JP3322073B2 - Error diffusion processing device for display device - Google Patents

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 a 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
DP (plasma display panel) has attracted attention. The driving method of this PDP is completely different from the conventional CRT driving method, and is a direct driving method using digitized video input signals. Therefore, the luminance gradation emitted from the panel surface is determined by the number of bits of the signal to be handled.

[0003] In the AC type PDP, there has been only a report on the gradation display up to a maximum of 64 gradation display at the prototype level, but the address / display separation type driving method (ADS subfield method).
Has proposed a future 256 gradation method.

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 luminances of 8 screens
The gradation is displayed. Each subfield is composed of an address period in which data for one refreshed screen is written and a sustain period for determining a luminance level of the subfield. In the address period, first, wall charges are initially formed on each pixel at the same time for the entire screen, and then a sustain pulse is applied to the entire screen to perform display. The brightness of the subfield is proportional to the number of sustain pulses,
The brightness is set to a predetermined value. In this way, 256 gradation display is realized.

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

The error diffusion process for minimizing the shading error between the input signal and the emission luminance while reducing the number of bits of the output drive signal from the number of bits of the input signal is a process for expressing a pseudo halftone. , Which is used when expressing gradation with a small number of gradations. In a conventional general error diffusion circuit, a video signal of an original pixel Ai, j of p (for example, 8) bits is input from a video signal input terminal to the error diffusion circuit, and the number of bits is further reduced to q ( For example, 4) light is emitted from the PDP by performing processing for reducing the number of bits.

A light emission luminance characteristic calculating unit such as a ROM measures and stores the light emission luminance characteristic of the PDP from representative input data (solid line) as close as possible to y = x (dotted line) shown in FIG. Keep it. This light emission luminance characteristic is sent to an error amount calculation unit to calculate an error, which is added to an input video signal by a processing circuit unit and diffused to perform pseudo halftone display.

As a result, although the light emission luminance level is instantaneously like a stair-like solid line, it is actually recognized in an averaged state, and becomes a corrected luminance line similar to the dotted line y = x. .

However, the light emission luminance characteristic of a display device such as a PDP changes depending on data to be displayed, and there are cases where the light emission luminance characteristic is greatly deviated from y = x (dotted line) as shown by a solid line in FIG. . In such a case, with the method of adjusting to the typical emission luminance characteristics as shown in FIG. 9, data other than when the representative characteristics are obtained cannot be adapted to the gradation characteristics. There has been a problem that a pseudo contour due to gradation non-adaptation appears.

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

Referring to FIG. 7, a diffusion output signal is obtained by adding an error diffusion circuit 11 to the original pixel video signal quantized and input from the video signal input terminal 10 and a reproduction error generated in the past from the original pixel. In the apparatus for performing pseudo halftone display, a loop from the error diffusion circuit 11 to the error diffusion circuit 11 via the video output monitoring unit 15, the one-field delay ROM 27, the generated luminance characteristic acquisition circuit 19, and the threshold value transfer unit 26 The video output monitoring unit 15 includes a sampling clock generation circuit 16 and M
A data counter 17 that counts the number of displayed bits in one or a plurality of frames with M counters corresponding to each bit of the video data of bits, and the number of display dots counted by the data counter 17 is the total number of dots. And a count value selection circuit 18 for calculating a display area ratio (Sk) by dividing by the expression (1).
9 is a deviation calculator 20 for calculating the luminance deviation characteristic of each bit.
A luminance characteristic calculating unit 21 for calculating a luminance deviation amount of each level based on the data of the deviation calculating unit 20;
The arithmetic control unit 23 includes a processing subfield control unit 24 and a processing level control unit 25.

In the above-described configuration, the error diffusion circuit 11 includes the error amount calculation unit 12 and the processing circuit unit 13
Error diffusion processing is performed based on the given light emission luminance characteristics, and pseudo halftone display is performed. When data is transmitted from the error diffusion circuit 11 to the video output monitoring unit 15, the data counter 17 converts the M-bit video data into one or more frames of each bit by M counters corresponding to each bit. The number of display dots “the number of display dots of the subfield K” is counted. The count value selection circuit 18
"Subfield K" counted by the data counter 17
The display area ratio (Sk) is obtained by performing an operation of dividing the “display dot number” by “the total number of dots”. And the deviation calculation unit 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 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 ratio 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. Have been.

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

[0015]

However, as described above, “acquisition of gradation characteristics” → “error diffusion” → “acquisition of gradation characteristics” →
When the image vibrates in the loop of ..., there is a problem that the mixture ratio of white and black changes for each frame and changes at a fast cycle.

According to the present invention, the light emission luminance characteristic for each frame 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 is updated to perform error diffusion, thereby performing pseudo contour. It is an object of the present invention to obtain an apparatus which prevents the appearance of the image, in particular, in which the image flicker due to the loop vibration is inconspicuous.

[0017]

According to the present invention, pseudo-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 diffuse output signal. The error diffusion circuit 11, a video output monitoring unit 15 for calculating a display area ratio (Sk), and a generated luminance characteristic acquisition circuit 19 for obtaining a luminance deviation amount of each level from the luminance deviation characteristic of each bit and converting the luminance deviation amount into a threshold value are looped. In the apparatus connected in a vertical manner, the video output monitoring unit 15 sends 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 up to and including the error diffusion processing device for a display device. It is.

[0018]

The display area ratio (Sk) of the quantized original pixel video signal is obtained by the video output monitoring unit 15. Then, the luminance deviation characteristic of each bit is obtained by the generated luminance characteristic acquisition circuit 19, the luminance deviation amount of each level is calculated based on the luminance deviation characteristic, converted into a threshold value, and fed back to the error diffusion circuit 11. If there is a change in the input signal, “Get gradation characteristics” → “Error diffusion” →
The image vibrates in the loop of “Get gradation characteristics” →…
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 the change becomes a smooth change.
High quality images without flicker can be obtained.

[0019]

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

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 converts the M-bit video data to each bit. The “number of display dots of the subfield K”, which is the number of display of each bit in one or a plurality of frames, is counted by the M counters.
The count value selection circuit 18 calculates the display area ratio (Sk) by dividing the “display dot number of the subfield K” counted by the data counter 17 by the “total dot number”. Then, it is sent to the deviation calculating unit 20 via the one-field delay ROM 27, and the deviation calculating unit 20 calculates the luminance deviation characteristic of each bit. The threshold value is converted into a threshold value by the threshold value conversion unit 22.

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

By inserting the loop filter 28 as described above, the vibration of the image in the loop of “acquisition of gradation characteristics” → “error diffusion” → “acquisition of gradation characteristics” →. For this reason, 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 and a smooth change is obtained, and a high-quality image without flicker is obtained.

As a second embodiment, the loop filter 28 is of a two-tap type in which a one-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 one-field delay unit 31 is, as described above, as shown in FIG.
Assuming that the value changes from “0” to “1” at t1, 1
The signal delayed by one field in the field delay unit 31 and the signal not delayed are added in an adder 29, and the output of the adder 29 is multiplied by a coefficient unit 30 by, for example, a coefficient ２. As a result, as shown in FIG. 6C, at time t1, only a half of the change is output. Next, at t2, it becomes "1".

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

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.
1 and a second coefficient unit 30 inserted in the feedback path from the one-field delay unit 31 to the adder 29.
It is also possible to use a saturation integral type consisting of b (for example, 1/2 as a coefficient). In this case, as in FIG. 2, the values become 1/2, 3/4, 7/8,... As shown in FIG.

In the above-described embodiment, the loop filter 28 is inserted between the threshold value conversion unit 22 and the threshold value transfer unit 26. However, the present invention is not limited to this example, and the output side of the data counter 17 and the input side of the error diffusion circuit 11 The same result can be obtained by inserting any position between the sides.

[0027]

According to the present invention, since the loop filter 28 is inserted as described above, "acquisition of gradation characteristics" → "error diffusion"
→ Vibration of an image in the loop of “acquisition of gradation characteristics” → is suppressed. For this reason, 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 and a smooth change is obtained, and a high-quality image without flicker can be obtained.

[Brief description of the 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 used in the apparatus of the present invention.

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

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

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

FIG. 6 is an operation waveform diagram by different loop filters 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 present applicant.

FIG. 8 is a characteristic diagram illustrating an example of light 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 calculation unit, 13 processing circuit unit, 14 PDP, 15
... video output monitoring unit, 16 ... sampling clock generation circuit, 17 ... data counter, 18 ... count value selection circuit, 19 ... generated luminance characteristic acquisition circuit, 20 ... deviation calculation unit,
Reference numeral 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 value transfer unit, 27: one-field delay ROM, 28: loop Filter, 29 ... Adder, 30, 30a, 30b ... Coefficient unit, 31 ... One field delay unit.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masayuki Kobayashi 1116, Suenaga, Takatsu-ku, Kawasaki, Kanagawa Prefecture Inside Fujitsu General Limited (72) Inventor Hayato Denda 1116, Suenaga, Takatsu-ku, Kawasaki, Kanagawa Prefecture Fujitsu General Limited (72) Inventor Seiji Matsunaga 1116 Suenaga, Takatsu-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu General Limited (56) References JP-A-6-68250 (JP, A) JP-A-8-294013 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) G09G 3/28 G09G 3/20 641 G09G 3/36 G09G 5/00 H04N 5/66

Claims (5)

(57) [Claims] An error diffusion circuit for adding a reproduction error generated in the past from an original pixel to a quantized input original pixel video signal to obtain a diffusion output signal and performing pseudo halftone display.
When the number of display dots, a video output monitor 15 for obtaining the Table <br/> Display area ratio performs an operation of dividing by the total number of dots (Sk), a plurality
In a device in which a luminance deviation amount of each level is obtained by a luminance deviation characteristic of each bit corresponding to each bit of the video data of the bit, and a generation luminance characteristic acquisition circuit 19 that converts the luminance deviation amount into a threshold value is connected in a loop, An error diffusion processing device for a display device, wherein a loop filter 28 for suppressing a vibration of an image in the loop is inserted in a loop from the video output monitoring unit 15 to the error diffusion circuit 11. 2. The loop filter 28 includes an adder 29,
The coefficient unit 30 and the one-field delay unit 31 are sequentially connected, and the output of the one-field delay unit 31 is added to the adder 2.
9 and a coefficient integrating unit 3
2. The error diffusion processing device for a display device according to claim 1, wherein a signal multiplied by 0 and smaller than 1 and a signal delayed by one field by a one-field delay unit is added to an input signal by said adder. 3. A loop filter 28, a one-field delay unit 31, an adder 29 for an output signal of the one-field delay unit 31 and a signal not delayed, and a multiplication factor smaller than 1 connected to the adder 29. 2. An error diffusion processing device for a display device according to claim 1, wherein said error diffusion processing device is of a two-tap type with a coefficient unit 30 for performing the calculation. 4. The loop filter 28 includes an adder 29,
The one-field delay device 31 is connected sequentially, and
It is a non-saturated integral type in which the output of the field delay unit 31 is fed back to the adder 29, and the one-field delay unit 3
2. The error diffusion processing device for a display device according to claim 1, wherein the signal delayed by one field by 1 is added to the input signal by the adder 29. 5. The loop filter 28 includes a first coefficient unit 3
0a, the adder 29, and the one-field delay unit 31 are sequentially connected, and the output of the one-field delay unit 31 is fed back to the adder 29 via the second coefficient unit 30b. The first coefficient unit 30
The adder 29 adds an input signal multiplied by a coefficient smaller than 1 by a and a signal delayed by one field by a one-field delay unit 31 and multiplied by a coefficient smaller than 1 by a second coefficient unit 30b. The error diffusion processing device for a display device according to claim 1, wherein