WO2000007173A1

WO2000007173A1 - Subframe-controlled image display device

Info

Publication number: WO2000007173A1
Application number: PCT/EP1999/004632
Authority: WO
Inventors: Udo Fischbeck; Eckhard Guettner
Original assignee: Grundig Ag
Priority date: 1998-07-25
Filing date: 1999-07-03
Publication date: 2000-02-10
Also published as: EP1099211B1; EP1099211A1; DE59911003D1; ES2232148T3

Abstract

The invention relates to a pulsewidth-modulated image display device, notably a plasma display, comprising control means for controlling a screen. The time interval available for displaying an image is divided into several chronologically sequential partial time intervals. The picture elements of the image display device are divided into two partial time groups. The brightness signal assigned to a picture element is generated from a RGB signal via an activation scheme and an activation sequence derived therefrom. The image display device comprises a motion sensor, as well as means for modifying the sequence of the partial time intervals and/or means for modifying the activation sequence. The sequence of the partial time intervals and/or the activation sequence are modified in accordance with the output signal of the motion sensor.

Description

PULSE WIDTH-CONTROLLED IMAGE DISPLAY DEVICE

description

The invention relates to a pulse-width-controlled image display device, in particular a plasma display, with control means for controlling a screen with the features specified in the preamble of claim 1. The invention further relates to a method for controlling a pulse-width-controlled image display device with the features specified in the preamble of claim 12

Such a method and such a device are used, for example, in color plasma displays, which in the future will replace the color picture tubes still used in high-quality television sets. In connection with color image tubes, the user of high-quality television sets has been in contact with one since the end of the eighties due to the 100 Hz technology flicker-free display

From the magazine Radio Fernsehen Elektronik RFE, volume 2, 1997, pages 18-20, a plasma display is known that consists of two glass plates with electrodes arranged in a matrix, between which there is a noble gas mixture. The image information is not shown line by line in plasma displays as in cathode steel tubes but full frame-wise since the individual pixels cannot be switched on and off individually at any time due to the matrix addressing of a plasma display, the pixels must be activated for the entire display in one activation cycle The control of a plasma display consists of several phases of an addressing or initialization, a holding or activation and an erasing phase

In the addressing or initialization phase, all cells of the plasma display are preloaded which are to be activated in the subsequent holding or activation phase. In the last step, the deletion phase, the preloaded cells are discharged again and the image information is deleted

The time interval available for displaying a television picture is broken down into partial time intervals of different durations, during which a predetermined activation sequence is selected depending on the brightness value of the respective pixel. This corresponds to one or more lighting up of the respective pixel during the time interval available for displaying the picture, a predetermined period of time being assigned to each lighting up

Such known plasma displays are marketed by the Fujitsu company, for example, as a 42 plasma display

The object of the invention is to provide a device and a method for controlling a pulse-width-controlled image display device, which lead to improved image reproduction

This object is achieved by a device with the features of claim 1 and a method with the features of claim 12. Advantageous refinements of the invention are specified in the dependent claims The invention is based on the finding that when slow-moving or stationary images are present, when they are displayed on a pulse-controlled display device, flickering, particularly in the 50 Hz range, can occur, although the partial-time interval frequency is used to display a full image in a time interval of 20 msec For example, when using 8 part-time intervals of 400 Hz, the same applies to systems in the 60 Hz range. The invention is described below using a 50 Hz system

Simulations have confirmed that such a flickering, which is particularly noticeable in slow moving images, can be reduced by varying the sequence of the part-time intervals and / or their activation sequence in a certain way.This variation aims to reduce the flickering on the screen minimize images to be displayed

In order to achieve a flicker-free display as possible, it has proven to be advantageous to distribute the activation of the part-time intervals essentially uniformly

Different gray levels are generated by a suitable selection of the activated part-time intervals

If fast moving images are available, the sequence of the part-time intervals and / or their activation sequence is selected so that an image display free of motion artifacts is achieved

In practical applications, it has currently proven to be advantageous to set the ratio of the shortest to the longest activation duration to 1 12. The number of part-time intervals is fixed at 8. The part-time intervals are divided into two part-time groups In a preferred embodiment of the invention, a time interval of 20 msec is provided for displaying a full image and the partial time interval frequency is therefore 400 Hz

The corresponding tasks of the deflection control provided in picture tube television sets are carried out in the case of the pulse-width-controlled image display device in such a way that the control means for controlling the screen have a timing control device which processes vertical and horizontal synchronous signals and controls the timing of the pulse-width modulator as well as a horizontal driver device of the plasma picture screen

The invention is described and explained in more detail below with reference to the exemplary embodiments shown in the figures

Show it

FIG. 1 shows a block diagram of a television receiver with a pulse-width-controlled plasma display,

FIG. 2 shows a representation of a first part-time interval pattern,

FIG. 3 shows a diagram belonging to the part-time interval pattern from FIG. 2 to illustrate the 50 Hz flickering,

FIG. 4 shows a diagram to illustrate the brightness distribution during a full frame podode for a special input signal level at which a strong 50 Hz flickering occurs,

FIG. 5 shows an optimized part-time interval pattern in which the 50 Hz flickering is reduced, FIG. 6 shows a diagram belonging to the part-time interval pattern from FIG. 5 to illustrate the reduced 50 Hz flickering,

Figure 7 is a diagram illustrating the motion detector-dependent mode switching with, for example, two

Operating states

1 shows a block diagram of a television receiver with a pulse-width-controlled plasma display display. The television receiver 1, 2 has a television signal processing part 1 and an image processing part 2. The television signal processing part 1 has a first input 17, to which the signals of an antenna device 19 are fed. The signals of the input 17 become forwarded to a high-frequency and intermediate-frequency processing unit 4 and an audio signal processing unit 3 At the output of the high-frequency and intermediate-frequency processing unit 4 there is a CVBS signal which is fed to an analog / digital converter 5. The feeding of an external CVBS signal is via a second signal input 20 possible The output signal of the analog / digital converter 5 is then passed to a so-called feature box 6. The feature box 6 performs certain functions such as demodulation of the composite signal, still image, zoom, format adaptation, B Image sharpness optimization, picture-in-picture etc by the resulting digital components Y, U, V of an image signal 21 are forwarded to a digital matrix unit 8 of the image processing part 2. The feature box 6 also serves to convert the interlace signal into an interlace-free signal and the like necessary adaptation of the signals to the screen 14 by line interpolation. This is done with the aid of the synchronization signals 23, 24 for vertical and horizontal synchronization The digital Matπxeinheit 8 also has a connection 27 for supplying a VGA signal supplied via an external signal input 18, which is converted into a digital signal by means of an analog / digital converter 25. At the output of the digital matrix unit 8 there is an RGB signal 22 The controller 10, 13 generates the control signals 26 for an address driver 11. For this signal generation, a memory 9 is coupled to the controller 10, 13. The controller 10 13 has a part-time interval assignment unit that defines the The order and duration of the part-time intervals serves

The column driver device 11 controls the individual columns of the plasma screen 14. The associated time control takes place with the aid of the controller 10, 13, which defines the start of the part-time intervals and the times for the addressing and activation phase. The part-time interval line control device contained in the time control is used for this purpose. The controller 10, 13 is connected to a horizontal driver 12. This horizontal driver 12 is active during the activation phases. The voltage supply takes place with the aid of a power supply unit 7

During the functioning and structure of the

TV signal processing part 1 essentially corresponds to that of a conventional television receiver with picture tube, the structure of the picture processing part 2 is fundamentally different.The main reason for this is mainly that the plasma display device 14 has a digital relationship between the input size and the luminance.There are therefore only two states switched on or off In order nevertheless to be able to achieve a large range of different intermediate gray levels, a digital time-division multiplexing method is used in the image processing part 2 shown in FIG. 1, in which the RGB signals 22 are broken down into several part-time intervals of different durations.This is done with the controller 10, 13 and other units such as a memory 9 Due to the sluggishness of the human eye, individual image changes no longer appear on the plasma display device 14, but rather a gray scale value that depends on the average activation duration. If this duration is weighted in the part-time intervals, then many gray levels can be displayed with a few part-time intervals With a binary weighting 1, 2, 4, 8, two levels of gray levels can be displayed exponentiated with the number of part-time intervals. To be able to display as many gray levels as possible, it is therefore desirable to use as many part-time intervals as possible, which is not possible due to technological constraints Controller 10, 13 determines the sequence and activation of the individual part-time intervals by means of an assignment which is dependent on its input signal level. In the case of binary weighting, this assignment looks such that the digitally most highly weighted bit has the longest Part time interval, the second longest weighted bit assigned the second longest part time interval, etc.

Simulations and subjective considerations have shown that, despite a part-time interval frequency of 400 Hz, flickering artifacts of 50 Hz, particularly from medium luminance levels, can be disruptive.The conspicuousness of 50 Hz flickering varies with the luminance to be displayed and depends on the luminance level of the activated part-time interval and on the Order of the part-time intervals within the 20 msec frame period. For this reason, the controller 10 13 of the image display device 2 is controlled such that the order of the part-time intervals and their

Activation sequence can be changed as a function of the movement content of the image signal. In an operating state, when there are rapid movements, the signals displayed on the screen are displayed in the correct movement and in an operating state with slow movements, a flicker-free image is displayed FIG. 2 shows a diagram of a part-time interval pattern, in which the images shown are shown with the correct movement. The letter L denotes the luminance input level of the RGB signal designated by reference number 22 in FIG. 1. The part-time groups TG1 and TG2 are characteristic of an image representation Plasma displays are assigned to one of the two part-time groups TG1 or TG2. The image is built up in several temporally successive part-time intervals t1 to t8. The luminance signal L assigned to a respective pixel results from the analog brightness value via the activation scheme, according to FIG. 2, and the activation sequence derived therefrom, the ratio the shortest activation period to the longest activation period is in a ratio of 1 to 12. The number of activation periods generated in the part-time intervals t1 to t8 is that shown in FIG lth exemplary embodiment 12 The number of part-time intervals t1 to t8 is 8 The activation duration of the part-time groups TG1 and TG2 is identical

The temporal length of the part-time intervals t1 to t8 is different, which is expressed in FIG. 2 by the "weighting factors" 12, 8, 4, 2 and 1 indicated on the underside of the diagram

For example, if the luminance input level L assigned to a pixel of the plasma display 14 has the value 44, then this pixel lights up during the part-time intervals t1, t2, t3, t7 and t8 of the part-time group TG1 and during the part-time intervals t1, t2, t6, t7 and t8 of the second Part-time group TG2 and is dark during the part-time intervals t4, t5 and t6 of the first part-time group TG1 and during the part-time intervals t3 t4 and t5 of the second part-time group TG2 FIG. 3 shows a diagram belonging to the part-time interval pattern of FIG. 2 to illustrate a 50 Hz flickering as a function of the brightness H and the input signal level L. The course of the characteristic curve F, which characterizes the 50 Hz flickering, shows in particular at input signal levels L> 30 Increased 50 Hz flickering A maximum can be determined on the basis of this simulation result with an input signal amplitude of 44 as flicker value Fm

FIG. 4 shows the course of the average brightness Hm for a special input signal amplitude level of 44 as a function of time t. The 50 Hz flicker disturbance can be clearly seen from the sinusoidal or cosmic brightness course Hv

FIG. 5 shows a partial time interval pattern optimized with respect to the 50 Hz flickering. The reference symbols already introduced in connection with FIG. 2 are used. The partial time interval pattern shown in FIG. 5, in contrast to the pattern shown in FIG. 2, has a changed sequence of the partial time intervals t1 to In the exemplary embodiment shown in FIG. 5, t8 on So is the order of the weights 12, 4, 8, 1, 2, 12, 4, 8, while the order of

Weightings in the partial time interval pattern 12, 8, 4, 2, 1, 4, 8, 12 shown in FIG. 2 are: The corresponding sequence of the partial time intervals in FIG. 511 is t3, t2, t5, t4, t8, t6, t7, while the sequence of the partial time intervals in Figure 2 is t1, t2, t3, t4 t5, t6, t7 t8

FIG. 6 shows the simulation result for the partial time interval pattern shown in t5. The reference symbols already introduced in connection with FIG. 3 are used. The simulation shows that the partial time interval pattern shown in FIG. 5 leads to a significantly reduced 50 Hz flickering, in particular at higher input signal levels Since the aforementioned 50 Hz flickering only occurs with standing or slowly moving picture content, the part-time interval pattern according to FIG. 5 is used according to the invention only with standing or slowly moving picture content. In the case of rapidly moving image contents, however, the part-time interval pattern according to FIG. 2 is used, in which less movement artifacts occur.

For this purpose, the television receiver shown in FIG. 1 has a motion detector 6a as part of the feature box 6, the output signals of which are fed to the controller 10, 13. In a first operating state, when there are still or slowly moving images, the sequence of the part-time intervals and / or the activation sequence is specified in such a way that the flickering of the images shown on the display 14 is minimized. Furthermore, in a second operating state when fast moving images are present, he specifies the order of the part-time intervals and / or the activation sequence of the part-time groups in such a way that the movement artifacts in the images shown on the display 14 are minimized.

To implement these operating states, the controller 10, 13 accesses data records assigned to the respective movement content and stored in different memory areas of the memory 9.

This is illustrated in FIG. 7. FIG. 7 shows that the memory 9 has, for example, two different memory areas 9a and 9b. Data corresponding to the respective part-time interval pattern are stored in each of these memory areas. Depending on the motion content of the image, which is detected by the motion detector 6a, one of the two memory areas is addressed in order to read out the data associated with the respective part-time interval pattern. An advantageous development of the invention then consists in providing, in addition to the two operating states already mentioned, further operating states, each of these further operating states corresponding to a specific movement content. In this case, the memory 9 has further storage areas which contain data records for these further operating states

In an advantageous embodiment of the invention, the controller 10, 13 is implemented by a pulse width modulator 10 and a timing control device 13

Claims

PATENT CLAIMS

1. Pulse-width-controlled image display device (1, 2), in particular a plasma display, with control means (10-13) for controlling a screen (14), the time interval available for image display being divided into a plurality of temporally successive partial time intervals (t1, t8), the pixels of the image display device (1, 2) are divided into two part-time groups (TG1, TG2), the brightness signal assigned to a pixel being generated from an RGB signal via an activation scheme and an activation sequence derived therefrom, characterized in that - the image display device has one Has motion detector (6a),

the image display device has means (9, 10) for changing the order of the part-time intervals (t1, ...., t8) and / or means (9, 10) for changing the activation sequence,

- and the change in the order of the part-time intervals (t1, ...., t8) and / or the change in the activation sequence depending on the

Output signal of the motion detector (6a) takes place.

2 pulse-width-controlled image display device according to claim 1, characterized in that the pulse-width-controlled image display device (1, 2) can be operated in a plurality of operating states, the sequence of the part-time intervals (t1,, t8) and / or. In a first operating state when there are still or slowly moving images the activation sequence is predetermined in such a way that the flickering of images displayed on the screen (14) is minimized, and in a second operating state in the presence of rapidly moving images the sequence of the part-time intervals (t1,, t8) and / or the activation sequence are predetermined in this way that the motion artifacts in the images displayed on the screen (14) are minimized

3 pulse width controlled image display device according to claim 2, characterized. that the part-time intervals (t1,, t8) in the first operating state in the presence of still or slowly moving images are occupied substantially uniformly within an activation sequence

4 pulse width controlled image display device according to claim 1 or 2, characterized. the activation time of the part-time intervals (t1, t8) in relation

4 8 1 2 12 4 8 stand to each other

5 pulse-width-controlled image display device according to claim 2, characterized in that the pulse-width-controlled image display device has a memory (9) with a plurality of memory areas, each memory area being provided for storing data records which are associated with one of the operating states

6. Pulse width controlled image display device according to one or more of the preceding claims, characterized in that the control means (10-13) have a controller (10, 13), which is composed of a pulse width modulator (10) and a timing control device (13).

7. Pulse width controlled image display device according to one or more of the preceding claims, characterized in that the pulse width controlled image display device has a digital matrix (8) which is provided for processing a digital image signal (21, 27) and the pulse width modulator (10) as the output signal Control means (10-13) supplied RGB signal.

8. Pulse width controlled image display device according to one or more of the preceding claims, characterized in that the control means (10-13) have a timing control device (13), which vertical and horizontal signals (23, 24) are supplied and which output side with the pulse width modulator (10 ) and a horizontal driver (12) is connected.

9 pulse width controlled image display device according to one of claims 2

characterized in that in the first operating state the sequence of the part-time intervals is selected such that one of the relationships t1 t2 t3 t4 t5 t6 t7 t8 = 12 4 8 1 2 12 4 8 or t1 t2 t3 t4 t5 t6 t7 t8 for the activation periods of the part-time intervals = 4 8 1 2 12 4 8

10 pulse width controlled image display device according to one of claims 2

characterized in that in the second operating state the sequence of the part-time intervals is selected such that the following relationship applies to the activation periods of the part-time intervals t1 t2 t3 t4 t5 t6 t7 t8 = 12 8 4 2 1 4 8 12

11 pulse width controlled image display device according to one of claims 2

characterized in that in the first operating state the sequence of the part-time intervals (t1,, t8) is predetermined such that there is an essentially uniform distribution of the activation sequence over the part-time intervals (t1 t8)

12. A method for controlling a pulse-width-controlled image display device, in which the one available for an image display is divided into a plurality of temporally successive part-time intervals (t1, ..., t8) and the pixels of the image display device (1, 2) into two part-time groups (TG1, TG2) can be divided, whereby the brightness signal assigned to a pixel is generated from an RGB signal via an activation scheme and an activation sequence derived therefrom, characterized in that the sequence of the part-time intervals (t1, t8) and / or the

Activation sequence is changed depending on the movement content of the image to be displayed.