JP2023104353A - Image display device, signal processing method, and signal processing program - Google Patents

Abstract

To provide an image display device, a signal processing method, and a signal processing program, which can display a high-quality image at a lower driving frequency while maintaining stability and high speed of digital driving using a pulse density driving method.SOLUTION: An image display device 1 comprises: a reference image creation section 121 that creates a reference image having a reference value as a pixel value; and a dither processing section 122 that converts a pixel value of an input video into 1 or 0 using a reference value of the same pixel as that of the input video as a threshold. The reference image creation section 121 creates a reference image group composed of a plurality of reference images in which any pixel does not have the same value, and sequentially provides the reference image from the reference image group to the dither processing section 122.SELECTED DRAWING: Figure 1

Description

The present invention relates to an image display device that displays an image, a signal processing method, and a signal processing program.

2. Description of the Related Art In recent years, high-resolution displays have been actively developed, and very fine image display has become possible. However, the conventional active matrix drive using TFTs in the backplane cannot provide sufficient moving picture quality because motion blur occurs in the moving picture due to its display characteristics. Therefore, various moving image quality improvement methods such as black insertion and control of light emission time have been proposed (see Patent Documents 1 and 2, for example). However, in order to fundamentally solve the problem of moving picture quality, it is essential to improve the frame rate of the display, but the existing display driving method is not necessarily suitable for increasing the frame rate.

In addition, driving methods for displaying gradation on a display mainly include an analog modulation method that adjusts the voltage or current applied to a light-emitting element according to the gradation value, and a pulse width modulation method that adjusts the pulse width according to the gradation value. Alternatively, there is a digital modulation method that adjusts the number of times of light emission.

Analog modulation methods are widely used in LCD and organic EL televisions on the market, but organic EL displays and LED displays are susceptible to fluctuations in current and voltage, and image quality can be affected by fluctuations in TFT thresholds. It was not necessarily suitable for applying analog modulation, such as deterioration.

On the other hand, digital driving can drive with a constant voltage or current, so high-speed and stable driving is possible. However, the commonly used time-division driving method requires many subfields to express gradation. Further, subfield driving has a problem of image quality deterioration due to color breakup. In order to prevent this, more subfields are required, making it difficult to achieve a high frame rate.

JP-A-2004-144928 Japanese Unexamined Patent Application Publication No. 2016-12068 JP 2019-39958 A

By the way, a digital driving method has also been proposed that expresses gradation by controlling the pulse density for a certain period of time using a random mask (see, for example, Patent Document 3). However, in order to obtain a high-quality image display, a very high driving frequency is required. Sufficient display quality was not obtained.

For example, when the pixel value of the input signal exceeds the random value, the pixel value is converted to "1", and when the pixel value is equal to or less than the random value, the pixel value is converted to "0" and displayed at high speed. Consider the case where 50% luminance is represented by the density of directions. As shown in FIG. 12, when the drive frequency is low and the number of random values is reduced, the frequency of successively similar random values relatively increases, thereby increasing the perceived display brightness (level). Since the variation becomes large, a feeling of noise was to be felt.

The present invention provides an image display device, a signal processing method, and a signal processing program that can display high-quality images at a lower driving frequency while maintaining the stability and speed of digital driving using a pulse density driving method. for the purpose.

An image display device according to the present invention includes a reference image creation unit that creates a reference image having a reference value as a pixel value, and a pixel value of the input video that is set to 1 or 0 using the reference value of the same pixel as the input video as a threshold. and a dither processing unit that converts to Provided to the dither processing unit.

The image display device may include a reference value converter that converts the reference values into values within a specific range that are different for each of a plurality of fields within the same frame.

The reference image creation unit may cut out the reference image from among tiled reference original images that are smaller than the input video.

The reference image creation unit may make the density of each of the reference values constant in the reference image.

The reference image creating unit may set the number of gradations of the reference image to be one less than the number of gradations of the input video.

The reference image creating unit may add a predetermined number p to the reference value and sequentially create reference images in which the remainder obtained by dividing by the number of gradations n of the reference image is used as a new reference value.

The predetermined number p may be a value relatively prime to the number n of gradations of the reference image.

When d reference images are provided for the same image frame with field number k, the predetermined number p is {(d/k)/(n/p)−1}×(n mod p)≧ p may be satisfied.

A signal processing method according to the present invention includes a reference image creating step of creating a reference image having reference values as pixel values; and a computer executes a dither processing step of converting to A reference image is provided to the dithering step.

A signal processing program according to the present invention is for causing a computer to function as the image display device.

According to the present invention, high-quality images can be displayed at a lower driving frequency while maintaining the stability and high speed of digital driving by using the pulse density driving method.

1 is a block diagram showing the functional configuration of an image display device according to a first embodiment; FIG. 3 is a block diagram showing the functional configuration of a signal processing section according to the first embodiment; FIG. 4 is a configuration example of a reference image created by a reference image creating unit according to the first embodiment; FIG. 8 is a block diagram showing the functional configuration of a signal processing unit according to the second embodiment; FIG. 11 is a diagram showing an example of creating a reference image according to the third embodiment; FIG. 14 is a diagram showing an example of generating a reference original image according to the fourth embodiment; FIG. 12 is a diagram showing the degree of temporal variation in luminance with respect to the value p in the case where field division is not performed according to the fourth embodiment; FIG. 11 is a diagram showing the degree of luminance time variation with respect to a value p in the case of performing field division according to the fourth embodiment; FIG. 12 is a diagram showing how reference values change according to the fourth embodiment; FIG. 14 is a diagram showing a case where d reference values exist substantially uniformly according to the fourth embodiment; FIG. 14 is a diagram showing a case where d reference values are unevenly present according to the fourth embodiment; FIG. 7B is a diagram showing those corresponding to p that is coprime to n in FIG. 7A , divided into those that satisfy the compatibility condition and those that do not. FIG. 7B is a diagram showing those corresponding to p that is coprime to n, divided into those that satisfy the compatibility condition and those that do not. It is a figure which illustrates the image perceived when blue noise is used as a reference image and converted into 1 bit. FIG. 12 is a diagram illustrating an image perceived when converted to 1-bit using the reference image according to the third and fourth embodiments; It is a figure which illustrates the image perceived when blue noise is used for a reference image, and it divides into fields and converts to 1 bit. FIG. 11 is a diagram illustrating an image perceived when the reference image according to the second to fourth embodiments is converted to 1-bit; FIG. 10 is a diagram showing display variations depending on the number of random values in a conventional pulse density modulation method using random values;

[First embodiment]
A first embodiment of the present invention will be described below.
FIG. 1 is a block diagram showing the functional configuration of an image display device 1 according to this embodiment.
The image display device 1 includes a video input section 11 , a signal processing section 12 , a row driver section 13 , a column driver section 14 and a display panel 15 .

When a video signal is input, the video input unit 11 temporarily stores image data of frames included in the video signal in an input buffer, and sequentially provides the image data to the subsequent signal processing unit 12 in accordance with processing timing. .
Further, the video input unit 11 gamma-corrects the image data as necessary, and performs gamma conversion processing for linearly converting the relationship between the level (pixel value) of the corrected image data and the display brightness.

Note that when the frame rate displayed on the display panel 15 is higher than the frame rate of the input video, the video input unit 11 converts the image data according to the frame rate displayed on the display panel 15 based on the input video. It is created and provided to the signal processing unit 12 .
For example, assume that a video with a frame rate of 60 Hz is input to the video input unit 11 . Assuming that the frame rate displayed on the display panel 15 is 2880 (=60×48) Hz, the video input unit 11 generates image data whose frame rate is 48 times faster. An increase in frame rate can be realized, for example, by interpolating multiple times with the same input image.

The signal processing unit 12 receives image data from the video input unit 11, generates data for controlling the timing of writing data to the display panel 15 and light emission, and outputs data to the display unit (row driver unit 13 and column driver unit 14). Send to

A plurality of selection signal lines arranged in the horizontal direction are connected to the row driver section 13 . The row driver unit 13 supplies selection signals to each of the plurality of selection signal lines. A plurality of light emission time control signal lines extending in the horizontal direction are connected to the row driver section 13 . Each light emission time control signal line is connected to a plurality of light emission time control transistors existing in the region along the horizontal direction where the light emission time control signal line is arranged.

A plurality of data signal lines arranged in the vertical direction are connected to the column driver section 14 . The column driver section 14 supplies image data signals for each pixel to each of the plurality of data signal lines.

The display panel 15 is an image display module. As a more specific example, the display panel 15 may be an active matrix organic EL display module, an LED display module, a discharge display module, or the like.

FIG. 2 is a block diagram showing the functional configuration of the signal processing section 12 according to this embodiment.
The signal processor 12 includes a reference image generator 121 and a dither processor 122 .

The reference image creating unit 121 outputs a reference image having, as pixel values, a reference value in the range of 0 or more and less than the maximum value that the pixel value of the video signal after correction by the video input unit 11 can take, and outputs the reference image to the dither processing unit 122. offer.

The dither processing unit 122 dithers the buffered image data into 1-bit data. The 1-bit data is sent to the column driver section 14, and an ON or OFF value is written to each pixel circuit in accordance with the timing of the write signal from the row driver section 13. FIG.
The signal processing unit 12 performs this operation for all horizontal lines to display one frame of video. Furthermore, the signal processing unit 12 can display 2880 Hz by performing the operation of displaying one frame of video, for example, 2880 times per second, and at the same time can express gradation by visual integration effect.

FIG. 3 is a configuration example of a reference image created by the reference image creating unit 121 according to this embodiment.
Assuming that the number of gradations to be displayed on the display panel 15 is s, the reference image creating unit 121 prepares a reference image group in which a plurality of (m) reference images having the number of gradations (s−1) are set. , the dither processing unit 122 is sequentially provided with reference images from this reference image group.

For example, when it is desired to display in 8-bit (=256) gradation, the reference image creation unit 121 creates a reference image having any one of 0 to 254 as pixel values (gradation number n=2 ⁸ −1 = 255).
At this time, the density of each level (pixel value) existing within a unit area in the reference image is assumed to be constant. Also, within one reference image group, a plurality of reference images are created so that any pixels (coordinates) do not have the same value. Therefore, the number of reference images (m) in the reference image group does not exceed the number of gradations (n) of the reference images.

A method for creating a reference image group will be specifically described. Here, as an example, consider a case where the number of pixels of the input video is 1920 horizontal×1080 vertical.
The reference image creation unit 121 first creates a first reference image by randomly arranging 255 levels from 0 to 254 in 1920×1080=2,073,600 pixels. At this time, the reference image creation unit 121 divides the total number of pixels by the number of reference values (the number of gradations) of the reference image in order to keep the density of each level in the reference image approximately constant. Determines the number to place the value of . If it is not divisible, it is adjusted so that the number of each level is approximately equal and the total number is equal to the total number of pixels, using rounding or the like as appropriate.

In the case of this example, 2,073,600 pixels/255 levels ≈ 8,131.7. An image containing 132 pixels is obtained. Which level is assigned to which pixel is randomly determined using, for example, random numbers.

Subsequently, the reference image creation unit 121 creates a second reference image based on the pixel values of the first reference image.
Let R(i, j, k) be the reference value in frame k for an arbitrary pixel [i, j] (1 ≤ i ≤ 1080, 1 ≤ j ≤ 1920), then each pixel (i , j) level (reference value) R(i, j, 2) is based on the level (reference value) R(i, j, 1) of each pixel (i, j) of the first reference image. , with a numerical value p (1≤p<n),
R(i, j, 2)=(R(i, j, 1)+p) mod n (Formula 1)
is set to be Note that A mod B represents the remainder when A is divided by B.

By determining the reference value by (Equation 1), the second reference image has different pixel values from the first reference image for all pixels, and each pixel value in the second reference image is The density of (reference value) can be approximately constant.
and so on,
R(i, j, u+1)=(R(i, j, u)+p) mod n (1≦u) (Formula 2)
By doing so, the third and subsequent reference images can be created.

In this example, since the number of gradations n of the reference image is 255, the maximum value of u is n−1=254. Since it is preferable to increase the number of reference images in the reference image group as much as possible, p is selected to be coprime to n (=255) (only the common divisor is 1) so that the reference values do not overlap. good.
In this way, by selecting p that is coprime to n (=255), n (=255) reference images can be created, and the reference image creating unit 121 creates n (=255) Let the reference images be a reference image group.

When the input video is color, the signal processing unit 12 performs dithering using a reference image for each of the red, green and blue signals. An image may be used, or a common reference image may be used.

The reference image creation unit 121 sequentially provides the reference images from the reference image group to the dither processing unit 122 one by one. After providing all the reference images in the reference image group, the reference image creating unit 121 repeatedly provides reference images one by one from the same reference image group.
Note that when all the reference images in the reference image group have been provided, the reference image creating unit 121 uses another reference image group created in the same procedure as described above to provide the reference image to the dither processing unit 122. You may Also, the number m of reference images in the reference image group may be less than the number n of gradations of each pixel.

The dither processing unit 122 sets the pixel value a of each pixel in the input image to 1 when the pixel value a of each pixel in the input image exceeds the threshold value, which is the pixel value x of the same coordinates of the reference image corresponding to this pixel, and sets the pixel value a to 1 when the pixel value a exceeds the threshold value. In this case, by converting the pixel value a to 0, the pixel value is converted to 1 bit.
The row driving driver unit 13 and the column driving driver unit 14 are based on the 1-bit value (1 or 0) of each pixel determined by the signal processing unit 12. If the value is 1, the corresponding pixel of the display panel 15 emits light. If it is 0, the corresponding pixel of the display panel 15 is extinguished to display an image of one frame.

[Second embodiment]
A second embodiment of the present invention will be described below.
The image display device 1 of this embodiment has the same video input unit 11, row driver unit 13, column driver unit 14, and display panel 15 as those of the first embodiment, but the function of the signal processing unit 12 is different. .

FIG. 4 is a block diagram showing the functional configuration of the signal processing section 12 according to this embodiment.
The signal processing unit 12 includes a reference image generation unit 121 and a dither processing unit 122, and further includes a reference value conversion unit 123, as in the first embodiment.

The reference value converter 123 outputs a reference value obtained by converting each pixel value of the input reference image into a specific range for each field.
Assuming that the number of gradations s of the image to be displayed is 8 bits (=256), the reference value conversion unit 123 converts the reference value from 0 to Convert to values in the range of 63, 64-127, 128-191, 192-254. In this case, the reference value conversion unit 123 divides the reference value conversion range into four and applies each to four fields, thereby controlling the reference value range for each field.

When the reference value conversion range is divided into k (4 in the above example), the reference value conversion unit 123 controls the reference value range by repeating k (=4) fields.
The reference value conversion unit 123 provides the reference image having the converted reference values as pixel values to the dither processing unit 122, and the dither processing unit 122 performs the same processing as in the first embodiment. , to display an image on the display panel 15 .

[Third Embodiment]
A third embodiment of the present invention will be described below.
The image display device 1 of this embodiment has the same functional configuration as that of the first embodiment or the second embodiment, but the function of the reference image creating section 121 in the signal processing section 12 is different.

FIG. 5 is a diagram showing an example of creating a reference image according to this embodiment.
The reference image creation unit 121 creates a reference original image with a small number of pixels as a base in creating a reference image, and arranges these in tiles to create a reference image with a large number of pixels.

Specifically, for example, when the number of gradations s of an image to be displayed is 256, the reference image creation unit 121 creates a reference original image having a size of n×n pixels (n=s−1), that is, 255×255 pixels. prepare.
The reference image creating unit 121 arranges 255 levels from 0 to 254 in this 255×255 pixels. At this time, each level is arranged by (255×255 pixels)/255 levels=255 pixels in order to keep the density of each level in the reference original image constant. That is, the created reference original image is an image having 255 pixels each of 255 levels from 0 to 254. FIG.

The reference image creation unit 121 creates a plurality of such reference original images to create a reference original image group. to place.
When the number of pixels of the input video is 1920×1080 pixels, the number of pixels of the reference image is also required to be 1920×1080 pixels. In this case, as shown in FIG. 5, after arranging the reference original image of 255×255 pixels in the form of 8 horizontal and 5 vertical tiles, it is cut from an arbitrary place so as to become 1920×1080 pixels, A reference image of 1920×1080 pixels can be created.

The reference image creation unit 121 can create a reference image group having the same number of pixels as the input video by performing the same pixel number conversion on each reference original image of the reference original image group. This reduces the load of the process of creating the reference image group.

[Fourth Embodiment]
A fourth embodiment of the present invention will be described below.
The image display apparatus 1 of this embodiment has the same functional configuration as that of the third embodiment, but the function of the reference image creating section 121 in the signal processing section 12 is different.
The reference image creation unit 121 appropriately selects the value p described above in order to uniformly distribute the reference values.

FIG. 6 is a diagram showing an example of generating a reference original image according to this embodiment.
Here, as in the third embodiment, a reference original image group having 255 pixels each having 255 levels from 0 to 254 (the number of gradations of the reference image n=255) will be described as an example.

In this case, it is possible to create a maximum of 255 reference original images in the reference image group. In order to prevent all pixels in the reference original image from having the same pixel value in the reference image group, the same value (p) can be added to create a new reference original image. Since the pixel value (reference value) can take a range of 0 to 254, for pixels exceeding 254 by adding p, n (= 255) is changed from the value obtained by adding p (<n). By subtracting, a reference value different from the original reference value can be obtained.

By repeating this, it is possible to create a plurality of reference original images, but the reference original images having the same reference values for the same pixels cannot be obtained before the n (255) reference original images have been created. In order to do so, p and n must be relatively prime as described in the first embodiment. By using p, which is relatively prime to p and n, it is possible to create a reference original image group having n reference original images.

By the way, as described in the first embodiment, when the frame rate displayed on the display panel 15 is higher than the frame rate of the input video, the frame rate displayed on the display panel is adjusted based on the input video. A video will be created. In this case, since the same image is digitized using a plurality of (d) reference images, it is necessary to consider the value of d as well.
As an example, assuming that a video with a frame rate of 60 Hz is input to the video input unit 11 and the display panel 15 speeds up the frame rate to 2880 (=60×48) Hz, one frame of the input video is displayed. On the panel 15, the same image is displayed in 48 frames.

Here, attention is focused on one pixel in the display panel 15, and temporal variations in brightness are considered. It is assumed that the signal level of one target pixel is level 144 out of 256 gradations, and that the input signal level does not fluctuate. Consider the case where this is displayed at 2880 Hz using 1-bit pulse density modulation.
It is assumed that due to the integration effect as a visual characteristic, the light emission density due to blinking of light for (1/60) second (48 frames) is taken as luminance.

7A and 7B are diagrams showing the degree of temporal variation (fluctuation) of luminance with respect to the value p according to the present embodiment.
Here, for each of p from 1 to 254, the degree of perceived luminance variation over time (fluctuation) is calculated as the standard deviation. In the figure, the thick line indicates the variation for p coprime to n=255.

In FIG. 7A, one frame of the input video is displayed as 48 frames on the display panel 15 and no field division is performed. Variation when divided into four fields is shown.
In both graphs, the horizontal axis represents the value of p (1 to 254), and the vertical axis represents luminance variation (standard deviation) in the time direction. In both graphs, the variation changes greatly depending on the value of p. This indicates that the value of p reduces luminance variation when uniform reference values can be provided over 255 gray scales during 48 frames, and increases luminance variation when it cannot be provided.

Next, consider how much the variation range of the reference value within one frame of the input image, that is, within d frames of the image to be displayed, depending on the value of p.

FIG. 8A is a diagram showing how the reference value changes according to the present embodiment.
For the sake of simplicity, it is assumed that the pixel value (reference value) of the first reference image in the reference image group is 0. Then, the value of the corresponding pixel in the second reference image is p, and the value of the corresponding pixel in the third reference image is 2×p.
When the reference value is increased by p in this way, the reference value becomes p, 2×p, .
r = 255 mod p ... (Formula 3)
Then, the reference value before exceeding the value 254 is 255-r.

Therefore, the next reference value is (255-r+p)-255=pr, and until the next value 254 is exceeded (second cycle), it is pr, 2×pr, .
That is, the reference values in the second round are values that are smaller by r than the sequence of reference values in the first round.
Similarly, the reference value of the third round is a value smaller than that of the first round by 2×r, and the reference value of the fourth round is a value smaller than that of the first round by 3×r.

FIG. 8B is a diagram showing a case where d reference values exist substantially uniformly according to this embodiment.
Since one cycle is about 255/p times, the number of cycles of the reference value unit of 255 until the reference value is presented d times for one frame of the input video is approximately d/(255/ p) rounds, and from the first round, the reference value moves by {d/(255/p)−1}×r.

Therefore, in order to cover the range of p, which is one increment of the reference value in the sequence of the first round, in subsequent d/(255/p)−1 rounds,
{d/(255/p)−1}×r≧p (Formula 4)
If it is

FIG. 8C is a diagram showing a case where the d reference values exist unevenly according to this embodiment.
If p does not satisfy (Formula 4), d reference values are presented for one frame of the input video, but there is an area where the reference values are collectively missing, and the entire n gradation to be expressed Reference values cannot be uniformly provided.

Also, as shown in the second embodiment, when field division is used, one frame is divided into k (for example, four) fields. The number of images is 48/4=12.
Therefore, d in (Formula 4) should be replaced with d/4.

From the above, the general condition that the pixel value increment p should satisfy when creating a reference image is
{(d/k)/(n/p)−1}×r≧p (Formula 5)
becomes.

9A and 9B show graphs of the variability shown in FIGS. 7A and 7B that correspond to p coprime to n and are divided into those that satisfy the compatibility condition of (Equation 5) and those that do not. is shown.
Now looking at Figures 7A and 7B, both graphs are symmetrical. This is because increasing the reference value by p is equivalent to increasing the reference value by 255−p (that is, decreasing by p) in the reference image group, and the left half (p is 1 to n/ 2) and FIGS. 9A and 9B correspond to the left half of FIGS. 7A and 7B, ie for p values from 1 to 127. FIG.

In FIG. 9, black bars satisfy the condition of (Equation 5), and others do not satisfy the condition.
In the case of p that satisfies the condition of (Equation 5), variations are relatively suppressed. Although the degree of variation varies depending on the signal level, this graph shows a case where the signal level is 144 levels out of 256 gradations, as an example. In the case of other signal levels as well, by using p that satisfies the condition of (Equation 5), luminance variation can be suppressed, which is effective for gradation display by pulse density modulation.

Below, simulation results comparing the image displayed by the above-described embodiment with the conventional one will be illustrated.
In FIG. 10A, for comparison with the embodiment, blue noise, which is known to be able to reduce noise by utilizing the spatial frequency characteristics of the human visual system, is used as a reference image, and is converted to 1 bit by the dither processing unit 122. FIG. 10 is a diagram illustrating an image perceived when

Here, when an image of 1920×1080 pixels is displayed in 8-bit gradation (s=256), 1-bit display of 48 (=d) frames is complemented without field division for 1 frame of input image. The simulation image at the time is illustrated.
It can be seen that the image is displayed, but the noise level is high.

FIG. 10B is a diagram illustrating an image perceived when the reference image created by the method according to the third and fourth embodiments is converted to 1-bit by the dither processing unit 122. FIG.

Here, as in the third embodiment, 255 reference original images of 255×255 pixels are created, each reference original image is arranged in a tile shape, and a reference image group is created by cutting out 1920×1080 pixels. there is
Also, the level increment p of the same pixel between the reference original images is set to 89, which is a relatively prime value of n=255 and satisfies the condition of (Equation 5) in the fourth embodiment.
It can be seen that the noise feeling is reduced and the image quality is improved compared to the conventional image in FIG. 10A.

FIG. 11A is a diagram illustrating an image perceived when blue noise is used as a reference image, field-divided, and converted to 1-bit by the dither processing unit 122 for comparison with the embodiment.

Here, when displaying an image of 1920×1080 pixels in 8-bit gradation (s=256), 48 (=d) frames interpolated from one input image frame are divided into four fields (k=4). The simulation image is illustrated when divided and 1-bit display is performed.

FIG. 11B is a diagram illustrating an image perceived when the reference image created by the method according to the second to fourth embodiments is converted to 1-bit by the dither processing unit 122. FIG.

Here, as in the third embodiment, 255 reference original images of 255×255 pixels are created, each reference original image is arranged in a tile shape, and a reference image group is created by cutting out 1920×1080 pixels. there is
Also, the level increment p of the same pixel between the reference original images is set to 89, which is a relatively prime value of n=255 and satisfies the condition of (Equation 5) in the fourth embodiment.

Further, as in the second embodiment, the reference image provided to the dither processing unit 122 has the reference values converted by the reference value conversion unit 123 into a range obtained by dividing 0 to 254 into four for each field. .
It can be seen that the noise is reduced and the image quality is improved compared to the conventional image in FIG. 11A.

As described above, according to the above-described embodiments, by sequentially providing reference images from a reference image group having different reference values, the reference values are uniformly distributed, and the frame rate is lower than in the conventional art. can also suppress bias in values due to dither processing. Therefore, the image display device 1 can display high-quality images at a lower driving frequency using the pulse density driving method while maintaining the stability and high speed of digital driving.

The image display device 1 may convert the reference value into a specific range of values that differ for each of a plurality of fields within the same frame. As a result, variations in reference values due to dithering are limited to a specific range, which leads to suppression of variations in brightness and reduces visual noise, enabling good image quality to be obtained even at low drive frequencies. .

By arranging reference original images in tiles to create reference images, the image display device 1 can efficiently create reference images with a large number of pixels and reduce the processing load.

By making the density of each reference value constant in the reference image, the image display device 1 can further suppress the deviation of the values due to the dithering process and realize high image quality at a low driving frequency.

The image display device 1 may set the number of gradations of the reference image to be one less than the number of gradations of the input video. As a result, it is possible to avoid the phenomenon that the result of dither processing is determined regardless of the signal level with respect to the minimum value or maximum value of the reference value.
For simplification, the number of gradations of the reference image may be equal to the number of gradations of the input video, which can also be expected to provide a sufficiently high image quality.

The image display device 1 adds a predetermined number p to the reference value and sequentially creates reference images in which the remainder obtained by dividing by the number of gradations n of the reference image is used as a new reference value.
Thereby, the image display apparatus 1 can easily create a reference image group, and can reduce the processing load.

At this time, the image display device 1 avoids duplication of reference values by setting the predetermined number p to a value relatively prime to the gradation number n of the reference images, thereby easily creating a large number of reference images as a reference image group. can.

In addition, the image display device 1 can suppress the bias of the reference values by selecting the value of the predetermined number p so as to satisfy the condition of the expression (5), and can reduce the frequency of consecutively close values. , high image quality can be achieved at a low drive frequency.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. Moreover, the effects described in the present embodiment are merely enumerations of the most suitable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the present embodiment.

In the above-described embodiment, a reference image having a reference value (0 to 254) in the range of the minimum value 0 or more and the maximum value less than 255 of the pixel values of the input video is created, and the pixel value of the input video is Although the pixel value is converted to 1 when the value exceeds the reference value and is converted to 0 when the value is equal to or less than the reference value, the present invention is not limited to this.
For example, the reference value may range from 0-255. Alternatively, the range of the reference value may be 1 to 255 (or 0 to 255), and the pixel value may be converted to 1 when the reference value is greater than or equal to the reference value, and to 0 when the reference value is less than the reference value.

In the present embodiment, the configuration and operation of the image display device 1 have been mainly described, but the present invention is not limited to this, and includes each component and is configured as a method or program for displaying an image on a display. good too.

Further, the program for realizing the functions of the image display device 1 may be recorded in a computer-readable recording medium, and the program recorded in the recording medium may be read by a computer system and executed. good.

The "computer system" here includes hardware such as an OS and peripheral devices. The term "computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, ROMs and CD-ROMs, and storage devices such as hard disks built into computer systems.

In addition, "computer-readable recording medium" means dynamically storing programs for a short period of time, like a communication line when sending a program via a network such as the Internet or a communication line such as a telephone line. However, it may also include a volatile memory inside a computer system that serves as a server or a client in that case, which holds the program at a fixed time. In addition, the program may be for realizing part of the functions described above, or may be capable of realizing the functions described above in combination with a program already recorded in the computer system. .

REFERENCE SIGNS LIST 1 image display device 11 video input section 12 signal processing section 13 row driver section 14 column driver section 15 display panel 121 reference image creation section 122 dither processing section 123 reference value conversion section

Claims (10)

a reference image creation unit that creates a reference image having reference values as pixel values;
a dither processing unit that converts the pixel value of the input image to 1 or 0 using the reference value of the same pixel as the input image as a threshold,
The reference image creation unit creates a reference image group composed of a plurality of reference images that do not have the same value in any pixel, and sequentially provides the reference images from the reference image group to the dither processing unit. 2. The image display device according to claim 1, further comprising a reference value converter that converts the reference value into a specific range of values that are different for each of a plurality of fields within the same frame. 3. The image display device according to claim 1, wherein the reference image creation unit cuts out the reference image from a tile array of reference original images smaller than the input video. 4. The image display device according to any one of claims 1 to 3, wherein the reference image creation section makes the density of each of the reference values constant in the reference image. 5. The image display device according to any one of claims 1 to 4, wherein the reference image creating unit sets the number of gradations of the reference image to be one less than the number of gradations of the input video. 6. The reference image creation unit adds a predetermined number p to the reference value and sequentially creates reference images having a remainder obtained by dividing by the number of gradations n of the reference image as a new reference value. The image display device according to any one of 1. 7. The image display device according to claim 6, wherein the predetermined number p is a value relatively prime to the number n of gradations of the reference image. When d reference images are provided for the same image frame with field number k, the predetermined number p is {(d/k)/(n/p)−1}×(n mod p)≧ 8. The image display device according to claim 7, wherein p is satisfied. a reference image creating step of creating a reference image having the reference values as pixel values;
a dither processing step of converting the pixel value of the input image to 1 or 0 using the reference value of the same pixel as the input image as a threshold,
A signal processing method in which, in the reference image creation step, a reference image group is created from a plurality of reference images that do not have the same value in any pixel, and the reference images are sequentially provided to the dither processing step from the reference image group. A signal processing program for causing a computer to function as the image display device according to any one of claims 1 to 8.

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