JP2015138108A - Display and image quality adjusting unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow reproduction of brightness feeling which is felt when one looked at an original at a dark place, when one looks at a display at a bright place, to reproduce and display an image and video which were looked at when one looked at them mainly by rod photoreceptor cell view.SOLUTION: A display for displaying an image and video comprises: calculation means for calculating an estimated average luminance value during imaging, based on an average luminance value and a gradation number of a displayed image; and contrast correction means for changing contrast of the displayed image. The contrast correction means performs contrast correction to the displayed image, when the luminance value calculated by the calculation means is lower than a threshold.

Description

  The present invention relates to a display device and an image quality adjustment device, and more particularly to a technique suitable for use in an image quality improvement circuit that improves display image quality in a display or television that needs to be displayed in a bright environment such as a living room.

  Conventionally, when viewing a display device in a bright environment, the brightness is increased by the illuminance around the display device, the color saturation is increased, or the contrast is increased so that the viewer can easily see the display device. Processing of images is performed. Furthermore, the color temperature of the display device is changed in accordance with the sunlight around the display device or the color temperature of illumination. This is because, due to eye characteristics, there is a phenomenon in which the color temperature of the display device looks high in an environment where the color temperature is low, and the color temperature of the display device appears low in an environment where the color temperature is high.

  Here, as a characteristic of the eye, the working ratio of two photoreceptor cells of cone cells (hereinafter referred to as cones) and rod cells (hereinafter referred to as rods) changes according to the brightness. I know. In bright places, cones mainly work, and in dark places, rods mainly work. Such changes in eye characteristics due to brightness are referred to as Purkinje transition. The cone can recognize three colors of RGB, whereas the rod can recognize only monochrome, and the frequency that is the center of sensitivity is different. Therefore, when the proportion of the body vision increases in a dark place, the color density and the color temperature look different due to Purkinje transition.

  Therefore, Patent Documents 1, 2, and 3 disclose techniques for correcting color temperature and color density with respect to Purkinje transition that occurs according to the viewing environment. That is, when the environmental luminance and the APL value are lower than a certain level, image processing is performed so that the color temperature is increased and the color density is increased. Here, APL is an abbreviation of Average Picture Level, and is a value obtained by averaging the number of gradations of one frame image.

  Further, as another characteristic of the eye, there is a Bartleson-Breneman effect in which the brightness that appears to be the same brightness is different between dark and bright. Patent Document 4 discloses a technique for changing the gamma curve according to the brightness of the external environment according to this effect. That is, the technique disclosed in Patent Document 4 uses a gamma curve that increases the contrast when the external environmental brightness is bright, and uses a gamma curve that decreases the contrast when the environmental brightness is dark. .

  Patent Document 5 discloses a technique for changing the brightness of a screen in accordance with the Bartleson-Breneman effect. That is, the technique disclosed in Patent Document 5 increases the luminance accordingly when the viewing environment is bright. Note that increasing the brightness means increasing the contrast as a whole.

  Japanese Patent Application Laid-Open No. H10-228688 discloses a technique for setting the lightness to an inverse S-curve and the chromaticity to an S-curve according to the characteristics of the cone with respect to the output of the photographing apparatus. The technique disclosed in Patent Document 6 changes the brightness and chromaticity according to the characteristics of only the cone, and the brightness and chromaticity are constant regardless of the shooting environment or viewing environment.

  Further, Non-Patent Document 1 discloses a variation in brightness feeling due to human visual characteristics according to environmental brightness.

JP 2006-285063 A JP 2007-248936 A JP 2007-248935 A JP 2010-72141 A JP 2010-79064 A JP 2007-158388 A

Herbert Grosskopf: Der Einfluss der Heligkeit-sempfindung die Bilbertragung Fernseheu, Rundfundtechniche Mittelungen, Jg 7, Nr. 4, (1963) 205-223

  Here, let us consider a case where an image or video captured electronically in a dark place (hereinafter referred to as a dark place) is viewed in a bright environment. When an image is taken in a dark place and the image or video is viewed using a display device in a bright environment, the following mismatch occurs. Unlike a human eye, a Purkinje transition does not occur in an imaging device in a dark place, and the Purkinje transition does not occur visually because an image is viewed on a display device placed in a bright environment. In this case, the display on the display device is seen differently from the way it looks when it is seen under the influence of Purkinje transition in a dark place.

  It is disclosed in Non-Patent Document 1 that the difference between the rod and the cone is not only the influence on the color that is considered to be Purkinje transition, but also the contrast looks different. In the dark, there was a problem that the dynamic range was widened by the main work of the frame.

  In view of the above-described problems, the present invention makes it possible to reproduce the feeling of brightness that was seen when viewing the real object in a dark place when viewing the display device in a bright place. The purpose is to make it possible to reproduce and display images and videos that were visible at the time.

  The display device of the present invention is a display device for displaying an image and a video, a calculation means for calculating an assumed average luminance value at the time of photographing from the average luminance value and the number of gradations of the display image, and the contrast of the display image. And a contrast correction unit that changes the display image when the luminance value calculated by the calculation unit is lower than a certain threshold value.

  According to the present invention, it is possible to reproduce the feeling of brightness that was seen when the real thing was seen in a dark place when the display device was seen in a bright place. Reproduced images and videos can be displayed. As a result, it is possible to display an image and a video that have an atmosphere in the dark part area and look at the real thing in the dark place.

It is a block diagram which shows the structural example of the contrast correction circuit of 1st Embodiment. It is a block diagram which shows the example of a whole structure of the display apparatus in 1st Embodiment. It is a figure for demonstrating an inverse gamma conversion process. It is the figure which evaluated the perception of the brightness with respect to different ambient luminance. It is a figure which shows the ratio which acts on the sensitivity of a cone and a rod with respect to the average brightness | luminance in a visual field. It is the figure which showed the ratio of contrast with the assumption average luminance value at the time of imaging | photography. It is a figure which shows the ratio of the contrast with respect to the average luminance in a visual field at the time of viewing. It is a figure which shows the result of having calculated the ratio with respect to the contrast value of contrast value and the gamma 2.2 for every reverse gamma value. It is a characteristic view which shows the control value of the reverse gamma value of the dark part with respect to the average brightness | luminance in a visual field. It is a figure for demonstrating the relationship between the real image image | photographed in the real environment of different brightness, and the display image in different ambient luminance. It is a figure which shows the brightness | luminance detection range of the cone view and the rod view with respect to the average brightness | luminance in a visual field. It is a figure which shows the result of having calculated the average luminance value in a visual field from screen edge illumination intensity and an average gradation. It is a block diagram which shows the structural example of the contrast correction circuit of 3rd Embodiment. It is a block diagram which shows the structural example of the contrast correction circuit of 4th Embodiment. It is a block diagram which shows the structural example of the image quality adjustment apparatus of 5th Embodiment. It is explanatory drawing of the contrast correction table in 6th Embodiment. It is a figure which shows the relationship between the average brightness | luminance in a visual field, and the contrast correction amount implemented. It is a figure which shows the 2nd example of the ratio exerted on the sensitivity of a cone and a rod with respect to the average luminance within a visual field. It is a figure which shows the 2nd example of required contrast with respect to the average brightness | luminance in a visual field.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments to which the invention is applied will be described in detail with reference to the accompanying drawings.
First, an outline of the present embodiment will be described with reference to FIG. FIG. 10 is a diagram for explaining the relationship between an actual image shot in an actual environment with different brightness and a display image with different ambient luminance.

  In FIG. 10, 101 is a real image taken in a bright real environment, 102 is an environment where the periphery of the display device is dark, and 103 is a bright display image. Reference numeral 104 denotes a real image taken in a dark real environment, 105 denotes an environment in which the periphery of the display device is bright, and 106 denotes a dark display image.

  When the real image 101 photographed in a bright real environment is viewed as the display image 103 in the dark environment 102, Purkinje transition occurs because the environment is dark, and the display image 103 looks bluish and the color appears light.

  On the other hand, in the real image 104 photographed in a dark real environment, the scenery that is actually viewed looks like a state in which Purkinje transition has occurred. However, no Purkinje transition occurs in the camera, and no Purkinje transition occurs in the bright environment 105. Therefore, as a result, the display image 106 also appears as an image in which no Purkinje transition has occurred.

As described above, the appearance changes depending on whether it is actually viewed in a dark place or on a display device.
Therefore, in an embodiment to be described later, when the actual image 104 photographed in a dark actual environment is an image within a range where Purkinje transition occurs, the contrast ratio of the display image 106 is lowered. As a result, a display state as if viewed in a dark environment 102 is created.

  In order to change the contrast ratio according to the ratio of the rod vision and to fully exhibit the effect of the present invention, the brightness is switched from the cone to the rod according to the change in the brightness. It is necessary to know the characteristics. Moreover, in order to fully demonstrate the effects of the present invention, it is necessary to know the characteristics of the brightness at which the cone is switched to the rod according to the change in brightness.

FIG. 11 is a diagram illustrating a luminance detection range of cone-view and rod-view with respect to the average brightness in the visual field.
In FIG. 11, the vertical axis represents the average luminance within the visual field. The visual luminance detection range, that is, the dynamic range of the eye is said to be 10 6 to 10 power. On the other hand, the in-view luminance range when watching TV in the living room is between several Cd / m ² and several hundred Cd / m ² . The luminance range in the field of view when looking at the projector in the theater room is 0. It is between several Cd / m ² and several tens of Cd / m ² .

The luminance range in which the cone view works is 0.1 Cd / m ² or more, and the luminance detection range in the rod view is 10 Cd / m ² or less. In the region of 0.1 Cd / m ² to 10 Cd / m ² , both photoreceptor cells work without being saturated.

The view from the cone view to the rod view is not switched like a switch, but is seen with a synthetic sensitivity composed of a composite view of the cone and the rod. When the eye adaptation is finished, when the average luminance in the visual field is about 1 Cd / m ² , the ratio of the cone view to the rod view on the sensitivity of the composite view is about 1: 1, that is, about It is said to be half each.

  In the theater room, viewing is performed almost within the luminance detection range of synthetic vision, so viewing is performed with a contrast obtained by combining the contrasts of both photoreceptor cells. In a normal living room, viewing is mostly performed in a cone-shaped luminance detection range, and only in a dark living room, viewing is performed in a synthetic vision luminance detection range.

On the other hand, when the actual object is directly viewed, if it is 10 Cd / m ² or less, it is the luminance detection range of the body vision, and the contrast characteristic felt at that time depends on the contrast property under the influence of the body vision. It is a thing. For this reason, the contrast of a dark part is felt lower than a measured value. When this is viewed in an environment of 10 Cd / m ² or more, since it is viewed with the contrast characteristic of only the cone view, the contrast in the dark part of the image is particularly felt high.

Therefore, when viewing the display device in a living room environment, the contrast ratio is low in an image region that can be inferred to be 10 Cd / m ² or less when the displayed image is viewed. The processing to be performed will be performed. In addition, you may determine whether it is a living room environment according to whether the average brightness | luminance in a visual field is 10 Cd / m < ² > or more.

(First embodiment)
Hereinafter, a display device according to a first embodiment of the present invention will be described with reference to FIGS.
FIG. 5 is a graph showing the ratio of the rod to the combined visual sensitivity of the cone and the rod with respect to the average luminance in the visual field. The horizontal axis represents the average luminance in the visual field, and the vertical axis represents the composite visual sensitivity. The ratio of the affected body is shown.
In FIG. 5, 51 is a characteristic line showing the body ratio that affects the sensitivity of synthetic vision when the average in-field luminance is from 0.1 Cd / m ² to 10 Cd / m ² . Reference numeral 52 is a characteristic line showing the ratio of the body that affects the sensitivity of synthetic vision when the average luminance in the visual field is 0.1 Cd / m ² or less. Reference numeral 53 is a characteristic line showing the ratio of the body that affects the sensitivity of the composite vision when the average luminance in the visual field is 10 Cd / m ² or more.

Assuming that the average luminance in the field of view = k (Cd / m ² ) and the ratio of the casing to the sensitivity of the composite vision = s, these relationships can be expressed as follows.
s = 0 in the range of k <0.1
In the range of 0.1 <k <10, s = 1−0.5 * logk
In the range of k> 10, s = 0
It is expressed.

FIG. 4 is a citation from Non-Patent Document 1 and shows the result of evaluating the sense of brightness with respect to different ambient luminances. The horizontal axis represents the luminance of the test screen, and the vertical axis represents the subjective evaluation value with 10 levels of brightness perceived by the subject. In the following description, the value on the vertical axis is referred to as a brightness feeling evaluation value or a brightness feeling.
Each curve shown in FIG. 4 is a characteristic line with ambient luminance as a parameter. The unit is a unit asb representing luminance. The unit conversion equation with the unit of luminance Cd / m ² used in the embodiments described later is 1asb = 1 / π Cd / m ² .

  In FIG. 4, 41 is a characteristic line with an ambient luminance of 0 asb, 42 is a characteristic line with an ambient luminance of 1 asb, 43 is a characteristic line with an ambient luminance of 10 asb, and 44 is a characteristic line with an ambient luminance of 100 asb. is there.

Consider the viewing environment of a display such as a TV for FIG. If the reflectance of the wall surface is 80% under an illuminance of 100 Lux as a normal living room, the wall surface luminance is 100 / π * 0.8 = 25 Cd / m ² . Since this is 8 asb, the characteristic line 43 of 10 asb is substantially equivalent.

In a bright shop or office environment, if the reflectance of the wall surface is 80% under an illuminance of 400 Lux, the wall surface luminance is 400 / π * 0.8 = 102 Cd / m ² . Although this is 32 asb, the characteristic line closer to the logarithm is considered to correspond to the characteristic line 44 of 100 asb.

  Here, the brightness feeling evaluation value 8 is a representative of the bright part, and the brightness feeling evaluation value 2 is the representative of the dark part, and the ratio is the contrast ratio. Then, in the characteristic line 43, the ratio between the test surface brightness of the brightness feeling evaluation value 8 = 100 asb and the test face brightness of the brightness feeling evaluation value 2 = 1 asb, and the contrast ratio is about 100. Since the characteristic line 44 has a ratio of the test surface brightness of the brightness feeling evaluation value 8 = 50 asb and the test face brightness = 5 asb of the brightness feeling evaluation value 2, the contrast ratio is about 100 which is substantially the same value. Similarly, a characteristic line 42 corresponding to a dim room of about 10 Lux has a contrast ratio of about 100, which is almost the same.

  However, in the characteristic line 41 corresponding to the dark room, the ratio of the test surface luminance of the brightness feeling evaluation value 8 = 5 asb and the test surface luminance of the brightness feeling evaluation value 2 = 0.005 asb, so the contrast ratio becomes 1000. It has become.

  This result is considered to be due to the characteristics of two types of human eye cells. Cone cells that work in bright places have a narrow dynamic range and become invisible in dark areas. It is thought that rod cells that work in dark places have a wide dynamic range and a wide increase in sensitivity to dark places.

  Next, the contrast ratio with respect to the average luminance in the visual field is calculated based on FIGS. When the contrast of the cone is c, the contrast of the rod is 10c from the description of FIG. 4 described above.

The composite contrast C ′ between the cone and the rod is expressed as follows using the rod ratio s.
C '= c (1-s) + 10c * s
To simplify, it is expressed as C ′ = c (1 + 9s).
Here, s = 1−0.5 * logk.

The composite contrast C ′ between the cone and the rod can be expressed as shown in FIG. FIG. 6 is a diagram showing the ratio of contrast to the assumed average luminance value at the time of shooting, in which the horizontal axis shows the assumed average luminance value at the time of shooting, and the vertical axis shows the ratio of contrast.
In FIG. 6, reference numeral 61 denotes a characteristic line indicating a contrast ratio in which the assumed average luminance at the time of photographing is 0.1 Cd / m ² to 10 Cd / m ² . Reference numeral 62 denotes a characteristic line indicating a contrast ratio in which an assumed average luminance at the time of photographing is 0.1 Cd / m ² or less. Reference numeral 63 denotes a characteristic line indicating a contrast ratio in which an assumed average luminance at the time of photographing is 10 Cd / m ² or more.

  There are two methods for obtaining the assumed average luminance at the time of shooting, and one method is to assume the average luminance from the ISO sensitivity value, aperture value, shutter speed value, etc., which are shooting parameters. In the case of a still image or a moving image, the shutter speed value is almost constant, and the ND filter multiple is also used. This calculation method will be described later.

Another method is to assume an average luminance from an APL value or a histogram as a feature amount of a video or image when shooting parameters cannot be obtained for the broadcast video or the like. Here, the assumed average luminance is expressed by the following equation.
Assumed average brightness = A * (APL value * number of gradations)
A is a constant. For example, if A = 1 Cd / m ² with respect to the number of 10-bit gradations, an assumed average luminance of the number of 10-bit gradations can be obtained. For example, when APL = 0.2, the number of 10-bit gradations = 1024 and the assumed average luminance is 200 Cd / m ² . This is a level corresponding to the brightness of a bright indoor or light outdoor.

  This assumed brightness value is the expected brightness to the last, and does not accurately indicate the situation at the shooting site, but it shows a tendency of the image and is sufficient for use in this correction, By adjusting the constant A in the range of 0.3 to 3.0, it is possible to further adjust. If the number of 8-bit gradations is not 10-bit gradation number, A is four times as large (about 1 to 10), and if it is 12-bit gradation number, A is a quarter-fold value (0. 1 to 1).

  The ratio of the contrast on the vertical axis is proportionally determined corresponding to the ratio of the casing on the vertical axis in FIG. In other words, the contrast ratio is determined as the characteristic lines 61, 62, and 63 corresponding to the characteristic lines 51, 52, and 53 indicating the ratio of the casings.

FIG. 7 is a diagram showing the ratio of contrast to the average luminance in the field of view at the time of viewing. The horizontal axis shows the average luminance value in the field of view at the time of viewing, and the vertical axis shows the ratio of contrast.
In FIG. 7, reference numeral 71 denotes a characteristic line indicating a contrast ratio in which the in-field average luminance is from 0.1 Cd / m ² to 10 Cd / m ² . Reference numeral 72 denotes a characteristic line indicating a contrast ratio in which the average luminance in the visual field is 0.1 Cd / m ² or less. Reference numeral 73 denotes a characteristic line indicating a contrast ratio having an average in-field luminance of 10 Cd / m ² or more.

  The ratio of the contrast on the vertical axis is proportionally determined corresponding to the ratio of the casing on the vertical axis in FIG. That is, the contrast ratio is determined as characteristic lines 71, 72, and 73 corresponding to the characteristic lines 51, 52, and 53 indicating the ratio of the casings. The method for obtaining the average luminance value in the visual field during viewing will be described later.

  The determination of the contrast ratio according to the ratio of the casing has been described above with reference to FIGS. 6 and 7. However, the contrast is not corrected to 0 when the ratio is 1 by correcting the contrast with the value of the contrast ratio as it is. Then, the contrast ratio changes so much that it gives a sense of incongruity.

  In order to convert the above-described contrast ratio into a contrast correction ratio for an image, it is necessary to weaken the correction effect by applying an appropriate value within the range of 0 to 1.0 as the magnification. In this embodiment, the following calculation is performed with this constant as B.

If the contrast ratio in the assumed average brightness at the time of shooting is X and the contrast ratio in the average brightness in the visual field at the time of viewing is Y, the correction ratio Z for reducing the contrast is determined as follows.
If the viewing environment is brighter than the shooting environment (if Y> X)
Z = 1-B * (1-Y / X)
If the viewing environment is darker than the shooting environment (if Y ≤ X),
Z = 1

  The reason why the correction ratio is set to 0 when Y <X is that when a picture taken in a bright field is viewed in a dark environment, the Purkinje transition works without permission, so that correction is not necessary.

  As the value of the correction ratio B, about 0.5 times is natural and desirable, and therefore, it is only necessary to select from 0.2 times where the correction effect is weak to about 0.8 times where the correction effect is strong. Since the contrast decreases as the correction ratio B increases, the situation seen in a dark place can be reproduced in a bright environment.

Specifically, a calculation example in which the correction ratio B = 0.7 is given. For example, if the assumed average luminance at the time of shooting is 20 Cd / m ² and the average luminance in the visual field at the time of viewing is also 20 Cd / m ² , X = 1.0 from FIG. 6 and Y = 1.0 from FIG. Therefore, Z = 0.

Further, if the assumed average luminance at the time of shooting is 1 Cd / m ² and the average luminance in the visual field at the time of viewing is 20 Cd / m ² , X = 5.0 from FIG. 6 and Y = 1.0 from FIG. Because there is
Z = 1-0.7 * (1-1.0 / 5.0) = 0.44
It becomes. Since it is only necessary to reduce the contrast correction, the contrast amount in the dark portion should be 0.44 times.

  By the way, the calculation so far was performed by a standard evaluation value. Actually, there are variations in evaluation values among individuals, and there is a risk that the correction amount may exceed the characteristics of the viewer. If the correction is too strong, it will feel that the image quality is unnatural rather than good.

  Therefore, the correction ratio B may be set so that the actual correction amount becomes a standard value or less. This time, as an example, a correction ratio of 0.7 will be described below. However, as long as it is between 0.3 and 0.9, it may be 0.5, for example.

  FIG. 17 is a diagram showing the relationship between the average luminance in the visual field and the contrast correction amount to be performed. In FIG. 17, the horizontal axis indicates the average luminance value in the visual field, and the vertical axis indicates the contrast correction amount. The correction ratio B here is 0.7.

In FIG. 17, solid lines 171, 172, and 173 are contrast correction characteristic lines required for the average visual field luminance when the photographing luminance is 1.0 Cd / m ² . Dotted lines 174, 175, and 176 are contrast correction amount characteristic lines required for the average visual field luminance when the photographing luminance is 0.1 Cd / m ² .

As described above, when the correction amount is 0.7, the contrast amount is controlled between 0.44c and 1.0c with respect to the original contrast when the photographing luminance is 1.0 Cd / m ^2. It will be good. Further, when the photographing luminance is 0.1 Cd / m ² , the contrast amount may be controlled between 0.37c and 1.0c with respect to the original contrast.

Next, there are various methods for controlling the contrast amount. As an example, a method for controlling with the inverse gamma value used in the inverse gamma conversion table is shown.
When the value that enters the inverse gamma conversion table is 256 gradations from 0 to 255, the 256 gradations are divided into three parts of a dark part, an intermediate part, and a bright part, and 0 to 83, 84 to 167, and 168. It is divided into three gradation parts of ~ 255. Further, when the dark part is divided into the darkest part, the intermediate dark part, and the slightly dark part, it is divided into three gradation parts of 0 to 27, 28 to 55, and 56 to 83.

  If the intermediate gradation values of the gradation portions are set as the representative gradation values, 14, 42 and 60 are representative gradation values, respectively. In order to correct the contrast of the dark part of the image, the brightness ratio of the representative gradation 14 of the darkest part and the representative gradation 60 of the slightly dark part in gamma 2.2 (γ value = 2.2) is set as the dark part contrast c.

According to the normalized luminance, the gradation value 14 is 0.00169 and the gradation value 60 is 0.0415.
c = 0.0415 / 0.00169 = 24.6
It is.
Similarly, FIG. 8 shows the result of calculating the ratio of the dark part contrast value and the gamma 2.2 contrast value for each inverse gamma value.

The horizontal axis in FIG. 8 represents the inverse gamma value, the left vertical axis represents the contrast value, and the right vertical axis represents the contrast ratio of each gamma with respect to the contrast value of gamma 2.2.
From FIG. 8, the reverse gamma 1.6 is 0.4 times the contrast of the reverse gamma 2.2. In contrast, the reverse gamma 1.2 is 0.2 times the contrast of the reverse gamma 2.2.

  From FIG. 17 and FIG. 8, in order to control the contrast from 1 to 0.2 times with respect to the photographing brightness and the average brightness within the field of view, the gamma value of the dark part is set within the field of view from 2.2 to 1.2. It can be seen that the change may be made in stages according to the average luminance.

FIG. 9 is a characteristic diagram showing the control value of the reverse gamma value in the dark portion with respect to the average luminance in the visual field. The horizontal axis shows the average luminance value in the visual field, and the vertical axis shows the reverse gamma value in the dark portion.
In FIG. 9, 91 is a characteristic line of the inverse gamma value of the dark part controlled with respect to the average luminance in the field of view when the photographing luminance is 1 Cd / m ² , and 92 is in the field of view when the photographing luminance is 0.1 Cd / m ² . It is a characteristic line of the inverse gamma value of the dark part controlled with respect to the average luminance. As shown in FIG. 9, the inverse gamma value of the dark portion may be controlled between 2.2 and 1.2 according to the luminance within the field of view.

In the case of display devices for consumer use except for business use, the average luminance in the field of view is hardly 1 Cd / m ² or less. In this case, the reverse gamma value in the dark area is shown in FIG. Depending on the average luminance, it may be controlled between 2.2 and 1.6.

  Furthermore, in the case of a consumer display device, there is a display device in which the initial value of the inverse gamma value is set to 2.4 instead of 2.2 because the image quality with high contrast looks better. In this case, it may be offset by 0.2 and controlled between 2.4 and 1.8 according to the average luminance in the visual field.

Next, a method for calculating the in-field average luminance will be described. The average luminance within the visual field can be obtained by the following equation.
Average luminance in the field of view = Environmental average luminance (1-Screen field ratio) + Screen average brightness * Screen field ratio

Next, how to obtain the environmental average brightness, the screen view rate, and the in-screen average brightness will be described. The average luminance (environment average luminance) of ambient light entering the field of view from the wall surface outside the screen can be obtained by the following equation.
Environmental average brightness = Screen illuminance / π * Wall reflectance

  The screen edge illuminance is measured by an illuminometer attached to the edge of the screen of the display device. The wall reflectivity is suitably set to 0.8 for white walls and about 0.5 for other walls. When the value in the actual environment is not set, it is appropriate to set the initial value to about 0.6. In addition, if the image quality (contrast) is immediately reflected in accordance with the change in the environmental average brightness, the image quality changes abruptly in a short time and becomes difficult to see. Therefore, it is effective to set a time average value of about 10 seconds. .

Next, how to obtain the screen view rate will be described.
According to Non-Patent Document 1 described above, when the viewing angle is 10 degrees, the screen viewing rate, that is, the proportion of the screen viewing field is 57%. Since this screen view rate is a value when the screen is being watched, it is appropriate to reduce the screen view rate to about half when the screen is not watched. In this case, it is appropriate to set the influence of ambient illuminance to about 0.7 and the influence of the APL value in the screen to about 0.3. The aforementioned Non-Patent Document 1 is NII-Electronic Library Service: The Institute of Image Information and Television Engineers Vol. 19, No. 5, 55-56.

  When the angle of view of the display device that occupies the field of view is unknown, the screen field-of-view ratio, which is an influence within the screen, is arbitrarily designated between 0.3 and 0.7. In the present embodiment, the screen view rate is set to 0.4 as an intermediate provisional value.

Next, how to obtain the average luminance within the screen, that is, the APL value will be described. The in-screen average brightness is given by the following equation.
In-screen average brightness = average of linear tone values of all pixels / full tone value * peak brightness

  In addition, if the image quality (contrast) is reflected immediately in response to the change in the average brightness within the screen, the image quality changes suddenly in a short time and becomes difficult to see. Therefore, it is effective to set a time average value of about 10 seconds. is there.

The average luminance within the visual field during viewing is obtained as follows.
Average luminance in field of view = environmental luminance * (1-angle of view) + luminance in screen * angle of view The environmental luminance is obtained by measuring environmental illuminance and multiplying the reflectance of the wall. The reflectivity of the wall varies depending on the viewing environment, but in Japan there are many whitish walls, so if you set it to 0.6,
Environmental brightness = Environmental illuminance * 0.6 / π
It becomes.

The in-screen brightness is obtained by multiplying the APL value by the peak brightness. The peak luminance varies depending on the mode of the display device, but is, for example, 200 Cd / m ² . The angle of view is not the true screen angle, but the ratio of the in-screen brightness and the off-screen brightness to the viewer. It depends on the viewing distance and screen size, and is a value of about 0.2 to 0.7. . In this embodiment, the calculation is performed as 0.3. In the case of the above numerical example, the average luminance in the visual field is as follows.
Average luminance in the field of view = ambient illuminance ** 0.6 * 0.7 / π + APL value * 200 * 0.3

FIG. 12 is a diagram illustrating a result of calculating the average luminance in the visual field from the screen edge illuminance and the average gradation. In FIG. 12, it is assumed that the wall surface reflectance is 0.6, the screen view rate is 0.4, and the peak luminance of the display device is 100 Cd / m ² . The screen edge illuminance takes a value from 1 to 1000 Lux, and the average gradation takes a value from 4 to 255 gradations.

For example, in a 1 Lux environment corresponding to a dark room, the average luminance in the visual field for an image close to true black with an average gradation of 16 is 0.21 Cd / m ² . In the 100 Lux environment corresponding to the living room, the average luminance in the visual field in the case of a bright image having an average gradation of 128 is 20.24 Cd / m ² .

According to the calculation formula and the characteristic diagram described above, when an image with an average gradation of 140 or less is displayed in an environment where the screen edge illuminance is 100 Lux or less, the average luminance in the visual field corresponds to 10 Cd / m ² or less. . In this region, the contrast correction according to the present embodiment works, and it is possible to improve the image quality by lowering the contrast of the dark part to create an atmosphere of the dark part.

If the value in FIG. 12 showing the result of calculating the average luminance in the field of view and the characteristic line in FIG. 9 are used, the dark portion to be used in the inverse gamma conversion table from the measured value of the screen edge illuminance and the APL value of the input image. The inverse gamma value of is obtained. For example, in the case of the living room of the above-described example, when the ambient illuminance is 100 Lux and the APL value of the input image is 16, the average luminance in the visual field is 11.55 Cd / m ² from FIG. In this field the average brightness, the inverse gamma value of the dark area from FIG. 9, when the luminance at the time of photographing of 1 Cd / m ² 1.6, and 1.5 when shooting luminance of 0.1 cd / m ² Become.

In viewing environment is a dark room = 1Lux, if APL values 32, for viewing the average brightness is 0.53Cd / m ^2, the inverse gamma dark portion when seen from FIG. 9, shooting luminance of 1 Cd / m ² When the value is 2.2 and the luminance at the time of photographing is 0.1 Cd / m ² , the inverse gamma value of the dark portion is 2.1.

Next, the configuration of the display device according to the embodiment of the present invention will be described.
FIG. 2 is a block diagram illustrating a configuration example of the display device according to the present embodiment. When the luminance value is lower than a certain threshold value, contrast correction is performed on the displayed image.
In FIG. 2, reference numeral 21 denotes a gamma image quality adjustment circuit that performs gamma image quality correction on an input image. Reference numeral 22 denotes an illuminance sensor. Reference numeral 23 denotes a contrast correction circuit that corrects the contrast of an image in accordance with the average luminance in the visual field. Reference numeral 24 denotes a linear image quality adjustment circuit that converts the gradation of the image output from the contrast correction circuit 23 into a linear system.

  A panel driver 25 converts an image output from the linear image quality adjustment circuit 24 into a display panel drive signal. A display panel 26 displays an image based on a display panel drive signal output from the panel driver 25. Since an input image is generally obtained by decoding an external input or a signal received by a tuner, the block of the image input unit is not shown in FIG.

  The input image input to the display device is a gamma-based image that normally has a gamma of 2.2, and the gamma-based image quality adjustment circuit 21 performs gamma-based image processing such as enlargement / reduction in the gamma system. An illuminance sensor 22 is provided on the edge of the display panel 26, and the illuminance on the screen edge can be sensed.

  The contrast correction circuit 23 calculates the average luminance in the visual field from the image output from the gamma image quality adjustment circuit 21 and the screen edge luminance input from the illuminance sensor 22, and performs an appropriate color correction process based on the calculated average luminance in the visual field. I do. Since the image output from the contrast correction circuit 23 is a linear system, the linear system image quality adjustment circuit 24 performs image quality adjustment such as linear edge enhancement processing.

FIG. 1 is a block diagram showing a configuration example of the contrast correction circuit 23 according to the embodiment of the present invention.
In FIG. 1, reference numeral 11 denotes an environmental average luminance calculation unit that calculates environmental average luminance using an input from the illuminance sensor 22. Reference numeral 12 denotes an in-screen average luminance calculation unit that calculates the in-screen average luminance from the input image. Reference numeral 13 denotes an averaging unit that averages the average luminance in the screen over time. Reference numeral 14 denotes an in-field average luminance calculation unit that calculates the in-field average luminance. Reference numeral 15 denotes a correction switching unit that switches whether to perform correction according to the average luminance in the visual field.

  Reference numeral 16 denotes a luminance estimation unit that calculates the assumed average luminance at the time of shooting from the average luminance within the screen averaged over time. Reference numeral 17 denotes a Purkinje transition amount calculation unit that calculates the Purkinje transition amount from the assumed average luminance at the time of photographing and the average luminance within the visual field. Reference numeral 18 denotes an inverse gamma conversion table generation unit that generates an inverse gamma conversion table for contrast correction. Reference numeral 19 denotes an inverse gamma conversion unit that generates a linear image obtained by performing contrast correction from a gamma input image based on an inverse gamma conversion table for contrast correction.

  Based on the input from the illuminance sensor 22, the environmental average luminance calculation unit 11 calculates the environmental average luminance within the visual field that is temporally averaged. The in-screen average brightness calculation unit 12 calculates the in-screen average brightness within the field of view from the input image. The in-screen average brightness calculated by the in-screen average brightness calculation unit 12 is temporally averaged by the averaging unit 13.

The in-field average luminance calculation unit 14 calculates the in-field average luminance that is temporally averaged using the above-mentioned environmental average luminance, the in-screen average luminance that is temporally averaged, and the in-screen visual field ratio.
When the average luminance in the visual field is equal to or less than 0.1 Cd / m ² , the correction switching unit 15 stops the correction because it is almost rod-like.
The luminance estimation unit 16 calculates the estimated average luminance from the average luminance in the screen averaged over time using the assumed luminance value = A * (APL value * number of gradations).

The Purkinje transition amount calculation unit 17 calculates the correction ratio Z as follows using the Purkinje transition amounts X and Y and the magnification B.
Z = 1-B * (1-Y / X)

  The inverse gamma conversion table generation unit 18 generates an inverse gamma conversion table that corrects a desired contrast using the correction ratio Z described above. Details of the inverse gamma conversion table will be described later with reference to FIG.

  The inverse gamma conversion unit 19 converts the input image from a gamma system to a linear system. The inverse gamma conversion unit 19 is written with the inverse gamma conversion table from the inverse gamma conversion table generation unit 18, but if the reverse gamma conversion table is switched in the middle of the frame of the input image, the display image has a sense of interference, so Prepare two conversion tables. The reverse gamma conversion table used for processing the current input image and the reverse gamma conversion table in which the table is rewritten for contrast correction are switched at the frame sync timing.

  The inverse gamma conversion unit 19 performs an inverse gamma conversion process with contrast correction on the gamma input image and outputs a linear output image. Note that when the inverse gamma conversion table is switched in the middle of the frame of the input image, the display image is disturbed, so the blank line between the frames is changed.

  In addition, if the reverse gamma value is suddenly switched greatly, a sense of interference is generated, and the amount of change per frame is 0.001 in terms of gamma value. As a result, the maximum amount of change per second is 0.06 times as the gamma value, and if this is the case, visual discomfort does not occur, which is acceptable.

FIG. 3 is a diagram for explaining the inverse gamma conversion processing.
In FIG. 3, the horizontal axis indicates a 256 gradation scale as an input gamma gradation, and the vertical axis indicates a 4096 gradation scale as an output linear gradation.

  In FIG. 3, 31 is a characteristic line of an inverse gamma value 2.2 as an initial value. Reference numeral 32 denotes a part of the characteristic line of the dark portion inverse gamma value 1.8. Reference numeral 33 denotes a part of the characteristic line of the dark portion inverse gamma value 1.4. Reference numeral 34 denotes a characteristic line of a portion connected from the dark portion reverse gamma value 1.8 to the reverse gamma 2.2. Reference numeral 35 denotes a characteristic line of a portion connected from the dark portion reverse gamma value 1.4 to the reverse gamma 2.2.

  When a gradation value having a 256 gradation scale with a gamma gradation is input as an input to this characteristic line, a gradation value within a 4096 gradation scale is output as a linear gradation according to the inverse gamma value. It is shown that.

  In the following, numerical values are given for easy understanding as a specific example. However, the present embodiment is not limited to these numbers as long as the same means is used to solve the above-described problems. is there.

  Based on the value of the contrast correction ratio Z, the dark portion gamma value is obtained using the relationship shown in FIG. 8, and the value is applied to the gradation value of 0 to 60. This gradation value 60 is a slightly bright gradation value in the dark part gradations 0 to 83 as described above. Then, since the characteristic line 31 of the original gamma 2.2 is separated at the gradation value 60, it is necessary to return to the characteristic line 31 up to the gradation value 127. This gradation value 127 is a central gradation value of the entire gradation values 0 to 255. Although not strictly this value, it is desirable that the value be near the median value so as not to affect the bright part.

  As shown in FIG. 8, when 0.55 is required as the correction ratio, the dark portion gamma value is set to 1.8. Therefore, the dark portion reverse gamma 1.8 curve is applied from 0 to 60 gradations. This is the characteristic line 32 of the dark portion inverse gamma 1.8, and the connection line characteristic line 34 connects the gradations 60 to 127 with a curve or a straight line.

  When 0.3 is necessary as the correction ratio, the dark portion gamma value is set to 1.4, and the dark portion inverse gamma 1.4 curve is applied from 0 to 60 gradations. This is the characteristic line 33 of the dark portion inverse gamma 1.4, and the characteristic line 35 of the connecting portion is a connection between the gradations 60 to 127 with a curve or a straight line.

  From the characteristic line 32 → 34 → 31 or the characteristic line 33 → 35 → 31, a reverse gamma conversion table is generated and written in the reverse gamma conversion table, thereby making it possible to correct the dark part contrast.

(Second Embodiment)
Next, a second embodiment of the present invention will be described.
FIG. 18 is a diagram illustrating another example of the ratio of the rod on the combined visual sensitivity of the cone and the rod with respect to the average luminance within the visual field. In FIG. 18, the horizontal axis indicates the average luminance value in the visual field, and the vertical axis indicates the ratio of the housing that affects the sensitivity of the combined vision. In FIG. 18, reference numeral 181 denotes a characteristic line indicating the ratio of the housing to the sensitivity of the composite vision when the average in-field luminance is 0.01 Cd / m ² to 100 Cd / m ² .

  In the example of FIG. 4, the contrast of the housing is 10 times, but is not limited to 10 times and may be a value of about 3 to 10 times. Therefore, if the contrast ratio of the casing to the cone is 6 times and the ratio of the casing in which the curve values shown in FIG. 4 are tabulated is used, the contrast correction is gentler than that of the first embodiment. A curve is obtained. This curve is shown in FIG.

  FIG. 19 is a diagram showing a necessary contrast with respect to the average luminance in the visual field. In FIG. 19, the horizontal axis indicates the average luminance value in the visual field, and the vertical axis indicates the contrast necessary for the eyes to feel the same. Reference numeral 191 denotes a characteristic line of contrast necessary for the eyes to feel the same with respect to the average luminance within the visual field.

  As shown in FIG. 19, the contrast value with respect to the average luminance in the field of view becomes a curve. Since the correction method for this value can be corrected by the same method as in the first embodiment, description thereof is omitted.

  As a second embodiment, consider an example of a display device with a small screen. In a TV with a small screen such as a screen size of 30 inches or less, the influence of the screen luminance in the field of view is small, and the influence of the environmental illumination is mostly. The in-screen average brightness may not be obtained from the input image, and the environmental average brightness value may be obtained from the illuminometer to obtain the in-field average brightness. In the second embodiment, the in-screen average luminance calculation unit 12 is not necessary.

(Third embodiment)
Next, a third embodiment of the present invention will be described.
In the third embodiment, a case where the average luminance at the time of shooting is calculated based on the shooting parameters will be described. If the shooting parameters such as ISO sensitivity, aperture, shutter speed, and ND filter multiple are known, the average luminance during shooting can be calculated. According to the CIPA DC-X004 standard, when the aperture value is F, the exposure time is T (s), and the luminance value is D (Cd / m ² ), the image plane exposure amount Hm (Lx · s) is It is given by the following equation 1.
Hm = 0.65 * B * T / F ** 2 (** is a multiplier) Equation 1
The sensitivity S is given by the following equation 2.
S = 10 / Hm Equation 2

By transforming the above formula 1 into a formula for obtaining luminance, it is expressed by the following formula 3.
D = Hm * F ** 2 / 0.65T Equation 3
Substituting Equation 2 into Equation 3 yields Equation 4 below.
D = 10 * F ** 2 / (0.65 * T * S) Equation 4
Furthermore, if the ND filter multiple is U times, it is expressed by the following equation 5.
D = U * 10 * F ** 2 / (0.65 * T * S) ... Formula 5

For example, if the ISO sensitivity value is 400, the aperture is 4, the exposure time is 1 / 250th, and the filter magnification is 1, the luminance of the appropriate exposure portion is 154 Cd / s. m ² .

Using the brightness B of the appropriate exposure portion calculated in this way, the in-screen average brightness at the time of shooting is estimated from the APL value of the image. Since the brightness of the proper exposure portion is considered to be a median value of 0.5 in gamma 2.2, it is a position of 0.2 when converted to a linear system. Therefore, the average luminance at the time of photographing is expressed by the following formula 6.
Average luminance at the time of shooting = D * APL value / 0.2 Equation 6

FIG. 13 is a diagram showing a detailed configuration of the contrast correction circuit according to the third embodiment of the present invention.
In FIG. 13, 11-15 and 17-19 are the same as the structure of the same code | symbol in FIG. Reference numeral 131 denotes an appropriate luminance calculation unit that calculates the luminance of the appropriate exposure portion from the shooting parameters. Reference numeral 132 denotes a photographing average luminance calculation unit that calculates photographing average luminance.

  The appropriate luminance calculation unit 131 calculates the aperture value F, the exposure time T, and the ISO sensitivity value S, which are imaging parameters, according to the above-described formula 5, D = U * 10 * F ** 2 / (0.65 * T * S). Then, the luminance D of the appropriate exposed portion is calculated.

  The shooting average luminance calculation unit 132 calculates the shooting average luminance from the luminance B of the appropriate exposure portion and the APL value according to the above-described equation 6, shooting average luminance value = D * APL value / 0.2.

  Although the operation of the other configuration is the same as that of the first embodiment, the Purkinje transition amount calculation unit 17 uses the average luminance at the time of shooting instead of the assumed average luminance at the time of shooting in the first embodiment, The correction amount is calculated.

  In the first embodiment, the assumed average brightness at the time of shooting is calculated using only the APL value, but in the third embodiment, by using the shooting parameters, the more accurate average brightness at the time of shooting is used. It is possible to determine the correction amount.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described.
In the fourth embodiment, a case where only the contrast of the dark area is corrected will be described. In the first to third embodiments described above, contrast correction is performed on the entire screen.

In contrast, in the fourth embodiment, the correction is not limited to the entire screen, but is limited to the dark area, or the dark area is corrected more strongly than the bright area. It is.
For example, an APL value obtained by averaging the surrounding N × N pixels of the target pixel is set as the surrounding APL value G as follows.
G = Σ (Y value of surrounding N × N pixels) / N ** 2
By appropriately mixing the inverse gamma conversion table output to be corrected and the normal inverse gamma conversion table output according to the peripheral APL value, it is possible to correct only the dark area. Moreover, it is strong only in the dark area and weak in the bright area, and can be corrected.

  The mixing ratio K, which is the ratio for mixing the quantity output, will be described below as correction table output / (correction table output + normal table output).

When the dark area is almost completely dark (when G = 0), correction output: normal output is set to 1: 0, and the bright area is near white (when G = 1), correction If the output is set so that the normal output = 0: 1 and the intermediate region is linear, K = 1−G. Further, if the correction output is set to 0 when the peripheral APL value is intermediate or higher and is linear when the peripheral APL value is lower than the intermediate value, it is possible to correct only the dark area.
In that case, since it is delimited by the value of G, it is as follows.
When G <0.5, K = 1−2 * G
When G ≦ 0.5, K = 0
It becomes.

Further, when a certain input pixel value C is given, the corrected inverse gamma conversion table output is H, the normal inverse gamma conversion table output is T, and the mixed output is Q. The
Q = K * H + (1-K) * T Equation 7

  As described above, it has been shown that the intensity of contrast correction can be appropriately adjusted from the pixel value and the peripheral pixel value according to the brightness of the pixel peripheral region by using several expressions.

FIG. 14 is a diagram showing a detailed configuration of a contrast correction circuit according to the fourth embodiment of the present invention. In FIG. 14, reference numerals 11 to 19 are the same as those in FIG.
Reference numeral 141 denotes a luminance extraction unit that extracts the luminance of the region around the target pixel. Reference numeral 142 denotes a mixture ratio calculation unit that calculates a mixture ratio from the average luminance of the region around the target pixel. Reference numeral 143 denotes a normal inverse gamma conversion unit. A mixing unit 144 mixes the correction table output and the normal table output according to the mixing ratio.

The luminance extraction unit 141 includes, for example, a plurality of shift registers, and can refer to luminance values in the NxN region around the target pixel at a time. Then, the luminance extraction unit 141 calculates the peripheral APL value using the above-described equation, G = Σ (Y value of the peripheral N × N pixel) / N / N, using the Y value of the N × N region.
The mixing ratio calculation unit 142 calculates the mixing ratio from the peripheral average luminance value using the above-described formula, K = 1−G or K = 1−2 * G.

Reference numeral 143 denotes a normal inverse gamma conversion table, which is a table that does not include correction, but is an inverse gamma conversion table that includes other elements such as image quality. Outputs a linear value. The inverse gamma conversion table with correction is an inverse gamma conversion table that includes the correction function of the present invention in addition to other elements such as image quality.
The mixing unit 144 uses the above-described equation Q = K * H + (1−K) * T from the output H of the corrected inverse gamma conversion unit 19 and the output T of the normal inverse gamma conversion unit 143 to generate an image. The linear value of each pixel is sequentially output.

(Fifth embodiment)
The present invention can be applied not only to a display device but also to an image quality adjustment device inserted between a photographing device or a recording device and the display device. Hereinafter, an example thereof will be described as a fifth embodiment.

FIG. 15 is a block diagram showing a configuration example of an image quality adjustment apparatus according to the fifth embodiment of the present invention.
In FIG. 15, reference numeral 221 denotes a gamma image quality adjustment circuit that performs gamma image quality correction on an input image. Reference numeral 222 denotes an illuminance sensor. Reference numeral 223 denotes a contrast correction circuit that corrects the contrast of an image in accordance with the average luminance in the visual field.

  Since the input image input to the image quality adjustment apparatus according to the present embodiment is a gamma-based image that is normally subjected to gamma 2.2, the gamma-based image processing such as enlargement / reduction in the gamma system is performed by the gamma-based image quality adjustment circuit 221. I do. The image quality adjusting device is provided with an illuminance sensor 222, and can sense environmental illuminance.

The contrast correction circuit 223 calculates the average luminance in the visual field from the output image from the gamma image quality adjustment circuit 221 and the illuminance value from the illuminance sensor 222, and performs an appropriate dark region contrast correction based on the calculated value.
The output from the contrast correction circuit 223 remains the gamma system, and the output image is connected to a general display device for display.

(Sixth embodiment)
The details of the contrast correction circuit 223 in the sixth embodiment are similar to the configuration of FIG. 1, and the only difference is that the inverse gamma conversion table generation unit 18 is a contrast conversion table generation unit. To do.

  Next, a table generated by the contrast conversion table generation unit will be described with reference to FIG.

FIG. 16 is an explanatory diagram of a contrast conversion table according to the sixth embodiment, where the horizontal axis represents an input gamma system gradation and a 256 gradation scale, and the vertical axis represents an output gamma system gradation. Scale.
In FIG. 16, reference numeral 331 denotes a linear characteristic line without initial value correction, and reference numeral 332 denotes a curved characteristic line obtained by modifying the dark portion gradation.
When the correction is not performed, the input gradation value becomes the output gradation value as it is by the linear characteristic line 331.

Since the contrast of the dark image portion is corrected in the same manner as described with reference to FIG. 7, the luminance ratio of the representative gradation 14 of the darkest portion and the representative gradation 60 of the slightly dark portion in gamma 2.2 is set as the dark portion contrast c.
According to the normalized luminance, the gradation value 14 is 0.00169 and the gradation value 60 is 0.0415, so the original dark portion contrast is
c = 0.0415 / 0.00169 = 24.6
It is.

As in the first embodiment, the dark portion contrast correction ratio is calculated from the assumed luminance at the time of shooting and the average luminance in the visual field at the time of viewing, and the dark portion contrast correction ratio to be corrected is, for example, 0.5. .
C = 24.6 * 0.5 = 12.3.
For this purpose, the normalized luminance 0.00169 of the gradation value 14 is set to four times 0.00676, and the normalized luminance 0.0415 of the gradation value 60 is set to twice twice 0.0830.
When converted to 256 gradation values of the gamma 2.2 system, 27 and 83 are obtained.

Therefore, the correction curve 332 passes through the points of the input gradation value 14 and the output gradation value 27, the input gradation value 60 and the output gradation value 83, and is a straight line at the input gradation value 127 and the output gradation value 127. You just need to create it so that it connects smoothly. The dark curve contrast conversion table is obtained by converting the correction curve 332 into a table.
Even in a correction ratio other than the correction ratio 0.5, a desired dark portion contrast correction table can be obtained by the same calculation.

(Other embodiments)
The present invention can also be realized by executing the following processing. That is, software (computer program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various computer-readable storage media. Then, the computer (or CPU, MPU, etc.) of the system or apparatus reads out and executes the program.

DESCRIPTION OF SYMBOLS 11 Environmental average brightness | luminance calculation part 12 In-screen average brightness | luminance calculation part 13 Averaging part 14 In-field average brightness | luminance calculation part 15 Correction | amendment switching part 16 Brightness estimation part 17 Purkinje transition amount calculation part 18 Reverse gamma conversion table generation part 19 Reverse gamma conversion part

Claims (20)

A display device for displaying images and videos,
A calculating means for calculating an assumed average luminance value at the time of shooting from the average luminance value of the display image and the number of gradations;
Contrast correction means for changing the contrast of the display image,
The contrast correction means includes
A display device, wherein the display image is subjected to contrast correction when the luminance value calculated by the calculating means is lower than a certain threshold value. The contrast correction means includes
The display device according to claim 1, wherein contrast correction is performed when the average luminance value in the field of view calculated from the ambient illuminance is an area of 10 Cd / m ² or more. An illuminance sensor for sensing the illuminance around the display device;
In-field average luminance calculating means for calculating the average luminance in the field of view from the ambient illuminance and the average luminance value of the screen,
The contrast correction means includes
^2. The display device according to claim 1, wherein contrast correction is performed when the in-field average luminance value calculated by the in-field average luminance calculating means is an area of 10 Cd / m ² or more. A display device for displaying images and videos,
A calculation means for calculating an assumed average luminance value at the time of shooting from shooting parameters at the time of shooting;
Contrast correction means for changing the contrast of the image,
The contrast correction means includes
A display device, wherein contrast correction is performed on the image when the luminance value calculated by the calculating means is lower than a certain threshold value. A display device for displaying images and videos,
A calculating means for calculating an assumed average luminance value at the time of shooting from the average luminance value of the display image and the number of gradations;
When the luminance value calculated by the calculating means is lower than a certain threshold, the image to be displayed is referred to according to the luminance value calculated by the calculating means and the peripheral average luminance value by referring to the average luminance value around the pixel. And a contrast correction means for changing a ratio of contrast correction to the display device. An illuminance sensor for sensing the illuminance around the display device;
In-field average luminance calculating means for calculating the average luminance in the field of view from the ambient illuminance and the average luminance value of the screen,
The contrast correction means includes
The display device according to claim 5, wherein contrast correction is performed when the in-field average luminance value calculated by the in-field average luminance calculating means is an area of 10 Cd / m ² or more.   The display device according to claim 4, wherein the contrast correction unit uses a table with numerical values obtained by changing an inverse gamma value. An image quality adjustment device for adjusting the image quality of images and videos,
A calculating means for calculating an assumed average luminance value at the time of shooting from the average luminance value of the display image and the number of gradations;
An image quality adjusting apparatus comprising: a contrast correcting unit that corrects a contrast of the image to be displayed when the luminance value calculated by the calculating unit is lower than a threshold value. The contrast correction means includes
9. The image quality adjustment apparatus according to claim 8, wherein contrast correction is performed when an average luminance value in the field of view calculated from ambient illuminance is an area of 10 Cd / m ² or more. An illuminance sensor for sensing the illuminance around the display device;
In-field average luminance calculating means for calculating the average luminance in the field of view from the ambient illuminance and the average luminance value of the screen,
The contrast correction means includes
9. The image quality adjusting apparatus according to claim 8, wherein contrast correction is performed when the in-field average luminance value calculated by the in-field average luminance calculating means is an area of 10 Cd / m ² or more. An image quality adjustment device for adjusting the image quality of images and videos,
A calculation means for calculating an assumed average luminance value at the time of shooting from shooting parameters at the time of shooting;
Contrast correction means for changing the contrast of the image,
The contrast correction means includes
An image quality adjusting apparatus, wherein the image is subjected to contrast correction when the luminance value calculated by the calculating means is lower than a certain threshold value. An image quality adjustment device for adjusting the image quality of images and videos,
A calculating means for calculating an assumed average luminance value at the time of shooting from the average luminance value of the display image and the number of gradations;
When the luminance value calculated by the calculating means is lower than a certain threshold, the image to be displayed is referred to according to the luminance value calculated by the calculating means and the peripheral average luminance value by referring to the average luminance value around the pixel. An image quality adjusting apparatus comprising: contrast correction means for changing a ratio of performing contrast correction on the image. An illuminance sensor for sensing the illuminance around the display device;
In-field average luminance calculating means for calculating the average luminance in the field of view from the ambient illuminance and the average luminance value of the screen,
The contrast correction means includes
13. The image quality adjusting apparatus according to claim 12, wherein contrast correction is performed when the in-field average luminance value calculated by the in-field average luminance calculating means is an area of 10 Cd / m ² or more.   The image quality adjustment apparatus according to any one of claims 8 to 13, wherein the contrast correction unit uses a table with numerical values obtained by changing a dark portion contrast value. A control method for a display device that displays images and videos,
A calculation step of calculating an assumed average luminance value at the time of shooting from the average luminance value of the display image and the number of gradations;
A contrast correction step of changing the contrast of the display image,
The contrast correction step includes
A method for controlling a display device, comprising: performing contrast correction on the display image when the luminance value calculated in the calculation step is lower than a threshold value. A control method for a display device that displays images and videos,
A calculation step of calculating an assumed average luminance value at the time of shooting from shooting parameters at the time of shooting;
A contrast correction step of changing the contrast of the display image,
The contrast correction step includes
A method for controlling a display device, comprising: performing contrast correction on the display image when the luminance value calculated in the calculation step is lower than a threshold value. A control method for a display device that displays images and videos,
A calculation step of calculating an assumed average luminance value at the time of shooting from the average luminance value of the display image and the number of gradations;
When the luminance value calculated in the calculation step is lower than a certain threshold, the image to be displayed is referred to according to the luminance value calculated in the calculation step and the peripheral average luminance value by referring to the average luminance value around the pixel And a contrast correction step of changing a ratio of performing contrast correction on the display device. A control method of an image quality adjustment device for adjusting image and video image quality,
A calculation step of calculating an assumed average luminance value at the time of shooting from the average luminance value of the display image and the number of gradations;
And a contrast correction step of correcting the contrast of the image to be displayed when the luminance value calculated in the calculation step is lower than a certain threshold value. A control method of an image quality adjustment device for adjusting image and video image quality,
A calculation step of calculating an assumed average luminance value at the time of shooting from shooting parameters at the time of shooting;
A contrast correction step of changing the contrast of the display image,
The contrast correction step includes
A control method for an image quality adjustment apparatus, wherein contrast correction is performed on the display image when the luminance value calculated in the calculation step is lower than a threshold value. A control method of an image quality adjustment device for adjusting image and video image quality,
A calculation step of calculating an assumed average luminance value at the time of shooting from the average luminance value of the display image and the number of gradations;
When the luminance value calculated in the calculation step is lower than a certain threshold, the image to be displayed is referred to according to the luminance value calculated in the calculation step and the peripheral average luminance value by referring to the average luminance value around the pixel And a contrast correction step of changing a ratio of performing the contrast correction on the image quality adjustment apparatus.

Images