JP2011203715A - Display control device and display control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the reduction of power consumption of a backlight from being reduced, when a bright image is input.SOLUTION: A display control device is configured so as to count, with respect to input image data, the number of pixels constituting the image data in descending order of brightness value, determine a provisional amount of emission of the backlight, on the basis of the brightness value when the cumulative number of the counted pixels reaches a predetermined number, compare the provisional amount of light emission with a predetermined threshold, and determine an amount of light emission less than the provisional amount of light emission as a determinate amount of light emission of the backlight, when the provisional amount of light emission exceeds the predetermined threshold as a result of the comparison.

Description

  The present invention relates to a display control device and a display control method, and more particularly to a display control device and a display control method capable of suppressing a reduction in the amount of power consumption of a backlight when a bright image is input.

  In recent years, with the spread of car navigation, it has become common for automobiles to be equipped with in-vehicle devices having a liquid crystal display.

  LCDs display images by partially blocking or transmitting light emitted from the backlight, but the high power consumption of the backlight hinders power saving . Therefore, in recent years, various attempts have been made to reduce power consumption by the backlight.

  For example, Patent Document 1 discloses a technique for reducing the power consumption of a backlight by controlling the light emission amount of the backlight according to the brightness of the video. Specifically, in the technique described in Patent Document 1, a luminance distribution (histogram) of pixels included in a video is created, and the cumulative number of pixels is counted from the high luminance side using the created histogram. The luminance value at the position reaching the number is determined as the backlight emission amount.

  As a result, in the technique described in Patent Document 1, in the case of a dark image, the number of pixels positioned on the high luminance side is small, so that the light emission amount of the backlight is set small. In the case of a bright image, the high luminance side is set. Since the number of pixels located at is large, the light emission amount of the backlight is set to be large.

JP 2007-219477 A

  However, the technique described in Patent Document 1 has a problem that the power saving effect is reduced when a bright image is input. This is because, in the case of a bright image, the amount of power consumption is reduced as a result of setting a larger amount of backlight emission.

  Such a problem is particularly noticeable in an in-vehicle device that displays many bright images such as navigation images.

  For these reasons, when a bright image is input, how to realize a display control device or a display control method capable of suppressing a reduction in the amount of reduction in power consumption of the backlight is a major issue. .

  The present invention has been made to solve the above-described problems caused by the prior art, and is capable of suppressing a reduction in the amount of reduction in power consumption of the backlight when a bright image is input. It is another object of the present invention to provide a display control method.

  In order to solve the above-described problems and achieve the object, a display control device according to the present invention is a display control device that controls the amount of light emitted from a backlight that irradiates light to a display panel. On the other hand, the counting means for counting the pixels constituting the image data in descending order of the luminance value, and the luminance value when the cumulative number of pixels counted by the counting means reaches a predetermined number Comparison between the provisional light emission amount determining means for determining the provisional light emission amount of the backlight, comparison means for comparing the provisional light emission amount determined by the provisional light emission amount determination means with a predetermined threshold, and comparison by the comparison means As a result, when the provisional light emission amount exceeds the predetermined threshold value, a definite light emission amount determination unit that determines a light emission amount smaller than the temporary light emission amount as the definite light emission amount of the backlight. Characterized by comprising and.

  The display control method according to the present invention is a display control method for controlling the light emission amount of the backlight that irradiates light to the display panel, and for the input image data, the pixels constituting the image data are changed. Counting step for counting in descending order of luminance value, and provisional light emission for determining the provisional light emission amount of the backlight based on the luminance value when the cumulative number of pixels counted in the counting step reaches a predetermined number An amount determination step, a comparison step of comparing the provisional light emission amount determined in the provisional light emission amount determination step with a predetermined threshold value, and a result of comparison in the comparison step, the provisional light emission amount becomes the predetermined threshold value. A definite light emission amount determining step of determining a light emission amount smaller than the provisional light emission amount as a definite light emission amount of the backlight.

  According to the present invention, with respect to input image data, the pixels constituting the image data are counted in descending order of luminance value, and the luminance value when the cumulative number of counted pixels reaches a predetermined number is obtained. Based on this, the provisional light emission amount of the backlight is determined, the provisional light emission amount is compared with a predetermined threshold value, and if the result of comparison indicates that the provisional light emission amount exceeds the predetermined threshold value, the provisional light emission amount Since the amount of light emission smaller than the amount of light is determined as the definite amount of light emission of the backlight, it is possible to suppress the reduction in the amount of reduction in backlight power consumption when a bright image is input. Play.

FIG. 1 is a diagram showing an overview of a display control method according to the present invention. FIG. 2 is a block diagram illustrating the configuration of the display control apparatus according to the first embodiment. FIG. 3 is a block diagram illustrating the configuration of the histogram analysis unit according to the first embodiment. FIG. 4 is a diagram illustrating an operation example of the histogram analysis unit. FIG. 5 is a diagram illustrating an example of RGB conversion information. FIG. 6 is a flowchart illustrating the processing procedure of the display control apparatus according to the first embodiment. FIG. 7 is a diagram illustrating an outline of the halation avoidance technique according to the second embodiment. FIG. 8 is a block diagram illustrating the configuration of the histogram analysis unit according to the second embodiment. FIG. 9 is a flowchart illustrating the processing procedure of the display control apparatus according to the second embodiment. FIG. 10 is a diagram for explaining a halation avoidance function and an H offset setting change. FIG. 11 is a diagram for explaining a case where the L offset is set.

  Exemplary embodiments of a display control device and a display control method according to the present invention will be described below in detail with reference to the accompanying drawings.

  First, prior to detailed description of the embodiment, an outline of a display control method according to the present invention will be described with reference to FIG. FIG. 1 is a diagram showing an overview of a display control method according to the present invention. Note that (A) in the figure shows a case where a light emission amount lower than the provisionally determined light emission amount is determined as a definite light emission amount when a bright image is input. Further, (B) of FIG. 5 shows a case where the light emission amount tentatively determined is determined as a definite light emission amount when a dark image is input.

  As shown in the figure, in the display control method according to the present invention, when the backlight emission amount is controlled according to the brightness of the image, even if a bright image is input, the backlight emission amount is a predetermined amount. The main feature is that an upper limit is set for the amount of light emitted from the backlight so as not to exceed.

  Specifically, in the display control method according to the present invention, first, when image data is input, the pixels constituting the image data are counted in descending order of luminance value. That is, in the display control method according to the present invention, as shown in (A) of the figure, the luminance distribution (hereinafter referred to as “histogram”) of the pixels constituting the image data is generated, and from the high luminance side. The pixels are counted in order.

  Here, as shown in FIG. 5A, the luminance value of the pixel takes a value from 0 to 255, and the light emission amount of the backlight is 0% when the luminance value is 0, and 255. Is taken as 100%, and takes a value of 0 to 100%. Thus, the light emission amount of the backlight is associated with the luminance value in advance.

  Subsequently, in the display control method according to the present invention, provisional light emission of the backlight is performed based on the luminance value when the accumulated number of counted pixels (hereinafter referred to as “accumulated pixel number”) reaches a predetermined number. Determine the amount. Specifically, as shown in (A) of the figure, a position where the cumulative number of pixels exceeds a predetermined number on the histogram is set as a calculation point, and a light emission amount corresponding to the calculation point is set as a temporary light emission of the backlight. It is determined as an amount (hereinafter referred to as “provisional luminescence amount”).

  Subsequently, in the display control method according to the present invention, the provisional light emission amount is compared with a predetermined threshold (hereinafter referred to as “H offset”). In the display control method according to the present invention, when the provisional light emission amount is larger than the H offset, the light emission amount smaller than the provisional light emission amount is defined as the definite light emission amount (hereinafter referred to as “determined light emission amount”). decide.

  For example, as shown in FIG. 5A, when a bright image is input, the number of pixels positioned on the high luminance side of the histogram increases, and as a result, the calculation point is positioned on the high luminance side of the H offset. Will be. In such a case, since the provisional light emission amount is larger than the H offset, the display control method according to the present invention determines the H offset as the final light emission amount.

  As described above, when a bright image is input, the light emission amount of the backlight is set to be relatively large, but the H offset located on the lower luminance side than the calculation point is set as the final light emission amount. As a result, the light emission amount of the backlight can be reduced as compared with the case where the light emission amount corresponding to the calculation point is set as the fixed light emission amount. Therefore, it is possible to increase the power consumption reduction amount as compared with the case where the light emission amount at the calculation point is set as the fixed light emission amount.

  As described above, in the display control method according to the present invention, by introducing the H offset as the upper limit value of the light emission amount of the backlight, even when a bright image is input, the determined light emission amount is equal to or higher than the H offset. It was decided to restrict so that it would not be. Therefore, according to the display control method according to the present invention, it is possible to suppress a reduction in the amount of reduction in power consumption of the backlight when a bright image is input.

  When the provisional light emission amount is smaller than the H offset, the provisional light emission amount is determined as the definite light emission amount of the backlight. For example, as shown in FIG. 5B, when a dark image is input, the number of pixels positioned on the low luminance side of the histogram increases, and as a result, the calculation point is positioned on the low luminance side of the H offset. Will be. In such a case, since the provisional light emission amount is smaller than the H offset, the provisional light emission amount is determined as the determined light emission amount.

  By the way, when a bright image is input, if a backlight emits light with a small amount of light emission, a phenomenon that the color of a particularly bright part in the image appears to be crushed (hereinafter referred to as “halation”) occurs. This may cause image quality degradation. Therefore, in the display control method according to the present invention, when there is a possibility that halation may occur, a process for avoiding the occurrence of halation by determining a light emission amount larger than the H offset as a determined light emission amount is also performed. Yes. The specific contents of the halation avoidance will be described in the second embodiment.

  In the above description, the case where the temporary light emission amount is larger than the H offset and the H offset is set as the definite light emission amount has been described. However, the present invention is not limited to this. For example, when the provisional emission amount is larger than the H offset, a value obtained by converting the provisional emission amount by a predetermined conversion formula may be determined as the determined emission amount. This point will also be described in an embodiment described later.

  Below, the Example about the display control apparatus to which the display control method demonstrated using FIG. 1 is applied is described in detail. In the embodiment described below, a case will be described in which the present invention is applied to a display control device that performs display control of a liquid crystal display mounted on an in-vehicle device. However, the display control device according to the present invention is not limited to this, and various types of display units that display using a backlight, such as a portable terminal device, a PC (Personal Computer), or a TV (Television). It can be applied to other devices.

  FIG. 2 is a block diagram illustrating the configuration of the display control apparatus according to the first embodiment. In the figure, only components necessary for explaining the characteristics of the display control device are shown, and descriptions of general components are omitted.

  As shown in the figure, a display control device 10 according to the present embodiment is a device that performs display control of a liquid crystal display 20 mounted on an in-vehicle device. Here, the liquid crystal display 20 includes a liquid crystal panel 21 and a backlight module 22. The liquid crystal panel 21 is a display unit that displays image data output from the display control device 10. The backlight module 22 is a lighting device provided on the back side of the liquid crystal panel 21 and irradiates the liquid crystal panel 21 with light from the back side. The high power consumption by the backlight module 22 hinders power saving.

  Next, the configuration of the display control apparatus 10 according to the present embodiment will be described. The display control apparatus 10 according to the present embodiment includes a control unit 11 and a storage unit 12. The control unit 11 includes an image data acquisition unit 11a, a sub-sampling unit 11b, a histogram generation unit 11c, a histogram analysis unit 11d, a light emission amount change unit 11e, a PWM (Pulse Width Modulation) generation unit 11f, RGB conversion unit 11g. The storage unit 12 stores threshold information 12a and RGB conversion information 12b.

  The control unit 11 is a processing unit that executes processing such as acquisition of image data from the in-vehicle device, sub-sampling of the acquired image data, generation and analysis of a histogram, light emission amount change processing, PWM generation, or RGB conversion processing. . The image data acquisition unit 11a is a processing unit that acquires image data such as navigation images from the in-vehicle device. The image data acquisition unit 11a also performs a process of passing the acquired image data to the sub-sampling unit 11b and the RGB conversion unit 11g.

  The sub-sampling unit 11b is a processing unit that performs sub-sampling on the acquired image data when the image data is acquired from the image data acquisition unit 11a. Further, the sub-sampling unit 11b also performs a process of passing the image data after sub-sampling to the histogram generation unit 11c.

  Here, sub-sampling indicates a process of thinning out pixels from acquired image data. Thus, by performing subsampling on the acquired image data, the processing speed of processing units such as a histogram generation unit 11c and a histogram analysis unit 11d described later can be increased. Here, it is assumed that the image data of WVGA size (800 × 480) is reduced to a size of 128 × 64.

  The histogram generation unit 11c is a processing unit that generates a histogram using the image data after sub-sampling acquired from the sub-sampling unit 11b. As described above, the histogram is information representing the luminance distribution of the pixels constituting the image data. Here, the histogram generation unit 11c generates a histogram using the component having the largest value among the R, G, and B components included in the image data. The histogram generation unit 11c also performs a process of passing the generated histogram to the histogram analysis unit 11d.

  The histogram analysis unit 11d is a processing unit that determines the determined light emission amount of the backlight module 22 by analyzing the histogram generated by the histogram generation unit 11c using the threshold information 12a.

  Here, a specific configuration of the histogram analysis unit 11d will be described with reference to FIG. FIG. 3 is a block diagram illustrating the configuration of the histogram analysis unit 11d according to the first embodiment. As shown in the figure, the histogram analysis unit 11d includes a provisional light emission amount determination unit 111, a comparison unit 112, and a fixed light emission amount determination unit 113. The threshold information 12a includes a DNUM 121 and an H offset 122.

  The provisional light emission amount determining unit 111 is a processing unit that determines the provisional light emission amount using the histogram acquired from the histogram generation unit 11c and the DNUM 121 included in the threshold information 12a. The DNUM 121 is information indicating a threshold value for the cumulative number of pixels.

  Specifically, the provisional light emission amount determination unit 111 sequentially counts the number of pixels from the high luminance side of the histogram, and the light emission corresponding to the position (luminance value) on the histogram when the accumulated pixel number exceeds DNUM 121. The amount is determined as the provisional light emission amount. In addition, when the provisional light emission amount determination unit 111 determines the provisional light emission amount, the provisional light emission amount determination unit 111 also performs a process of passing the determined provisional light emission amount to the comparison unit 112.

  The comparison unit 112 is a processing unit that compares the provisional emission amount determined by the provisional emission amount determination unit 111 with the H offset 122 stored in the storage unit 12. Here, the H offset 122 is threshold information indicating the upper limit value of the light emission amount of the backlight module 22. The comparison unit 112 also performs a process of passing the comparison result between the provisional light emission amount and the H offset 122 to the fixed light emission amount determination unit 113.

  The determined light emission amount determination unit 113 is a processing unit that determines the determined light emission amount according to the comparison result by the comparison unit 112. The determined light emission amount determination unit 113 also performs a process of passing the determined determined light emission amount to the light emission amount change unit 11e.

  Here, an example of the operation of the histogram analysis unit 11d will be described with reference to FIG. FIG. 4 is a diagram illustrating an operation example of the histogram analysis unit 11d. Note that (A) in the figure shows an operation example of the provisional light emission amount determination unit 111, and (B) and (C) in the same figure show operation examples of the comparison unit 112 and the fixed light emission amount determination unit 113. Each is shown.

  As shown in FIG. 5A, the provisional light emission amount determination unit 111 sets the position of the luminance value “255” in the histogram as the counting start point. The provisional light emission amount determination unit 111 sequentially counts the number of pixels corresponding to each luminance value from the counting start point toward the low luminance side. Then, the provisional light emission amount determination unit 111 determines a position where the cumulative number of pixels has reached DNUM 121 as a calculation point, and determines the light emission amount corresponding to the luminance value of the calculation point as the provisional light emission amount.

  For example, when the luminance value at the position where the cumulative number of pixels reaches DNUM 121 is “200”, the provisional light emission amount determination unit 111 sets the light emission amount “78%” corresponding to the luminance value “200” to the provisional light emission. Determine as quantity.

  Further, the comparison unit 112 compares the provisional light emission amount determined by the provisional light emission amount determination unit 111 with the H offset 122 and passes the comparison result to the fixed light emission amount determination unit 113. Then, as shown in FIG. 5B, the determined light emission amount determination unit 113 determines the temporary light emission amount as the determined light emission amount when the temporary light emission amount is equal to or smaller than the H offset 122. On the other hand, when the provisional light emission amount exceeds the H offset 122, the determined light emission amount determination unit 113 determines the H offset 122 as the fixed light emission amount.

  For example, as shown in (C) of the figure, when the calculation point is located on the lower luminance side than the H offset 122, such as the calculation point a and the calculation point b, that is, the input image is dark. In the case of an image, the light emission amount (provisional light emission amount) corresponding to each calculation point is the determined light emission amount. On the other hand, when the calculation point is located on the higher luminance side than the H offset 122 as in the calculation points c to e, that is, when the input image is a bright image, the determined light emission amount corresponds to each calculation point. The H offset 122 is a light emission amount smaller than the light emission amount (provisional light emission amount).

  As described above, in this embodiment, when the provisional light emission amount exceeds the H offset 122, a bright image is input by setting the H offset 122, which is a light emission amount smaller than the provisional light emission amount, as the fixed light emission amount. Even if it is a case, the reduction amount of the power consumption of the backlight module 22 can be increased as much as possible.

  Returning to FIG. 2, the description of the control unit 11 will be continued. The light emission amount changing unit 11e emits light based on the difference between the determined light emission amount acquired from the histogram analysis unit 11d and the current light emission amount in order to prevent screen flickering caused by a sudden change in the light emission amount of the backlight module 22. It is a processing unit for performing a light emission amount changing process for limiting the amount of change in the amount.

  Specifically, when the difference between the determined light emission amount and the current light emission amount is greater than a predetermined threshold value, the light emission amount changing unit 11e sets a predetermined value as the upper limit value of the change amount to the current light emission amount. A value obtained by addition (or subtraction) is determined as a final light emission amount. Further, when the light emission amount changing unit 11e determines the final light emission amount (hereinafter referred to as “changed light emission amount”), it passes this changed light emission amount to the PWM generation unit 11f.

  In addition, when the changed light emission amount is determined, the light emission amount changing unit 11e also determines an RGB conversion coefficient corresponding to the changed light emission amount using the RGB conversion information 12b, and passes the determined RGB conversion coefficient to the RGB conversion unit 11g. Do. Here, the contents of the RGB conversion information 12b will be described with reference to FIG. FIG. 5 is a diagram illustrating an example of the RGB conversion information 12b.

  As shown in the figure, the RGB conversion information 12b is information in which “RGB conversion coefficient” is associated with each “changed light emission amount”. Here, “changed emission amount” indicates the changed emission amount determined by the emission amount changing unit 11e. The “RGB conversion coefficient” is a coefficient to be multiplied with the values (RGB values) of R, G, and B components.

  For example, when the light emission amount after change is “100%”, the RGB conversion coefficient is “1.00”. This indicates that the RGB value of the input data becomes the RGB value of the output data as it is. When the light emission after change is “50%”, the RGB conversion coefficient is “1.26”. This indicates that a value obtained by multiplying the RGB value of the input data by 1.26 becomes the RGB value of the output data. Here, it is assumed that R, G, and B components are respectively multiplied by RGB conversion coefficients.

  As described above, the RGB conversion information 12b is set so that the RGB conversion coefficient increases as the light emission amount after change decreases, that is, as the light emission amount of the backlight module 22 decreases and the screen becomes darker. When the light emission amount changing unit 11e determines the light emission amount after change, the light emission amount changing unit 11e extracts the RGB conversion coefficient associated with the determined light emission amount after change from the RGB conversion information 12b, and passes the extracted RGB conversion coefficient to the RGB conversion unit 11g.

  When the changed light emission amount is acquired from the light emission amount changing unit 11e, the PWM generation unit 11f generates a PWM signal whose pulse width is adjusted so that the light emission amount of the backlight module 22 becomes the changed light emission amount, and the backlight module 22 It is a processing part which outputs to. The PWM generator 11f outputs the PWM signal four times each time VSYNC (Vertical Synchronizing signal) is output once.

  The RGB conversion unit 11g performs an RGB conversion process of multiplying the R, G, and B component values included in the image data acquired from the image data acquisition unit 11a by the RGB conversion coefficient acquired from the light emission amount change unit 11e. Is a processing unit. The RGB converter 11g also performs a process of outputting the image data after the RGB conversion process to the liquid crystal panel 21.

  For example, when the RGB conversion unit 11g acquires the RGB conversion coefficient “1.26”, the RGB conversion unit 11g multiplies the values of the R, G, and B components included in the image data acquired from the image data acquisition unit 11a by 1.26. . The RGB converter 11g outputs image data obtained by multiplying the values of the R, G, and B components by 1.26 to the liquid crystal panel 21.

  Next, a specific operation of the display control apparatus 10 according to the first embodiment will be described with reference to FIG. FIG. 6 is a flowchart illustrating the processing procedure of the display control apparatus according to the first embodiment. In the figure, only the processing procedure related to the light emission amount control of the backlight among the processing procedures executed by the display control device 10 is shown.

  As shown in the figure, in the display control apparatus 10, when the image data acquisition unit 11a acquires image data (step S101), the sub-sampling unit 11b performs sub-sampling on the acquired image data (step S102). ). Subsequently, in the display control apparatus 10, the histogram generation unit 11 c generates a histogram using the image data after sub-sampling (step S 103), and the provisional light emission amount determination unit 111 uses the histogram and DNUM 121. Is determined (step S104).

  Subsequently, in the display control apparatus 10, the comparison unit 112 compares the provisional light emission amount with the H offset 122 (step S <b> 105), and the determined light emission amount determination unit 113 determines whether the provisional light emission amount is greater than the H offset 122. Is determined (step S106). Then, when the provisional emission amount is larger than the H offset 122 (Yes in step S106), the determined emission amount determination unit 113 sets the H offset 122 as the decision emission amount (step S107), and the provisional emission amount is the H offset 122. In the case of the following (No in Step S106), the provisional light emission amount is set as the fixed light emission amount (Step S108).

  Subsequently, the light emission amount changing unit 11e performs a light emission amount changing process to determine the changed light emission amount (step S109). Subsequently, the PWM generator 11f generates a PWM signal corresponding to the changed light emission amount and outputs the PWM signal to the backlight module 22 (step S110).

  Further, the RGB conversion unit 11g performs an RGB conversion process of multiplying R, G, and B component values included in the image data acquired from the image data acquisition unit 11a by an RGB conversion coefficient corresponding to the changed light emission amount. Is performed (step S111). Then, the RGB conversion unit 11g outputs the image data after the RGB conversion processing to the liquid crystal panel 21 (step S112), and ends the processing.

  As described above, in the first embodiment, the provisional light emission amount determination unit counts the pixels constituting the image data in descending order of the luminance value with respect to the input image data. The provisional light emission amount of the backlight is determined based on the luminance value when the cumulative number reaches the predetermined number, and the comparison unit compares the provisional light emission amount with a predetermined threshold value to determine the fixed light emission amount determination unit. However, when the provisional light emission amount exceeds a predetermined threshold as a result of comparison by the comparison unit, the light emission amount smaller than the provisional light emission amount is determined as the definite light emission amount of the backlight. Accordingly, it is possible to suppress a reduction in the amount of reduction in power consumption of the backlight when a bright image is input.

  By the way, in the above-described first embodiment, even when the light emission amount of the backlight module 22 is reduced, the image quality deterioration is prevented by performing the correction for increasing the RGB value by the RGB conversion processing.

  However, as described in the first embodiment, when a bright image is input, if the backlight module 22 is caused to emit light with a light emission amount smaller than the provisional light emission amount, the correction amount of the RGB value reaches a peak, and halation occurs. May occur. Therefore, in Example 2, it is determined whether there is a possibility that halation will occur when the provisional light emission amount is larger than the H offset, and when it is determined that there is a possibility that it will occur, it is larger than the H offset. By determining the light emission amount as the definite light emission amount, the occurrence of halation was avoided.

  Hereinafter, the second embodiment will be described. First, the outline of the halation avoidance technique will be described with reference to FIG. FIG. 7 is a diagram illustrating an outline of the halation avoidance technique according to the second embodiment. In addition, (A) of the figure shows the situation where halation occurs, and (B) of the figure shows an outline of the halation avoidance technique.

  As shown in FIG. 5A, when the light emission amount after change is determined to be “100%” by the light emission amount changing unit 11e, the RGB conversion coefficient is “1.00” (see FIG. 5). . That is, when the input RGB value is “255”, the output RGB value is also “255”.

  On the other hand, when the changed light emission amount is determined to be “12.5%” by the light emission amount changing unit 11e, the RGB conversion coefficient is “2.05” (see FIG. 5).

  In this case, as shown in FIG. 5A, when the input RGB value is “124” or more, the output RGB values are all “255” (that is, the output RGB value is “255”). ) For example, when the input RGB value is “200”, the output RGB value is supposed to be “410”. However, since the limit value of the RGB value is “255”, the output RGB value is “255”. It becomes.

  As described above, when the image data includes a pixel having a large RGB value, the converted RGB value (output RGB value) may reach a peak by performing the RGB conversion process. As a result, portions that should originally be expressed with different RGB values (for example, 124 to 255) are all expressed with the same RGB value (255) by the RGB conversion processing. May deteriorate.

  Therefore, the display control apparatus 10 according to the second embodiment determines whether or not there is a possibility of halation when a bright image is input, that is, when the provisional light emission amount is larger than the H offset, When it is determined that there is a risk of occurrence, the light emission amount larger than the H offset is determined as the determined light emission amount.

  Here, the possibility of occurrence of halation is higher as image data includes a larger number of pixels having a large RGB value. For this reason, the display control apparatus 10 according to the second embodiment calculates the average luminance of the image data after sub-sampling as shown in (B) of the figure, and the average luminance corresponds to the H offset 122. If it is higher than the value, it is determined that there is a possibility that halation will occur.

  If the display control apparatus 10 according to the second embodiment determines that there is a high possibility that halation will occur, the display control device 10 does not set the H offset as the fixed light emission amount, but instead determines the light emission amount corresponding to the average luminance. Amount.

  As described above, in the second embodiment, when there is a possibility that halation may occur, the RGB conversion coefficient may be reduced and the output RGB value may reach a peak by setting the determined light emission amount to be higher than the H offset. Since it is suppressed, the occurrence of halation can be avoided.

  Next, the configuration of the histogram analysis unit 11d 'according to the second embodiment will be described with reference to FIG. Here, components having the same functions as those described in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. As shown in the figure, the histogram analysis unit 11d 'according to the second embodiment further includes an average luminance calculation unit 114 in addition to the configuration of the histogram analysis unit 11d described in the first embodiment.

  The average luminance calculation unit 114 is a processing unit that acquires a histogram from the histogram generation unit 11c and calculates the average luminance of the image data after sub-sampling using the acquired histogram. The average luminance calculation unit 114 also performs a process of passing the calculated average luminance to the comparison unit 112.

  The comparison unit 112 further compares the average luminance acquired from the average luminance calculation unit 114 with the luminance value corresponding to the H offset 122. Further, the comparison unit 112 also performs a process of passing this comparison result to the definite light emission amount determination unit 113.

  Further, when the provisional light emission amount is larger than the H offset, the determined light emission amount determination unit 113 determines whether or not the average luminance is higher than the luminance value corresponding to the H offset. If the determined light emission amount determining unit 113 determines that the average luminance is higher than the luminance value corresponding to the H offset 122, the determined light emission amount determining unit 113 determines the light emission amount corresponding to the average luminance as the determined light emission amount.

  Next, a specific operation of the display control apparatus 10 according to the second embodiment will be described with reference to FIG. FIG. 9 is a flowchart illustrating a processing procedure of the display control apparatus 10 according to the second embodiment. In the figure, only the processing procedure related to the light emission amount control of the backlight among the processing procedures executed by the display control device 10 is shown.

  As shown in the figure, in the display control apparatus 10, when the image data acquisition unit 11a acquires image data (step S201), the sub-sampling unit 11b performs sub-sampling on the acquired image data (step S202). ). Subsequently, in the display control apparatus 10, the histogram generation unit 11c generates a histogram using the image data after sub-sampling (step S203), and the average luminance calculation unit 114 uses the histogram to output the image data after sub-sampling. Is calculated (step S204). Further, the provisional light emission amount determining unit 111 determines the provisional light emission amount using the histogram and the DNUM 121 (step S205).

  Subsequently, in the display control device 10, the comparison unit 112 compares the provisional light emission amount with the H offset 122 (step S <b> 206), and the confirmed light emission amount determination unit 113 determines whether the provisional light emission amount is greater than the H offset 122. Is determined (step S207). Subsequently, when the provisional light emission amount is larger than the H offset 122 (Yes in step S207), the determined light emission amount determination unit 113 further determines whether or not the average luminance is higher than the luminance value corresponding to the H offset 122. Determination is made (step S208). If it is determined that the average luminance is higher than the luminance value corresponding to the H offset 122 (Yes in step S208), the determined light emission amount determination unit 113 determines the light emission amount corresponding to the average luminance as the determined light emission amount. (Step S209).

  On the other hand, when the average luminance is not higher than the luminance value corresponding to the H offset 122 (No in step S208), the determined light emission amount determination unit 113 determines the H offset 122 as the determined light emission amount (step S210). In step S207, if the provisional light emission amount is not greater than the H offset 122 (No in step S207), the provisional light emission amount is determined as the determined light emission amount (step S211).

  Subsequently, the light emission amount changing unit 11e performs a light emission amount changing process based on the difference between the determined light emission amount acquired from the fixed light emission amount determining unit 113 and the current light emission amount, and determines the changed light emission amount (step S212). Subsequently, the PWM generation unit 11f generates a PWM signal corresponding to the changed light emission amount and outputs the PWM signal to the backlight module 22 (step S213).

  Further, the RGB conversion unit 11g performs an RGB conversion process of multiplying R, G, and B component values included in the image data acquired from the image data acquisition unit 11a by an RGB conversion coefficient corresponding to the changed light emission amount. Is performed (step S214). Then, the RGB conversion unit 11g outputs the image data after the RGB conversion processing to the liquid crystal panel 21 (step S215), and ends the processing.

  As described above, in the second embodiment, the average luminance calculation unit calculates the average luminance of the image data, and the comparison unit further compares the average luminance calculated by the average luminance calculation unit with the H offset and confirms it. If the provisional light emission amount exceeds the H offset and the average luminance exceeds the H offset as a result of the comparison by the comparison unit, the light emission amount determination unit determines the average luminance as the definite light emission amount of the backlight. It was.

  Therefore, according to the second embodiment, when a bright image is input, it is possible to prevent image quality deterioration due to the occurrence of halation while suppressing a reduction in power consumption of the backlight module 22 from being reduced.

  By the way, the above-described halation avoidance function may be switched on / off according to a user operation. Further, the value of the H offset 122 may be changed according to a user operation. Hereinafter, these points will be described with reference to FIG. FIG. 10 is a diagram for explaining the halation avoidance function and the setting change of the H offset 122. Here, the state where the halation avoidance function is ON is referred to as “image quality emphasis mode”, and the case where it is OFF is referred to as “power saving mode”.

  Note that (A) in the figure shows an example of a screen displayed on the liquid crystal panel 21, (B) in the figure shows image quality and power saving effect in each mode, and (C) in FIG. ) Shows the relationship between the H offset and the power saving effect. It is assumed that the liquid crystal panel 21 shown in FIG.

  As shown in FIG. 5A, the liquid crystal panel 21 displays a mode selection button 21a, a “dark” button 21c and a “bright” button 21d for adjusting the screen brightness. The liquid crystal panel 21 displays the current power consumption reduction rate 21b. For example, in FIG. 5A, “image quality emphasis mode” is selected, and “brightness” is set to 4 out of 7 levels. Moreover, in (A) of the figure, “30%” is displayed as the current power consumption reduction rate.

  Here, the user can select either the image quality emphasis mode or the power saving mode according to his / her preference by pressing the mode selection button 21a while confirming the image displayed on the liquid crystal panel 21. .

  Here, as shown in FIG. 5B, in the image quality emphasis mode, the image quality is improved because halation is prevented, and the light emission amount less than the provisional light emission amount is emitted from the backlight module 22. Since it is used as a quantity, it has a high power saving effect. On the other hand, in the power saving mode, there is a possibility that halation may occur. Therefore, although the image quality is inferior to that in the image quality emphasis mode, the light emission amount of the backlight module 22 is further reduced. Compared to higher.

  For example, when a navigation image is displayed, a user who thinks that the image quality is good enough to recognize characters can increase the power saving effect by selecting the power saving mode.

  In addition, the user can confirm the image quality of the image displayed on the liquid crystal panel 21 and the power consumption reduction rate 21b, and press the “dark” button 21c and the “bright” button 21d, so that the brightness according to the user's preference can be obtained. Can be adjusted.

  Here, as shown in FIG. 10C, the value of the H offset 122 decreases as the “dark” button 21c is pressed, and increases as the “bright” button 21d is pressed. Is set. In particular, when the “dark” button 21c is pressed to decrease the value of the H offset 122, the upper limit value of the light emission amount of the backlight module 22 is lowered, and the power saving effect is further enhanced.

  By the way, when no one is looking at the image displayed on the liquid crystal display 20, the value of the H offset 122 may be extremely lowered to greatly increase the power saving effect. Specifically, a line-of-sight detection sensor is provided on the liquid crystal display 20. Here, the gaze detection sensor is a sensor that detects the gaze direction of the user, and outputs the detection result to the display control device 10.

  In addition, the control unit 11 of the display control device 10 determines whether or not the user's line of sight is on the liquid crystal panel 21, and detects the viewer of the image when determining that the user's line of sight is on the liquid crystal panel 21. And the control part 11 of the display control apparatus 10 reduces the value of H offset significantly, when the viewer of an image is not detected.

  As described above, the control unit 11 of the display control device 10 functions as a viewer detection unit, thereby detecting a viewer of an image displayed on the liquid crystal panel 21. Further, the control unit 11 of the display control device 10 functions as a threshold value changing unit, so that when the image viewer is not detected, the value of the H offset is compared with the case where the image viewer is detected. Lower.

  That is, when there is no image viewer (that is, when there is no need to display an image on the liquid crystal panel 21), the upper limit value of the light emission amount of the backlight module 22 is greatly reduced, so that a power saving effect is achieved. It can be further increased.

  If no viewer of the image is detected, if the value of the H offset 122 is set to 0, the definite light emission amount is 0% regardless of what image data is input. The power consumption of the light module 22 can be reduced to the maximum.

  Further, in each of the embodiments described above, the case where the H offset 122 is set as the fixed light emission amount when the provisional light emission amount is larger than the H offset 122 has been described, but the present invention is not limited to this. For example, when the provisional emission amount is larger than the H offset 122, a value obtained by converting the provisional emission amount using a predetermined conversion formula may be determined as the determined emission amount.

  Specifically, the determined light emission amount determination unit 113 is obtained by converting the provisional light emission amount using the above conversion formula when the provisional light emission amount exceeds the H offset 122 as a result of the comparison by the comparison unit 112. The value is determined as the final light emission amount.

  Here, the deterministic light emission amount determination unit 113 uses, for example, a linear function that obtains a definite light emission amount smaller than the provisional light emission amount by multiplying the provisional light emission amount by a coefficient larger than 0 and smaller than 1 as the conversion formula. be able to.

  As a result, the determined light emission amount becomes smaller than the provisional light emission amount, and the fixed light emission amount changes depending on the provisional light emission amount, so that the reduction in the amount of power consumption of the backlight is reduced. On the other hand, the backlight can be emitted with a fixed light emission amount suitable for each image. The conversion expression may be any conversion expression as long as the value before conversion is smaller than the value after conversion.

  Further, in each of the embodiments described above, the case where only the upper limit value is determined for the light emission amount of the backlight module 22 has been described, but the lower limit value may be determined for the light emission amount of the backlight module 22. Hereinafter, this point will be described with reference to FIG. FIG. 11 is a diagram for explaining a case where the L offset is set.

  As shown in the figure, the provisional light emission amount determination unit 111 sequentially counts the number of pixels from the high luminance side of the histogram, and corresponds to the position (luminance value) on the histogram when the cumulative number of pixels exceeds DNUM 121. The amount of light emitted is determined as the provisional light emission amount. Subsequently, the comparison unit 112 compares the provisional light emission amount with another threshold value (L offset) set on the lower luminance side than the H offset 122.

  Then, when the provisional light emission amount is larger than the L offset, the determined light emission amount determination unit 113 determines the provisional light emission amount as the fixed light emission amount as it is. On the other hand, when the L offset is larger than the provisional light emission amount, the determined light emission amount determination unit 113 determines the L offset as the determined light emission amount. Thereby, since it is prevented that a screen becomes too dark, the visibility of a screen can be improved.

  As described above, the display control device and the display control method according to the present invention are useful when it is desired to suppress a reduction in the amount of power consumption of the backlight when a bright image is input, It is suitable when you want to reduce the power consumption of the liquid crystal display of the in-vehicle device.

DESCRIPTION OF SYMBOLS 10 Display control apparatus 11 Control part 11a Image data acquisition part 11b Subsampling part 11c Histogram generation part 11d Histogram analysis part 111 Provisional light emission amount determination part 112 Comparison part 113 Final light emission amount determination part 114 Average luminance calculation part 11e Light emission amount change part 11f PWM generator 11g RGB converter 12 Storage unit 12a Threshold information 121 DNUM
122 H offset 12b RGB conversion information 20 Liquid crystal display 21 Liquid crystal panel 21a Mode selection button 21c “Dark” button 21d “Bright” button 22 Backlight module

Claims (6)

A display control device for controlling a light emission amount of a backlight that irradiates light to a display panel,
Counting means for counting the pixels constituting the image data in order from the highest luminance value for the input image data;
Provisional light emission amount determining means for determining a provisional light emission amount of the backlight based on a luminance value when the cumulative number of pixels counted by the counting means reaches a predetermined number;
A comparison means for comparing the provisional light emission amount determined by the provisional light emission amount determination means with a predetermined threshold;
When the provisional light emission amount exceeds the predetermined threshold as a result of the comparison by the comparison unit, the definite light emission that determines the light emission amount smaller than the temporary light emission amount as the definite light emission amount of the backlight A display control apparatus comprising: a quantity determining unit. The determined light emission amount determining means includes
The predetermined threshold value is determined as a definite light emission amount of the backlight when the provisional light emission amount exceeds the predetermined threshold value as a result of comparison by the comparison unit. The display control apparatus described. Average luminance calculating means for calculating an average luminance of the image data;
The comparison means includes
Further comparing the average brightness calculated by the average brightness calculation means and the predetermined threshold,
The determined light emission amount determining means includes
As a result of the comparison by the comparison means, when the provisional light emission amount exceeds the predetermined threshold value and the average luminance exceeds the predetermined threshold value, the average luminance is determined as the definite light emission of the backlight. The display control apparatus according to claim 1, wherein the display control apparatus determines the quantity. A viewer detecting means for detecting a viewer of an image displayed on the display panel;
A threshold value changing means for lowering the predetermined threshold value when a viewer of the image is not detected by the viewer detecting means compared to a case where a viewer of the image is detected by the viewer detecting means; The display control apparatus according to claim 1, further comprising:   If the provisional light emission amount exceeds the predetermined threshold as a result of the comparison by the comparison means, the provisional light emission amount is converted using a conversion formula in which the value before conversion is smaller than the value after conversion. The display control apparatus according to claim 1, wherein a value obtained by performing the determination is determined as the definite light emission amount. A display control method for controlling a light emission amount of a backlight that irradiates light to a display panel,
A counting step for counting the pixels constituting the image data in order from the highest luminance value for the input image data;
A provisional light emission amount determining step of determining a provisional light emission amount of the backlight based on a luminance value when the cumulative number of pixels counted in the counting step reaches a predetermined number;
A comparison step of comparing the provisional light emission amount determined in the provisional light emission amount determination step with a predetermined threshold;
As a result of the comparison in the comparison step, when the provisional light emission amount exceeds the predetermined threshold value, the definite light emission that determines a light emission amount smaller than the temporary light emission amount as the definite light emission amount of the backlight A display control method comprising: a quantity determining step.

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