JP7560386B2 - Display device, correction method, and control program - Google Patents

Description

The present invention relates to a display device, a correction method, and a control program.

Display devices such as television receivers, VTRs (Video Tape Recorders), digital cameras, television cameras, and printers have the ability to correct the brightness of pixels contained in an input image (brightness of the input image), for example by adjusting contrast, in order to improve image quality. Techniques for correcting the brightness of an input image include techniques that use a gamma curve.

Patent document 1 discloses an image display device that can display a stable image even when a video signal containing large time-axis noise is input by limiting the range in which the gamma curve can be set to within a predetermined allowable range.

JP 2010-28609 A

However, in the conventional technology described above, the range in which the gamma curve can be set is uniform regardless of the brightness of the target image, so depending on the brightness of the image, the contrast may be perceived as reduced.

One aspect of the present invention was made in consideration of the above problems, and aims to make it possible to display a stable image while suppressing a decrease in contrast.

To solve the above problem, a display device according to one aspect of the present invention is a display device that corrects the luminance of an input image based on a gamma curve that represents the relationship between pre-correction luminance and post-correction luminance, and is characterized by comprising: a gamma curve setting unit that limits the amount of correction in at least a portion of the range of the gamma curve according to the brightness of the input image; and a luminance correction unit that corrects the luminance of the input image based on the gamma curve with the amount of correction limited by the gamma curve setting unit.

In order to solve the above problem, a correction method according to one aspect of the present invention is a correction method for correcting the luminance of an input image based on a gamma curve that represents the relationship between pre-correction luminance and post-correction luminance, and is characterized in that it includes a gamma curve setting process for limiting the amount of correction in at least a portion of the range of the gamma curve depending on the brightness of the input image, and a luminance correction process for correcting the luminance of the input image based on the gamma curve whose correction amount has been limited in the gamma curve setting process.

According to one aspect of the present invention, it is possible to display a stable image while suppressing a decrease in contrast.

1 is a functional block diagram showing a configuration of a display device according to an embodiment. 1 is a schematic diagram showing an external appearance of a display device according to an embodiment. FIG. 11 is a diagram illustrating an example of a limit range of a gamma curve. FIG. 11 is a diagram illustrating an example of a limit range of a gamma curve. FIG. 13 is a diagram illustrating an example of a sigmoid function. FIG. 13 is a diagram illustrating an example of a sigmoid function. FIG. 13 is a diagram illustrating an example of a sigmoid function. FIG. 11 is a diagram illustrating an example of a limit range of a gamma curve. FIG. 11 is a diagram illustrating an example of a limit range of a gamma curve. FIG. 11 is a diagram illustrating an example of a limit range of a gamma curve. FIG. 11 is a diagram illustrating an example of a limit range of a gamma curve. FIG. 11 is a diagram illustrating an example of a limit range of a gamma curve. 10 is a flowchart showing the flow of a correction method for correcting the luminance of an input image.

<Embodiment>
Hereinafter, a display device 1 according to the first embodiment and a correction method for correcting the luminance of an input image will be described with reference to FIGS.

[Display device 1]
The display device 1 is a display device that corrects the luminance of an input image based on a gamma curve that represents the correspondence between pre-correction luminance and post-correction luminance.

Fig. 1 is a functional block diagram showing the configuration of a display device 1 according to the first embodiment. Fig. 2 is a schematic diagram showing the external appearance of the display device 1 according to the first embodiment. As shown in Fig. 1, the display device 1 includes an input image acquisition unit 11, a gamma curve setting unit 12, a luminance correction unit 13, and a display unit 14.

[Input image acquisition unit 11]
The input image acquisition unit 11 acquires input images from, for example, a receiving unit (not shown) that receives broadcast waves, an input unit (not shown) that accepts input from an external device (such as a BD player, a DVD player, a personal computer, or a game device), or a reading unit (not shown) that reads a recording medium (not shown).

[Gamma curve setting unit 12]
The gamma curve setting unit 12 limits the amount of correction in at least a part of the range of the gamma curve according to the brightness of the input image acquired by the input image acquisition unit 11 .

In the example shown in FIG. 1, the gamma curve setting unit 12 includes a gamma curve calculation unit 122, a luminance calculation unit 123, a range determination unit 124, and a gamma curve correction unit 125. Each unit included in the gamma curve setting unit 12 will be described below.

(Gamma curve calculation unit 122)
The gamma curve calculation unit 122 calculates a gamma curve that represents the correspondence relationship between pre-correction luminance and post-correction luminance. The gamma value used in the calculation of the gamma curve may be a fixed value set by the user via an input device (not shown), or a dynamic value derived by the gamma curve calculation unit 122 with reference to pixel values of an input image, etc.

(Brightness calculation unit 123)
The luminance calculation unit 123 calculates an index value indicating the brightness of the input image acquired by the input image acquisition unit 11. For example, the luminance calculation unit 123 may use an average picture level (APL) of the input image as an index indicating the brightness of the input image.

(Range Determination Unit 124)
The range determination unit 124 determines a limiting range for limiting the correction amount of the gamma curve according to the value calculated by the luminance calculation unit 123. As an example, the range determination unit 124 may set the limiting range such that the correction amount of the gamma curve in the direction of increasing the luminance in a low luminance region is more significantly limited as the brightness of the input image becomes darker. In other words, the range determination unit 124 may determine an allowable range within which the gamma curve can be set such that the improvement in luminance in a low luminance region of the input image due to the gamma correction of the input image is more significantly suppressed as the brightness of the input image becomes darker.

3 and 4 are diagrams showing an example of the limit range of a gamma curve. In FIG. 3 and FIG. 4, region 21 corresponds to the limit range, and region 22 corresponds to the allowable range. In other words, even a part of the gamma curve after correction is not included in the limit range, but is entirely included in the allowable range. In addition, in the graphs of FIG. 3 and FIG. 4, the horizontal axis of the graph indicates the input gradation value for the luminance of the input image, and the vertical axis indicates the output gradation value for the luminance. That is, for the luminance, an input gradation value of 256 corresponds to an output gradation value of 1024. In addition, line 23 is linear and passes through coordinates (0, 0) and (256, 1024).

Figure 3 also shows the limited range that the range determination unit 124 can determine when the input image is dark. As shown by the arrow in Figure 3, the allowable range of the gamma curve that makes the post-correction luminance higher than the pre-correction luminance is narrower in the low-luminance region than in the high-luminance region. Here, the range to the upper left of the line 23 corresponds to the range in which the post-correction luminance is higher than the pre-correction luminance. In a configuration corresponding to Figure 3, the allowable range in the low-luminance region of the gamma curve that attempts to increase the luminance of the input image is more restricted than the allowable range in the high-luminance region. Also, the allowable range of the gamma curve is gradually restricted to a greater extent as it goes from the high-luminance region to the low-luminance region.

In other words, in the configuration corresponding to FIG. 3, the low-luminance areas of the input image will not become brighter than a certain amount due to gamma correction, beyond the allowable degree in the high-luminance areas. This limits the increase in the luminance value of the low-luminance areas to a certain range when the input image is dark, making it possible to suppress the decrease in contrast of the input image when gamma correction is performed.

The range determination unit 124 may set the limit range so that the amount of correction of the gamma curve in the direction of reducing the luminance in high-luminance regions is more significantly limited as the brightness of the input image increases. In other words, the range determination unit 124 may determine the allowable range within which the gamma curve can be set so that the brighter the input image is, the more the reduction in luminance in high-luminance regions of the input image due to the gamma correction of the input image is more significantly suppressed.

Figure 4 shows the limiting range that the range determination unit 124 can determine when the input image is bright. In Figure 4, as indicated by the arrow, the allowable range of the gamma curve that makes the post-correction luminance lower than the pre-correction luminance is narrower in the high-luminance region than in the low-luminance region. Here, the range to the lower right of the line 23 corresponds to the range in which the post-correction luminance is lower than the pre-correction luminance. In a configuration corresponding to Figure 4, the allowable range in the high-luminance region of the gamma curve that attempts to lower the luminance of the input image is more restricted than the allowable range in the low-luminance region. Also, the allowable range of the gamma curve is gradually restricted to a greater extent as it goes from the low-luminance region to the high-luminance region.

In other words, in the configuration corresponding to FIG. 4, the high-luminance areas of the input image do not become darker than a certain amount due to gamma correction than is permitted in the low-luminance areas. This limits the reduction in the luminance value of the high-luminance areas to a certain range when the input image is bright, making it possible to suppress the decrease in contrast of the input image when gamma correction is performed.

The range determination unit 124 may define a straight line or a curve indicating the boundary between the limited range and the allowable range using, for example, a step function, but it is preferable to define an S-shaped curve using a sigmoid function. For example, the S-shaped curve R _upper indicating the upper limit of the allowable range and the S-shaped curve R _lower indicating the lower limit of the allowable range can be defined by the following formulas 1 to 4 using a sigmoid function. In each formula, a, b, and c are arbitrary coefficients. The values of these coefficients may be configured to be set by the user by inputting them into the display device 1 via an input device not shown. Furthermore, Y _apl indicates the APL, and Y _max indicates the maximum luminance value in the input image.

Fig. 5 shows curves obtained when b is fixed and a is changed in the sigmoid function shown in the first term on the right side of the formula 3. In Fig. 5 and Fig. 6 described later, the horizontal axis indicates the value of _x1 , and the vertical axis indicates the value of the sigmoid function. As shown in Fig. 5, when b is fixed and a is changed, the vertical width of the entire curve does not change, but the steepness of the S-shape changes.

Figure 6 shows the curves when a is fixed and b is changed for the sigmoid function mentioned above. As shown in Figure 6, when a is fixed and b is changed, the upper and lower widths of the entire curve change.

In addition to the embodiment using the sigmoid function, an S-shaped curve based on the formula y=x/(1+|x|) or y=tanh(x) may also be used.

In addition, rather than performing the calculations illustrated in the formulas 1 to 4 every time the input image is updated, it is preferable that the range determination unit 124 calculates the limit range of the gamma curve by shifting the range in which the correction amount is limited in the gamma curve according to the brightness of the input image. This has the effect of reducing the processing load on the display device 1. This is described in detail below with reference to Figs. 7 to 12.

Fig. 7 is a diagram showing an example of a sigmoid function. In the graph of Fig. 7, the horizontal axis is the gradation value corresponding to the input gradation value for the luminance of the input image, and the vertical axis is the gradation value corresponding to the output gradation value for the luminance. Curve 31 corresponds to R _upper calculated by the formula 3, and curve 32 corresponds to R _lower calculated by the formula 4. Straight line 33 is linear and is an asymptote of curves 31 and 32 or a straight line equivalent thereto.

Moreover, the frame 34 corresponds to a single limit range exemplified in Fig. 8 etc., which will be described later. Here, the left frame 34 corresponds to the limit range when Y _apl = 32, and the right frame 34 corresponds to the limit range when Y _apl = 224.

The range determination unit 124 calculates the restricted range by shifting the frame 34 to the right when the brightness of the input image is greater, and by shifting the frame 34 to the left when the brightness is smaller.

Figure 8 and Figures 9 to 12 are diagrams showing examples of the limit range of a gamma curve. In addition, in the graphs of Figure 8 and Figures 9 to 12, the horizontal axis indicates the input gradation value for the luminance of the input image, and the vertical axis indicates the output gradation value for the luminance. That is, in the example of Figure 8 etc., an input gradation value of 256 corresponds to an output gradation value of 256.

In addition, in FIG. 8 and FIG. 9 to FIG. 12, the range above curve 36 and the range below curve 37 correspond to the restricted range, and the range between curves 36 and 37 corresponds to the allowable range. Note that the boundary lines on curves 36 and 37 may correspond to either the restricted range or the allowable range. Straight line 38 is linear and passes through the coordinates (0, 0) and (256, 256).

Fig. 8 shows an example of the limit range when Y _apl =32 and the input image is very dark. A frame 39 in Fig. 8 corresponds to the left frame 34 in Fig. 7, and a straight line 38 corresponds to the straight line 33 in Fig. 7. A curve 36 corresponds to the curve 31 in Fig. 7, and a curve 37 corresponds to the curve 32 in Fig. 7. For example, the range determination unit 124 may perform a linear transformation on the curves 31 and 32 in the range included in at least the frame 34 in Fig. 7, respectively, to calculate the curves 36 and 37.

Fig. 9 shows an example of the limit range when Y _apl =64 and the input image is somewhat dark. The graphs in Fig. 9 to Fig. 12 correspond to positions obtained by gradually shifting the left frame 34 in Fig. 7 to the right. Since the input image corresponding to Fig. 9 is not as dark as the input image corresponding to Fig. 8, the limit range shown in Fig. 9 limits the correction amount in the direction of increasing luminance in the low luminance region of the gamma curve to a smaller degree than the limit range shown in Fig. 8.

Fig. 10 shows an example of the limit range when Y _apl = 128 and the brightness of the input image is intermediate tones. In the example of Fig. 10, curves 36 and 37 are arranged point-symmetrically with respect to the coordinates (128, 128).

FIG. 11 shows an example of the limit range when Y _apl =192 and the input image is somewhat bright.

Fig. 12 shows an example of the limit range when the input image is very bright, with Y _apl = 224. Since the input image corresponding to Fig. 12 is brighter than the input image corresponding to Fig. 11, the limit range shown in Fig. 12 limits the correction amount in the direction of decreasing luminance in the high luminance region of the gamma curve to a greater extent than the limit range shown in Fig. 11.

Furthermore, with regard to the above-mentioned coefficients a, b, and c, if the value of a is increased, the limited range of the gamma curve becomes steeper in the low brightness region and the high brightness region, and the effect of the display device 1 according to this embodiment becomes greater. Furthermore, if the value of a is decreased, the limited range of the gamma curve becomes gentler, and more natural gamma correction becomes possible. Furthermore, if the value of b is changed, the size of the limited range can be adjusted for the entire input gradation. Furthermore, if the value of c is changed, the S-shaped curve illustrated in FIG. 7 shifts left or right, and the input gradation value that sharply increases the limited range can be adjusted.

The range determination unit 124 may store the value indicating the limited range once calculated in a lookup table, and may refer to the lookup table from the next time onward to determine the limited range. In other words, the gamma curve setting unit 12 may generate a gamma curve with a limited correction amount by referring to a range according to the brightness of the input image in a lookup table that defines the limited range of the gamma curve. As an example, the input value of the lookup table may be a value such as APL indicating the brightness of the input image, or the number or ratio of pixels described later in Modification 1, and the output value of the lookup table may be a value indicating the range in which the recorded S-curves R _upper and R _lower are used. Alternatively, the output value may be an array indicating the upper and lower limits of the allowable range corresponding to each input gradation for the brightness of the input image.

(Gamma Curve Correction Unit 125)
The gamma curve correction unit 125 determines the correction amount of the gamma curve based on the limited range determined by the range determination unit 124, and corrects the gamma curve. For example, the gamma curve correction unit 125 may correct the gamma curve by performing the processes shown in the following (1) to (3) for each input gradation value i. Here, y[i] indicates the output gradation value when the gamma curve before correction is applied to the input gradation value i. Furthermore, upper_range[i] indicates the upper limit of the allowable range corresponding to the input gradation value i, and lower_range[i] indicates the lower limit of the allowable range corresponding to the input gradation value i. The processes shown in the following (1) to (3) have a relatively low processing load on the display device 1, and can perform gamma curve correction at high speed.

(1) If the value of y[i] is greater than the value of upper_range[i], clip the portion of the gamma curve that corresponds to the input tone value i so that the value of y[i] becomes the value of upper_range[i].

(2) If the value of y[i] is smaller than the value of lower_range[i], clip the portion of the gamma curve that corresponds to the input tone value i so that the value of y[i] becomes the value of lower_range[i].

(3) If neither condition (1) nor (2) is met, the value of y[i] is left unchanged, and no clipping is performed on the gamma curve portion corresponding to the input tone value i.

[Brightness correction unit 13]
The luminance correction unit 13 performs gamma correction based on the gamma curve whose correction amount is limited by the gamma curve setting unit 12, and corrects the luminance of the input image.

[Display unit 14]
The display unit 14 is a display panel that displays an image, etc., whose luminance has been corrected by the luminance correction unit 13 .

[Correction method using display device 1]
Next, a correction method for correcting the luminance of an input image, which is executed by the display device 1 according to the first embodiment, will be described with reference to Fig. 13. Fig. 13 is a flowchart showing the flow of the correction method.

(Step S101)
The input image acquisition unit 11 of the display device 1 acquires an input image (input image acquisition step).

(Step S102)
The gamma curve calculation unit 122 calculates a gamma curve by referring to the gamma value (gamma curve calculation step).

(Step S103)
The luminance calculation unit 123 calculates an index value indicating the brightness of the input image acquired by the input image acquisition unit 11 (luminance calculation step).

(Step S104)
The range determination unit 124 determines the limit range of the gamma curve according to the value calculated by the luminance calculation unit 123 (limit range determination step).

(Step S105)
The gamma curve correction unit 125 determines the amount of correction of the gamma curve based on the limited range determined by the range determination unit 124, and corrects the gamma curve (gamma curve correction step).

In addition, steps S102 to S105 correspond to a gamma curve setting process that limits the amount of correction in at least a portion of the gamma curve depending on the brightness of the input image.

(Step S106)
The luminance correction unit 13 performs gamma correction based on the gamma curve corrected in the gamma curve setting process, and corrects the luminance of the input image (luminance correction process).

(Step S107)
The display unit 14 displays the image whose luminance has been corrected in the luminance correction process (display process).

The above describes an example of a correction method for correcting the luminance of an input image based on a gamma curve that represents the relationship between pre-correction luminance and post-correction luminance, the correction method including a gamma curve setting process and a luminance correction process. As described above, in the gamma curve setting process, the amount of correction in at least a part of the range of the gamma curve is limited according to the brightness of the input image. In addition, in the luminance correction process, the luminance of the input image is corrected based on the gamma curve in which the amount of correction is limited in the gamma curve setting process.

This configuration makes it possible to display stable images while suppressing a decrease in contrast.

[Modifications]
In the following, modifications of the above embodiment will be described. For the sake of convenience, the same reference numerals will be used to designate members having the same functions as those described in the above embodiment, and redundant description will not be repeated.

(Variation 1)
The luminance calculation unit 123 may use, as an index indicating the brightness of the input image, the number or the ratio of pixels having a luminance value that satisfies a predetermined condition in the input image.

In the configuration of this modified example, the frame 34 in FIG. 7 may be shifted to the right as the number of pixels having a luminance value equal to or greater than a predetermined value as a luminance value that satisfies a predetermined condition increases, and the frame 34 may be shifted to the left as the number of pixels is fewer, and the subsequent processing may be performed. Alternatively, the frame 34 may be shifted to the left as the number of pixels having a luminance value equal to or less than a predetermined value as a luminance value that satisfies a predetermined condition increases, and the frame 34 may be shifted to the right as the number of pixels is greater, and the subsequent processing may be performed.

Note that in this disclosure, "brightness of the input image" does not necessarily mean the brightness of the entire input image. For example, the brightness calculation unit 123 may calculate an index value indicating the brightness of the input image based on an area that includes the center position of the input image and is approximately 80% to 90% in size of the input image.

The luminance calculation unit 123 may also divide the input image into a plurality of regions and calculate an index value indicating the brightness of the input image based on one or more of the regions. Alternatively, the luminance calculation unit 123 may calculate a different index value for each region, the range determination unit 124 may determine a limited range for each region, and the gamma curve correction unit 125 may correct the gamma curve applied to each region.

The luminance calculation unit 123 may also extract objects such as people, buildings, or backgrounds in the input image based on color or shape, for example using machine learning, and calculate an index value indicating the brightness of the extracted object and use either one of them. The luminance calculation unit 123 may also be configured to define the above-mentioned areas for each object extracted by the luminance calculation unit 123.

(Variation 2)
In the above embodiment, a configuration in which the range determination unit 124 determines a stepped restricted range, for example by shifting the frame 34 in accordance with the brightness of the input image, has been described with reference to Figures 7 to 12, but the range determination unit 124 is not limited to the above configuration.

The range determination unit 124 may limit the amount of correction within a predefined range when an index value indicating the brightness of the input image satisfies a predetermined condition. For example, the range determination unit 124 may determine that the predefined limit range illustrated in FIG. 3 is to be used when the index value indicating the brightness of the entire input image is less than a first predetermined value as the case where the index value satisfies the predetermined condition. The range determination unit 124 may also determine that the predefined limit range illustrated in FIG. 4 is to be used when the index value satisfies the predetermined condition and exceeds a second predetermined value as the case where the index value does not satisfy the predetermined condition. The range determination unit 124 may also determine that the limit range is, for example, a region that combines the lower right region 21 in FIG. 3 and the upper left region 21 in FIG. 4 as the limit range when the index value is equal to or greater than a first predetermined value and equal to or less than a second predetermined value.

In addition, this disclosure also includes a configuration in which the range determination unit 124 determines, for example, the area combining the upper left area 21 in FIG. 3 and the lower right area 21 in FIG. 4 as the restricted range, regardless of whether a predetermined condition for the index value is satisfied.

(Variation 3)
In the embodiment, a configuration in which the gamma curve is clipped when the gamma curve is within a limited range has been described, but the gamma curve correction unit 125 is not limited to the above configuration. For example, the gamma curve correction unit 125 may be configured to divide the gamma curve into certain sections and multiply the gain so that the gamma curve falls within an allowable range. If y[i] is the output gradation value when the gamma curve before correction is applied to the input gradation value i and the gain value is α, the gamma curve correction unit 125 may use, for example, the value of α*(y[i]-i)+i as the new value of y[i]. Moreover, the value of α is different for each section of the divided gamma curve.

The gamma curve correction unit 125 is not limited to a configuration that corrects the gamma curve based on the limited range determined by the range determination unit 124. For example, when a gamma curve portion corresponding to a low luminance region acts to increase the luminance of an input pixel, the gamma curve correction unit 125 may correct the gamma curve so as to multiply the correction amount corresponding to the gamma curve portion by a coefficient of 1 or less. When a gamma curve portion corresponding to a high luminance region acts to decrease the luminance of an input pixel, the gamma curve correction unit 125 may correct the gamma curve so as to multiply the correction amount corresponding to the gamma curve portion by a coefficient of 1 or less.

[Software implementation example]
The functions of the display device 1 (hereinafter referred to as the "device") can be realized by a program for causing a computer to function as the device, and a program for causing a computer to function as each control block of the device (particularly the input image control unit, the gamma curve setting unit 12, and the brightness correction unit 13).

In this case, the device includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., a memory) as hardware for executing the program. The functions described in each of the above embodiments are realized by executing the program using this control device and storage device.

The program may be non-transiently recorded on one or more computer-readable recording media. The recording media may or may not be included in the device. In the latter case, the program may be supplied to the device via any wired or wireless transmission medium.

In addition, some or all of the functions of each of the control blocks can be realized by a logic circuit. For example, an integrated circuit in which a logic circuit that functions as each of the control blocks is formed is also included in the scope of the present invention. In addition, it is also possible to realize the functions of each of the control blocks by, for example, a quantum computer.

The processes described in each of the above embodiments may be executed by AI (Artificial Intelligence). In this case, the AI may run on the control device, or on another device (such as an edge computer or a cloud server).

〔summary〕
A display device according to aspect 1 of the present invention is a display device that corrects the luminance of an input image based on a gamma curve that represents the relationship between pre-correction luminance and post-correction luminance, and is configured to include a gamma curve setting unit that limits the amount of correction in at least a portion of the gamma curve depending on the brightness of the input image, and a luminance correction unit that corrects the luminance of the input image based on the gamma curve with the amount of correction limited by the gamma curve setting unit.

In the display device according to aspect 2 of the present invention, in the above aspect 1, the gamma curve setting unit may be configured to limit the amount of correction of the gamma curve in the direction of increasing the brightness in low brightness areas to a greater extent as the brightness of the input image becomes darker.

The display device according to aspect 3 of the present invention may be configured in the above-mentioned aspect 1 or 2 such that the gamma curve setting unit limits the amount of correction of the gamma curve in the direction of decreasing the luminance in high luminance areas to a greater extent as the brightness of the input image increases.

In the display device according to aspect 4 of the present invention, in any one of aspects 1 to 3, the gamma curve setting unit may be configured to generate the gamma curve with the amount of correction limited by referring to a range corresponding to the brightness of the input image in a table that specifies the limited range of the gamma curve.

In the display device according to aspect 5 of the present invention, in any one of aspects 1 to 3, the gamma curve setting unit may be configured to limit the amount of correction within a predefined range when an index value indicating the brightness of the input image satisfies a predetermined condition.

The display device according to aspect 6 of the present invention may be configured in any one of aspects 1 to 5 above, such that the brightness of the input image is the average luminance level of the input image.

The display device according to aspect 7 of the present invention may be configured in any one of aspects 1 to 5 above, such that the brightness of the input image is the number or percentage of pixels in the input image that have a luminance value that is greater than or less than a predetermined value.

The correction method according to aspect 8 of the present invention is a correction method for correcting the luminance of an input image based on a gamma curve that represents the relationship between pre-correction luminance and post-correction luminance, and includes a gamma curve setting process that limits the amount of correction in at least a portion of the range of the gamma curve according to the brightness of the input image, and a luminance correction process that corrects the luminance of the input image based on the gamma curve with the amount of correction limited by the gamma curve setting unit.

The control program according to aspect 9 of the present invention is a control program for causing a computer to function as the display device according to aspect 1, and is a control program for causing a computer to function as the gamma curve setting unit and the brightness correction unit.

The display device according to each aspect of the present invention may be realized by a computer. In this case, the control program for the display device that causes the computer to operate as each unit (software element) of the display device to realize the display device, and the computer-readable recording medium on which the control program is recorded, also fall within the scope of the present invention.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Furthermore, new technical features can be formed by combining the technical means disclosed in the respective embodiments.

REFERENCE SIGNS LIST 1 Display device 11 Input image acquisition unit 12 Gamma curve setting unit 13 Luminance correction unit 14 Display unit 122 Gamma curve calculation unit 123 Luminance calculation unit 124 Range determination unit 125 Gamma curve correction unit

Claims (7)

A display device that corrects the luminance of an input image based on a gamma curve that represents a relationship between pre-correction luminance and post-correction luminance,
a gamma curve setting unit that performs a process of limiting a correction amount in at least a part of the range of the gamma curve by determining a limit range of the gamma curve in accordance with a brightness of the input image, and, if the gamma curve exceeds the limit range, corrects the gamma curve so that it falls within the limit range ;
a luminance correction unit that corrects the luminance of the input image based on the gamma curve in which the correction amount is limited by the gamma curve setting unit;
Equipped with
The gamma curve setting unit is
(1) A process for limiting the amount of correction of the gamma curve in a direction to increase luminance in a low luminance region to a greater extent as the brightness of the input image becomes darker, and (2) a process for limiting the amount of correction of the gamma curve in a direction to decrease luminance in a high luminance region to a greater extent as the brightness of the input image becomes brighter.
A display device comprising: The gamma curve setting unit is
2. The display device according to claim 1 , wherein the gamma curve with the limited correction amount is generated by referring to a range according to the brightness of the input image in a table that defines a limited range of the gamma curve. The gamma curve setting unit is
3. The display device according to claim 1, wherein, when the index value indicating the brightness of the input image satisfies a predetermined condition, an amount of correction is limited within a predefined range. 4. The display device according to claim 1, wherein the brightness of the input image is an average luminance level of the input image. 5. The display device according to claim 1, wherein the brightness of the input image is the number or ratio of pixels in the input image that have a luminance value that satisfies a predetermined condition. A correction method for correcting luminance of an input image based on a gamma curve that represents a relationship between pre-correction luminance and post-correction luminance, comprising:
a gamma curve setting step of determining a limit range of the gamma curve in accordance with the brightness of the input image as a process of limiting a correction amount in at least a part of the range of the gamma curve, and, if the gamma curve exceeds the limit range, correcting the gamma curve so that it falls within the limit range;
a luminance correction step of correcting the luminance of the input image based on the gamma curve in which the correction amount is limited in the gamma curve setting step;
Including,
In the gamma curve setting step,
(1) A process for limiting the amount of correction of the gamma curve in a direction to increase luminance in a low luminance region to a greater extent as the brightness of the input image becomes darker, and (2) a process for limiting the amount of correction of the gamma curve in a direction to decrease luminance in a high luminance region to a greater extent as the brightness of the input image becomes brighter.
A correction method comprising: A control program for causing a computer to function as the display device according to claim 1, the control program causing the computer to function as the gamma curve setting unit and the luminance correction unit.

Images