JP2021018343A - Display device and display method - Google Patents

Abstract

To provide a display device that can favorably display an image even when it is required to reduce display luminance of the image.SOLUTION: A display device comprises: processing means that performs gradation conversion processing converting a gradation value of an image; and control means that controls an upper limit value of luminance which can be displayed on display means according to a parameter indicating brightness of the image after the gradation conversion processing. The gradation conversion processing is performed using a transfer function which is represented by means of a function of exponentiation using a γ value for the gradation value, the processing means determines the γ value on the basis of the upper limit value, and the γ value in a case where the upper limit value is a second value being higher than a first value is characterized to be larger than the γ value in a case where the upper limit value is the first value.SELECTED DRAWING: Figure 4

Description

The present invention relates to a display device and a display method.

Display gradation conversion processing (luminance adjustment processing) using OOTF (Opto-Optical Transfer Function), which is a function for performing brightness conversion, for the purpose of correcting the difference in appearance due to the difference between the shooting environment and the display environment. The device may apply. For example, ITU-R (Radio Communication Sector of ITU) BT. In 2100, it is stipulated that the OOTF function is adjusted according to the maximum value (upper limit brightness) of the display brightness preset in the display device.

On the other hand, there is a display device capable of suppressing an increase in power consumption by limiting the display brightness according to the image data used for display for the purpose of suppressing power consumption.

In Patent Document 1, the display device estimates the power consumption based on the average gradation value of the image data, and when the estimated power consumption exceeds the reference value, the upper limit brightness of the display device is lowered. The actual power consumption is limited to a predetermined range.

Japanese Unexamined Patent Publication No. 2006-119465

However, in the display device according to Patent Document 1, when displaying an image having a high average gradation value, it is the same as when displaying an image having a low average gradation value even though the upper limit brightness of the displayed image is lowered. Gradation conversion processing using OOTF is performed. For this reason, since the dark part is displayed darker than when it is preferable, there arises a problem that the visibility of the dark part is impaired.

Therefore, an object of the present invention is to provide a display device capable of suitably displaying an image even when it is necessary to reduce the display brightness of the image.

The first aspect of the present invention is
A processing means for executing a gradation conversion process for converting the gradation value of an image,
A control means for controlling the upper limit of the brightness that can be displayed on the display means according to a parameter indicating the brightness of the image after the gradation conversion process.
Have,
The gradation conversion process is executed by using a transfer function represented by a power function using a γ value with respect to the gradation value.
The processing means determines the γ value based on the upper limit value, and determines the γ value.
The γ value when the upper limit value is a second value higher than the first value is larger than the γ value when the upper limit value is the first value. It is a display device.

The second aspect of the present invention is
When the brightness range of the image is wider than the brightness range of the display means, the lowering means for reducing the brightness of the image so that the brightness range of the image is included in the brightness range of the display means.
It has a processing means for executing a gradation conversion process for converting the gradation value of an image after the brightness is reduced.
The gradation conversion process is executed by using a transfer function represented by a power function using a γ value with respect to the gradation value.
The processing means determines the γ value based on the degree of decrease in brightness due to the reducing means.
It is characterized in that the γ value when the degree of decrease is a second value larger than the first value is smaller than the γ value when the degree of decrease is the first value. It is a display device.

A third aspect of the present invention is
A processing process that executes a gradation conversion process that converts the gradation value of an image,
A control step of controlling the upper limit of the brightness that can be displayed on the display means according to the parameter indicating the brightness of the image after the gradation conversion process.
Have,
The gradation conversion process is executed by using a transfer function represented by a power function using a γ value with respect to the gradation value.
In the processing step, the γ value is determined based on the upper limit value.
It is characterized in that the γ value when the upper limit value is a second value higher than the first value is larger than the γ value when the upper limit value is the first value. This is the display method.

A fourth aspect of the present invention is
When the brightness range of the image is wider than the brightness range of the display means, a reduction step of reducing the brightness of the image so that the brightness range of the image is included in the brightness range of the display means.
It has a processing step of executing a gradation conversion process for converting the gradation value of the image after the brightness is reduced.
The gradation conversion process is executed by using a transfer function represented by a power function using a γ value with respect to the gradation value.
In the processing step, the γ value is determined based on the degree of decrease in brightness in the reduction step.
It is characterized in that the γ value when the degree of decrease is a second value larger than the first value is smaller than the γ value when the degree of decrease is the first value. This is the display method.

According to the present invention, an image can be suitably displayed even when it is necessary to reduce the display brightness of the image.

It is a block diagram of the display device which concerns on Embodiment 1. FIG. It is a figure explaining the ABL control which concerns on Embodiment 1. FIG. It is a figure explaining the effect of the system γ which concerns on Embodiment 1. It is a figure which shows the timing chart of the processing of the display device which concerns on Embodiment 1. FIG. It is a block diagram of the display device which concerns on Embodiment 2. It is a figure explaining the clip processing and compression processing which concerns on Embodiment 2. It is a figure explaining the process of image display of an image pickup apparatus and a display apparatus.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings.

[Overview of HDR image display workflow]
First, a workflow in which an HDR image is acquired by an imaging device and the display device displays an image based on the HDR image will be described.

In recent years, BT. An image having a wider dynamic range (luminance range) than an SDR (Standard Dynamic Range) image standardized by 709 is used. An image having such a wide dynamic range is referred to as an HDR (High Dynamic Range) image.

FIG. 7A is a schematic diagram showing a workflow in which an HDR image is acquired by an imaging device and the display device displays an image based on the HDR image. The image pickup device receives OETF (Opto-Electronic) for a signal corresponding to the brightness (scene brightness) of the subject output from the sensor.
An image signal is acquired by performing a process using (Transfer Function). OETF is a transfer function that converts the light captured by the imaging device into an image signal. The display device performs Inverse OETF processing on the image signal to acquire image data. The Inverse OETF process is a process of converting an image signal into a luminance signal by performing an inverse conversion of the OETF process.

The display device performs a process using OOTF (Opto-Optical Transfer Function) on the image data to acquire the display image data. OOTF is a transfer function showing the relationship between the light intensity corresponding to the brightness of the subject detected by the sensor of the image pickup device and the light intensity reproduced by the display device. OOTF is a non-linear (non-linear) graph that is convex downward if the gradation value of the input image data is used as the horizontal axis and the gradation value of the output image data is used as the vertical axis. Will be done. OOTF is expressed as a function of power (γ power) with respect to the gradation value of the input image data. The coefficient γ (gamma value; value indicating gradation conversion characteristics) used in OOTF is defined as the system γ. The display device performs Inverse OETF processing and OOTF processing on the image signal, and displays an image based on the obtained display image data. As a result, the image signal (electric signal) input to the display device can be converted into the brightness of the image displayed by the display device. Here, the Inverse OETF process and the OOTF process are collectively referred to as an EOTF (Electro-Optical Transfer Function) process.

ITU-R (Radiocommunication Sector of ITU)
BT. In the HLG (Hybrid Log-Gamma) system, which is the HDR standard defined by 2100, the OOTF system γ is defined by the following formula 1. That is, in the HLG method, the system γ of the OOTF is determined based on the upper limit luminance Lw set in the display device.

<Embodiment 1>
Hereinafter, the configuration of the display device 100 according to the first embodiment of the present invention will be described with reference to the configuration diagram shown in FIG. The display device 100 includes an input unit 101, an OOTF processing unit 102, a display unit 103, a setting unit 104, a gain determination unit 105, a gain processing unit 106, and a system γ determination unit 107.

The input unit 101 acquires an image signal from an image pickup device or the like. The input unit 101 has an input terminal such as SDI (Serial Digital Interface) or HDMI (High Definition Multimedia Interface; registered trademark).

In the present embodiment, a 10-bit HLG system image signal processed by the image pickup apparatus using OETF is input to the input unit 101. The input unit 101 performs a conversion process (Inverse OETF process) using the Inverse OETF on the image signal to generate image data. 10-bit (range of 0 to 1023 gradation values) image data is generated so that the correspondence between the gradation value indicated by the image data and the scene brightness has a linear characteristic.

The OOTF processing unit 102 executes a gradation conversion process that applies OOTF to the gradation value of the input image data by using the system γ (gamma value) determined by the system γ determination unit 107 described later. OOTF is a transfer function that outputs the power of the system γ with respect to the gradation value g of the input image data.

The display unit 103 is a display panel that displays an image based on the input image data. In the present embodiment, the display unit 103 is a display unit using an OLED (Organic Light Emitting Diode), but it may be any display unit as long as it can display an image.

The setting unit 104 sets the setting upper limit brightness Lw of the display unit 103 according to a user operation using a graphic image such as an OSD (On-screen display). It is not always necessary for the setting unit 104 to set the set upper limit brightness Lw, and the set upper limit brightness Lw may be set in advance at the time of factory shipment or the like. In this embodiment, it is assumed that 1000 nits is set as the set upper limit brightness Lw.

The gain determination unit 105 determines the ABL gain G based on the APL (Average Picture Level) of the image data (after the gradation conversion process) input from the OOTF processing unit 102. Here, APL is a parameter indicating the brightness of the image indicated by the image data, and is a value standardized with the case where the image is an all-white image as 100%. For example, when the image indicated by the image data is an image including a completely white area having an area of 50% of the image on a black background, the APL of the image data is assumed to be 50%. In addition, ABL means Auto Brightness Limiter (automatic brightness limiter). The ABL gain G does not necessarily have to be determined based on the APL, but is based on the median value of the gradation value of the image data, the average value of the maximum gradation value for each predetermined region in the image data, and the like. It may be decided.

FIG. 2A is a schematic diagram showing the relationship between APL and ABL gain G. In this embodiment, the gain determination unit 105 sets the ABL gain G to 1 when the APL is between 0% (all black) and 30%. Further, the gain determination unit 105 reduces the ABL gain G as the APL increases while the APL is greater than 30% and 50% or less, and sets the ABL gain G to 0.6 when the APL is 50%. decide. Further, the gain determination unit 105 reduces the ABL gain G as the APL increases while the APL is greater than 50% and 100% or less, and sets the ABL gain G to 0.3 when the APL is 100%. decide. The relationship between APL and ABL gain G is not limited to this. For example, the gain determination unit 105 may decrease the ABL gain G in steps with respect to the increase in the APL.

The gain processing unit 106 OO based on the ABL gain G determined by the gain determination unit 105.
The TF processing unit 102 executes a process of correcting the brightness indicated by the processed image data. The display brightness in the display unit 103 is corrected by the processing by the gain processing unit 106. The gain processing unit 106 multiplies the gradation value of each pixel of the input image data by the ABL gain G. As a result, the display brightness of the image on the display unit 103 is reduced, so that an increase in power consumption of the display device 100 can be suppressed. By applying the ABL gain G to the image data, the possible upper limit value of the display brightness of the image data (display upper limit value Lwd; upper limit value of the brightness that can be displayed by the display unit 103) is controlled (changed). When the ABL gain G is a value smaller than 1, the display upper limit value Lwd decreases.

The system γ determination unit 107 determines the system γ based on the set upper limit luminance Lw set by the setting unit 104 and the ABL gain G determined by the gain determination unit 105.

In the present embodiment, the system γ determination unit 107 determines the system γ based on the following equation 2. As shown in Equation 2, the smaller the ABL gain G, the smaller the system γ. That is, the lower the upper limit brightness of the displayed image, the smaller the system γ.

Here, the processing when the image data in which the APL is 50% is input and the ABL gain G is 0.6 will be described as an example. Further, as described above, Lw = 1000 nits. Therefore, the display upper limit brightness Lwd is 600 nits. Therefore, the system γ determination unit 107 determines the system γ as 1.11. Based on the equation 2.

Then, the OOTF processing unit 102 converts the gradation value of the input image data by using the system γ determined by the system γ determination unit 107. As a result, the OOTF processing unit 102 can apply an appropriate system γ to the image data according to the ABL control (ABL gain G).

As a comparative example, when the system γ is determined with ABL gain = 1 based on the set upper limit luminance Lw, the system γ is determined to be 1.20 from Equation 1. As described above, in the present embodiment, the system γ when the set upper limit luminance Lw is a second value higher than the first value than the system γ when the set upper limit luminance Lw is the first value. Is bigger.

FIG. 3 is input to the OOTF processing unit 102 in the case of system γ = 1.11 (system γ corresponding to ABL control) as in the present embodiment and in the case of system γ = 1.20 regardless of ABL control. The characteristics of the gradation value output by the OOTF processing unit 102 with respect to the gradation value to be performed are shown.

As shown in FIG. 3, the image is displayed brighter in the case of the system γ = 1.11 as in the present embodiment because the output gradation value is larger than in the case of the system γ = 1.20. As a result, it is possible to prevent the dark area gradation in the image data from being darkened more than necessary, so that the visibility of the region corresponding to the dark area gradation can be improved.

Further, in the case of the system γ = 1.11 as in the present embodiment, the dark part of the image is displayed with better gradation than in the case of the system γ = 1.20. This is because the OOTF processing unit 102
This is because a gradation range lower than a predetermined gradation value in the image data is converted into a wider gradation range in the case of system γ = 1.11 than in the case of system γ = 1.20. This also makes it possible to improve the visibility of the region corresponding to the dark area gradation.

As described above, in the display device 100 according to the present embodiment, the system γ can be appropriately determined according to the ABL control, so that the visibility of the image is improved and the image is displayed with a more suitable display brightness. Can be done.

[Display processing flow of display device]
Hereinafter, the processing of the display device 100 for the n-frame (n-th frame) of the image data will be described with reference to FIG. FIG. 4 shows a timing chart of the operation performed by the display device 100 for each frame.

In S401, the input unit 101 performs a process using the Inverse OETF on the image signal to acquire n frames of the image data. The input unit 101 outputs the acquired n frames to the OOTF processing unit 102. The function f shown in FIG. 4 indicates that the frame of the number indicated by the argument is acquired.

In S402, the OOTF processing unit 102 acquires the system γ determined by the system γ determination unit 107 for the n-1 frame of the image data. Then, the OOTF processing unit 102 uses this system γ to convert the gradation value of n frames acquired from the input unit 101. That is, in the present embodiment, the OOTF processing unit 102 performs gradation conversion processing on the target frame by using the system γ determined for the frame before the target frame. The OOTF processing unit 102 outputs the n-frame in which the gradation value is converted to the gain determination unit 105 and the gain processing unit 106. The function γ shown in FIG. 4 indicates that gradation conversion using the system γ is performed on the frame of the number indicated by the argument.

In S403, the gain determination unit 105 determines the ABL gain G based on the n frames processed by the OOTF processing unit 102. The gain determination unit 105 outputs the determined ABL gain G to the system γ determination unit 107 and the gain processing unit 106. It should be noted that the function gd shown in FIG. 4 indicates that the ABL gain G for the frame of the number indicated by the argument is determined.

In S404, the system γ determination unit 107 determines the system γ for n frames based on the ABL gain G and the set upper limit brightness Lw. The system γ determination unit 107 outputs the determined system λ to the OOTF processing unit 102. Note that the function γd shown in FIG. 4 indicates that the system γ for the frame of the number indicated by the argument is determined.

In S405, the gain processing unit 106 delays n frames for a period of one frame, and performs ABL control on the n frames according to the ABL gain G. This delay is realized by the gain processing unit 106 having a frame buffer. The gain processing unit 106 outputs an ABL-controlled n-frame to the display unit 103. The function G shown in FIG. 4 indicates that ABL control is performed on the frame of the number indicated by the argument.

In S406, the display unit 103 displays the acquired n frames. The function p shown in FIG. 4 indicates that the frame of the number indicated by the argument is displayed.

As described above, the system γ determined by the system γ determination unit 107 is applied to the frame next to the frame used for the determination. However, the frame of the image data used when determining the system γ and the frame of the image data to which the system γ is applied may be the same, and for this purpose, the system γ determination unit 107 has a frame buffer. You may be.

Further, in the present embodiment, the display device 100 changes and displays the system γ according to the ABL gain G (display upper limit brightness Lwd). Here, the system γ determination unit 107 may limit the width of the change (time change) between frames of the system γ so that the system γ does not change significantly between frames.

Further, in the present embodiment, the system γ determination unit 107 determines the system γ for each frame, but changes the system γ from the system γ of the previous frame only when the ABL gain G is equal to or less than a predetermined value. It may be. That is, if the ABL gain G is larger than the predetermined value (if the degree of decrease in the display luminance due to ABL control is smaller than the predetermined value; if the display upper limit luminance Lwd is larger than the predetermined value), the system γ determination unit 107 is in front of Do not change from the frame system γ. According to this, it is possible to suppress a feeling of interference such as screen flicker caused by the system γ changing for each frame.

Further, the display unit 103 may display the system γ determined by the above-mentioned processing by using the OSD (graphic image). This allows the user to easily grasp the system γ applied to the image data.

In the present embodiment, the display device 100 has an OLED, but may be a liquid crystal display device having a backlight (light emitting unit). In that case, the backlight emits light to the display unit 103, and the display unit 103 modulates the light from the backlight to display an image. Then, the gain processing unit 106 controls (decreases) the display brightness (display upper limit brightness Lwd) in the display unit 103 by controlling (decreasing) the brightness (light emission amount) of the backlight. Good.

In the present embodiment, an example of reducing the display brightness by multiplying the gradation value of the image data by the ABL gain G has been given, but the present invention is not limited to this, and all the gradation value values are set by a fixed amount. Offset control for lowering may be performed. In this case, the display device 100 may determine the value of the system γ to be smaller as the degree of decrease in the display luminance due to the offset control is larger.

Further, in addition to the mode in which the system γ is changed and displayed according to the ABL control as in the present embodiment, a mode in which the system γ is displayed as a predetermined fixed value (characteristic) regardless of the ABL control is provided. May be good. In this case, for example, the switching unit (not shown) may switch between the two modes according to user input or metadata of image data. That is, the system γ determination unit 107 determines the system γ as in the present embodiment in the case of a certain mode, and in the case of a mode different from the mode, the value of the system γ is set to a predetermined fixed value. To decide.

<Embodiment 2>
In the first embodiment, a display device that performs ABL control has been described. In the following, when the luminance range (dynamic range; luminance range) that the HDR image can express is wider than the luminance range (dynamic range; luminance range) that the display device (display unit) can display, the dynamic of the HDR image A display device that converts a range will be described. Here, the brightness (brightness) indicated by the HDR image is reduced so that the dynamic range of the HDR image is included in the dynamic range of the display device.

As the first example of the dynamic range conversion method, the brightness of the image data corresponding to the brightness range that can be displayed by the display device is displayed without conversion, and the brightness of the image data outside the brightness range can be displayed. There is a method of displaying the brightness at the upper limit of the brightness range. Such luminance conversion (gradation value conversion) is hereinafter referred to as clip processing.

As a second example of the dynamic range conversion method, there is a method called compression processing that reduces the brightness of the entire range of image data at a constant rate so that the brightness range of the image data falls within the brightness range of the display device. is there.

The display device 200 according to the second embodiment will be described with reference to the configuration diagram shown in FIG. The display device 200 according to the present embodiment further includes a range information acquisition unit 208, a display range setting unit 209, and a range conversion unit 210 with respect to the display device 100 in the first embodiment. Further, the system γ determination unit 207 has a different process from the system γ determination unit 107 according to the first embodiment. The input unit 101 outputs the image data to the range conversion unit 210. Hereinafter, a configuration different from that of the first embodiment will be described, and a description of the same configuration will be omitted.

In the present embodiment, the set upper limit luminance Lw of the display unit 103 is 500 nits, unlike the first embodiment. Further, the dynamic range (input range) of the input image data is assumed to be in the range of 0 to 1000 nits.

The range information acquisition unit 208 acquires the dynamic range information of the image data (input image data) input to the input unit 101. The range information acquisition unit 208 acquires input range information according to, for example, an image setting for the display device 200.

Specifically, the range information acquisition unit 208 sets the image for the display device 200 to BT. If it is 709, the dynamic range is determined to be in the range of 0 to 100 nits. Further, if the image setting corresponds to HDR, the range information acquisition unit 208 determines the dynamic range corresponding to the image setting. The range information acquisition unit 208 may acquire dynamic range information from the metadata added to the input image data.

The display range setting unit 209 sets the dynamic range (display range), which is the range that the display unit 103 can express in the dynamic range of the input image data, according to the user operation (setting).

For example, when the dynamic range of the display unit 103 is 0 to 500 nits and the image data having the dynamic range of 0 to 1000 nits is clipped, the brightness of the image data larger than 500 nits is displayed at 500 nits. On the other hand, the brightness of 0 to 500 bits in the image data is displayed on the display unit 103 with the same brightness. Therefore, in this case, the display unit 103 expresses 0 to 500 nits in the image data, so that the display range is 0 to 500 nits.

On the other hand, for example, when the dynamic range of the display unit 103 is 0 to 500 nits and the image data having the dynamic range of 0 to 1000 nits is compressed, the brightness of the image data is uniformly 0. It is displayed multiplied by 5. Therefore, since the brightness of the entire range in the input range can be expressed by the display unit 103, in this case, the display range is 0 to 1000 nits.

The range conversion unit 210 performs range conversion processing on the image data acquired from the input unit 101 based on the display range set by the display range setting unit 209 and the information (input range) acquired by the range information acquisition unit 208. Give. Therefore, in the present embodiment, the range conversion unit 210 lowers the brightness indicated by the image data and lowers the display brightness.

The range conversion unit 210 performs a clip process or a compression process as a range conversion process for each pixel of the image data input from the input unit 101 based on the following formula 3 according to the maximum value of the display range. However, when the gradation value of the pixel determined by the formula 3 is 1023 or more, the range conversion unit 210 converts the gradation value to 1023. Here, the range conversion unit 210 converts the gradation value so that the larger the maximum value of the display range, the greater the degree of decrease in brightness (degree of decrease in display brightness) indicated by the image data.

FIG. 6A is a graph for explaining the range conversion process, and shows a case where the display range setting unit 209 sets the maximum value of the display range to 500 nits and a case where the maximum value of the display range is set to 1000 nits. In FIG. 6A, the horizontal axis represents the gradation value (luminance) of the image data input to the range conversion unit 210, and the vertical axis represents the gradation value of the image data output by the range conversion unit 210. ing.

As shown in FIG. 6A, the range conversion unit 210 performs clipping processing on the image data if the maximum value of the display range is 500 nits. On the other hand, if the maximum value of the display range is 1000 nits, the range conversion unit 210 performs compression processing on the image data.

Therefore, when the clip processing is performed, if the processing of the OOTF processing unit 102 and the gain processing unit 106 is not performed, as shown in FIG. 6B, the region of 500 nits in the HDR image is 500 nits. It is displayed in display brightness.

On the other hand, when the compression process is performed, as shown in FIG. 6B, the region of 500 nits in the HDR image is displayed with the display brightness of 250 nits.

That is, the low to intermediate gradations in the input image data are brighter when the clip processing is applied than when the compression processing is applied, and are displayed on the display unit 103. Therefore, in the present embodiment, the system γ determination unit 207 determines the system γ as described later in consideration of the brightness of low to intermediate gradations when this clip processing is performed.

The system γ determination unit 207 determines the system γ as shown by the following equation 4 based on the input range, the display range, and the ABL gain G.

Therefore, if the maximum value of the display range is 500 nits at which the clip processing is performed and the ABL gain G is 0.6, the system γ determination unit 207 sets the system γ to 1.11 based on the equation 4. decide. In the present embodiment, the maximum value of the display range is first than that of the system γ when the maximum value of the display range (degree of decrease in display brightness; degree of decrease in brightness indicated by image data) is the first value. The system γ is smaller when the second value is higher than the value.

On the other hand, if the maximum value of the display range is 1000 nits at which the compression process is performed and the ABL gain G is 0.6, the system γ determination unit 207 sets the system γ to 0.98 based on the equation 4. decide. Here, the larger the maximum value of the display range, the greater the degree of decrease in the display brightness by the range conversion unit 210. Further, the larger the ABL gain G, the greater the degree of decrease in the display brightness by the gain processing unit 106. Therefore, in the present embodiment, it can be said that the system γ determination unit 207 determines a smaller system γ as the degree of decrease in display brightness by the gain processing unit 106 and the range conversion unit 210 increases.

In this way, when the clip processing is performed, the system γ is determined to be 1.11. Therefore, the dark part is larger than the case where the compression processing is performed (when the system γ is 0.98). It is displayed dark (sunk). Therefore, according to the present embodiment, the image can be displayed with good contrast.

In the present embodiment, the display device 200 does not have to include the gain processing unit 106 and the gain determining unit 105. That is, the system γ determination unit 207 may determine the system γ by fixing the ABL gain G = 1.

As described above, the display device according to the present embodiment can improve the visibility of the dark part in the image by displaying the system γ by changing it according to the ABL control and the display range.

Further, as another embodiment, for example, as shown in FIG. 7B, when an image signal to which OOTF is applied is input to the display device, the display device cancels (cancels) the OOTF. Perform key conversion. Then, after that, the display device may further execute any of the processes of the above-described first and second embodiments.

Specifically, an image signal in which a gradation conversion process (luminance adjustment process) using OOTF (first OOTF) is performed by an image pickup device or a converter with the system γ as 1.2 is input to the display device. Imagine a case. In this case, the display device uses an OOTF having a system γ of 1 / 1.2 with respect to the image data acquired from the image signal, and an OOTF having a system γ of 1.2 (first OOTF). Perform a process to cancel. After that, the display device may execute the OOTF (second OOTF) process according to the first or second embodiment.

It should be noted that each functional unit of each of the above embodiments may or may not be individual hardware. The functions of two or more functional units may be realized by common hardware. Each of the plurality of functions of one functional unit may be realized by individual hardware. Two or more functions of one functional unit may be realized by common hardware. Further, each functional unit may or may not be realized by hardware such as ASIC, FPGA, and DSP. For example, the device may have a processor and a memory (storage medium) in which a control program is stored. Then, the function of at least a part of the functional parts of the device may be realized by the processor reading the control program from the memory and executing it.

(Other embodiments)
The present invention supplies a program that realizes one or more functions of the above embodiments to a system or device via a network or storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by the processing to be performed. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

100: Display device, 102: OOTF processing unit, 103: Display unit 106: Gain processing unit, 107: System γ determination unit

Claims (18)

A processing means for executing a gradation conversion process for converting the gradation value of an image,
A control means for controlling the upper limit of the brightness that can be displayed on the display means according to a parameter indicating the brightness of the image after the gradation conversion process.
Have,
The gradation conversion process is executed by using a transfer function represented by a power function using a γ value with respect to the gradation value.
The processing means determines the γ value based on the upper limit value, and determines the γ value.
The γ value when the upper limit value is a second value higher than the first value is larger than the γ value when the upper limit value is the first value. Display device. When the luminance range of the image is wider than the luminance range of the display means, it further has a reducing means for reducing the brightness of the image so that the luminance range of the image is included in the luminance range of the display means.
The processing means determines the γ value based on the degree of decrease in brightness by the reducing means and the upper limit value, and executes the gradation conversion process on an image whose brightness is reduced by the reducing means.
The display device according to claim 1, wherein the display device is characterized by the above. The control means controls the upper limit value by lowering the gradation value after the gradation conversion process.
The display device according to claim 1 or 2. Further having a light emitting means for emitting light to the display means,
The display means modulates the light from the light emitting means to display an image.
The control means controls the upper limit value by reducing the amount of light emitted by the light emitting means.
The display device according to claim 1 or 2. When the APL (Average Picture Level), which is the parameter, is larger than a predetermined value, the control means controls the upper limit value according to the APL.
The display device according to any one of claims 1 to 4, wherein the display device is characterized by the above. When the APL is larger than a predetermined value, the control means lowers the upper limit value at a rate corresponding to the APL.
The display device according to claim 5, wherein the display device is characterized by the above. The processing means
Determine the gamma value for each frame and
The gradation conversion process is executed for each frame.
The display device according to any one of claims 1 to 6, wherein the display device is characterized by the above. The processing means limits the time change of the γ value according to the upper limit value, and determines the γ value of each frame.
The display device according to claim 7. The processing means does not change the γ value from the previous frame if the upper limit value of the target frame is larger than a predetermined value.
The display device according to claim 7 or 8. The processing means
In the case of the first mode, the γ value is determined based on the upper limit value.
In the case of the second mode, a predetermined value is determined as the γ value.
The display device according to any one of claims 1 to 9, wherein the display device is characterized by the above. Further, it has a switching means for switching between the first mode and the second mode according to a user operation.
10. The display device according to claim 10. When the brightness range of the image is wider than the brightness range of the display means, the lowering means for reducing the brightness of the image so that the brightness range of the image is included in the brightness range of the display means.
It has a processing means for executing a gradation conversion process for converting the gradation value of an image after the brightness is reduced.
The gradation conversion process is executed by using a transfer function represented by a power function using a γ value with respect to the gradation value.
The processing means determines the γ value based on the degree of decrease in brightness due to the reducing means.
It is characterized in that the γ value when the degree of decrease is a second value larger than the first value is smaller than the γ value when the degree of decrease is the first value. Display device. The display means further displays a graphic image showing the γ value.
The display device according to any one of claims 1 to 12, characterized in that. The γ value is a γ value in an HLG (Hybrid Log-Gamma) method OOTF (Opto-Optical Transfer Function).
The display device according to any one of claims 1 to 13, characterized in that. A processing process that executes a gradation conversion process that converts the gradation value of an image,
A control step of controlling the upper limit of the brightness that can be displayed on the display means according to the parameter indicating the brightness of the image after the gradation conversion process.
Have,
The gradation conversion process is executed by using a transfer function represented by a power function using a γ value with respect to the gradation value.
In the processing step, the γ value is determined based on the upper limit value.
It is characterized in that the γ value when the upper limit value is a second value higher than the first value is larger than the γ value when the upper limit value is the first value. Display method. When the brightness range of the image is wider than the brightness range of the display means, a reduction step of reducing the brightness of the image so that the brightness range of the image is included in the brightness range of the display means.
It has a processing step of executing a gradation conversion process for converting the gradation value of the image after the brightness is reduced.
The gradation conversion process is executed by using a transfer function represented by a power function using a γ value with respect to the gradation value.
In the processing step, the γ value is determined based on the degree of decrease in brightness in the reduction step.
It is characterized in that the γ value when the degree of decrease is a second value larger than the first value is smaller than the γ value when the degree of decrease is the first value. Display method. A program for causing a computer to perform each step of the method according to claim 15 or 16. A computer-readable storage medium that stores the program of claim 17.

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