Drive circuit

Abstract

[Problem] To suppress disorder of video and the like. [Solution] This drive circuit drives each of pixels arranged in a matrix in a display device, and is provided with a noise addition unit. The noise addition unit adds one of a plurality of correction values to gradation data of the pixel when the gradation of the pixel is a predetermined gradation.

Description

[Technical field]

[0001] The present disclosure relates to a drive circuit. [Background technology]

[0002] Today, devices that realize display such as projectors by digital drive are widely used. In digitally driven display devices, gradation display is realized by using, for example, a PWM (Pulse Width Modulation) method. In display devices such as projectors using the PWM method, black streaks occur due to liquid crystal disturbances in projections near the intensity where the modulation time changes significantly. These black streaks can be reduced, for example, by adding a correction value to the gradation data for each pixel for all pixels for each frame, but this correction strength is in a trade-off relationship with the occurrence of flicker. For this reason, it is difficult to set a strong correction value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-50679 A Summary of the Invention [Problem to be solved by the invention]

[0004] In view of this, the present disclosure provides a drive circuit, a drive method, and a display device that suppress disturbances in images and the like. [Means for solving the problem]

[0005] According to one embodiment, the drive circuit is a drive circuit that drives each pixel in a display device arranged in a matrix, and includes a noise imparting unit that imparts one of a plurality of correction values ​​to the gradation data of a pixel when the gradation of the pixel is a predetermined gradation.

[0006] The gradation data may be a signal encoded in a PWM (Pulse Width Modulation) format or a PM (Phase Modulation) format that indicates control to maintain the on state or off state of the pixel during each subframe period that is time-divided in one frame, and the pixel may be controlled to emit the encoded signal in a time series.

[0007] The noise adding section may set a base value based on the predetermined gradation value, and add a correction value having an absolute value within the base value to the gradation data of the pixel.

[0008] The maximum value of the gradation data may be n (n is an arbitrary natural number), and the predetermined gradation may include at least a gradation indicating a gradation value of floor((n-1) / 2).

[0009] The predetermined gradation may include a plurality of gradation values, and a correction value may be applied to the gradation data of the pixel having a gradation of floor((n - 1) / 2) based on the base value that is larger than the base value of the other pixels having the predetermined gradation.

[0010] The noise adding section may add a correction value, the correction value having a sign opposite to that of the correction value added in the previous frame, to the gradation data of each of the pixels to which the correction value has been added.

[0011] The noise adding section may add a correction value that randomly varies to the gradation data of the pixel.

[0012] The noise adding section may add a periodically varying correction value to the gradation data of each of the pixels to which the correction value has been added.

[0013] The noise adding unit may add a correction value to the gradation data of two adjacent pixels in the same frame when a period during which the phases of the gradation data in the PWM format differ from each other is equal to or longer than a predetermined period.

[0014] The image forming apparatus may further include a gamma correction section for performing gamma correction on the grayscale data, the gamma correction section switching between a plurality of gamma curves for each frame.

[0015] The gamma correction unit may perform gamma correction based on a gamma curve that corrects gradations of the same value in both positive and negative directions from a reference gamma curve.

[0016] The gamma correction section may perform gamma correction based on a gamma curve in which at least a central gradation value is different from the reference gamma curve.

[0017] The gamma correction unit may perform gamma correction based on a gamma curve having a gradation different from the reference gamma curve at least in a gradation where a period during which the phases of the PWM-format gradation data for each of two adjacent pixels in the same frame differ is equal to or longer than a predetermined period.

[0018] The gamma correction unit may perform gamma correction based on a gamma curve having a gradation where a period during which the phases of the PWM-format gradation data for each of two adjacent pixels in the same frame differ is equal to or longer than a predetermined period, and where a difference from the reference gamma curve is larger than the gradation values ​​before and after the gradation.

[0019] According to one embodiment, a drive circuit for driving each pixel in a display device arranged in a matrix is ​​provided with a gamma correction unit that gamma corrects gradation data for the pixels and switches between multiple gamma curves for each frame. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a block diagram illustrating a display device according to an embodiment. [Diagram 2] FIG. 1 is a block diagram illustrating a signal processing circuit according to an embodiment. [Diagram 3]FIG. 4 is a diagram showing an example of gradation processing using a PWM method. [Figure 4] FIG. 2 is a block diagram illustrating an example of a gamma correction circuit according to an embodiment. [Diagram 5] FIG. 4 is a diagram showing an example of gamma correction according to an embodiment. [Figure 6] FIG. 11 is a diagram showing an example of gradation output by gamma correction according to an embodiment. [Figure 7] FIG. 4 is a diagram showing an example of gamma correction according to an embodiment. [Figure 8] FIG. 4 is a diagram showing an example of gamma correction according to an embodiment. [Figure 9] FIG. 4 is a diagram showing an example of gamma correction according to an embodiment. [Figure 10] FIG. 4 is a diagram showing an example of a position where noise is added according to an embodiment. [Figure 11] 10 is a flowchart showing a process of a gamma correction circuit according to an embodiment. [Figure 12] 6 is a flowchart showing a process of a noise adding circuit according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, the embodiments of the present disclosure will be described with reference to the drawings. The drawings are used for explanation, and the shape, size, or size ratio of each component in an actual device to other components does not necessarily have to be as shown in the drawings. In addition, since the drawings are simplified, components necessary for implementation other than those shown in the drawings are also appropriately provided.

[0022] [Display device] 1 is a block diagram illustrating a display device according to an embodiment of the present invention. The display device 1 includes a display panel 10 and a drive circuit 20.

[0023] The display panel 10 includes a pixel region 12. The display panel 10 outputs information on images and videos (hereinafter, referred to as videos and the like). This display includes pixels in the pixel region 12 that control light emitted from a light source, for example, by liquid crystal.

[0024] The pixel area 12 includes pixels 14 , data lines 16 and scan lines 18 .

[0025] The pixels 14 are provided in an array along, for example, a first direction (horizontal direction) and a second direction (vertical direction). The pixels are provided in, for example, regions where the data lines 16 and scanning lines 18 intersect. The pixels 14 are connected to the corresponding data lines 16 and scanning lines 18. The pixels 14 include, for example, liquid crystal cells. The liquid crystal cells control the brightness of light emitted by a backlight or the like and output it.

[0026] The driving circuit 20 controls the gradation by PWM driving the pixels 14 in a time series based on the gradation data. The pixels 14 express gradation based on the ratio of the ON and OFF states of light emission in one frame. That is, in the display device 1, gradation is expressed in the form of a time integration of the light emission state of the pixels 14.

[0027] The pixel 14 outputs light of a gradation based on an input signal, for example. The gradation may be controlled using a liquid crystal element such as a liquid crystal cell. The pixel 14 may also be a pixel with a built-in memory. The memory may be, for example, a static random access memory (SRAM), a dynamic random access memory (DRAM), or the like.

[0028] The data lines 16 transmit data for outputting video information and the like to the pixels 14. For example, the drive circuit 20 outputs a data signal based on color information and intensity information of light emitted by each of the pixels 14 via the data lines 16, and controls the light emission state of each of the pixels 14.

[0029] The scanning lines 18 output scanning signals to the pixels 14 for selecting a line of the pixels 14 arranged in the second direction. For example, the driving circuit 20 outputs a signal via the scanning lines 18 for selecting which pixel of the pixels 14 arranged in the vertical direction is to receive a data signal.

[0030] The driving circuit 20 outputs data signals to the pixels 14 via the data lines 16, and selects which pixels 14 to supply the data signals to by propagating control signals to the scanning lines 18. In this manner, the gradation output by each pixel 14 is controlled by the corresponding data line 16 and scanning line 18. For example, a common data line 16 is connected to the pixels 14 arranged along the second direction, and this connection state is controlled by the scanning line 18 corresponding to each pixel 14. In this manner, the scanning line 18 controls the gradation of light output by the pixels 14 belonging to the selected row based on the signal applied to the data line 16.

[0031] The drive circuit 20 includes a signal processing circuit 22, a controller 24, a horizontal drive circuit 26, and a vertical drive circuit 28. The drive circuit 20 is a circuit that outputs video signals and control signals to the pixels 14 so as to cause the display panel 10 to display an image or the like.

[0032] The signal processing circuit 22 receives a video signal 20A and a synchronization signal 20B supplied from a higher-level device (not shown). The video signal 20A includes gradation data, and the signal processing circuit 22 converts the video signal 20A into a PWM signal 22A corresponding to the gradation data and outputs it to the horizontal drive circuit 26. The signal processing executed in the signal processing circuit 22 includes, for example, an image quality adjustment process as well as a process related to gradation for avoiding image degradation in the present disclosure. The signal processing circuit 22 and the contents of the signal processing will be described in detail later.

[0033] The controller 24 is a circuit that generates control signals 24A, 24B, and 24C that control the operation timing of the signal processing circuit 22, the horizontal drive circuit 26, and the vertical drive circuit 28 from the synchronization signal 20B. The synchronization signal 20B may be, for example, a horizontal synchronization signal, a vertical synchronization signal, a clock signal, etc. The control signals 24A, 24B, and 24C may be, for example, a clock signal, a latch signal, a frame start signal, a subfield start signal, etc.

[0034] The horizontal drive circuit 26 outputs a data signal to each of the data lines 16 based on the PWM signal 22A and the control signal 24B.

[0035] The vertical drive circuit 28 outputs scanning signals to the scanning lines 18 for selecting each pixel 14 on a row-by-row basis, based on the control signal 26A output from the horizontal drive circuit 26 and the address data specified by the control signal 24C. The vertical drive circuit 28, for example, outputs scanning signals to each of the scanning lines 18 in a predetermined order, and executes control to select a line of pixels 14 to which a data signal is to be supplied.

[0036] In this way, the drive circuit 20 performs signal processing on the received video signal 20A, and controls the pixels 14 to emit light at a timing based on the PWM signal 22A and the synchronization signal 20B resulting from the signal processing.

[0037] [Drive circuit] 2 is a schematic diagram illustrating an example of the signal processing circuit 22 according to an embodiment. The signal processing circuit 22 includes a pre-processing circuit 220, a gamma correction circuit 221, a noise adding circuit 222, a frame memory 223, a write circuit 224, a read circuit 225, and a decoder 226.

[0038] The pre-processing circuit 220 performs various processes on the video signal 20A to output it as an appropriate video. As pre-processing, the pre-processing circuit 220 performs signal processing such as distortion correction and various filter processes, and image processing such as brightness adjustment and various image filter processes. This pre-processing is not limited to the above description, and includes various processes performed to generate appropriate video data.

[0039] The gamma correction circuit 221 performs gamma correction on the video signal processed by the pre-processing circuit 220, and corrects the luminance value of the light output by the pixel 14. The gamma correction circuit 221 performs gamma correction to generate a signal that reduces the visibility of black stripes caused by digital driving in, for example, an image, video, etc. displayed on the display panel 10. Details of this gamma correction will be described later.

[0040] The noise adding circuit 222 adds random noise to the video signal that has been gamma corrected by the gamma correction circuit 221, and corrects the luminance value of the light output by the pixel 14. By adding noise, the noise adding circuit 222 generates a signal that reduces the visibility of black stripes caused by digital driving in an image, video, etc. displayed on the display panel 10, similar to the gamma correction circuit 221, for example. The details of this noise addition will also be described later.

[0041] The frame memory 223 is a video display memory having a storage capacity greater than at least the resolution of the pixel area 12. The frame memory 223 can store, for example, addresses in the first direction, addresses in the second direction, and gradation data of the pixels 14 associated with these addresses.

[0042] The write circuit 224 generates a write address Wad of the video signal to which the noise adding process has been performed by the noise adding circuit 222 based on the synchronization signal 20B, and outputs the write address Wad to the frame memory 223 in synchronization with the synchronization signal 20B. The write address Wad is information including, for example, an address in the first direction and an address in the second direction.

[0043] The read circuit 225 generates a read address Rad based on the control signal 24 A and outputs it to the frame memory 223 .

[0044] The decoder 226 converts the grayscale data output from the frame memory 223 into a PWM signal 22A and outputs it.

[0045] 2, the signal output from the pre-processing circuit 220 is input to the gamma correction circuit 221 and the noise adding circuit 222 in this order, but this is not limited to the above. For example, the noise adding circuit 222 may be connected after the pre-processing circuit 220, and the gamma correction circuit 221 may be connected between the noise adding circuit 222 and the frame memory 223. This is not limited to the above, and the signal processing circuit 22 may be configured not to include either the gamma correction circuit 221 or the noise adding circuit 222. In other words, in the following description, the signal processing circuit 22 is configured to apply both gamma correction and noise adding, but this is not limited to the above, and the signal processing circuit 22 may be configured to include a circuit that executes either one of the tone conversions of these tone processes.

[0046] [Gradation processing using PWM method] The pixel 14 generates and displays a luminance value corresponding to the gradation in a pseudo manner by switching between 0 (minimum value) and 1 (maximum value) in a frame in a time-division manner in response to the PWM signal 22A.

[0047] 3 is a diagram showing an example of gray scale switching in the PWM method. The control of one frame is shown for an example in which the display is expressed in 32 gray scales. The gray scale is not limited to 32, and may be an even larger number of gray scales, such as 64, 128, etc. The number of gray scales does not have to be a power of 2. Even in this case, the same processing as that of the display device according to the present embodiment can be performed between consecutive or adjacent bits whose values ​​may be significantly affected by inversion.

[0048] In Fig. 3, the gray scale is shown in decimal and binary. The display timing for this gray scale value, i.e., the switching timing of each pixel between 0 and 1, is shown on the right. For example, when gray scale values ​​are expressed using the PWM method, the time is divided into subframes that display 0 or 1 during 1 unit time (e.g., 1 msec), 2 unit times, 4 unit times, 8 unit times, or 16 unit times. Each pixel expresses gray scales by combining subframes by switching which subframes are turned off (0) or on (1) based on the gray scale value coded in binary.

[0049] For example, if the gradation value is 0 (00000), then all subframes are turned off to represent 0. If the gradation value is 1 (00001), then only the first subframe is turned on, and the subsequent second to fifth subframes are turned off to represent 1. Similarly, if the gradation value is 2 (00010), then after the first subframe is turned off, the second subframe is turned on, and then the third to fifth subframes are turned off again. In this way, by controlling the time for turning off and on the lights according to the gradation value, the human eye is made to perceive a luminance that corresponds to the gradation value in a pseudo manner.

[0050] When the frame is switched in a time-division manner in this manner, for example, when the gradation value is in the vicinity of 15 to 16, the off state and the on state are switched in approximately 1 / 2 the time within the frame. For example, the pixel 14 with a gradation value of 15 (01111) is turned on in the first to fourth subframes (15 / 31 frame period) in the first half, and turned off in the fifth subframe (16 / 31 frame period) in the second half. On the other hand, the pixel 14 with a gradation value of 16 (10000) is turned off in the first to fourth subframes (15 / 31 frame period) in the first half, and turned on in the fifth subframe (16 / 31 frame period) in the second half. Therefore, the PWM signal 22A for the pixel 14 with a gradation value of 15 (01111) and the PWM signal 22A for the pixel 14 with a gradation value of 16 (10000) are out of phase with each other for 100% of one frame period.

[0051] In this case, the off state and the on state continue consecutively in the relatively long periods of the first to fourth subframes and the fifth subframe, respectively. In particular, when the subframes in the first half and the second half are distinguished, a phenomenon occurs in which the luminance is inverted between the gradation values ​​of 15 and 16 in both the first half and the second half. For this reason, in an image having gradually changing gradations such as gradation, this luminance inversion may appear as a black stripe. This may occur not only for 15 to 16, but also for gradation values ​​of 7 to 8 and 23 to 24, where a similar gradation conversion occurs in a shorter period in the first half of the subframes. For example, the PWM signal 22A for the pixel 14 with a gradation value of 7 (00111) and the PWM signal 22A for the pixel 14 with a gradation value of 8 (01000) have different phases for approximately 50% of one frame period. Furthermore, the PWM signal 22A for the pixel 14 with a gradation value of 23 (10111) and the PWM signal 22A for the pixel 14 with a gradation value of 24 (11000) also differ in phase for approximately 50% of one frame period.

[0052] This phenomenon is not simply caused by switching between 0 and 1, but also occurs due to the characteristics of liquid crystal. With technological improvements, the pixel pitch of liquid crystal has become smaller, down to a few micrometers. As a result, when the grayscale value is switched, the reflectance of the liquid crystal element cannot be appropriately controlled due to the influence of the electric field developed laterally between adjacent pixels, and black streaks occur in regions where the phases differ for a long period as described above (for example, regions where the phases differ for approximately 50% or more of one frame period).

[0053] In order to reduce the visibility of black streaks (digital disclination) caused by the phase difference in the gradation value, the gamma correction circuit 221 executes gamma correction, and the noise adding circuit 222 adds noise to the gradation value.

[0054] The above is a description of luminance, but of course it is not limited to grayscale images. For example, each pixel 14 may be equipped with a color filter. By switching the light emission state of the luminance value for each color in a time-division manner as described above, it is possible to handle full-color images and the like.

[0055] Gamma Correction 4 is a block diagram showing an example of a gamma correction circuit 221 according to an embodiment. The gamma correction circuit 221 includes a gradation correction circuit. The gradation correction circuit gamma-corrects input gradation data 220A based on a gamma table represented by a look-up table (LUT), and outputs the result as gradation data 221A.

[0056] In this embodiment, a plurality of LUTs for gamma correction are provided. The LUTs may be stored in the gamma correction circuit 221. As another embodiment, the LUTs may be stored in a storage unit (not shown) provided in the signal processing circuit 22 or the drive circuit 2.

[0057] The gamma correction circuit 221 switches between a plurality of LUTs depending on the frame number for conversion. For example, as shown in Fig. 4, the gamma correction circuit 221 converts the gradation by switching between gamma correction LUT A and gamma correction LUT B. In this way, by switching the gamma correction LUT for each frame, gamma correction is performed with a different gamma curve for each frame, thereby reducing the visibility of the above-mentioned black stripes.

[0058] When two LUTs are used, each gamma curve may be, for example, a curve in which the positive and negative signs are reversed with respect to a linear tone conversion (non-tone conversion) curve. Also, if there is a suitable gamma curve in advance for display on the display device 1, the two gamma curves may be set so that the positive and negative signs are reversed with respect to the gamma curve.

[0059] Some examples of table settings are given below. In the following examples, a case where the reference gamma curve is linear (straight line) will be described, but similar processing can be performed even if the reference gamma curve is a curve. When the reference gamma curve is a curve, it is desirable to perform a gradation conversion similar to that described below based on the output gradation value.

[0060] 5 is a diagram showing an example of an LUT for gamma correction. The dashed and dotted line is a reference LUT, the solid line is a gamma curve showing LUT A which is one of the multiple LUTs, and the dashed line is a gamma curve showing LUT B which is symmetrical with respect to LUT A and the reference LUT.

[0061] The gamma correction circuit 221 performs gamma correction by, for example, switching between two LUTs for each frame. For example, gamma correction is performed using the gamma curve of LUT A in one frame, and gamma correction is performed using the gamma curve of LUT B in the next frame. By switching the LUT that performs gamma correction for each frame in this way, the position where black streaks occur changes for each frame. This makes it possible to reduce the visibility of black streaks compared to when black streaks occur at the same position in multiple consecutive frames.

[0062] For example, in consideration of the characteristics of the human eye, the position of the black stripe may be changed more significantly in a low-luminance area than in a high-luminance area. This curve may also be changed according to the display performance of the display device 1. That is, the curve may be such that the position of the black stripe is changed more significantly in a display device 1 having a certain resolution than in a display device 1 having a lower resolution.

[0063] Conversely, it is also considered that in high luminance areas, black stripes caused by gradation disturbance in the liquid crystal in response to actual gradation changes are easily perceived by humans. In this case, in low luminance areas and high luminance areas where the degree of disturbance caused by the PWM method is similar, the degree of gradation correction may be made greater in the high luminance area than in the low luminance area in order to more efficiently reduce the visibility of black stripes in the high luminance area.

[0064] The settings of this curve are shown as a few examples, but are not limited to these, and may be appropriately set by comparing the display device 1 with the user's perception results (for example, the results of a sensory experiment, etc.). In this way, the gamma curve may be appropriately set based on the characteristics of the environment, device, etc. This is not limited to FIG. 5, and is the same in the following examples.

[0065] Note that, although the LUT diagrams, including this one, are shown with emphasis so that the differences are easy to see, the change in the gamma curve may be smaller than that shown in the diagram. For example, when gamma correction is performed in each LUT shown in the following Fig. 6, the curve may shift the position of the black stripe by a few pixels (for example, up to 5 pixels). Note that, without being limited to these, the LUT may be an LUT showing a gamma curve that makes a larger change so long as it is not visually unnatural to the user.

[0066] 6 is a diagram showing the position of black stripes when two such gamma correction LUTs are used. This diagram shows a case where a gradation is displayed, and is an enlarged diagram showing the vicinity of the median luminance where black stripes are most likely to appear when, for example, the gamma correction according to this embodiment is not performed. The upper diagram shows the case where LUT A is used, and the lower diagram shows the case where LUT B is used.

[0067] The position indicated by diagonal lines is the position of the black streak when the reference LUT is used. With respect to this position, with LUT A, the black streak appears on the left side, and with LUT B, the black streak appears on the right side. The position of the black streak alternates for each frame. By integrating the images in these figures over time, the original gradation image is output, and the position of the black streak changes for each frame, making it difficult to perceive the black streak.

[0068] As described above, the position of the gradation changes drastically in the figure, but this is shown in an exaggerated manner for the purpose of explanation, and in reality, it is sufficient to use an LUT that shifts the position of the black stripe to an extent that the human eye cannot perceive it. For example, an LUT that shifts the position of the black stripe by about 1 pixel, or 2 to 5 pixels may be used.

[0069] The present invention is not limited to this, and the black stripe may be shifted more significantly. For example, in Fig. 6, the diagram is shown in the center of the luminance value, but the shift may be set to about 1 pixel at 1 / 4 and 3 / 4 of the luminance value, and the shift may be set to about 2 to 3 pixels at the center of the luminance value, and a gamma curve that smoothly connects these shifts may be stored as an LUT.

[0070] 7 is a diagram showing another example of the LUT. Instead of using a different curve for LUT A and LUT B overall compared to the reference LUT, the LUTs may have different curves in areas where black streaks are likely to appear. For example, as described above, in areas where the luminance value is 1 / 2, the possibility of black streaks appearing is high. In areas including such areas, LUT A and LUT B may have different values ​​compared to the reference LUT.

[0071] In this way, the LUT may be set so that the degree of correction is greater in areas where black streaks are likely to occur, and the LUT is set to the reference LUT in other areas. By setting the LUT in this way, it becomes possible to set the luminance values ​​in areas other than those where black streaks occur to the luminance values ​​of the original image, etc.

[0072] Fig. 8 is a diagram showing another example of the LUT. The curves of LUT A and LUT B may be set so that the transition from the reference LUT becomes large in an area where black streaks are likely to appear, for example, in the area of ​​1 / 2, 1 / 4, 3 / 4, 1 / 8, ... of the luminance value. In Fig. 8, the curves are set to be the same in all areas where the difference between the LUTs becomes large, but this is not limiting. For example, the LUT may be set so that the smaller the luminance value, the greater the difference in luminance after correction, or vice versa.

[0073] As another example, a curve may be used in which the correction value of the luminance value fluctuates more greatly in a region including 1 / 2 of the maximum value than in regions including 1 / 4 and 3 / 4 of the maximum value.

[0074] In Fig. 8, there are three regions where the degree of correction by the LUT is greater than the surroundings, but this is not limited to this. For example, the degree of correction may be greater in 1 / 8 units of the maximum brightness value than the surroundings, that is, the degree of correction may be greater in seven regions than the surroundings.

[0075] Fig. 9 is a diagram showing another example of the LUT. As in Fig. 8, the LUT is shifted from the reference LUT in areas where black streaks are likely to occur, but in areas other than the areas where black streaks are likely to occur, the LUT has a curve equivalent to that of the reference LUT.

[0076] 8, for example, an LUT may be used that allows correction to occur with greater fluctuations in an area of ​​1 / 2 the maximum brightness value than in other areas.Furthermore, an LUT may be used that allows correction to occur with greater fluctuations in areas of 1 / 4 and 3 / 4 the maximum brightness than in areas of 1 / 8, ..., etc.

[0077] By setting the LUT as shown in Fig. 9, it is possible to selectively increase the fluctuation range in the gradation where black streaks occur, and prevent gradation fluctuation from occurring in other areas. As a result, for example, the user will be less likely to see black streaks, and will be able to perceive an image that is closer to the original image, etc., in other gradations.

[0078] 5 to 9, two LUTs are provided, but three or more LUTs may be provided. For example, when three LUTs are used, in addition to the above-mentioned LUT A and LUT B, a reference LUT may be used and the LUT may be changed in three cycles, from reference LUT → LUT A → LUT B, or in four cycles, from LUT A → reference LUT → LUT B → reference LUT.

[0079] Without being limited thereto, an LUT C between LUT A and the reference LUT, and an LUT D between LUT B and the reference LUT may be further set, and the cycle may include LUT C and LUT D. As another example, the cycle may include both LUT A and LUT B in Fig. 8 and LUT A and LUT B in Fig. 9. For example, the gamma curve may be varied in a cycle of LUT A in Fig. 8 → LUT B in Fig. 8 → LUT A in Fig. 9 → LUT B in Fig. 9, etc.

[0080] The combination of LUTs to be used and the transition of LUTs are shown as an example, and are not limited to this. For example, in the above, LUTs that swing positive and negative with respect to the reference LUT are alternately used, but the present invention is not limited to this, and the gamma curve to be used may be smoothly transitioned such as positive and large swing → positive and small swing → reference LUT → negative and small swing → negative and large swing → negative and small swing → reference LUT → positive and small swing.

[0081] As described above, the gamma correction according to this embodiment changes the gamma curve for each frame, so that the amount of correction for gradations where black stripes are easily visible can be increased, and the amount of correction for gradations where black stripes are less easily visible can be decreased. This can reduce the visibility of black stripes. Furthermore, by avoiding the need to change the gradations uniformly for all gradations, it is possible to avoid the occurrence of flicker caused by gamma correction for reducing the visibility of black stripes.

[0082] [Noise addition] As described above, depending on the gradation, if the period during which the phases of the PWM signals 22A for two adjacent pixels differ is longer than a predetermined period (for example, 50% or more of one frame period), a black stripe appears between the two pixels. In the gradation where such a black stripe appears, the noise adding circuit 222 adds noise to the gradation data to reduce the visibility of the black stripe.

[0083] The noise adding circuit 222 adds noise to the grayscale data when the grayscale output from each pixel 14 is a grayscale at which black streaks may occur. As in the case of gamma correction, the grayscale at which black streaks may occur is a grayscale at which the phase changes significantly when the grayscale value is expressed digitally.

[0084] For example, when the digital representation of the gradation values ​​is as shown in Fig. 3, noise is added to the gradation data for pixel 14 having a gradation value of 15. Furthermore, noise may be added to the gradation data for pixel 14 having a gradation value of 7 and pixel 14 having a gradation value of 23. In this way, the noise adding circuit 222 adds noise to the gradation data for pixel 14 that outputs a gradation value that is a boundary where black streaks may occur.

[0085] As an alternative to the above, noise may be added to the gradation data for pixels 14 having gradation values ​​of 16, 8, and 24. As yet another alternative, noise may be added to the gradation data for pixels 14 having gradation values ​​of 15, 16, 7, 8, 23, and 24.

[0086] As described above, these conversions of gradation data are performed, for example, at gradations around gradation values ​​15 and 16. To express this quantitatively, if the maximum value of the gradation data is n (n is any natural number), noise may be added to the gradation data of a pixel with a gradation value of floor((n - 1) / 2), where floor() represents the floor function.

[0087] The noise adding circuit 222 outputs A * 2 m Noise may be added to the gradation data of pixels with a gradation value of -1 (however, pixels with a gradation value less than the maximum gradation value) (A and m are each any natural number). As another example, the above-mentioned floor((n - 1) / 2) or A * 2 may be added to a memory circuit (not shown). m A gradation value of -1 may be stored, and noise may be added to the gradation data if this gradation value applies.

[0088] The noise adding circuit 222 may determine the strength of the noise to be added based on the gradation value to which the noise is added. For example, when the gradation values ​​are shown as in FIG. 3, the base value may be 1 for a gradation value of 7, 4 for a gradation value of 15, and 2 for a gradation value of 23. The noise adding circuit 222 adds noise to the gradation data based on this base value. For example, the noise adding circuit 222 adds noise between −4 and +4 to the gradation data of pixel 14 with a gradation value of 15.

[0089] The noise adding circuit 222 adds this noise for each frame. For example, if a noise of -4 is added to the gradation data of a pixel 14 with a gradation value of 15 in a certain frame, a noise of +4 may be added in the next frame. That is, in this case, the gradation value of this pixel 14 is 11 in one frame and 19 in the next frame. In this way, the positive and negative of the added noise may be switched for each frame.

[0090] As another example, the noise adding circuit 222 may repeat the addition of noise from a positive base value → 0 → a negative base value → 0 → a positive base value.

[0091] Furthermore, the noise adding circuit 222 may add noise whose absolute value is equal to or less than the basic value, instead of the basic value. For example, when the basic value is 4, the noise adding circuit 222 may vary the noise added to a certain pixel 14 from +2 → -2 → +2 or from +2 → 0 → -2, and may vary the noise added to a different pixel 14 from +3 → -3 → +3 or from +3 → 0 → -3.

[0092] As another example, the noise adding circuit 222 may add random noise within ±a basic value to each frame, regardless of whether the noise is positive or negative.

[0093] As another example, the noise adding circuit 222 may add noise for each frame so as to smoothly transition from a positive base value to a negative base value like a triangular wave or a sine wave. For example, for a gradation value whose base value is 4, the noise to be added may be changed as follows: +4 → +3 → +2 → +1 → 0 → -1 → ... → -4 → -3 → ... → +3 → +4, etc.

[0094] 10 is a diagram showing an example in which positive and negative values ​​are alternately added as noise. In this diagram, for example, a gradation image with 32 gradations is shown with an enlarged view of the periphery of gradation values ​​15 and 16. The diagonal lined area is the region of pixel 14 where a difference in gradation value that causes a black streak may occur, and the thickness indicates the magnitude (strength and / or width) of the influence of the black streak. In this example, the noise adding circuit 222 adds noise to the gradation data of pixel 14 with a gradation value of 15.

[0095] Before correction, black streaks appear between gradation values ​​15 and 16.

[0096] In frame t, for example, the noise adding circuit 222 adds noise of +2 to the top line, -1 to the next line, -2 to the line after that, and +1 to the bottom line. In this case, the position of the pixel 14 that may become a black stripe shifts for each line. The effect of this shift is also smaller than the effect between the gradation values ​​of 15 and 16.

[0097] In the next frame, frame (t+1), the noise adding circuit 222 adds noise with the opposite sign to the noise added in frame t. By reversing the sign of the added noise in this way, the locations where black streaks may occur are switched between frames t and (t+1). Also, the degree of this change is less influential than the disturbance that occurs between the gradation values ​​of 15 and 16, as described above.

[0098] As a result, as a result of time integration that can be sensed by the human eye, black streaks do not appear as they do before correction, but rather it is possible to reduce the visibility of black streaks on average.

[0099] As described above, the noise addition according to this embodiment makes it possible to reduce the visibility of black stripes. Also, as with the gamma correction described above, a uniform value is not added or subtracted from the gradation values ​​of the entire image, so it is possible to reduce the visibility of black stripes while suppressing the occurrence of flicker.

[0100] As described in the configuration of the signal processing circuit 22, the gamma correction circuit 221 and the noise adding circuit 222 may be arranged in any order, or neither may be arranged. That is, only gamma correction may be performed, or only noise adding may be performed. Moreover, noise adding may be performed after gamma correction, or gamma correction may be performed after noise adding.

[0101] [Processing flow for each correction] FIG. 11 is a flowchart showing the process of the gamma correction circuit 221 according to an embodiment.

[0102] First, the gamma correction circuit 221 obtains a frame number (S10).

[0103] Next, the gamma correction circuit 221 acquires a signal (S12). This signal is, for example, a signal that represents the gradation value of an image or the like for each pixel. In the case where gamma correction is performed after noise addition, this is the signal output by the noise addition circuit 222. Note that S10 and S12 may be in the reverse order or may be at the same timing. It is sufficient that the frame number and the signal are received in correspondence with each other.

[0104] Next, the gamma correction circuit 221 executes gamma correction (S14). As described above, this gamma correction is executed based on a plurality of LUTs set for each frame, for example.

[0105] Next, the gamma correction circuit 221 outputs the gamma-corrected signal (S16).

[0106] In this way, the gamma correction circuit 221 switches between gamma corrections based on a plurality of different LUTs depending on the frame, and outputs the results.

[0107] FIG. 12 is a flowchart showing the process of the noise adding circuit 222 according to an embodiment.

[0108] The noise adding circuit 222 first acquires a signal (S20). This signal is, for example, a signal that represents a gradation value of an image or the like for each pixel. If the noise adding is performed after gamma correction, the signal is the signal output by the gamma correction circuit 221.

[0109] Next, the noise adding circuit 222 determines whether or not the gradation value in each pixel 14 is a gradation value to be corrected (S22).

[0110] Next, if the gradation value is to be corrected (S22: YES), the noise adding circuit 222 corrects the gradation value (S24). The processes from S22 to S24 are executed for all pixels 14 to be output. These processes may be executed sequentially for each pixel 14, or may be executed in parallel.

[0111] The noise adding circuit 222 outputs the corrected gradation value, and if the gradation value is not the gradation value to be corrected (S22: NO), the gradation value in the acquired signal is output without change (S26). Then, based on this output gradation value, light with an intensity based on the signal is output from the pixel 14.

[0112] These circuits may be implemented by dedicated circuits for implementing the processing, or by general-purpose processing circuits (processors). That is, they may be implemented as dedicated analog or digital circuits such as ASICs (Application Specific Integrated Circuits), or may be implemented so that software processing is specifically implemented by hardware resources using analog or digital circuits having various functions such as CPUs (Central Processing Units). In the case of software processing, a program for executing the processing may be stored in a storage unit (not shown). In addition, when a dedicated circuit is used, each component may be implemented as a programmable circuit such as an FPGA (Field Programmable Gate Array).

[0113] The technology described in this disclosure can be applied to, for example, digitally driven liquid crystal panels in general, such as projection-type projectors, televisions, etc. This display-related technology can be applied to the display units of, as some non-limiting examples, digital cameras, digital video cameras, computer displays, tablet-type terminals, wristwatch-type terminals, eyeglass-type terminals, smartphones, feature phones, etc. The display unit may have a built-in touch panel.

[0114] The technology described in this disclosure can also be applied to display devices using a PM (Phase Modulation) system. When a PM signal is input or output, the drive circuit executes the same process as described above for multiple grayscales in which the phase switches significantly in a range where the grayscale difference is small (for example, the grayscale difference is 1 / 32 or less of the minimum and maximum values) as with a PWM signal. Specifically, the drive circuit switches the gamma curve or adds random noise. As a result, liquid crystal disturbances in such grayscales can be suppressed.

[0115] The above-described embodiment may be modified as follows.

[0116] (1) A drive circuit for driving each pixel in a display device arranged in a matrix, comprising: a noise adding unit that adds one of a plurality of correction values ​​to the gradation data of the pixel when the gradation of the pixel is a predetermined gradation; A drive circuit comprising:

[0117] (2) the gradation data is a signal encoded in a PWM (Pulse Width Modulation) format or a PM (Phase Modulation) format that indicates control for maintaining an on state or an off state of the pixel during each subframe period that is time-divided in one frame, Controlling the pixels to emit light in accordance with the encoded signals in a time sequence; The drive circuit according to (1).

[0118] (3) the noise adding unit sets a base value based on the predetermined gradation value, and adds a correction value having an absolute value within the base value to the gradation data of the pixel. The drive circuit according to (2).

[0119] (4) The maximum value of the gradation data is n (n is any natural number), and the predetermined gradation includes at least a gradation indicating a gradation value of floor((n-1) / 2). The drive circuit according to (3).

[0120] (5) the predetermined gradation includes a plurality of gradation values, a correction value is applied to the gradation data of the pixel having a gradation of floor((n-1) / 2) based on the base value that is larger than the base value of the other pixels having the predetermined gradation; The drive circuit according to (4).

[0121] (6) the noise adding unit adds a correction value, the positive and negative signs of which are reversed from those of the correction value added to the previous frame, to the gradation data of each of the pixels to which the correction value has been added; A driving circuit according to any one of (3) to (5).

[0122] (7) the noise adding unit adds a correction value that randomly varies to the gradation data of the pixel; A driving circuit according to any one of (3) to (5).

[0123] (8) the noise adding unit adds a periodically varying correction value to the gradation data of each of the pixels to which the correction value has been added; A driving circuit according to any one of (3) to (5).

[0124] (9) the noise adding unit adds a correction value to the gradation data of the pixels when a period during which the phases of the gradation data in the PWM format for two adjacent pixels in the same frame differ is equal to or longer than a predetermined period; The drive circuit according to (3).

[0125] (10) a gamma correction unit for gamma-correcting the gradation data, the gamma correction unit switching between a plurality of gamma curves for each frame; The drive circuit according to any one of (1) to (9), further comprising:

[0126] (11) the gamma correction unit executes gamma correction based on a gamma curve that corrects gradations of the same value in both positive and negative directions from a reference gamma curve; The drive circuit according to (10).

[0127] (12) the gamma correction unit executes gamma correction based on a gamma curve in which at least a central gradation value is different from the reference gamma curve. The drive circuit according to (11).

[0128] (13) the gamma correction unit performs gamma correction based on a gamma curve having a gradation different from the reference gamma curve at least in a gradation where a period in which the phases of the gradation data in the PWM format for each of two adjacent pixels in the same frame differ is equal to or longer than a predetermined period. The drive circuit according to (12).

[0129] (14) The gamma correction unit performs gamma correction based on a gamma curve having a gradation where a period during which the phases of the gradation data in the PWM format for each of two adjacent pixels in the same frame differ is equal to or longer than a predetermined period, and a difference from the reference gamma curve is larger than the gradation values ​​before and after the gradation. The drive circuit according to (12).

[0130] (15) A drive circuit for driving each pixel in a display device arranged in a matrix, comprising: a gamma correction unit for gamma-correcting gradation data for the pixel, the gamma correction unit switching between a plurality of gamma curves for each frame; A drive circuit comprising:

[0131] (16) A display device comprising a driving circuit according to any one of (1) to (15).

[0132] (17) A driving method for controlling a display device by controlling a driving circuit according to any one of (1) to (15).

[0133] The aspects of the present disclosure are not limited to the above-described embodiments, but include various conceivable modifications, and the effects of the present disclosure are not limited to the above-described contents. The components in each embodiment may be appropriately combined and applied. In other words, various additions, modifications, and partial deletions are possible within the scope of the conceptual idea and intent of the present disclosure derived from the contents defined in the claims and their equivalents. [Explanation of symbols]

[0134] 1:Display device, 10: display panel, 12: pixel area, 14: pixel, 16: data line, 18: scan line, 20: drive circuit, 22: signal processing circuit, 24: controller, 26: horizontal drive circuit, 28: vertical drive circuit, 220: pre-processing circuit, 221: gamma correction circuit, 222: noise adding circuit, 223: frame memory, 224: write circuit, 225: read circuit, 226: decoder

Claims

1. A drive circuit for driving each pixel in a display device arranged in a matrix, comprising: a noise adding unit that adds one of a plurality of correction values ​​to the gradation data of the pixel when the gradation value of the pixel is a predetermined gradation value; Equipped with the gradation data is a signal encoded in a format that indicates control for maintaining an on state or an off state of the pixel during each of subframe periods that are time-divided in one frame, The pixels are controlled to emit light in accordance with the encoded signals in a time sequence; the noise adding unit sets a base value based on the predetermined gradation value, and adds a correction value having an absolute value within the base value to the gradation data of the pixel; The correction value is a correction value obtained by reversing the sign of the correction value applied to the previous frame for the gradation data of each of the pixels to which the correction value is applied. Drive circuit.

2. A drive circuit for driving each pixel in a display device arranged in a matrix, comprising: a noise adding unit that adds one of a plurality of correction values ​​to the gradation data of the pixel when the gradation value of the pixel is a predetermined gradation value; Equipped with the gradation data is a signal encoded in a format that indicates control for maintaining an on state or an off state of the pixel during each of subframe periods that are time-divided in one frame, The pixels are controlled to emit light in accordance with the encoded signals in a time sequence; the noise adding unit sets a base value based on the predetermined gradation value, and adds a correction value having an absolute value within the base value to the gradation data of the pixel; the noise adding unit adds a periodically varying correction value to the gradation data of each of the pixels to which the correction value has been added; Drive circuit.

3. The encoding format is a PWM (Pulse Width Modulation) format or a PM (Phase Modulation) format.

3. The drive circuit according to claim 1 or 2.

4. The maximum value of the gradation data is n (n is any natural number), and the predetermined gradation value includes at least a gradation value of floor((n-1) / 2).

4. The drive circuit according to claim 3.

5. the predetermined gradation value includes a plurality of gradation values, a correction value is applied to the gradation data of the pixel having a gradation value of floor((n-1) / 2) based on the base value that is larger than the base value of the other pixels having the predetermined gradation value; 5. The drive circuit according to claim 4.

6. the noise adding unit adds a correction value to the gradation data of two adjacent pixels when a period during which the gradation data of the two adjacent pixels in the same frame differ in phase is equal to or longer than a predetermined period; 4. The drive circuit according to claim 3.

7. a gamma correction unit for gamma-correcting the gradation data, the gamma correction unit switching between a plurality of gamma curves for each frame; 3. The drive circuit according to claim 1 or 2, further comprising:

8. the gamma correction unit executes gamma correction based on a gamma curve that corrects gradations of the same value in both positive and negative directions from a reference gamma curve; 8. The drive circuit according to claim 7.

9. the gamma correction unit executes gamma correction based on a gamma curve in which at least a central gradation value is different from the reference gamma curve.

9. The drive circuit according to claim 8.

10. the gamma correction unit performs gamma correction based on a gamma curve having a gradation different from the reference gamma curve at least in a gradation where a period during which the phases of gradation data for two adjacent pixels in the same frame differ is equal to or longer than a predetermined period.

10. The drive circuit of claim 9.

11. the gamma correction unit performs gamma correction based on a gamma curve having a gradation where a difference between the gradation curve and the reference gamma curve is larger than the gradation values ​​before and after the gradation curve at least in a gradation where a period during which the gradation data for each of two adjacent pixels in the same frame differ in phase is equal to or longer than a predetermined period.

10. The drive circuit of claim 9.

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