JP2008158313A - Image data converting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image data converting device which converts image data such that an image can be prevented from being whitish in conversion processing for the image data for controlling the luminance of a back light. <P>SOLUTION: A maximum detector 2 detects a maximum value of data values of image data after degamma processing, and a scaling factor calculator 3 calculates a scaling factor P based upon the maximum. A scaling unit 4 multiplies data values of respective R, G, and B components after the degamma processing by T/T' when one of the data values of the respective R, G, and B components is smaller than P, and by T/P otherwise. Here, T is a maximum value that the data values of the degamma processing possibly reach. Further, T' is the largest data value among a set of R, G, and B components. A gamma processing unit 5 performs reverse conversion of the degamma processing for the data values after the conversion by the scaling unit 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image data conversion apparatus that converts image data to improve display quality.

  The liquid crystal display panel includes a pair of transparent substrates that sandwich a liquid crystal layer. A polarizing plate is provided on the surface of each transparent substrate opposite to the liquid crystal layer. A transparent electrode is provided on the surface of each transparent substrate on the liquid crystal layer side, and a portion where the transparent electrode on one transparent substrate and the transparent electrode on the other transparent substrate overlap is a pixel. An illuminating device such as a backlight is disposed on the back side (non-viewing side) of the liquid crystal display panel, and the illuminating device irradiates light toward the liquid crystal display panel. A drive driver that drives the liquid crystal display panel sets the potential of each transparent electrode in accordance with the image data, and controls the orientation of the liquid crystal in each pixel. The transmittance of light irradiated from the backlight and passing through each pixel varies depending on the alignment state of the liquid crystal. Therefore, a desired image can be displayed by the drive driver controlling the alignment state of the liquid crystal as described above.

  In recent years, liquid crystal display panels have been used as display devices in various devices such as mobile phones and television receivers, and movies and television broadcast programs can be viewed on these devices. Many movies and television broadcast programs (particularly movies) have dark screens. FIG. 11 is an explanatory diagram schematically illustrating an example of luminance distribution in image data of a screen such as a movie. As shown in FIG. 11, in image data such as a movie or a television broadcast program, the number of pixels with dark brightness is large, but the number of pixels with bright brightness is small.

  FIG. 12 is an explanatory diagram showing an example of image display control in a conventional liquid crystal display panel. FIG. 12A shows a state in which the backlight 102 irradiates the liquid crystal display panel 101 with light. FIG. 12B is an explanatory diagram schematically showing an example of the light transmittance distribution of each pixel in the liquid crystal display panel 101. The vertical axis in FIG. 12B indicates the number of pixels set for each transmittance. FIG. 12C is an explanatory diagram showing a state in which the backlight 102 irradiates light with 100% luminance (maximum luminance).

  The backlight 102 always irradiates light with the maximum luminance regardless of the image data. Therefore, even when a dark image is displayed, the backlight 102 emits light with the maximum luminance. On the other hand, a drive driver (not shown) controls the orientation state of each pixel according to image data. Therefore, as shown in FIG. 11, if there are many pixels designated to be dark in the image data, as shown in FIG. 12B, the number of pixels whose light transmittance is lowered increases, and the transmittance is increased. The number of pixels to be increased is reduced. In such control, the backlight 102 always irradiates light with a constant luminance, and the liquid crystal display panel 101 displays a dark screen by blocking the light from the backlight 102.

  When image display control is performed in this way, even when a dark image is displayed on the liquid crystal display panel 101, the backlight 102 emits light at the maximum luminance, so there is room for reduction in power consumption of the backlight 102. was there.

  FIG. 13 is an explanatory diagram showing another example of image display control in a conventional liquid crystal display panel. FIG. 13A shows a state where the backlight 102 irradiates the liquid crystal display panel 101 with light. FIG. 13B is an explanatory diagram schematically showing an example of the light transmittance distribution of each pixel in the liquid crystal display panel 101. The vertical axis in FIG. 13B indicates the number of pixels set for each transmittance. FIG. 13C is an explanatory diagram showing the luminance of the backlight 102.

  In the example illustrated in FIG. 13, the luminance of light emitted from the backlight 102 is changed according to image data. That is, the brightness of the backlight 102 is decreased when displaying a dark image, and the brightness of the backlight 102 is increased when displaying a bright image. Then, the image data is converted so that the light transmittance distribution of each pixel in the liquid crystal display panel 101 does not concentrate on a low transmittance. For example, in the distribution illustrated in FIG. 12B, there are many pixels controlled to have low transmittance, but in the distribution illustrated in FIG. 13B, not only pixels controlled to low transmittance but also high luminance. There are also pixels that are controlled. As illustrated in FIG. 13B, image data is converted so that the transmittance of each pixel is widely dispersed, and an image is displayed on the liquid crystal display panel 101 based on the image data. As a result, the light transmittance of the liquid crystal display panel 101 increases compared to the case illustrated in FIG. In such control, when the luminance of the backlight 102 is changed in accordance with the image data and the luminance of the backlight 102 is reduced, the light transmittance in the liquid crystal display panel 102 is increased.

  In the case where image display control is performed in this way, an image similar to the case where the control described with reference to FIG. 12 is performed can be displayed. In the display control described with reference to FIG. 13, the luminance of the backlight 102 is reduced when a dark image is displayed, so that the power consumption of the backlight 102 can be reduced.

  A specific example of the image display control described with reference to FIG. 13 will be described. First, de-gamma processing (processing for converting data values included in image data so that the relationship between the data values and the luminance of the pixels of the liquid crystal display panel is proportional) is performed on the image data of the original image. Then, the maximum data value is detected from the image data of each pixel for one screen after the degamma processing. Note that the image data is RGB format data, and the data values of the R (red), G (green), and B (blue) components indicate higher brightness as the value increases. The detected maximum data value is set as a scaling factor, and the value is set as P.

  Here, the scaling factor will be described. Consider a conversion that expands the range from 0 to a certain value to the range from 0 to the maximum value (T) that the data value included in the image data after degamma processing can take. FIG. 14 is a schematic diagram showing an example of such conversion. In this conversion, the maximum value in the range before conversion is called a scaling factor. For example, when a range from 0 to k is converted into a range from 0 to T as shown in FIG. 14, k is a scaling factor (that is, P = k). In order to perform conversion to expand the range from 0 to the scaling factor P to the range from 0 to T, the value before conversion may be multiplied by T / P. Further, it is assumed that the distribution of data values after the degamma processing is a distribution as illustrated in FIG. At this time, if the conversion as illustrated in FIG. 14 is performed on each data value after the degamma process, the distribution of the converted data value becomes a distribution as illustrated in FIG.

  Let T be the maximum value that can be taken by the data values of the R, G, and B components contained in the image data after the degamma processing. For example, when each component of R, G, B after degamma processing is represented by 8 bits, the maximum value that each of these components can take is 255. The image data is converted by multiplying the data values of the R, G, and B components included in the image data after the degamma processing by T / P. By this calculation, it is possible to convert the image data so that the light transmittance distribution of each pixel in the image for one screen does not concentrate on a low transmittance. Gamma processing is performed on the converted image data, and an image is displayed on the liquid crystal display panel using the image data after the gamma processing.

  Further, the backlight is controlled so that the luminance of the backlight is P / T times the maximum luminance of the backlight. The above operation is performed for each screen.

Patent Document 1 describes a method of displaying data by modulating data as described below. In the method described in Patent Document 1, for detecting a peak level V _p of the video signal V _in supplied from outside to a predetermined cycle. Then, the gain G _s = V _p / V ₀ is calculated from the detected peak level V _p . Here, the reference peak level V ₀ is defined as a standard peak level of the supplied video signal. After calculating the gain G _s , the video signal level is modulated as V _c = V _in / G _s . The spatial light modulation element is driven by the modulated video signal. Further, the light output level L _out of the light emitting unit is set to L _out = G _s × L ₀ using the gain G _s . Here, L ₀ is the reference light output level of the light emitting unit. With this method, the power consumption of the light source can be reduced.

JP-A-6-102484 (paragraphs 0019-0022, 0033)

  If the image display control described with reference to FIG. 13 is individually performed for each screen image data (one frame image data), there is a problem that the screen flickers.

  Therefore, it is conceivable that the maximum value of the data value (data value after degamma processing) in the image data of each screen is smoothed and the value obtained by smoothing the maximum value is used as the scaling factor. That is, when the maximum value of the image data on each screen changes like 100, 200, 100,..., Those maximum values are not used as they are as scaling factors, but instead of those as the screen changes. It is conceivable that the maximum value of the image data is smoothed so that the change amount of the maximum value is small, and the value after smoothing is used as a scaling factor. In smoothing, the amount of change in the maximum value may be reduced. For example, the maximum value that changes as “100, 200, 100,...” May be changed as “105, 110, 105,. Flickering of the screen can be suppressed by using a value obtained by smoothing the maximum data value of each screen as a scaling factor.

  However, if the value obtained by smoothing the maximum value of the data value of each screen in this way is used as the scaling factor, the data value of the R component, G component, or B component included in the image data is larger than the scale factor. Cases arise. When the data value of the R component, G component, or B component is a value larger than the scale factor, the result of multiplying the value by T / P is a value larger than T. However, because the bit length is limited, the maximum value that the data value can take is T, and a value larger than T cannot be expressed as a data value. Therefore, in the calculation of multiplying the data value by T / P, even if the calculation result is larger than T, the calculation result is T.

  For example, when the maximum value of the data value for each screen is smoothed, the smoothed value of the maximum value corresponding to a certain screen is 20, and the scaling factor P = 20. Each component of R, G, B after degamma processing on the screen is represented by 8 bits, and the maximum value T that each R, G, B component can take is 255. When multiplying (R, G, B) = (200, 10, 10), which is a set of R, G, B components included in image data, by T / P, the values of the R, G, B components (R, G, B) = (200 · (255/20), 10 · (255/20), 10 · (255/20)). The calculation for the R component is 200 · (255/20) = 2550. However, since the R component is actually represented by 8 bits, only values up to 255 can be expressed. Therefore, the calculation result is 255 instead of 2550. Therefore, the calculation result for (R, G, B) = (200, 10, 10) is (R, G, B) = (255, 128, 128). Note that the three values shown in parentheses as “(R, G, B) =” are the data values of the R component, G component, and B component, respectively.

  As described above, if the R component (or G component or B component) cannot be expressed by the original calculation result and is set to a value smaller than the original calculation result, the whiteness is higher than the color to be originally displayed. It is displayed in a garbled color. That is, a color (color with low saturation) in which the difference between the R, G, and B components is smaller than the original difference between the components is displayed.

  Such a phenomenon is observed, for example, when the screen is changed such that a bright portion suddenly appears in a dark image.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image data conversion device that converts image data so that the image can be prevented from being whitish in conversion processing of image data for controlling the luminance of a backlight. And

  An image data conversion apparatus according to the present invention is an image data conversion apparatus for converting RGB format image data for a liquid crystal display panel, and converts the data value of each screen image data to be an original image into a data value and a liquid crystal display. A degamma processing unit that converts the relationship between the brightness of the panel pixels to be a proportional relationship, a maximum value detection unit that obtains the maximum value of the image data after conversion by the degamma processing unit for each screen, The maximum value detection unit obtains the scaling factor that is one of the values in the conversion that expands the range from 0 to one to the maximum value that can be taken by the data value after conversion by the degamma processing unit. A scaling factor calculation unit that calculates based on the maximum value of the obtained data values, and T represents the maximum value that can be taken by the data value after conversion by the degamma processing unit. When the factor is P, if P is greater than or equal to the data value of each component in a combination of R component, G component, and B component, the data value of each component of that combination is multiplied by T / P. , P is smaller than the data value of any component in the combination of the R component, G component, and B component, the maximum value of the data values of the R component, G component, and B component of the combination is set to T ', By multiplying the data value of each component of the combination by T / T', the scaling unit for converting the data value of the image data after conversion by the degamma processing unit, and the data of the image data after conversion by the scaling unit And a gamma processing unit that performs inverse conversion of conversion by the degamma processing unit.

  The scaling factor calculation unit determines the scaling factor corresponding to one screen as the average value of the maximum values obtained by the maximum value detection unit and corresponding to a plurality of consecutive screens including the one screen. The structure to calculate may be sufficient.

The scaling factor calculation unit sets the scaling factor corresponding to the previous screen of one screen to P _n−1 , sets the maximum value corresponding to the one screen obtained by the maximum value detection unit to M, and is 0 or more and less than 1 The scaling factor corresponding to the one screen may be calculated as α · P _n−1 + (1−α) · M using α that is the number of.

  A scaling factor is converted by a conversion equation for converting the minimum value 0 that can be taken by the data value of the image data after conversion by the degamma processing unit to a value larger than 0 and converting the maximum value T that the data value of the image data can take into T. The configuration includes a value conversion unit that converts the scaling factor calculated by the calculation unit, and the scaling unit converts the data value of the image data converted by the degamma processing unit using the scaling factor converted by the value conversion unit. There may be. According to such a configuration, flicker can be prevented.

  The minimum value 0 that the data value of the image data after the conversion by the degamma processing unit can take is converted to a value larger than 0, and the maximum value T that the data value of the image data can take is converted to T by the conversion equation. A value conversion unit for converting, the value conversion unit converts the maximum value of each data value obtained by the maximum value detection unit, and the scaling factor calculation unit converts the maximum value after conversion by the value conversion unit The scaling factor may be calculated from the above. According to such a configuration, flicker can be prevented.

  According to the present invention, when the scaling factor P is equal to or larger than the data value of each component in the combination of the R component, the G component, and the B component, the scaling unit converts the data value of each component of the combination to T / P, and when P is smaller than the data value of any component in the combination of R, G, and B components, the data values of the R, G, and B components of that combination The data value of the image data after the conversion by the degamma processing unit is converted by multiplying the data value of each component of the combination by T / T ′, where T ′ is the maximum value. As described above, the multiplication result is obtained by switching the value to be multiplied by the data value between the case where the scaling factor P is equal to or larger than the data value of each component in the combination of the R component, the G component and the B component. Can be prevented from becoming larger than T (the maximum value that the data value after conversion by the degamma processing unit can take). Therefore, the multiplication result can always be expressed accurately, and as a result, the image can be prevented from being whitish.

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

[First Embodiment] FIG. 1 is a block diagram showing an example of an image data conversion apparatus according to a first embodiment of the present invention. The image data conversion apparatus 10 of the present invention receives image data from a video source 11 that generates image data. The image data conversion apparatus 10 of the present invention converts the data value of the image data and outputs the image data obtained by converting the data value to the drive driver 13. The drive driver 13 drives a liquid crystal display panel (hereinafter referred to as LCD) 14 in accordance with the image data output from the image data converter 10.

  Further, the LCD 14 is provided with a backlight 15 that emits light. The backlight driver 12 controls the luminance of light emitted from the backlight 15. The image data conversion apparatus 10 performs data processing on the image data input from the video source 11 and outputs a value specifying the luminance of the backlight 15 to the backlight driver 12. The backlight driver 12 controls the luminance of light emitted from the backlight 15 according to the value.

  Here, a case where the video source 11 is a personal computer (hereinafter referred to as a PC) will be described as an example, but the video source 11 may be a device other than a PC. In addition, the video source 11 outputs the image data of each screen in the moving image to the image data conversion device 10. These individual screens become the original images to be converted.

  The image data output from the PC 11 is RGB format image data. That is, the image data includes a plurality of combinations of data values corresponding to R (red), G (green), and B (blue) pixels. 1 exemplifies a case where the PC 11 outputs image data in which R component, G component, and B component data values are each represented by a fixed length of 6 bits, and all of the three types of components are represented by 18 bits. However, the bit lengths of the R component, G component, and B component data values are not limited to 6 bits.

  The image data conversion apparatus 10 according to the first embodiment includes a degamma processing unit 1, a maximum value detection unit 2, a scaling factor calculation unit 3, a scaling unit 4, and a gamma processing unit 5.

  The degamma processing unit 1 receives image data of individual screens as original images from the PC 11. A data value included in image data (image data of an individual screen serving as an original image) input from the PC 11 to the degamma processing unit is denoted as Data_in. FIG. 2 is an explanatory diagram showing the relationship between the data value included in the image data in the RGB format and the luminance of the pixels of the LCD 14. The horizontal axis shown in FIG. 2 indicates the data value (Data_in) included in the RGB format image data output from the PC 11. As shown in FIG. 2, in RGB format image data, there is a relationship that the luminance of the pixel of the LCD 14 increases as the data value increases, but the proportional relationship between the data value and the luminance of the pixel of the LCD 14 is Absent. The degamma processing unit 1 converts the data value (Data_in) included in the image data input from the PC 11 into a data value in which the relationship between the data value and the luminance of the pixel of the LCD 14 is proportional.

  Note that the luminance of the pixels of the LCD 14 shown on the vertical axis in FIG. 2 displays an image on the LCD 14 by a general method (for example, amplitude modulation method) according to the value of Data_in while keeping the luminance of the backlight constant. The luminance of the pixel.

The image data input from the PC 11 includes a plurality of combinations of R component, G component, and B component data values. The data values of the R component, G component, and B component in each combination are Data_in, and the degamma processing unit 1 converts the data values of the R component, G component, and B component, respectively. For example, when the data values of the R component, G component, and B component are D _r , D _g , and D _b , the degamma processing unit 1 converts D _r , D _g , and D _b , respectively.

  The data value after conversion by the degamma processing unit 1 is denoted as Data_tmp. FIG. 3 is an explanatory diagram showing the relationship between Data_tmp and Data_in. The degamma processing unit 1 converts Data_in to Data_tmp so that the method of increasing the luminance accompanying the increase of Data_in and the method of increasing the Data_tmp accompanying the increase of Data_in are the same. This conversion method will be described later. The relationship between the data value (Data_tmp) converted by the degamma processing unit 1 and the luminance of the pixels of the LCD 14 is proportional as shown in FIG.

  Note that the luminance of the pixels of the LCD 14 shown on the vertical axis in FIG. 4 displays an image on the LCD 14 by a general method (for example, amplitude modulation method) according to the value of Data_tmp while keeping the luminance of the backlight constant. The luminance of the pixel.

  The degamma processing unit 1 outputs the image data obtained by converting Data_in to Data_tmp to the scaling unit 4 and the maximum value detection unit 2.

  The maximum possible value of Data_tmp, which is the data value converted by the degamma processing unit 1, is T. T is determined by the bit length representing Data_tmp. The bit length representing Data_tmp is a fixed length and is equal to or longer than the bit length representing Data_in. Here, a case where the bit length representing Data_tmp is 8 bits will be described as an example. The maximum value T of Data_tmp that can be represented by 8 bits is 255.

  The maximum value detection unit 2 detects the maximum value of the image data included in the image data for each image data of each screen. The image data for one screen input to the maximum value detection unit 2 includes a plurality of combinations of R, G, and B component data values converted by the degamma processing unit 1. The maximum detector 2 detects the maximum value among the data values of the R component, G component, and B component. The maximum value detection unit 2 detects the maximum value of the data value for each image data of each screen, and outputs the maximum value for each screen to the scaling factor calculation unit 3.

The scaling factor calculation unit 3 calculates a scaling factor (P) corresponding to each screen based on the maximum value input from the maximum value detection unit 2 (the maximum value of Data_tmp in each screen). The scaling factor is the above-described “in the conversion in which the range from 0 to a certain value is expanded to the range from 0 to the maximum value T that the data value (Data_tmp) included in the image data after conversion by the degamma processing unit 1 can take. It is a certain value. The scaling factor calculation unit 3 calculates the scaling factor as a value obtained by smoothing the maximum value for each screen detected by the maximum value detection unit 2. Here, the value obtained by smoothing the maximum value is a value that changes with a change amount smaller than the change in the maximum value. FIG. 5 is an explanatory diagram illustrating an example of a value obtained by smoothing the maximum value. A _{1 to} a ₃ shown in FIG. 5 are maximum values of Data_tmp in three consecutive screens. In FIG. 5, changes in b _{1 to} b ₃ are smaller than changes in a _{1 to} a ₃ , and b _{1 to} b ₃ are values obtained by smoothing the maximum values a ₁ , a ₂ , and a ₃ . A specific method for calculating the scaling factor by the scaling factor calculator 3 will be described later. The scaling factor calculation unit 3 outputs the calculated scaling factor P to the scaling unit 4 and the backlight driver 12.

  The scaling unit 4 performs conversion that expands the range from 0 to the scaling factor P to 0 to the maximum value T that the data value (Data_tmp) included in the image data after conversion by the degamma processing unit 1 can take. To do. This conversion may be performed by multiplying Data_tmp by T / P. This P is a scaling factor corresponding to the screen of image data including Data_tmp.

  However, when the scaling factor P is smaller than the data value of any component in the combination of the R component, G component, and B component included in the image data converted by the degamma processing unit 1, the scaling unit 4 The following multiplication is performed on the data values of the R, G, and B components of the combination. That is, among the data values of the R, G, and B components, the maximum value is T ′, and the data values of the R, G, and B components are multiplied by T / T ′.

  When the scaling factor P is equal to or greater than the data value of each component in the combination of the R component, G component, and B component included in the image data converted by the degamma processing unit 1, the scaling unit 4 The data value of each component of G and B is multiplied by T / P.

For example, it is assumed that the combination of R, G, and B components included in the image data converted by the degamma processing unit 1 is (R, G, B) = (E _r , E _g , E _b ). Note that the three values shown in parentheses as “(R, G, B) =” are data values of the R component, G component, and B component, respectively. Further, P is a scaling factor corresponding to image data for one screen including a combination of data values of R, G, and B components of (R, G, B) = (E _r , E _g , E _b ). And

It is assumed that the scaling factor P is greater than or equal to the data value of each component in the combination of the R component, G component, and B component. That is, it is assumed that P ≧ E _r , P ≧ E _g , and P ≧ E _b . In this case, the scaling unit 4 converts the data values of the R, G, and B components by multiplying these data values by T / P. That is, (R, G, B) = (E _r , E _g , E _b ), (R, G, B) = (E _r · (T / P), E _g · (T / P), E _b · (T / P)).

Further, it is assumed that the scaling factor P is a value smaller than the data value of any component in the combination of the R component, the G component, and the B component. That is, it is assumed that any one of P <E _r , P <E _g , and P <E _b is established. In this case, the scaling unit 4 converts the data values of the R, G, and B components by multiplying these data values by T / T ′. That is, (R, G, B) = (E _r , E _g , E _b ), (R, G, B) = (E _r · (T / T ′), E _g · (T / T ′) , E _b · (T / T ′)).

  The scaling unit 4 performs the above conversion on the image data of each screen, and outputs the converted image data of each screen to the gamma processing unit 5.

  The gamma processing unit 5 performs inverse conversion of conversion performed by the degamma processing unit 1 on each data value included in the image data of each screen input from the scaling unit 4. The gamma processing unit 5 outputs the image data of each screen after conversion to the drive driver 13.

  The drive driver 13 displays an image on the LCD 14 based on the image data input from the gamma processing unit 5.

  Further, the backlight driver 12 responds to the scaling factor when the drive driver 13 displays an image on the LCD 14 based on the screen image data corresponding to the scaling factor input from the scaling factor 3 calculator 3. The backlight 15 is controlled so that the backlight 15 irradiates light with high brightness. The luminance according to the scaling factor is a luminance P / T times the maximum luminance of the backlight 15. T is the maximum value that Data_tmp can take.

Next, the operation will be described.
FIG. 6 is a flowchart showing an example of processing progress of the image data conversion apparatus of the present invention. When image data of individual screens serving as original images is input from the PC 11 to the degamma processing unit 1, the degamma processing unit 1 sets the data value (Data_in) included in the image data, the data value, and the pixel of the LCD 14. The data is converted into a data value that is proportional to the luminance, and the image data of each screen converted from the data value is output to the maximum value detector 2 and the scaling unit 4 (step S1).

In step S1, the degamma processing unit 1 may convert Data_in by raising each data value (Data_in) included in the image data input from the PC 11 to the γ power. For example, when the image data includes a data value of (R, G, B) = (D _r , D _g , D _b ), D _r ^γ is calculated and the calculation result is converted into a value after conversion of D _r . A data value (Data_tmp) may be used. Similarly, D _g and D _b may be converted by raising each data to the γ power. Further, the degamma processing unit 1 may multiply each data value by γ and further multiply by a constant. Here, the value of γ may be any value from 2 to 3, but γ is preferably 2.2.

  In addition, what value may be converted to Data_in may be previously examined by actual measurement to determine whether a proportional relationship is established between the converted data value and the luminance of the pixel of the LCD 14. Then, the correspondence between the converted data value (Data_tmp) and Data_in may be stored in advance in a storage device (not shown) included in the image data conversion device 10. In this case, the degamma processing unit 1 reads a data value (Data_tmp) corresponding to each data value (Data_in) included in the input image data from the storage device, and uses the read value as a converted data value. Good.

When the image data of each screen (image data subjected to the conversion in step S1) is input from the degamma processing unit 1, the maximum value detection unit 2 receives the maximum value of the data value included in the image data for each screen. Is detected (step S2). The image data of each screen is a set of combinations of R component, G component, and B component data values. The maximum value detector 2 may detect the data value having the largest value from the image data for one screen. For example, since the image data is a set of combinations such as (R, G, B) = (E _r , E _g , E _b ), etc., the maximum value detection unit 2 is capable of displaying all of the image data for one screen. What is necessary is just to detect the maximum value among the data values of R component, G component, and B component. The maximum value detection unit 2 detects the maximum value of the data value for each screen and outputs the maximum value of the data value in each screen to the scaling factor calculation unit 3.

  The scaling factor calculation unit 3 calculates the scaling factor for each screen as a smoothed value for each screen, and outputs the scaling factor corresponding to each screen to the scaling unit 4 and the backlight driver 12 ( Step S3).

The scaling factor calculation unit 3 may calculate the scaling factor as follows, for example. The scaling factor calculation unit 3 calculates the scaling factor of a certain screen as an average value of maximum values (maximum values detected by the maximum value detection unit 2 in step S2) corresponding to a plurality of continuous screens including the screen. That's fine. For example, the maximum value of the data value in each of the (n−2) th, (n−1) th, nth, n + 1th, n + 2th... Screen is M _n−2 , M _n−1 , M _n , M _{n + 1} , M _{Let n + 2} ... The scaling factor calculation unit 3 may obtain a scaling factor corresponding to the nth screen as an average value of M _n−1 , M _n , and M _{n + 1} . Similarly, the scaling factor corresponding to the (n + 1) th screen may be obtained as an average value of M _n , M _{n + 1} , and M _{n + 2} . Although the case where the scaling factor calculation unit 3 calculates the scaling factor as an average value of the three maximum values is illustrated here, the scaling factor may be calculated as an average value of more maximum values. In particular, it is preferable to calculate the scaling factor as an average value of 32 or more screens. Further, it is more preferable to calculate the scaling factor as an average value of 64 or more screens, and it is further preferable to calculate the scaling factor as an average value of 128 or more screens. If the scaling factor is calculated as the average value of more screens, the screen flicker can be made less noticeable.

  Thus, when calculating a scaling factor as the average of the maximum value in a some screen, the scaling factor calculation part 3 is provided with the some memory (not shown) which stores the maximum value corresponding to each screen. That's fine. The plurality of memories are memories for storing the maximum value of each screen in the detected order. The maximum value detection unit 2 may write the detected maximum value in a memory for storing the most recently detected maximum value among the plurality of memories. Then, the scaling factor calculation unit 3 calculates the sum of the maximum values stored in each memory, divides the sum by the number of memories, and uses the result as the scaling factor. In addition, after calculating the scaling factor, the scaling factor calculation unit 3 deletes the oldest maximum value and continues the maximum value stored in each memory while maintaining the order of detection by the maximum value detection unit 2. Move to memory. By repeating this operation, the scaling factor can be calculated as an average value of the maximum values of a plurality of screens. The number of memories may be adjusted to the number of maximum values for obtaining the average value.

The scaling factor calculation unit 3 may recursively calculate the scaling factor corresponding to one screen using the scaling factor corresponding to the previous screen. The screen on which the scaling factor is to be calculated is the nth screen, and the scaling factor corresponding to the screen is _Pn . A scaling factor corresponding to the previous (n−1) -th screen is P _n−1 . Further, the maximum value detected by the maximum value detection unit 2 is set as M as the maximum value of Data_tmp on the nth screen. At this time, the scaling factor calculation unit 3 calculates the scaling factor P _n of the _nth screen by the following equation (1).

P _n = α · P _n−1 + (1−α) · M Formula (1)

  The scaling factor calculation unit 3 rounds up the decimal point of the scaling factor calculated by the equation (1).

As described above, when the scaling factor is recursively calculated using the scaling factor corresponding to the previous screen, the scaling factor calculation unit 3 stores the calculated scaling factor (not shown). As long as it has. The scaling factor calculation unit 3 stores the newly calculated scaling factor in the memory, and the next time the scaling factor is calculated, the scaling factor stored in the memory corresponds to the scaling factor (formula P _n-1 in (1) may be used.

  Further, α in the formula (1) is a number satisfying 0 ≦ α <1. The value of α is preferably 0.80 ≦ α, more preferably 0.92 ≦ α, and still more preferably 0.97 ≦ α. α = 0.80 is an allowable level of flicker. If the value of α is 0.92 or more, the flicker can be almost eliminated. Further, if the value of α is 0.97 or more, flicker can be prevented from being visually recognized at all.

  When the scaling factor P is input from the scaling factor calculation unit 3, the scaling unit 4 converts the data value included in the image data of the screen corresponding to the scaling factor P as follows (step S4).

  When the scaling factor P is equal to or greater than the data value of each component in the combination of the R component, G component, and B component included in the image data converted by the degamma processing unit 1, the scaling unit 4 The data value of each component of G and B is multiplied by T / P. As already described, T is the maximum value that Data_tmp, which is a data value after conversion by the degamma processing unit 1, can take.

  Assume that the data length of Data_tmp is 8 bits and T = 255. For example, the R component, G component, and B component data values included in the image data converted by the degamma processing unit 1 are (R, G, B) = (10, 10, 10), and the scaling factor P = 20. Suppose that P is larger than any data value of each component of R, G, and B. Therefore, the scaling unit 4 converts the data value by multiplying the combination of the data values of the R, G, and B components by T / P = 255/20. Therefore, the data values of the R, G, and B components after conversion are (R, G, B) = (10 · (255/20), 10 · (255/20), 10 · (255/20) ) = (128, 128, 128).

  Further, when the scaling factor P is smaller than the data value of any component in the combination of the R component, the G component, and the B component included in the image data converted by the degamma processing unit 1, the scaling unit 4 The data value of each component of the combination R, G, B is multiplied by T / T ′. As already described, T ′ is the maximum value among the data values of the R, G, and B components.

  For example, the R component, G component, and B component data values included in the image data converted by the degamma processing unit 1 are (R, G, B) = (200, 10, 10), and the scaling factor P = 20. Suppose that P is smaller than the data value 200 of the R component. In this case, the maximum value T ′ among the data values of the R, G, and B components is 200. The scaling unit 4 converts the data value by multiplying the combination of the data values of the R, G, and B components by T / T ′ = 255/200. Therefore, the data values of the R, G, and B components after conversion are (R, G, B) = (10 · (255/200), 10 · (255/200), 10 · (255/200) ) = (255, 13, 13).

  The gamma processing unit 5 performs inverse conversion of the conversion performed by the degamma processing unit 1 on each data value included in the image data input from the scaling unit 4 (step S5). When the degamma processing unit 1 converts Data_in by raising Data_in to the γ power, the gamma processing unit 5 raises each data value included in the image data input from the scaling unit 4 to the (1 / γ) power. It may be converted depending on the situation.

  When the degamma processing unit 1 performs conversion by multiplying Data_in by γ and further multiplying by a constant, the gamma processing unit 5 converts each data value included in the image data input from the scaling unit 4 with the constant. What is necessary is just to convert by dividing and further raising to (1 / γ) power.

  Further, the correspondence relationship between Data_in and Data_tmp obtained by actual measurement is stored in a storage device (not shown) included in the image data conversion device 10, and the degamma processing unit 1 includes each of the pieces of image data included in the input image data. It is assumed that Data_tmp corresponding to the data value is read from the storage device. In this case, the gamma processing unit 5 reads each data value included in the image data input from the scaling unit 4 as Data_tmp, reads the value of Data_in corresponding to the Data_tmp from the storage device, and converts the read data value Data.

  The gamma processing unit 5 outputs the image data obtained by converting the data value to the drive driver 13, and the drive driver 13 causes the LCD 14 to display an image according to the image data.

  In step S3, the backlight driver 12 to which the scaling factor is input from the scaling factor calculation unit 3 is displayed when the drive driver 13 displays an image on the LCD 14 based on the screen image data corresponding to the scaling factor. In addition, the backlight 15 is controlled so as to emit light with a luminance P / T times the maximum luminance of the backlight 15.

  According to the present invention, when the scaling factor P is smaller than the data value of any component in the combination of the R component, the G component, and the B component included in the image data converted by the degamma processing unit 1, the scaling unit 4 multiplies the data value of each component of R, G, B of the combination by T / T ′. Therefore, even if the scaling factor P is smaller than the data value, the conversion result by the scaling unit 4 does not become larger than T. That is, the conversion result by the scaling unit 4 does not become a value that cannot be expressed with a predetermined bit length (bit length of Data_tmp). As a result, it is possible to prevent the display of an image with a lower saturation that is whiter than the original color. For example, even when the screen is changed such that a bright portion suddenly appears in a dark image, it is possible to prevent a whited image from being displayed.

  In the present embodiment, the degamma processing unit 1, the maximum value detection unit 2, the scaling factor calculation unit 3, the scaling unit 4, and the gamma processing unit 5 may be realized by the same computer that operates according to a program. In addition, each of these components may be realized by separate hardware.

[Second Embodiment] FIG. 7 is a block diagram showing an example of an image data conversion apparatus according to a second embodiment of the present invention. Components that perform the same operations as those in the first embodiment are denoted by the same reference numerals as those in FIG. The image data conversion apparatus 10 a according to the second embodiment includes a value conversion unit 7 in addition to the degamma processing unit 1, the maximum value detection unit 2, the scaling factor calculation unit 3, the scaling unit 4, and the gamma processing unit 5. The scaling factor calculation unit 3 calculates the scaling factor in the same manner as in the first embodiment, but differs from the first embodiment in that the scaling factor is output to the value conversion unit 7.

  The value conversion unit 7 converts the scaling factor input from the scaling factor calculation unit 3, and outputs the converted scaling factor to the backlight driver 12 and the scaling unit 4. The operation of the value conversion unit 7 will be described.

  When the input value (scaling factor) is P, the backlight driver 12 controls the backlight 15 so that the backlight 15 emits light at a brightness P / T times the maximum brightness of the backlight 15. . Therefore, when the backlight driver 12 receives the maximum value T that can be taken by the data value of the image data converted by the degamma processing unit 1, the luminance of the backlight 15 becomes the maximum luminance. When the minimum value 0 that can be taken by the data value of the image data converted by the degamma processing unit 1 is input to the backlight driver 12, the luminance of the backlight 15 is turned off. A proportional relationship is established between the value input to the backlight driver 12 and the luminance of the backlight 15. The relationship between each value from the minimum value to the maximum value that can be taken by the data value of the image data converted by the degamma processing unit 1 and the brightness of the backlight 15 when those values are input to the backlight driver 12 is as follows. As shown in FIG.

  The value conversion unit 7 converts values that can be taken by the data values of the image data converted by the degamma processing unit 1 into values that satisfy the following conditions. The value conversion unit 7 converts the minimum value 0 that the data value of the image data after the conversion by the degamma processing unit 1 can take into a value larger than 0 (but less than T), and the image after the conversion by the degamma processing unit 1 The maximum value T that the data value of the data can take is converted to T as it is. In addition, the value conversion unit 7 performs conversion so that the value after conversion changes smoothly as the value before conversion increases.

  Such conversion is realized by, for example, the following expression (2). X shown in Formula (2) is a value before conversion, and y is a value after conversion. A is a value greater than 0 and less than T.

  y = x · ((T−a) / T) + a Formula (2)

  Further, the value conversion unit 7 may be a quadratic or higher-order expression as shown in Expression (3) instead of a linear expression as shown in Expression (2). Also in Formula (3), x is a value before conversion, and y is a value after conversion. A is a value greater than 0 and less than T.

y = (T−a) · (x / T) ² + a Formula (3)

  Expressions (2) and (3) are examples of conversion expressions for conversion performed by the value conversion unit 7. The conversion expressions for conversion performed by the value conversion unit 7 are not limited to Expressions (2) and (3). A general multi-order formula as exemplified in Formula (4) may be used.

y = a _n · x ⁿ + a _n−1 · x ⁿ⁻¹ +... + a ₁ · x + a Equation (4)

  However, when x = T, y = T.

  The value conversion unit 7 performs the above conversion on the scaling factor input from the scaling factor calculation unit 3, and outputs the converted scaling factor to the backlight driver 12 and the scaling unit 4. In addition, here, a case is shown in which the value conversion unit 7 performs the calculation according to the conversion formula (for example, the formula (2) or the formula (3)) to realize the above-described conversion. The information may be stored in advance in a storage device (not shown) provided in the image data conversion apparatus 10. Then, the value conversion unit 7 may specify the value after conversion by reading a value corresponding to the value before conversion from the storage device.

  The backlight driver 12 controls the backlight 15 using the scaling factor after conversion by the value conversion unit 7. Even if the scaling factor input from the scaling factor calculator 3 is 0, the converted scaling factor is a value greater than 0. Therefore, even if the scaling factor input from the scaling factor calculation unit 3 to the value conversion unit 7 is 0, the backlight 15 emits light without turning off. When the scaling factor input from the scaling factor calculator 3 to the value converter 7 is T, the converted scaling factor is also T, so the backlight 15 emits light at the maximum luminance. The relationship between the scaling factor input from the scaling factor calculator 3 to the value converter 7 and the luminance of the backlight 15 when the scaling factor is converted by the value converter 7 and input to the backlight driver 12 is shown in FIG. It comes to illustrate.

  As described above, even if the scaling factor input from the scaling factor calculation unit 3 to the value conversion unit 7 is 0, the value conversion unit 7 converts the scaling factor so that the backlight 15 is not turned off. As a result, the backlight 15 can emit light with a luminance higher than the minimum luminance. In addition, the minimum luminance of the backlight at this time is preferably about 25 to 50 when the maximum luminance is 100.

  The scaling 4 converts the data value of the image data converted by the degamma processing unit 1 using the scaling factor converted by the value conversion unit 7. That is, when the scaling factor P after conversion by the value conversion unit 7 is greater than or equal to the data value of each component in the combination of the R component, G component, and B component included in the image data after conversion by the degamma processing unit 1 The data values of the R, G, and B components of the combination are multiplied by T / P. When the scaling factor P after conversion by the value conversion unit 7 is smaller than the data value of any component in the combination of the R component, G component, and B component included in the image data after conversion by the degamma processing unit 1 Is multiplied by T / T ′ to the data value of each component of R, G, B of the combination.

  Other operations are the same as those in the first embodiment.

  According to the present embodiment, as in the first embodiment, it is possible to prevent the display of an image with lower saturation that is whiter than the original color. Further, since the backlight 15 is not turned off, flicker can be prevented.

[Third Embodiment] FIG. 10 is a block diagram showing an example of an image data conversion apparatus according to a third embodiment of the present invention. The image data conversion device 10 _{b according to the} present embodiment also includes a value conversion unit 7. Components that perform the same operations as those in the first embodiment and the second embodiment are denoted by the same reference numerals as those in FIG. 1 and FIG. 7, and detailed description thereof is omitted. However, the maximum value detection unit 2 outputs the detected maximum value for each screen to the value conversion unit 7. The value conversion unit 7 performs the same conversion as the value conversion unit 7 in the second embodiment on the maximum value for each screen input from the maximum value detection unit 2, and sets each converted maximum value. Output to scaling factor 3.

  In the second embodiment described above, the value conversion unit 7 converts the scaling factor calculated by the scaling factor calculation unit 3 and outputs the converted scaling factor to the backlight driver 12 and the scaling unit 4. showed that. In the third embodiment, the value conversion unit 7 converts the maximum value corresponding to each screen detected by the maximum value detection unit 2 and outputs each converted maximum value to the scaling factor calculation unit 3. .

  The conversion operation performed by the value conversion unit 7 is the same as the conversion operation of the value conversion unit 7 in the second embodiment. That is, the value conversion unit 7 converts the minimum value 0 that the data value of the image data after the conversion by the degamma processing unit 1 can take into a value larger than 0 (but less than T), and after the conversion by the degamma processing unit 1 The maximum value T that the data value of the image data can take is converted to T as it is. In addition, the value conversion unit 7 performs conversion so that the value after conversion changes smoothly as the value before conversion increases. The value conversion unit 7 converts the maximum value of the data value for each screen input from the maximum value detection unit 2 using a conversion formula (for example, Formula (2), Formula (3), etc.) for performing such conversion. To do. Then, the value conversion unit 7 outputs each converted maximum value to the scaling factor calculation unit 3. Note that the value before conversion and the value after conversion in this conversion may be associated with each other, and information indicating the correspondence may be stored in advance in a storage device (not shown) included in the image data conversion apparatus 10. . Then, the value conversion unit 7 may specify the value after conversion by reading a value corresponding to the value before conversion from the storage device.

  The scaling factor calculation unit 3 uses each converted maximum value (maximum value for each screen) input from the value conversion unit 7 in the same manner as the scaling factor calculation unit 3 described in the first embodiment. Calculate the scaling factor. The scaling factor calculation unit 3 outputs the calculated scaling factor to the scaling unit 4 and the backlight driver 12.

  Other operations are the same as those already described.

  Also in this embodiment, it is possible to prevent the display of an image with a lower saturation that is whiter than the original color. Further, as in the second embodiment, since the backlight 15 is not turned off, flickering can be prevented.

  In the second embodiment and the third embodiment, the degamma processing unit 1, the maximum value detection unit 2, the scaling factor calculation unit 3, the scaling unit 4, the gamma processing unit 5, and the value conversion unit 7 are in accordance with a program. It may be realized by the same computer that operates. In addition, each of these components may be realized by separate hardware.

  In each of the first to third embodiments described above, the backlight driver 12 may be included in the image data converter. Further, the drive driver 13 may be included in the image data conversion apparatus.

  The present invention is preferably applied to an image data conversion device that converts image data for controlling the luminance of a backlight.

1 is a block diagram illustrating an example of an image data conversion apparatus according to a first embodiment. Explanatory drawing which shows the relationship between the data value contained in the image data of RGB format, and the brightness | luminance of the pixel of LCD. Explanatory drawing which shows the relationship between Data_tmp and Data_in. Explanatory drawing which shows the relationship between Data_tmp and the brightness | luminance of the pixel of LCD. Explanatory drawing which shows the example of the value which smoothed the maximum value. 6 is a flowchart showing an example of processing progress of the image data conversion apparatus of the present invention. The block diagram which shows the example of the image data converter of 2nd Embodiment. Explanatory drawing which shows the relationship between each value from the minimum value which the data value of the image data after conversion by the degamma processing part can take to the maximum value, and the brightness | luminance of the backlight when those values are input into a backlight driver . Explanatory drawing which shows the relationship between the scaling factor input into the value conversion part from a scaling factor calculation part, and the brightness | luminance of a backlight when the scaling factor is converted in a value conversion part and input into the backlight driver. The block diagram which shows the example of the image data converter of 3rd Embodiment. Explanatory drawing which shows typically the example of distribution of the brightness | luminance in the image data of screens, such as a movie. Explanatory drawing which shows the example of the display control of the image in the conventional liquid crystal display panel. Explanatory drawing which shows the other example of the display control of the image in the conventional liquid crystal display panel. The schematic diagram which shows the example of the conversion which expands the range from 0 to a certain value to the range from 0 to T. Explanatory drawing which shows the change of distribution of a data value when conversion as illustrated in FIG. 14 is performed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Degamma processing part 2 Maximum value detection part 3 Scaling factor detection part 4 Scaling part 5 Gamma processing part 11 Video source 12 Backlight driver

Claims (5)

An image data converter for converting RGB format image data for a liquid crystal display panel,
A degamma processing unit that converts the data value of the image data of each screen that is an original image so that the relationship between the data value and the luminance of the pixel of the liquid crystal display panel is proportional;
A maximum value detection unit that obtains the maximum value of the data value of the image data after conversion by the degamma processing unit for each screen;
The maximum value detection unit obtains the scaling factor that is the one value in the conversion that expands the range from 0 to 1 to the range from 0 to the maximum value that can be taken by the data value after conversion by the degamma processing unit. A scaling factor calculation unit for calculating based on the maximum value of the obtained data values;
When the maximum value that can be taken by the data value after conversion by the degamma processing unit is T and the scaling factor is P, P is equal to or greater than the data value of each component in a combination of a set of R, G, and B components. If the data value of each component of the combination is multiplied by T / P, and P is smaller than the data value of any component in the combination of the R component, G component, and B component, The maximum value of the data values of the R component, G component, and B component of the combination is T ′, and the data value of each component of the combination is multiplied by T / T ′, thereby converting the image data after conversion by the degamma processing unit. A scaling unit that converts the data value of
An image data conversion apparatus comprising: a gamma processing unit that performs inverse conversion of conversion by a degamma processing unit on a data value of image data converted by a scaling unit. The scaling factor calculation unit calculates the scaling factor corresponding to one screen as the maximum value obtained by the maximum value detection unit, and is an average value of the maximum values corresponding to a plurality of consecutive screens including the one screen. The image data conversion device according to claim 1 to calculate. The scaling factor calculation unit sets P _n−1 as the scaling factor corresponding to the previous screen of one screen, sets M as the maximum value corresponding to the one screen obtained by the maximum value detection unit, and ranges from 0 to less than 1. The image data conversion apparatus according to claim 1, wherein a scaling factor corresponding to the one screen is calculated as α · P _n−1 + (1−α) · M using α which is the number of the image data. A scaling factor is converted by a conversion equation for converting a minimum value 0 that can be taken by the data value of the image data after conversion by the degamma processing unit to a value larger than 0 and converting the maximum value T that the data value of the image data can take into T. A value conversion unit for converting the scaling factor calculated by the calculation unit;
The image data conversion apparatus according to claim 1, wherein the scaling unit converts the data value of the image data after conversion by the degamma processing unit using the scaling factor after conversion by the value conversion unit. The minimum value 0 that can be taken by the data value of the image data after conversion by the degamma processing unit is converted to a value greater than 0, and the maximum value T that can be taken by the data value of the image data is converted to T. A value conversion unit for conversion,
The value conversion unit converts the maximum value of the data value for each individual screen obtained by the maximum value detection unit,
The image data conversion apparatus according to claim 1, wherein the scaling factor calculation unit calculates a scaling factor from the maximum value after conversion by the value conversion unit.

Images