DE102004010725A1 - Image optimizing device for optimizing color shots taken with an image-capture unit detects reflected/transmitted light with an electronic camera - Google Patents

Abstract

Spectral properties in an image-capture unit's lighting adapt to the spectral properties of a detector by taking into account the spectral distribution of an object's reflection or the object's transmission. An optical filter (4) is inserted into a fundus camera's beam path (2) for lighting.

Description

The The present invention relates to a device for optimization of color images obtained with an image pickup unit the detection of the reflected or transmitted light with an electronic camera (CCD or CMOS camera) is realized.

application finds the device according to the invention especially in ophthalmology for the recording of the ocular fundus (Fundus). In addition, applications such as e.g. Photographs for the industrial Image processing possible.

The Inclusion of fundus images for documentation purposes is described in the Ophthalmology with special imaging units (fundus camera) realized. Such fundus cameras basically consist of one Light source, optical components for steering the incident in the eye Light and the light reflected from the retina and a Detector. The light source is a flash or halogen lamp and the pictures are taken using a photographic camera (e.g. 35mm camera) onto a photographic film (e.g., a slide film) saved.

In In recent years, the photographic cameras have become increasingly popular electronic cameras (e.g., CCD or CMOS camera, monochrome) or color). The electronic color cameras become the spectrum of the light to be recorded in three spectral ranges (red, green and blue) divided and on the corresponding detection areas of the camera directed. With the help of electronic cameras can take different frames or sequences of images recorded, stored and later evaluated accordingly or processed in image processing programs. For some Special imaging techniques (e.g., angiography) become specialized Filter introduced into the beam path of the fundus camera, wherein the Fundus cameras according to the prior art equipped with filter slides are, so the user can use any filter in the beam path can bring in or take out.

at The previously known image recording method affects the spectral Distribution of the light intensity present in the recorded image, that of the spectral distribution of the whole transmission chain - lighting, Object reflection, transmission of the entire image acquisition unit - depends, as particularly disadvantageous.

So leads e.g. the special spectral distribution of the fundus reflection during recordings of the ocular fundus without special measures that the individual color channels (Red Green, Blue) in the recorded image are exposed to different levels. At optimal exposure in the red channel are the other two channels (Green and Blue) strongly underexposed. On the other hand, optimal exposure results Out in the open Channel for override in the red channel. Underexposed images do not use the whole Dynamic range of the detector and lead to a reduction the photometric resolution.

Besides there are also spectral transition areas, which not only illuminate one but two channels of the color camera. Thereby can in fundus recordings, special structures of the fundus (e.g. Nerve fiber layer, blood vessels, subretinal Structures or pigmentations) by image processing techniques difficult to highlight.

One Another disadvantage of the known from the prior art image recording units is that the detector for insensitive some spectral regions of the illuminating light is, i. a part of the illuminating light does not contribute to the image acquisition at, leads but to an unnecessary Light load of the object to be examined.

task It is therefore an object of the present invention to provide a device for Optimization of color images obtained with an image acquisition unit, in the detection of the reflected or transmitted light realized with an electronic camera (CCD or CMOS camera) will provide. The spectral properties of the lighting an image pickup unit should, taking into account the spectral distribution the object reflection or object transmission to the spectral properties the detector (electronic camera).

According to the invention Task with the characterizing features of claim 1 solved.

advantageous Embodiments of the device according to the invention are in the dependent claims specified.

The The present invention is characterized by a number of advantages out. Due to the balanced exposure of the three detector color channels and the Suppression more convincing Exposure in the peripheral areas of the detector color channels becomes the Information content of a device according to the invention having captured image capture unit color photographs significantly elevated. additionally the light load of the object to be recorded is kept to a minimum reduced.

The The invention is explained in more detail below with reference to drawings. In the associated Drawings show:

1 - Basic structure of the device according to the invention having imaging unit

2 Relative spectral distribution of the illumination in the exit pupil of a fundus camera (without filter according to the invention in the illumination beam path)

3 - Spectral distribution of fundus reflection (Source: Delori, FC, and KP Pflibsen, Spectral reflectance of the human ocular fundus, Appl. Optics 28: 1061-1077, 1989)

4 Relative spectral distribution of the sensitivity of the three color channels of the detecting electronic camera

5 - Relative spectral distribution of the exposure of the three color channels of the detecting electronic camera in a Fundusaufnahme

6 - Histogram of a fundus image with conventional illumination

7 - Relative transmission of the optical filter according to the invention according to the embodiment

8th - Relative spectral distribution of the exposure of the three color channels of the detecting electronic camera and the resulting relative transmission of the optical filter according to the invention

9 - Histogram of a Fundusaufnahme using the device according to the invention The following embodiment will be described with reference to a Zeiss fundus camera. In 1 shows the basic structure of an apparatus according to the invention comprising the image recording unit. The light of the illumination source 1 is via deflection mirror 3 and optics directed to the eye (illumination beam path 2 ). In this illumination beam path is an optical filter 4 brought in. That of the retina (fundus) of the eye 5 Reflected light is transmitted to the detecting electronic camera via further optics and deflecting mirrors 7 steered (observation beam path 6 ), where it is saved as an image and processed further.

In 2 the spectral distribution of the illumination of a fundus camera is shown in the plane of the exit pupil of the fundus camera, wherein no inventive optical filter is located in the illumination beam path. The illumination light (flash lamp) is distributed over the entire light spectrum from 400 to over 1050 nm. Out 3 the spectral distribution of the fundus reflection can be taken. The retinal reflection is very low in the blue spectral range. In normal recordings of the fundus without special measures, the special spectral distribution of fundus reflection causes the individual color channels (red, green, blue) of the detecting electronic camera in the image to be exposed to different levels of intensity: Exposure = illumination intensity · detector sensitivity

For the exposure in the blue channel BE _B :

The same applies to the exposure BE _G in the green and BE _R in the red channel.

beträgt ungefähr 25/50/100.The ratio of the exposures in the three channels blue / green / red

is about 25/50/100.

at optimal exposure in the red channel, the other two channels are strong underexposed. On the other hand leads an optimal exposure in the green Channel for override in the red channel.

The electronic camera used for image acquisition (CCD color camera) is sensitive only in certain areas of the spectrum ( 4 ).

In a fundus recording, one obtains a relative spectral distribution of the exposure of the three color channels of the detecting electronic camera as in 5 shown. The exposure of the red color channel of the electronic camera is significantly larger than that of the green and the blue.

In 6 is a histogram of a Fundusaufnahme shown in conventional lighting.

In order to increase the information content of the recorded color images and to minimize the light load of the object to be examined according to the invention in the illumination beam path of the fundus camera, an optical filter 4 brought in.

• (A) Um die unterschiedlichen Belichtungen der drei Farbkanäle der detektierenden elektronischen Kamera auszugleichen, muß gelten:
  
  D.h. die Belichtung aller drei Farbkanäle der detektierenden elektronischen Kamera ist nahezu gleich stark.
• (B) Für die Bildinformation wird bei der Verwendung einer elektronischen Kamera folgender Anteil der Beleuchtung genutzt:
  
  Der Anteil der Beleuchtung
  
  wird für die Bildinformation nicht genutzt. Um eine effektive Lichtausnutzung und minimale Lichtbelastung des zu untersuchenden Objektes zu realisieren, muss der nicht zur Bildinformation beitragende Anteil der Beleuchtung minimiert werden. Daher muß für die Transmission des optischen Filters gelten:
  
• (C) Zur Verhinderung des Übersprechens zwischen den Farbkanälen der verwendeten elektronischen Kamera, muss die Transmission des erfindungsgemäßen optischen Filters folgenden Bedingungen genügen:
  

The transmission T (λ) of this filter 4 is chosen so that the known from the prior art disadvantages are overcome:

• (A) To compensate for the different exposures of the three color channels of the detecting electronic camera, the following must apply:
  
  That is, the exposure of all three color channels of the detecting electronic camera is almost equally strong.
• (B) For image information, when using an electronic camera, the following proportion of lighting is used:
  
  The proportion of lighting
  
  is not used for the image information. In order to realize an effective utilization of light and minimal exposure to light of the object to be examined, the proportion of the illumination that does not contribute to the image information must be minimized. Therefore, for the transmission of the optical filter:
  
• (C) To prevent the crosstalk between the color channels of the electronic Ka used Mera, the transmission of the optical filter according to the invention must satisfy the following conditions:
  

In order to is guaranteed that there are no wavelengths There are two color channels the electronic camera are detected.

Based on the requirements of (A), (B) and (C), the following transmission bands for the optical filter result for the exemplary embodiment ( 7 ):

All three transmission ranges have the same transmission: T B = T G = T R

Outside In these three transmission ranges the optical filter is impermeable.

The optical filter of the embodiment is a 3-band dielectric interference filter. It has a diameter of 28 mm and one strength of 1 mm. With the help of a standard filter slide of the Zeiss fundus camera the filter can be brought into the illumination beam path and again be removed.

Should the image acquisition unit used in the illumination beam path none Have filter slide, the optical filter can also by means corresponding holders directly in the illumination beam path be positioned.

The relative spectral distribution of the exposure of the three color channels of the detecting electronic camera and the relative transmission of the optical filter according to the invention determined therefrom is shown in FIG 8th shown. A histogram of a Fundusaufnahme using the device according to the invention is in 9 shown.

The Image recording unit with the device according to the invention allows color images with electronic cameras whose image information versus color photographs with known devices are significantly more extensive. Besides the light load of the object to be examined is reduced to a minimum. Since the appropriately sized optical filter only in the illumination beam path must be introduced are only minor or no structural transformations of the recording device necessary. The optimization of color images with an electronic camera can be very cheap and easy.

1

lighting source

2

Illumination beam path

3

deflecting

4

optical filter

5

to examining object (eye)

6

Observation beam path

7

detected electronic color camera

Abbreviations

• L (λ)

  relative spectral Distribution of lighting

  T (λ)

  relative transmission of the optical filter

  R (λ)

  relative spectral Distribution of the reflection of the retina

  B _of (λ)

  relative illuminance in the Detector level without inventive optical filter in the illumination beam path

  B _mf (λ)

  relative illuminance in the Detector level with inventive optical filter in the illumination beam path

  E _R (λ), E _G (λ), E _B (λ)

  relative spectral Sensitivity of the detector (red, green, blue channel). All values E (λ) are on the highest Sensitivity normalized in the entire spectral range.

  BE _R , BE _G , BE _B

  Exposure of the detector (Red Green-, Blue channel)

Claims (3)

Device for optimizing color images obtained with an image acquisition unit, in which the detection of the reflected or transmitted light with an electronic camera (CCD or CMOS camera) is realized, characterized in that in the illumination beam path of the image recording unit, an optical filter with transmissive transmission regions in the red (λ _R1 ... λ _R2 ), in the green (λ _G1 ... λ _G2 ) and in the blue (λ _B1 ... λ _B2 ) wavelength range of the illuminating light is arranged, wherein: a) the wavelength range λ _R1 .. λ _R2 lies in the red, but not in the green and blue sensitivity range of the detecting electronic camera, b) the wavelength range λ _G1 ... λ _G2 lies in the green, but not in the red and blue sensitivity range of the detecting electronic camera, c) the wavelength range λ _B1 ... λ _B2 in the blue, but not in the green and red sensitivity range of the detecting electronically d) the wavelength ranges λ _R1 ... λ _R2 , λ _G1 ... λ _G2 and λ _B1 ... λ _B2 and the transmissions T _R , T _G and T _{B are selected} in the respective wavelength ranges, the exposures of the three spectral sensitivity ranges of the detecting electronic camera (BE _R , BE _G and BE _B ) are almost equal. and e) the optical filter, with the exception of the wavelength ranges λ _R1 ... λ _R2 , λ _G1 ... λ _G2 and λ _B1 ... λ _{B2, is} impermeable to the entire spectral range of the illuminating light. Device according to claim 1, characterized that the optical filter by means of a filter slide in the illumination beam path the receiving unit is introduced. Device according to claim 1, characterized that the optical filter by means of a holder in the illumination beam path the recording unit is integrated.