JPH08292747A - Error diffusion processing device for display device - Google Patents

Abstract

PURPOSE: To obtain a high quality picture by suppressing the vibration of the picture in a 'gradation characteristic acquisition' to 'error diffusion' to 'gradation characteristic acquisition' loop. CONSTITUTION: The device consists of an error diffusion circuit 11 which obtains diffused output signals by adding reproducing errors, which were generated before an original picture element, to the quantized original picture element video signals and conducts a pseudo-intermediate level display and a video output monitoring section 15 which obtains a display area rate (Sk). Furthermore, the above sections are connected with a generated luminance characteristics acquisition circuit 19 to form a loop. The circuit 19 obtains the amount of luminance deviation of each level by the luminance deviation characteristics of each bit and converts the above amount into a threshold value. A loop filter 28 is inserted in the loop to suppress the vibration of the picture. Then, the vibration of the picture in the loop is suppressed and the vibrations become smoothed changes and a good quality picture is obtained without fluctuation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an error diffusion processing device for displaying pseudo-halftone by error diffusion in a display device for displaying images, characters and the like.

[0002]

2. Description of the Related Art Recently, as a thin and lightweight display device, P
Attention has been paid to DP (plasma display panel). This PDP driving method is completely different from the conventional CRT driving method and is a direct driving method using a digitized video input signal. Therefore, the brightness gradation emitted from the panel surface is determined by the number of bits of the signal to be handled.

In the AC type PDP, there was only a report about a gray scale display up to a maximum of 64 gray scale displays at the trial production level, but the address / display separation type driving method (ADS subfield method).
Proposed a method of 256 gradations in the future.

One frame in the ADS subfield method has a relative luminance ratio of, for example, 1, 2, 4, 8, 1.
6, 32, 64, and 8 subfields of the loop filter 28, and 256 combinations of luminance of 8 screens.
The gradation is displayed. Each subfield is composed of an address period for writing refreshed data for one screen and a sustain period for determining the luminance level of the subfield. In the address period, wall charges are initially formed in each pixel at the same time on the entire screen, and then sustain pulses are applied to the entire screen for display. The brightness of the subfield is proportional to the number of sustain pulses,
It is set to a predetermined brightness. In this way, 256 gradation display is realized.

In the AC driving method as described above, as the number of gradations is increased, the number of bits in the address period as a preparation period for lighting and emitting the panel is increased within one frame period. The period is relatively short and the maximum brightness is low. In this way, since the brightness gradation emitted from the panel surface is determined by the number of bits of the signal to be handled, if the number of bits of the signal to be handled is increased, the image quality is improved, but the light emission luminance is reduced, and conversely If the number of bits is reduced, the light emission luminance is increased, but gradation display is reduced and the image quality is deteriorated.

The error diffusion process for reducing the grayscale error between the input signal and the emission luminance while reducing the bit number of the output drive signal more than the bit number of the input signal is a process for expressing a pseudo halftone. , Used when expressing light and shade with few gradations. In a conventional general error diffusion circuit, a video signal of a p (eg, 8) -bit original pixel Ai, j is input from the video signal input terminal to the error diffusion circuit, and the number of bits is further changed to q ( For example, 4) Reduce the number of bits to emit light from the PDP.

Further, the light emission luminance characteristic calculation unit including a ROM or the like measures and stores the light emission luminance characteristic of the PDP from representative input data (solid line) that is as close as possible to y = x (dotted line) shown in FIG. 9, for example. Keep it. This emission luminance characteristic is sent to the error amount calculation unit to calculate the error, and the processing circuit unit adds the error to the input video signal and diffuses it to perform pseudo halftone display.

As a result, although the light emission luminance level is like a step of a solid line in a moment, it is actually recognized in an averaged state, and a corrected luminance line similar to the dotted line y = x is obtained. .

However, the emission luminance characteristic of a display device such as a PDP varies depending on the data to be displayed, and there is a case where the emission luminance characteristic greatly deviates from y = x (dotted line) as shown by the solid line in FIG. . In such a case, the method of adjusting to the typical emission luminance characteristic as shown in FIG. 9 cannot adapt to the gradation characteristic for the data other than when the representative characteristic is acquired. There is a problem that a pseudo contour appears due to gray scale inadequacy.

Therefore, the applicant of the present invention has proposed that the conventional ROM
Instead of the light emission luminance characteristic given by the above, the light emission luminance characteristic for each one or a plurality of frames is calculated based on the luminance deviation characteristic obtained from the load factor of the input data of the display device such as a PDP. We have proposed a device that prevents the appearance of false contours by updating the emission luminance characteristics every time and performing error diffusion.

Explaining this with reference to FIG. 7, a reproduction output error generated by the error diffusion circuit 11 in the past from the original pixel is added to the original pixel video signal quantized and input from the video signal input terminal 10 to obtain a diffused output signal. In the device for performing pseudo-halftone display by obtaining a loop from the error diffusion circuit 11 to the error diffusion circuit 11 via the video output monitoring unit 15, the 1-field delay ROM 27, the generated luminance characteristic acquisition circuit 19, and the threshold value transfer unit 26. The video output monitoring section 15 includes a sampling clock generating circuit 16 and an M
The data counter 17 that counts the number of bits of video data displayed in one or a plurality of frames by M counters corresponding to each bit, and the number of display dots counted by the data counter 17 are the total number of dots. And a count value selection circuit 18 for calculating the display area ratio (Sk) by dividing by 1.
Reference numeral 9 denotes a deviation calculator 20 for obtaining the brightness deviation characteristic of each bit.
And a brightness characteristic calculation unit 21 for obtaining a brightness deviation amount of each level based on the data of the deviation calculation unit 20, and a threshold conversion unit 2
2, the operation control unit 23 includes a processing subfield control unit 24 and a processing level control unit 25.

In the configuration described above, the error diffusion circuit 11 has the error amount calculation section 12 and the processing circuit section 13,
Error diffusion processing is performed based on the given emission luminance characteristic, and pseudo halftone display is performed. When the data is transmitted from the error diffusion circuit 11 to the video output monitoring unit 15, the data counter 17 uses M counters for the M-bit video data in M number of counters corresponding to the respective bits, in one or a plurality of frames of each bit. The “display dot number of subfield K”, which is the display number, is counted. The count value selection circuit 18 is
“Subfield K counted by the data counter 17
The display area ratio (Sk) is calculated by dividing the “display dot number of” by the “total dot number”. And the deviation calculator 2
The luminance deviation characteristic of each bit is obtained by 0, the luminance deviation amount of each level is obtained by the luminance characteristic calculation unit 21, converted into a threshold value by the threshold conversion unit 22, and returned to the error diffusion circuit 11.

Here, the luminance deviation characteristic (δ) obtained from the display area ratio (Sk) and the load factor of the input data is a unique characteristic line, and the function for obtaining this δ is stored in the processing level control unit 25. Has been done.

In the brightness deviation amount calculation for each level, the gradation characteristic is updated for each one or every plural frames and transmitted to the error diffusion circuit 11. The error diffusion circuit 11 performs error diffusion processing based on the light emission luminance characteristic and outputs it to the PDP 14.
With such a configuration, "gradation characteristic acquisition" →
The image is processed in a loop of “error diffusion” → “gray scale characteristic acquisition” →. As a result, it is possible to sufficiently adapt the gradation characteristic to the data that changes every moment.

[0015]

However, in this way, "gradation characteristic acquisition" → "error diffusion" → "gradation characteristic acquisition" →
When the image vibrates in the loop of ..., the mixing ratio of white and black changes for each frame, and there is a problem that it changes at a fast cycle.

According to the present invention, the light emission luminance characteristic for each one or a plurality of frames is calculated based on the luminance deviation characteristic obtained from the load factor of the input data of the display device, and the error is diffused by updating this to obtain the pseudo contour. It is an object of the present invention to provide a device for preventing the occurrence of noises, in particular, an inconspicuous image flickering due to loop vibration.

[0017]

According to the present invention, a pseudo error halftone display is performed by adding a reproduction error generated in the past from an original pixel to a quantized input original pixel video signal to obtain a diffused output signal. The error diffusion circuit 11, the video output monitoring unit 15 for obtaining the display area ratio (Sk), and the generated luminance characteristic acquisition circuit 19 for obtaining the luminance deviation amount at each level from the luminance deviation characteristic of each bit and converting the luminance deviation amount into a threshold value are looped. In a device that is connected in a line, the video output monitoring unit 15 to the error diffusion circuit 11
And an error diffusion processing device for a display device, wherein a loop filter 28 for suppressing image vibration in the loop is inserted in the loop. Is.

[0018]

In the quantized original pixel video signal, the video output monitor 15 determines the display area ratio (Sk). Then, the generated luminance characteristic acquisition circuit 19 obtains the luminance deviation characteristic of each bit, and the luminance deviation amount of each level is obtained based on this, converted into a threshold value and fed back to the error diffusion circuit 11. If there is a change in the input signal, "Gradation characteristic acquisition" → "Error diffusion" →
The image vibrates in the loop of "Gradation characteristics acquisition" → ...
Since the loop filter 28 is inserted, this vibration is suppressed. Therefore, by monitoring the past state and gradually changing the threshold value, a steep change, that is, a change due to a high frequency component is suppressed and becomes a smooth change.
You can obtain high quality images without flicker.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. PD driven by the address / display separation type driving method (ADS subfield method) as a display device
The case of using for P14 will be described as an example. FIG. 1 shows the conventional circuit of FIG. 7 in which a loop filter 28 is inserted on the output side of the threshold value converter 22. As the loop filter 28, a saturation integral type filter including an adder 29, a coefficient unit 30 (for example, 1/2 as a coefficient) and a 1-field delay unit 31 as shown in FIG. 2 is used as the first embodiment. Other configurations are the same as those in FIG. 7.

The operation of the above configuration will be described.
When the original pixel video signal quantized and input to the video signal input terminal 10 is sent to the data counter 17 of the video output monitoring unit 15, the data counter 17 corresponds the M-bit video data to each bit. The "count of display dots in subfield K", which is the display number of each bit in one or a plurality of frames, is counted by M counters.
The count value selection circuit 18 calculates the display area ratio (Sk) by dividing the "display dot number of subfield K" counted by the data counter 17 by the "total dot number". Then, it is sent to the deviation calculator 20 via the 1-field delay ROM 27, and the brightness deviation characteristic of each bit is calculated by the deviation calculator 20. Based on this, the brightness characteristic calculator 21 calculates the brightness deviation amount of each level. Then, the threshold conversion unit 22 converts the threshold value.

Here, it is assumed that the input signal from the threshold converter 22 to the adder 29 changes from "0" to "1" at t1 as shown in (a) of FIG. This adder 2
The output of 9 is multiplied by, for example, a coefficient of 1/2 in the coefficient unit 30, and its output is delayed by 1 field in the 1-field delay unit 31 and returned to the adder 29. As a result, FIG.
As shown in (b), at t2, only 1/2 of the change is output. Similarly, at t3, 1/2 of 1/2
Is added to 1/2 and only 3/4 is output, and further, t
At 4 o'clock, 1/2 of 1/4 is added to 3/4 to 7/8
Only outputs. In the same manner, the value is saturated to "1".

By inserting the loop filter 28 as described above, the vibration of the image in the loop of “gradation characteristic acquisition” → “error diffusion” → “gradation characteristic acquisition” → ... Is suppressed. Therefore, by monitoring the past state and gradually changing the threshold value, a sharp change, that is, a change due to a high frequency component is suppressed to be a smooth change, and a high-quality image without flicker can be obtained.

As the second embodiment, the loop filter 28 is of a 2-tap type in which a 1-field delay unit 31, an adder 29, and a coefficient unit 30 (for example, 1/2 as a coefficient) are connected in this order as shown in FIG. Can also be used. In this case, the input signal from the threshold conversion unit 22 to the 1-field delay unit 31 is, as described above, as shown in (a) of FIG.
If it changes from "0" to "1" at t1, 1
A signal delayed by one field in the field delay unit 31 and a signal not delayed by the field delay unit 31 are added in the adder 29, and the output of the adder 29 is multiplied by, for example, a coefficient of 1/2 in the coefficient unit 30. As a result, as shown in FIG. 6C, at t2, only 1/2 of the change is output. Next, it becomes "1" at t3.

As the loop filter 28, a non-saturation type filter having only an adder 29 and a one-field delay unit 31 as shown in FIG. 4 can be used as the third embodiment. In this case, the input signal from the threshold conversion unit 22 to the 1-field delay unit 31 is, as described above, as shown in (a) of FIG.
If it changes from "0" to "1" at t1, 1
The signal delayed by one field by the field delay unit 31 and the signal not delayed by the field delay unit 31 are added by the adder 29 and output. As a result, as shown in FIG. 6D, it becomes “1” at t2. The output that further increases after t3 is processed by adding another circuit such as a suppression circuit.

The loop filter 28 includes a first coefficient unit 30a (for example, 1/2 as a coefficient), an adder 29, and a one-field delay unit 3 as shown in FIG. 5 as a fourth embodiment.
The second coefficient multiplier 30 connected in the order of 1 and inserted in the feedback path from the 1-field delay device 31 to the adder 29
It is also possible to use a saturation integral type of b (for example, 1/2 as a coefficient). In this case, similarly to FIG. 2, it becomes 1/2, 3/4, 7/8 ... As shown in FIG.

In the above embodiment, the loop filter 28 is inserted between the threshold conversion unit 22 and the threshold transfer unit 26, but the present invention is not limited to this example, and the output side of the data counter 17 and the input of the error diffusion circuit 11 are not limited to this example. Similar results can be obtained regardless of the position of insertion between the two sides.

[0027]

According to the present invention, since the loop filter 28 is inserted as described above, "gradation characteristic acquisition" → "error diffusion"
→ Vibration of image in the loop of “Gradation characteristic acquisition” →… is suppressed. Therefore, by monitoring the past state and gradually changing the threshold value, a sharp change, that is, a change due to a high frequency component is suppressed to be a smooth change, and a high-quality image without flicker can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an error diffusion processing device of a display device according to the present invention.

FIG. 2 is a block diagram showing a first embodiment of a loop filter 28 used in the device of the present invention.

FIG. 3 is a block diagram showing a second embodiment of a loop filter 28 used in the device of the present invention.

FIG. 4 is a block diagram showing a third embodiment of a loop filter 28 used in the device of the present invention.

FIG. 5 is a block diagram showing a third embodiment of the loop filter 28 used in the device of the present invention.

FIG. 6 is an operation waveform diagram of a different loop filter 28 used in the device of the present invention.

FIG. 7 is a block diagram showing an error diffusion processing device of a display device previously proposed by the applicant.

FIG. 8 is a characteristic diagram showing an example of emission luminance characteristics.

FIG. 9 is a characteristic diagram showing a typical example of emission luminance characteristics.

[Explanation of symbols]

10 ... Video signal input terminal, 11 ... Error diffusion circuit, 12 ...
Error amount calculation unit, 13 ... Processing circuit unit, 14 ... PDP, 15
... video output monitoring section, 16 ... sampling clock generation circuit, 17 ... data counter, 18 ... count value selection circuit, 19 ... generated luminance characteristic acquisition circuit, 20 ... deviation calculation section,
21 ... Luminance characteristic calculation unit, 22 ... Threshold conversion unit, 23 ... Calculation control unit, 24 ... Processing subfield control unit, 25 ... Processing level control unit, 26 ... Threshold transfer unit, 27 ... 1 field delay ROM, 28 ... Loop Filter, 29 ... Adder, 30, 30a, 30b ... Coefficient multiplier, 31 ... 1-field delay device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masayuki Kobayashi, 1116 Suenaga, Takatsu-ku, Kawasaki-shi, Kanagawa, Fujitsu General Co., Ltd. 72) Inventor Seiji Matsunaga 1116 Suenaga, Takatsu-ku, Kawasaki City, Kanagawa Prefecture Fujitsu General Limited

Claims (5)

[Claims] 1. An error diffusion circuit 11 for adding a reproduction error generated in the past from an original pixel to a quantized input original pixel video signal to obtain a diffused output signal and performing pseudo halftone display.
And the video output monitoring unit 15 for obtaining the display area ratio (Sk)
And a generated luminance characteristic acquisition circuit 19 for obtaining a luminance deviation amount at each level based on the luminance deviation characteristic of each bit and converting it to a threshold value, in a device connected in a loop. An error diffusion processing device for a display device, wherein a loop filter 28 for suppressing image vibration in the loop is inserted in the loops up to 11. 2. The loop filter 28 includes an adder 29,
The coefficient unit 30 and the 1-field delay unit 31 are sequentially connected, and the output of the 1-field delay unit 31 is added to the adder 2
It is composed of a saturation integral type that is fed back to 9 and has a coefficient unit 3
The error diffusion processing device for a display device according to claim 1, wherein a signal obtained by multiplying a coefficient smaller than 1 by 0 and delayed by 1 field by the 1-field delay unit 31 is added to the input signal by the adder 29. 3. The loop filter 28 includes a 1-field delay unit 31, an adder 29 for adding an output signal of the 1-field delay unit 31 and a signal that is not delayed, and is connected to the adder 29 and multiplies a coefficient smaller than 1. 2. The error diffusion processing device for a display device according to claim 1, wherein the error diffusion processing device is of a 2-tap type with a coefficient unit 30 for performing. 4. The loop filter 28 includes an adder 29,
The 1-field delay device 31 is sequentially connected, and
The output of the field delay device 31 is fed back to the adder 29 and is of a non-saturated integral type.
2. The error diffusion processing device for a display device according to claim 1, wherein the signal delayed by 1 field by 1 is added to the input signal by the adder 29. 5. The loop filter 28 comprises a first coefficient unit 3
0a, the adder 29, and the 1-field delay unit 31 are sequentially connected, and the output of the 1-field delay unit 31 is fed back to the adder 29 via the second coefficient unit 30b. And the first coefficient unit 30
The adder 29 adds the input signal multiplied by a coefficient smaller than 1 by a and the signal delayed by 1 field by the 1 field delay unit 31 and multiplied by a coefficient smaller than 1 by the second coefficient unit 30b. The error diffusion processing device for a display device according to claim 1.