JP7483537B2 - Image display device, signal processing method, and signal processing program - Google Patents

Description

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

In recent years, high-resolution displays have been actively developed, making it possible to display extremely detailed images. However, the display characteristics of the conventional active matrix drive with TFTs on the backplane cause motion blur in moving images, and the display does not provide sufficient moving image quality. As a result, various methods for improving moving image quality have been proposed, such as black insertion and control of light emission time (see, for example, Patent Documents 1 and 2).

JP 2004-144928 A JP 2016-12068 A JP 2019-39958 A

To fundamentally resolve the video quality issue, it is necessary to improve the frame rate of the display, but existing display driving methods are not necessarily suitable for high frame rates.

In addition, the methods of driving displays to display gradations mainly include an analog modulation method, which adjusts the voltage or current applied to the light-emitting element according to the gradation value, and a digital modulation method, which adjusts the pulse width or the number of times light is emitted according to the gradation value.
Analog modulation is widely used in commercially available LCD and OLED TVs. However, low voltage control is required to display low brightness, which has been a bottleneck in improving drive speed. In addition, OLED and LED displays are easily affected by current and voltage fluctuations, and image quality degradation occurs due to TFT threshold fluctuations, so they are not necessarily suitable for applying analog modulation.

On the other hand, digital driving allows for high-speed and stable driving because it can be driven with a constant voltage and current. A time-division driving method is generally used, but this method requires many subfields to express gradations. In addition, subfield driving has the problem of image quality degradation due to color breakup. To prevent this, even more subfields are required, making it difficult to achieve a high frame rate.

A pulse density driving method has also been proposed that uses a random mask to control the pulse density over a certain period of time to express gradation (see, for example, Patent Document 3), but this method has the problem that an extremely high driving frequency is required to obtain a high-quality image display.

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.

The image display device according to the present invention includes a gamma conversion unit that performs gamma correction on an input video signal and linearly converts the relationship between the level of the corrected video signal and the display brightness, a random signal generation unit that outputs random values, a random signal conversion unit that converts the random values output from the random signal generation unit into values in a range allocated to each field, which is an equal division of the range of values that pixel values of the corrected video signal can take, and a dither processing unit that converts the pixel value to "1" if the pixel value is equal to or greater than the random value, and to "0" if the pixel value is less than the random value.

The image display device may include a display unit in which a plurality of display panels are arranged in a tiled pattern, and an image division unit that generates a plurality of image data by dividing the image frame converted by the dither processing unit, corresponding to the plurality of display panels.

The image display device may include a display unit in which a plurality of display panels are arranged in a tiled pattern, and a video division unit that generates a plurality of image data by dividing a video frame of the input video signal corresponding to the plurality of display panels.

The random signal conversion unit may divide the range of possible pixel values into a number equal to the number of fields per frame in the video signal, and assign the random value conversion range to each field within a frame.

The random signal conversion unit may detect motion in the video, and if the detected amount of motion is less than a threshold, may equally divide the range of possible pixel values into a number greater than the number of fields per frame in the video signal, and assign each field across frames as the conversion range of the random value.

The random signal conversion unit may determine the number of divisions of the conversion range of the random value for each region of the frame image.

The signal processing method according to the present invention is executed by a computer in a gamma conversion step of gamma correcting an input video signal and linearly converting the relationship between the level of the corrected video signal and the display brightness, a random signal generation step of outputting a random value, a random signal conversion step of converting the random value output in the random signal generation step into a value in a range allocated to each field, which is an equal division of the range of values that the pixel values of the corrected video signal can take, and a dither processing step of converting the pixel value to "1" if the pixel value is equal to or greater than the random value, and converting the pixel value to "0" if the pixel value is less than the random value.

The signal processing program of the present invention causes a computer to execute a gamma conversion step of gamma correcting an input video signal and linearly converting the relationship between the level of the corrected video signal and the display brightness, a random signal generation step of outputting a random value, a random signal conversion step of converting the random value output in the random signal generation step into a value in a range allocated to each field, which is an equal division of the range of values that the pixel values of the corrected video signal can take, and a dither processing step of converting the pixel value to "1" if the pixel value is equal to or greater than the random value, and converting the pixel value to "0" if the pixel value is less than the random value.

The present invention makes it possible to display high-quality images at a lower drive frequency while maintaining the stability and high speed of digital drive.

1 is a block diagram showing a functional configuration of an image display device according to a first embodiment. FIG. 2 is a block diagram showing a functional configuration of a signal processing unit according to the first embodiment. 2 is a diagram showing an example of a circuit constituting each pixel of the display panel according to the first embodiment; FIG. 5A to 5C are diagrams illustrating examples of voltage waveforms of drive signals in the display panel according to the first embodiment. 5A to 5C are diagrams illustrating an example of an image converted to 1 bit by the dither processing unit according to the first embodiment using a white noise mask; 5A to 5C are diagrams illustrating an example of an image converted to 1 bit using a blue noise mask by the dither processing unit according to the first embodiment; FIG. 2 is a first diagram showing an image simulating the visual integral effect according to the first embodiment; FIG. 4 is a second diagram showing an image simulating the visual integral effect according to the first embodiment. FIG. 11 is a block diagram showing the functional configuration of a signal processing unit in an image display device having a multi-display according to a second embodiment. FIG. 11 is a block diagram showing a functional configuration of an image display device having a multi-display according to a third embodiment.

An example of an embodiment of the present invention will now be described.
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 13 , a row driver section 14 , a column driver section 15 , and a display panel 16 .

When a video signal is input, the video input unit 11 temporarily stores the image data of the frames contained in this video signal in an input buffer, and provides it to the downstream signal processing unit 13 in sequence in accordance with the processing timing.

The signal processing unit 13 receives image data from the video input unit 11, generates data that controls the timing of data writing and light emission, and transmits it to the row driver unit 14 and the column driver unit 15.

A number of selection signal lines arranged in the horizontal direction are connected to the row driver section 14. The row driver section 14 supplies a selection signal to each of the selection signal lines. A number of emission time control signal lines arranged in the horizontal direction are also connected to the row driver section 14. A number of emission time control transistors are connected to each emission time control signal line in the horizontal area in which the emission time control signal line is arranged.

A number of data signal lines arranged in the vertical direction are connected to the column driver unit 15. The column driver unit 15 supplies image data signals for each pixel to each of the multiple data signal lines.

The display panel 16 is a hold-type image display module. As a more specific example, the display panel 16 is an active matrix type organic EL display module.

For example, the frame rate of the video signal input to the video input unit 11 is 480 Hz, and the drive frequency of the display panel 16 is 1920 (=480×4) Hz. In this case, four fields are displayed during one frame.
In the video input unit 11, when one frame of image data is stored in the input buffer, this image data is supplied to the signal processing unit 13 in accordance with the driving frequency of the display panel 16, and becomes one field of image data that has been converted to 1 bit by random dithering.

The 1-bit image data is sent to the column driver section 15, 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 14. The image display device 1 can display one frame of video by performing this operation for all horizontal lines. Furthermore, the image display device 1 can display one frame of video at 1920 Hz by performing the operation of displaying one frame of video more than 1920 times per second, and at the same time can express gradation through the visual integral effect.

FIG. 2 is a block diagram showing the functional configuration of the signal processing unit 13 according to the present embodiment.
The signal processing unit 13 includes a gamma conversion unit 131 , a random signal generation unit 132 , a random signal conversion unit 133 , a dither processing unit 134 , and a video buffer unit 135 .

The gamma conversion unit 131 performs gamma correction on the image data, and converts the relationship between the level (pixel value) of the corrected image data and the display luminance into a linear relationship.
Digital driving makes the gamma characteristic of the display panel 16 linear. Normally, the transfer function between the signal level and the display luminance in the captured image is nonlinear, so the gamma conversion unit 131 performs inverse gamma conversion to convert the relationship between the signal level and the display luminance to a linear one.

The random signal generating unit 132 outputs a random value and provides it to the random signal converting unit 133. Note that the range of the random value is adjusted by the random signal converting unit 133, so the random signal generating unit 132 outputs a random value within an arbitrary range.

The random signal conversion unit 133 converts the input random value into a random value in a specific range and outputs it. For example, if the pixel value of the input video signal is 10 bits, the random signal conversion unit 133 converts the random value into values in the ranges of 0 to 255, 256 to 511, 512 to 767, and 768 to 1023 for the mth, m+1th, m+2nd, and m+3rd fields, respectively. In this example, the pixel value range of the video signal (0 to 1023) is divided into four equal parts and each part is applied to four fields, and the range of the random value is controlled for each field.

In addition, the random signal conversion unit 133 may, for example, divide the range of possible pixel values into k ranges to create k ranges of random values after conversion, and control the range of random values for each field by repeating k fields.
Although the range of pixel values of the video signal (eg, 0 to 1023) is divided into k here, the range of pixel values +1 (eg, 1 to 1024) may also be divided into k.

Here, the random signal conversion unit 133 may divide the range of possible pixel values into a number equal to the number of fields per frame in the video signal and assign them to each field, but the number of divisions is not limited to this.
For example, when one frame has four fields, a range divided into two may be repeated twice within one frame, or a range divided into eight may be repeated in units of two frames (eight fields).

The dither processing unit 134 converts the pixel value a of the video signal to 1 if the pixel value a is equal to or greater than the random value x (or is greater than x), and converts the pixel value a to 0 if the pixel value a is less than the random value x (or is equal to or less than x), thereby making the pixel value 1 bit.

The video buffer unit 135 temporarily stores the image data converted to 1 bit by the dither processing unit 134 and provides it to the column driver unit 15 in accordance with the drive timing.

FIG. 3 is a diagram showing an example of a circuit constituting each pixel of the display panel 16 according to the present embodiment.
Here, the pixel structure of an organic EL panel is shown as an example.

When a gate voltage Vga is applied in response to a selection signal and a data voltage Vda in response to an image data level (0 or 1) is simultaneously applied, a certain amount of charge is accumulated in the capacitor C1 via the gate transistor Tr1.
Furthermore, when a drive voltage Vdd is applied in response to a light emission time control signal, a current flows through the organic EL element Del via the drive transistor Tr2, causing the organic EL element Del to emit light.

Figure 4 is a diagram illustrating the voltage waveforms of each drive signal in the display panel 16 according to this embodiment.

The row driver unit 14 applies a gate voltage Vga to each horizontal line in sequence, one line at a time, based on a selection signal for gate control. In addition, by continuing to apply a drive voltage Vdd and supplying a drive current to the pixels, light emission continues for one field period.

The column driver unit 15 writes data to each pixel at a constant data voltage Vda in accordance with the write signal for each horizontal line based on the 1-bit video data sent. When driving 1080 horizontal lines at 1920 Hz, the drive time for one horizontal line is approximately 0.5 μsec or less, but with digital drive, the data voltage has only two states, On/Off, and writing can be done at a moderately high voltage, making it possible to write at high speed. In the written pixel, a constant current flows between the source and drain of Tr2, causing the organic EL element Del to emit light.

5A is a diagram illustrating an example of an image converted to 1 bit using a white noise mask by the dither processing unit 134 according to the present embodiment. Note that this diagram illustrates a 1-bit color image in grayscale.
When pixel values are converted to 1 bit by random dithering, the image is recognizable to some extent in only one field, as shown in the figure, but the image has a very high sense of noise and is not natural.

The image display device 1 of this embodiment uses such 1-bit images to express the gradation of the images through the visual integration effect. By increasing the driving frequency by digital driving, the number of fields to be integrated increases, so the image display device 1 can express more natural images.

Figure 5B is a diagram illustrating an example of an image converted to 1 bit using a blue noise mask by the dither processing unit 134 according to this embodiment. Note that this diagram shows a 1 bit color image in grayscale.

Blue noise masks are random noise that are characterized by strong high-frequency components, and are known to be able to reduce the sense of noise by taking advantage of the fact that the spatial frequency characteristics of the human visual system have low-pass filter (LPF) characteristics. In addition, for example, spatial modulation by ordered dithering using a fixed pattern such as a Bayer array can cause the pattern to be visually recognized, but the blue noise mask uses a random pattern, resulting in a visually natural spatial modulation effect.

Here, the white noise mask is a completely random two-dimensional array that corresponds to the number of pixels in the video data, whereas the blue noise mask is a random array arranged so that the difference between adjacent values is large, i.e., the high frequency components are high.
Specifically, the white noise mask is, for example,
31 167 215 101 63 163 163 94
113 239 169 149 58 152 205 173
229 158 208 155 179 127 63 145
90 72 202 182 192 145 16 166
The difference between adjacent values is also a randomly distributed sequence, but the blue noise mask is, for example,
248 10 202 54 228 192 122 160
213 87 150 100 180 39 237 93
63 173 36 244 6 145 63 116
27 236 115 136 96 170 207 33
As shown above, the difference between adjacent values is biased toward the higher side.

Since the process of generating a blue noise mask in real time is a heavy load, the random signal generating unit 132 may output a two-dimensional blue noise mask created in advance, for example, sequentially from one end. Furthermore, the output start position may be changed randomly for each field.

6A is a first diagram showing an image simulating the visual integral effect according to the present embodiment, where the image is shown in grayscale instead of a color image.
This example shows an image obtained by smoothing 8 video frames (=32 fields) with 1-bit pixel values using random dithering when random values are not divided into fields and the same range is used for all fields. Since the visual integral effect is known to be about 1/60 sec, when the drive frequency (refresh rate) is 1920 Hz, the image is equivalent to smoothing 32 fields.

6B is a second diagram showing an image simulating the visual integral effect according to the present embodiment, where the color image is shown in grayscale.
This example shows an image obtained by smoothing 8 frames (=32 fields) equivalent to 1/60 sec, taking into account the visual integration effect when the drive frequency is 1920 Hz, as in Figure 6A, when random values are converted by dividing into 4 fields.
It can be seen that in FIG. 6B, the image quality is improved by dividing the image into four fields, as compared with FIG. 6A.

According to this embodiment, the image display device 1 uses digital driving to speed up driving by controlling at a constant voltage, and at the same time, achieves a high frame rate by reducing the bit depth used for image display to 1 bit. In addition, noise is smoothed by the integral effect of vision, and normal, natural images can be displayed.
Furthermore, the image display device 1 uses random dithering to binarize each pixel, and further divides and provides a range of random values for each field, thereby enabling gradation to be expressed even within one frame, and thus enabling the drive frequency to be kept low. In this case, if the number of fields per frame is increased to express gradation, the frame rate will decrease in inverse proportion thereto, but if, for example, four fields are repeated, a frame rate of 480 Hz can be achieved even with a drive frequency of 1920 Hz.
Therefore, the image display device 1 can display high-quality images at a lower drive frequency while maintaining the stability and high speed of digital drive.

[Second embodiment]
A second embodiment of the present invention will now be described.
In the first embodiment, a display (display unit) is configured with one display panel 16, but the present invention is not limited to this. The display unit of the image display device 1 may be a multi-display in which a plurality of display panels 16 are arranged in a tiled pattern.

FIG. 7 is a block diagram showing the functional configuration of a signal processing unit 13 in an image display device 1 having a multi-display according to the second embodiment.
The signal processing unit 13 further includes a video dividing unit 136 that generates a plurality of pieces of image data by dividing a video frame, corresponding to the plurality of display panels 16 .

The video division unit 136 generates a plurality of image data by dividing a video frame corresponding to a plurality of display panels, and provides the image data to the column driver units 15 corresponding to each display panel 16 via the video buffer unit 135 .
A portion of image data obtained by dividing a video frame is input to each of the multiple display panels 16, and as a result, one video frame is displayed on the entire multi-display.

The image display device 1 drives the multiple display panels 16 in parallel (divided drive), thereby making it possible to speed up the drawing of video frames and improve the frame rate.
6A and 6B show a simulation example in which the driving frequency is 1920 Hz, but when 1080 horizontal lines are driven at 1920 Hz on a single conventional display, the driving time for one horizontal line is about 500 nsec. When the driving time is shortened in this way, if divided driving using a multi-display is applied, it is possible to achieve a high frame rate of 3840 Hz or more even with the current performance of transistors.

Note that split driving is not limited to multi-displays, and can also be achieved with a single display, for example, by forming through electrodes in the substrate and wiring from the back surface. In this case, each area (display area) to be split-driven corresponds to each display panel 16 of the multi-display.

[Third embodiment]
A third embodiment of the present invention will now be described.

FIG. 8 is a block diagram showing a functional configuration of an image display device 1 having a multi-display according to the third embodiment.
The image display device 1 further includes a video dividing section 12 .

The video splitter 12 splits the video frame received from the video inputter 11 into multiple pieces of image data corresponding to the multiple display panels 16. The split image data is input to multiple signal processors 13 corresponding to each of the multiple display panels 16.

Since a single video frame is processed in parallel by multiple signal processing units 13, the processing load is reduced, and the image display device 1 can speed up the drawing of video frames and improve the frame rate.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment. Furthermore, the effects described in this embodiment are merely a list of the most favorable effects resulting from the present invention, and the effects of the present invention are not limited to those described in this embodiment.

In the above-described embodiment, an example was shown in which the random value conversion range in the random signal conversion unit 133 was divided into four and applied to four fields in one frame. However, for example, if the random value conversion range is divided into eight fields, the image quality can be further improved; that is, the image quality can be improved by increasing the number of fields per frame.
On the other hand, the more the number of divisions of the random value conversion range is increased, the more the number of fields increases and the lower the frame rate becomes, so it is not necessarily the case that the higher the division number, the better. In other words, there is a trade-off between frame rate and image quality.

Therefore, the signal processing unit 13 may detect the motion of the image from the difference between frame images, and vary the number of divisions of the conversion range of the random value according to the amount of motion. For example, when there is no motion (still image, or when the amount of detected motion is less than a threshold), the image quality can be improved by dividing the image into multiple times the number of fields per frame, such as 8 divisions or 16 divisions, and allocating the image across multiple frames. On the other hand, when there is motion, the number of divisions can be reduced to be equal to the number of fields per frame, thereby reducing the blurring that occurs in fast-moving objects.
Furthermore, the number of divisions into which the conversion range of the random values is divided may be determined for each region (block or each image) of the frame image.

In the above embodiment, the case where each pixel value of the video signal is converted to 1 bit was described, but this is not limited to this and it may be 2 bits or 3 bits, etc., and a similar effect can be expected by reducing the number of possible values.
In this case, the signal processing unit 13 can reduce the bit depth by performing random dithering on only the lower bits of the pixel values in the video signal using random values. For example, a 10-bit pixel value becomes a 2-bit value by converting the lower 9 bits to 1 bit.
Since the bit depth is reduced and high resolution is no longer required for the emission intensity, the column driver section 15 performs D/A conversion of the pixel values and controls the gradation by analog modulation.

In the above embodiment, an organic EL panel was used as the display panel 16, but this is not limiting, and a similar method can be applied to a projector that uses DLP (registered trademark), for example. In this case, binarization of each pixel is performed by random dithering for each time-divided subfield.

In the above 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 may be configured as a method or program for displaying an image on a display, including each component.

Furthermore, the functions of the image display device 1 may be realized by recording a program for realizing the functions on a computer-readable recording medium, and reading and executing the program recorded on the recording medium into a computer system.

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

Furthermore, "computer-readable recording medium" may include something that dynamically holds a program for a short period of time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, or something that holds a program for a fixed period of time, such as volatile memory within a computer system that serves as a server or client in such cases. Furthermore, the above program may be one that realizes part of the functions described above, or may be one that can realize 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 video division section 13 signal processing section 14 row driver section 15 column driver section 16 display panel 131 gamma conversion section 132 random signal generation section 133 random signal conversion section 134 dither processing section 135 video buffer section 136 video division section

Claims (8)

a gamma conversion unit that performs gamma correction on an input video signal and converts the relationship between the level of the corrected video signal and display luminance into a linear relationship;
A random signal generating unit that outputs a random value;
a random signal conversion unit that converts the random values output from the random signal generation unit into values within a range allocated to each field, the range being equal to the range of values that pixel values of the corrected video signal can take;
a dithering processing unit that converts the pixel value to "1" when the pixel value is equal to or greater than the random value, and converts the pixel value to "0" when the pixel value is less than the random value. A display unit in which a plurality of display panels are arranged in a tiled pattern;
2. The image display device according to claim 1, further comprising: a video dividing section that generates a plurality of pieces of image data by dividing the video frame converted by the dither processing section, corresponding to the plurality of display panels. A display unit in which a plurality of display panels are arranged in a tiled pattern;
The image display device according to claim 1 , further comprising: a video division unit that generates a plurality of pieces of image data by dividing a video frame of the input video signal, corresponding to the plurality of display panels. An image display device according to any one of claims 1 to 3, wherein the random signal conversion unit divides the range of possible values of the pixel values into a number equal to the number of fields per frame in the video signal, and assigns each field in one frame as the conversion range of the random value. The image display device according to claim 4, wherein the random signal conversion unit detects motion in the image, and when the detected amount of motion is less than a threshold, equally divides the range of possible pixel values into a number greater than the number of fields per frame in the image signal, and assigns each field across frames as the conversion range of the random value. The image display device according to claim 5, wherein the random signal conversion unit determines the number of divisions of the conversion range of the random value for each region of the frame image. a gamma conversion step of gamma-correcting an input video signal and converting a relationship between the level of the corrected video signal and display luminance into a linear relationship;
A random signal generating step of outputting a random value;
a random signal conversion step of converting the random values outputted in the random signal generation step into values in a range allocated to each field, the range of possible values of pixel values of the corrected video signal being equally divided;
a dithering step of converting the pixel value to "1" if the pixel value is equal to or greater than the random value, and converting the pixel value to "0" if the pixel value is less than the random value. a gamma conversion step of gamma-correcting an input video signal and converting a relationship between the level of the corrected video signal and display luminance into a linear relationship;
a random signal generating step for outputting a random value;
a random signal conversion step of converting the random values outputted in the random signal generation step into values in a range allocated to each field, the range of possible values of pixel values of the corrected video signal being equally divided;
a dithering step of converting the pixel value to "1" when the pixel value is equal to or greater than the random value, and converting the pixel value to "0" when the pixel value is less than the random value.

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