JP7601625B2 - Display device and display device control method - Google Patents

Description

The present invention relates to a display device and a method for controlling the display device.

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 (the 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.

For example, Patent Document 1 describes an image processing device (display device) that includes a correction interval setting unit, a correction interval division unit, a histogram calculation unit, a gain setting unit, a gamma curve generation unit, a gamma curve synthesis unit, and a luminance conversion unit.

The correction interval setting unit sets a correction interval, which is a range of luminance levels for which luminance correction processing is performed. The correction interval division unit divides the correction interval into a black side interval and a white side interval. The histogram calculation unit calculates the total number of luminance histograms in the black side interval and the white side interval.

The gain setting unit sets the gains of the gamma curve that increases the luminance and the gamma curve that decreases the luminance based on the total number of luminance histograms in the black side section and the white side section. For example, when the total number of luminance histograms in the black side section is greater, the gain setting unit sets a gain that increases the luminance of the correction section (e.g., the black side section), and when the total number of luminance histograms in the white side section is greater, the gain setting unit sets a gain that decreases the output luminance of the correction section.

The gamma curve generation unit generates a gamma curve that increases luminance and a gamma curve that decreases luminance based on the set gain. The gamma curve synthesis unit synthesizes the gamma curve that increases luminance and the gamma curve that decreases luminance outside the correction interval. The luminance conversion unit performs luminance conversion processing on the input luminance data within the correction interval using the synthesized gamma curve.

JP 2009-17200 A

However, while the conventional technology described above can reduce crushed blacks in the black section and blown whites in the white section, it does not generate a gamma curve that corrects the mid-luminance region of the correction section, and therefore cannot perform appropriate correction for each luminance in the entire input image.

Therefore, when the input image is corrected using the conventional techniques described above, for example, certain brightness areas are overemphasized, resulting in a lack of natural contrast. In other words, the contrast of the entire image cannot be increased.

One aspect of the present invention aims to correct an input image so that areas of specific luminance are not overly emphasized and a natural contrast is achieved.

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 in that it includes a gamma curve generation unit that generates a gamma curve based on the luminance distribution of the input image, a gamma curve correction unit that corrects the gamma curve generated by the gamma curve generation unit so that the difference between the gamma curve and a preset reference gamma curve falls within a first predetermined range, and a luminance correction unit that corrects the luminance of the input image based on the gamma curve corrected by the gamma curve correction unit.

A display device control method according to one aspect of the present invention is a display device control method 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 in that the display device includes a gamma curve generation process in which the display device generates a gamma curve based on the luminance distribution of the input image, a gamma curve correction process in which the display device corrects the gamma curve generated in the gamma curve generation process so that the difference between the gamma curve and a preset reference gamma curve falls within a first predetermined range, and a luminance correction process in which the display device corrects the luminance of the input image based on the gamma curve corrected in the gamma curve correction process.

According to one aspect of the present invention, an input image can be corrected so that areas of specific luminance are not overly emphasized and a natural contrast is achieved.

1 is a block diagram showing a configuration of a display device according to a first embodiment. 1 is a schematic diagram showing an external appearance of a display device according to a first embodiment. FIG. 4 is a diagram illustrating an example of a first histogram of an input image. FIG. 11 is a diagram illustrating an example of a second histogram. 11A and 11B are diagrams illustrating an example of a generated gamma curve and a histogram of the generated gamma curve. 11A and 11B are diagrams for explaining correction of a generated gamma curve. FIG. 2 is a diagram for explaining division of a gamma curve into a plurality of sections. 11A and 11B are diagrams illustrating an example of a corrected gamma curve and a histogram of the corrected gamma curve. 4 is a flowchart showing a control method of the display device according to the first embodiment. FIG. 11 is a block diagram showing a configuration of a display device according to a second embodiment. FIG. 11 is a diagram for explaining division of a generated gamma curve into a plurality of sections. 10 is a flowchart showing a control method of the display device according to the second embodiment.

<Embodiment 1>
A display device 1 according to the first embodiment and a method for controlling the display device 1 will be described below 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 relationship between pre-correction luminance and post-correction luminance.

Fig. 1 is a diagram showing the configuration of a display device 1 according to embodiment 1. Fig. 2 is a schematic diagram showing the external appearance of the display device 1 according to embodiment 1. As shown in Fig. 1, the display device 1 includes an input image acquisition unit 11, a gamma curve generation unit 12, a gamma curve correction unit 13, a luminance correction unit 14, and a display unit 15.

[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 generator 12]
The gamma curve generator 12 generates a gamma curve based on the luminance distribution of the input image. In the example shown in FIG. 1, the gamma curve generator 12 includes a first histogram generator 121 and a second histogram generator 122.

The gamma curve generating unit 12 generates a first histogram of the luminance of the input image, then generates a second histogram, which is a cumulative histogram of the luminance of the input image, based on the first histogram, and generates a gamma curve based on the second histogram.

For example, the gamma curve generation unit 12 generates a gamma curve that conforms to the shape of the cumulative histogram, which is the second histogram.

In this way, by generating a gamma curve based on the cumulative histogram of luminance of the input image, a gamma curve can be generated that more appropriately flattens the frequencies of all luminance.

The first histogram generation unit 121 and the second histogram generation unit 122 are described in detail below.

(First histogram generating unit 121)
The first histogram generation unit 121 generates a first histogram indicating the relationship between the luminance of pixels included in the input image acquired by the input image acquisition unit 11 and the frequency of each luminance in the input image, based on the luminance of pixels included in the input image acquired by the input image acquisition unit 11.

(Second histogram generating unit 122)
The second histogram generating unit 122 generates a second histogram based on the first histogram generated by the first histogram generating unit 121 .

Specifically, the second histogram generating unit 122 generates, based on the first histogram, a cumulative histogram that indicates the relationship between the luminance of pixels included in the input image and the cumulative relative frequency, which is the total frequency of the luminance of pixels included in the input image that is equal to or lower than a certain luminance, as the second histogram.

[Example of gamma curve generation by the gamma curve generation unit 12]
An example of the generation of a gamma curve by the gamma curve generator 12 will be described below with reference to FIGS.

Figure 3 shows an example of a first histogram of an input image. Figure 4 shows an example of a second histogram. Figure 5 shows the generated gamma curve C1 and the histogram of the generated gamma curve C1.

(Example of First Histogram Generation by First Histogram Generator 121)
First, the first histogram generating unit 121 in the gamma curve generating unit 12 generates a first histogram indicating the relationship between the luminance of pixels included in the input image and the frequency of each luminance in the input image, as shown in Fig. 3, based on the luminance of pixels included in the input image acquired by the input image acquiring unit 11. As shown in Fig. 3, the first histogram of the input image has a high frequency of a particular luminance, causing a bias.

(Example of Generation of Second Histogram by Second Histogram Generator 122)
Next, based on the first histogram, the second histogram generation unit 122 generates a cumulative histogram as a second histogram, which shows the relationship between the luminance of pixels contained in the input image and the cumulative relative frequency of each luminance in the input image, as shown in Figure 4.

(Example of gamma curve generation by the gamma curve generator 12)
Next, the gamma curve generator 12 generates a gamma curve C1 shown in the diagram of the generated gamma curve C1 in Fig. 5 based on the cumulative histogram, which is the second histogram. This reduces the bias in the frequency for each correction luminance, as shown in the diagram of the generated gamma curve C1 in Fig. 5.

In this way, by generating a gamma curve, it is possible to flatten the frequencies of histograms such as the second histogram. Also, by generating a gamma curve based on a cumulative histogram, which is the second histogram, it is possible to generate a gamma curve that more suitably flattens the frequencies of all luminances.

[Gamma curve correction unit 13]
The gamma curve correction unit 13 corrects the gamma curve generated by the gamma curve generation unit 12 so that the difference between the gamma curve and a preset reference gamma curve falls within a first predetermined range.

If the luminance of an input image is corrected using the gamma curve generated by the gamma curve generation unit 12 without correction, there is a possibility that highlight blowout and shadow crush will occur.

In contrast, in this embodiment, the luminance of the input image is corrected based on the gamma curve corrected by the gamma curve correction unit 13. This makes it possible to correct the luminance of the input image to achieve a natural contrast while preventing areas of specific luminance from being overemphasized, resulting in blown-out highlights and crushed shadows.

The reference gamma curve is a curve that serves as a reference when correcting the gamma curve generated by the gamma curve generation unit 12 by applying a gain, and the shape of the gamma curve after correction changes depending on the shape of the reference gamma curve. The shape of the reference gamma curve is not particularly limited, but may be linear.

By using a linear reference gamma curve, the gamma curve can be more appropriately corrected so that specific luminance regions of the generated gamma curve are not overly emphasized. This allows for a more appropriately corrected gamma curve that increases the contrast of the entire image while creating an image with natural contrast.

The reference gamma curve may also be one that reduces low luminance such as the black side section. This allows the input image to be corrected so that the contrast is emphasized.

In one aspect, the first predetermined range may be a range in which the absolute value is 10% or less of the maximum possible value of the pre-correction luminance and the post-correction luminance, centered on the reference gamma curve. For example, the first predetermined range may be a range from a value obtained by subtracting 10% from the maximum possible value of the pre-correction luminance and the post-correction luminance, centered on the reference gamma curve, to a value obtained by adding 10% to the maximum possible value of the pre-correction luminance and the post-correction luminance.

By setting the first predetermined range as such, it is possible to more effectively prevent areas of specific brightness from being overemphasized in the end, and to more appropriately correct each brightness of the entire input image to achieve a natural contrast.

In the above example, the first predetermined range is a range in which the absolute value of the pre-correction luminance and post-correction luminance is 10% or less of the maximum possible value centered on the reference gamma curve. However, the first predetermined range may be any range as long as it is a range in which a gamma curve that can be appropriately corrected for each luminance of the entire input image can be corrected to a natural contrast while preventing a specific luminance area from being overly emphasized.

For example, the first predetermined range may be a range from a value obtained by subtracting 5% of the maximum value of the pre-correction luminance and the post-correction luminance to a value obtained by adding 15% of the maximum value of the pre-correction luminance and the post-correction luminance, with the reference gamma curve at the center. The first predetermined range may also be a range from a value obtained by subtracting 15% of the maximum value of the pre-correction luminance and the post-correction luminance to a value obtained by adding 5% of the maximum value of the pre-correction luminance and the post-correction luminance, with the reference gamma curve at the center.

As shown in FIG. 1, the gamma curve correction unit 13 includes a section division unit (gamma curve correction unit) 141 and a correction amount determination unit (gamma curve correction unit) 142.

(Section division unit 131)
The section division unit 131 divides the gamma curve into a plurality of sections. This makes it possible to appropriately correct the gamma curve for each section without destroying the original shape of the gamma curve to such an extent that the characteristics of the gamma curve obtained by flattening a histogram such as the second histogram are lost. As a result, based on the corrected gamma curve, it is possible to correct the luminance of the input image to achieve a natural contrast by preventing crushed shadows and blown highlights while maintaining the effect of flattening the histogram.

The interval division unit 131 may divide the gamma curve into a plurality of intervals based on at least one of the intersections between the gamma curve generated by the gamma curve generation unit 12 and the reference gamma curve and the points between adjacent intersections on the gamma curve generated by the gamma curve generation unit 12. This makes it possible to more appropriately correct the gamma curve for each interval without destroying the original shape of the gamma curve to the extent that the characteristics of the gamma curve obtained by flattening a histogram such as the second histogram are lost.

For example, the interval division unit 131 may divide the gamma curve into multiple intervals based on the above-mentioned intersection point and a point on the gamma curve generated by the gamma curve generation unit 12 that is within a second predetermined range from the point where the difference between the gamma curve generated by the gamma curve generation unit 12 and the reference gamma curve is maximized. This makes it possible to more appropriately correct the gamma curve for each interval without destroying the original shape of the gamma curve to the extent that the characteristics of a gamma curve that flattens a histogram such as the second histogram are lost.

In one aspect, the second predetermined range may be a range in which the absolute value of the maximum possible value of the pre-correction luminance and the post-correction luminance is 10% or less, centered on the point where the difference between the gamma curve generated by the gamma curve generation unit 12 and the reference gamma curve is maximum. For example, the second predetermined range may be a range from a value obtained by subtracting 10% of the maximum value of the pre-correction luminance and the post-correction luminance to a value obtained by adding 10%, centered on the point where the difference between the gamma curve generated by the gamma curve generation unit 12 and the reference gamma curve is maximum.

By setting the second predetermined range to this range, the gamma curve can be corrected more appropriately so as to maintain the effect of flattening the histogram.

In the above example, the second predetermined range is a range in which the absolute value of the maximum possible value of the pre-correction luminance and post-correction luminance is 10% or less, centered on the point where the difference between the gamma curve generated by the gamma curve generating unit 12 and the reference gamma curve is maximum. However, the second predetermined range may be any range that can obtain the effect of appropriately correcting the gamma curve for each section so as not to lose the characteristics of the gamma curve obtained by flattening a histogram such as the second histogram.

For example, the second predetermined range may be a range from a value obtained by subtracting 5% of the maximum possible value of the pre-correction luminance and the post-correction luminance to a value obtained by adding 15% thereto, with the point at which the difference between the gamma curve generated by the gamma curve generation unit 12 and the reference gamma curve at its maximum center. Also, the second predetermined range may be a range from a value obtained by subtracting 15% of the maximum possible value of the pre-correction luminance and the post-correction luminance to a value obtained by adding 5% thereto, with the point at which the difference between the gamma curve generated by the gamma curve generation unit 12 and the reference gamma curve at its maximum center.

The number of sections into which the gamma curve is divided is preferably 2 or more and 4 or less. By dividing the gamma curve into 2 or more and 4 or less sections, the gamma curve can be corrected more appropriately for each section without destroying the original shape of the gamma curve to the extent that the characteristics of the gamma curve obtained by flattening a histogram such as the second histogram are lost.

[Example of section division of gamma curve by section division unit 131]
(Example 1 of Section Division of Gamma Curve by Section Division Unit 131)
An example of division of a gamma curve into sections by the section division unit 131 will be described below with reference to Fig. 6. Fig. 6 is a diagram for explaining correction of a generated gamma curve.

The section division unit 131 divides the gamma curve C1 into a number of sections based on the intersection points P1, P3, and P5 between the gamma curve C1 generated by the gamma curve generation unit 12 and the reference gamma curve C2, and on the points P2 and P4 between adjacent intersection points P1, P3, and P5 on the gamma curve C1 where the difference between the gamma curve C1 and the reference gamma curve C2 is maximum.

Specifically, the interval division unit 131 divides the gamma curve C1 into intervals S1, S2, S3, and S4 surrounded by intersection points P1, P3, and P5, and points P2 and P4 where the difference between the gamma curve C1 and the reference gamma curve C2 is maximum, as division points.

This allows the gamma curve to be appropriately corrected for each section without distorting the original shape of the gamma curve so much that the characteristics of the gamma curve obtained by flattening a histogram such as the second histogram are lost.

(Example 2 of Section Division of Gamma Curve by Section Division Unit 131)
Another example of division of a gamma curve into sections by the section division section 131 will be described below with reference to Fig. 7. Fig. 7 is a diagram for explaining division of a gamma curve C1 into a plurality of sections.

The section division unit 131 divides the gamma curve C1 into a plurality of sections based on the intersection points P1, P3, and P5 between the gamma curve C1 generated by the gamma curve generation unit 12 and the reference gamma curve C2, and on points P6 and P7 between adjacent intersection points P1, P3, and P5 on the gamma curve C1 that are within a second predetermined range R2 from points P2 and P4 where the difference between the gamma curve C1 and the reference gamma curve C2 is maximum.

Specifically, the section division unit 131 divides the gamma curve C1 into sections S1a, S2a, S3a, and S4a surrounded by intersection points P1, P3, and P5, as well as points P6 and P7 that are within a second predetermined range R2 from points P2 and P4 where the difference between the gamma curve C1 and the reference gamma curve C2 is at a maximum.

The second predetermined range R2 shown in FIG. 7 is centered on points P2 and P4 where the difference between gamma curve C1 and reference gamma curve C2 is maximum, and is a range from a value obtained by subtracting 10% of the maximum value on the X axis in FIG. 7, which is the maximum value of the pre-correction luminance, to a value obtained by adding 10%, and from a value obtained by subtracting 10% of the maximum value on the Y axis in FIG. 7, which is the maximum value of the post-correction luminance, to a value obtained by adding 10%. In addition, the X-axis values of points P6 and P7 are the pre-correction luminances of points P2 and P4, respectively, plus 10% of the maximum value on the X axis in FIG. 7, which is the maximum value of the pre-correction luminance.

(Correction Amount Determination Unit 142)
The correction amount determination unit 142 determines the amount of correction for the gamma curve generated by the gamma curve generation unit 12 so that the difference from the reference gamma curve falls within a first predetermined range.

For example, the correction amount determination unit 142 determines the amount of correction for the gamma curve in each of the multiple sections into which the gamma curve is divided, so that the difference from the reference gamma curve falls within a first predetermined range.

In this way, by determining the amount of gamma curve correction for each divided section and locally applying a gain corresponding to the amount of correction to the gamma curve for each divided section, the input image can be more suitably corrected to improve contrast without creating an unnatural image.

(Example of gamma curve correction amount determination by the correction amount determination unit 142)
An example of how the correction amount determination unit 142 determines the correction amount of the gamma curve will be described below with reference to Figures 6 and 8. Figure 8 is a diagram showing a corrected gamma curve C1a and a histogram of the corrected gamma curve C1a.

The correction amount determination unit 142 determines the correction amount of the gamma curve C1 in each section S1, S2, S3, and S4 surrounded by the division points so that the differences L1 and L2 from the reference gamma curve C2 fall within a first predetermined range R1.

The first predetermined range R1 shown in FIG. 6 is centered on the reference gamma curve C2 and ranges from a value obtained by subtracting 10% from the maximum value on the horizontal axis in FIG. 6, which is the maximum value of the pre-correction luminance, to a value obtained by adding 10%, and from a value obtained by subtracting 10% from the maximum value on the Y axis in FIG. 6, which is the maximum value of the post-correction luminance, to a value obtained by adding 10%.

(Determination of the correction amount of the gamma curve C1 in the sections S1 and S2)
In sections S1 and S2, the difference L1 from the reference gamma curve C2, which is the difference from point P2 where the difference between the gamma curve C1 and the reference gamma curve C2 is maximized, falls within a first predetermined range R1.

In this way, when L1≦R1, the correction amount determination unit 142 determines the value of the gain (correction amount) α to be multiplied by the gamma curve C1 in sections S1 and S2 to be 1, and determines the correction amount of the gamma curve C1 so as to correct the gamma curve C1 to the gamma curve C1a shown in the following equation (1).
Yout(X)=α*(Yin(X)-X)+Yref(X)...(1)
Here, X is the X-axis coordinate of the graph in FIG. 6, Y is the Y-axis coordinate of the graph in FIG. 6, Yin(X) is the gamma curve C1, Yout(X) is the corrected gamma curve C1a, and Yref(X) is the reference gamma curve C2.

By determining the correction amount in this manner, in sections S1 and S2, which are the low-luminance black side sections, the shape of the gamma curve obtained by flattening a histogram such as the cumulative histogram, which is the second histogram, can be maintained, and the effect of flattening the histogram can be maintained.

In the above example, the correction amount determination unit 142 determines the gain α by which the gamma curve C1 in the sections S1 and S2 is multiplied to 1 depending on the difference L1 from the reference gamma curve C2 and the size of the first predetermined range R1. However, in this embodiment, the correction amount determination unit 142 may determine the gain α by which the gamma curve C1 in each section is multiplied based on the following equations (2) and (3) using a and b that indicate the X coordinates of the start point and end point of each section.
|(Yin(a)-a)-(Yin(b)-b)|>R1, α=R1/|(Yin(a)-a)-(Yin(b)-b)|...(2)
|(Yin(a)-a)-(Yin(b)-b)|≦R1, α=1...(3)
That is, in section S1, the correction amount determination unit 142 may use X1, which is the start point of section S1, and X2, which is the end point of section S1, to determine the gain α to be multiplied by the gamma curve C1 in section S1 depending on whether |(Yin(X1)-X1)-(Yin(X2)-X2)| is larger than the first predetermined range R1.

In addition, in section S2, the correction amount determination unit 142 may use X2, which is the start point of section S2, and X3, which is the end point of section S2, to determine the gain α to be multiplied by the gamma curve C1 in section S2 depending on whether |(Yin(X2)-X2)-(Yin(X3)-X3)| is larger than the first predetermined range R1.

(Determination of the correction amount of the gamma curve C1 in sections S3 and S4)
In sections S3 and S4, the difference L2 from the reference gamma curve C2, which is the difference between the point P4 at which the difference between the gamma curve C1 and the reference gamma curve C2 is maximized and is the difference between the point P4 and the reference gamma curve C2, does not fall within the first predetermined range R1, and L2>R1.

In this case, the correction amount determination unit 142 determines the amount of correction to move point P4, where the difference between the gamma curve C1 and the reference gamma curve C2 is maximized, in the direction of the arrow in FIG. 6 so that the point falls within the first predetermined range R1 in sections S3 and S4.

For example, in section S3, the correction amount determination unit 142 determines the value of gain α to be the value shown in the following formula (4) using X3, which is the start point of section S3, and X4, which is the end point of section S3. The correction amount determination unit 142 also determines the correction amount of the gamma curve C1 so as to correct the gamma curve C1a obtained by substituting formula (4) into the above formula (1).
α=R1/|(Yin(X3)-X3)-(Yin(X4)-X4)|...(4)
In addition, in section S4, the correction amount determination unit 142 determines the value of gain α to be the value shown in the following formula (5) using X4, which is the start point of section S4, and X5, which is the end point of section S4. In addition, the correction amount determination unit 142 determines the correction amount of the gamma curve C1 so as to correct the gamma curve C1 to the gamma curve C1a obtained by substituting formula (5) into the above formula (1).
α=R1/|(Yin(X4)-X4)-(Yin(X5)-X5)|...(5)
Based on the amount of correction determined by the correction amount determination unit 142, the gamma curve correction unit 13 corrects the gamma curve C1 to C1a shown in the diagram of the gamma curve after correction in Fig. 8. As a result, as shown in the histogram of the gamma curve after correction in Fig. 8, in sections S3 and S4 that are high-luminance white-side sections, it is possible to correct the gamma curve C1 to the gamma curve C1a of the histogram that can correct the input image to prevent overexposure and achieve a natural contrast.

In the above example, the correction amount determination unit 142 determines the gain α by which the gamma curve C1 in the sections S3 and S4 is multiplied depending on whether the difference L2 from the reference gamma curve C2 is larger or smaller than the first predetermined range R1. However, in this embodiment, the correction amount determination unit 142 may determine the gain α by which the gamma curve C1 in the section S3 is multiplied depending on whether |(Yin(X3)-X3)-(Yin(X4)-X4)| is larger or smaller than the first predetermined range R1, using X3, which is the start point of the section S3, and X4, which is the end point of the section S3.

In addition, in section S4, the correction amount determination unit 142 may use X4, which is the start point of section S4, and X5, which is the end point of section S4, to determine the gain α to be multiplied by the gamma curve C1 in section S4 depending on whether |(Yin(X4)-X4)-(Yin(X5)-X5)| is larger than the first predetermined range R1.

[Brightness correction unit 14]
The luminance correction unit 14 corrects the luminance of the input image based on the gamma curve corrected by the gamma curve correction unit 14. This makes it possible to perform appropriate correction for each luminance of the entire input image based on the corrected gamma curve so that a specific luminance area is not overemphasized and a natural contrast is achieved.

[Display unit 15]
The display unit 15 displays the image whose luminance has been corrected by the luminance correction unit 14 .

[Control method of display device 1]
Next, a method for controlling the display device 1 according to the first embodiment will be described with reference to Fig. 9. Fig. 9 is a flowchart showing the method for controlling the display device 1 according to the first embodiment.

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

(Step S102)
The first histogram generating section 121 in the gamma curve generating section 12 of the display device 1 generates a first histogram based on the luminance of pixels included in the input image acquired by the input image acquiring section 11 (first histogram generating step).

Specifically, the first histogram generating unit 121 generates a first histogram that indicates the relationship between the luminance of pixels contained in the input image and the frequency of each luminance in the input image, based on the luminance of the pixels in the input image acquired by the input image acquiring unit 11.

(Step S103)
The second histogram generating section 122 in the gamma curve generating section 12 of the display device 1 generates a second histogram based on the first histogram generated by the first histogram generating section 121 (second histogram generating step).

Specifically, the second histogram generating unit 122 generates a cumulative histogram as the second histogram based on the first histogram, which indicates the relationship between the luminance of pixels included in the input image and the cumulative relative frequency of each luminance in the input image.

(Step S104)
The gamma curve generating section 12 of the display device 1 generates a gamma curve based on the luminance distribution of the input image (gamma curve generating step).

For example, the gamma curve generation unit 12 generates a gamma curve based on the second histogram generated by the second histogram generation unit 122.

(Step S105)
The section dividing section 131 in the gamma curve correction section 13 of the display device 1 divides the gamma curve into a plurality of sections (section dividing step).

The interval division unit 131 may divide the gamma curve into multiple intervals based on at least one of the intersection points between the gamma curve generated by the gamma curve generation unit 12 and the reference gamma curve and the points between adjacent intersection points on the gamma curve generated by the gamma curve generation unit 12.

For example, the section division unit 131 may divide the gamma curve into multiple sections based on the above-mentioned intersection points and points on the gamma curve generated by the gamma curve generation unit 12 where the difference between the gamma curve generated by the gamma curve generation unit 12 and the reference gamma curve is maximum.

(Step S106)
The correction amount determination section 142 in the gamma curve correction section 13 of the display device 1 determines the amount of correction for the gamma curve generated by the gamma curve generation section 12 so that the difference from the reference gamma curve falls within a first predetermined range.

For example, the correction amount determination unit 142 determines the correction amount of the gamma curve for each of the multiple intervals into which the gamma curve generated by the gamma curve generation unit 12 is divided, so that the difference from the reference gamma curve falls within a first predetermined range (correction amount determination process).

(Step S107)
The gamma curve correction unit 13 of the display device 1 corrects the gamma curve generated in the gamma curve generation process so that the difference between the gamma curve and a preset reference gamma curve falls within a first predetermined range (gamma curve correction process).

For example, the gamma curve correction unit 13 corrects the gamma curve generated in the gamma curve generation process based on the correction amount determined for each of the multiple divided sections.

(Step S108)
The luminance correction unit 14 of the display device 1 corrects the luminance of the input image based on the gamma curve corrected in the gamma curve correction process (luminance correction process).

(Step S109)
The display unit 15 of the display device 1 displays the image whose luminance has been corrected in the luminance correction process (display process).

[Modifications]
(Variation 1)
In the above example, the gamma curve generator 12 includes a first histogram generator 121 and a second histogram generator 122. After generating a first histogram of the luminance of the input image, the gamma curve generator 12 generates a second histogram, which is a cumulative histogram of the luminance of the input image, based on the first histogram, and generates a gamma curve based on the second histogram.

However, in this embodiment, the gamma curve generator 12 may generate a gamma curve by any method as long as it can generate a gamma curve in which the luminance frequency is flattened based on the luminance distribution of the input image. For example, the gamma curve generator 12 may not include either or both of the first histogram generator 121 and the second histogram generator 122.

As an example, the gamma curve generating unit 12 may include only the first histogram generating unit 121, and generate a gamma curve based on the first histogram generated by the first histogram generating unit 121.

The gamma curve generating unit 12 may include only the second histogram generating unit 122, which generates a cumulative histogram directly from the input image, and generates a gamma curve based on the cumulative histogram.

The gamma curve generating unit 12 may generate a gamma curve based on the first histogram or the second histogram acquired together with the input image from an external receiving unit, an external device, or a reading unit via the input image acquiring unit 11.

The gamma curve generation unit 12 may also acquire a histogram other than the first histogram and the second histogram along with the input image from an external receiving unit, external device, or reading unit via the input image acquisition unit 11, and generate a gamma curve based on the histogram.

However, since the gamma curve generating unit 12 can generate a gamma curve so that the frequencies of all luminances are more suitably flattened, it is preferable to generate the gamma curve based on the cumulative histogram, which is the second histogram.

(Variation 2)
The display device 1 may further include a high dynamic range processing unit (not shown).

For example, the high dynamic range processing unit may perform high dynamic range processing to expand the dynamic range of the subject in the image signal of the input image whose luminance has been corrected by the luminance correction unit. This makes it possible to correct the input image to enhance contrast while preventing blown-out highlights and crushed blacks in the shadow areas.

Examples of high dynamic range processing include, but are not limited to, well-known high dynamic range processing using absolute luminance methods such as PQ (Perceptual Quantization) and relative luminance methods such as HLG (Hybrid log gamma).

<Embodiment 2>
The display device according to the present invention may divide the gamma curve into a plurality of equal intervals, like the display device 1X according to the second embodiment.

The display device 1X according to the second embodiment will be described below with reference to Figures 10 to 12. For ease of explanation, the same reference numerals are used to designate components having the same functions as those described in the above embodiment, and their explanation will be omitted.

[Display device 1X]
Fig. 10 is a block diagram showing the configuration of a display device 1X according to embodiment 2. As shown in Fig. 10, the display device 1X includes a gamma curve correction unit 13X instead of the gamma curve correction unit 13 in embodiment 1. Except for this, the display device 1X according to embodiment 2 has the same configuration as the display device 1 according to embodiment 1.

[Gamma curve correction unit 13X]
The gamma curve correction section 13X includes a section division section 131X instead of the section division section 131 in the first embodiment. Except for this, the gamma curve correction section 13X has the same configuration as the gamma curve correction section 13 in the first embodiment.

(Section division unit 131X)
The interval division unit 131X divides the gamma curve into a plurality of equal intervals, thereby making it possible to effectively divide the gamma curve while appropriately correcting the gamma curve for each interval without destroying the original shape of the gamma curve to such an extent that the characteristics of the gamma curve obtained by flattening a histogram such as the second histogram are lost.

(Example of Section Division of Gamma Curve by Section Division Unit 131X)
An example of division of a gamma curve into sections by the section division unit 131X will be described below with reference to Fig. 11. Fig. 11 is a diagram for explaining division of the generated gamma curve C1 into a plurality of sections.

The interval division unit 131X divides the gamma curve C1 into four equal intervals S1X, S2X, S3X, and S4X. In this way, by equally dividing the gamma curve C1 into a number between 2 and 4, the gamma curve C1 can be divided efficiently while appropriately correcting the gamma curve C1 for each interval so as not to lose the characteristics of the gamma curve C1, which has a flattened histogram such as the second histogram.

[Control method of display device 1X]
Next, a control method of the display device 1X according to the second embodiment will be described with reference to Fig. 12. Fig. 12 is a flowchart showing a control method of the display device 1X according to the second embodiment. Steps S201 to S204 and S206 to S209 in Fig. 12 are similar to steps S101 to S104 and S106 to S109 in Fig. 10, and therefore description thereof will be omitted here.

(Step S205)
The section dividing section 131X in the gamma curve correction section 13X of the display device 1X divides the gamma curve into a plurality of equal sections (section dividing step).

[Software implementation example]
The control blocks of the display devices 1 and 1X may be realized by a logic circuit (hardware) formed in an integrated circuit (IC chip) or the like, or may be realized by software.

In the latter case, the display devices 1 and 1X are provided with a computer that executes instructions of a program, which is software that realizes each function. This computer is provided with, for example, at least one processor (control device) and at least one computer-readable recording medium that stores the program. The object of the present invention is achieved by the processor reading the program from the recording medium and executing it in the computer. The processor can be, for example, a CPU (Central Processing Unit). The recording medium can be a "non-transient tangible medium", such as a ROM (Read Only Memory), tape, disk, card, semiconductor memory, programmable logic circuit, etc. The display device can also be provided with a RAM (Random Access Memory) that expands the program. The program can also be supplied to the computer via any transmission medium (such as a communication network or broadcast waves) that can transmit the program. Note that one aspect of the present invention can also be realized in the form of a data signal embedded in a carrier wave, in which the program is embodied by electronic transmission.

〔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 includes a gamma curve generation unit that generates a gamma curve based on the luminance distribution of the input image, a gamma curve correction unit that corrects the gamma curve generated by the gamma curve generation unit so that a difference between the gamma curve and a preset reference gamma curve falls within a first predetermined range, and a luminance correction unit that corrects the luminance of the input image based on the gamma curve corrected by the gamma curve correction unit.

In the display device according to aspect 2 of the present invention, in the above aspect 1, the gamma curve generation unit may be configured to generate the gamma curve based on a cumulative histogram of the luminance of the input image.

The display device according to aspect 3 of the present invention may be configured in accordance with aspect 1 or 2 above, in which the reference gamma curve is linear.

In the display device according to aspect 4 of the present invention, in any one of aspects 1 to 3 above, the gamma curve correction unit may be configured to determine the amount of correction of the gamma curve in each of a plurality of sections into which the gamma curve is divided, so that the difference from the reference gamma curve falls within the first predetermined range.

The display device according to aspect 5 of the present invention may be configured in the above-mentioned aspect 4 such that the gamma curve correction unit divides the gamma curve into the multiple sections based on at least one of the intersection points between the gamma curve generated by the gamma curve generation unit and the reference gamma curve and the points between adjacent intersection points on the gamma curve generated by the gamma curve generation unit.

In the display device according to aspect 6 of the present invention, in the above aspect 5, the gamma curve correction unit may be configured to divide the gamma curve into the multiple sections based on the intersection point and a point within a second predetermined range from a point on the gamma curve generated by the gamma curve generation unit where the difference between the gamma curve generated by the gamma curve generation unit and the reference gamma curve is maximized.

The display device control method according to aspect 7 of the present invention is a 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 generation process in which the display device generates a gamma curve based on the luminance distribution of the input image, a gamma curve correction process in which the display device corrects the gamma curve generated in the gamma curve generation process so that the difference between the gamma curve and a preset reference gamma curve falls within a first predetermined range, and a luminance correction process in which the display device corrects the luminance of the input image based on the gamma curve corrected in the gamma curve correction process.

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 on the computer, 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.

1, 1X Display device 12 Gamma curve generation unit 13, 13X Gamma curve correction unit 14 Brightness correction unit 131, 131X Section division unit (gamma curve correction unit)
132 Correction amount determination unit (gamma curve correction unit)
C1, C1a Gamma curve C2 Reference gamma curve L1, L2 Difference P1, P3, P5 Intersection P2, P4, P6, P7 Point R1 First predetermined range R2 Second predetermined range S1, S1a, S1X, S2, S2a, S2X, S3, S3a, S3X, S4, S4a, S4X Section α Gain (correction amount)

Claims (6)

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 generator that generates a gamma curve based on the luminance distribution of the input image;
a gamma curve correction unit that corrects the gamma curve generated by the gamma curve generation unit so that a difference between the gamma curve and a preset reference gamma curve falls within a first predetermined range;
a luminance correction unit that corrects the luminance of the input image based on the gamma curve corrected by the gamma curve correction unit ,
The display device is characterized in that the gamma curve correction unit determines, for each of a plurality of intervals into which the gamma curve is divided, an amount of correction of the gamma curve in that interval so that a difference from the reference gamma curve falls within the first predetermined range . The display device according to claim 1, characterized in that the gamma curve generation unit generates the gamma curve based on a cumulative histogram of the luminance of the input image. The display device according to claim 1 or 2, characterized in that the reference gamma curve is linear. 3. The display device according to claim 1, wherein the gamma curve correction unit divides the gamma curve into the plurality of sections based on at least one of an intersection point between the gamma curve generated by the gamma curve generation unit and the reference gamma curve and a point between adjacent intersection points on the gamma curve generated by the gamma curve generation unit. 5. The display device according to claim 4, wherein the gamma curve correction unit divides the gamma curve into the plurality of sections based on the intersection point and a point within a second predetermined range from a point on the gamma curve generated by the gamma curve generation unit where a difference between the gamma curve generated by the gamma curve generation unit and the reference gamma curve is maximized. A method for controlling 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, comprising:
a gamma curve generating step in which the display device generates a gamma curve based on a luminance distribution of the input image;
a gamma curve correction step in which the display device corrects the gamma curve generated in the gamma curve generation step so that a difference between the gamma curve and a preset reference gamma curve falls within a first predetermined range;
a luminance correction step of correcting a luminance of the input image based on the gamma curve corrected in the gamma curve correction step ,
a step of determining, for each of a plurality of sections into which the gamma curve is divided, a correction amount for the gamma curve in that section so that a difference from the reference gamma curve falls within the first predetermined range .

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