JPH09179522A - Error diffusion processor for display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a pattern inconspicuous when a pseudo halftone image by error diffusion processing is displayed on a PDP(plasma display panel) of the gradation number out of 2 factorial display. SOLUTION: This device is provided with an error diffusion circuit 10a obtaining a diffusion output signal from an input video signal by the error diffusion processing, a data conversion circuit 14a converting the diffusion output signal to a drive signal for displaying a halftone image on the PDP 16a using a sub-field method and a light emission luminous characteristic acquisition circuit 18a obtaining the light emission luminous characteristic on the PDP 16a answering toe a prescribed light emission luminance line P in a preset figure (b) at intervals of a fixed period based on the drive signal and outputting it to the error diffusion circuit 10a. Then, since the light emission luminance like P is set so that a light emission luminance level is increased stepwise at the ratio of 1:1 from a level 0 to the level Dk answering to the number k of display gradation, the matter that the same gradation is used twice in a dark level that a difference of gradation is recognized easily by a human eye is eliminated, and the pattern in a low level is made inconspicuous.

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 of a display device using a display panel having a gradation number outside the factorial display of 2. The number of gradations out of the factorial display of 2 is, for example, 12 (2 to the third power is 2
4) and 28 (not 2 4 or 2 5), and the display panel means a digital display panel such as PDP (plasma display panel) or LCD (liquid crystal display panel).

[0002]

2. Description of the Related Art Recently, as a thin and lightweight display device, a device using a PDP or LCD 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 a digitized input video signal. Therefore, the brightness gradation emitted from the panel surface of the display panel is determined by the number of bits of the signal to be handled.

[0003] PDPs are AC type and D type having different basic characteristics.
It is divided into two types of C type. In the AC type PDP, sufficient characteristics have been obtained with respect to luminance and life, but as for gradation display, only a maximum of 64 gradation display has been reported at the prototype level, but the address / display separation type driving method (ADS) A method of 256 gradations in the future by the subfield method has been proposed.

In the ADS subfield method, for example, in the case of 8 bits and 256 gradations, one frame has a relative luminance ratio of 1, 2, 4, 8, 16, 32, 64, 128.
, And 256 gradations are displayed by the combination of the luminances of the eight screens. 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 above-described AC driving method, as the number of gradations increases, the number of bits in an address period as a preparation period for lighting and emitting light in the panel within one frame period increases. The period becomes relatively short, and the maximum luminance decreases. 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 minimizing the contrast error between the input signal and the emission luminance while reducing the bit number of the output diffusion output signal than the bit number of the input signal is a process for expressing a pseudo halftone. Yes, it is used when expressing light and shade with few gradations.

A conventional display device using a general subfield method and error diffusion processing is configured as shown in FIG. That is, the error diffusion circuit 10 performs error diffusion processing using the light emission luminance level set in the ROM 12 in advance, so that m (≦ n−) from the n-bit input video signal.
1) Obtain a spread output signal of bits. Next, the data conversion circuit 14 time-divides the m-bit diffused output signal into one frame into a plurality of sub-fields, and the display gradation number p (p = p
It is converted into a drive signal for displaying a halftone image by the PDP 16 of 2 m).

As a result, as shown in FIG. 5, although the light emission luminance levels like the steps of the solid line are momentarily output, the light emission luminance levels above and below the steps of the solid line are actually output. Are alternately output at a predetermined ratio, so that they are recognized in an averaged state and become a corrected luminance line of y = x like a dotted line.

[0009]

However, the light emission luminance characteristic of the PDP 16 may change depending on the data to be displayed and may be different from the light emission luminance characteristic shown in FIG. 5. In such a case, as shown in FIG. However, in the method of adjusting to the typical emission luminance characteristic, there is a problem that it cannot fully adapt to the gradation characteristic, and a pseudo contour appears due to the gradation non-adaptation. In order to solve such a problem, the present applicant has already proposed a display device using a gradation adaptive error diffusion process as shown in FIG.

In addition, one frame is composed of a plurality of subfields SF1 to SFm having different luminance relative ratios, and in the case of displaying 2 m-th gradation by combining the luminance of m screens, the luminance level of the drive signal is Is from "2 to the m-1" to "2
M-th power ”(eg, from“ 7 ”to“ 8 ”or“ 15 ”)
There is a problem that granular noise is seen on the screen corresponding to the changed portion when changing from "16" to "16". In order to solve such a problem, the present applicant has already proposed that the weighting of at least two subfields among a plurality of subfields forming one frame is equalized as shown in FIG. did.

That is, the display device using the gradation adaptive type error diffusion processing as shown in FIG.
The error diffusion circuit 10 obtains the emission luminance characteristic of the PDP 16 for each one or a plurality of frames based on the drive signal output from the error diffusion circuit 10.
a light emission luminance characteristic acquisition circuit 18 for outputting to a, and instead of the light emission luminance level provided from the ROM 12 of FIG. 4, the light emission luminance level is updated for each frame or every plural frames to perform error diffusion. Prevent the appearance of false contours.

Further, FIG. 7 showing a frame structure for preventing granular noise from appearing on the screen is shown in FIG. 7, in which a plurality of sub-frames constituting one frame have a relative luminance ratio of 1, 2,
Six subfields SF1, SF of 4, 4, 8 and 8
2, SF3, SF4, SF5, and SF6 are provided to prevent a large change in brightness when the brightness level changes, thereby preventing deterioration of image quality. At this time, the six subfields SF1, SF2, SF3, SF4, SF
28 with a combination of 5 and 6 screen brightness corresponding to SF6
A gradation display is performed.

A factorial of 2 as described above (eg 2 of 6)
PD having a gradation number (eg 28) less than the power of 64
Considering the case where the error diffusion process is performed in P16, a method may be considered in which the emission luminance level stored in advance in the ROM 12 of FIG. 4 is configured as shown in FIG. 8 in order to bring the gradation steps closer to a straight line. In other words, it is a method of compensating for a gradation that is insufficient in the factorial of 2 by using one gradation twice in the middle of the gradation. However, when the gradation adaptive error diffusion processing as shown in FIG. 6 is performed in response to the emission luminance characteristics as shown in FIG. 8, the following problems occur.

That is, the characteristic of the light emission luminance level with respect to the drive signal of the PDP 16 is stepped so that the same gradation in the middle is used twice as shown in FIG.
(Or multiple frames), the light emission luminance characteristic is obtained and the light emission luminance level is updated.
If the gradation adaptive error diffusion process is performed in this gradation staircase, the error becomes large near the same gradation used at a low level, and the pattern generated due to the error diffusion process. There was a problem that would be conspicuous.

The present invention has been made in view of the above-mentioned problems, and a pseudo-halftone image is subjected to grayscale adaptive error diffusion processing by using a display panel having a grayscale number deviating from 2-tone display. It is an object of the present invention to provide an error diffusion processing device of a display device capable of making a pattern, which is generated at a dark level in which a difference in gradation is easily recognized by human eyes, inconspicuous when is displayed.

[0016]

According to a first aspect of the present invention, an error diffusion process using a light emission luminance characteristic is performed.
From the (for example, 8) -bit input video signal, m (≦ n−1,
For example, an error diffusion circuit for obtaining a 4) bit diffusion output signal, and an m-bit diffusion output signal obtained by this error diffusion circuit are time-divided into a plurality of subfields for one frame, and the number of display gradations k (< 2 m, for example, 12) A data conversion circuit for converting into a drive signal for displaying a halftone image on a display panel, and based on the drive signal obtained by this data conversion circuit, a preset light emission luminance characteristic is obtained. And a light emission luminance characteristic acquisition circuit that obtains the light emission luminance characteristic of the corresponding display panel at fixed intervals and outputs the light emission luminance characteristic to the error diffusion circuit. The set light emission luminance characteristic is from the level 0 of the drive signal to the number of display gradations k. The emission brightness level is 1: 1 up to the level Dk corresponding to
It is characterized in that the emission luminance level is set so as to repeat the maximum luminance level with respect to the drive signal which exceeds the level Dk in a stepwise manner.

In order to perform gradation adaptive error diffusion processing,
The light emission luminance characteristic obtained and updated by the light emission luminance characteristic acquisition circuit every fixed period (for example, one or a plurality of frames) is from the level 0 of the drive signal to the display gradation number k (for example, 1).
2) The emission brightness level gradually increases up to a level Dk (eg, 176) corresponding to 2) at a ratio of 1: 1, and the emission brightness level reaches the maximum brightness level (eg, for a drive signal exceeding the level Dk). 176) is repeated so that it corresponds to the emission brightness characteristic set in advance, and therefore, when the gradation adaptive error diffusion process is performed, it is easy for the human eye to recognize the difference in gradation at a dark level. Since the same gradation is not used twice, low level patterns are less noticeable.

Further, for the drive signals (eg, 192, 208, 224, ...) Exceeding the level Dk, the emission brightness level is set to repeat the maximum brightness level (eg, 176), so that high brightness is achieved. Although the error in the level becomes large, the gradation difference at the high brightness level is hard to be perceived by human eyes, and the pattern of the error diffusion process becomes hard to be noticed. Although the gradation staircase is extremely refracted, gradation linearity is maintained by the gradation adaptation processing.

According to a second aspect of the present invention, in the first aspect of the invention, the data conversion circuit is obtained by an error diffusion circuit so that granular noise is not visible on the screen corresponding to the brightness level changing portion. The m-bit spread output signal is time-divided into a plurality of sub-fields including two sub-fields having at least equal weighting in one frame, and a halftone image is displayed on a display panel having a display gradation number k (<2 m power). Is converted into a signal for displaying.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of an error diffusion processing device for a display device according to the present invention. FIG. 1A shows a block diagram of the apparatus. In this figure, 10a is an error diffusion circuit for performing an error diffusion process for minimizing a grayscale error between the input video signal and the emission brightness of the PDP 16a. . The error diffusion circuit 10a
Is configured to obtain an m (≦ n−1, for example, 4) -bit diffused output signal from an n-bit input video signal by performing an error diffusion process using the emission luminance level.

A data conversion circuit 14a is coupled to the output side of the error diffusion circuit 10a. The data conversion circuit 14a outputs the diffusion output signal output from the error diffusion circuit 10a to 4, 2, 1 for one frame as shown in FIG.
4 subfields SF1 and SF weighted to 4
2, SF3, and SF4, and is configured to be converted into a drive signal for displaying a halftone image of the display gradation number 12 (when k = 12) of the PDP 16a and output to the PDP 16a. There is.

A light emission luminance characteristic acquisition circuit 18a is coupled to the output side of the data conversion circuit 14a. The light emission luminance characteristic acquisition circuit 18a includes the data conversion circuit 14a.
Based on the drive signal obtained in step (b), preset emission luminance characteristics (displayed by emission luminance line P)
The light emission luminance characteristic of the PDP 16a for each one or a plurality of frames is calculated and output to the error diffusion circuit 10a. As shown in FIG. 1B, the set emission luminance characteristic is that the emission luminance level is 1: 1 from the level 0 of the drive signal to the level Dk (= 176) corresponding to the number k of display gradations. So 0, 16, 32, ...
The emission brightness level repeats the maximum brightness level 176 for the drive signals (192, 208, 224, ...) Which increase in a stepwise manner to 176 and exceed the level Dk.

The light emission luminance characteristic acquisition circuit 18a is mainly composed of, for example, a display area calculation section for obtaining a display area ratio for each field of the PDP 16a and a luminance deviation amount calculation section for obtaining a luminance deviation amount of each level. ing.

Next, the operation of FIG. 1A will be described with reference to FIG.
(B) will be described together. The error diffusion circuit 10a performs an error diffusion process using the light emission luminance level of the light emission luminance characteristic to obtain a 4-bit (when m = 4) bit diffusion output from an 8-bit (when n = 8) input video signal. Get the signal.

The data conversion circuit 14a includes the error diffusion circuit 1
The diffused output signal of 0a is converted into a drive signal corresponding to the subfield display method and output to the PDP 16a. This PD
As shown in FIG. 2, the drive signal to the P16a has four subfields SF1, SF2, SF3, SF for one frame.
4 time division, using the combination of the brightness of 4 screens, P
This is a drive signal for displaying a halftone image (176 pseudo halftone) of 12 gradations (when k = 12) on the DP 16a.

The light emission luminance characteristic acquisition circuit 18a is based on the drive signal obtained by the data conversion circuit 14a.
Corresponding to the preset light emission luminance characteristic (light emission luminance line P) as shown in (b), the light emission luminance characteristic of the PDP 16a for each one or a plurality of frames is obtained and output to the error diffusion circuit 10a. Therefore, the gradation adaptive error diffusion processing in which the emission luminance characteristic is updated is performed for each one or every plural frames.

As described above, the emission brightness characteristic obtained and updated by the emission brightness characteristic acquisition circuit 18a for performing the gradation adaptive error diffusion processing is the display gradation number 12 from the level 0 of the drive signal. Level 1 corresponding to (k = 12)
Up to 76 (Dk = 176), the emission luminance level increases stepwise at a ratio of 1: 1, and the emission luminance level repeats the maximum luminance level 176 for a drive signal exceeding the level 176. Since it corresponds to the characteristics, when the gradation adaptive error diffusion processing is performed, the same gradation is not used twice at a dark level where the difference in gradation is easily recognized by the human eye, and the low gradation is reduced. The pattern on the level is less noticeable.

Further, for the drive signal levels (192, 208, 224, ...) Exceeding the drive signal level 176, the emission brightness level is set to repeat the maximum brightness level 176, so that at the high brightness level. However, the difference in gradation at a high brightness level is hard to be perceived by human eyes, and the pattern of the error diffusion process is hard to be noticed. Although the gradation staircase is extremely refracted, gradation linearity can be maintained by the gradation adaptation processing.

In the above-described embodiment, in order to prevent granular noise from being seen on the screen corresponding to the changing portion of the brightness level, as shown in FIG. 2, one frame is divided into two subfields SF1 having the same weight, The description has been given of the case where the halftone image is displayed by the time division of the four subfields SF1 to SF4 including SF4 and the PDP having the gradation number 12 which is out of the factorial display of 2. However, the present invention is not limited to this. Instead of time-dividing one frame into multiple sub-fields,
It can be used for displaying a halftone image on a display panel having a gray scale number outside the factorial display.

For example, as shown in FIG. 3, one frame is divided into two sets of subfields (SF1 and SF6, which have the same weighting) in order to prevent granular noise from being seen on the screen corresponding to the changing portion of the brightness level. It is also possible to use the one that displays a halftone image with a PDP having a gray scale number of 28 out of the factorial display of 2 by time-division into 6 subfields SF1 to SF6 including SF2 and SF5). Or
It is also possible to use one in which one frame is time-divided into a plurality of subfields having different weightings and a pseudo halftone is displayed on a digital display panel having a gray scale number outside the factorial display of 2.

In the above embodiment, the display panel is the PDP.
However, the present invention is not limited to this, and can be applied to the case of a digital display panel (for example, LCD).

[0032]

According to the present invention, in a device for displaying a pseudo-halftone image on a display panel by the subfield method and the gradation adaptive error diffusion processing, the gradation adaptive error diffusion processing is performed at regular intervals. The emission luminance characteristics obtained and updated (for example, for each one or a plurality of frames) have emission luminance levels from the level 0 of the drive signal to the level Dk (for example, 176) corresponding to the display gradation number k (for example, 12). It corresponds to a preset emission luminance characteristic that the emission luminance level repeats the maximum luminance level (for example, 176) for a drive signal that exceeds the level Dk and increases stepwise at a ratio of 1: 1. Therefore, when the gradation adaptive error diffusion processing is performed, the same gradation is not used twice at a dark level where the difference in gradation is easily recognized by human eyes.
Low-level patterns are less noticeable.

Moreover, since the emission brightness level is set to repeat the maximum brightness level (eg, 176) for the drive signals (eg, 192, 208, 224, ...) Exceeding the level Dk, high brightness is achieved. Although the error in the level becomes large, the gradation difference at the high brightness level is hard to be perceived by human eyes, and the pattern of the error diffusion process becomes hard to be noticed.
Although the gradation staircase is extremely refracted, gradation linearity is maintained by the gradation adaptation processing.

The data conversion circuit time-divides the m-bit diffusion output signal obtained by the error diffusion circuit into a plurality of subfields including at least two subfields of equal weighting, and the number of display gradations k (<2 to the mth power)
When the display panel is configured to convert into a signal for displaying a halftone image, it is possible to prevent granular noise from being seen on the screen corresponding to the changing portion of the brightness level.

[Brief description of the drawings]

1A and 1B show an embodiment of an error diffusion processing device for a display device according to the present invention, wherein FIG. 1A is a block diagram of the device, and FIG. 1B is a gradation adaptive error diffusion by the device of FIG. Corresponding to the emission brightness characteristics updated by processing,
It is a light emission luminance characteristic chart set up beforehand.

2 illustrates the structure of one frame time-divided by a data conversion circuit when the number of display gradations k of the PDP of FIG.
It is explanatory drawing of the drive sequence in 2-gradation display.

3 is an explanatory diagram of a drive sequence in 28 gradation display by a subfield method when the number of display gradations k of the PDP in FIG. 1 is 28;

FIG. 4 is a block diagram of an error diffusion processing device of a display device using a general subfield method and an error diffusion process.

FIG. 5 is a characteristic diagram showing a typical example of emission luminance characteristics.

FIG. 6 is a block diagram of an error diffusion processing device of a display device which performs gradation adaptive error diffusion processing.

FIG. 7 is an explanatory diagram of a drive sequence in 28 gradation display.

FIG. 8 is pre-stored in a ROM, which is conceived to bring the steps of the gradation closer to a straight line when the error diffusion process is performed in the PDP displaying the gradation number less than the factorial of 2 (for example, 12). It is a characteristic view of a light emission luminance level.

[Explanation of symbols]

10, 10a ... Error diffusion circuit, 12 ... ROM, 14,
14a ... Data conversion circuit, 16, 16a ... PDP (one example of display panel), 18, 18a ... Emission luminance characteristic acquisition circuit, Dk ... Drive signal level corresponding to display gradation number k,
k ... Display gradation number of PDP, P ... Set emission luminance line (emission luminance characteristic), SF1 to SF4 ... Subfields.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Junichi Onodera, 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 (2)

[Claims] 1. An error diffusion process using light emission luminance characteristics is performed to convert m (≦ n−) from an n-bit input video signal.
1) An error diffusion circuit for obtaining a bit diffusion output signal and an m-bit diffusion output signal obtained by the error diffusion circuit
A data conversion circuit that time-divides a frame into a plurality of subfields and converts into a drive signal for displaying a halftone image on a display panel with a display gradation number k (<2 to the m-th power), and this data conversion circuit A light emission luminance characteristic acquisition circuit for obtaining a light emission luminance characteristic of the display panel corresponding to a preset light emission luminance characteristic at regular intervals based on the obtained drive signal and outputting the light emission luminance characteristic to the error diffusion circuit. The emission luminance characteristic is that the emission luminance level increases stepwise at a ratio of 1: 1 from the level 0 of the drive signal to the level Dk corresponding to the number k of display gradations, and the emission signal level exceeds the level Dk. An error diffusion processing device for a display device, wherein the emission brightness level is set to repeat the maximum brightness level. 2. A data converter circuit divides an m-bit diffused output signal obtained by an error diffusion circuit into a plurality of sub-fields including at least two sub-fields having the same weighting, and time-divisions the same on a display panel. The error diffusion processing device for a display device according to claim 2, wherein the error diffusion processing device is formed by converting into a drive signal for displaying a halftone image.