JP2003066896A - Subfield image display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a moving picture false contour and to excellently make a gradation display. SOLUTION: When one field of an input image signal is divided into a plurality of subfields of one field and gradations are represented by controlling the light emission of a plasma display 9 according to a combination of light emissions by the subfields, an encoding method for blue light emission bodies of the plasma display 9 is made different from other colors and blue parts are encoded while priority is given to the suppression of noise rather than the number of gradations to perform an image display which is excellent on the whole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a subfield image display device for displaying an image by dividing one field of an image into a plurality of subfield images for display.

[0002]

2. Description of the Related Art When a multi-gradation image is displayed using a display device such as a plasma display (PDP) which is basically a binary display, one field of the image is divided into a plurality of sub-fields. A method is known in which a subfield is given a predetermined luminance weight to control the presence or absence of light emission for each subfield to display an image.

For example, in order to display 256 gradations, one field of the input signal is divided into eight subfields, and the luminance weights of the respective subfields are "1", "2", "4", ". 8 ”,“ 16 ”,“ 3 ”
2 ”,“ 64 ”, and“ 128 ”. The input signal is 8
If it is a bit digital signal, it is assigned to eight subfield images in order from the least significant bit, and 256
Display as a gradation image. Note that each subfield image is a binary image.

However, in such a conventional method of displaying 256 gradations using eight subfields,
It is known that so-called pseudo contour-like gradation disturbance occurs in moving image display. As a method of eliminating these gradation irregularities, an attempt to detect the movement of an image and change the encoding for each pixel or each area has been filed.

FIG. 5 shows a method proposed for the purpose of eliminating the disturbance of gradation in a moving image, that is, a so-called moving image pseudo contour by changing the encoding method for each image region.
In, the still image encoding circuit 51 and the moving image encoding circuit 5
2. Based on the input image signal 55, the motion detection circuit 53 and the selection circuit 54 determine whether the motion detection circuit 53 is a still image or a moving image, and controls the subfield control circuit 56 according to the still image and the moving image, respectively. Plasma display 57
Is a configuration for controlling the emission of light.

FIG. 6 shows the arrangement of subfields in this plasma display, and FIG. 7 shows an example of coding switching. That is, in the still image encoding circuit 51, as shown in FIG.
As shown in FIG. 7A, all the gradations are displayed, and the moving image coding circuit 52 is used for the moving image portion, as shown in FIG.
Since the encoding is performed so that the continuity of changes in the light emission pattern is secured to some extent, it is possible to expect a significant reduction in the moving image pseudo contour in the moving image portion. Moreover, the original sufficient gradation is secured in the still image portion.

[0007]

However, with such a conventional method alone, when it is theoretically difficult or uncertain to detect the motion of an image, such as when a flat image portion is moving, a moving image is displayed. Despite this, it was processed as a still image, and as a result, pseudo contours in moving images were sometimes observed. In such a case, for example, as a phosphor, such as a phosphor used in a plasma display,
When the time constants of green and red light emission (including response characteristics and afterglow characteristics) are large relative to blue light emission, there is a problem that the pseudo contour of a moving image generated due to blue light emission is conspicuously observed. It was In particular, in the image part where the line of sight moves while it is a flat part of the image, motion detection based on the difference between frames of the image or motion vector detection in block units cannot be calculated accurately in principle. However, there was a problem that proper moving image processing could not be performed and it was processed as a still image, and a moving image pseudo contour was generated and observed.

The present invention has been made in view of the above problems, and an object of the present invention is to enable suppression of a moving image pseudo contour and good gradation display.

[0009]

In order to solve the above-mentioned problems, the present invention divides one field of an input image signal into a plurality of sub-fields, and makes the display means emit light by combining the light-emission for each of the sub-fields. A sub-field image display device which controls and expresses gradation, and which constitutes the image display device when controlling a combination of light emission of each of the sub-fields according to a characteristic of the input image signal. The sub-field image display device is characterized in that it is made different depending on the emission color of.

[0010]

A subfield image display device according to claim 1 of the present invention divides one field of an input image signal into a plurality of subfields, and combines the light emission of each subfield to display the display means. A sub-field image display device for controlling light emission to express gradation, wherein when controlling a combination of light emission of each of the sub-fields according to a characteristic of an input image signal, it is possible to make different for each light emission color. It is a characteristic sub-field image display device.
For this reason, it is possible to effectively suppress the display of gradation disturbance and noise caused by the gradation display method using subfields by paying attention to the characteristics of the display device for each color and the visual characteristics for each color. It becomes possible to do. For example, a blue phosphor generally has a short afterglow characteristic, and a green phosphor used in a PDP or the like has a relatively long afterglow characteristic. On the other hand, regarding the visual characteristics, the resolution with respect to the spatial frequency of blue is lower than that of other colors.

Therefore, according to the present invention, when blue is displayed, the original number of gray scales is small, but the gray scale disturbance and noise resulting from the gray scale display method using the subfields are less generated. On the other hand, for a green color having a long afterglow, even if there is a gradation disturbance or noise that is generated or recognized by displaying a moving image, it is reduced and displayed by the afterglow. Therefore, by displaying the green color with emphasis on finer gradation, it is possible to display a good image as a whole. Note that the number of gradations that are insufficient when displaying blue can be increased in a pseudo manner by a so-called dither method or error diffusion. In addition,
As a side effect at this time, noise in a dot unit or a checkered pattern occurs, but in this regard, it is less noticeable because the visual characteristic of the observer, that is, the resolution for the spatial frequency of blue is relatively low, Good image quality can be obtained.

The subfield image display device according to a second aspect of the present invention determines the characteristics of the input image signal based on the inclination of the image in addition to distinguishing the display colors. For this reason, in a portion where the image has a gradual inclination, even when it is difficult to detect the motion because the image changes slowly, it is possible to perform the encoding suitable for this portion. Especially, in the past, when the image was a gentle slope such as a blue background, noise-like interference was sometimes observed due to the irregular / random movement of the line of sight of the observer looking at the screen. Only the encoding method can be the encoding in which the pseudo contour of the moving image is less likely to occur. It is not necessary to select a different encoding method depending on the display color, because no moving image pseudo-contour is generated in an almost completely flat portion, and image movement is easily detected in an image portion having an appropriate inclination. .

Further, in the sub-field image display device according to a third aspect of the present invention, the method of controlling the combination of the light emission of each sub-field is a method of controlling the number of gradations used for each pixel. It has a feature. Therefore, the encoding in which the number of gradations is suppressed and the generation of the moving image pseudo contour is suppressed can be used under the condition that the moving image pseudo contour is easily recognized. For example, in a moving image portion or a blue area having a large area, the gradation values used for displaying blue are limited to combinations of gradation values in which the occurrence of moving image pseudo contours is small, and particularly noticeable blue moving image pseudo contours are suppressed. can do.

Further, claim 4 and claim 10 of the present invention.
In the sub-field image display device described in, the method of controlling the combination of light emission of each of the sub-fields is such that the number of gradations used for display in pixels of blue emission color is changed to display in pixels of other emission color. The feature is that the number of gradations used is smaller than that used. Therefore, for blue, it is possible to obtain a good image display as a whole by displaying with a reduced number of gradations so that the encoding is performed with the occurrence of the pseudo contour of the moving image being suppressed.
In particular, when the gradation value of blue is darker than a predetermined value, the pseudo contour of the moving image is relatively inconspicuous, so that it is possible not to suppress the gradation number.

Even if the number of gradations used for the display itself is limited, it is natural that a means for recovering the gradation expression in a pseudo-equivalent manner such as so-called error diffusion or dither can be used together. is there. In this way, for blue, the gradation number is suppressed and coded and displayed, and the practical gradation number is compensated by error diffusion or the like, whereby a good image display can be achieved as a whole. The reason for this is as follows.

Insufficient gradation that may be caused by a decrease in the number of gradations is recovered to a practically sufficient level by the above-mentioned error diffusion. In particular, in this case, side effects such as error diffusion are not so remarkable in view of the visual characteristics of the observer for blue. On the other hand, the moving image pseudo contour generated due to the gradation expression using the subfield varies depending on the image, and may appear as a low-frequency component in terms of spatial frequency depending on the pattern. Therefore, with respect to blue color, it is possible to prevent the occurrence of a pseudo contour of a moving image that appears as a low frequency component in the spatial frequency due to the gradation limitation in advance, and to recover the lack of gradation without significant side effects by using a means such as error diffusion. It will be possible.

Further, in the sub-field image display device according to claim 5 of the present invention, the method of controlling the combination of the light emission of each of the sub-fields is used for display in a pixel of a color having a short time constant of the light emitter. It is characterized in that the number of gradations is made smaller than the number of gradations used for display in pixels of other emission colors. For this reason, with respect to the light-emitting body having a short time constant, it is possible to obtain a good image display as a whole by displaying with a reduced number of gradations so that the encoding can be performed while suppressing the occurrence of a moving image pseudo contour. Even if the number of gradations used for the display itself is limited, it is natural that a means for recovering the gradation expression in a pseudo-equivalent manner such as so-called error diffusion or dither can be used together.

As described above, the luminous body having a short time constant is encoded and displayed while suppressing the gradation number, and the practical gradation number is compensated by error diffusion or the like, so that a good image display as a whole is obtained. can do. The reason for this can be explained as follows.

The moving image pseudo contour generated by the luminescent color of a light emitter having a long time constant is relaxed according to the time constant when actually observed on the retina of the observer, whereas The moving image pseudo contour generated by the emission color of the short light emitter does not have such a mitigating factor and may be recognized. For this reason, it is effective to suppress the number of gradations corresponding to the light-emitting body having a short time constant in advance to suppress the generation of the pseudo contour of the moving image.

The time constant of the blue luminous body is often short, and in such a case, both the conditions of the invention of claim 4 and the invention of claim 5 are satisfied. For blue, it is possible to eliminate the more noticeable moving image pseudo contour, restore the gradation characteristics by means of error diffusion, and perform good image display.

In the sub-field image display device according to the sixth aspect of the present invention, a method of reducing the number of gradations used for each pixel is selected from all possible combinations of light emission of sub-fields. It is characterized in that only gradations limited to combinations of light emission of subfields having a high correlation with increase / decrease in gradation value and increase / decrease in temporal distribution of main light emission patterns are selected. For this reason, when selecting the encoding, it is possible to select and encode the encoding in which the occurrence of the moving image pseudo contour is suppressed and the encoding in which the number of gradations is secured.

Further, in the sub-field image display device according to a seventh aspect of the present invention, one field of the input image signal is divided into a plurality of sub-fields, and gradation is expressed by a combination of light emission of each sub-field. In the sub-field image display device, a signal corresponding to display of a color having a short time constant and a signal corresponding to display of another color of the display light emitters constituting the image display device, which are different from each other. The feature is that it is processed and displayed. Therefore, for example, a good image display can be performed by performing a process different from other colors on a display color in which a false contour of a moving image or the occurrence of noise is easily detected.

Further, in the sub-field image display device according to claim 8 of the present invention, the signal processing corresponding to the display of the color having the short time constant is noise reduction processing performed in advance on the signal corresponding to the display of the corresponding color. It is characterized by having been given. Therefore, for example, it is possible to reduce the occurrence probability of the noise or the like in the display color in which the false contour of the moving image or the noise is easily detected, and to display a good image.

Further, in the sub-field image display device according to claim 9 of the present invention, the signal processing corresponding to the display of the color having a short time constant is subjected to the noise reduction processing in advance to the signal corresponding to the display of the corresponding color. It is characterized in that it is a process in which a regular signal or an irregular signal is added after the process. Therefore, for example, the probability of occurrence of the noise or the like is reduced in advance for the display color in which the pseudo contour of the moving image or the generation of noise is easily detected, and the residual noise is diffused regularly or randomly. As a result, perceived moving image false contours and other noises can be substantially reduced.

(Embodiment 1) Hereinafter, Embodiment 1 of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a plasma display which is a sub-field image display device according to the first embodiment of the present invention. In FIG. 1, 1 is an input image signal, 2 is an encoding circuit for red color,
Reference numeral 3 is an encoding circuit for green, 4 is a blue gentle slope encoding circuit for a blue flat portion of an image, 5 is a blue flat / steep slope encoding circuit for a blue flat portion and a steep slope portion, and 6 is a slope portion. A detection circuit, 7 is a selection circuit, 8 is a subfield control circuit for converting a signal representing a luminance level into a subfield pattern which is a binary signal, and 9 is a plasma display.

The operation of the embodiment of the present invention configured as described above will be described below. Input image signal 1
Is a digital signal in which the value of the video signal is represented by 8 bits, for example. The input image signal 1 is a red encoding circuit 2,
It is supplied to the green encoding circuit 3, the blue gentle slope encoding circuit 4, the blue flat / steep slope encoding circuit 5 and the slope detecting circuit 6, respectively. The red encoding circuit 2, the green encoding circuit 3, and the blue flat / steep slope encoding circuit 5 can be substantially the same in processing, and, for example, as shown in FIG. Encoding is performed with a sufficient number of gradations for the field configuration.

On the other hand, the processing in the blue gentle slope portion encoding circuit 4 is performed by further reducing the number of gradations and by setting encoding as shown in FIG. From the configuration of the sub-fields, only the combination of gradation values in which a pseudo contour of a moving image is unlikely to occur is selected for encoding. In this way, for blue, the encoding method is made different between the gently sloping portion and other portions. More specifically, the gently sloping portion performs the encoding limited to the combination of gradation values such that the pseudo false contour of the moving image is less generated than the completely flat portion or the steeply sloping portion.

The inclination of the image is detected by the inclination detecting circuit 6, and the output of the blue gentle inclination encoding circuit 4 and the output of the blue flat and steep inclination encoding circuit 5 are selected based on the result. Select based on circuit 7 and coded in blue b
Is supplied to the subfield control circuit 8 and is displayed on the plasma display 9 as a gradation image. With the above operation, it is possible to suppress the occurrence of a moving image pseudo contour or noise in a slightly inclined blue image portion or the like that is easily perceived by the observer's eye movement even if it is a still image.

As described above, different processing is performed on a portion of the image having a slightly inclined blue portion and the other portion, and gradation is less likely to generate a moving image pseudo contour in the slightly inclined blue portion of the image. By limiting the combination of values, it is possible to suppress noise and pseudo contours that might be perceived by the movement of the observer's line of sight in a blue background image or an image in which a blue sky is projected in a wide range. it can.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a configuration diagram of a plasma display which is an image display device according to the second embodiment of the present invention. 2, the same parts as those in FIG. 1 are designated by the same reference numerals. Reference numeral 14 denotes a blue encoding circuit for blue. The blue encoding circuit 14 receives the input image signal 1 from the grouping circuit 10 and the signal applying circuit 11.
And supply via. Note that the grouping circuit 10 is provided with information such as a subfield coding method and each subfield weight based on the subfield information 12.

Regarding the embodiments of the present invention configured as described above, the differences from the first embodiment will be described below.
The operation will be described. The blue signal of the input image signal is subjected to noise removal or the like by the grouping circuit 10. This process may be a normal noise reduction process, and based on the information of subfields such as brightness weighting and coding, it suppresses image signal changes across a portion where the generation level of the moving image pseudo contour is as large as possible. Such grouping is also possible. After that, a signal having a regular or random small amplitude is intentionally applied by the signal application circuit 11, encoded by the blue encoding circuit 14, and subjected to subfield control in the same manner as other colors, and then plasma is generated. Display on the display 9.

The grouping circuit 10 and the signal application circuit 1
The operation 1 will be described with reference to FIG. FIG. 3A schematically shows a moving image pseudo contour generated when the grouping circuit 10 and the signal applying circuit 11 are not provided. When the gradation level of the image crosses a level at which the moving image pseudo contour is likely to occur. In some cases, noise-like interference indicated by the black line in FIG. 3 (a) was observed. This is because a natural image generally has a certain degree of random component, and the gradation level fluctuates in the vicinity of a certain gradation value where a moving image pseudo contour is likely to occur.
It shows that the pseudo contour of a moving image may be observed as noise over a wide range.

The grouping circuit 10 suppresses a change in gradation value that tends to generate a pseudo contour of a moving image, and shapes a signal. As a result, the frequency and location of occurrence of the moving picture pseudo contours are reduced, but the positions of occurrence are aligned, and as shown in FIG.
On the contrary, as shown in (b), noise associated with the moving image pseudo contour may be conspicuous. Therefore, by applying a small amplitude regular signal or a small amplitude irregular signal by the signal applying circuit 11, as shown in FIG.
It is possible to avoid the concentration of residual moving image pseudo contours and make the moving image pseudo contours inconspicuous.

As described above, noise reduction processing may be performed prior to the encoding of the blue signal, or a regular or irregular signal may be applied after the noise reduction processing to make the moving image pseudo contour inconspicuous. it can.

(Third Embodiment) A third embodiment of the present invention will be described below with reference to the drawings. FIG. 4 is a configuration diagram of a plasma display which is an image display device according to the third embodiment of the present invention. 4, the same parts as those in FIG. 1 are designated by the same reference numerals. Reference numeral 21 is a red still image encoding circuit for a red still image, 22 is a red moving image encoding circuit for a red moving image, 23 is a red motion detection circuit for detecting red movement, 24 is a selection circuit, and 31 is a green still image. To the green still image encoding circuit, 32 to a green moving image encoding circuit for a green moving image, 33 to a green motion detecting circuit for detecting a green movement, 34 to a selection circuit, 41 to a blue still image encoding to a blue still image. Reference numeral 42 is a circuit, 42 is a blue gentle gradient coding circuit for a blue gentle gradient portion, 43 is a blue moving picture coding circuit for a blue moving picture portion, 44 is a blue motion / tilt for detecting a blue movement and a gradient of a blue image signal. The detection circuit and 45 are selection circuits.

The operation of the third embodiment of the present invention configured as described above will be described below. From the image, the amount of motion of the image is detected by the red motion detection circuit 23 and the green motion detection circuit 33 by a method such as interframe difference.
In addition, for the blue color, in addition to the movement of the image, the part that changes across the gradation value where moving image pseudo contours are likely to occur,
It is detected by the blue movement / tilt detection circuit 44.

For red and green, moving images and still images are encoded with different numbers of gradations. Basically, these two colors are encoded according to the same rule.
The number of gradations is limited in a portion having a large amount of motion to suppress a pseudo contour of a moving image, while the still image portion is encoded with a sufficient number of gradations.

On the other hand, for blue, there are a "still image" portion in which there is no possibility of occurrence of a moving image pseudo contour, and a "slow slope" portion in which there is no detection of motion but in which there is a possibility of occurrence of a moving image pseudo contour. The motion / tilt detection circuit 44 detects each part of the “moving image” for which Then, for the "still image" portion, the blue still image encoding circuit 41 performs encoding using all the gradation values. Also, regarding the "slow slope" part, although it is highly likely that it is not a moving image, if it is processed as a still image, especially if this part is a large blue background image, the observer's line of sight will not be visible. Since noise-like disturbances were sometimes observed due to regular movements, signal processing corresponding to the suppression of the moving image pseudo contour is performed only for the portion where the blue brightness is high for this “slow slope” portion.

More specifically, the encoding can be performed by performing the dithering or the error diffusion processing by performing the gradation limitation that suppresses the signal change that crosses the gradation where the moving image pseudo contour is likely to occur.

On the other hand, for the portion determined as "moving image", further gradation control is performed to give priority to the suppression of the moving image pseudo contour, whereby a good image display as a whole becomes possible. In addition,
The selection circuit 2 is used to switch the encoding of still images and moving images of each color.
Although it is selected by 4, 34, 45,
In practice, the encoding method may be continuously changed according to the detected motion amount, or conversion may be performed using a ROM table.

As described above, with respect to the blue color of the image, there is a portion where there is no fear of occurrence of a moving image pseudo contour and a gentle slope, and noise similar to that of the moving image pseudo contour is perceived depending on the movement of the line of sight of the observer. By performing a different encoding process by classifying into a portion that may be displayed and a moving image portion, and performing different encoding processes, it is possible to perform good image display in which both the moving image pseudo contour characteristic and the gradation characteristic are compatible.

In each of the above embodiments of the present invention, the weighting and coding of the subfields have been described by way of example. However, the number of subfields is further increased and a code using a luminance weight that is not a power of 2 is used. It goes without saying that similar effects can be obtained even when the conversion is performed.

[0043]

As described above, according to the present invention, the following effects can be obtained when gradation display is performed by subfields. (1) By changing the encoding method depending on the display color,
It is possible to suppress the moving image pseudo contour and display the gradation well. (2) By limiting the number of display gradations in the blue pixel to a combination of gradation values in which the occurrence of a moving image pseudo contour is small, good image display can be performed as a whole. (3) By limiting the display gradation in the pixel of the display color with short afterglow to the combination of the gradation values in which the pseudo false contour of the moving image is less generated,
A good image display can be performed as a whole. (4) By limiting the display gradation in the pixel of the display color with short afterglow to the combination of the gradation values in which the pseudo false contour of the moving image is less generated,
A good image display can be performed as a whole. (5) The frequency of occurrence of a pseudo contour of a moving image is determined by adding a regular signal or an irregular signal after performing signal processing on pixels of a display color having short afterglow and noise reduction processing on a corresponding signal in advance. The noise can be reduced and the residual noise can be made less noticeable.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a subfield image display device according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a subfield image display device according to a second embodiment of the present invention.

3A to 3C are schematic diagrams showing blue moving image false contour reduction processing according to the second embodiment of the present invention.

FIG. 4 is a configuration diagram of a subfield image display device according to a third embodiment of the present invention.

FIG. 5 is a configuration diagram of a conventional subfield image display device.

FIG. 6 is a subfield layout diagram of a conventional subfield image display device.

7A and 7B are explanatory diagrams showing an example of encoding switching in a conventional subfield image display device.

[Explanation of symbols]

1 Input image signal 2 Red encoding circuit 3 Green coding circuit 4 Blue gentle slope coding circuit 5 Blue flat and steep slope coding circuit 6 Slope detection circuit 7, 24, 34, 45, 54 selection circuit 8 Subfield control circuit 9 Plasma display 10 grouping circuit 11 Signal application circuit 12 Subfield information 21 Red still image coding circuit 22 Red video coding circuit 23 Red motion detection circuit 31 Green still image coding circuit 32 Green Video Coding Circuit 33 Green motion detection circuit 41 Blue still picture coding circuit 42 Blue Slow Gradient Encoding Circuit 43 Blue video coding circuit 44 Blue motion / tilt detection circuit

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Claims (10)

[Claims] 1. A subfield image display device in which one field of an input image signal is divided into a plurality of subfields, and light emission of a display means is controlled by a combination of light emission of each subfield to express gradation. The subfield image display device is characterized in that when the combination of the light emission of each of the subfields is controlled according to the characteristic of the input image signal, it is made different depending on the light emission color of the display means. 2. The subfield image display apparatus according to claim 1, wherein the characteristic of the input image signal is based on the inclination of the image. 3. The sub-field image display device according to claim 1, wherein the method of controlling the combination of the light emission of each sub-field is a method of controlling the number of gradations used for each pixel. 4. A method for controlling a combination of light emission of each subfield, wherein the number of gradations used for display in pixels of blue emission color is smaller than the number of gradations used for display in pixels of other emission color. The subfield image display device according to claim 1, wherein 5. A method for controlling a combination of light emission in each subfield, wherein the number of gradations used for display in a pixel of a color having a short time constant of a light emitting body of a display means is displayed in a pixel of another light emitting color. 2. The subfield image display device according to claim 1, wherein the number of gradations used is less than that of the subfield image display device. 6. When the number of gradations used for each pixel is reduced, the corresponding gradation value is increased / decreased and the temporal distribution of main light emission patterns is increased / decreased from among all possible combinations of light emission of subfields. 6. The subfield image display device according to claim 4, wherein only gradations limited to combinations of light emission of subfields having high correlation with each other are selected. 7. A sub-field image display device, wherein one field of an input image signal is divided into a plurality of sub-fields, and light emission of a display means is controlled by a combination of light emission of each sub-field to express gradation. A sub-field image display device characterized in that a signal corresponding to display of a color having a short time constant and a signal corresponding to display of another color are subjected to different signal processing for display. 8. The subfield image display according to claim 7, wherein the signal processing corresponding to the display of a color having a short time constant is performed by previously performing noise reduction processing on the signal corresponding to the display of the corresponding color. apparatus. 9. The signal processing corresponding to the display of a color having a short time constant is performed by subjecting the signal corresponding to the display of the corresponding color to noise reduction processing in advance, and then adding a regular signal or an irregular signal. The subfield image display device according to claim 7, wherein the subfield image display device is a process. 10. The number of gradations used for display in pixels of blue emission color is the number of gradations used for display in pixels of other emission color when the blue gradation value is a predetermined value or more. 5. The subfield image display device according to claim 4, wherein the number is smaller.