JP2025010718A - Circuit device and display system - Google Patents

Abstract

To provide a circuit device or the like that can prevent the problem that a value of image data after color correction is required to be large or the like.SOLUTION: A circuit device 10 that controls a display device 100 which includes a plurality of light source elements and a display panel 110, comprises: a light source luminance determination circuit 30 that determines light source luminance information indicating luminance, in which each light source element of the plurality of light source elements emits light, from image data; an illumination luminance calculation circuit 40 that calculates illumination luminance information indicating luminance, in which an object pixel of the display panel 110 is illuminated by the plurality of light source elements, on the basis of the light source luminance information; and a color correction circuit 50 that performs luminance conversion processing, in which a change amount of output luminance for change of input luminance is larger in a low luminance area than a high luminance area, for illumination luminance information, and performs color correction of image data of the object pixel on the basis of luminance conversion processed illumination luminance information.SELECTED DRAWING: Figure 1

Description

The present invention relates to a circuit device and a display system, etc.

Patent document 1 discloses an image display device that performs local dimming. In this document, an image data correction unit corrects input image data based on the luminance distribution calculated by a luminance distribution calculation unit, and generates corrected image data.

JP 2021-9170 A

Color correction, which is the correction of image data in local dimming, can be achieved by, for example, dividing the image data by the luminance of the lighting luminance information. However, it has been found that if the luminance of the lighting luminance information is low, problems such as the image data values becoming excessively high can occur, resulting in a deterioration in display quality.

One aspect of the present disclosure relates to a circuit device for controlling a display device including a plurality of light source elements and a display panel, the circuit device including: a light source luminance determination circuit for determining, from image data, light source luminance information indicating the luminance at which each of the plurality of light source elements emits light; an illumination luminance calculation circuit for calculating illumination luminance information indicating the luminance at which a target pixel of the display panel is illuminated by the plurality of light source elements based on the light source luminance information; and a color correction circuit for performing a luminance conversion process on the illumination luminance information such that the amount of change in output luminance relative to a change in input luminance is greater in low luminance regions than in high luminance regions, and for performing color correction on the image data of the target pixel based on the illumination luminance information after the luminance conversion process.

Another aspect of the present disclosure relates to a display system including the circuit device described above and the display device.

3 shows an example of the configuration of a circuit device and a display system according to the present embodiment. 3 shows a detailed configuration example of the circuit device and the display system according to the present embodiment. An example of the backlight and display panel configuration. FIG. 4 is an explanatory diagram of a light source element and a display area. 11 is a flowchart illustrating an example of a light adjustment process. FIG. An example of lighting brightness data. 1 shows an example of conversion characteristics of luminance conversion processing. 13 is a first calculation example of color correction. 2 shows a second calculation example of color correction. 10 is a flowchart illustrating an example of a lighting luminance calculation process. An example of an ambient light source element. An example of a lookup table. An example of decay rate distribution. 1 shows an example of the configuration of a head-up display, which is an example of a display system.

A preferred embodiment of the present disclosure is described in detail below. Note that the present embodiment described below does not unduly limit the content described in the claims, and not all of the configurations described in the present embodiment are necessarily essential components.

1 shows an example of the configuration of a circuit device 10 according to the present embodiment and a display system 5 including the circuit device 10. The circuit device 10 includes a light source luminance determination circuit 30, an illumination luminance calculation circuit 40, and a color correction circuit 50. The circuit device 10 may also include a light source control circuit 60. The display system 5 includes the circuit device 10 and a display device 100. The display system 5 may also include a processing device 200.

The display device 100 displays an image based on image data. The display device 100 is, for example, a head-up display that displays a virtual image in the user's field of vision, a cluster display that is a display of a meter panel, a center information display, or an in-vehicle display device such as an electronic mirror. Alternatively, the display device 100 may be a head-mounted display device called an HMD, a television device, or a display of an information processing device.

The display device 100 includes a display panel 110 and a backlight 120. The display panel 110 is, for example, an electro-optical panel such as a liquid crystal display panel. The display device 100 may also include a light source driver that drives the light source elements of the backlight 120 and a display driver.

The processing device 200 is, for example, a SoC (System on Chip) and is also called, for example, a master device. The processing device 200 can be realized, for example, by a microcomputer, a CPU, or an MPU. For example, the circuit device 10 is communicatively connected to the processing device 200, and image data IMI from the processing device 200 is input to the circuit device 10.

The circuit device 10 is, for example, an integrated circuit device in which multiple circuit elements are integrated on a semiconductor substrate. The display device 100 displays an image based on image data IMQ output by the circuit device 10. When the display device 100 is a head-up display (HUD), the circuit device 10 is a HUD controller.

The light source luminance determination circuit 30 determines the light source luminance information BRL indicating the luminance emitted by each of the multiple light source elements of the display device 100 from the image data IMI. For example, the image data IMI is input to the light source luminance determination circuit 30 from the processing device 200. The image data IMI input to the light source luminance determination circuit 30 is also called input image data. The light source luminance determination circuit 30 analyzes the luminance of the image data IMI, and based on the results of the analysis, determines the emission luminance of each light-emitting element of the display device 100, and outputs it as light source luminance information BRL indicating the emission luminance of each light-emitting element. The light source luminance information BRL can also be called light source luminance data. Specifically, the light source luminance determination circuit 30 determines the maximum luminance of pixel data belonging to an area corresponding to the light-emitting element of the backlight 120. The light source luminance determination circuit 30 determines the minimum emission luminance within the range that can be displayed on the display device 100 from the maximum luminance, and sets it as the emission luminance of the light-emitting element. Specifically, the light source luminance determination circuit 30 determines the emission luminance of each light source element based on, for example, the image data IMI and attenuation rate distribution information described later. This realizes local dimming control that controls the brightness of the light source device, which is the backlight 120, for each of the multiple areas.

The illumination luminance calculation circuit 40 calculates illumination luminance information BR indicating the luminance at which a target pixel of the display panel 110 is illuminated by a plurality of light source elements based on the light source luminance information BRL. The illumination luminance information BR indicates the illumination luminance at each pixel of the display panel 110 when the display panel 110 is illuminated by the backlight 120. The illumination luminance information BR can also be referred to as illumination luminance data.

The color correction circuit 50 performs color correction on the image data IMI based on the illumination luminance information BR, and outputs the corrected image data IMQ to the display device 100. Specifically, the color correction circuit 50 multiplies the pixel data of each pixel by the inverse of the luminance of the light reaching that pixel, and the result becomes the new pixel data for that pixel. The pixel data is color data. Color correction is, for example, a color adjustment process for the image data IMI, and is a correction process that adjusts the color level. Color correction can also be called a luminance correction or gradation correction for the image data IMI.

The light source control circuit 60 controls a light source driver (not shown) of the display device 100 based on the light source luminance information BRL. Details of the light source control circuit 60 will be described later.

The light source luminance determination circuit 30, the illumination luminance calculation circuit 40, the color correction circuit 50, and the light source control circuit 60 are logic circuits that process digital signals. Each of the light source luminance determination circuit 30, the illumination luminance calculation circuit 40, the color correction circuit 50, and the light source control circuit 60 may be configured as a separate logic circuit, or a part or all of them may be configured as an integrated logic circuit. Alternatively, a processor such as a DSP may execute an instruction set or program in which the functions of the light source luminance determination circuit 30, the illumination luminance calculation circuit 40, the color correction circuit 50, and the light source control circuit 60 are described, thereby realizing the functions of these circuits. Alternatively, the circuit device 10 may be a processor such as a CPU, a GPU, a microcomputer, a DSP, an ASIC, or an FPGA. The processor may execute an instruction set or program in which the functions of each part of the circuit device 10 are described, thereby realizing the functions of the circuit device 10.

The circuit device 10 may also include a distortion correction circuit. The distortion correction circuit corrects image distortion caused by an optical system that projects an image displayed on the display panel 110 onto a screen or the like, or image distortion caused by screen distortion. Specifically, the distortion correction circuit performs image correction on the image data input from the processing device 200 to cancel or reduce the image distortion, and outputs the corrected image data to the light source luminance determination circuit 30, the illumination luminance calculation circuit 40, and the color correction circuit 50. Distortion correction is an image correction that applies image distortion to an image that is the opposite of the image distortion when the image displayed on the display panel 110 is projected, and is an image correction for displaying an image with no or reduced distortion. For example, the distortion correction circuit performs distortion correction on the input image data using coordinate conversion between pixel coordinates in the input image data and pixel coordinates in the output image data, and outputs the result as output image data. Note that the distortion correction circuit may be provided in the processing device 200 instead of the circuit device 10.

Figure 2 shows a detailed configuration example of the circuit device 10 and display system 5 of this embodiment. In Figure 2, the circuit device 10 includes an interface circuit 20 and a memory unit 70 in addition to the configuration of Figure 1. The circuit device 10 may also be provided with the distortion correction circuit described above. In this case, the distortion correction circuit performs distortion correction on the image data IMI input from the processing device 200 via the interface circuit 20, and the image data IMI after distortion correction is input to the light source luminance determination circuit 30, the illumination luminance calculation circuit 40, and the color correction circuit 50.

The interface circuit 20 is a circuit that performs interface processing with the processing device 200, and is, for example, a host interface circuit. The interface circuit 20 may be an interface circuit for various image interface methods such as LVDS (Low Voltage Differential Signaling), a parallel RGB method, or a display port.

The light source luminance determination circuit 30 includes a luminance analysis unit 32 and a light source luminance calculation unit 34. The luminance analysis unit 32 performs luminance analysis of the image data IMI. The light source luminance calculation unit 34 calculates the light source luminance information BRL of each light source element based on the result of the luminance analysis in the luminance analysis unit 32. The light source luminance information BRL corresponds to the dimming amount of the light source. Specifically, the luminance analysis unit 32 of the light source luminance determination circuit 30 searches for a pixel having a maximum luminance in each of the multiple areas of the display area based on the image data IMI. Then, the light source luminance calculation unit 34 of the light source luminance determination circuit 30 calculates the light source luminance information BRL by determining the luminance distribution of the multiple light source elements so that the searched color of the maximum luminance can be displayed. Then, the illumination luminance calculation circuit 40 performs a calculation process to recalculate the illumination luminance for each pixel based on the determined light source luminance information BRL and the attenuation rate distribution information of the light source element, and calculates the illumination luminance information BR indicating the luminance at which the pixel is illuminated by the light source element.

The illumination luminance calculation circuit 40 includes a luminance conversion unit 42. As will be described later with reference to FIG. 8 and other figures, the luminance conversion unit 42 performs a luminance conversion process on the illumination luminance information BR in such a way that the amount of change in output luminance relative to a change in input luminance is greater in low luminance regions than in high luminance regions.

The color correction circuit 50 performs color correction on the image data IMI of the target image based on the illumination luminance information BR from the illumination luminance calculation circuit 40. For example, the color correction circuit 50 performs color correction on the image data IMI according to the dimming amount in the dimming control by the light source luminance determination circuit 30 and the illumination luminance calculation circuit 40. Dimming control is a control that adjusts the light amount of a light source device such as the backlight 120. Dimming control includes local dimming dimming control that controls the brightness of the light source device for each of multiple areas, and dimming control that globally controls the brightness of the entire display screen. In this embodiment, the color correction circuit 50 performs color correction on the image data IMI based on the illumination luminance information BR that has been subjected to luminance conversion processing by the luminance conversion unit 42 of the illumination luminance calculation circuit 40.

The light source control circuit 60 controls the light source driver 130 of the display device 100 based on the light source luminance information BRL. Specifically, the light source control circuit 60 outputs a timing control signal to the light source driver 130 that controls the emission timing of the light source elements or the timing of updating the emission luminance, and outputs data corresponding to the light source luminance information BRL to the light source driver 130. The light source driver 130 drives each light-emitting element with a PWM signal having a pulse width corresponding to the emission luminance of each light source element indicated by the light source luminance information BRL, at the timing specified by the timing control signal. This causes each light-emitting element to emit light at an emission luminance controlled by local dimming.

A processing device such as an MCU may be provided between the light source control circuit 60 and the light source driver 130 to absorb differences in communication protocols that depend on the model of the light source driver 130. In this case, the light source driver 130 is controlled by the light source control circuit 60 via the processing device such as an MCU. The light source driver 130 may also be realized by multiple light source driver ICs. In this case, each of the multiple light source driver ICs drives each light source element group of the multiple light source elements.

The storage unit 70 stores attenuation rate distribution information and information for luminance conversion processing. Specifically, the storage unit 70 stores a lookup table LUTA for attenuation rate distribution and a lookup table LUTB for luminance conversion processing. The lookup table LUTA for attenuation rate distribution is a lookup table showing the attenuation rate distribution of light reaching the display panel from the light source element. The attenuation rate distribution shows the relationship between the distance from the light source element to the pixel and the attenuation rate of light with which the light source element illuminates the pixel. The attenuation rate distribution is also called attenuation characteristics or luminance distribution. The lookup table LUTB for luminance conversion processing is a lookup table for performing the luminance conversion processing of FIG. 8 described later. As an example, the luminance conversion processing is gamma correction, and the lookup table LUTB for luminance conversion processing is a lookup table for gamma correction.

Here, the storage unit 70 is a register or a memory. The memory is a volatile memory such as RAM, or a non-volatile memory such as OTP memory or EEPROM. RAM is an abbreviation for Random Access Memory. OTP is an abbreviation for One Time Programmable. EEPROM is an abbreviation for Electrically Erasable Programmable Read Only Memory.

In this way, the storage unit 70 stores attenuation rate distribution information that indicates the attenuation rate distribution of light with respect to the distance between each light source element and each pixel when each light source element illuminates each pixel. For example, the storage unit 70 stores a lookup table LUTA for attenuation rate distribution as attenuation rate distribution information. The illumination luminance calculation circuit 40 calculates the illumination luminance information BR based on the distance information between the target pixel and each light source element and the attenuation rate distribution information. For example, the illumination luminance information BR is calculated based on the distance information and the lookup table LUTA for attenuation rate distribution. The storage unit 70 also stores a lookup table LUTB for luminance conversion processing. The illumination luminance calculation circuit 40 performs luminance conversion processing on the illumination luminance information BR by referring to the lookup table LUTB for luminance conversion processing. For example, the lookup table LUTB is used to perform luminance conversion processing such as gamma correction as shown in FIG. 8 described later.

The display device 100 includes a display panel 110, a backlight 120, and a light source driver 130. For example, the backlight 120 is provided with a plurality of light source elements LS. The light source elements LS are the light source of the display device 100. Specifically, the backlight 120 has a plurality of light source elements LS realized by LEDs or the like arranged in an array. The light source driver 130 drives the plurality of light source elements LS to emit light. The display device 100 may also include a display controller (not shown) and a display driver (not shown) that drives the display panel 110. The display driver may include a data driver that drives the data lines of the display panel 110, a scan driver that drives the scan lines of the display panel 110, and the like.

Figure 3 shows an example of the configuration of the backlight 120 and the display panel 110. In Figure 3, direction D1 is the horizontal scanning direction of the display panel 110, and direction D2 is the vertical scanning direction of the display panel 110. Direction D3 is a direction perpendicular to directions D1 and D2, and is the direction in which the display panel 110 is viewed in a plan view. The backlight 120 is provided on the direction D3 side of the display panel 110, and emits illumination light in the opposite direction to direction D3, which is the direction toward the display panel 110.

The backlight 120 includes a plurality of light source elements LS. FIG. 3 illustrates an example in which 8×5 light source elements LS are arranged in a two-dimensional array. That is, eight light source elements LS are arranged along the direction D1, and five light source elements LS are arranged along the direction D2. For proper local dimming, it is desirable to provide, for example, 100 or more light source elements LS in the backlight 120. The light source elements LS are, for example, LEDs (Light Emitting Diodes). The light source elements LS are not limited to LEDs, and may be light source elements whose light amount is independently controlled and which are close to a point light source. A light source element close to a point light source is a light source element whose light-emitting portion is sufficiently smaller than the area AR corresponding to the light source element LS. The two-dimensional arrangement of the light source elements LS in FIG. 3 is a square arrangement in which light source elements are arranged at all intersections of multiple rows and multiple columns. However, the two-dimensional arrangement is not limited to a square arrangement. For example, the two-dimensional arrangement may be an arrangement called a rhombus arrangement or a staggered arrangement. In this arrangement, light source elements are placed at the intersections of one of the odd and even rows with the odd columns, and at the intersections of the other of the odd and even rows with the even columns, and no light source elements are placed at any other intersections.

The display panel 110 has a pixel array, and the area in the pixel array where the display image is displayed is the display area. The display area is divided into a number of areas AR. Each area AR is correspondingly arranged with a corresponding light source element LS. That is, one area AR corresponds to one light source element LS. For example, when the display panel 110 is viewed in a plan view, the light source element LS is arranged at the center of the area AR. However, the arrangement position of the light source element LS is not limited to this. In FIG. 3, the display area is divided into 8×5 areas AR corresponding to the 8×5 light source elements LS. Note that the areas AR are used for processing in the circuit device 10, and there is no boundary between the areas AR in the display image actually displayed on the display panel 110. The display panel 110 is a panel in which the transmittance of each pixel is controlled according to the display image, and each pixel transmits the illumination light of the backlight 120 to display the display image. The display panel 110 is, for example, a liquid crystal display panel.

In this way, when the display area of the display panel 110 is divided into a plurality of areas such that each light source element LS is disposed in each area AR, the light source element LS that illuminates the display panel 110 has a light intensity distribution in which the light intensity decreases the further away from the light source element LS. For this reason, the light intensity is smaller in the periphery of the area AR than in the center. This light intensity distribution of the light source element LS is called a PSF. Figure 4 shows an example of the light intensity distribution of the PSF. In Figure 4, the light intensity distribution is shown in a gradation, with the whiter the color, the larger the coefficient of the light intensity distribution. In Figure 4, the size of the PSF corresponds to 3 x 3 areas AR1 to AR9, and the center of the PSF is disposed at the position of the light source element. This light intensity distribution of the PSF corresponds to the attenuation rate distribution information.

The backlight 120 can be configured in a variety of ways, such as a direct type or an edge type. A dual LCD that uses a liquid crystal panel to perform dimming control such as local dimming may also be used. The light source element LS may be configured with a light-emitting device such as a laser diode or a halogen bulb.

Next, a specific example of the dimming process of this embodiment will be described. FIG. 5 is a flowchart for explaining an example of the process of calculating the brightness for each pixel. First, for each area of each light source element, a pixel with the maximum brightness is searched for (step S1). For example, in each area corresponding to each light source element described in FIG. 3 and FIG. 4, the brightness of the pixels existing in that area is searched for based on the image data IMI, and a pixel with the maximum brightness in that area is found. Then, the light source brightness information BRL of each light source element is determined so that the color of the pixel with the maximum brightness can be displayed (step S2). For example, assume that the brightness range is 0 to 100, and the brightness of the pixel with the maximum brightness in the target area is 50. In this case, the brightness distribution of the light source element is determined so that the pixel with the maximum brightness of 50 can be displayed in the color of the brightness of 100, which is the upper limit of the brightness range. If the brightness of the pixel with the maximum brightness is the upper limit of the brightness range, the brightness of the other pixels is guaranteed to be within the brightness range of 0 to 100. Then, for each pixel of the display panel 110, the illumination luminance information BR of each pixel illuminated by the light source element is calculated based on the light source luminance information BRL and the attenuation rate distribution information (step S3). The attenuation rate distribution information corresponds to, for example, the light intensity distribution PSF in FIG. 4.

For example, as shown in FIG. 15 described later, the display device 100 is provided with a diffusion plate 115 between the backlight 120 and the display panel 110 to diffuse the light from the light source element to achieve a uniform brightness distribution. For example, as shown in FIG. 4, the light intensity distribution PSF of the light source element is an intensity distribution in which the light intensity decreases the farther away from the light source element, but by providing a diffusion plate 115 to diffuse the light from the light source element, it is possible to reduce brightness unevenness and realize a uniform surface light source. Here, light diffusion methods include a direct type, a side light type, and an edge light type.

In this embodiment, the light source luminance determination circuit 30 performs a luminance analysis of the image data IMI to obtain the luminance distribution of the image data IMI, and calculates the light source luminance information BRL by obtaining the light source luminance distribution, which is the luminance distribution of multiple light source elements, from this luminance distribution. In this case, the light source luminance distribution may be obtained by performing downsampling to reduce the number of pixels in the luminance distribution of the image data IMI to, for example, the number of light source elements, and the light source luminance information BRL may be calculated. Alternatively, the calculation of the light source luminance information BRL may be realized by the following process.

For example, in this process, the light source luminance determination circuit 30 determines the luminance of each light source element by updating the emission luminance of each light source element based on the luminance value of each pixel of the image. In one update, the luminance value of one pixel is used. This pixel is referred to as the target pixel. The contents of one update are explained below. By repeating this update pixel by pixel, the emission luminance of all light source elements is determined.

First, the light source luminance determination circuit 30 selects n x m light source elements around the target pixel. The light source luminance determination circuit 30 then uses the emission luminance of the surrounding n x m light source elements before the update and the attenuation rate distribution information to calculate the illumination luminance, which is the luminance of light that reaches the target pixel from the surrounding n x m light source elements. Next, the light source luminance determination circuit 30 finds the difference between the luminance value of the target pixel and the illumination luminance. If the difference is positive, the light source luminance determination circuit 30 uses the difference and the attenuation rate distribution information to increase the emission luminance of each light source element of the surrounding n x m light source elements. This updates the emission luminance of the surrounding n x m light source elements. The target pixel is then shifted by one pixel horizontally, and the same update is repeated.

Figure 6 is an explanatory diagram of an example of color correction processing. First, the illumination luminance calculation circuit 40 calculates illumination luminance information BR, which is the luminance at which the target pixel is illuminated by the light source element. Then, the reciprocal IVB of the luminance of the illumination luminance information BR is calculated. The process of calculating this reciprocal IVB may be realized using a lookup table that outputs the reciprocal IVB for the luminance of the illumination luminance information BR. This lookup table outputs a reciprocal IVB that increases as the luminance of the illumination luminance information BR decreases. Note that the reciprocal IVB may be calculated from the illumination luminance information BR based on a predetermined formula without using such a lookup table. In the following, the luminance of the illumination luminance information BR may be simply referred to as illumination luminance, as appropriate.

The color correction circuit 50 multiplies the reciprocal IVB obtained in this way by the color data, which is the pixel data of the target pixel, to obtain color data after color correction. The color data is, for example, RGB data and is an RGB value. In this way, the color correction circuit 50 can obtain image data IMQ after color correction from the image data IMI and output it to the display device 100. The image data is color data. In the color correction of FIG. 6, the lower the illumination luminance (BR), the larger the reciprocal IVB, so that the lower the illumination luminance of the light source element, the larger the color data value (color level) of the target pixel is. Note that in FIG. 6, color correction is achieved by multiplying the image data IMI by the reciprocal IVB of the illumination luminance, but color correction may also be achieved by dividing the image data IMI by the illumination luminance.

6, in this embodiment, color correction is realized by multiplying the image data by the inverse (IVB) of the illumination luminance (BR) or by dividing the image data by the illumination luminance. However, it has been found that when the illumination luminance is low, for example, the image data value after color correction becomes excessively high, causing problems such as deterioration of display quality.

As shown in FIG. 7, suppose that data such as lighting luminance is, for example, 4.4 fixed-point data represented by a 4-bit integer part and a 4-bit decimal part. In FIG. 7, bit 0 indicates 1/16 = 0.0625, so the decimal part can express values in the range of 0.625 to 0.9375 in steps of 0.0625, and overall, values in the range of 7.9375 to 0 can be expressed. Suppose that the lighting luminance value at a certain point is 0.0625. 0.0625 is expressed in 8 bits as 0x00000001. In this case, in the color correction of FIG. 6, the color data is multiplied by 16, which is the reciprocal of 0.0625, or the color data is divided by 0.0625, so the input color data value is multiplied by 16, which causes the following problem.

For example, if the inverse of the lighting luminance close to 0 is multiplied by the color data, or if the color data is divided by the lighting luminance close to 0, the value of the color data after color correction will become extremely large. This will cause problems such as the value of the color data after color correction exceeding the upper limit of the data range. In addition, if the lighting luminance value is extremely low, for example, in the case of the lighting luminance value of 0.0625 as described above, the color data after color correction will only be able to take discrete values for every 16 gradations. In other words, the color data after color correction will have an accuracy of 16 gradations. This problem is more likely to occur the more accurate the value representing the lighting luminance is. In Figure 7, the decimal point has 4 bits of accuracy, but if the decimal point has 8 bits of accuracy, when the lighting luminance takes the minimum value, the value of the color data after color correction will be multiplied by 256.

In this embodiment, therefore, when performing color correction calculations in which color data is multiplied by the inverse of the lighting luminance or color data is divided by the lighting luminance, a luminance conversion process is performed to correct, for example, small lighting luminance values to large values. This makes it possible to solve problems such as color data values becoming extremely large after color correction or the gradation accuracy of color data decreasing after color correction. Instead, the color data will end up being slightly smaller than the expected color data, but because this is originally an area with a low lighting luminance value and an output color close to black, it can be considered that there is almost no problem in appearance.

As described above, the circuit device 10 of this embodiment, which controls the display device 100 including a plurality of light source elements and a display panel 110, includes a light source luminance determination circuit 30, an illumination luminance calculation circuit 40, and a color correction circuit 50. The light source luminance determination circuit 30 determines light source luminance information BRL indicating the luminance emitted by each of the plurality of light source elements from the image data IMI. The illumination luminance calculation circuit 40 calculates illumination luminance information BR indicating the luminance at which the target pixel of the display panel 110 is illuminated by the plurality of light source elements based on the light source luminance information BRL. Then, the color correction circuit 50 performs a luminance conversion process on the illumination luminance information BR from the illumination luminance calculation circuit 40, and performs color correction of the image data IMI of the target pixel based on the illumination luminance information after the luminance conversion process. Specifically, the color correction circuit 50 performs a luminance conversion process in which the amount of change in output luminance relative to a change in input luminance is greater in the low luminance region than in the high luminance region. Then, color correction, which is a correction to the data of each color channel of RGB of the image data IMI, is performed based on the illumination luminance information after the luminance conversion process.

Figure 8 shows an example of the conversion characteristics of the luminance conversion process of this embodiment. As shown in Figure 8, in the luminance conversion process of this embodiment, the amount of change in output luminance relative to a change in input luminance in the low luminance region RBL is larger than the amount of change in output luminance relative to a change in input luminance in the high luminance region RBH. For example, the amount of change in output luminance relative to a change in input luminance is larger as the luminance decreases. In this way, in this embodiment, the amount of change in output luminance relative to a change in input luminance is larger in the low luminance region RBL than in the high luminance region RBH, so that luminance conversion can be realized in which the output luminance is larger relative to the input luminance in the low luminance region RBL. This makes it possible to prevent problems such as the value of the color data after color correction becoming extremely large or the accuracy of the gradation of the color data after color correction decreasing. Therefore, it is possible to suppress the deterioration of the display quality of the image data after color correction due to color correction.

For example, the luminance conversion process of this embodiment may be gamma correction. Specifically, the luminance conversion process may be gamma correction with a gamma value smaller than 1. For example, when the input luminance is BI, the output luminance is BQ, the gamma value is γ, and the constant is A, the gamma correction can be expressed as BQ=A× ^BIγ . Here, for example, A=1. The luminance change process of this embodiment is a gamma correction with a gamma value of γ<1. As an example, a gamma correction with γ=1/2.2 can be adopted. However, the value of the gamma value γ is not limited to this, and can take various values. In this way, by effectively utilizing the gamma correction, a luminance conversion process in which the change in output luminance with respect to a change in input luminance is larger in a low luminance region than in a high luminance region can be realized, and problems such as the value of color data after color correction becoming extremely large can be solved.

The luminance conversion process of this embodiment is not limited to luminance conversion using gamma correction, and various luminance conversion processes can be used in which the amount of change in output luminance relative to a change in input luminance is greater in low luminance areas than in high luminance areas. The gamma correction is also not limited to the normal gamma correction described in the above formula, and may be a correction process that is a slight modification of the above formula. For example, a conversion process such as that used in sRGB may be applied to the luminance conversion process of this embodiment. For example, gamma correction in which the gamma value γ is different for each RGB color channel may be used.

In this embodiment, the color correction circuit 50 performs color correction by obtaining the inverse of the illumination luminance information that has been subjected to the luminance conversion process, and performing a multiplication process of the inverse and the image data of the target pixel. For example, as shown in FIG. 9, the color correction circuit 50 performs a luminance conversion process as shown in FIG. 8 on the illumination luminance information BR to obtain the illumination luminance information BRQ that has been subjected to the luminance conversion process, and obtains the inverse IVB of the illumination luminance information BRQ. Then, the color correction circuit 50 performs color correction by multiplying the obtained inverse IVB by the image data IMI. In this way, color correction can be realized without providing a division circuit that performs division process by the illumination luminance information BRQ that has been subjected to the luminance conversion process, and it is possible to reduce the circuit scale, etc. For example, the process of obtaining the inverse IVB from the illumination luminance information BRQ that has been subjected to the luminance conversion process can be realized by using a lookup table in which the luminance of the illumination luminance information BRQ is used as an input value and the inverse IVB is used as an output value. The input value of the lookup table is an index of the lookup table. Alternatively, a modified implementation is possible in which the reciprocal IVB is calculated from the illumination luminance information BR using a lookup table. This lookup table is stored in the storage unit 70 in FIG. 2. By using such a lookup table, it is possible to achieve color correction while suppressing an increase in circuit size.

In addition, in this embodiment, the color correction circuit 50 may perform color correction by dividing the image data of the target pixel by the illumination luminance information that has been subjected to the luminance conversion process. For example, as shown in FIG. 10, the color correction circuit 50 performs the luminance conversion process shown in FIG. 8 on the illumination luminance information BR to obtain illumination luminance information BRQ that has been subjected to the luminance conversion process. The color correction circuit 50 then performs color correction by multiplying the image data IMI by the illumination luminance information BRQ that has been subjected to the luminance conversion process. In this way, if the circuit device 10 has a division circuit that performs division processing, this division circuit can be effectively used to realize color correction.

As shown in FIG. 2, the circuit device 10 of this embodiment may also include a storage unit 70 that stores a lookup table LUTB for luminance conversion processing. The illumination luminance calculation circuit 40 performs luminance conversion processing on the illumination luminance information BR by referring to the lookup table LUTB for luminance conversion processing. The lookup table LUTB for luminance conversion processing is a lookup table in which the input luminance of FIG. 8 is the input value and the output luminance is the output value. The illumination luminance calculation circuit 40 calculates illumination luminance information based on the light source luminance information and attenuation rate distribution information from the light source luminance determination circuit 30, and inputs the luminance of this illumination luminance information as an input value of the lookup table LUTB for luminance conversion processing. The output value of the lookup table LUTB is output to the color correction circuit 50 as illumination luminance information BRQ that has been subjected to luminance conversion processing. In this way, it is possible to realize a luminance conversion processing in which the change in output luminance relative to a change in input luminance is greater in the low luminance area than in the high luminance area by using the lookup table LUTB for luminance conversion processing. For example, by storing a lookup table LUTB of desired luminance conversion characteristics in the memory unit 70, it becomes possible to realize luminance conversion processing with the desired luminance conversion characteristics.

3. Illumination Luminance Calculation Circuit Next, a detailed example of the process performed by the illumination luminance calculation circuit 40 will be described. For example, FIG.

First, in step S11, the illumination brightness calculation circuit 40 selects one pixel from the pixels contained in the image data IMI. The selected pixel is referred to as the target pixel. In the loop from step S11 to step S14, the target pixels are selected sequentially. For example, the first pixel of the first scan line of the image data IMI is selected in the first step S11, and the second pixel, third pixel, ... are selected sequentially in subsequent steps S11. When all the pixels of the first scan line have been selected, the pixels of the second scan line are selected sequentially, and this is repeated up to the final scan line.

In step S12, the illumination brightness calculation circuit 40 selects s×t light source elements around the target pixel. These s×t light source elements are also called surrounding light source elements. FIG. 12 shows an example of surrounding light source elements. Here, an example of s=4 and t=4 is shown, but s and t may each be an integer of 2 or more. In FIG. 12, the x direction is the horizontal scanning direction of the display panel 110, and the y direction is the vertical scanning direction of the display panel 110.

The position of the target pixel 22 is (i, j). i and j are integers, and the position (i, j) indicates the i-th pixel of the j-th scan line. The illumination brightness calculation circuit 40 selects light source elements L1 to L16 in the two nearest columns in each of the +x and -x directions and the two nearest rows in each of the +y and -y directions based on the position (i, j). When β is an integer between 1 and 16, the position of light source element Lβ is expressed as (xβ, yβ).

In step S13, the illumination luminance calculation circuit 40 uses the light source luminance information of the selected s × t light source elements and the lookup table LUTA for illumination luminance calculation to obtain illumination luminance information of the target pixel. The lookup table LUTA for illumination luminance calculation is a lookup table of attenuation rate distribution information.

In step S14, the illumination luminance calculation circuit 40 determines whether all pixels have been selected as target pixels, and if all pixels have been selected, ends the process, and if there are any pixels that have not been selected, returns to step S11.

The illumination luminance information calculation process in step S13 will be described using the example of FIG. 12. The illumination luminance calculation circuit 40 calculates the illumination luminance information of the target pixel 22 using the following equations (1) and (2).

In the above formula (1), PL(i,j) is the illumination luminance information for the pixel at position (i,j). pow(β) is the light source luminance information determined by the light source luminance determination circuit 30. lsf(β) is the attenuation rate of the light with which the light source element Lβ illuminates the target pixel 22. The illumination luminance calculation circuit 40 determines lsf(β) using the lookup table LUTA. In the above formula (2), the square of the distance is used as the input to the lookup table, but the distance may also be used as the input to the lookup table.

The illumination luminance calculation circuit 40 may obtain the illumination luminance information of the target pixel not only from the light source luminance information of the s × t light source elements surrounding the target pixel, but also from the light source luminance information of all the light source elements of the backlight 120.

Below, a detailed example of the lookup table LUTA is described. The lookup table LUTA outputs attenuation rate information associated with input distance information. Below, an example is shown in which the distance information is a distance or the square of the distance, and the attenuation rate information is an attenuation rate expressed as a percentage, but this is not limiting. The distance information may be the number of pixels, etc. The attenuation rate information may be an attenuation rate expressed in any unit.

Figure 13 shows a detailed example of a lookup table. Figure 14 shows an example of the attenuation rate distribution in a detailed example of a lookup table.

Light from the light source element is diffused by a diffusion sheet or the like, and the diffused light is irradiated onto the display panel 110. At this time, the luminance distribution of the light due to diffusion is the attenuation rate distribution. Specifically, the attenuation rate distribution according to the characteristics of the light source element and the diffusion sheet, or an attenuation rate distribution that approximates it, is tabulated and stored in the memory unit 70 as the lookup table LUTA. The processing device 200 in Figures 1 and 2 may write the lookup table LUTA to the memory unit 70, or, if the memory unit 70 includes a non-volatile memory, the lookup table LUTA may be stored in the non-volatile memory in advance. The lookup table LUTA is freely programmable and may be changed, for example, according to the model of the display device 100.

As shown in FIG. 13, the lookup table LUTA includes a first lookup table LUT1 in which distances are stored, and a second lookup table LUT2 in which attenuation rates are stored.

Each index in the first lookup table LUT1 stores a distance associated with that index. Here, an example is shown in which the indexes are 0 to 15, but the number of indexes is arbitrary. Also, an example is shown in which the distances range from 0 to 20, and the distance resolution is set independently for each of the three distance ranges, but the distance ranges are arbitrary, and the number of distance ranges may be two or more. As an example, the index is a memory address.

Each index in the second lookup table LUT2 stores an attenuation rate associated with that index. The attenuation rate is expressed as a normalized value with the maximum brightness being 100%. The attenuation rate distribution is maximum near zero distance, and decreases as the distance increases. The slope of the decrease changes according to the distance. However, in an attenuation rate distribution that takes into account reflected light, etc., a mixture of decreasing and increasing sections may be present.

For example, when the distance input to the lookup table LUTA is 2, the illumination brightness calculation circuit 40 sequentially reads out the distances of each index from the first lookup table LUT1 and compares them with the input distance = 2 to determine the indexes "1" and "2" corresponding to the distances = 1.5 and distance = 3 on either side of the input distance = 2. The selected index "1" is the first index, and the selected index "2" is the second index. The first index is the distance stored in the first lookup table LUT1 that is less than or equal to the input distance and is closest to the input distance. The second index is the distance stored in the first lookup table LUT1 that is greater than or equal to the input distance and is closest to the input distance. The illumination brightness calculation circuit 40 reads out the attenuation rates of 97.2% and 89.4% for the indexes "1" and "2" from the second lookup table LUT2. The attenuation rate of 97.2% stored in the first index "1" is set as the first attenuation rate information, and the attenuation rate of 89.4% stored in the second index "2" is set as the second attenuation rate information. The illumination luminance calculation circuit 40 interpolates the first attenuation rate information and the second attenuation rate information to obtain the attenuation rate corresponding to the input distance = 2. Examples of the interpolation include linear interpolation, spline interpolation, or Lagrange interpolation.

As shown in FIG. 14, the slope of the attenuation rate distribution in the distance range DRA where the distance is 0 to 3 is smaller than the slope of the attenuation rate distribution in the distance range DRB where the distance is 3 to 12. Also, the slope of the attenuation rate distribution in the distance range DRC where the distance is 12 to 20 is smaller than the slope of the attenuation rate distribution in the distance range DRB where the distance is 3 to 12. The "slope" is the absolute value of the slope, that is, the absolute value of the differential value obtained by differentiating the attenuation rate distribution with respect to the distance. "Small slope" means, for example, that the average value of the slope in the distance range is small, or the maximum value of the slope in the distance range is small.

As shown in Figs. 13 and 14, the lookup table LUTA is created with a distance resolution according to the above-mentioned gradient in each distance range. The distance resolution is the distance interval when the attenuation rate distribution is tabulated, and is the distance interval for one step of the index. "High distance resolution" means that the distance interval for one step of the index is small. The distance resolution Δd is 1.5 in the distance range DRA, 1 in the distance range DRB, and 2 in the distance range DRC. That is, the distance resolution Δd is high in the distance range DRB where the gradient of the attenuation rate distribution is relatively large, and the distance resolution Δd is low in the distance ranges DRA and DRC where the gradient of the attenuation rate distribution is relatively small. Although Fig. 13 shows an example where the distance resolution Δd in the distance range DRC is lower than the distance resolution Δd in the distance range DRA, the distance resolution Δd in the distance range DRC may be equal to or greater than the distance resolution Δd in the distance range DRA.

By increasing the distance resolution Δd in a distance range where the slope of the attenuation rate distribution is relatively large, the accuracy of the illumination brightness information can be improved. And by decreasing the distance resolution Δd in a distance range where the slope of the attenuation rate distribution is relatively small, it is possible to conserve the storage capacity of the lookup table LUTA.

As described above, in this embodiment, the storage unit 70 in FIG. 2 stores the attenuation rate distribution information. The attenuation rate distribution information indicates the attenuation rate distribution of light with respect to the distance between each light source element and each pixel when each light source element of the display device 100 illuminates each pixel, and corresponds to the light intensity distribution in FIG. 4, for example. In FIG. 2, the attenuation rate distribution information is stored in the storage unit 70 as a lookup table LUTA. The illumination luminance calculation circuit 40 calculates the illumination luminance information based on the distance information between the target pixel and each light source element and the attenuation rate distribution information. For example, the illumination luminance calculation circuit 40 calculates the illumination luminance information by processing as shown in the above formulas (1) and (2). Specifically, the illumination luminance calculation circuit 40 calculates the illumination luminance information by referring to the lookup table LUTA of the attenuation rate distribution information. For example, as described in FIG. 13 and FIG. 14, the calculation processing of the illumination luminance information is realized by referring to the first lookup table LUT1 and the second lookup table LUT2, which are the lookup tables LUTA. In this way, the attenuation rate distribution information of the light source elements is stored in the storage unit 70, and the illumination luminance information can be calculated based on this attenuation rate distribution information and the distance information between the target pixel and each light source element. This makes it possible to realize calculation processing of illumination luminance information that reflects the attenuation rate distribution information of the light source elements.

4. Display System FIG. 15 shows a configuration example of a head-up display 190 as an example of the display system 5 of this embodiment. The head-up display 190, which is the display system 5 of this embodiment, includes the circuit device 10 and the display device 100 of this embodiment. The display system 5 may include a processing device 200. The display device 100 displays a display image based on data of an output image from the circuit device 10. In the case of the display system 5 of the head-up display 190, the display device 100 projects a display image to display a virtual image to a user. For example, the display device 100 includes a display panel 110 and a backlight 120. The display device 100 may also include a display driver 140 that drives the display panel 110 and a diffusion plate 115 provided between the display panel 110 and the backlight 120. The display device 100 may also include a projection optical system such as a mirror 150 that reflects the projection light of the projection image.

The display driver 140 drives the data lines and scanning lines of the display panel 110 based on the output image data from the circuit device 10 to display an image. The light emitted by the backlight 120 passes through the diffusion plate 115 and the display panel 110, and is reflected by the mirror 150 towards the transparent screen 160. The transparent screen 160 is, for example, the windshield of an automobile. The reflective surface of the transparent screen 160 is, for example, concave, and the projected image appears as a virtual image when viewed by the user. In other words, when viewed by the user, the projected image appears to be formed farther away than the transparent screen 160. This makes it possible to display the projected image within a background.

The display system 5 of this embodiment is not limited to the configuration shown in FIG. 15, and various modifications are possible. For example, a display panel other than a liquid crystal display panel may be used as the display panel 110, and the arrangement of the diffuser 115 and the projection optical system may also be modified in various ways. The display system 5 of this embodiment is not limited to the head-up display 190 shown in FIG. 15, and may be other display systems for automobiles, such as a cluster display, or may be a display system other than for automobiles. For example, the display system 5 of this embodiment may be a head-mounted display device.

As described above, the circuit device of this embodiment that controls a display device including a plurality of light source elements and a display panel includes a light source luminance determination circuit that determines, from image data, light source luminance information indicating the luminance at which each of the plurality of light source elements emits light, and an illumination luminance calculation circuit that calculates illumination luminance information indicating the luminance at which a target pixel of the display panel is illuminated by the plurality of light source elements based on the light source luminance information. The circuit device also includes a color correction circuit that performs a luminance conversion process on the illumination luminance information in which the amount of change in output luminance relative to a change in input luminance is greater in low luminance areas than in high luminance areas, and performs color correction on the image data of the target pixel based on the illumination luminance information that has been subjected to the luminance conversion process.

According to this embodiment, a luminance conversion process is performed in which the amount of change in output luminance relative to a change in input luminance is greater in low luminance regions than in high luminance regions, making it possible to realize a luminance conversion process in which the output luminance is greater relative to the input luminance in low luminance regions. Then, color correction of the image data is performed based on the lighting luminance information that has been subjected to this luminance conversion process. In this way, it is possible to prevent problems such as the image data values after color correction becoming extremely large, and it is possible to suppress deterioration of display quality, etc.

In this embodiment, the brightness conversion process may be gamma correction with a gamma value less than 1.

In this way, gamma correction can be effectively used to achieve brightness conversion processing in which the amount of change in output brightness in response to a change in input brightness is greater in low-brightness areas than in high-brightness areas.

In addition, in this embodiment, the color correction circuit may perform color correction by calculating the inverse of the illumination luminance information that has been subjected to the luminance conversion process, and multiplying the inverse by the image data of the target pixel.

In this way, color correction can be achieved without providing a division circuit that performs division processing using the illumination luminance information that has been subjected to luminance conversion processing.

In this embodiment, the color correction circuit may also perform color correction by dividing the image data of the target pixel by the illumination luminance information that has been subjected to luminance conversion processing.

In this way, if the circuit device has a division circuit that performs division processing, this division circuit can be effectively used to achieve color correction.

In addition, this embodiment includes a storage unit that stores a lookup table for the luminance conversion process, and the lighting luminance calculation circuit may perform luminance conversion processing on the lighting luminance information by referring to the lookup table for the luminance conversion process.

In this way, a lookup table for brightness conversion processing can be used to realize brightness conversion processing in which the amount of change in output brightness in response to a change in input brightness is greater in low brightness areas than in high brightness areas.

In addition, this embodiment includes a memory unit that stores attenuation rate distribution information that indicates the distribution of the light attenuation rate with respect to the distance between each light source element and each pixel when each light source element illuminates each pixel, and the illumination luminance calculation circuit may calculate the illumination luminance information based on the distance information between the target pixel and each light source element and the attenuation rate distribution information.

In this way, the attenuation rate distribution information of the light source elements is stored in the memory unit, and the illumination brightness information can be calculated based on this attenuation rate distribution information and the distance information between the target pixel and each light source element.

The display system of this embodiment also includes the circuit device described above and a display device.

Although the present embodiment has been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible that do not substantially deviate from the novel matters and effects of the present disclosure. Therefore, all such modifications are intended to be included within the scope of the present disclosure. For example, a term described at least once in the specification or drawings together with a different term having a broader or similar meaning may be replaced with that different term anywhere in the specification or drawings. All combinations of the present embodiment and modifications are also included within the scope of the present disclosure. Furthermore, the configurations and operations of the circuit device, display system, display device, head-up display, etc. are not limited to those described in the present embodiment, and various modifications are possible.

5...display system, 10...circuit device, 20...interface circuit, 22...target pixel, 30...light source luminance determination circuit, 32...luminance analysis unit, 34...light source luminance calculation unit, 40...illumination luminance calculation circuit, 42...luminance conversion unit, 50...color correction circuit, 60...light source control circuit, 70...memory unit, 100...display device, 110...display panel, 115...diffuser, 120...backlight, 130...light source driver, 140...display driver, 150...mirror, 160...transparent screen, 190...head-up display, 200...processing device, BR...illumination luminance information, BRL...light source luminance information, BR...illumination luminance information, IMI, IMQ...image data, IVB...inverse, L1 to L16, LS...light source element, LUTA, LUTB...look-up table. LUT1: first lookup table, LUT2: second lookup table, RBH: high brightness area, RBL: low brightness area

Claims (7)

A circuit device for controlling a display device including a plurality of light source elements and a display panel,
a light source luminance determination circuit that determines light source luminance information indicating the luminance of light emitted by each of the plurality of light source elements from the image data;
an illumination luminance calculation circuit that calculates illumination luminance information indicating luminance at which a target pixel of the display panel is illuminated by the plurality of light source elements based on the light source luminance information;
a color correction circuit that performs a luminance conversion process on the illumination luminance information, in which the amount of change in output luminance relative to a change in input luminance is greater in a low luminance area than in a high luminance area, and performs color correction on the image data of the target pixel based on the illumination luminance information that has been subjected to the luminance conversion process;
A circuit device comprising: 2. The circuit device according to claim 1,
The luminance conversion process is a gamma correction process in which a gamma value is less than 1. 2. The circuit device according to claim 1,
The color correction circuit includes:
a circuit device for performing the color correction by calculating an inverse of the illumination luminance information that has been subjected to the luminance conversion processing, and multiplying the inverse by the image data of the target pixel. 2. The circuit device according to claim 1,
The color correction circuit includes:
a circuit device for performing the color correction by dividing the image data of the target pixel by the illumination luminance information that has been subjected to the luminance conversion processing. 2. The circuit device according to claim 1,
A storage unit stores a lookup table for a luminance conversion process,
The illumination luminance calculation circuit includes:
A circuit device comprising: a first input section that inputs a first luminance conversion process to the illumination luminance information; a second input section that inputs a second luminance conversion process to the illumination luminance information; 2. The circuit device according to claim 1,
a storage unit that stores attenuation rate distribution information indicating a distribution of attenuation rates of light with respect to a distance between each of the light source elements and each of the pixels when each of the light source elements illuminates each of the pixels;
The illumination luminance calculation circuit includes:
A circuit device which calculates the illumination luminance information based on distance information between the target pixel and each of the light source elements and the attenuation rate distribution information. A circuit arrangement according to any one of claims 1 to 6,
The display device;
A display system comprising:

Images