JP2006308631A - Device, method and program for image display, and recording medium with image display program recorded - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device, a method and a program for image display that can improve picture quality without any increase in power consumption, and a recording medium with the image display program recorded. <P>SOLUTION: The device for image display is equipped with a level correction section 43 which increases a contract by expanding a range wherein luminance values X of a frame image are distributed, a dimming rate setting section 47 which sets a dimming rate α, a light quantity control section 48 which controls (dims) the quantity of light emitted by a back light 32 based upon the dimming rate α, and a lightness correction section 44 which corrects level-corrected luminance values Y so as to reduce variation in luminance that an image displayed on a display panel 30 has as a result of the level correction and dimming. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image display apparatus, an image display method, an image display program, and a recording medium on which an image display program is recorded.

  2. Description of the Related Art Conventionally, in an image display device such as a notebook computer that employs a non-light emitting display device such as a liquid crystal panel, a light source (for example, a cold cathode tube) uses power supplied from a battery when no external power is supplied. Display is performed by controlling the amount of light that is converted into light and transmitted through the liquid crystal panel. In general, the proportion of power consumed by the light source is large in the power consumption of the entire apparatus. Therefore, the power consumption of the apparatus is reduced by reducing the amount of light emitted from the light source when the battery is driven. In addition, when the amount of light is reduced, the visibility decreases as the brightness of the entire screen decreases. Therefore, a technology that can achieve both reduction of power consumption and maintenance of visibility by reducing the amount of light is desired. . For example, in Patent Literature 1, conversion is performed on input image data to increase contrast by expanding the range of gradation values of the image data. Furthermore, since the luminance change due to the conversion is reduced by adjusting the amount of light emitted from the light source, a technique for suppressing the luminance change due to the conversion while improving the visual contrast of the image is disclosed.

  Further, in Patent Document 2, after the process of increasing the contrast, a process for correcting the brightness of the image is performed by performing gamma correction using a value calculated based on the median value of the luminance distribution as a gamma coefficient. .

Japanese Patent No. 3215388 (see FIG. 3 on page 39) Japanese Patent Laid-Open No. 10-198802 (refer to page 16, paragraphs [0123] to [128])

  However, in the technique described in Patent Document 1, when the average luminance is reduced after conversion for increasing the contrast, the amount of light emitted from the light source is increased so as to compensate for the decrease in luminance. It may end up. As described above, although it is possible to compensate for a change in luminance from the original image while improving the image quality by increasing the contrast, there is a problem that power consumption increases or decreases depending on the input image.

  Moreover, even if the process of correcting the brightness described in Patent Document 2 is performed after the conversion for increasing the contrast and adjusting the light amount described in Patent Document 1, appropriate brightness is obtained by performing gamma correction according to the image. However, the power consumption increases or decreases depending on the input image.

  As described above, according to the conventional technique, the power consumption cannot be surely suppressed while improving the image quality.

  SUMMARY An advantage of some aspects of the invention is that it provides an image display device, an image display method, an image display program, and a recording medium on which the image display program is recorded, which can improve image quality without increasing power consumption.

  In order to solve the above problems, an image display device of the present invention is an image display device for correcting image data representing an image by a gradation value for each pixel and displaying the corrected image. An image data acquisition unit that acquires image data, a gradation conversion unit that converts gradation values of the acquired image data so as to expand a range in which the gradation values of pixels are distributed, and gradations generated by the conversion A brightness correction unit that controls a gradation value of the converted image data so as to reduce a change in an average value.

  According to this configuration, it is possible to increase the contrast of an image by acquiring image data representing an image with a gradation value for each pixel and expanding a range in which the gradation value of the pixel is distributed. Further, by controlling the gradation value of the converted image data, the change in the average value of the gradation values caused by the conversion is reduced. That is, the change in the average value of the gradation values caused by increasing the contrast of the image is reduced. Therefore, it is possible to display an image with excellent image quality while suppressing the change in the gradation value generated by the conversion for the entire image.

  Further, unlike the technique of Patent Document 1, since the change in the gradation value is reduced by correcting the gradation value of the image data without controlling the amount of light generated by the light source, the power consumption of the image display device Will not increase.

  Here, the brightness correction unit corrects the gradation value of the converted image data so that the average value of the gradation values of the corrected image data approaches the average value of the gradation values of the image data before conversion. It is preferable to do.

  In this way, the product of the average value of the gradation value of the corrected image data and the light control rate approaches the average value of the gradation value of the image data before conversion, so without increasing power consumption, It is possible to reduce the change in the gradation value due to the conversion that increases the contrast.

  Here, the brightness correction unit maintains the same gradation value for the upper limit value and lower limit value of the gradation value within the range of gradation values of the converted image data, and between the upper limit value and the lower limit value. It is preferable to change the gradation value.

  In this way, since the upper limit value and lower limit value of the converted gradation range are maintained, there is no reduction by correcting the contrast once increased, and there is no reduction between the upper limit value and the lower limit value. By correcting the tone value, a change in the tone value due to the conversion can be suppressed.

  Further, another image display device of the present invention includes a spatial light modulator that corrects image data representing an image by a gradation value for each pixel and modulates light emitted from a light source based on the corrected image data. An image display device comprising: a dimming rate setting unit for setting a first dimming rate for reducing the light amount emitted from the light source from a predetermined light amount; an image data acquiring unit for acquiring image data; A brightness correction unit that controls the gradation value of the image data so as to reduce the change in brightness that occurs in the light modulated by the spatial light modulator by dimming according to the dimming rate, and a first dimming rate And a light amount control unit that controls the amount of light emitted from the light source.

  According to this configuration, the amount of light emitted from the light source is controlled (hereinafter referred to as dimming) on the basis of the first dimming rate for reducing the amount of light emitted from the light source from a predetermined amount of light. The power consumption can be reduced by lowering the power. In addition, a change in brightness that occurs in light modulated by the spatial light modulator by dimming is reduced by controlling the gradation value of the image data. Therefore, it is possible to reduce power consumption while suppressing a change in brightness that occurs in light modulated by the spatial light modulator by dimming.

  In addition, unlike the technique described in Patent Document 1, since the light is adjusted based on the dimming rate for dimming from the light amount, power consumption can be reliably reduced.

  Here, the image data further includes a gradation conversion unit that converts the gradation value so as to expand the range in which the gradation value of the pixel is distributed, and the brightness correction unit follows the first dimming rate. It is preferable to correct the gradation value of the converted image data so as to reduce the change in brightness that occurs in the light modulated by the spatial light modulator by dimming and conversion.

  In this way, the range in which the gradation values of the pixels are distributed is expanded by converting the gradation values, so that the contrast of the modulated light can be increased. Furthermore, the change in brightness that occurs in the light modulated by the spatial light modulator by the conversion and dimming is reduced by correcting the gradation value of the converted image data. Therefore, it is possible to suppress changes in brightness caused by conversion and dimming while improving image quality by increasing contrast and reducing power consumption.

  Here, the brightness correction unit is converted so that the product of the average value of the gradation value of the corrected image data and the light control rate approaches the average value of the gradation value of the image data before conversion. It is preferable to correct the gradation value of the obtained image data.

  In this case, the product of the average value of the gradation value of the corrected image data and the dimming rate approaches the average value of the gradation value of the image data before conversion, so that brightness by conversion and dimming is achieved. Can be reduced.

  Here, the brightness correction unit determines the brightness generated in the light modulated by the spatial light modulator when the gradation value of the image data before correction is corrected to be close to a predetermined reference gradation value. It is preferable to correct the gradation value of the image data before correction so as to reduce the change of the image data.

  In this way, the brightness generated in the light modulated by the spatial light modulator approaches when the gradation value of the image data before correction is corrected so as to approach a predetermined reference gradation value. Therefore, even if the modulated light is too bright or too dark because the distribution of the gradation values of the image data is biased, the moderate brightness when modulated based on the reference gradation values Can be approached.

  Here, the brightness correction unit calculates the gradation value of the image data before correction as a predetermined reference gradation by the product of the average value of the gradation values of the corrected image data and the first light control rate. It is preferable to correct the gradation value of the image data before correction so as to approach the average value of the gradation values when the correction is performed so as to approach the value.

  In this way, the product of the average value of the gradation values of the corrected image data and the first dimming rate makes the gradation value of the image data before correction approach the predetermined reference gradation value. Since it approaches the average value of gradation values when corrected to, the change in brightness due to light control can be reduced.

  Here, the brightness correction unit maintains the same gradation value for the upper limit value and lower limit value of the gradation value in the range of the gradation value before correction, and between the upper limit value and the lower limit value. It is preferable to change the gradation value.

  In this way, since the upper limit value and lower limit value of the converted gradation range are maintained, the gradation value between the upper limit value and the lower limit value is corrected without reducing the contrast by correction. The change in brightness can be reduced.

  Here, the brightness correction unit is generated in the light modulated by the spatial light modulator based on the image data before correction in a range where the gradation value is larger than the average value of the gradation values of the image data before correction. When the ratio of the brightness generated in the light modulated by the spatial light modulator based on the corrected image data with respect to the brightness is smaller than a predetermined ratio, the ratio of the brightness to the first dimming ratio is set to a predetermined value. It is preferable to set a second dimming rate that can be set to the ratio, and the light amount control unit controls the light amount emitted from the light source based on the second dimming rate.

  In this way, spatial light modulation based on the corrected image data is performed on the image to be displayed based on the image data before correction in a range where the gradation value is larger than the average value of the gradation values of the image data before correction. When the ratio of the brightness generated in the light modulated by the optical device is smaller than the predetermined ratio, the brightness ratio can be suppressed to the predetermined ratio by dimming according to the second dimming ratio. Accordingly, it is possible to suppress a change in brightness in a range where the gradation value is larger than the average gradation value of the image data before correction.

  Here, the first dimming rate and the second dimming rate represent a visual ratio according to the sensitivity characteristic of human vision with respect to light, and the light amount control unit can determine the first dimming rate or the second dimming rate. It is preferable to calculate a third dimming rate indicating the ratio of the amount of light actually emitted from the light source based on the visual sensitivity characteristic, and to control the light source according to the third dimming rate.

  In this way, it is possible to perform correction in accordance with human visual sensitivity characteristics with respect to light.

  The present invention may also be a method invention. That is, the image processing method of the present invention is an image display method for correcting image data representing an image by a gradation value for each pixel and displaying the corrected image, and for acquiring image data. A data acquisition process, a gradation conversion process for converting the gradation value of the acquired image data so as to expand a range in which the gradation value of the pixel is distributed, and a change in the average value of the gradation values generated by the conversion And a brightness correction step for controlling the gradation value of the converted image data.

  Another image display method of the present invention includes a spatial light modulator that corrects image data representing an image by a gradation value for each pixel and modulates light emitted from a light source based on the corrected image data. An image display method, a dimming rate setting step for setting a first dimming rate for dimming a light amount emitted from a light source from a predetermined light amount, an image data acquisition step for acquiring image data, A brightness correction step for controlling the gradation value of the image data so as to reduce a change in brightness generated in the light modulated by the spatial light modulator by dimming according to the rate, and based on the first dimming rate And a light amount control step for controlling the amount of light emitted from the light source.

  Furthermore, the present invention may be a program or a computer-readable recording medium that records the program. That is, the image display program of the present invention is an image display program for correcting image data representing an image by using a gradation value for each pixel and displaying the corrected image. The acquired image data acquisition unit, the acquired image data, the gradation conversion unit that converts the gradation value so as to expand the range in which the gradation value of the pixel is distributed, the average value of the gradation value generated by the conversion An image display device that functions as a brightness correction unit that controls gradation values of converted image data so as to reduce changes.

  Another image display program according to the present invention includes a spatial light modulator that corrects image data representing an image with a gradation value for each pixel and modulates light emitted from a light source based on the corrected image data. An image display program for displaying an image on an image display device, wherein the computer sets a first dimming rate for setting the first dimming rate for dimming the amount of light emitted by the light source from a predetermined amount of light, Image data acquisition unit that acquires image data, brightness correction that controls the tone value of the image data so as to reduce the change in brightness that occurs in the light modulated by the spatial light modulator by dimming according to the dimming rate And an image display program that functions as a light amount control unit that controls the amount of light emitted from the light source based on the first dimming rate.

  As the recording medium on which the image display program is recorded, various computer-readable media such as a flexible disk, a CD-ROM, and an IC card can be used.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a hardware configuration of the image display apparatus according to the first embodiment. As shown in FIG. 1, an image display apparatus 1 includes an input interface (hereinafter referred to as an input I / F) 10, a CPU 11, a ROM 12, a RAM 13, a hard disk (hereinafter referred to as an HD) 14, an image processing engine 15, and a CD-ROM drive. 16, a display interface (hereinafter referred to as a display I / F) 17, and a power interface (hereinafter referred to as a power I / F) 18. These components are connected to each other via a bus 19. A display panel 30 is connected to the display I / F 17, and a power supply device 31 is connected to the power I / F 18. Note that a specific example of the image display device 1 is assumed to be a notebook computer, a projector, a television, a mobile phone, or the like that can display an image on the display panel 30.

  The input I / F 10 is connected to a digital video camera 20 and a digital still camera 21 as devices for inputting moving images. In addition, distribution video from a network device, distribution video by radio waves, and the like are also input to the image display device 1 via the input I / F 10.

  The CPU 11 is a part that controls various processes performed in the image display device 1. In particular, when the input of moving image data via the input I / F 10 or the reproduction of a moving image stored in the HD 14 or the like is performed. The moving image data is transferred to the image processing engine 15 and processing for displaying the moving image is performed.

  The power supply device 31 supplies power stored in a battery set inside the power supply device 31 or power supplied from the outside of the image display device 1 to each component of the image display device 1 including the backlight 32. Supply.

  The backlight 32 is a light source such as a cold cathode tube or an LED (Light Emitting Diode) that converts electric power supplied from the power supply device 31 into light. The light from the backlight 32 is diffused by various sheets sandwiched between the backlight 32 and the display panel 30 to irradiate the display panel 30 as substantially uniform light.

  The display panel 30 modulates light according to the drive signal corresponding to the image data input via the display I / F 17, so that the amount of light received from the backlight 32 and the amount of light transmitted through the display panel 30 are changed. This is a transmissive liquid crystal panel that displays a color image by controlling the transmittance, which is a ratio, for each pixel. Since the display panel 30 performs display by controlling the light transmittance, the luminance of the displayed image changes in proportion to the amount of light supplied from the backlight 32.

  FIG. 2 is a diagram showing the configuration of the image processing engine. As shown in FIG. 2, the image processing engine 15 is roughly divided into a frame image acquisition unit 40, a color conversion unit 41, a frame memory 42, a level correction unit 43, a brightness correction unit 44, an image display signal generation unit 45, and A correction coefficient holding unit 46 is provided. The level correction unit 43 includes a histogram creation unit 50, a level correction parameter generation unit 51, and a level correction execution unit 52. The brightness correction unit 44 includes a luminance summation (ΣY) calculation unit 60, an average luminance (Yave) calculation unit 61, a coefficient summation (ΣF (Y)) calculation unit 62, a luminance summation (ΣX) calculation unit 63, and an average luminance (Xave). ) Calculation unit 64, correction amount calculation unit 65, and brightness correction execution unit 66. Note that the image processing engine 15 configured as described above is configured by a hardware circuit such as an ASIC. Hereinafter, processing performed by each component will be described.

  The frame image acquisition unit (image data acquisition unit) 40 sequentially acquires image data of a frame image that is an image of each frame of the moving image from the moving image data input to the image display device 1 via the input I / F 10. Process.

  Moreover, the moving image data to be input is, for example, data indicating a plurality of still images (hereinafter referred to as frame images) that are continuous in time series. The moving image data may be compressed data or the input moving image may be interlaced data. In such a case, the frame image acquisition unit 40 performs a process of decompressing the compressed data and a process of converting interlaced data to non-interlaced data, so that each frame image of the moving image data is processed. The image data is acquired by converting the image data into image data in a format that can be processed by the image processing engine 15. However, when still image data is input, still images can be handled by acquiring image data of the still images.

  In the present embodiment, the acquired image data starts from “0” for each color of R (red), G (green), and B (blue) for a large number of pixels arranged in a matrix such as 640 × 480 pixels vertically and horizontally. The RGB data is represented by a gradation value of 256 gradations (8 bits) of “255”. However, the number of pixels representing the frame image and the number of gradations of each pixel are not limited to this. Also, the representation format of the image data is not limited to RGB data. For example, K data represented by K (black), CMYK data represented by C (cyan), M (magenta), Y (yellow), and K, Data in various representation formats such as Yuv data represented by Y (luminance), u (blue color difference), and v (red color difference) may be used.

The color conversion unit 41 performs processing for converting the image data acquired by the frame image acquisition unit 40 into luminance data and color difference data. In the first embodiment, since the acquired image data is RGB data, a process of converting the RGB data into luminance data and color difference data is performed. In color conversion, it is possible to convert to luminance data X and color difference data uv, for example, by calculating a conversion formula shown below. The converted luminance data X and color difference data uv are stored in the frame memory 42.
X = 0.299R + 0.587G + 0.114B (1)
u = −0.1684R−0.3316G + 0.5000B (2)
v = 0.5000R-0.4187G-0.0813B (3)
Note that the color conversion unit 41 is a gradation represented by 256 gradations (8 bits) based on a color conversion table that represents the conversion results of Expressions (1) to (3) for each gradation of RGB (0 to 255). It may be converted to a value.

  The level correction unit (gradation conversion unit) 43 receives the luminance value X from the color conversion unit 41, and obtains the luminance value Y by performing level correction to expand the range in which the luminance value X is distributed. In level correction, first, the histogram creation unit 50 calculates a histogram for the luminance data X of the frame image, and the level correction parameter generation unit 51 calculates the upper limit value XH and the lower limit value XL of the luminance value X of the frame image from the histogram. Is acquired as a level correction parameter. For example, when a histogram as shown in FIG. 3 is created, the upper limit value XH and the lower limit value XL can be acquired from the histogram H (X). In the first embodiment, as shown in FIG. 3, the luminance value that takes the maximum value of the histogram H (X) is the upper limit value XH, and the luminance value that takes the minimum value is the lower limit value XL. However, in order to reduce the noise included in the frame image or the influence included in the non-image data portion such as subtitles and time display, the histogram H (X) has a luminance value X that is a predetermined frequency or higher, the upper limit value XH, and the lower limit value XL. May be requested. Further, an approximate curve is generated from the histogram H (X), and the upper limit value XH and the lower limit value XL are obtained from the brightness value at which the approximate curve intersects the X axis, or the brightness value at which the approximate curve becomes a predetermined value or more. Also good.

Next, as shown in FIG. 4, the level correction execution unit 52 linearly converts the range between the upper limit value XH and the lower limit value XL of the frame image into the maximum brightness value range that can be expressed in the brightness data. Thus, the luminance value Y is converted. That is, in the first embodiment, since the number of gradations expressing the luminance value is 256 gradations of “0 to 255”, level correction is performed according to the following equation.
Y (X) = 255 × (X−XL) / (XH−XL) (4)

  FIG. 4 is a diagram showing a gradation line representing the relationship between the luminance value X and the luminance value Y obtained by level correction, that is, the relationship of Expression (4). As shown in FIG. 4, the luminance value Y with respect to the luminance value XL is “0” and the luminance value Y with respect to the luminance value XH is “0” by performing conversion according to the correction straight line HL that is a gradation line representing the relationship of the expression (4). A linear transformation of 255 "will be performed. As is clear from the figure, the gradation range “XL to XH” of the luminance value X is expanded to the gradation range “0 to 255” for the luminance value Y, so that the contrast of the frame image is increased by level correction. Can do.

  Here, if the luminance value is level-corrected according to Equation (4), the luminance of the entire frame image changes. For example, when the distribution of the luminance value X of the frame image is biased from the lower limit value XL to the upper limit value XH, the average value of the luminance values of the entire frame image is increased by level correction, and the luminance of the entire frame image is increased. . Therefore, the image processing engine 15 of the first embodiment performs correction so as to reduce the change in luminance value due to level correction.

The brightness correction unit 44 performs brightness correction to reduce the luminance change caused by the level correction. The correction formula for brightness correction is defined as follows.
Y ′ (Y) = F (Y) G1 + Y (5)
Here, Y ′ is a luminance value whose level is corrected, G1 is a correction amount for brightness correction at a predetermined luminance value, and F (Y) is a value to be corrected for each luminance value Y with reference to the correction amount G1. A correction coefficient indicating a ratio. Hereinafter, a method for determining the correction curve shown in Expression (5), that is, a method for determining the correction coefficient F (Y) and the correction amount G1 will be described in order.

  A predetermined function is used as the correction coefficient F (Y). FIG. 5 shows the relationship between the luminance value Y and the correction coefficient F (Y). As the correction coefficient F (Y) of the first embodiment, as shown in FIG. 5A, a curve having a correction point “192” as a gradation value as a reference for correction, and a curve shown in FIG. As shown in FIG. 2), two curves, a curve with a correction point of “64”, are used. As shown in FIG. 5A, the correction coefficient F (Y) when the correction point is “192” is P1 (F1 is “0” at luminance values “0” and “255”). 0, 0) and P2 (255, 0), and a function represented by a spline curve passing through P3 (192, 1) where F (Y) becomes “1” at the correction point “192”. When the correction point is “64”, the correction coefficient F (Y) is F1 at P1 (0,0) and P2 (255,0) and the correction point “64” as shown in FIG. A function represented by a spline curve passing through P4 (64, 1) where (Y) is “1”. Note that the data of the correction coefficient F (Y) shown in FIG. 5 is stored in advance in the correction coefficient holding unit 46 as a table representing the value of F (Y) corresponding to each gradation value (0 to 255) of the luminance value Y. Has been.

  As described above, the image display device 1 according to the first embodiment has two correction coefficients F (Y), and the correction point is determined when the average value of the luminance values is reduced by the level correction. A correction coefficient F (Y) of “192” is used. When the average value of the luminance values is increased by the level correction, the correction coefficient F (Y) is properly used by using the correction coefficient F (Y) with the correction point being “64”.

When the correction coefficient F (Y) is determined, the correction amount G1 is next determined. The correction amount G1 is determined to be a value that equalizes the average value Xave of the luminance value X and the average value Y′ave of the luminance value Y ′ whose level has been corrected. That is, from the equation (6) representing the average value Y′ave of the luminance value Y ′ and the equation (7) representing the condition that the average value Y′ave is equal to the average value Xave of the luminance value X before level correction. The equation (8) representing the correction amount G1 can be obtained.
Y'ave = ΣY '/ N
= Σ (F (Y) G1 + Y) / N (6)
Y'ave = Xave (7)
G1 = (N × Xave−ΣY) / ΣF (Y)
= N × (Xave−Yave) / ΣF (Y) (8)

Here, a difference value Δave between the average value Xave of the luminance value X and the average value Yave after the level correction is determined as follows.
Δave = Yave−Xave (9)
That is, the difference value Δave indicates the amount of change in luminance value caused by level correction. From the equations (8) and (9) representing the correction amount G1, the correction amount G1 can also be expressed as the following equation.
G1 = −N × Δave / ΣF (Y) (10)
The correction amount G1 can be obtained from Expression (8) or Expression (10).

  Since the brightness correction unit 44 corrects the brightness value Y to the brightness value Y ′ so as to satisfy the condition of Expression (7), it is possible to eliminate the change in brightness value caused by the level correction.

  FIG. 6 is a diagram illustrating an example of a gradation curve for brightness correction (hereinafter referred to as a correction curve). FIG. 6A shows a correction curve HC1 when the luminance value is corrected to increase, that is, the correction amount G1 is a positive value. Since the correction coefficient F (Y) at this time is “1” at the correction point “192”, the correction curve HC1 uses the level-corrected luminance value Y “192” as the luminance value Y ′ of “192 + G1”. It is corrected to. Further, since the correction coefficient F (Y) for the luminance value Y of “0” and “255” is “0”, the luminance value Y for the level-corrected luminance value Y of “0” and “255” is set to “ It is corrected to “0” and “255”, and the luminance value does not change. That is, the correction curve HC1 is a curve connecting three points (192, 192 + G1), (0, 0), and (255, 255).

  FIG. 6B shows a correction curve HC1 when the luminance value is corrected to be small, that is, the correction amount G1 is a negative value. Since the correction coefficient F (Y) at this time is a coefficient that becomes “1” at the correction point “64”, the correction curve HC1 changes the level-corrected luminance value Y “64” to the luminance value Y ′ of “64 + G1”. to correct. The luminance value does not change when the luminance value Y is “0” or “255”. That is, the correction curve HC is a curve connecting three points (64, 64 + G1), (0, 0), and (255, 255).

The image display signal generation unit 45 performs a process of converting the brightness value Y ′ whose brightness has been corrected and the gradation value uv of the color difference data into RGB data. Here, it is possible to obtain RGB data whose brightness has been corrected according to the following equation for converting luminance data and color difference data into RGB data. Note that the conversions of the equations (11) to (13) may also be performed according to the color conversion table.
R = Y ′ + 1.420v (11)
G = Y′−0.3441u−0.7139v (12)
B = Y ′ + 1.71818u−0.0012v (13)

  The image display signal generation unit 45 sequentially outputs the converted RGB data as an image display signal corresponding to the display panel 30. The display panel 30 receives the image display signal output from the image display signal generation unit 45 and displays a moving image by sequentially displaying frame images based on the received image display signal.

  As described above, in the image display device 1 according to the first embodiment, the frame image is sequentially acquired from the input moving image data, and the level correction for increasing the contrast for the luminance value X of the frame image, and Brightness correction is performed to correct changes in luminance values caused by level correction.

  FIG. 7 is a timing chart showing processing performed by the image processing engine 15. Hereinafter, it demonstrates in order according to a timing chart.

  The image display device 1 starts the processing shown in FIG. 7 by using the input of moving image data from the input I / F 10 or the reproduction of moving image data stored in the HD 14 as a trigger. When the processing is started, first, the frame image acquisition unit 40 performs input processing for acquiring the gradation value of RGB data from the frame image of the input moving image data, and the color conversion unit 41 sequentially acquires the acquired RGB data. The brightness data X is converted into brightness data X and color difference data uv and stored in the frame memory 42.

  Next, the histogram creation unit 50 successively takes in the converted luminance value X into the histogram H (X). As shown in FIG. 7, the input / color conversion / histogram creation processing is performed in parallel while delaying the processing timing by a small amount of time required for the processing, so when the input of one frame image is completed, A histogram H (X) of the luminance value X for the frame image is completed with a slight delay. For example, as shown in FIG. 3, a histogram H (X) representing the number of pixels with respect to the luminance value X is obtained.

  Next, the level correction parameter generation unit 51 calculates the upper limit value XH and the lower limit value XL of the luminance value X from the histogram H (X), and sets them as level correction parameters. Specifically, as shown in FIG. 3, an operation is performed to obtain an upper limit value XH that takes the maximum value and a lower limit value XL that takes the minimum value from the histogram H (X).

Next, the luminance sum calculation unit 60 calculates the sum ΣY of the luminance values Y, and the average luminance calculation unit 61 calculates the average value Yave of the luminance values Y from the luminance sum ΣY. The luminance summation calculator 63 calculates the sum ΣX of the luminance values X, and the average luminance calculator 64 calculates the average value Xave of the luminance values X from the sum ΣX. In calculating the average, using the histogram H (X) generated as shown in the following equation, the amount of calculation is reduced compared to the case where the total calculation of X and Y is performed for all pixels. Yes.
Yave = ΣY (X) / N
_{= (Σ x H (X)} × Y (X)) / N ... (14)
Xave = ΣX / N
_{= (Σ x H (X)} × X) / N ... (15)

Next, the coefficient sum calculation unit 62 calculates the sum ΣF (Y) of the correction coefficients F (Y) read from the correction coefficient holding unit 46 according to the following equation. As for the correction point of the correction coefficient F (Y), of the average value Yave and the average value Xave, the correction point is “192” when Yave is large, and the correction point is “64” when Xave is large. The correction coefficient F (Y) to be used is selected.
_{ΣF (Y) = Σ Xi H} (Xi) × F (Y (Xi))
(However, Xi is a variable from XL to XH) (16)

  Next, the correction amount calculation unit 65 calculates the correction amount G1 according to Expression (8) or Expression (10).

  With the above processing, parameters used for executing level correction and brightness correction are obtained. Note that the process of calculating the correction amount G1 from the input of the frame image described above is performed during the inter-frame waiting time while the next frame image is input as shown in FIG. When the parameters for the image are calculated, the next frame image of the moving image data is input. The processing after level correction is performed in parallel with the processing for inputting the next frame image.

  Next, the level correction execution unit 52 reads the luminance data X and the color difference data uv from the frame memory 42, and then performs level correction on the luminance data X by performing an operation according to Expression (4).

  Once level correction is performed, the brightness correction execution unit 66 performs brightness correction. Here, using the correction amount G1, the brightness value Y ′ corrected for brightness is calculated according to the correction equation (5).

  When the brightness correction is performed, the image display signal generation unit 45 converts the luminance data (Y ′) and the color difference data (uv) into RGB data, and then the image display signal generation unit 45 converts the RGB data. The image is converted into an image display signal corresponding to the display panel 30 and output to the display panel 30 to perform processing for displaying the corrected frame image.

  As described above, the image display device 1 according to the first embodiment reduces the change in the luminance value generated by performing the level correction for the frame image of the moving image data by the brightness correction. .

  According to the image display device 1 according to the first embodiment, the following effects can be obtained.

  (1) Since the change of the brightness value generated by performing the level correction is reduced (more preferably eliminated) by the brightness correction, the brightness value of the entire frame image is increased while increasing the contrast of the input frame image. As an average value, the values are equal before the level correction. Therefore, it is possible to improve the image quality while suppressing the luminance change of the entire frame image.

  (2) In the technique described in Patent Document 1, the luminance change due to the level correction is reduced by dimming or increasing the light of the light source after performing the level correction. Increase or decrease depending on. On the other hand, according to the first embodiment, since the luminance value is only corrected, the power consumption does not increase.

  (3) In the level correction, the gradation range of the frame image is corrected to the maximum gradation range “0 to 255” of the image data, and in the brightness correction, the lower limit value “0” and the upper limit value of the luminance value subjected to the level correction For “255”, the correction coefficient F (Y) is “0”, so the brightness value is not changed, and the gradation curve HC1 between the brightness values “0” and “255” is bent to brighten the brightness. Correction. Since the contrast of the frame image once increased in the level correction is not lowered by the brightness correction, the contrast can be reliably increased to improve the image quality.

(Second Embodiment)
In the second embodiment, the amount of light emitted from the backlight 32 is controlled (dimming), and brightness correction is performed so as to reduce changes in brightness that occur in the image displayed on the display panel 30 by level correction and dimming. I do. The image display apparatus according to the second embodiment will be described below.

  FIG. 8 is a diagram illustrating a configuration of an image processing engine of the image display apparatus according to the second embodiment. In FIG. 8, the same reference numerals are given to the same components as those of the image processing engine 15 according to the first embodiment. As shown in FIG. 8, the image processing engine 100 includes a dimming rate setting unit 47 and a light amount control unit 48 in addition to the configuration of the image processing engine 15. The brightness correction unit 44 further includes a limit correction amount calculation unit 67 and a final correction amount determination unit 68.

  The dimming rate setting unit 47 sets the dimming rate α as a parameter for reducing the amount of light emitted by the backlight 32 from a predetermined amount and reducing the luminance of the image displayed on the display panel 30. Here, since the light control rate α is a positive number equal to or less than 1, when the light control rate α is “1”, the backlight 32 emits a predetermined maximum light amount. That is, the light is adjusted so that the light is always dimmed with respect to a predetermined light amount. The dimming rate α is a ratio having a linear relationship with a stimulus given to human vision. That is, since it is a ratio that takes into account the sensitivity characteristics of human vision, for example, if the dimming rate α is “0.5”, the stimulus that the luminance of the image displayed on the display panel 30 gives to human vision is This is 50% when the dimming rate α is “1”.

  The dimming rate setting unit 47 refers to a power storage amount remaining in a battery or the like provided in the image display device 1 and calculates a value that allows the image display device 1 to drive a predetermined target drive time. To set the light control rate α. However, the method of setting the dimming rate α is not limited to this, and the power saving is achieved when the image display apparatus 1 is switched from driving with external power to battery driving with power stored in the battery. In conjunction with the switching to the mode, the dimming rate α may be switched to a predetermined value. In addition, the user may arbitrarily set the dimming rate α by displaying a screen for setting power saving on the display panel 30.

The light quantity control unit 48 controls the amount of light generated by the backlight 32 by controlling the power supplied from the power supply device 31 to the backlight 32 according to the dimming rate α. Here, since the dimming rate α is a value that takes into account the sensitivity characteristics of human vision, the dimming rate K of the light source, which indicates the ratio of the actual light amount to the predetermined light amount emitted by the backlight 32, is the gamma coefficient γ. And can be determined by the following equation.
K = α ^γ (17)
For example, the gamma coefficient γ is a value such as “2.2”, and the light source ratio indicating the light amount ratio for actually dimming the backlight 32 from the dimming rate α in consideration of human visual characteristics according to the equation (17). The dimming rate K can be obtained. If the dimming rate α is “1”, the dimming rate K of the backlight 32 is “1”, and the backlight 32 emits the maximum amount of light.

Further, since the amount of light generated by the backlight 32 and the luminance of the image displayed on the display panel 30 are generally proportional, the actual luminance L of the image displayed on the display panel 30 when dimming is not dimmed. The relationship with the actual luminance LU0 of the image at that time can be expressed by the following equation.
LU = K × LU0 (18)

  For example, when the dimming rate α is set to “0.85” in order to reduce the luminance perceived by humans by 15%, the gamma coefficient γ is “2.2”. The dimming rate K is “0.7”. Since the luminance L when dimming from the equation (18) has only to be reduced by 30% compared to the luminance LU0 when not dimming, the power supplied to the backlight 32 can be reduced. The light quantity control unit 48 calculates a dimming rate K of the light source from the dimming rate α according to the equation (17), and outputs a control signal for controlling the power supplied to the backlight 32 according to the dimming rate K of the light source. Dimming is performed by transmitting to the power supply device 31.

  The image display signal generation unit 45 transmits the generated image display signal to the display panel 30 in synchronization with the timing at which the light amount control unit 48 controls the light source. The display panel 30 displays an image by modulating the light emitted from the backlight 32 based on the received image display signal and controlling the transmission amount for each pixel.

The brightness correction unit 44 performs brightness correction in order to reduce a change in luminance generated in an image displayed by dimming in addition to a change in luminance value due to level correction. When the brightness value Z is corrected for brightness, the correction formula is defined as follows.
Z (Y) = F (Y) × G2 + Y (19)
Here, the correction amount G2 is determined so that the product of the average value of the brightness value Z corrected for brightness and the dimming rate α is equal to the average value of the brightness value X. That is, a correction amount G2 that satisfies the following equation is calculated. It should be noted that the expression (20) shows that the brightness as the brightness for displaying an image based on the brightness value X of the image data when the light is not adjusted and the brightness for displaying the image based on the brightness value Z when the light is adjusted are visually recognized. It means that the top is equal.
α × Zave = Xave (20)

In order to eliminate the change in the luminance value due to the level correction and the change in the luminance caused by the dimming, the correction amount G2 should be set so as to satisfy the equation (20). From the equation (19), the correction is performed as follows. The amount G2 is obtained.
G2 = N (N × Xave−αΣY) / (αΣF (Y))
= −N × Δave2 / (αΣF (Y)) (21)
here,
Δave2 = α × Yave−Xave
= 255 * [alpha] * (Xave-XL) / (XH-XL) -Xave (22)
Using the correction coefficient F (Y) and the correction amount G2 expressed in Expression (21), brightness correction can be performed according to Expression (19) that is a correction expression.

  Here, when the brightness correction is performed as described above, the contrast corresponding to the high luminance region may be lowered. FIG. 9 is a diagram showing a correction curve HC2 for brightness correction when the brightness value is corrected to increase, that is, when the correction amount G2 is a positive value. In FIG. 9, the abscissa indicates the luminance value Y, the ordinate indicates the luminance value Y and the luminance value Z multiplied by the dimming rate, the effective luminance value α × Z is obtained, the correction curve corrected for brightness is HC2, and the correction for level correction is performed. A straight line is indicated by HL. As shown in FIG. 9, the gradation range of the correction straight line HL when the brightness correction corresponding to the luminance side higher than the average luminance Yave is not performed is “z1 (= Yave) to 255”. When the brightness correction is performed with the upwardly convex gradation curve HC2 using the correction amount G2 (> 0), the luminance corresponding to the region “Yave˜255” of the luminance value Y higher than the average value Yave of the luminance values Y The range of the effective luminance value obtained by multiplying the value Z by the dimming rate is “z2 (= α × Z (Yave)) to 255 × α” according to the correction curve HC2. That is, the luminance range of “z2 to 255 × α” corresponding to the luminance value Y equal to or higher than the average value Yave is smaller than the original luminance range of “z1 to 255”. This is because the range in which the level of the brightness value can be expressed is small, and the contrast is lowered.

  Therefore, in the second embodiment, the value of the dimming rate α is limited in order to suppress a decrease in contrast on the high luminance side due to dimming to a certain level.

Hereinafter, a process when the light control rate α is limited will be described. In order to add a restriction, first, the gradation difference L1 of the luminance value Y on the higher luminance side than the average luminance value Yave of Y when dimming is not performed, and the effective luminance value α × Z when dimming is on the higher luminance side. The gradation difference L2 is obtained as follows.
L1 = 255−Yave (23)
L2 = α × 255−α × Z (Yave)
= Α × (255− (F (Yave) × G2 + Yave)) (24)
If the ratio of gradation difference due to the presence or absence of light control is the contrast maintenance ratio, the contrast maintenance ratio R on the high luminance side can be determined by the following equation.
R = L2 / L1
= Α (255− (F (Yave) × G2 + Yave)) / (255−Yave)
... (25)
In order not to lower the contrast maintenance rate R obtained by the equation (25) below the predetermined ratio Rlim, the light control rate α and the correction amount G2 when the contrast maintenance rate is Rlim are obtained. If the dimming rate at this time is the limit dimming rate αlim and the correction amount is the limit correction amount G2lim, the following equation can be obtained from equation (25).
Rlim = αlim (255− (F (Yave) × G2lim + Yave))
/ (255-Yave) (26)
On the other hand, from equation (19),
Zave = (ΣF (Y (Xi)) × G2lim + Y) / N (27)
From the equations (27) and (20), the limit dimming rate αlim when the limitation is applied can be expressed by the following equation.
αlim = NXave / (ΣF (Y) G2lim + ΣY)
= ΣX / (ΣF (Y) G2lim + ΣY) (28)
From Equation (26) and Equation (28), the limit correction amount G2lim can be obtained as in the following equation. When the limit correction amount G2lim is determined, the limit dimming rate αlim is obtained from the equation (28).
G2lim = (ΣX−RlimΣY) × (255−Yave)
/ (F (Yave) ΣX + Rlim (255−Yave) ΣF (Y)
... (29)

The final dimming rate α ′ and the final correction amount G2 ′ used for actual brightness correction are determined as follows.
G2 ′ = min (G2, G2lim) (30)
α ′ = max (α, αlim) (31)
Here, min () is a function that returns the minimum value among the arguments, and max () is a function that returns the maximum value among the arguments.

By performing conversion according to the equation (19) using the final correction amount G2 ′, it is possible to perform brightness correction using the final dimming rate α ′. That is, if the luminance value corrected by the final dimming rate α ′ is Z ′, the brightness is corrected according to the following equation.
Z ′ (Y) = ΣF (Y) × G2 ′ + Y (32)
By converting the luminance value Y into the luminance value Z ′ according to the correction equation of the equation (32), the reduction in contrast on the high luminance side is suppressed while correcting the luminance change of the image caused by level correction and dimming. Can do.

  Further, the brightness correction unit 44 passes the final dimming rate α ′ obtained in the brightness correction to the light amount control unit 48. The light quantity control unit 48 calculates the dimming ratio K of the light source corresponding to the final dimming ratio α ′ by Expression (17), and performs control for causing the backlight 32 to generate a light quantity corresponding to the final dimming ratio α ′. Is going.

  The image display signal generation unit 45 generates an image display signal corresponding to the display panel 30 from RGB data obtained by converting the luminance value Z ′ and the color difference data uv according to the equations (11) to (13). The image display signal generation unit 45 transmits the generated image display signal to the display panel 30 in synchronization with the timing at which the light amount control unit 48 controls the backlight 32. The display panel 30 displays a corrected frame image by modulating the light received from the backlight 32 based on the received image display signal and controlling the transmission amount for each pixel.

  As described above, the image processing engine 100 according to the second embodiment sets the dimming rate α and performs level correction and back-up to increase the contrast of the luminance data of the frame image acquired from the moving image data. The light 32 is dimmed to perform level correction and brightness correction to reduce the change in luminance of the displayed image caused by the dimming. In the brightness correction, a process for suppressing a decrease in contrast on the high gradation side is also performed.

  FIG. 10 is a timing chart showing processing performed by the image processing engine 100, and will be described in order according to the timing chart.

  When the processing shown in FIG. 10 is started, first, the dimming rate setting unit 47 sets the dimming rate α.

  When the dimming rate α is set, as in the first embodiment, frame image input, color conversion, and histogram creation processing are performed in parallel, and level correction parameters XH and XL are generated from the created histogram H (X). Is calculated. Using the calculated level correction parameters XH and XL, brightness correction parameters ΣX, ΣY, Xave, Yave, and ΣF (Y) are calculated.

  Next, the correction amount calculation unit 65 calculates the correction amount G2 according to the equation (21), and the limit correction amount calculation unit 67 calculates the limit correction amount G2lim according to the equation (29) using the limit contrast maintenance rate Rlim.

  Next, the final correction amount determination unit 68 determines the final correction amount G2 'according to the equation (30) and the final dimming rate α' according to the equation (31).

  Next, as in the first embodiment, after the level correction execution unit 52 performs level correction using the luminance data read from the frame memory 42, the brightness correction execution unit 66 performs brightness according to the equation (32). By performing the brightness correction, the brightness value corrected brightness value Z ′ is calculated.

  Next, the image display signal generation unit 45 converts the luminance data (Z ′) and the color difference data (uv) into RGB data, and generates an image display signal from the RGB data. The generated image display signal is output to the display panel 30. At this time, the light quantity control unit 48 calculates the light control rate K of the light source from the final light control rate α ′, and adjusts the power supplied to the backlight 32 in accordance with the timing of outputting the image display signal to the display panel 30. To adjust the light. A frame image is displayed by the display panel 30 modulating the dimmed light.

  As described above, according to the image processing engine 100 according to the second embodiment, an image in which a change in luminance generated by performing level correction and dimming is displayed on the image data of the frame image is displayed. . In addition, by limiting the contrast maintenance ratio R in the high luminance region, the brightness correction is performed so that the reduction in the contrast in the high luminance side region falls within a certain level.

  FIG. 11 is a diagram showing an example of a correction curve HC2 'for brightness correction with a restriction when the correction amount is a positive value. As shown in FIG. 11, the image processing engine 100 according to the second embodiment has a restriction on dimming. Therefore, the final dimming ratio α ′ is the dimming ratio when the restriction shown in FIG. 9 is not provided. The value is larger than α. Therefore, the gradation range of the effective luminance value α × Z ′ of the luminance value Z ′ corresponding to the luminance value region (z1 to 255) higher than the average value Yave of the luminance value Y is a range of “z3 to α ′ × 255”. Thus, the gray level range “z2 to α × 255” of the effective luminance value α × Z in FIG. Therefore, by limiting the dimming, the amount of decrease in the gradation range of the effective luminance value in the high luminance region is reduced, and the decrease in contrast can be suppressed.

  According to the image display device of the second embodiment, in addition to the effect (3) in the first embodiment, the following effects can be obtained.

  (4) Since the correction is performed so as to reduce (more preferably eliminate) the change in luminance generated in the image displayed by the level correction and dimming, the power consumption due to the expansion of the contrast by the level correction and the dimming While realizing the reduction, the average luminance for displaying the frame image is equal to the average luminance when the frame image before the level correction is displayed. Therefore, it is possible to reduce power consumption and improve image quality without changing the luminance of the image displayed on the display panel 30 as the entire image.

  (5) In the technique described in Patent Document 1, since the amount of change due to level correction is eliminated by dimming or increasing the light of the light source after performing level correction, the power consumed depends on the frame image. To increase or decrease. On the other hand, according to the second embodiment, dimming is performed in accordance with the set dimming rate α, and the luminance value is corrected to reduce the change in luminance due to level correction and dimming. Electric power can be reliably reduced.

  (6) When the light is dimmed by dimming, the reduction in contrast in the high luminance region is limited to a certain level, that is, the contrast maintenance ratio Rlim, so that the reduction in contrast in the high luminance region can be suppressed. Since an image displayed on the display panel 30 is restrained from lowering the contrast in the high-luminance region, the possibility that the gradation is lost due to brightness correction and light control is reduced.

  (7) The correction for the image data is performed by the dimming rate α or the limit dimming rate αlim according to the human visual sensitivity characteristic with respect to light. Therefore, it is possible to perform brightness correction and dimming suitable for the sensitivity characteristics of human vision with respect to light.

(Third embodiment)
In the third embodiment, the brightness correction is performed so as to approach the predetermined reference brightness, thereby correcting the bias of the brightness value. The image display apparatus according to the third embodiment will be described below.

  FIG. 12 is a diagram illustrating a configuration of an image processing engine of the image display apparatus according to the third embodiment. As illustrated in FIG. 13, the brightness correction unit 44 of the image processing engine 200 calculates a correction amount for further correcting the bias of the luminance value in addition to the configuration of the image processing engine 100 according to the second embodiment. A correction amount (G3) calculation unit 69 is provided.

The brightness correction unit 44 of the third embodiment performs brightness correction so as to approach a predetermined brightness reference. In the brightness correction, the brightness value Y level-corrected according to the following equation is converted into a brightness value Y ″.
Y ″ = F (Y) × G3 + Y (33)
Here, since Expression (33) has the same shape as Expression (5) and Expression (19), the correction curve is convex upward or convex downward according to the sign of the correction amount G3. The correction amount G3 is given by the following equation.
G3 = Ga (Yth−Yave) (34)
Here, Ga is a brightness correction intensity coefficient, which is a predetermined value of 0 or more, and Yth is a brightness reference (reference gradation value). The value of the brightness correction intensity coefficient Ga and the brightness reference Yth may be a predetermined constant or set by the user. Alternatively, it may be determined according to the type of image data.

  As can be seen from the equation (34), the correction amount G3 is proportional to the value obtained by subtracting the average value Yave from the brightness reference Yth. Therefore, if the luminance value Y is corrected in the direction of the correction amount G3, the luminance value Y Can be corrected so as to be close to the brightness reference Yth, and the deviation of the luminance value of the image data can be reduced.

  If the correction amount G3 is determined, the brightness can be corrected by the equation (33), but actually, the correction amount G3 calculated by the correction amount calculation unit 69 without performing the calculation of the equation (33). Are passed to the correction amount calculation unit 65 and the limit correction amount calculation unit 67 as parameters.

The brightness correction unit 44 further performs a correction according to the following formula to correct the bias of the brightness value and perform an enhanced brightness correction that reduces a change in brightness generated in an image to be displayed by further dimming. Do. The enhanced brightness correction formula is defined by the following formula.
Z (Y) = F (Y) × G4 + Y (35)
Here, the correction amount G4 is determined so that the product of the enhanced brightness corrected average value Z of brightness values Z and the dimming rate α is equal to the average value of brightness corrected brightness values Y ″. Equation (36) means that the luminance for displaying an image based on the luminance value Y ″ is visually equal to the luminance for displaying an image based on the luminance value Z when dimming.
α × Zave = Y ″ ave (36)
Here, the right side and the left side of Expression (36) can be expressed as the following expression.
Y "ave = ΣY" / N
= (ΣF (Y) × G3 + ΣY) / N (37)
on the other hand,
Z'ave = ΣZ '/ N
= (ΣF (Y) × G4 + ΣY) / N (38)
From the equations (36) to (38), the following equation representing the correction amount G4 can be obtained.
G4 = G3 / α + (1-α) ΣY / (αΣF (Y)) (39)

  Here, since the correction amount G4 shown in the equation (39) is not a luminance value Y ″ but a function of the correction amount G3, the brightness correction unit 44 actually performs the calculation according to the equation (33). Therefore, it is possible to calculate the correction amount G4 from the correction amount G3, and thus the enhanced brightness correction that reduces the luminance change due to dimming after correcting the bias of the luminance value by using the obtained correction amount G4. It can be performed.

Next, similarly to the second embodiment, a restriction is provided on the light control rate α in order to suppress a decrease in contrast. On the higher gradation side than the luminance value corresponding to the average luminance value Yave of the luminance value Y, the gradation difference L1 ′ of the luminance value Y ″ without dimming, the effective luminance value α × Z ′ with dimming The gradation difference L2 ′ can be expressed by the following equation.
L1 ′ = 255−Y ″ (Yave)
= 255− (F (Yave) × G3 + Yave) (40)
L2 ′ = α × 255−α × Z ′ (Yave)
= Α × (255− (F (Yave) G4 + Yave)) (41)
At this time, an expression representing the contrast maintenance ratio R ′ and an expression that holds when the contrast maintenance ratio R ′ is limited to Rlim ′ are obtained as follows from the expressions (40) and (41).
R ′ = L2 ′ / L1 ′
= Α × (255− (F (Yave) G4 + Yave))
/ (255− (F (Yave) × G3 + Yave)) (42)
Rlim ′ = αlim × (255− (F (Yave) G4lim + Yave))
/ (255− (F (Yave) × G3 + Yave)) (43)
Here, based on the condition of Expression (36), the limit correction amount G4lim can be obtained from Expression (37), Expression (38), and Expression (43) as in the following expression.

また、式（４４）に示す限界補正量Ｇ４ｌｉｍおよび式（４３）より限界調光率αｌｉｍを求めることができる。

Further, the limit dimming rate αlim can be obtained from the limit correction amount G4lim shown in Expression (44) and Expression (43).

The final correction amount G4 ′ and the final dimming rate α ′ that are actually corrected are obtained by the following equations.
G4 ′ = min (G4, G4lim) (45)
α ′ = max (α, αlim) (46)
Further, by performing the correction according to the equation (35) using the final correction amount G4 ′, it is possible to perform the brightness correction when limited to the final dimming rate α ′. That is, if the luminance value corrected when limiting to the final dimming rate α ′ is Z ′, the brightness is corrected according to the following equation.
Z ′ (Y) = ΣF (Y) × G4 ′ + Y (47)

  As described above, the image processing engine 200 of the image display device according to the third embodiment sets the dimming rate α and corrects the deviation of the luminance value of the frame image acquired from the input moving image. While correcting, the luminance change caused by dimming is reduced.

  FIG. 13 is a timing chart showing processing performed by the image processing engine 200. Hereinafter, processing performed by the image processing engine 200 will be described in order.

  The processing shown in FIG. 13 is started, and first, in the same manner as the image processing engine 100 in the second embodiment, the dimming rate α setting, frame image input, color conversion, and histogram creation processing are performed in parallel. After that, level correction parameters XH and XL and ΣX, ΣY, Xave, Yave, and ΣF (Y) are calculated. The correction point for the correction coefficient F (Y) is selected based on the sign of the correction amount G3. Specifically, the correction coefficient “192” is used when the value obtained by subtracting the average luminance value Yave from the brightness reference Yth is positive, and the correction coefficient “64” is used when the value is negative.

  Next, the correction amount calculation unit 69 calculates the correction amount G3 from the brightness reference Yth and the average value Yave of the luminance value Y according to the equation (34).

  When the correction amount G3 is calculated, the correction amount calculation unit 65 calculates a correction amount G4 for enhanced brightness correction according to the equation (39), and the limit correction amount calculation unit 67 uses the limit contrast maintenance rate Rlim to calculate the equation (44). ) To calculate the limit correction amount G4lim and the limit light control rate αlim.

  Next, the final correction amount determination unit 68 determines the final correction amount G4 'according to the equation (45). At this time, the final dimming rate α ′ is also determined according to the equation (46).

  Next, the brightness correction execution unit 66 performs the brightness correction enhanced according to the equation (47) using the level correction and the final correction amount G4 ′ for the brightness value Y subjected to the level correction to obtain the brightness value Z ′. calculate.

  Next, an image display signal corresponding to the display panel 30 is generated from the RGB data converted from the luminance value Z ′ and the color difference data, and is output to the display panel 30. The light amount control unit 48 calculates the light control rate K of the light source from the final light control rate α ′, and the light amount control unit 48 supplies the backlight 32 with the timing of outputting the image display signal to the display panel 30. Dimming is performed by adjusting the power. A frame image is displayed by the display panel 30 modulating the dimmed light.

  FIG. 14 is a diagram illustrating an example of a correction curve for brightness correction and enhanced brightness correction. FIG. 14A shows an example when the correction curve HC3 for brightness correction is convex upward. In this case, since the entire image is biased to a gradation value lower than the predetermined brightness reference, the correction curve HC3 is corrected to increase the brightness of the entire image by converting the convex shape upward. Become. At this time, the enhanced brightness correction gradation curve HC4 ′ has an effective luminance value range that is α ′ times smaller than the gradation range of HC3 due to dimming according to the final dimming rate α ′, and changes in luminance occur. . Therefore, the correction curve H4 ′ has a convex shape that is larger than the correction curve HC3, thereby reducing the luminance change caused by the light control.

  FIG. 14B shows an example when the correction curve HC3 for brightness correction is convex downward. In this case, since the entire image is biased to a gradation value higher than a predetermined brightness reference, the correction curve HC3 is corrected so as to lower the gradation value of the entire image by converting the convex shape downward. It will be. At this time, the enhanced brightness correction correction curve HC4 'has a convex shape upward with respect to the correction curve HC3, thereby reducing a luminance change caused by dimming.

  According to the image display device of the third embodiment, in addition to the effect (3) in the first embodiment and the effects (5) to (7) in the second embodiment, the following effects are obtained. be able to.

  (8) Since the brightness correction is enhanced so as to reduce (preferably eliminate) the amount of change in brightness due to dimming based on the brightness that should be after brightness correction, the image quality is improved by level correction. While realizing a reduction in power consumption by dimming, it is possible to display an image with moderate brightness by further correcting the bias of the brightness value by brightness correction.

  The first to third embodiments of the present invention have been described above. The present invention is not limited to these embodiments, and can be implemented in various forms without departing from the spirit of the present invention. Hereinafter, a modification will be described.

  (Modification 1) In the above-described embodiment, the processing is performed on the frame image stored in the frame memory 42. However, even when there is no frame memory 42, the processing can be appropriately performed. In the first modification, a process performed when there is no frame memory 42 will be described. FIG. 15 is a diagram illustrating a processing timing chart in the first modification. In the timing chart of FIG. 15, the horizontal axis indicates time T in order by t0 to t5. In FIG. 15, when the input of the frame image F (0) is first started at time t0, for example, by playing a moving image, the frame image acquisition unit 40 displays the luminance value of the input pixel in the histogram H (X). Processing for incorporation is performed (time t0 to t1). When the input for all the pixels of the frame image F (0) is completed, the histogram H (X) for all the pixels of the frame image F (0) is acquired (time t1). Next, the level correction unit 43 calculates the upper limit value XH and the lower limit value XL of the luminance value using the histogram H (X) (time t1 to t2). When the upper limit value XH and the lower limit value XL are calculated, ΣX, ΣY, and ΣF (Y) are calculated from the histogram H (X) (time t2 to t3). Next, the correction amount G1 is calculated according to the equation (12) (time t3 to t4). The upper limit value XH and lower limit value XL, which are level correction parameters, and the correction amount G1, which is a parameter for performing brightness correction, are determined for the frame image F (0) by the processing at times t0 to t4. In the first modified example, since there is no frame memory 42, the parameter determined between times t0 and t4 is applied to the next frame image F (1). That is, when the next frame image F (1) is input, for each pixel of the input frame image F (1), level correction using the upper limit value XH and the lower limit value XL, and brightness using the correction amount G1. The corrected frame image F (1) is output (time t4 to t5). In this way, even if there is no frame memory 42, correction can be performed in real time by shifting the frame number by one in time series. Further, the processing amount required for the calculation performed between times t1 to t4 in FIG. 15 is a process that can be processed relatively easily during the frame waiting time if the calculation is performed by a general hardware circuit. Become. If the final correction amount G2 ′ or the final correction amount G4 ′ is calculated, in addition to dimming or dimming, the brightness correction of the second embodiment and the enhanced brightness correction of the third embodiment are performed. It is also possible to cope with the case of performing.

(Modification 2) In the third embodiment, since it is necessary to perform a complicated operation to calculate the limit correction amount G4lim when the contrast maintenance rate is limited as shown in the equation (44), The amount will increase. Therefore, in the second modification, the limit correction amount G4lim is simplified and expressed as shown in the following equation.
G4lim = −AXave + B (48)
Alternatively, the limit correction amount G4lim may be determined by the following equation using the average value Yave of the luminance value Y instead of the average value Xave of the luminance value X.
G4lim = −CYave + D (49)
According to experiments conducted by the inventors using a plurality of images, it has been found that the limit correction amount G4lim and the average value Xave or the average value Yave can be approximated to a linear relationship. Therefore, since the limit correction amount G4lim can be calculated by a simple calculation using the equation (48) or the equation (49), the processing amount can be reduced. At this time, as the values of the coefficients “A” and “B” or “C” and “D”, predetermined values may be used, or a predetermined number of frame images acquired from the input moving image. It may be calculated using. In this way, since the processing amount can be reduced, it is possible to reduce the load of calculation performed during the frame waiting time while the frame image is input. Further, the limit correction amount G4lim may be given as follows in a simplified manner. Here, Gconst is a constant set appropriately.
G4lim = G3 + Gconst (50)
Similarly, the limit correction amount G2lim in the second embodiment may be obtained simply as shown in Expression (48) or Expression (49).

  (Modification 3) In the above embodiment, the correction coefficient F (Y) is obtained using either “192” or “64” as a correction point. The correction point is not limited to this. For example, the luminance value “128” or the average value of the luminance value Y may be used as the correction point. Also, the types of curves are not limited to spline curves, and various commonly used curves such as approximate curves by the least square method and gamma curves may be used.

  (Modification 4) In the above embodiment, an example of processing by hardware has been described. As a fourth modification, the same processing may be realized by software. For example, the functions of the components of the image processing engine shown in FIG. 2, FIG. 8, or FIG. 12 are realized by an image display program that is executed by a CPU (computer) 11. The image processing program may be stored in advance in the hard disk 14 or the ROM 12, or supplied from the outside by a computer-readable recording medium such as the CD-ROM 22, and read by the CD-ROM drive 16. The image processing program may be stored in the hard disk 14. Alternatively, the data may be stored in the hard disk 14 by accessing a server or the like that supplies an image processing program via network means such as the Internet and downloading the data.

  Of course, a part of the functions may be realized by a hardware circuit, and a function that the hardware circuit does not have may be realized by software. At this time, for example, long-term routine processing performed in parallel with image input such as color conversion to Yuv data, histogram creation, level correction, brightness correction, and color conversion to RGB data is performed by a hardware circuit, Short-term atypical processing such as correction amount calculation performed during the inter-frame waiting time is performed by software. That is, when the input of one frame image is completed, the hardware circuit generates an interrupt request signal, and the CPU 11 calculates the correction amount in the interrupt handler and writes it in the correction amount setting register of the hardware circuit. The hardware circuit performs correction using the register setting in the next frame image.

  (Modification 5) In the embodiment described above, RGB data is converted into luminance data, and the luminance data is corrected. However, RGB data may be decomposed into R data, G data, and B data and corrected for each data. In addition, when a monochrome image having no color information is input, the gradation data of the image may be corrected as luminance data.

  (Modification 6) In the first embodiment, the image display apparatus includes the display panel 30. However, an image may be displayed on an external display or projector.

  (Modification 7) In the first embodiment, the display panel is a liquid crystal panel. However, a non-light emitting display panel such as a liquid crystal panel or a self light emitting display panel such as an organic EL (Electroluminescence) panel is used. It can also be applied.

  (Modification 8) The display panel 30 of the second and third embodiments is not limited to a transmissive liquid crystal panel as long as it is a non-luminous display panel provided with a light source separately. Alternatively, although not a direct-view type display device, it can also be applied to a projector using DMD (Digital Micromirror Device: trademark of Texas Instruments) or the like.

  (Modification 9) In the image display devices according to the second and third embodiments, light control is performed to control the amount of light by adjusting the power supplied to the light source. If the amount of emitted light cannot be changed as much as the high-pressure mercury lamp used in projectors, a mechanism for controlling the size of the diaphragm on the optical path that guides the light emitted from the light source can be provided to change the size of the diaphragm. The light control may be performed by Further, the light may be reduced by inserting an optical filter for reducing the amount of light passing therethrough into the optical path. In these cases, power consumption is not reduced, but dimming without increasing power consumption can be performed. In addition, it is good also as dimming combining several methods. When a light source that does not have a wide light control range or a light source that cannot implement an arbitrary light control rate, desired light control can be performed by using a stop that can be controlled steplessly. As described above, the spatial light modulator has been described taking as an example one in which other pixels of the liquid crystal panel are two-dimensionally arranged to modulate light. However, the spatial light modulator may be a device (for example, GLV: Grating Light Valve) that displays a two-dimensional image by scanning the modulated light with pixels arranged one-dimensionally.

The figure which showed the hardware constitutions of the image display apparatus in 1st Embodiment. The figure which showed the structure of the image processing engine. The figure which showed the histogram of the frame image. The figure which showed an example of the correction straight line of level correction. The figure which showed the correction coefficient. (A) is a figure which shows the correction coefficient corresponding to the correction point "192", (b) is a figure which shows the correction coefficient corresponding to the correction point "64". The figure which showed an example of the correction curve of brightness correction. (A) is a figure which showed the correction curve when performing the correction which increases a luminance value, (b) is the figure which showed the correction curve when performing the correction which reduces a luminance value. 6 is a timing chart showing processing performed by the image processing engine. The figure which showed the structure of the image processing engine of the image display apparatus which concerns on 2nd Embodiment. The figure which showed an example of the correction curve of brightness correction. The figure which showed the timing chart which shows the process which an image display apparatus performs. The figure which showed an example of the correction curve of brightness correction. The figure which showed the structure of the image processing engine of the image display apparatus which concerns on 3rd Embodiment. The figure which showed the timing chart which shows the process which an image display apparatus performs. The figure which showed an example of the correction curve of brightness correction and the enhanced brightness correction. (A) is a correction curve when the brightness correction correction curve is convex upward, and (b) is a diagram showing the correction curve when the brightness correction correction curve is convex downward. The figure which showed the timing chart of the process in a 1st modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image display apparatus, 10 ... Input interface, 11 ... CPU, 12 ... ROM, 13 ... RAM, 14 ... Hard disk, 15 ... Image processing engine, 16 ... Display interface, 17 ... Power interface, 18 ... Bus, 20 ... Digital Video camera, 21 ... Digital still camera, 30 ... Display panel as spatial light modulator, 31 ... Power supply device, 32 ... Backlight as light source, 40 ... Frame image acquisition unit as image data acquisition unit, 41 ... Color Conversion unit 42... Frame memory 43. Level correction unit as gradation conversion unit 44. Brightness correction unit 45. Image display signal generation unit 46. Correction coefficient holding unit 47. Dimming rate setting unit 48 ... light quantity control unit, 50 ... histogram generation unit, 51 ... level correction parameter generation unit, 52 ... level correction execution unit, 6 ... brightness summation calculation part, 61 ... average brightness calculation part, 62 ... coefficient summation calculation part, 63 ... brightness summation calculation part, 64 ... average brightness calculation part, 65 ... correction amount calculation part, 66 ... correction execution part, 67 ... limit Correction amount calculation unit, 68 ... Final correction amount determination unit, 69 ... Correction amount calculation unit, 100 ... Image processing engine of the image display apparatus according to the second embodiment, 200 ... Image display apparatus according to the third embodiment Image processing engine, X: luminance value of luminance data, XH: upper limit value of luminance value X, XL: lower limit value of luminance value X, Y: luminance value after level correction, Y ′: luminance value after brightness correction, Y ″ ... brightness corrected brightness value, Z ... brightness corrected brightness value, Z '... limited brightness corrected brightness value, uv ... color difference data, H (X) ... histogram, γ ... gamma coefficient, α ... A dimming rate as a dimming rate of 1, αlim as a second dimming rate Limit dimming rate, α ′: final dimming rate, G1: correction amount for brightness correction, G2: correction amount for brightness correction, G2lim: limit correction amount for brightness correction, G2 ′: final correction for brightness correction Amount, G3: correction amount for brightness correction, G4: correction amount for enhanced brightness correction, G4lim: limit correction amount for enhanced brightness correction, G4 ′: final correction amount for enhanced brightness correction, K: No. 3 is a dimming rate of the light source, R is a contrast maintaining rate, Rlim is a limit contrast maintaining rate, Yth is a brightness reference as a reference gradation value, A to D is a coefficient, and Gconst is a constant.

Claims (16)

An image display device for correcting image data representing an image with a gradation value for each pixel and displaying the corrected image,
An image data acquisition unit for acquiring the image data;
For the acquired image data, a gradation conversion unit that converts gradation values so as to expand a range in which gradation values of pixels are distributed;
An image display device comprising: a brightness correction unit that controls a gradation value of the converted image data so as to reduce a change in an average value of gradation values caused by the conversion. The image display device according to claim 1,
The brightness correction unit adjusts the gradation value of the converted image data so that the average value of the gradation values of the corrected image data approaches the average value of the gradation values of the image data before the conversion. An image display device characterized by correcting. The image display device according to claim 1 or 2,
The brightness correction unit maintains the same gradation value for the upper limit value and lower limit value of the gradation value in the range of gradation values of the converted image data, and between the upper limit value and the lower limit value. An image display device characterized by changing a gradation value. An image display device including a spatial light modulator that corrects image data representing an image with a gradation value for each pixel and modulates light emitted from a light source based on the corrected image data,
A dimming rate setting unit for setting a first dimming rate for reducing the amount of light emitted by the light source from a predetermined amount of light;
An image data acquisition unit for acquiring the image data;
A brightness correction unit that controls a gradation value of the image data so as to reduce a change in brightness that occurs in light modulated by the spatial light modulator by dimming according to the dimming rate;
An image display device comprising: a light amount control unit that controls a light amount emitted from the light source based on the first dimming rate. The image display device according to claim 4,
The image data further includes a gradation conversion unit that converts gradation values so as to expand a range in which the gradation values of pixels are distributed,
The brightness correction unit reduces the brightness change caused in the light modulated by the spatial light modulator by the dimming according to the first dimming rate and the conversion, and the conversion of the converted image data. An image display device which corrects a gradation value. The image display device according to claim 5,
The brightness correction unit is configured so that a product of an average value of gradation values of the corrected image data and the dimming rate approaches an average value of gradation values of the image data before the conversion. An image display device that corrects the gradation value of the image data. The image display device according to claim 4 or 5,
The brightness correction unit is a brightness generated in the light modulated by the spatial light modulator when the gradation value of the image data before correction is corrected to be close to a predetermined reference gradation value. An image display device that corrects a gradation value of image data before correction so as to reduce a change. The image display device according to claim 7,
The brightness correction unit calculates a gradation value of the image data before correction by a product of an average value of gradation values of the corrected image data and the first dimming rate, and calculates a predetermined reference gradation An image display device, wherein the gradation value of the image data before correction is corrected so as to approach an average value of gradation values when corrected so as to approach the value. The image display device according to any one of claims 4 to 8,
The brightness correction unit maintains the same gradation value for the upper limit value and the lower limit value of the gradation value in the range of gradation values before correction, and the gradation between the upper limit value and the lower limit value. An image display device characterized by changing a value. In the image display device according to any one of claims 4 to 9,
The brightness correction unit
In the range where the gradation value is larger than the average value of the gradation value of the image data before correction, the correction is made for the brightness generated in the light modulated by the spatial light modulator based on the image data before correction. When the ratio of the brightness generated in the light modulated by the spatial light modulator based on the image data is smaller than a predetermined ratio,
Setting a second dimming rate capable of setting the brightness ratio to the predetermined ratio with respect to the first dimming rate;
The light quantity control unit controls the light quantity emitted from the light source based on the second dimming rate. In the image display device according to any one of claims 4 to 10,
The first dimming rate and the second dimming rate represent a visual ratio according to a human visual sensitivity characteristic to light;
The light quantity control unit calculates a third dimming ratio indicating a ratio of the light quantity actually emitted from the light source based on the visual sensitivity characteristic from the first dimming ratio or the second dimming ratio. Then, the image display device controls the light source according to the third dimming rate. An image display method for correcting image data representing an image with a gradation value for each pixel and displaying the corrected image,
An image data acquisition step of acquiring the image data;
For the acquired image data, a gradation conversion step for converting a gradation value so as to expand a range in which gradation values of pixels are distributed;
An image display method comprising: a brightness correction step for controlling a gradation value of the converted image data so as to reduce a change in an average value of gradation values caused by the conversion. An image display method comprising a spatial light modulator that corrects image data representing an image with gradation values for each pixel and modulates light emitted from a light source based on the corrected image data,
A dimming rate setting step for setting a first dimming rate for reducing the light amount emitted from the light source from a predetermined light amount;
An image data acquisition step of acquiring the image data;
A brightness correction step for controlling a gradation value of the image data so as to reduce a change in brightness generated in the light modulated by the spatial light modulator by dimming according to the dimming rate;
A light amount control step of controlling a light amount emitted from the light source based on the first dimming rate. An image display program for correcting image data representing an image with gradation values for each pixel and displaying the corrected image,
Computer
An image data acquisition unit for acquiring the image data;
A gradation conversion unit that converts gradation values so as to expand a range in which gradation values of pixels are distributed with respect to the acquired image data,
An image display device that functions as a brightness correction unit that controls a gradation value of the converted image data so as to reduce a change in an average value of gradation values caused by the conversion. Image data is displayed on an image display device that includes a spatial light modulator that corrects image data representing an image with gradation values for each pixel and modulates light emitted from a light source based on the corrected image data. An image display program,
Computer
A dimming rate setting unit for setting a first dimming rate for reducing the amount of light emitted by the light source from a predetermined amount of light;
An image data acquisition unit for acquiring the image data;
A brightness correction unit that controls a gradation value of the image data so as to reduce a change in brightness generated in light modulated by the spatial light modulator by dimming according to the dimming rate;
An image display program that functions as a light amount control unit that controls a light amount emitted from the light source based on the first dimming rate. A computer-readable recording medium on which the image display program according to claim 14 is recorded.

Images