DE10320300A1 - Method and device for improving the gray value resolution of a pulse width controlled image display device - Google Patents

Abstract

The invention relates to a method and a device for improving the gray value resolution in a pulse-width-controlled image display device. The time interval available for an image display is divided into successive weighted part-time intervals, the part-time intervals containing activation sequences, which in turn consist of predetermined numbers of sustain pulses. If, by analyzing an image to be displayed, it is recognized that there is a dark image without large portions of bright image, the number of sustain pulses for all activation sequences that lie within a time interval for displaying the image is reduced by one depending on the determined image brightness conditions Percentage assigned to determined image brightness ratios changes and on the other hand influences the video signal in the analog part of the video signal path in such a way that the change in image brightness caused by the change in the number of sustain pulses is at least partially compensated for. This improves the gray value resolution when dark images are present.

Description

The The invention relates to a method and a device for improvement the gray value resolution a pulse width controlled image display device.

On Such a method and such an apparatus come for example for plasma displays, which will be used in the future for those with higher quality televisions Color tubes currently still in use will be supplemented or replaced. In connection with color picture tubes has been a user of high quality televisions since the late 1980s due to the 100 Hz technology to a flicker-free display used.

Out the magazine Radio Fernsehen Elektronik RFE, volume 2, 1997, pages 18-20, is a plasma display known that from two glass plates with electrodes arranged in a matrix exists 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 in full screen. Because the individual pixels of a plasma display are not arbitrary Activation must be possible for times to be switched on and off individually the pixels for the entire display is done in one activation pass.

The A plasma display is controlled in several phases: one Addressing or initialization phase, a hold or activation phase and a deletion phase.

In the addressing or initialization phase becomes all cells of the plasma display is electrically pre-charged, which is then or activation phase should be activated. In the last step, the deletion phase, the preloaded cells are discharged again, the image information will be deleted.

The time interval available for displaying a television picture is in part-time intervals of different duration or different weighting disassembled while depending on the Brightness value of a respective pixel a predetermined activation sequence chosen becomes. This corresponds to one or more flashes of the respective pixel during of available for image display standing time interval, each lighting up a predetermined period of time assigned.

such Known plasma displays are, for example, from Fujitsu and NEC manufactured and distributed.

From the DE A1 198 33 597 a method and a device for flicker reduction in pulse-width-controlled image display devices are known, in particular in a color plasma display. Such a color plasma display is used, for example, to display television pictures. The color plasma display is controlled by means of a pulse width modulator, with the duration of a television picture being broken down into a series of partial pictures or partial time intervals which are displayed one after the other. In order to reduce flicker, in particular a 50 Hz flicker reduction, the sequence of the part-time intervals and / or the activation sequences of the part-time intervals is specified in such a way that the flickering of the images to be displayed is minimal.

Furthermore, from the DE-A1 198 37 307 a motion detector-dependent change in the order of the part-time intervals is known. If there are movements, the order of the part-time intervals is selected in such a way that movement artifacts are avoided. Otherwise, the order of the part-time intervals is selected in such a way that 50 Hz flicker interference is reduced.

Farther brightness is already known in connection with plasma displays of an image to be displayed, from the detected brightness value for each of the part-time intervals of the image to be displayed a maximum permissible lighting duration derive and in the event of a change of the recorded brightness value the maximum permissible lighting duration for each to change the part-time intervals. This change takes place in such a way that when dark image content is recorded or little Brightness value the maximum permissible Lighting duration in each of the part-time intervals by the same length of time elevated becomes. On the other hand, the brightness detection of the one to be displayed results image; that there is overall bright image content, then the maximum allowable Burn time for each of the part-time intervals decreased by a period of time for all part-time intervals is equal to.

On The disadvantage of this approach is that the contrast of the image to be displayed is reduced, since the brightness is detected at a high level of the image to be displayed, the length of time for the display of bright image components is reduced and with a detected low brightness of a display Dark gray image components are shown in light gray, since this is due to the described application of a constant Offset is pulled up, i.e. shine longer.

From the DE 101 12 622 Finally, a method and a device for improving the gray value resolution in a pulse-width-controlled image display device are known. This is what is available for an image display The time interval is divided into successive weighted part-time intervals, part-time intervals with a low weighting and part-time intervals with a higher weighting being provided. If it is recognized by evaluating the brightness of an image to be displayed that a dark image is present, then use of part-time intervals with a higher weighting is dispensed with and instead the number of part-time intervals with low weightings is increased by using additional part-time intervals with low weightings, the weightings of the distinguish additional part-time intervals from the weightings of the first part-time intervals with low weightings. This improves the gray value resolution when dark images are present. A disadvantage of this method is that, in the case of commercially available plasma displays with integrated control, the assignment of the part-time intervals to be addressed for the display of a specific gray value is usually fixedly predefined in the control circuit, which is not accessible, ie it cannot be changed.

Color Plasma Displays point about it a regulation to control the power consumption. task This regulation is to protect the display from being destroyed by overheating. To it is known in connection with plasma displays, the power consumption either by measuring the sustainer current or by evaluating it the brightness of an image to be displayed. In the latter Case becomes from the detected brightness value for each of the part-time intervals derives a maximum permissible light duration from the image to be displayed and with a change of the recorded brightness value the maximum permissible lighting duration for each the part-time intervals changed. This change takes place in such a way that when dark image content is recorded or little Brightness value the maximum permissible Lighting duration is selected in each of the part-time intervals. On the other hand, gives the Brightness detection of the image to be displayed that a total If there is light image content, the maximum permissible lighting time for each the part-time intervals reduced by a period of time. The reduction the lighting duration follows - in dependence the integral brightness of the image to be displayed - a function which limits the output to the upper permissible value.

Independently of whether the measure of performance the sustainer current or the integral brightness of the displayed In the picture, the control takes place in that the number of sustainer pulses per Part-time interval is reduced by the power limitation at the top Realize limit. The reduction in the number of sustainer pulses per part-time interval is proportional to the duration of one Part-time interval.

The size The disadvantage of this procedure is that with high brightness of the image to be displayed, the length of time for the display of bright image components is reduced, turns white then gray. When the brightness of an image to be displayed is low in return, dark gray image components are displayed in light gray. This is particularly unpleasant in the image impression if the brightness exceeds the entire image area is low because then the brightness transitions between the individual Grayscale are very large. For the Image impression, this means that the step size between two brightness levels is very large. If there are only a few gray values for dark image content, this can do so to lead, that the extent of equally bright areas is very large. In Connection with the high step size between two brightness levels does this to a very unsightly Image impression.

outgoing From this prior art, the invention is based on the object to show a way, as in a pulse width controlled image display device the gray value resolution, while avoiding the disadvantages known from the prior art, can be improved.

This The object is achieved by a method, the features of which are set out in the claim 1 are specified, or by a device with the in claim 15 specified characteristics.

advantageous Refinements and developments of the invention result from the dependent Claims.

By the method of claim 1 can achieve that with relatively dark pictures without striking bright ones surfaces, the total number of discrete gray levels that can be displayed on the Gray value area of the image to be displayed is mapped, whereby for such image contents an optimal resolution of this gray scale area results in darkness without impairing the display Images with light areas goes hand in hand.

through the in the claims 2 and 5 specified analysis options of the image to be displayed becomes the one necessary for image analysis apparatus expenditure kept within reasonable limits. More beneficial Refinements and developments result from the features of claims 6 to 10.

By analyzing a plurality of images in succession according to claim 11, it can be achieved that in the event of abrupt changes in the image content, the adjustment takes place in stages, thereby creating a pleasant image pressure arises. Particularly advantageous further developments are given by the features according to claims 12 and 13.

With the circuit arrangement according to claim 15 can be easily an improvement in the gray value resolution for dark image content without concise bright areas achieve advantageous configurations for this are in claims 16 and 17 marked.

Further advantageous properties of the invention result from the explanation of an embodiment based on the figures.

It shows:

1 a block diagram of a television receiver with a gray value optimization circuit for controlling pulse-width-controlled plasma display;

1a a block diagram of a gray value optimization circuit

2 and 2a exemplary diagrams for explaining the invention and

3 to 4c further exemplary diagrams for explaining the invention.

The Process according to the invention the arrangement is described below in connection with a television receiver, without being limited to that to be. You can rather, each one is used in an application pulse-width controlled plasma display operated and image signals displays, such as Data monitors or video monitors with corresponding plasma displays.

The 1 shows a block diagram of a television receiver with a pulse width controlled plasma display. The television receiver 1 . 2 has a television signal processing part 1 and an image processing part 2 on. The television signal processing part 1 has a first entrance 17 , which the signals of an antenna device 19 are fed. The signals of the input 17 to a high frequency and intermediate frequency processing unit 4 and an audio signal processing unit 3 forwarded. At the output of the high frequency and intermediate frequency processing unit 4 there is a CVBS signal, which is via a gray value optimization circuit to be explained later 34 an analog / digital converter 5 is fed. An external CVBS signal is fed in via a second signal input 20 possible, other signals, eg RGB, Y / C, YUV etc. (not shown) can of course be fed into the circuit at appropriate points, if necessary, via additional circuits. The output signal of the analog / digital converter 5 then becomes a so-called feature box 6 directed. The feature box 6 performs certain functions such as demodulation of the CVBS signal, still image, zoom, format adjustment, image sharpness optimization, picture-in-picture, etc. The resulting digital components Y, U, V of an image signal 21 are connected to a digital matrix unit 8th of the image processing part 2 forwarded. The feature box 6 also serves to convert the interlaced signal into an interlaced signal and the necessary adaptation of the signals to the screen 14 by line interpolation. This is done using the synchronization signals 23 . 24 for vertical and horizontal synchronization.

The digital matrix unit 8th also has a connection 27 for feeding one via an external signal input 18 supplied VGA signal, which by means of an analog / digital converter 25 is converted into a digital signal. Of course, it is also possible to provide a gray value optimization circuit in the signal path of the VGA signal, which would be the analog / digital converter 25 upstream. At the output of the digital matrix unit 8th there is an RGB signal 22 with which a pulse width modulator 10 is controlled.

From the RGB signal 22 generates the pulse width modulator 10 the control signals 26 for an address driver 11 , For this signal generation is with the pulse width modulator 10 a memory 9 coupled. The pulse width modulator 10 has a part-time interval weighting unit, which serves to weight the part-time intervals, ie to determine their sequence and duration. The address driver facility 11 controls the individual columns of the plasma screen line by line 14 on. The associated time control takes place with the help of the time control device 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. The timing device 13 is with a horizontal driver 12 connected. This horizontal driver 12 is active during the activation phases. Power is supplied using a power supply 7 ,

As stated at the beginning, a plasma display device consists of a large number of very small gas discharge areas. Due to this design principle, such a display device has a digital relationship between the input variable and the luminance. There are therefore single for the gas discharge areas Two states: switched on or switched off. In order to still be able to achieve a wide range of different intermediate gray levels, the in 1 shown image processing part 2 a digital time-division multiplexing method is used for image display. With this the RGB signals 22 broken down into several part-time intervals of different duration, ie into part-time intervals of different weighting.

This is done using the pulse width modulator 10 , as well as the further units controlling the pulse width modulator, such as the timing control device 13 and a memory 9 , Due to the sluggishness of the human eye appear on the plasma display device 14 no longer individual image changes, but a gray value that depends on the average activation time. 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 . 8th , ...) two grayscales can be displayed exponentially with the number of part-time intervals. In order to be able to display as many gray levels as possible, it is therefore desirable to use as many part-time intervals as possible, but this is not possible due to technological constraints. A number of 256 gray levels has emerged as a practical compromise. The pulse width modulator 10 determines the sequence and activation of the individual part-time intervals for each pixel of the image to be displayed, based on an assignment that depends on its input signal level. In the case of binary weighting, this assignment is such that the longest part-time interval is assigned to the digitally weighted bit, the second longest part-time interval to the second-highest weighted bit, etc.

In 2 is an exemplary sequence of such part-time intervals, as it takes place during a frame, is shown. The time for displaying a full image is 20 milliseconds and is divided into eight part-time intervals, which are also referred to as subfields (SF1 to SF8). The subfields or partial time intervals are weighted in binary form, as has already been explained above. With such a weighting, a total of 256 grayscale can be displayed from “black” (minimum brightness) to “white” (maximum brightness).

The individual part-time intervals are divided into an addressing phase, as shown in the SF 6 subfield 28 and a sustain phase 29 , During the addressing phase 28 all pixels of the plasma display device 14 addressed that should light up in the subfield SF 6. The individual pixels are addressed in the manner already described above. During the addressing phase 28 subsequent actual activation of the display in the sustain phase 29 using a sustain pulse generator 31 who in the in 1 illustrated horizontal driver 12 contains a number of sustain pulses specific to the subfield - in the present example the subfield SF 6. These sustain pulses then cause a corresponding light emission from those pixels which were addressed during this subfield SF 6.

As shown above, a certain one is determined by the RGB signal 22 For a pixel, a given brightness or gray value is converted into a corresponding integral luminance in that certain sub-fields assigned to the gray value to be displayed are addressed for this pixel within the time interval given for the display of a full image, so that in the sustain phases, the respective Addressing phases follows, a corresponding light emission is generated. In today's common plasma display devices with integrated control, depending on the value of the RGB signal, 256 different brightness or gray values can be represented for each pixel by appropriate addressing of the subfield in order to represent the range from minimum luminance to maximum luminance.

The display options that the plasma display device 14 offers are, as already mentioned, subject to physical limits. For an overall good image impression, it is desirable to generate the highest possible luminance for images with an image content that lies in the middle gray area and contains bright or white areas for the brilliant display of these bright or white areas. However, this means that the gray levels that can be displayed, for example, 256, must be divided over a correspondingly large brightness range.

Become the light or white surfaces bigger, this leads This is due to the high luminance, which then extends over a large image area extends to a very high thermal load on the plasma display device comes. In the case of very bright image content, this limits the luminance required as later is described. A corresponding luminance limitation for bright ones Image content is generally not perceived as disturbing and is therefore for one overall good picture impression acceptable.

In contrast, in the case of images with relatively dark image content without bright areas, only a few of the 256 gray levels are actually available for displaying the image, because of the optimization described above for such image content that is in the middle gray area and contains bright or white areas. The image has a graded transition in terms of brightness, the areas of equal brightness are large and the display is too bright overall. All of this has a very negative effect on the image impression with dark image content. This could be remedied if the sub-fields could be re-assigned to the gray values for low-brightness image content. However, this is usually not possible with today's custom-made plasma display devices with integrated control, because the control is not accessible for such measures. Even with an accessible control, a dynamic change of the gray value resolution depending on the image content would be very complicated and time-consuming.

As already mentioned above, high luminance in pictures with very bright picture content leads to the plasma display device 14 too warm it warms. In order to counter the problem of overheating, the horizontal driver in today's plasma display device is in the horizontal driver 12 a video level integrator 30 included that from the RGB signal 22 generates the integral of the frame and a sustain pulse limiter with a signal corresponding to the integral of the frame 32 acted on such that this on the sustain pulse generator 31 has a limiting effect if this is from the video level integrator 30 to the sustain pulse limiter 32 delivered signal exceeds a predetermined value. The sustain pulses are limited in such a way that, as in 2a the number of sustain pulses shown as an example 29 in each subfield, compared to the maximum number of sustain pulses, is reduced by a predetermined percentage. Although this measure does not change the weighting of the part-time intervals or subfields among themselves, so that the number of gray values that can be displayed remains the same, it does, however, reduce the overall luminance of the plasma display device 14 causes, and evenly over all representable gray values.

The consequences which result from the procedure described above for the control of plasma display devices for the gray value display are to be discussed below in connection with the 3 . 3a and 3b be made clear.

Assuming that a relatively dark image with single white areas on the plasma display device 14 is present is in 3 a gray scale 33 shown, which covers the range from minimum luminance to maximum luminance. For the sake of simplicity, it is assumed below that the range from minimum luminance to maximum luminance can be represented by 12 discrete gray values G1 to G12. The entire available gray area is used to display the addressed image. Although the next to the white areas 37 occurring gray area 35 only includes the gray values G1 to G6. This causes the white areas to appear 37 very bright, the image appears brilliant in the image impression, the weaknesses in the gray value display are hardly significant.

However, if the white areas are omitted, the comparatively dark image, as in 3a shown, actually only the gray area 35 , so the grayscale G1 to G6. The consequence for the image impression is that the large step size between the individual discrete brightness values, eg G1 and G2, the associated gradation of the gray transitions and the consequently larger areas of the same brightness come into the foreground. The picture impression is unsatisfactory.

As in connection with 3b shown the white areas 37 ' larger, the high luminance cannot be maintained, the power limitation described above takes effect. This reduces the luminance evenly so that white areas 37 ' no longer appear with the maximum luminance, but with the gray value G12 ', which corresponds to the original gray value G9 in the example. The number of gray levels that can be displayed remains unchanged, ie 12 discrete gray levels G1 'to G12' can still be displayed, but the brightness values are shifted towards "black".

This Procedure described in the control, such as them common today is a compromise, accepting overall dark images on the one hand or overall bright images, on the other hand, with reduced quality for the brilliant presentation overall darker picture with white areas in optimally to enable what kind of an overall good picture impression is important.

In order to improve the unsatisfactory display of images with dark image content, it is necessary to increase the number of gray levels available for the display. Since an intervention in the assignment of the signal levels of the RGB signal to the partial time intervals or subfields to be addressed in a frame period is prohibited for the reasons described above, only the video signal itself and the control of the number of during the sustain phase remain as influenceable variables of the subfields sustain pulses. Based on this basic idea, it was found that if the video signal is amplified so that the brightest gray value in an image to be displayed corresponds to the signal level "white" and, in parallel, the number of sustain pulses is reduced to such an extent that in the Representation again the gray values arise as they correspond to the original unamplified video signal, the total number of, for example, 256 gray values that can be represented can be transformed to the actually occurring gray area. In this way it is possible for each image to be displayed to map the total number of gray values that can be displayed to the gray area actually occurring in the image.

To do this, the in 1 shown gray value optimization circuit 34 used, their functionality in connection with 1a , following is explained in more detail. A video signal, in the example the CVBS signal, is on the one hand due to a delay circuit 38 , the purpose of which will be explained later and on the other hand to an analog / digital converter 39 , From the analog / digital converter 39 the now digital video signal arrives in an image memory 40 , in such a way that it is written with the digital data of at least one video image. The control measures when writing to an image memory are known to the person skilled in the art and therefore do not require any further explanation. The content of the image memory is checked using an image analyzer 41 With regard to its image content, it is analyzed whether white areas appear in the image which lie above a predetermined area dimension and whether the image to be displayed corresponds to predetermined values in its integral brightness and / or in its maximum brightness value. Depending on the image analysis described above in the image analyzer 41 generates this when the analyzed image for display on the display device 14 is present, an output signal with which he the sustain pulse limiter 32 to the effect that this is via the sustain pulse generator 31 reduces the number of sustain pulses per part-time interval or subfield of the frame to be displayed. The time at which the output signal is sent to the sustain pulse limiter 32 can be from the timing circuit 13 ( 1 ) can be triggered. The sustain pulses per subfield are reduced, for example, as a percentage of the maximum number of sustain pulses occurring within a subfield. All gray values that can be represented are shifted towards black by this measure. The sustain pulse correction is selected, for example, so that the maximum gray value that can be represented corresponds to the brightest gray value that occurs in the image. The total number of gray values that can be represented is thus mapped onto the gray area actually occurring in the image, which results in a significant reduction in the step size between two successive gray values and thus also in a corresponding reduction in the areas occurring in an image with the same gray value. This transformation goes hand in hand with the fact that the original gray values in the image are now different gray values. In order to cancel this shift in the direction of black again and a color-correct display on the plasma display device 14 To achieve this, compensation must be made. This compensation is accomplished, for example, by an intervention in the composite signal in such a way that this composite signal is amplified in inverse proportion to the sustain pulse correction described above, such that after amplification the maximum level occurring in the signal, for example the color White corresponds. The minimum level in the signal remains unchanged, so it still corresponds to the color black. The gain is via an amplifier 42 accomplished that with the output of the delay circuit 38 is connected and through the image analyzer 41 a corresponding one, the amplification of the amplifier 42 determining signal. The delay circuit 38 has the purpose of delaying the video signal, in the example the CVBS signal, until the corresponding video frame is analyzed and the sustain pulse correction on the one hand and the amplification factor on the other hand from the image analyzer 41 are determined so that the amplifier 42 amplifies the video signal associated with the analyzed video frame with the gain factor obtained by the analysis. For timely delivery of the signal determining the gain by the image analyzer 41 can this from the delay circuit 38 be triggered.

The corrected video signal, in the example the modified CVBS signal 43 , now reaches the analog / digital converter 5 and is processed as in connection with 1 described. The in the analysis process from the image analyzer 41 The sustain pulse correction determined is accomplished via a corresponding signal that the image analyzer 41 then to the sustain pulse limiter 32 from when the associated image for display on the plasma display device 14 pending for presentation. The synchronization processes necessary for this are familiar to the person skilled in the art and require no further explanation.

To the impact of the above in connection with 1a To clarify the measures described on the display on a plasma display device, is subsequently referred to in the 3 to 3b used representation form. The requirements made there also apply to the 4 to 4c ,

The starting point for consideration are the in 4 shown relationships. The comparatively dark image covers the gray area 35 , so the grayscale G1 to G6. The consequence for the image impression is that the large step size between the individual discrete brightness values, for example G1 and G2, the associated gradation of the gray transitions and the resulting size surfaces of the same brightness are clearly recognizable. The picture impression is unsatisfactory.

Now the in 1 shown and in 1a Gray value optimization circuit described in more detail 34 used, takes place as in 4a shown, on the one hand a reduction in the sustain pulses for all part-time intervals or subfields activated in the relevant frame period, such that the maximum gray value that can be represented corresponds to the brightest gray value G6 occurring in the image. This measure would thus transform the maximum gray value G12 that can be displayed before the sustain pulses are reduced to the new maximum gray value G12 '(= G6). This would also change the lightest gray value G6 occurring in the image before the sustain pulses were reduced to the new gray value G6 '. All of the gray values that can be represented would thus be shifted towards “black” by reducing the sustain pulses.

Contrary to this measure, however, the video signal is amplified, in the example according to 1 respectively. 1a of the CVBS signal, such that the highest level occurring in the signal - in the selected example this level is assigned the gray value G6 - corresponds to the level for the color "white". This means for addressing the part-time intervals or subfields within the relevant image, that with this modified CVBS signal, or the digital modified RGB signal derived from it, all available gray levels are actually addressed and used. So if you consider a pixel with the highest signal level in the original video signal, in the example this corresponds to the gray value G6 becomes the signal level for "white" after amplification and now corresponds to the gray value G12. The partial time intervals for the pixel in question are thus also addressed in accordance with the gray value G12, but due to the sustain pulse correction described above, only the real value G12 'is actually shown which corresponds to the gray value G6.

In this way it can be achieved that the maximum possible number of grayscale is available for each image to be displayed, regardless of its image content. This principle can, of course, be deviated from if the image content, such as 4b described, a compromise between optimal gray value resolution on the one hand and brilliant display of white areas on the other, is required.

Kick in like this 4b is shown as an example in a dark image that has only a small gray area 35 includes small bright areas 36 with a gray value of G10, for example, the image analyzer detects this 41 and influences via the sustain pulse limiter 32 and the sustain pulse generator 31 the number of sustain pulses per part-time interval or subfield for all subfields within the full image to be displayed so that for the display of the bright areas 36 a lighter gray value is available than that outside the small bright areas 36 occurring maximum gray value G6. However, this lighter gray value can be darker than the gray value G10, which is the light areas 36 have, predetermined, for example correspond to the gray value G9. This procedure makes sense if, as mentioned above, a compromise between good gray value resolution on the one hand and brilliant display of the light areas on the other hand is to be achieved. For this purpose, the image analyzer reduces, as already explained above, the number of sustain pulses so that the maximum gray value that can be represented corresponds to the gray value G9 and controls the amplification of the amplifier 42 such that the highest level occurring in the modified video signal corresponds to the level for the gray value G11. For the addressing of the part-time intervals or sub-fields within the relevant image, this means that with this modified CVBS signal, or the digital RGB signal derived from it, all gray levels between G1 and G11 are addressed and thus used. The sustain pluls correction only shows the gray area up to the gray value G9. With this procedure, the bright areas are reproduced somewhat too darkly, but the gray value resolution is improved, which is conducive to a more balanced image impression.

Become as in 4c shown, the bright, especially white areas 37 Larger relative to the screen area, there is a need to set the maximum displayable gray value G 12 to the maximum luminance in order to display these bright areas more brilliantly 37 to reach. In such cases, the image analyzer leaves 41 the sustain pulse limiter 32 unaffected and acts on the amplifier 42 so that it does not change the video signal.

How already executed, in such cases the worse gray value resolution accepted in favor of a brilliant display of the white areas.

If the proportion of light or white areas continues to increase, the overriding power limitation comes into effect, which is already mentioned in connection with 1 and 2 was described.

The in connection with 1a described image analyzer 41 offers the possibility of analyzing the image to be displayed according to all possible criteria and, depending on the analysis result, the sustain pulse limiter 32 on the one hand and the amplifier 42 on the other hand, to be influenced in such a way that an optimal gray value display of dark images is achieved without at the same time impairing the display of light areas.

We already hinted at using the image analyzer 41 the possibility of examining the image to be displayed with regard to the presence of bright image areas, the brightness value of such bright image areas, the area dimension of such bright image areas, the maximum brightness value occurring outside of these bright image areas and the integral brightness value of the image. Further examination options are of course possible. Whether or not all or only a part of the evaluation options mentioned above are used, you will be in the image analyzer 41 or with the image analyzer 41 in operative connection, provide a memory in which reference values relating to the image analysis are stored, which are compared with the values that the image analyzer 41 wins from the image analysis, the reference values then being assigned control values with which the image analyzer 41 the sustain pulse limiter 32 and the amplifier 42 acted upon in order to optimize the gray value resolution as a function of the image content in the manner described above.

The above in connection with the 1 to 4c Exemplary embodiment of the method according to the invention or the arrangement according to the invention described can of course be supplemented and expanded by measures accessible to the person skilled in the art. For example, it is easy to imagine the gray value optimization circuit 34 to implement on the basis of a microcomputer.

Of course it has one looks at the above for simplification in connection with a gray value display described methods on the three used in a video image Primary colors red, green, Presented in blue, the principle of operation changes thereby nothing.

A An advantageous development of the invention consists in the analysis of several successive images in the sense of a temporal Perform filtering. This leaves e.g. achieve brightness jumps in successive Images do not abruptly switch the number of generated ones Sustain pulses or the gain to lead, but a gradual adjustment in the sense of a transition function.

Claims (18)

Method for improving the gray value resolution in a pulse-width-controlled image display device to which a video signal is applied, in which the time interval available for image display is divided into successive differently weighted partial time intervals and the brightness signals associated with the pixels of the image to be displayed are generated by conversion in the partial time intervals, wherein the activation sequences consist of predetermined numbers of sustain pulses and the number of sustain pulses for all activation sequences that lie within a time interval for the display of an image can be changed, characterized in that in an analysis of the image to be displayed, the image brightness ratios of the image to be displayed Image are captured, whereby the image analysis recognizes when images with predominantly dark areas of the image without larger bright B Image areas are to be displayed, a first signal then being generated as a function of the determined image brightness ratios, which changes the number of sustain pulses for activation sequences that lie within the time interval for the display of the image by a degree assigned to the determined image brightness ratios and a second Signal is generated, which is arranged in the analog part of the video signal path amplifier ( 42 ) influences the video signal so that the change in image brightness caused by the first signal is at least partially compensated for. A method according to claim 1, characterized in that the maximum brightness occurring is determined in an analysis of the image to be displayed and a first signal is generated as a function of the brightness found in each case, which is the number of sustain pulses for activation sequences within a time interval for display of an image are changed by a degree assigned to the brightness and - a second signal is generated which is transmitted via the amplifier ( 42 ) influences the video signal such that the change in image brightness caused by the first signal is at least partially compensated for. Method according to claim 1, characterized in that an analysis of the image to be displayed determines whether there are areas in the image to be displayed whose brightness and surface area lie within predetermined value ranges and that a first signal is generated depending on the value range pairs found in each case, that the number of sustain pulses for activation sequences which lie within a time interval for displaying an image is changed by an amount assigned to the value range pairs and - a second signal is generated which is transmitted via the ver stronger ( 42 ) influences the video signal such that the change in image brightness caused by the first signal is at least partially compensated for. A method according to claim 1, characterized in that the maximum brightness occurring is determined in an analysis of the image to be displayed and that if the value falls below a predetermined maximum brightness depending on the brightness found in each case - a first signal is generated which indicates the number of sustain pulses for Activation sequences that lie within a time interval for displaying an image, are changed by a degree assigned to the brightness and - a second signal is generated which is transmitted via the amplifier ( 42 ) influences the video signal in such a way that the change in image brightness caused by the first signal is at least partially compensated; if the predetermined maximum brightness value is exceeded, an analysis of the image to be displayed determines whether there are coherent areas in the image to be displayed, their brightness and their surface area within predetermined value ranges and that depending on the value range pairs found in each case - a first signal is generated which changes the number of sustain pulses for activation sequences which lie within a time interval for displaying an image by a degree assigned to the value range pairs and - a second signal is generated that over the amplifier ( 42 ) influences the video signal so that the change in image brightness caused by the first signal is at least partially compensated for. Method according to one of claims 2 or 3 or 4, characterized characterized that in addition the integral brightness of the image to be displayed is determined and with the largest in individual brightness value or image to be displayed the brightness value of the brightest in the image to be displayed area is compared and the difference in brightness is assigned to value ranges will in turn be degrees of change are assigned and that depending of the range of values in which the difference in brightness lies, that first signal and the second signal around a value range assigned Degrees changed becomes. Method according to one of the preceding claims, characterized characterized that change the number of sustain pulses based on a maximum number done by reduction. Method according to one of the preceding claims, characterized characterized that change the number of sustain pulses for all activation sequences within the time interval Representation of the picture, follows a predetermined function, such that the function for each part-time interval indicates the degree of change. A method according to claim 7, characterized in that the function is a linear function. A method according to claim 7, characterized in that the function is a logarithmic function. A method according to claim 7, characterized in that the function is an empirically determined function. Method according to one of the preceding claims, characterized characterized that the analysis of several successive Images in the sense of a temporal filtering is carried out and that with sudden changes in successive images the change in the first signal and of the second signal takes place in stages. A method according to claim 11, characterized in that the gradual change in first signal and the second signal of a predetermined transition function follows. A method according to claim 12, characterized in that the course of the transition function on the nature of the sudden change depends. Method according to one of the preceding claims, characterized characterized in that it is the pulse width controlled image display device a ready-made one that already contains the control circuits Image display device is. Device for improving the gray value display in a ready-made, pulse-width-controlled image display device, with - control means ( 9-13 ) for the division of the time interval available for an image display into successive weighted partial time intervals and for the generation of brightness signals which are associated with the pixels of the image to be displayed, the control means ( 9-13 ) convert the activation sequences assigned to the time intervals, the activation sequences consisting of predefined numbers of sustain pulses which are generated by a sustain pulse generator ( 31 ) are generated which has an input which can be acted upon externally and via this input the number of sustain pulses for activation sequences which lie within a time interval for displaying an image can be changed, - With a gray value optimization circuit loaded by an analog video signal ( 34 ), the gray value optimization circuit ( 34 ) detects whether images with predominantly dark areas of the image should not be displayed without large bright image areas and then generates first signals and second signals depending on the image parameters determined, - with a sustain pulse limiter ( 32 ) via its input from the gray value optimization circuit ( 34 ) can be acted upon with the first signals in such a way that the sustain pulse limiter ( 32 ) the sustain pulse generator ( 31 ) in such a way that it changes the number of sustain pulses for activation sequences that lie within the time interval for displaying the image to be displayed by a degree predetermined by the first signals, - the gray value optimization circuit ( 34 ) Depending on the second signals, the video signal is changed to its output in such a way that the change in brightness of the image to be displayed caused by the change in the number of sustain pulses is at least partially compensated for. Apparatus according to claim 15, characterized in that the gray value optimization circuit ( 34 ) a delay circuit ( 38 ), an amplifier ( 42 ), an analog / digital converter ( 39 ), an image memory ( 40 ) and an image analyzer ( 41 ) contains, whereby - the video signal on the one hand the delay circuit ( 38 ) and on the other hand the analog / digital converter ( 39 ) acted upon, - the digitized video signal in the image memory ( 40 ) is read in such a way that it contains at least one complete image to be displayed, - the image analyzer ( 41 ) the brightness conditions of the in the image memory ( 40 ) contained image, and as a result of this analysis the first and second signals are generated, - the image analyzer ( 41 ) the second signals to the amplifier ( 42 ) when the delay circuit receives the delayed video signal of the analyzed image, - the image analyzer ( 41 ) the first signals to the sustain pulse limiter ( 32 ) when the image is displayed on the plasma display device ( 14 ) pending. Device according to claim 16, characterized in that the image analyzer ( 41 ) to output the second signals through the delay circuit ( 38 ) is triggered. Device according to claim 16, characterized in that the image analyzer ( 41 ) for the delivery of the first signals by a time control device ( 13 ) is triggered.