Image display device, signal processing method, and signal processing program

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

Technical Field

[0001] The present invention relates to an image display device for displaying an image, a signal processing method, and a signal processing program.

Background Art

[0002] In recent years, the development of high-resolution displays has been actively carried out, enabling very delicate video display. However, in the conventional active matrix driving using TFTs in the backplane, due to its display characteristics, motion blur occurs in moving images, so sufficient video quality cannot be provided. Therefore, various video quality improvement methods such as black insertion and control of emission time have been proposed (see, for example, Patent Documents 1 and 2). However, in order to fundamentally solve the video quality problem, it is essential to improve the frame rate of the display. However, the existing display driving methods have not necessarily been suitable for increasing the frame rate.

[0003] In addition, as driving methods for displaying the gradation of a display, mainly, there are an analog modulation method of adjusting the voltage or current applied to a light-emitting element according to the gradation value, and a digital modulation method of adjusting the width or emission frequency of a pulse according to the gradation value.

[0004] In commercially available liquid crystal TVs and organic EL TVs, the analog modulation method is widely used. However, organic EL displays and LED displays are easily affected by fluctuations in current and voltage, and image quality degradation occurs due to fluctuations in the threshold value of TFTs, etc., and they have not necessarily been suitable for applying analog modulation. [[ID=​​​​[Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2004-144928 [Patent Document 2] Japanese Patent Publication No. 2016-12068 [Patent Document 3] Japanese Patent Publication No. 2019-39958 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Incidentally, 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 high-quality video display, a very high driving frequency is required, and when the driving frequency is low, it is difficult to generate the pixel level of the noise pattern used across the entire range of display gradation, so sufficient display quality cannot be obtained.

[0008] For example, consider a case where the pixel value of the input signal is converted to "1" when it exceeds a random value, and to "0" when it is less than or equal to the random value, and displayed at high speed, with 50% brightness represented by the density of pixel values ​​"1" in the time direction. As shown in Figure 12, when the number of random values ​​decreases due to a low driving frequency, the frequency of consecutive similar values ​​increases relatively, resulting in a larger variation in the perceived display brightness (level), which leads to a sense of noise.

[0009] The present invention aims to provide an image display device, a signal processing method, and a signal processing program that can display high-quality images at a lower drive frequency while maintaining the stability and high speed of digital drive using a pulse density drive method. [Means for solving the problem]

[0010] The image display device according to the present invention comprises a reference image creation unit that creates a reference image having a reference value as a pixel value, and a dithering processing unit that converts the pixel value of the input video to 1 or 0 using the reference value of the same pixel as the input video as a threshold value, wherein the reference image creation unit creates a group of reference images consisting of a plurality of reference images in which no pixels have the same value, and sequentially provides the reference images from the group of reference images to the dithering processing unit.

[0011] The image display device may include a reference value conversion unit that converts the reference value into a value within a specific range that differs for each of the multiple fields within the same frame.

[0012] The reference image creation unit may cut out the reference image from a tiled arrangement of reference source images that are smaller than the input video.

[0013] The reference image creation unit may keep the density of each of the reference values ​​constant in the reference image.

[0014] The reference image creation unit may set the number of grayscale levels of the reference image to be one less than the number of grayscale levels of the input video.

[0015] The reference image creation unit may sequentially create reference images in which a predetermined number p is added to the reference value and the remainder obtained by dividing the result by the number of grayscale levels n of the reference image is used as the new reference value.

[0016] The predetermined number p may be a value relatively prime to the number of grayscale levels n of the reference image.

[0017] When providing d reference images for a frame of the same image with k fields, the predetermined number p may satisfy {(d / k) / (n / p)-1}×(n mod p)≧p.

[0018] The signal processing method according to the present invention includes a reference image creation step of creating a reference image having a reference value as a pixel value, and a dithering step of converting the pixel value of the input video to 1 or 0 using the reference value of the same pixel as the input video as a threshold value. The computer executes these steps. In the reference image creation step, a reference image group composed of a plurality of reference images having different values for each pixel is created, and the reference images are sequentially provided to the dithering step from the reference image group.

[0019] The signal processing program according to the present invention is for causing a computer to function as the image display device.

Advantages of the Invention

[0020] According to the present invention, it is possible to display a high-quality video at a lower driving frequency while maintaining the stability and high speed of digital driving using the pulse density driving method.

Brief Description of the Drawings

[0021] [Figure 1] It is a block diagram showing the functional configuration of the image display device according to the first embodiment. [Figure 2] It is a block diagram showing the functional configuration of the signal processing unit according to the first embodiment. [Figure 3] It is a configuration example of a reference image created by the reference image creation unit according to the first embodiment. [Figure 4] It is a block diagram showing the functional configuration of the signal processing unit according to the second embodiment. [Figure 5] It is a diagram showing an example of creating a reference image according to the third embodiment. [Figure 6] It is a diagram showing an example of generating a reference original image according to the fourth embodiment. [Figure 7A] It is a diagram showing the degree of temporal variation of luminance with respect to the value p according to the fourth embodiment when field division is not performed. [Figure 7B]This figure shows the degree of temporal variation in brightness with respect to the value p according to the fourth embodiment, when field division is performed. [Figure 8A] This figure shows how the reference value changes according to the fourth embodiment. [Figure 8B] This figure shows the case where d reference values ​​according to the fourth embodiment are substantially uniform. [Figure 8C] This figure shows the case where d reference values ​​according to the fourth embodiment are unevenly distributed. [Figure 9A] This figure shows the elements corresponding to p, which is relatively prime to n, in Figure 7A, divided into those that satisfy the compatibility conditions and those that do not. [Figure 9B] This figure shows the elements corresponding to p, which is relatively prime to n, divided into those that satisfy the compatibility conditions and those that do not, as shown in Figure 7B. [Figure 10A] This figure illustrates the perceived image when blue noise is used as a reference image and converted to 1-bit. [Figure 10B] This figure illustrates the image perceived when the reference images according to the third and fourth embodiments are converted to 1-bit. [Figure 11A] This figure illustrates the perceived image when blue noise is used as a reference image, the field is segmented, and then the image is converted to 1-bit. [Figure 11B] This figure illustrates the perceived image when the reference images according to the second to fourth embodiments are converted to 1-bit. [Figure 12] This figure shows the display variation depending on the number of random values ​​in a conventional pulse density modulation method using random values. [Modes for carrying out the invention]

[0022] [First Embodiment] The first embodiment of the present invention will be described below. Figure 1 is a block diagram showing the functional configuration of the image display device 1 according to this embodiment. The image display device 1 comprises a video input unit 11, a signal processing unit 12, a row drive driver unit 13, a column drive driver unit 14, and a display panel 15.

[0023] When a video signal is input to the video input unit 11, it temporarily stores the image data of the frames contained in the video signal in an input buffer and sequentially provides it to the subsequent signal processing unit 12 according to the processing timing. Furthermore, the video input unit 11 performs gamma correction on the image data as needed, and performs gamma conversion processing to linearly convert the relationship between the level (pixel value) of the corrected image data and the display brightness.

[0024] Furthermore, if the frame rate displayed on the display panel 15 is higher than the frame rate of the input video, the video input unit 11 creates image data based on the input video that matches the frame rate to be displayed on the display panel 15 and provides it to the signal processing unit 12. For example, suppose a video with a frame rate of 60Hz is input to the video input unit 11. If the frame rate displayed on the display panel 15 is set to 2880 (=60 × 48) Hz, the video input unit 11 will create image data with a frame rate 48 times faster. This increase in frame rate can be achieved, for example, by interpolating the same input image multiple times.

[0025] The signal processing unit 12 receives image data from the video input unit 11, generates data to control the timing of data writing and light emission to the display panel 15, and transmits it to the display unit (row drive driver unit 13 and column drive driver unit 14).

[0026] Multiple selection signal lines arranged horizontally are connected to the row drive driver unit 13. The row drive driver unit 13 supplies a selection signal to each of the multiple selection signal lines. In addition, multiple light emission time control line lines are connected to the row drive driver unit 13 along the horizontal direction. Multiple light emission time control transistors located in the region along the horizontal direction in which the light emission time control line is arranged are connected to each light emission time control line.

[0027] Multiple data signal lines arranged vertically are connected to the column drive driver unit 14. The column drive driver unit 14 supplies the image data signal for each pixel to each of the multiple data signal lines.

[0028] The display panel 15 is an image display module. More specifically, the display panel 15 may be an active-matrix type organic EL display module, an LED display module, or a discharge type display module.

[0029] Figure 2 is a block diagram showing the functional configuration of the signal processing unit 12 according to this embodiment. The signal processing unit 12 includes a reference image creation unit 121 and a dithering processing unit 122.

[0030] The reference image creation unit 121 outputs a reference image having reference values ​​as pixel values ​​that are in the range of 0 or greater and less than the maximum value that the pixel values ​​of the video signal after correction by the video input unit 11 can take, and provides it to the dithering processing unit 122.

[0031] The dithering processing unit 122 converts the buffered image data into 1-bit data using dithering. The 1-bit data is sent to the column drive driver unit 14, and ON or OFF values ​​are written to each pixel circuit in accordance with the timing of the write signal from the row drive driver unit 13. The signal processing unit 12 performs this operation for all horizontal lines to display one frame of video. Furthermore, by performing the operation of displaying one frame of video for, for example, 2880 times per second, the signal processing unit 12 can display at 2880Hz, and at the same time, it can express gradation through the visual integration effect.

[0032] Figure 3 shows an example of the configuration of a reference image created by the reference image creation unit 121 according to this embodiment. If the number of grayscale levels to be displayed on the display panel 15 is denoted as s, the reference image creation unit 121 prepares a reference image group consisting of multiple reference images (m images) having a number of grayscale levels (s-1), and sequentially provides the reference images from this reference image group to the dithering processing unit 122.

[0033] For example, if you want to display with 8 bits (=256), the reference image creation unit 121 will create a reference image in which the pixel values ​​are one of 0 to 254 (number of gradations n=2 8 (-1=255). In this case, the density of each level (pixel value) within a unit area of ​​the reference image is assumed to be constant. Furthermore, within a single set of reference images, multiple reference images are created so that no two pixels (coordinates) have the same value. For this reason, the number of reference images (m) in a set of reference images will not exceed the number of grayscale levels (n) of the reference image.

[0034] This section will explain in detail how to create a set of reference images. Here, as an example, we will consider the case where the input video has a resolution of 1920 pixels horizontally and 1080 pixels vertically. The reference image creation unit 121 first creates the first reference image by randomly arranging 255 levels from 0 to 254 across 1920 × 1080 = 2,073,600 pixels. At this time, in order to make the density of each level present in the reference image roughly constant, the reference image creation unit 121 determines the number of values ​​to place for each level by dividing the total number of pixels by the number of reference values ​​(number of gradations) in the reference image. If the division is not exact, rounding or other methods are used as appropriate to adjust the number so that the number of each level is roughly equal and the total number is equal to the total number of pixels.

[0035] In this example, 2,073,600 pixels ÷ 255 levels ≈ 8,131.7, so the reference image to be created will contain 255 levels from 0 to 254, each with either 8,131 or 8,132 pixels. The assignment of each level to each pixel is determined randomly, for example, using random numbers.

[0036] Subsequently, the reference image creation unit 121 creates the second reference image based on the values of each pixel of the first reference image. Assuming that the reference value in frame k for an arbitrary pixel [i, j] (1 ≤ i ≤ 1080, 1 ≤ j ≤ 1920) is R(i, j, k), the level (reference value) R(i, j, 2) of each pixel (i, j) of the second reference image is based on the level (reference value) R(i, j, 1) of each pixel (i, j) of the first reference image, and using a numerical value p (1 ≤ p < n), R(i, j, 2) = (R(i, j, 1) + p) mod n … (Equation 1) is set as such. Note that A mod B represents the remainder when A is divided by B.

[0037] By determining the reference value according to (Equation 1), for all pixels, the second reference image has different pixel values from the first reference image, and in the second reference image, the density of each pixel value (reference value) can be made approximately constant. Similarly hereinafter, R(i, j, u + 1) = (R(i, j, u) + p) mod n (1 ≤ u) … (Equation 2) By doing so, reference images from the third onwards can be created.

[0038] 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 have as many reference images as possible in the reference image group, p is preferably selected as a number that is relatively prime to n (= 255) (having only a common divisor of 1) so that the reference values do not overlap. By thus selecting p that is relatively prime to n (= 255), n (= 255) reference images can be created, and the reference image creation unit 121 uses these n (= 255) reference images as the reference image group.

[0039] When the input video is in color, the signal processing unit 12 dithers each of the red, green, and blue signals using a reference image. However, within the same frame, different reference images may be used for each color, or a common reference image may be used.

[0040] The reference image creation unit 121 sequentially provides reference images one by one from the reference image group to the dithering processing unit 122. Once all the reference images in the reference image group have been provided, the reference image creation unit 121 repeats the process of providing reference images one by one from the same reference image group. Furthermore, once the reference image creation unit 121 has finished providing all the reference images in the reference image group, it may provide the reference images to the dithering processing unit 122 using another set of reference images created using the same procedure as described above. Also, the number of reference images m in the reference image group may be less than the number of grayscale levels n for each pixel.

[0041] The dithering processing unit 122 converts the pixel value a of each pixel in the input video to 1 bit by using the pixel value x of the same coordinate in the corresponding reference image as a threshold, setting the pixel value a to 1 if it exceeds the threshold, and to 0 if it is below the threshold. The row drive driver unit 13 and the column drive driver unit 14 display one frame of an image by illuminating the corresponding pixel on the display panel 15 if the value is 1, and turning off the corresponding pixel on the display panel 15 if the value is 0, based on the 1-bit value (1 or 0) of each pixel determined by the signal processing unit 12.

[0042] [Second Embodiment] A second embodiment of the present invention will be described below. In this embodiment, the image display device 1 has the same video input unit 11, row drive driver unit 13, column drive driver unit 14, and display panel 15 as in the first embodiment, but the function of the signal processing unit 12 is different.

[0043] Figure 4 is a block diagram showing the functional configuration of the signal processing unit 12 according to this embodiment. The signal processing unit 12, similar to the first embodiment, includes a reference image creation unit 121 and a dithering processing unit 122, and further includes a reference value conversion unit 123.

[0044] The reference value conversion unit 123 outputs a reference value obtained by converting the pixel values ​​of the input reference image to a specific range for each field. If the number of grayscale levels s of the image to be displayed is 8 bits (=256), the reference value conversion unit 123 converts the reference value for each of the f-th, f+1-th, f+2-th, and f+3-th fields to a range of 0 to 63, 64 to 127, 128 to 191, and 192 to 254, respectively. In this case, the reference value conversion unit 123 divides the conversion range of the reference value into four parts and applies each to the four fields, controlling the range of the reference value for each field.

[0045] The reference value conversion unit 123 controls the range of the reference value by repeating k (=4) fields when the conversion range of the reference value is divided into k (4 in the example above). The reference value conversion unit 123 provides the reference image having the converted reference values ​​as pixel values ​​to the dithering processing unit 122, and the dithering processing unit 122 displays the image on the display panel 15 by performing the same processing as in the first embodiment.

[0046] [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 the first or second embodiment, but the function of the reference image creation unit 121 in the signal processing unit 12 is different.

[0047] Figure 5 shows an example of creating a reference image according to this embodiment. The reference image creation unit 121, in creating a reference image, first creates a reference image with a small number of pixels as the base, and then arranges these in a tile pattern to create a reference image with a large number of pixels.

[0048] Specifically, for example, if the number of grayscale levels s of the video to be displayed is 256, the reference image creation unit 121 prepares a reference source image with a size of n × n pixels (n = s - 1), that is, 255 × 255 pixels. The reference image creation unit 121 places 255 levels, ranging from 0 to 254, within this 255 x 255 pixel area. In order to maintain a constant density of each level within the reference source image, each level is allocated (255 x 255 pixels) ÷ 255 levels = 255 pixels. In other words, the created reference source image will have 255 levels, ranging from 0 to 254, each with 255 pixels.

[0049] The reference image creation unit 121 creates a group of reference original images by creating multiple such reference original images, and within this group, it arranges the pixel levels so that the pixel levels of each pixel are not the same as those of the other pixels. If the input video has a resolution of 1920 x 1080 pixels, the reference image must also have a resolution of 1920 x 1080 pixels. In this case, as shown in Figure 5, a 255 x 255 pixel reference source image can be tiled in a grid of 8 tiles horizontally and 5 tiles vertically, and then cropped from an arbitrary location to create a 1920 x 1080 pixel reference image.

[0050] The reference image creation unit 121 can create a group of reference images with the same number of pixels as the input video by performing the same pixel count conversion on each of the reference source images in the reference source image group. This reduces the processing load for creating the reference image group.

[0051] [Fourth Embodiment] A fourth 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 third embodiment, but the function of the reference image creation unit 121 in the signal processing unit 12 is different. The reference image creation unit 121 appropriately selects the aforementioned value p in order to uniformly distribute the reference values.

[0052] FIG. 6 is a diagram showing an example of generation of a reference original image according to this embodiment. Here, as in the third embodiment, the case of a group of reference original images each having 255 levels from 0 to 254 (the number of gradations n of the reference image = 255) and having 255 pixels each will be described as an example.

[0053] 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 within the reference image group, a new reference original image can be created by adding the same value (p) to all pixels as in Equation (2) of the first embodiment. Since the range of possible pixel values (reference values) is 0 to 254, for pixels that exceed 254 by adding p, a reference value different from the original reference value can be obtained by subtracting n (= 255) from the value obtained by adding p (<n).

[0054] By repeating this, a plurality of reference original images can be created. However, in order to prevent a reference original image having the same reference value for the same pixel before finishing creating n (255) reference original images, as described above in the first embodiment, it is necessary for p and n to be relatively prime to each other. By using p such that p and n are relatively prime to each other, it is possible to create a group of reference original images with n reference original images.

[0055] Incidentally, as described in the first embodiment, if the frame rate displayed on the display panel 15 is greater than the frame rate of the input video, a video will be created based on the input video to match the frame rate displayed on the display panel. In this case, since the same image will be digitized using multiple (d) reference images, the value of d also needs to be taken into consideration. For example, if a video with a frame rate of 60Hz is input to the video input unit 11, and the frame rate is accelerated to 2880 (=60 × 48) Hz on the display panel 15, then one frame of the input video will be displayed as 48 identical frames on the display panel 15.

[0056] Here, we focus on a single pixel within the display panel 15 and consider the time variation in brightness. We assume that the signal level of the target pixel is level 144 out of 256 gradations, and that there is no fluctuation in the input signal level. We consider the case where this is displayed at 2880Hz using 1-bit pulse density modulation. Furthermore, due to the integration effect as a visual characteristic, we assume that the luminance is determined by the light emission density from the flashing of light over (1 / 60) seconds (48 frames).

[0057] Figures 7A and 7B show the degree of temporal variation (fluctuation) of luminance with respect to the value p according to this embodiment. Here, the standard deviation of the temporal variation (fluctuation) of perceived brightness is calculated for each p value from 1 to 254. In the figure, the dark lines represent the variation for p values ​​that are relatively prime to n=255.

[0058] Figure 7A shows the variation when one frame of the input video is displayed as 48 frames on the display panel 15 without field division, while Figure 7B shows the variation when one frame of the input video is displayed as 48 frames on the display panel 15 and one frame is divided into four fields. In both graphs, the horizontal axis represents the p value (from 1 to 254), and the vertical axis represents the luminance variation (standard deviation) over time. In both graphs, the variation changes significantly depending on the p value. This indicates that the luminance variation is small when a balanced reference value can be provided across all 255 gradations over 48 frames, and large when this cannot be achieved.

[0059] Next, we consider how much the range of variation of the reference value within one frame of the input video, i.e., within d frames of the displayed video, depends on the value of p.

[0060] Figure 8A shows the fluctuations of the reference value according to this embodiment. For simplicity, let's assume that the pixel value (reference value) of the first reference image in the set of reference images is 0. Then, the value of the corresponding pixel in the second reference image will be p, and the value of the corresponding pixel in the third reference image will be 2 × p. As we increase the reference value by p in this way, the reference value becomes p, 2 × p, ... (for the first cycle with n = 255 as the unit), r=255 mod p...(Formula 3) Therefore, the reference value just before exceeding 254 is 255-r.

[0061] Therefore, the next reference value is (255-r+p)-255=pr, and until the value exceeds 254 (second cycle), it will be pr, 2×pr, ... In other words, the reference values ​​in the second iteration will be smaller by r compared to the sequence of reference values ​​in the first iteration. Similarly, the reference value for the third lap will be 2 × r smaller than the reference value for the first lap, and the reference value for the fourth lap will be 3 × r smaller than the reference value for the first lap.

[0062] Figure 8B shows the case where the d reference values ​​according to this embodiment are substantially uniform. For each frame of the input video, the number of cycles the reference value goes through in units of 255 until the reference value is presented d times can be roughly calculated as d / (255 / p) cycles, since one cycle is approximately 255 / p times. From the first cycle, the reference value moves by {d / (255 / p)-1}×r.

[0063] Therefore, in order to cover the range of p, which is one increment of the reference value in the first sequence, in the subsequent d / (255 / p)-1 cycles, {d / (255 / p)-1}×r≧p…(Equation 4) That would be fine.

[0064] Figure 8C shows the case where the d reference values ​​according to this embodiment are unevenly distributed. If p does not satisfy (Equation 4), although d reference values ​​are presented for one frame of the input video, there are regions where reference values ​​are missing, and it is not possible to provide reference values ​​uniformly across the entire range of n grayscale levels to be represented.

[0065] Furthermore, as shown in the second embodiment, when field division is used, one frame is divided into k fields (for example, 4), so the number of reference images used for one frame of the input video is 48 / 4 = 12. Therefore, d in (Equation 4) can be replaced with d / 4.

[0066] From the above, the general conditions that the pixel value increment p should satisfy when creating a reference image are: {(d / k) / (n / p)-1}×r≧p…(Equation 5) This is the result.

[0067] Figures 9A and 9B show the variability graphs shown in Figures 7A and 7B, separated into those that satisfy the compatibility condition of (Equation 5) and those that do not, for each corresponding to p which is relatively prime to n. Looking at Figures 7A and 7B, we can see that both graphs are symmetrical. This is because increasing the reference value by p is equivalent to increasing the reference value by 255-p (i.e., decreasing it by p) within the reference image group. Therefore, it is sufficient to look only at the left half (from p 1 to n / 2), and Figures 9A and 9B show the left half of Figures 7A and 7B, i.e., p values ​​from 1 to 127.

[0068] In Figure 9, the bars that are filled in black satisfy the conditions of (Equation 5), while the others do not. When p satisfies the conditions of (Equation 5), the variation is relatively suppressed. Note that the degree of variation varies depending on the signal level, but this graph shows an example where the signal level is 144 out of 256 levels. Similarly, for other signal levels, using p that satisfies the conditions of (Equation 5) suppresses luminance variation and is effective for grayscale display using pulse density modulation.

[0069] The following examples illustrate the simulation results comparing the images displayed by the aforementioned embodiment with those from the conventional method. Figure 10A is a diagram illustrating the perceived image when blue noise, known to reduce noise by utilizing the spatial frequency characteristics of the human visual system, is used as a reference image for comparison with the embodiment, and the image is converted to 1-bit by the dithering processing unit 122.

[0070] Here, we show an example of a simulated image when displaying a 1920x1080 pixel video with 8-bit grayscale (s=256), where no field division is performed on a single frame of the input video, and instead, 48 (=d) interpolated frames are displayed in 1-bit. The image is displayed, but it appears to have a high level of noise.

[0071] Figure 10B illustrates an example of an image perceived when a reference image created by the methods according to the third and fourth embodiments is converted to 1-bit by the dithering processing unit 122.

[0072] Here, as in the third embodiment, 255 reference source images of 255 x 255 pixels are created, and a group of reference images is created by arranging each of the reference source images in a tile-like manner and cropping out an area of ​​1920 x 1080 pixels. Furthermore, the level increase p for identical pixels between reference source images is set to 89, which is a relatively prime value to n=255 and satisfies the condition of (Equation 5) in the fourth embodiment. Compared to the conventional image in Figure 10A, the noise level has been reduced and the image quality has been improved.

[0073] Figure 11A is a diagram illustrating the perceived image when blue noise is used as the reference image, the field is divided, and then the dithering unit 122 converts it to 1 bit, for comparison with the embodiment.

[0074] Here, we show an example of a simulated image when displaying a 1920x1080 pixel video with 8-bit grayscale (s=256). For each input video frame, the 48 (=d) interpolated frames are divided into four fields (k=4) and displayed using 1-bit color depth.

[0075] Figure 11B illustrates the perceived image when a reference image created by the method according to the second to fourth embodiments is converted to 1-bit by the dithering processing unit 122.

[0076] Here, as in the third embodiment, 255 reference source images of 255 x 255 pixels are created, and a group of reference images is created by arranging each of the reference source images in a tile-like manner and cropping out an area of ​​1920 x 1080 pixels. Furthermore, the level increase p for identical pixels between reference source images is set to 89, which is a relatively prime value to n=255 and satisfies the condition of (Equation 5) in the fourth embodiment.

[0077] Furthermore, as in the second embodiment, the reference image provided to the dithering processing unit 122 has its reference values ​​converted by the reference value conversion unit 123 to a range of 0 to 254 divided into four parts for each field. Compared to the conventional image in Figure 11A, the noise level has been reduced and the image quality has been improved.

[0078] As described above, according to the embodiment described, by sequentially providing reference images from a group of reference images whose reference values ​​are not identical, the reference values ​​are uniformly distributed, and bias in values ​​due to dithering can be suppressed even at a lower frame rate than in the conventional method. Therefore, the image display device 1 can display high-quality images at a lower drive frequency using the pulse density drive method while maintaining the stability and high speed of digital drive.

[0079] The image display device 1 may convert the reference value to a different specific range for each of the multiple fields within the same frame. This limits the variation in the reference value due to dithering to a specific range, which also helps suppress brightness variations and reduces visible noise, thereby enabling good image quality even at low drive frequencies.

[0080] The image display device 1 can create reference images by arranging the original reference images in a tile-like pattern, thereby streamlining the creation of reference images with a high pixel count and reducing the processing load.

[0081] The image display device 1 can further suppress value bias caused by dithering by keeping the density of each reference value constant within the reference image, thereby achieving high image quality at a low drive frequency.

[0082] The image display device 1 may set the number of grayscale levels of the reference image to one less than the number of grayscale levels of the input video. This avoids the phenomenon where the dithering result is determined regardless of the signal level based on the minimum or maximum value of the reference value. For simplicity, the number of grayscale levels in the reference image may be equal to that of the input video, and this alone can still be expected to result in sufficiently high image quality.

[0083] The image display device 1 sequentially creates reference images by adding a predetermined number p to the reference value and using the remainder obtained by dividing by the number of grayscale levels n of the reference image as the new reference value. This allows the image display device 1 to easily create a group of reference images and reduce the processing load.

[0084] In this case, the image display device 1 can easily create a large number of reference images as a group of reference images by setting a predetermined number p to a value relatively prime to the number of grayscale levels n of the reference image, thereby avoiding duplication of reference values.

[0085] Furthermore, by selecting a predetermined number of p values ​​that satisfy the conditions of equation (5), the image display device 1 can suppress bias in the reference value and reduce the frequency of consecutive close values, thereby enabling high image quality at low drive frequencies.

[0086] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above. Furthermore, the effects described in these embodiments are merely a list of the most preferred effects arising from the present invention, and the effects of the present invention are not limited to those described in these embodiments.

[0087] In the embodiment described above, a reference image is created in which the pixel values ​​of the input video are in the range of a minimum value of 0 or more and a maximum value of less than 255 (0 to 254). If the pixel values ​​of the input video exceed the reference values, the pixel values ​​are converted to 1, and if they are less than or equal to the reference values, the pixel values ​​are converted to 0. However, the embodiment is not limited to this. For example, the reference value range could be 0 to 255. Alternatively, the reference value range could be 1 to 255 (or 0 to 255), where the pixel value is converted to 1 if it is greater than or equal to the reference value, and to 0 if it is less than the reference value.

[0088] In this embodiment, the configuration and operation of the image display device 1 have been mainly described, but the present invention is not limited thereto and may be configured as a method or program for displaying an image on a display, comprising each of the components.

[0089] Furthermore, this may be achieved by recording a program for realizing the functions of the image display device 1 on a computer-readable recording medium, and then having a computer system read and execute the program recorded on this recording medium.

[0090] In this context, "computer system" includes hardware such as the operating system and peripheral devices. Furthermore, "computer-readable recording media" refers to portable media such as flexible disks, magneto-optical disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems.

[0091] Furthermore, "computer-readable recording media" may include those that dynamically hold programs for a short period of time, such as communication lines used when transmitting programs via networks such as the Internet or communication lines such as telephone lines, as well as those that hold programs for a fixed period of time, such as volatile memory within computer systems that act as servers or clients in such cases. In addition, the above-mentioned program may be for the purpose of realizing some of the functions described above, and may also be a program that can realize the above-mentioned functions in combination with a program already recorded in the computer system. [Explanation of Symbols]

[0092] 1. Image display device 11. Video Input Section 12 Signal Processing Unit 13. Line drive driver section 14-row drive driver unit 15 Display Panel 121 Reference Image Creation Section 122 Dithering Processing Unit 123 Reference Value Conversion Unit

Claims

1. A reference image creation unit that creates a reference image having reference values ​​as pixel values, The system includes a dithering processing unit that converts the pixel values ​​of the input video to 1 or 0, using the reference value of the same pixel as the input video as a threshold. The reference image creation unit sequentially creates a group of reference images consisting of multiple reference images, each having a different value for every pixel, by adding a predetermined number p to the reference value and using the remainder obtained by dividing the reference value by the number of grayscale levels n of the reference image as the new reference value. The image display device then sequentially provides the reference images from this group to the dithering unit.

2. The image display device according to claim 1, further comprising a reference value conversion unit that converts the aforementioned reference value into a value within a specific range that differs for each of multiple fields within the same frame.

3. The image display device according to claim 1 or 2, wherein the reference image creation unit cuts out the reference image from a tiled arrangement of reference source 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 unit equalizes the number of each of the reference values ​​within the reference image.

5. The image display device according to any one of claims 1 to 4, wherein the reference image creation unit sets the number of gradations of the reference image to one less than the number of gradations of the input video.

6. The image display device according to any one of claims 1 to 5, wherein the predetermined number p is a value relatively prime to the number of grayscale levels n of the reference image.

7. The image display device according to claim 6, where d reference images are provided for a frame of the same image with k fields, and the predetermined number p satisfies {(d / k) / (n / p)-1} × (n mod p) ≥ p.

8. A reference image creation step involves creating a reference image in which the reference values ​​are used as pixel values, The computer performs a dithering step that converts the pixel values ​​of the input video to 1 or 0, using the reference value of the same pixel as the input video as a threshold. A signal processing method comprising the above-mentioned reference image creation step, in which a predetermined number p is added to the reference value and the remainder obtained by dividing the reference image by the number of grayscale levels n is used as the new reference value, thereby creating a group of reference images consisting of multiple reference images in which no pixel has the same value, and sequentially providing the reference images from this group of reference images to the dithering step.

9. A signal processing program for causing a computer to function as an image display device according to any one of claims 1 to 7.

Images