
-
FIG. 2 is a diagram showing the overall configuration of an electrophotographic color image forming apparatus according toembodiment 1. This color image forming apparatus comprises an image processing portion and an image forming portion. - First, a process in the image processing portion will be described below. With a color matching table 111, the RGB signals representing the colors of an image sent from a personal computer are converted into device RGB signals (hereafter referred to as “DevRGB”) in conformance with a color reproduction range of the color image forming apparatus. Then, the converted DevRGB signals are converted into the CMYK signals indicating the colors of toner color materials for the color image forming apparatus, using a color separation table 112. A calibration table 113 is a table for correcting the density-gradation characteristics intrinsic to the color image forming apparatus and employed to convert the CMYK signals into the C′M′Y′K′ signals in which the density-gradation characteristics are corrected. Moreover, with a PWM (Pulse Width Modulation) table 114, the C′M′Y′K′ signals are converted into the exposure times Tc, Tm, Ty and Tk of
corresponding scanner portions FIG. 3 ). - Next, the image forming portion will be described. Main means involved in the image formation include charging means 122, exposing
means 123, developingmeans 124, transferringmeans 125 and fixing means 126, which are controlled by aCPU 121. Moreover, acolor sensor 42 is connected to the CPU. -
FIG. 3 is a cross-sectional view of the color image forming apparatus. This apparatus is the color image forming apparatus of tandem type employing anintermediate transfer member 28, which is one example of the electrophotographic color image forming apparatus, as shown inFIG. 3 . Referring toFIG. 3 , the operation of the image forming portion in the electrophotographic color image forming apparatus will be described below. - The image forming portion forms an electrostatic latent image with exposing light applied based on an exposure time converted by the image processing portion, forming the monochromatic toner images by developing this electrostatic latent image, forming a multi-color toner image by superposing the monochromatic toner images, transferring this multi-color toner image onto a
recording medium 11, and fixing the multi-color toner image on the recording medium. - The charging means 122 comprises four
injection charge devices photosensitive members - The
photosensitive members photosensitive members - The exposing
means 123 applies exposing light from thescanner portions photosensitive members photosensitive members - The developing
means 124 comprises four developingdevices - The transferring means 125 transfers the monochrome toner images, along with the rotation of the
photosensitive members primary transfer rollers intermediate transfer member 28 in a clockwise direction to transfer the monochrome toner images from the photosensitive members 22 to theintermediate transfer member 28. By applying an appropriate bias voltage to the primary transfer rollers 27 and giving a difference between the rotating speed of the photosensitive members 22 and the rotating speed of theintermediate transfer member 28, the monochrome toner images are transferred onto theintermediate transfer member 28 efficiently. This operation is called a primary transfer. - Moreover, the transferring means 125 superposes the monochrome toner images on the
intermediate transfer member 28 at respective stations, conveys the superposed multi-color toner image up to a secondary transfer roller 29 along with the rotation of theintermediate transfer member 28, picks up and conveys arecording medium 11 from a sheet feeding tray 21 to the secondary transfer roller 29, and transfers the multi-color toner image on theintermediate transfer member 28 onto therecording medium 11. The toner image is electrostatically transferred by applying an appropriate bias voltage to the secondary transfer roller 29. This operation is called a secondary transfer. The secondary transfer roller 29 contacts therecording medium 11 at aposition 29 a, while transferring the multi-color toner image onto therecording medium 11, and is spaced to aposition 29 b after the printing process. - The fixing means 126 comprises a fixing
roller 32 for heating therecording medium 11 and apressure roller 33 for pressing therecording medium 11 onto the fixingroller 32 to fuse and fix the transferred multi-color toner image on therecording medium 11. The fixingroller 32 and thepressure roller 33 are hollow and internally compriseheaters apparatus 31 conveys therecording medium 11 holding the multi-color toner image onto the fixingroller 32 and thepressure roller 33, and fixes the toner on the recording medium by applying heat and pressure. - The
recording medium 11 after the fixing of the toner is then discharged to a sheet discharge tray, not shown, by a sheet discharge roller, not shown, whereby the image forming operation is ended. - Cleaning means 30 cleans the toner remaining on the
intermediate transfer member 28, in which after the transfer of the multi-color toner image of four colors formed on theintermediate transfer member 28 onto therecording medium 11, waste toner is stored in a cleaner container. - A
color sensor 42 is disposed downstream of the fixingapparatus 31 on a conveying path of the recording medium, opposed to an image forming face of therecording medium 11, detecting the color of a mixed color patch that, after fixing, is formed on therecording medium 11. This detection process is for the purpose of outputting the RGB values. Disposed inside the color image forming apparatus, the color sensor can automatically detect the color before the sheet with image fixed is discharged to a sheet discharging portion. -
FIG. 4 is a block diagram showing the configuration of thecolor sensor 42 and its peripheral devices. The color sensor and its peripheral devices are a light emittingelement 101, alight receiving element 102, an A/D converter 104 and aCPU 121. Thelight emitting element 101 is a light source of the color sensor that emits light to ameasurement object 103. Then, irregular light is reflected, as the reflection factor depends on a body color of the measurement object. The irregular reflected light enters thelight receiving element 102 that converts light into an electric signal. Moreover, an analog electric signal is converted into a digital electric signal by the A/D converter 104. And the digital electric signal is taken into theCPU 121, and the XYZ chromaticity values are outputted through a linear conversion process as shown in formula (1). -
FIG. 5 is a cross-sectional view of thecolor sensor 42. Thecolor sensor 42 employs awhite color LED 53 as thelight emitting element 101 and a chargestorage type sensor 54 a with on-chip filters for three or more colors, such as RGB, as thelight receiving element 102. Light from thewhite color LED 53 is made incident obliquely at an angle of 45° upon therecording medium 11 on which is formed the patch after fixing, and the intensity of irregular reflected light in a direction of 0° is detected by the chargestorage type sensor 54 a with the RGB on-chip filters. A light receiving portion of the chargestorage type sensor 54 a with RGB on-chip filters has independent pixels of RGB like 54 b. Thelight receiving element 102 may be a photodiode. A set of three pixels of RGB may be arranged multiply. Also, instead of the mentioned arrangement, the angle of incidence may be 0° and the angle of reflection may be 45°. Moreover, an LED for emitting light of three or more colors such as RGB and a sensor without filter may be combined. -
FIG. 6 is a diagram showing one example of a test chart detected by thecolor sensor 42. A color stabilizationcontrol test chart 60 is a gradation patch pattern of gray that is the most important color in making the color balance, and composed of a gray gradation patch 61 of only black (K) and a process gray gradation patch 62 in which yellow (Y), magenta (M) and cyan (C) are mixed. The gray gradation patch 61 of only black (K) and the process gray gradation patch 62, which have the same chromaticity in the image processing portion of the image forming apparatus, are paired, such as 61 a and 62 a, 61 b and 62 b, 61 c and 62 c. The chromaticity of this patch is detected by thecolor sensor 42, and is fed back to a calibration table so that there may be no color difference between the gray gradation patch 61 of only black (K) and the process gray gradation patch 62 which are paired. - To convert the RGB outputs of the sensor into the XYZ chromaticity values, the following formula (1) is employed:
-
- where XYZ are XYZ chromaticity values calculated by converting the RGB outputs of the sensor, r, g and b are sensor outputs, A is a conversion matrix, and a is a matrix element.
- In the following, a color conversion method for reducing the differences between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor in this embodiment and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination is given.
- This method involves changing the matrix A in formula (1) for every attribute of patch. A gray gradation patch matrix A1 of only black (K) and a process gray gradation patch matrix A2 are set up. The matrices A1 and A2 are optimized to convert the RGB outputs of the sensor detecting the patch of each attribute into the XYZ chromaticity values.
-
FIG. 1 is a flowchart for converting the RGB outputs of the sensor into the XYZ chromaticity values. - In step 211, it is determined whether or not the detected patch is gray gradation patch 61 of only black (K) or process gray gradation patch 62. Since the patch format of the color stabilization
control test chart 60 is fixed in the image forming apparatus, the determination may be made in the sequence of detecting the patch. - If it is determined in step 211 that the detected patch is a gray gradation patch 61 of only black (K) because the patch is detected at an odd number in the color stabilization
control test chart 60, the RGB outputs of the sensor are converted into the XYZ chromaticity values, using the gray gradation patch matrix A1 of only black (K), in accordance with formula (1), in step 212. - If it is determined in step 211 that the detected patch is the process gray gradation patch 62, because the patch is detected at an even number in the color stabilization
control test chart 60, the RGB outputs of the sensor are converted into the XYZ chromaticity values, using the process gray gradation patch matrix A2, in accordance with formula (1), in step 213. - Next, the experimental results are shown below in which the differences between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination could be reduced by changing the matrix A in formula (1) for every attribute of patch.
- In the experiment, because the relations between the spectral sensitivity of the RGB outputs of the color sensor and the XYZ chromaticity values as defined by the International Commission on Illumination are not completely linear, formula (2) using the RGB outputs of the sensor up to the third order is employed, instead of formula (1), to decrease the influence of not completely linear relations as much as possible:
-
- The number of measured patches is about 250 for the gray gradation patch of only black, and about 500 for the process gray gradation patch. The results are shown in Table 1:
-
TABLE 1 Experimental results Gray gradation patch Process gray ΔE(Ave.) of only black gradation patch Matrix A is changed for 0.53 0.99 every attribute of patch Matrix A is common for 3.90 1.53 all patches - The numerical values as listed in the table are average values of chromaticity value differences occurring between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination. Both the XYZ values are converted into L*a*b* as defined by the International Commission on Illumination and then calculated as the color difference (ΔE).
- The above results reveal that the method for changing the matrix A for every attribute of patch that is the kind of color material for use, whether the measured patch is gray gradation patch of only black or process gray gradation patch, can make smaller the color difference (ΔE) occurring between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination. This is because the non-linearity of the color matching functions for the spectral sensitivity of the RGB outputs of the color sensor and the XYZ chromaticity values as defined by the International Commission on Illumination is reduced in the extent of influence by changing the matrix A for every attribute of patch.
- Accordingly, it is possible to reduce the color differences between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination by employing the color conversion method for changing the matrix A for every attribute of patch.
- This method is based on the premise that the attribute of a patch can be determined when detecting the patch. In an image forming apparatus having a color sensor, as described, because the patch is detected in the sequence of forming the image, the attribute of patch detected by the color sensor can be judged, and thus this method is applicable.
- Though the RGB outputs of the sensor are converted into the XYZ chromaticity values here, it is apparent that the method as described in connection with this embodiment is effective when the color matching function in two different color specifications systems has non-linearity.
- Moreover, there are two attributes here, including the gray gradation patch of only black (K) and the process gray gradation patch in which yellow (Y), magenta (M) and cyan (C) are mixed, but the classification method for attributes is not limited to the combination of color materials as indicated here.
- Moreover, the methods for converting the RGB outputs of the sensor into XYZ chromaticity values include a linear conversion method by matrix, a neural network method and a method using a look-up table. In any method, if the attribute of the patch is judged, it is possible to reduce the differences between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination, by changing the weight of connection between neurons for use in the neural network for every attribute of patch, or by changing the contents of the look-up table.
- As described above, by changing various parameters for use in converting the RGB outputs of the sensor into the XYZ chromaticity values for every attribute of patch, it is possible to reduce the differences between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination, whereby the precision of color stabilization control using the XYZ chromaticity values can be improved.
- In
embodiment 2, an image forming apparatus not having a color sensor likecolor sensor 42 above implements color stabilization control equivalent to that described inembodiment 1, employing an external image reading apparatus, instead ofcolor sensor 42, and using a color conversion method that reduces the differences between the XYZ chromaticity values obtained by converting the RGB outputs of the external image reading apparatus and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination. -
FIG. 7 andFIG. 8 are diagrams showing a connection method between color image forming apparatus and color image reading apparatus. InFIG. 7 , the color image forming apparatus and color image reading apparatus are directly connected, but inFIG. 8 , they are connected via a network. The color image reading apparatus, like the color sensor, mounts a white color source and a sensor with the filters of three or more colors such as RGB, or light sources of three or more colors such as RGB and a sensor having sensitivity in the visible region, and outputs the RGB sensor signals. -
FIG. 9 is a view showing a flat bed image scanner as seen from above as one example of the color image reading apparatus. The of this apparatus operation will be described below. The user of the image reading apparatus sets a medium formed with the image on aplaten 402. Once the medium is set, thesensor 401 is moved in a direction as indicated by the arrow. The sensor proceeds in step operation, and reads the image one line at each step. By integrating these images of one line each, the entire image formed on one medium can be read. - In this embodiment, a monochrome gradation patch of cyan (C), magenta (M), yellow (Y) and black (K) or a patch in which CMY are mixed is formed on the recording medium, and the outputted recording medium formed with the patch is set on the color image reading apparatus to detect the chromaticity of the patch. By feeding back the detection result to the calibration table for correcting the exposure amount, process conditions and the color gradation characteristics of the image forming portion, the color stabilization control of the final output image equivalent to that described in connection with
embodiment 1 can be achieved. -
FIG. 10 is a view showing one example of the test chart detected by the color image reading apparatus. A color stabilizationcontrol test chart 63 is a gradation patch pattern of gray, which is the most important color in making the color balance, and is composed of a gray gradation patch of only black (K) 61 and a process gray gradation patch 62 in which yellow (Y), magenta (M) and cyan (C) are mixed. The gray gradation patch 61 of only black (K) and the process gray gradation patch 62, which have the same chromaticity in the image processing portion of the image forming apparatus, are paired, such as 61 a and 62 a, 61 b and 62 b, 61 c and 62 c. A different point from the color sensor test chart as shown inFIG. 6 inembodiment 1 is that the patches 61, 62 are arranged over the entire face of therecording medium 1, since the color image reading apparatus can read the images on the overall face of the recording medium at one time. - In this embodiment, the color conversion method for reducing the differences between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination is identical to the method shown in
FIG. 1 inembodiment 1. In step 211 inFIG. 1 , it is determined whether the detected patch is a gray gradation patch of only black (K) like patch 61 or a process gray gradation patch like patch 62. - The image reading apparatus can selectively detect the gray gradation patch of only black (K) 61 or process gray gradation patch 62 using patch position coordinate information of the color stabilization
control test chart 63. The image reading apparatus is connected to the image forming apparatus, and notifies the image reading apparatus of the patch position coordinate information of the color stabilizationcontrol test chart 63. In this way the determination in step 211 inFIG. 1 is made. - Though the RGB outputs of the sensor are converted into XYZ chromaticity values here, it is apparent that the method described in this embodiment is effective also in other situations where the color matching function in two different color specifications systems is non-linear.
- Moreover, there are two attributes here, including the gray gradation patch of only black (K) and the process gray gradation patch in which yellow (Y), magenta (M) and cyan (C) are mixed, but the classification method for attributes is not limited to this combination of color materials.
- Moreover, the methods for converting the RGB outputs of the sensor into XYZ chromaticity values include a linear conversion method using a matrix, a neural network method and a method using a look-up table. In any method, if the attribute of the patch is judged, it is possible to reduce the differences between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination by changing the weight of connection between neurons for use in the neural network for every attribute of patch, or by changing the look-up table that is used.
- As described above, the color image forming apparatus having no color sensor is connected to the color image reading apparatus, and by changing various parameters for use in converting the RGB outputs of the color image reading apparatus into XYZ chromaticity values for every attribute of patch, it is possible to reduce the differences between the XYZ chromaticity values obtained by converting the RGB outputs of the color reading apparatus and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination, whereby the precision of color stabilization control using the XYZ chromaticity values can be improved.
- In
embodiment 3, the method for changing the matrix for use in converting the RGB outputs into XYZ chromaticity values as described inembodiments -
FIG. 11 is a flowchart for converting the RGB outputs into XYZ chromaticity values inembodiment 3. - In
step 221, therecording medium 11 in an area where the patch is not formed as the substratum color of patch is detected, and it is judged into which of (1) to (6) the sizes of the RGB outputs are classified: (1) R>G>B, (2) R>B>G, (3) B>R>G, (4) B>G>R, (5) G>R>B and (6) G>B>R. - Since the following steps are common except that the matrix A is different in each of (1) to (6), the flow F301 for the classification of (1) will be described below.
- In
step 222, it is determined whether the detected patch is a gray gradation patch of only black (K) like patch 61 or a process gray gradation patch like patch 62. The patch format of color stabilizationcontrol test charts - If it is determined in
step 222 that the detected patch is a gray gradation patch of only black (K) like patch 61, the RGB outputs of the sensor are converted into XYZ chromaticity values in accordance with formula (1), employing matrix A1 for gray gradation patch of only black (K) instep 223. - If it is determined in
step 222 that the detected patch is a process gray gradation patch like patch 62, the RGB outputs of the sensor are converted into XYZ chromaticity values in accordance with formula (1), employing matrix A2 for process gray gradation patch instep 224. - If it is determined that the color area is classified into any one of (2) to (6) in
step 221, the procedure goes respectively tone of flows F302 to F306. In F302, the matrix for gray gradation patch of only black (K) is A3, and the matrix for process gray gradation patch is A4, these matrixes differing from A1 and A2 in F301, and the others being the same. Likewise, in F303, the matrix for gray gradation patch of only black (K) is A5, and the matrix for process gray gradation patch is A6, in F304, the matrix for gray gradation patch of only black (K) is A7, and the matrix for process gray gradation patch is A8, in F305, the matrix for gray gradation patch of only black (K) is A9, and the matrix for process gray gradation patch is A10, and in F306, the matrix for gray gradation patch of only black (K) is A11, and the matrix for process gray gradation patch is A12. - The color of patch formed on the
recording medium 11 is affected by the substratum color of patch, namely, the color of therecording medium 11, without regard to the color material used for the gray gradation patch of only black (K) or process gray gradation patch. For example, if the recording medium is red, the color of patch formed on a red recording medium is redder than the color of the same patch formed on a white recording medium. That is, even when the color image forming apparatus forms the same patch, the spectral reflectance of the patch may differ according to the color of the recording medium on which the patch is formed. Accordingly, it is possible further to reduce the differences between the XYZ chromaticity values obtained by converting the RGB outputs and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination by changing the matrix A that is used, depending on the color area of therecording medium 11. - Also, the color areas of substratum color of patch are classified into six attributes, but the classification method for attributes is not limited to the method shown herein.
- Through the RGB outputs of the sensor are converted into the XYZ chromaticity values, it is apparent that the method described in this embodiment is effective in other situations where the color matching function in two different color specification systems is non-linear.
- Moreover, there are two attributes here, including the gray gradation patch of only black (K) and the process gray gradation patch in which yellow (Y), magenta (M) and cyan (C) are mixed, but the classification method for attributes is not limited to this combination of color materials.
- Moreover, the methods for converting the RGB outputs of the sensor into XYZ chromaticity values include a linear conversion method by means of a matrix, a neural network method and a method using a look-up table. In any method, if the color area of the recording medium and the attribute of the patch are judged, it is possible to reduce the differences between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination by changing the weight of connection between neurons for use in the neural network for every color area of the recording medium and every attribute of patch, or using the look-up table.
- As described above, by changing various parameters for use in converting the RGB outputs of the sensor into the XYZ chromaticity values according to the combination of the attribute of patch and the color area of the recording medium, it is possible further to reduce the difference between the XYZ chromaticity values obtained by converting the RGB outputs of the sensor and the XYZ chromaticity values obtained from the spectral reflectance as defined by the International Commission on Illumination, whereby the precision of color stabilization control using the XYZ chromaticity values can be improved.
- While the invention has been described in terms of its preferred embodiments, various modifications may be made thereto without departing from the spirit and scope of the invention as defined by the appended claims.
- This application claims priority from Japanese Patent Application No. 2004-219971, filed Jul. 28, 2004, which is hereby incorporated by reference herein.
Claims (7)
1.-9. (canceled)
10. A color image forming apparatus comprising:
a sheet discharging portion to which a recording medium is discharged after an image formation;
a forming portion that forms a plurality of fixed patches in a row on the recording medium;
a detecting portion disposed on a recording medium conveying path to detect, before the recording medium is discharged to the sheet discharging portion, colors of the plurality of fixed patches formed on the recording medium;
a converting portion that converts a color signal, obtained by the detecting portion and corresponding to a detection signal in a first color specification system, into a color signal in a second color specification system as color signal conversion processes; and
an adjusting portion that adjusts an image forming condition for the color image forming apparatus, based on the color signal in the second color specification system,
wherein the plurality of fixed patches include plural kinds of patches, an order of formation and an order of detection of the plural kinds of patches being predetermined, and the converting portion uses a parameter of each of the plurality of fixed patches to be subject to color measurement to perform the color signal conversion processes for the respective patches based on the order of detection or detection positions of the plurality of fixed patches.
11. A color image forming apparatus according to claim 10 , wherein the color signal conversion processes include selecting a matrix used in converting the color signal in the first color specification system into the color signal in the second color specification system, or changing a look-up table used in converting the color signal in the first color specification system into the color signal in the second color specification system.
12. A color image forming apparatus according to claim 10 , wherein the plurality of fixed patches include a monochromatic patch formed with only black and a color mixture patch formed by yellow, magenta, and cyan.
13. A method of adjusting a color image forming apparatus, comprising:
forming a plurality of patches in a row on a recording medium;
fixing the plurality of patches to the recording medium;
detecting colors of the plurality of patches fixed to the recording medium in a medium conveying path before the recording medium is discharged to a sheet discharging portion;
converting a color signal, obtained in the detecting and corresponding to a detection signal in a first color specification system, into a color signal in a second color specification system as color signal conversion processes; and
adjusting an image forming condition for the color image forming apparatus, based on the color signal in the second color specification system,
wherein the plurality of patches fixed to the recording medium include plural kinds of patches, an order of formation and an order of detection of the plural kinds of patches being predetermined, and the converting uses a parameter of each of the plurality of patches fixed to the recording medium to be subject to color measurement to perform the color signal conversion processes for the respective patches based on the order of detection or detection positions of the plurality of patches fixed to the recording medium.
14. A method according to claim 13 , wherein the color signal conversion processes include selecting a matrix used in converting the color signal in the first color specification system into the color signal in the second color specification system, or changing a look-up table used in converting the color signal in the first color specification system into the color signal in the second color specification system.
15. A method according to claim 13 , wherein the plurality of patches fixed to the recording medium include a monochromatic patch formed with only black and a color mixture patch formed by yellow, magenta, and cyan.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US13/244,171 US20120019850A1 (en) | 2004-07-28 | 2011-09-23 | Method for calibrating color image forming apparatus |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2004-219971 | 2004-07-28 | ||
JP2004219971A JP4442879B2 (en) | 2004-07-28 | 2004-07-28 | Image forming apparatus and color signal conversion method |
US11/187,808 US8040581B2 (en) | 2004-07-28 | 2005-07-25 | Method for calibrating color image forming apparatus |
US13/244,171 US20120019850A1 (en) | 2004-07-28 | 2011-09-23 | Method for calibrating color image forming apparatus |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/187,808 Continuation US8040581B2 (en) | 2004-07-28 | 2005-07-25 | Method for calibrating color image forming apparatus |
Publications (1)
Publication Number | Publication Date |
---|---|
US20120019850A1 true US20120019850A1 (en) | 2012-01-26 |
Family
ID=35731811
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/187,808 Expired - Fee Related US8040581B2 (en) | 2004-07-28 | 2005-07-25 | Method for calibrating color image forming apparatus |
US13/244,171 Abandoned US20120019850A1 (en) | 2004-07-28 | 2011-09-23 | Method for calibrating color image forming apparatus |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/187,808 Expired - Fee Related US8040581B2 (en) | 2004-07-28 | 2005-07-25 | Method for calibrating color image forming apparatus |
Country Status (2)
Country | Link |
---|---|
US (2) | US8040581B2 (en) |
JP (1) | JP4442879B2 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2020101633A1 (en) * | 2018-11-12 | 2020-05-22 | Hewlett-Packard Development Company, L.P. | Detection of print material density abnormalities |
Families Citing this family (19)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP4386268B2 (en) | 2004-05-07 | 2009-12-16 | キヤノン株式会社 | Color image forming apparatus and control method thereof |
JP4652720B2 (en) * | 2004-05-07 | 2011-03-16 | キヤノン株式会社 | Color image forming apparatus and control method thereof |
JP2005321568A (en) * | 2004-05-07 | 2005-11-17 | Canon Inc | Image forming apparatus |
JP4442879B2 (en) | 2004-07-28 | 2010-03-31 | キヤノン株式会社 | Image forming apparatus and color signal conversion method |
JP4439541B2 (en) | 2007-07-13 | 2010-03-24 | シャープ株式会社 | Image forming apparatus |
US7733547B2 (en) | 2007-10-01 | 2010-06-08 | Kabushiki Kaisha Toshiba | Image forming apparatus, image quality control method |
US7899341B2 (en) | 2007-10-01 | 2011-03-01 | Kabushiki Kaisha Toshiba | Image forming apparatus, analysis information management method |
JP2009251229A (en) * | 2008-04-04 | 2009-10-29 | Canon Inc | Color image forming apparatus, and image forming condition setting method for color image forming apparatus |
JP4873265B2 (en) | 2008-09-29 | 2012-02-08 | ブラザー工業株式会社 | Image forming apparatus |
US8208170B2 (en) | 2008-10-10 | 2012-06-26 | Xerox Corporation | System and method for printing target colors with process colors utilizing parallel feedforward neural networks |
JP2010137474A (en) * | 2008-12-12 | 2010-06-24 | Fujifilm Corp | Image forming apparatus and image forming method |
EP2200268B1 (en) | 2008-12-22 | 2012-02-08 | Thomson Licensing | Method of calibration of a target color reproduction device |
JP5617567B2 (en) * | 2010-11-30 | 2014-11-05 | コニカミノルタ株式会社 | Calibration system, calibration method and program |
JP2017053805A (en) * | 2015-09-11 | 2017-03-16 | セイコーエプソン株式会社 | Colorimeter and printer |
JP6948585B2 (en) * | 2016-05-16 | 2021-10-13 | 株式会社リコー | Image forming apparatus, image forming system and image forming method |
US10400967B2 (en) * | 2016-06-13 | 2019-09-03 | Novartis Ag | Ophthalmic illumination system with controlled chromaticity |
JP6844196B2 (en) * | 2016-10-25 | 2021-03-17 | コニカミノルタ株式会社 | Image forming device and image forming program |
US11740132B2 (en) * | 2019-10-02 | 2023-08-29 | Datacolor, Inc. | Method and apparatus for color lookup using a mobile device |
CN115225837A (en) * | 2021-03-31 | 2022-10-21 | 京东方科技集团股份有限公司 | Video processing method, video processing device and display device |
Citations (25)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5774238A (en) * | 1994-04-19 | 1998-06-30 | Nec Corporation | Color conversion for realizing color reproduction without using color reproduction model |
US5933578A (en) * | 1997-04-08 | 1999-08-03 | Barco Graphics, N.V. | Method and device for determining the color appearance of color overprints |
US5978506A (en) * | 1995-12-28 | 1999-11-02 | Ricoh & Company, Ltd. | Colorant-independent color balancing methods and systems |
US6081678A (en) * | 1998-02-04 | 2000-06-27 | Ricoh Company, Ltd. | Image forming apparatus and method to detect amount of toner adhered to a toner image |
US20010022663A1 (en) * | 1997-05-12 | 2001-09-20 | Takatoshi Ishikawa | Method for image formation and apparatus for development processing |
US20010028471A1 (en) * | 1997-12-15 | 2001-10-11 | Fuji Photo Film Co., Ltd. | Method of and apparatus for correcting color of print medium, and proofer used therein |
US6396595B1 (en) * | 1997-07-17 | 2002-05-28 | Fuji Photo Film Co., Ltd. | Method of and apparatus for color conversion data |
US20030063146A1 (en) * | 2001-10-01 | 2003-04-03 | Minako Kato | Image processing method, image processing apparatus, storage medium and computer program |
US6546131B1 (en) * | 1990-12-19 | 2003-04-08 | Canon Kabushiki Kaisha | Image processing method and apparatus for achieving tone reproduction suited to the image |
US20030085941A1 (en) * | 2001-09-27 | 2003-05-08 | Hiroki Tezuka | Color image forming apparatus and method for controlling color image forming apparatus |
US20030147088A1 (en) * | 1998-11-20 | 2003-08-07 | Manish Kulkarni | Determining color mappings for a color printer |
US20040051889A1 (en) * | 1997-07-04 | 2004-03-18 | Seiko Epson Corporation | Print data adjusting system, print data adjusting method, and software storage medium containing print data adjusting program |
US20040113978A1 (en) * | 2002-12-16 | 2004-06-17 | Xuan-Chao Huang | Method of mixing multi-level black and color inks in a printing system |
US20040190019A1 (en) * | 2003-03-28 | 2004-09-30 | Hong Li | Methods, systems, and media to enhance image processing in a color reprographic system |
US20050018226A1 (en) * | 2003-07-25 | 2005-01-27 | Pentax Corporation | Color-space transformation-matrix calculating system and calculating method |
US20050024654A1 (en) * | 2003-07-24 | 2005-02-03 | Canon Kabushiki Kaisha | Method for forming a color image |
US20050071104A1 (en) * | 2003-09-29 | 2005-03-31 | Xerox Corporation | Method for calibrating a marking system to maintain color output consistency across multiple printers |
US20050073731A1 (en) * | 2003-10-03 | 2005-04-07 | Deer Anna Y. | Color correction method for an imaging system |
US20050151982A1 (en) * | 2004-01-14 | 2005-07-14 | Xerox Corporation | Gray component replacement as part of marking process control algorithm |
US20050243119A1 (en) * | 2004-04-30 | 2005-11-03 | Mario Kuhn | Methods and apparatus for calibrating a digital color imaging device that uses multi-hue colorants |
US20050243337A1 (en) * | 2004-04-30 | 2005-11-03 | Mario Kuhn | Methods and apparatus for determining colorant limits for calibrating digital imaging devices |
US20050243335A1 (en) * | 2004-04-30 | 2005-11-03 | Markus Giesselmann | Methods and apparatus for profiling color output devices |
US20050243336A1 (en) * | 2004-04-30 | 2005-11-03 | Mario Kuhn | Methods and apparatus for determining a total colorant limit for digital imaging devices |
US7027187B1 (en) * | 1995-08-07 | 2006-04-11 | Electronics For Imaging, Inc. | Real time calibration of a marking engine in a print system |
US7050196B1 (en) * | 2000-06-20 | 2006-05-23 | Eastman Kodak Company | Color printer calibration |
Family Cites Families (20)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0860988B1 (en) * | 1991-02-20 | 2002-06-19 | Canon Kabushiki Kaisha | Image processing apparatus |
JP3536564B2 (en) * | 1997-01-06 | 2004-06-14 | 富士ゼロックス株式会社 | Color image forming equipment |
US6480299B1 (en) * | 1997-11-25 | 2002-11-12 | University Technology Corporation | Color printer characterization using optimization theory and neural networks |
JP2002033933A (en) | 2000-07-18 | 2002-01-31 | Matsushita Electric Ind Co Ltd | Apparatus and method for image processing |
US6888963B2 (en) | 2000-07-18 | 2005-05-03 | Matsushita Electric Industrial Co., Ltd. | Image processing apparatus and image processing method |
JP2002237946A (en) * | 2001-02-07 | 2002-08-23 | Ricoh Co Ltd | Imaging system, imaging device, imaging method, and program for making computer execute the method |
US6853815B2 (en) * | 2001-09-10 | 2005-02-08 | Canon Kabushiki Kaisha | Image forming apparatus and adjustment method of the same |
JP4785301B2 (en) | 2001-09-10 | 2011-10-05 | キヤノン株式会社 | Color image forming apparatus |
JP4123354B2 (en) * | 2001-09-20 | 2008-07-23 | 富士ゼロックス株式会社 | Calibration apparatus and calibration method |
US7286261B2 (en) * | 2001-10-02 | 2007-10-23 | Hewlett-Packard Development Company, L.P. | Color calibration color value correction |
JP4065485B2 (en) * | 2001-11-09 | 2008-03-26 | キヤノン株式会社 | Method for correcting output value of color detection means of color image forming apparatus, and color image forming apparatus provided with the method |
US6898381B2 (en) * | 2001-11-09 | 2005-05-24 | Canon Kabushiki Kaisha | Color image forming apparatus and method for controlling the same |
JP2004069947A (en) * | 2002-08-06 | 2004-03-04 | Canon Inc | Color image forming apparatus and control method for its density-gradation property |
JP4194363B2 (en) * | 2002-12-24 | 2008-12-10 | キヤノン株式会社 | Image forming apparatus |
US7277196B2 (en) * | 2003-01-15 | 2007-10-02 | Xerox Corporation | Iterative printer control and color balancing system and method using a high quantization resolution halftone array to achieve improved image quality with reduced processing overhead |
US7025266B2 (en) * | 2003-07-29 | 2006-04-11 | Douglas Gen Keithley | Device and method for digitizing a serialized scanner output signal |
JP4591745B2 (en) * | 2003-12-02 | 2010-12-01 | 富士ゼロックス株式会社 | Image forming apparatus, pattern forming method and program thereof |
JP2005321568A (en) | 2004-05-07 | 2005-11-17 | Canon Inc | Image forming apparatus |
JP4652720B2 (en) | 2004-05-07 | 2011-03-16 | キヤノン株式会社 | Color image forming apparatus and control method thereof |
JP4442879B2 (en) | 2004-07-28 | 2010-03-31 | キヤノン株式会社 | Image forming apparatus and color signal conversion method |
-
2004
- 2004-07-28 JP JP2004219971A patent/JP4442879B2/en not_active Expired - Fee Related
-
2005
- 2005-07-25 US US11/187,808 patent/US8040581B2/en not_active Expired - Fee Related
-
2011
- 2011-09-23 US US13/244,171 patent/US20120019850A1/en not_active Abandoned
Patent Citations (30)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6546131B1 (en) * | 1990-12-19 | 2003-04-08 | Canon Kabushiki Kaisha | Image processing method and apparatus for achieving tone reproduction suited to the image |
US5774238A (en) * | 1994-04-19 | 1998-06-30 | Nec Corporation | Color conversion for realizing color reproduction without using color reproduction model |
US7027187B1 (en) * | 1995-08-07 | 2006-04-11 | Electronics For Imaging, Inc. | Real time calibration of a marking engine in a print system |
US5978506A (en) * | 1995-12-28 | 1999-11-02 | Ricoh & Company, Ltd. | Colorant-independent color balancing methods and systems |
US6483607B1 (en) * | 1997-04-08 | 2002-11-19 | Detrix N. V. | Method and device for determining the color appearance of color overprints |
US5933578A (en) * | 1997-04-08 | 1999-08-03 | Barco Graphics, N.V. | Method and device for determining the color appearance of color overprints |
US20020193956A1 (en) * | 1997-04-08 | 2002-12-19 | Van De Capelle Jean-Pierre | Method and device for determining the color appearance of color overprints |
US20010022663A1 (en) * | 1997-05-12 | 2001-09-20 | Takatoshi Ishikawa | Method for image formation and apparatus for development processing |
US20040051889A1 (en) * | 1997-07-04 | 2004-03-18 | Seiko Epson Corporation | Print data adjusting system, print data adjusting method, and software storage medium containing print data adjusting program |
US6396595B1 (en) * | 1997-07-17 | 2002-05-28 | Fuji Photo Film Co., Ltd. | Method of and apparatus for color conversion data |
US20010028471A1 (en) * | 1997-12-15 | 2001-10-11 | Fuji Photo Film Co., Ltd. | Method of and apparatus for correcting color of print medium, and proofer used therein |
US6081678A (en) * | 1998-02-04 | 2000-06-27 | Ricoh Company, Ltd. | Image forming apparatus and method to detect amount of toner adhered to a toner image |
US20030147088A1 (en) * | 1998-11-20 | 2003-08-07 | Manish Kulkarni | Determining color mappings for a color printer |
US7050196B1 (en) * | 2000-06-20 | 2006-05-23 | Eastman Kodak Company | Color printer calibration |
US20030085941A1 (en) * | 2001-09-27 | 2003-05-08 | Hiroki Tezuka | Color image forming apparatus and method for controlling color image forming apparatus |
US20030063146A1 (en) * | 2001-10-01 | 2003-04-03 | Minako Kato | Image processing method, image processing apparatus, storage medium and computer program |
US20040113978A1 (en) * | 2002-12-16 | 2004-06-17 | Xuan-Chao Huang | Method of mixing multi-level black and color inks in a printing system |
US20090174902A1 (en) * | 2003-03-28 | 2009-07-09 | Hong Li | Methods, systems, and media to enhance image processing in a color reprographic system |
US20090174909A1 (en) * | 2003-03-28 | 2009-07-09 | Hong Li | Methods, systems, and media to enhance image processing in a color reprographic system |
US20040190019A1 (en) * | 2003-03-28 | 2004-09-30 | Hong Li | Methods, systems, and media to enhance image processing in a color reprographic system |
US20050024654A1 (en) * | 2003-07-24 | 2005-02-03 | Canon Kabushiki Kaisha | Method for forming a color image |
US20050018226A1 (en) * | 2003-07-25 | 2005-01-27 | Pentax Corporation | Color-space transformation-matrix calculating system and calculating method |
US20050071104A1 (en) * | 2003-09-29 | 2005-03-31 | Xerox Corporation | Method for calibrating a marking system to maintain color output consistency across multiple printers |
US20050073731A1 (en) * | 2003-10-03 | 2005-04-07 | Deer Anna Y. | Color correction method for an imaging system |
US20090190194A1 (en) * | 2003-10-03 | 2009-07-30 | Deer Anna Y | Color Correction Method for an Imaging System |
US20050151982A1 (en) * | 2004-01-14 | 2005-07-14 | Xerox Corporation | Gray component replacement as part of marking process control algorithm |
US20050243336A1 (en) * | 2004-04-30 | 2005-11-03 | Mario Kuhn | Methods and apparatus for determining a total colorant limit for digital imaging devices |
US20050243335A1 (en) * | 2004-04-30 | 2005-11-03 | Markus Giesselmann | Methods and apparatus for profiling color output devices |
US20050243337A1 (en) * | 2004-04-30 | 2005-11-03 | Mario Kuhn | Methods and apparatus for determining colorant limits for calibrating digital imaging devices |
US20050243119A1 (en) * | 2004-04-30 | 2005-11-03 | Mario Kuhn | Methods and apparatus for calibrating a digital color imaging device that uses multi-hue colorants |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2020101633A1 (en) * | 2018-11-12 | 2020-05-22 | Hewlett-Packard Development Company, L.P. | Detection of print material density abnormalities |
US11415918B2 (en) | 2018-11-12 | 2022-08-16 | Hewlett-Packard Development Company, L.P. | Detection of print material density abnormalities |
Also Published As
Publication number | Publication date |
---|---|
JP2006042002A (en) | 2006-02-09 |
US20060023272A1 (en) | 2006-02-02 |
JP4442879B2 (en) | 2010-03-31 |
US8040581B2 (en) | 2011-10-18 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US8040581B2 (en) | Method for calibrating color image forming apparatus | |
US7982908B2 (en) | Color image forming apparatus and control method therefor | |
EP2597522B1 (en) | Color image forming apparatus and method for controlling color image forming apparatus | |
KR100544557B1 (en) | Iamge forming apparatus and adjustment method of the same | |
US8831443B2 (en) | Image forming apparatus and method for calibrating density and color | |
EP1311110B1 (en) | Method of making correction for color sensor output values in color image forming apparatus | |
JP2005321568A (en) | Image forming apparatus | |
JP2007274438A (en) | Image forming apparatus and control method | |
JP2006235490A (en) | Color correction method in color image forming device, and the color image forming device | |
JP4860854B2 (en) | Color image forming system | |
JP4785301B2 (en) | Color image forming apparatus | |
JP4136351B2 (en) | Color image forming apparatus and processing method in color image forming apparatus | |
JP2005352051A (en) | Image forming apparatus | |
JP2005062273A (en) | Color image forming apparatus system | |
JP2005027276A (en) | Image forming method and its apparatus | |
JP2005319675A (en) | Image forming apparatus and method of controlling it | |
JP4502373B2 (en) | Image forming apparatus and control method thereof | |
JP2004126278A (en) | Color image forming apparatus | |
JP2004069832A (en) | Color image forming apparatus |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |