JP5604136B2 - Display control apparatus and display control method - Google Patents

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 that can reduce screen flicker that occurs when the brightness of an image frequently changes while suppressing power consumption by a backlight. It relates to a control method.

  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 flicker may occur on the screen displayed on the liquid crystal display when the brightness of the image changes frequently. This is because a dark portion of an image is easily affected by luminance due to a change in the amount of backlight emission, and a sudden change in the amount of backlight emission causes flickering.

  For this reason, in particular, when a dark scene and a bright scene are alternately repeated, the backlight emission amount is set to be large even though the scene is dark, or conversely, even though the scene is bright. In some cases, the amount of light emitted from the backlight may be set to be small, which causes flickering on the screen.

  Therefore, how to realize a display control device or a display control method that can reduce screen flicker that occurs when the brightness of an image changes frequently while suppressing power consumption by the backlight. It has become a big issue.

  The present invention has been made to solve the above-described problems caused by the prior art, and reduces screen flicker that occurs when the brightness of an image changes frequently while suppressing power consumption by a backlight. An object of the present invention is to provide a display control device and a display control method capable of performing the above.

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. A target light emission amount determining means for determining a target light emission amount of the backlight based on a luminance value of the backlight, and a difference value between the target light emission amount determined by the target light emission amount determination means and the current light emission amount of the backlight. And a change amount determining means for determining a change amount from the current light emission amount, and a light emission amount obtained by changing the current light emission amount by the change amount determined by the change amount determining means. comprising a light emission amount determination means for determining, and a light emission amount history storage means for storing a predetermined number of frames the light emission amount of the backlight is determined by the light emission amount determination means as the change amount determined The means determines that the screen is blinking when all the difference values of the light emission amounts between adjacent frames out of the light emission amounts for the predetermined frames stored in the light emission amount history storage means are equal to or larger than the predetermined value. And when it determines with the screen blinking, compared with the case where the image is not blinking, the variation | change_quantity from the said present light emission amount is decreased, It is characterized by the above-mentioned.

The display control method according to the present invention is a display control method for controlling a light emission amount of a backlight that irradiates light to a display panel, and is based on a luminance value of input image data. The amount of change from the current light emission amount is determined in accordance with a target light emission amount determination step for determining the amount, and a difference value between the target light emission amount determined in the target light emission amount determination step and the current light emission amount of the backlight A change amount determination step, a light emission amount determination step for determining a light emission amount obtained by changing the current light emission amount by the change amount determined in the change amount determination step, and a light emission amount determination step. seen containing a light-emitting amount history storage step, a of a predetermined number of frames stored the light emission amount of the backlight determined in the amount of change determining step, storing in the light emitting amount history storage step It is determined that the screen is blinking and the screen is blinking when all the difference values of the light emission amounts between adjacent frames among the light emission amounts for the predetermined frame are equal to or greater than the predetermined value. In this case, the amount of change from the current light emission amount is reduced compared to the case where the image is not blinking .

  According to the present invention, the target light emission amount of the backlight is determined based on the luminance value of the input image data, and the current value is determined according to the difference value between the determined target light emission amount and the current light emission amount of the backlight. The amount of change from the amount of emitted light is determined, and the amount of light emitted by changing the current amount of emitted light by the determined amount of change is determined as the amount of emitted light from the backlight, so reducing the power consumption by the backlight, There is an effect that the flickering of the screen that occurs when the brightness of the image frequently changes can be reduced.

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 present embodiment. FIG. 3 is a diagram illustrating an operation example of the histogram analysis unit. FIG. 4 is a block diagram illustrating a configuration of the light emission amount changing unit according to the present embodiment. FIG. 5 is a diagram illustrating an example of the change amount setting information. FIG. 6 is a diagram illustrating an operation example of the change amount determination unit and the light emission amount determination unit. FIG. 7 is a flowchart illustrating the processing procedure of the display control apparatus according to the present embodiment. FIG. 8 is a diagram illustrating another operation example of the change amount determination unit. FIG. 9 is a diagram illustrating another operation example of the change amount determination unit.

  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. Here, (A) in the figure shows an outline of the conventional display control technique, and (B) in the figure shows an outline of the display control technique according to the present invention. In addition, the graph shown to (A) and (B) of the figure represents the time-dependent change of the emitted light quantity of a backlight. Times t0 to t3 attached to the horizontal axis represent frame update timings.

  In the conventional display control method, when the target light emission amount is determined based on the luminance distribution of a certain frame, the determined target light emission amount is directly adopted as the light emission amount of the backlight in the next frame. For example, as shown in FIG. 6A, in the conventional display control method, the target light emission amount determined based on the luminance distribution of the frame updated at time t0 is used as the light emission amount of the backlight at time t1. Was determined as.

  As described above, when the target light emission amount is immediately reflected as the backlight light emission amount, when the actual light emission amount and the target light emission amount are greatly different, the backlight light emission amount changes abruptly. There is a risk of flickering. In particular, when a bright image and a dark image are alternately repeated, the difference between the light emission amount to be applied and the light emission amount actually applied tends to increase, and the flickering of the screen becomes remarkable.

  Therefore, in the display control method according to the present invention, when the target light emission amount of the backlight is determined based on the luminance distribution of the input image, the current light emission amount is changed stepwise over a plurality of frames. It is characterized in that it matches the emitted light amount. Further, in the display control method according to the present invention, the current light emission amount is not changed linearly, but is increased as the difference from the target light emission amount is larger, and the change amount is decreased as the target light emission amount is approached. It also has a feature in that it is changed to.

  Specifically, as shown in (B) of the figure, in the display control method according to the present invention, the amount of change from the current light emission amount is determined according to the difference value between the target light emission amount and the current light emission amount. The light emission amount obtained by changing the current light emission amount by the determined change amount is adopted as the light emission amount of the backlight.

  For example, as shown in FIG. 5B, when the difference value between the light emission amount (current light emission amount) at time t0 and the target light emission amount is relatively large, the amount of change from the current light emission amount is Determine the amount of change (large). In the display control method according to the present invention, the light emission amount obtained by changing the current light emission amount by the change amount (large) is applied to the frame updated at t1. Here, the amount of change (large) is an amount of change that does not cause screen flickering.

  Further, the difference value between the light emission amount (current light emission amount) and the target light emission amount at time t1 is smaller than the difference value between the light emission amount (current light emission amount) and the target light emission amount at time t0. For this reason, in the display control method according to the present invention, the change amount (medium) is determined as the change amount from the current light emission amount. In the display control method according to the present invention, the light emission amount obtained by changing the current light emission amount by the change amount (medium) is applied to the frame updated at t2.

  Similarly, the difference value between the light emission amount (current light emission amount) and the target light emission amount at time t2 is smaller than the difference value between the light emission amount (current light emission amount) and the target light emission amount at time t1. For this reason, in the display control method according to the present invention, the change amount (small) is determined as the change amount from the current light emission amount. In the display control method according to the present invention, the light emission amount obtained by changing the current light emission amount by the change amount (small) is applied to the frame updated at t3.

  As a result, the actual light emission amount of the backlight coincides with the target light emission amount determined based on the luminance distribution of the frame updated at time t0 at time t3.

  As described above, in the display control method according to the present invention, when the current light emission amount is changed to the target light emission amount, the change is made in stages over a plurality of frames. As a result, flickering of the screen can be prevented.

  In addition, in the display control method according to the present invention, when the difference value between the current light emission amount and the target light emission amount is large, the current light emission amount is largely changed by a change amount that does not cause flickering of the screen, As the difference value decreases, the amount of change is also reduced, so that the current light emission amount is gradually converged to the target light emission amount. As a result, the light emission amount of the backlight can be brought close to the target light emission amount as quickly as possible, so that the color collapse that tends to occur when the difference between the light emission amount of the backlight and the target light emission amount is large can be prevented.

  By the way, depending on the liquid crystal display used, the screen may flicker even if the amount of light emitted from the backlight is slightly changed. Therefore, if the difference value between the target light emission amount and the current light emission amount is a predetermined value or less, the light emission amount of the backlight may not be changed. Accordingly, it is possible to prevent screen flickering caused by a slight change in the light emission amount of the backlight.

  In addition, when a dark image and a bright image are alternately repeated, the amount of change from the current light emission amount may be reduced. As a result, it is possible to reduce the processing load caused by frequently changing the light emission amount of the backlight in a short period.

  1A and 1B, the case where the backlight emission amount is increased toward the target emission amount has been described. However, in the display control method according to the present invention, the backlight emission amount is set to the target emission amount. Similarly, in the case of decreasing toward the amount, the light emission amount of the backlight is changed stepwise.

  Here, halation is likely to occur when the backlight control is changed from dark to light, and conversely, it is difficult to occur when the backlight control is changed from light to dark. Therefore, when the light emission amount of the backlight is decreased, the amount of change may be larger than when the light emission amount of the backlight is increased. Thereby, when reducing the light emission amount of the backlight, the light emission amount of the backlight module 22 can be brought closer to the target light emission amount without causing the viewer to feel the flickering of the screen.

  In FIGS. 1A and 1B, the case where the actual light emission amount of the backlight is changed in three stages has been described. However, the present invention is not limited to this. There is no problem.

  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 present 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 a DNUM 12a and setting information 12b.

  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. The histogram generation unit 11c also performs a process of passing the generated histogram to the histogram analysis unit 11d. Here, as described above, the histogram is information representing the luminance distribution of the pixels constituting the image data. 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 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 DNUM 12a. The DNUM 12a is information indicating a threshold value of the cumulative pixel number described later.

  Here, an example of the operation of the histogram analysis unit 11d will be described with reference to FIG. FIG. 3 is a diagram illustrating an operation example of the histogram analysis unit 11d. Here, (A) in the figure shows an operation example of the cumulative pixel counting process using the histogram, and (B) in the figure shows an operation example of the target light emission amount determination process. .

  In addition, as shown to (A) and (B) of the figure, the luminance value of a pixel takes the value of 0-255. Further, the light emission amount of the backlight is associated with the luminance value in advance so that the luminance value is 0% when the luminance value is 0, and 100% when the luminance value is 255.

  When the histogram analysis unit 11d acquires the histogram from the histogram generation unit 11c, first, the histogram analysis unit 11d performs a counting process of counting the number of pixels in order from the high luminance side of the histogram. Specifically, as illustrated in (A) of FIG. 11, the histogram analysis unit 11 d uses the position of the luminance value “255” in the histogram as the counting start point, and sets the number of pixels corresponding to each luminance value as the counting start point. Counts in order from the low brightness side. Here, as shown in FIG. 5A, the position corresponding to the luminance value being analyzed is referred to as “calculation point”.

  The histogram analysis unit 11d then calculates a calculated point (luminance value) when the accumulated number of counted pixels (hereinafter referred to as “accumulated pixel number”) reaches DNUM12a, as shown in FIG. ) Is determined as the target light emission amount.

  For example, if the luminance value at the position where the cumulative number of pixels reaches DNUM12a is “200”, the histogram analysis unit 11d sets the light emission amount “78%” corresponding to the luminance value “200” as the target light emission amount. decide.

  As described above, the histogram generation unit 11c and the histogram analysis unit 11d function as an example of a target light emission amount determination unit that determines the target light emission amount of the backlight based on the luminance distribution of the input image data.

  Returning to FIG. 2, the light emission amount changing unit 11e will be described. The light emission amount changing unit 11e is a processing unit that determines the light emission amount of the backlight module based on the difference between the target light emission amount acquired from the histogram analysis unit 11d and the current light emission amount. Here, the configuration of the light emission amount changing unit 11e will be described with reference to FIG. FIG. 4 is a block diagram illustrating a configuration of the light emission amount changing unit 11e according to the present embodiment.

  As shown in the figure, the light emission amount change unit 11e includes a difference value calculation unit 111, a change amount determination unit 112, a light emission amount determination unit 113, and a conversion coefficient determination unit 114. The setting information 12b stores light emission amount history information 121, change amount setting information 122, and RGB conversion information 123.

  Here, the setting information 12b will be described. The light emission amount history information 121 is history information of the light emission amount of the backlight module 22 determined by the light emission amount determination unit 113. The light emission amount history information 121 includes the current light emission amount of the backlight module 22 as history information. The change amount setting information 122 is information used when determining the change amount of the light emission amount of the backlight module 22. The light emission amount history information 121 will be described later with reference to FIG.

  The RGB conversion information 123 is information in which “RGB conversion coefficient” is associated with each light emission amount of the backlight module 22 determined by the light emission amount determination unit 113. The “RGB conversion coefficient” is a coefficient that is multiplied with the values (RGB values) of R, G, and B components. Here, the RGB conversion information 123 is set so that the RGB conversion coefficient increases as the light emission amount of the backlight module 22 determined by the light emission amount determination unit 113 decreases, that is, as the screen becomes darker.

  The difference value calculation unit 111 is a processing unit that calculates a difference value between the target light emission amount acquired from the histogram analysis unit 11d and the current light emission amount. Specifically, when obtaining the target light emission amount from the histogram analysis unit 11d, the difference value calculation unit 111 extracts the current light emission amount included in the light emission amount history information 121 and subtracts the current light emission amount from the target light emission amount. The absolute value is the difference value.

  Further, the difference value calculation unit 111 is information indicating whether a value obtained by subtracting the current light emission amount from the target light emission amount is a positive value or a negative value, that is, the current light emission amount should be increased or decreased. A process of passing information indicating whether or not to be performed to the change amount determination unit 112 together with the calculated difference value is also performed.

  The change amount determination unit 112 is a processing unit that determines a change amount from the current light emission amount according to the difference value acquired from the difference value calculation unit 111. Specifically, the change amount determination unit 112 uses the change amount setting information 122 for the change amount associated with the range to which the difference value acquired from the difference value calculation unit 111 belongs among the ranges delimited by a plurality of threshold values. The determined change amount is determined as a change amount from the current light emission amount.

  Here, the contents of the change amount setting information 122 will be described with reference to FIG. FIG. 5 is a diagram illustrating an example of the change amount setting information 122.

  As shown in the figure, the change amount setting information 122 is information in which a change amount is associated with each range divided by a plurality of threshold values (threshold value L1 and threshold value L2) having different sizes. Specifically, the change amount setting information 122 is information in which “change amount (increase)” and “change amount (decrease)” are associated with each “range” delimited by the threshold L1 and the threshold L2. .

  Here, the “range” includes the ranges “A1” to “A3”. Specifically, the range “A1” indicates a range where “threshold L1 ≦ difference value”, the range “A2” indicates a range where “threshold L2 ≦ difference value <threshold L1”, and the range “A3” indicates “ A range where difference value <threshold value L2 ”is shown. As shown in the figure, the threshold value L1 is assumed to be larger than the threshold value L2.

  Further, “change amount (when increasing)” is information indicating a change amount applied when the light emission amount of the backlight module 22 is increased. In the figure, “HI_1” is stored in association with the range “A1”, “MID_1” is stored in association with the range “A2”, and “LOW_1” is stored in association with the range “A3”. . Here, it is assumed that the amount of change (at the time of increase) is “HI_1” is the largest and “LOW_1” is the smallest among “HI_1”, “MID_1”, and “LOW_1”. Further, it is assumed that the change amount “HI — 1” is a change amount that does not cause screen flicker in the liquid crystal display 20.

  The “change amount (decrease)” is information indicating the change amount used when the light emission amount of the backlight module 22 is reduced. In the figure, “HI_2” is stored in association with the range “A1”, “MID_2” is stored in association with the range “A2”, and “LOW_2” is stored in association with the range “A3”. . Here, it is assumed that the amount of change (at the time of decrease) is “HI_2” is the largest and “LOW_2” is the smallest among “HI_2”, “MID_2”, and “LOW_2”. Further, it is assumed that “HI_2” of the amount of change (when decreasing) is larger than “HI_1” of the amount of change (when increasing).

  As described above, the change amount setting information 122 associates a larger amount of change with a range delimited by a threshold having a larger value among ranges delimited by a plurality of thresholds. The change amount setting information 122 is first change amount setting information used when the target light emission amount is larger than the current light emission amount and second change information used when the target light emission amount is smaller than the current light emission amount. Change amount setting information.

  The change amount determination unit 112 determines the change amount corresponding to the range to which the difference value acquired from the difference value calculation unit 111 belongs as the change amount of the backlight module 22 by referring to the change amount setting information 122. Further, the change amount determination unit 112 also performs a process of passing the determined change amount and information indicating whether the current light emission amount should be increased or decreased to the light emission amount determination unit 113.

  As described above, the difference value calculation unit 111 and the change amount determination unit 112 are based on the difference value between the target light emission amount determined by the target light emission amount determination unit and the current light emission amount of the backlight. It functions as an example of a change amount determining means for determining a change amount.

  The light emission amount determination unit 113 is a processing unit that determines the light emission amount obtained by changing the current light emission amount by the change amount determined by the change amount determination unit 112 as the light emission amount of the backlight module 22. Specifically, the light emission amount determination unit 113 extracts the current light emission amount from the light emission amount history information 121 and changes the extracted current light emission amount by the change amount acquired from the change amount determination unit 112.

  More specifically, when the light emission amount determination unit 113 acquires information indicating that the current light emission amount should be increased from the change amount determination unit 112, the light emission amount determination unit 113 uses the current light emission amount extracted from the light emission amount history information 121. On the other hand, a value obtained by adding the change amounts acquired from the change amount determination unit 112 is determined as the light emission amount of the backlight module 22. When the information indicating that the current light emission amount should be decreased is acquired from the change amount determination unit 112, the light emission amount determination unit 113 changes with respect to the current light emission amount extracted from the light emission amount history information 121. A value obtained by subtracting the change amount acquired from the amount determination unit 112 is determined as the light emission amount of the backlight module 22.

  In addition, when the light emission amount determination unit 113 determines the light emission amount of the backlight module 22, the light emission amount determination unit 113 passes the determined light emission amount to the PWM generation unit 11 f and the conversion coefficient determination unit 114. In addition, when the light emission amount determination unit 113 determines the light emission amount of the backlight module 22, the light emission amount determination unit 113 also performs a process of storing the determined light emission amount in the light emission amount history information 121.

  Here, operation examples of the change amount determination unit 112 and the light emission amount determination unit 113 will be described with reference to FIG. FIG. 6 is a diagram illustrating an operation example of the change amount determination unit 112 and the light emission amount determination unit 113. 2A shows an operation example when the light emission amount of the backlight module 22 is increased, and FIG. 2B shows an operation example when the light emission amount of the backlight module 22 is decreased. Respectively.

  Further, the target light emission amount shown in (A) of the figure is a target light emission quantity based on the histogram of the frame (image data) updated at time t0, and the target light emission quantity shown in (B) of FIG. It is assumed that the target light emission amount is based on the histogram of the frame updated at time t4.

  As shown in FIG. 5A, the difference value D1 between the light emission amount (current light emission amount) applied to the frame updated at time t0 and the target light emission amount is within the range “A1” shown in FIG. ". In such a case, the change amount determination unit 112 extracts the change amount (when increasing) “HI_1” corresponding to the range “A1” from the change amount setting information 122 and passes the extracted change amount “HI_1” to the light emission amount determination unit 113. .

  When the light emission amount determination unit 113 acquires the change amount “HI_1” from the change amount determination unit 112, the light emission amount determination unit 113 extracts the current light emission amount from the light emission amount history information 121, and the change amount “HI_1” with respect to the extracted current light emission amount. ] Is determined as the backlight module 22. As a result, the light emission amount of the backlight module 22 is increased by the change amount “HI_1” at the time t1.

  Further, it is assumed that a difference value D2 between the light emission amount (current light emission amount) applied to the frame updated at time t1 and the target light emission amount belongs to the range “A2” illustrated in FIG. In such a case, the change amount determination unit 112 extracts the change amount (when increasing) “MID_1” corresponding to the range “A2” from the change amount setting information 122 and passes the extracted change amount “MID_1” to the light emission amount determination unit 113. . As described above, the change amount “MID_1” is a value smaller than the change amount “HI_1”.

  Then, when the change amount “MID_1” is acquired from the change amount determination unit 112, the light emission amount determination unit 113 extracts the current light emission amount from the light emission amount history information 121, and the change amount “MID_1” with respect to the extracted current light emission amount. ] Is determined as the backlight module 22. As a result, the light emission amount of the backlight module 22 is increased by the change amount “MID_1” at the time t2.

  Further, it is assumed that a difference value D3 between the light emission amount (current light emission amount) applied to the frame updated at time t2 and the target light emission amount belongs to the range “A3” illustrated in FIG. In this case, the change amount determination unit 112 extracts the change amount (at the time of increase) “LOW_1” corresponding to the range “A3” from the change amount setting information 122 and passes the extracted change amount “LOW_1” to the light emission amount determination unit 113. . As described above, the change amount “LOW_1” is smaller than the change amount “MID_1”.

  When the light emission amount determination unit 113 acquires the change amount “LOW_1” from the change amount determination unit 112, the light emission amount determination unit 113 extracts the current light emission amount from the light emission amount history information 121, and the change amount “LOW_1” with respect to the extracted current light emission amount. ] Is determined as the backlight module 22. As a result, the light emission amount of the backlight module 22 is increased by the change amount “LOW_1” at time t3.

  As described above, in this embodiment, when the light emission amount of the backlight module 22 is made to coincide with the target light emission amount, the light emission amount of the backlight module 22 is not changed suddenly in one frame, but is performed over a plurality of frames. It was decided to make it correspond with the target light emission amount by changing it periodically. Therefore, a rapid change in the light emission amount of the backlight module 22 can be suppressed, and as a result, flickering of the screen can be prevented.

  In addition, in this embodiment, when the difference value between the current light emission amount and the target light emission amount is large, the current light emission amount is largely changed by a change amount that does not cause flickering of the screen, while the difference value is small. As the amount of change gradually decreases, the current light emission amount is gradually converged to the target light emission amount. As a result, the light emission amount of the backlight module 22 can be brought close to the target light emission amount as soon as possible, so that color collapse that is likely to occur when the difference between the light emission amount of the backlight module 22 and the target light emission amount is large can be prevented. .

  On the other hand, as shown in FIG. 5B, the difference value D4 between the light emission amount (current light emission amount) applied to the frame updated at time t4 and the target light emission amount is within the range shown in FIG. It belongs to “A1”. In such a case, the change amount determination unit 112 extracts the change amount (when decreasing) “HI_2” corresponding to the range “A1” from the change amount setting information 122 and passes the extracted change amount “HI_2” to the light emission amount determination unit 113. .

  When the light emission amount determining unit 113 acquires the change amount “HI_2” from the change amount determining unit 112, the light emission amount determining unit 113 extracts the current light emission amount from the light emission amount history information 121, and the change amount “HI_2” with respect to the extracted current light emission amount. The value obtained by subtracting “is determined as the backlight module 22. As a result, the light emission amount of the backlight module 22 is reduced by the change amount “HI_2” at time t5.

  Here, in this embodiment, as described above, the amount of change “HI_2” used when the backlight module 22 is decreased is larger than the amount of change “HI_1” used when the backlight module 22 is increased. Value. This is because the viewer is less likely to recognize when the screen is darkened instantaneously than when the screen is brightened instantaneously.

  In this way, by making the maximum light emission amount when the light emission amount of the backlight module 22 is decreased larger than the maximum light emission amount when the light emission amount of the backlight module 22 is increased, the viewer feels flickering on the screen. Without this, the light emission amount of the backlight module 22 can be brought closer to the target light emission amount more quickly.

  Moreover, since the reduction amount of the power consumption by the backlight module 22 increases by increasing the maximum reduction amount of the light emission amount of the backlight module 22, the power saving effect can be further enhanced.

  When the difference value D5 between the light emission amount applied to the frame updated at time t5 and the target light emission amount belongs to the range “A2”, the light emission amount of the backlight module 22 changes at time t6. It will decrease by “MID_2”. When the difference value D6 between the light emission amount applied to the frame updated at time t6 and the target light emission amount belongs to the range “A3”, the light emission amount of the backlight module 22 changes at time t7. It will decrease by “LOW_2”.

  By the way, the value of the change amount stored as the light emission amount history information 121 can be arbitrarily set. For example, by setting each change amount (for example, “HI — 1”, “MID — 1”, etc.) to be a little smaller as a whole, the light emission amount of the backlight module 22 gradually changes toward the target light emission amount. For this reason, it is possible to more reliably prevent the occurrence of screen flicker.

  However, in such a case, since the actual light emission amount slowly follows the target light emission amount, halation is likely to occur. Here, halation refers to a phenomenon in which the color of a particularly bright portion in an image appears to be crushed by causing the backlight module 22 to emit light with a small amount of light emission when a bright image is input.

  On the other hand, when each change amount stored as the light emission amount history information 121 is set to be large as a whole, since the actual light emission amount quickly follows the target light emission amount, occurrence of halation can be prevented. it can. However, in such a case, the amount of change in the actual light emission amount increases, and thus the screen flickers easily. Considering such circumstances, if the value of the change amount stored as the light emission amount history information 121 is set to an appropriate value according to the device characteristics of the liquid crystal display 20, etc., the occurrence of halation and the screen It is possible to prevent the occurrence of flickering with a good balance.

  In addition, the threshold value L1 and the threshold value L2 stored as the light emission amount history information 121 can be arbitrarily set. Similarly, the set number of thresholds can be arbitrarily changed. In particular, when the number of thresholds is set to 0, the target light emission amount can be immediately reflected on the actual light emission amount.

  Returning to FIG. 4, the conversion coefficient determination unit 114 will be described. The conversion coefficient determination unit 114 is a processing unit that determines an RGB conversion coefficient corresponding to the acquired light emission amount using the RGB conversion information 123 when the light emission amount of the backlight module 22 is acquired from the light emission amount determination unit 113. . Further, the conversion coefficient determination unit 114 also performs a process of passing the determined RGB conversion coefficient to the RGB conversion unit 11g.

  Returning to FIG. 2, the PWM generator 11f will be described. The PWM generation unit 11 f is a processing unit that generates a PWM signal whose pulse width is adjusted so that the light emission amount of the backlight module 22 becomes the light emission amount acquired from the light emission amount determination unit 113 and outputs the PWM signal to the backlight module 22. is there. The PWM generator 11f outputs the PWM signal four times each time VSYNC (Vertical Synchronizing signal) is output once.

  The RGB conversion unit 11g multiplies 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 conversion coefficient determination unit 114. 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.

  As described above, the RGB conversion information 123 is set so that the RGB conversion coefficient increases as the light emission amount of the backlight module 22 determined by the light emission amount determination unit 113 decreases. Therefore, the RGB conversion unit 11g corrects the RGB value to be larger as the light emission amount of the backlight module 22 is smaller. As described above, in this embodiment, even when the light emission amount of the backlight module 22 is reduced, the RGB conversion unit 11g performs correction to increase the RGB value, so that the apparent brightness is kept constant and the image quality is improved. Deterioration is to be prevented.

  Next, a specific operation of the display control apparatus 10 according to the present embodiment will be described with reference to FIG. FIG. 7 is a flowchart illustrating the processing procedure of the display control apparatus 10 according to the present embodiment. Here, the figure shows a processing procedure of the display control apparatus 10 when the light emission amount of the backlight module 22 is increased. Note that the change amount determination unit 112 of the display control device 10 determines whether to increase or decrease the light emission amount of the backlight module 22 based on information from the difference value calculation unit 111 as described above.

  As shown in the figure, in the display control apparatus 10, the sub-sampling unit 11b performs sub-sampling on the image data acquired by the image data acquisition unit 11a (step S101). Subsequently, in the display control device 10, the histogram generation unit 11c generates a histogram using the image data after sub-sampling (step S102), and the histogram analysis unit 11d determines the target light emission amount using the histogram and the DNUM 12a. (Step S103).

  Subsequently, in the display control device 10, the difference value calculation unit 111 calculates a difference value between the target light emission amount and the current light emission amount (step S <b> 104), and the change amount determination unit 112 calculates the difference value within the range “ It is determined whether it belongs to “A1” (step S105). If it is determined that the difference value belongs to the range “A1” (step S105, Yes), the change amount determination unit 112 selects the change amount “HI_1” with reference to the change amount setting information 122 (step S105). S106).

  On the other hand, when the difference value calculated by the difference value calculation unit 111 does not belong to the range “A1” (step S105, No), the change amount determination unit 112 determines whether or not the calculated difference value belongs to the range “A2”. Determination is made (step S107). If it is determined that the difference value belongs to the range “A2” (step S107, Yes), the change amount determination unit 112 selects the change amount “MID_1” with reference to the change amount setting information 122 (step S107). S108).

  On the other hand, when the difference value calculated by the difference value calculation unit 111 does not belong to the range “A2” (step S107, No), the change amount determination unit 112 refers to the change amount setting information 122 and sets the change amount “LOW_1”. Select (step S109).

  Subsequently, the light emission amount determination unit 113 adds a value obtained by adding the amount of change selected in any of steps S106, 108, and 109 to the current light emission amount extracted from the light emission amount history information 121. Is determined as the amount of emitted light (step S110). Further, the light emission amount determination unit 113 stores the determined light emission amount in the light emission amount history information 121 (step S111).

  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 S112). Subsequently, the RGB converter 11g multiplies 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 corresponding to the changed light emission amount. Processing is performed (step S113). In the display control device 10, the RGB conversion unit 11g outputs the image data after the RGB conversion processing to the liquid crystal panel 21 (step S114), and ends the processing.

  As described above, in this embodiment, the histogram analysis unit determines the target light emission amount of the backlight based on the luminance value of the input image data, and the change amount determination unit determines the determined target light emission amount. The amount of change from the current light emission amount is determined according to the difference value between the current light emission amount of the backlight and the backlight, and the light emission amount determination unit changes the current light emission amount by the determined change amount. The amount of light emitted from the backlight was determined. Therefore, according to the present embodiment, it is possible to reduce screen flicker that occurs when the brightness of an image frequently changes while suppressing power consumption by the backlight.

  By the way, in the embodiments described above, the light emission amount of the backlight module 22 is changed even when the difference between the light emission amount of the backlight module 22 and the target light emission amount is slight. However, depending on the performance of the liquid crystal display 20, the screen may flicker even if the light emission amount of the backlight module 22 is slightly changed.

  Therefore, when the difference value between the light emission amount of the backlight module 22 and the target light emission amount is less than a predetermined value, the light emission amount of the backlight module 22 may not be changed. Hereinafter, such a case will be described with reference to FIG. FIG. 8 is a diagram illustrating another operation example of the change amount determination unit 112. Note that (A) in the figure shows another example of the change amount setting information 122, and (B) in the figure shows another example of operation when the light emission amount of the backlight module 22 is increased. Show.

  As shown in FIG. 6A, in the change amount setting information 122, “0” is associated with the range “A3” for both the change amount (when increasing) and the change amount (when decreasing). (See (A-1) in the figure).

  As shown in FIG. 5B, the change amount determination unit 112 changes when the difference value at the time t2 belongs to the range “A3”, that is, when the difference value at the time t2 falls below the threshold L2. The amount of change “0” is selected with reference to the amount setting information 122 and passed to the light emission amount determination unit 113.

  Then, since the change amount acquired from the change amount determination unit 112 is “0”, the light emission amount determination unit 113 determines the current light emission amount extracted from the light emission amount history information 121 as the light emission amount of the backlight module 22. . As a result, the light emission amount of the backlight module 22 does not change despite a difference from the target light emission amount.

  As described above, when the difference value between the light emission amount of the backlight module 22 and the target light emission amount is lower than the predetermined value, the amount of change from the current light emission amount of the backlight module 22 is set to 0, thereby the backlight module. The flickering of the screen caused by a slight change in the light emission amount 22 can be prevented.

  Although the threshold value L2 has been described as a predetermined value here, the present invention is not limited to this, and a value smaller than the threshold value L2 may be separately provided as the predetermined value.

  By the way, when the dark image and the bright image are alternately repeated as in the blinking scene, the light emission amount of the backlight module 22 is changed one by one as in the above-described embodiment. A large processing load is applied to the liquid crystal display 20.

  Therefore, when a dark image and a bright image are alternately repeated, the amount of change from the current light emission amount may be reduced or set to zero. Specifically, the change amount determination unit 112 determines that the screen is blinking based on the light emission amount history of the backlight module 22 stored as the light emission amount history information 121. When the change amount determination unit 112 determines that the screen is blinking, the change amount is reduced by multiplying the change amount extracted from the change amount setting information 122 by a predetermined coefficient (or 0). And).

  Hereinafter, such a case will be described with reference to FIG. FIG. 9 is a diagram illustrating another operation example of the change amount determination unit 112. In addition, (A) in the figure shows a state in which a bright image and a dark image are alternately repeated, and (B) in the figure shows a history of the light emission amount of the backlight module 22. (C) shows a change amount of the light emission amount of the backlight module 22 determined by the change amount determination unit 112.

  Assume that bright frames F1 and F3 and dark frames F2 and F4 are displayed in the order of F1, F2, F3, and F4 as shown in FIG. In such a case, when the light emission amount determination unit 113 determines the light emission amount of the backlight module 22 in each of the frames F1 to F4, the determined light emission amount is stored in the storage unit 12 as light emission amount history information 121 each time. Go.

  As a result, as shown in FIG. 5B, the storage unit 12 determines the light emission amount “E1” determined in the frame F1, the light emission amount “E2” determined in the frame F2, and the frame F3. The light emission amount “E3” and the light emission amount “E4” determined in the frame F4 are stored as the light emission amount history information 121.

  Then, the change amount setting information 122 determines that the screen is blinking based on the light emission amount history of the backlight module 22. Specifically, the change amount determination unit 112 determines that the screen is blinking when the difference values of the light emission amounts between adjacent frames are all equal to or greater than a predetermined value.

  That is, the difference value “E1-E2” (absolute value) of the light emission amount between the frames F1 and F2, the difference value “E2-E3” (absolute value) of the light emission amount between the frames F2 and F3, the frame F3 and the frame When the difference values “E3-E4” (absolute values) of the light emission amounts between F4 are all equal to or greater than the predetermined value, the change amount determination unit 112 determines that the screen is blinking.

  Then, as shown in FIG. 5C, when the change amount determination unit 112 determines that the screen is blinking, the change amount extracted from the change amount setting information 122 is multiplied by a predetermined coefficient. To reduce the amount of change (or 0).

  For example, it is assumed that the target light emission amount determined based on the histogram of the frame F5 is more than the threshold L1 than the actual light emission amount in the frame F5. In such a case, the change amount determination unit 112 extracts the change amount “HI_1” from the change amount setting information 122, and multiplies the extracted change amount “HI_1” by a predetermined coefficient “0” to thereby change the backlight module 22. The change amount of the light emission amount is set to “0”. As a result, the light emission amount of the backlight module 22 is the same as that of the frame F5 in the frame F6.

  Thus, the storage unit 12 stores the light emission amount of the backlight module 22 determined by the light emission amount determination unit 113 for a predetermined frame, and the change amount determination unit 112 is based on the light emission amount stored in the storage unit 12. When it is determined that the screen is blinking, the amount of change from the current light emission amount is reduced compared to the case where the image is not blinking. As a result, the processing load caused by frequently changing the light emission amount of the backlight module 22 in a short period can be reduced. Although the predetermined coefficient is described as “0” here, the present invention is not limited to this, and the predetermined coefficient can be arbitrarily set within a range of 0 or more and not exceeding 1.

  The amount of change may be changed between daytime and nighttime. For example, in the case of daytime (for example, 9 am to 5 pm), the light emission amount determination unit 113 multiplies the change amount extracted from the change amount setting information 122 by the daytime coefficient, and the backlight module 22. Is determined as the amount of change. Further, in the case of nighttime (for example, 5 to 9 pm), the light emission amount determining unit 113 multiplies the change amount extracted from the change amount setting information 122 by the night coefficient, and the backlight module 22. Is determined as the amount of change. Here, the daytime coefficient is larger than the nighttime coefficient. As a result, the light emission amount of the backlight module 22 can be changed in consideration of not only the brightness of the image but also the brightness of the surroundings.

  In the embodiment described above, the amount of change from the current light emission amount is determined in accordance with the light emission amount of the backlight module 22, the target light emission amount, and the difference value. The light emission amount of the module 22 may be forcibly changed to a designated light emission amount.

  As described above, the display control device and the display control method according to the present invention are useful when it is desired to reduce screen flicker that occurs when the brightness of an image frequently changes while suppressing power consumption by the backlight. Especially, it is suitable when it is desired to suppress 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 11e Light emission amount change part 111 Difference value calculation part 112 Change amount determination part 113 Light emission amount determination part 114 Conversion coefficient determination part 11f PWM generator 11g RGB converter 12 Storage unit 12a DNUM
12b Setting information 121 Light emission amount history information 122 Change amount setting information 123 RGB conversion information 20 Liquid crystal display 21 Liquid crystal panel 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,
Target light emission amount determining means for determining the target light emission amount of the backlight based on the luminance value of the input image data;
Change amount determining means for determining a change amount from the current light emission amount in accordance with a difference value between the target light emission amount determined by the target light emission amount determining means and the current light emission amount of the backlight;
A light emission amount determining means for determining a light emission amount obtained by changing the current light emission amount by a change amount determined by the change amount determining means as a light emission amount of the backlight ;
A light emission amount history storage unit for storing the light emission amount of the backlight determined by the light emission amount determination unit for a predetermined frame;
With
The change amount determining means includes
It is determined that the screen is blinking when all the difference values of the light emission amounts between adjacent frames among the light emission amounts for the predetermined frames stored in the light emission amount history storage means are greater than or equal to a predetermined value, and A display control device characterized in that, when it is determined that the screen is blinking, the amount of change from the current light emission amount is reduced as compared with the case where the image is not blinking . A change amount storage means for storing change amount setting information in which a change amount is associated with each range divided by a plurality of thresholds having different sizes;
The change amount determining means includes
A change amount associated with a range to which the difference value belongs among the ranges divided by the plurality of threshold values is specified using the change amount setting information, and the specified change amount is set as a change amount from the current light emission amount. The display control device according to claim 1, wherein the display control device is determined. The change amount storage means includes:
The display control apparatus according to claim 2, wherein change setting information in which a larger change amount is associated with a range delimited by a threshold having a larger value among the ranges delimited by the plurality of threshold values is stored. The change amount storage means includes:
First change amount setting information used when the target light emission amount is larger than the current light emission amount of the backlight, and a first change amount setting information used when the target light emission amount is smaller than the current light emission amount of the backlight. 2 change amount setting information,
The change amount determining means includes
When the target light emission amount is larger than the current light emission amount of the backlight, the change amount from the current light emission amount is determined using the first change amount setting information, and the target light emission amount is If less than the current amount of light emission of the backlight according to claim 2 or 3, characterized in that to determine the amount of change from the current light emission amount by using the second variation-setting information Display control device. The change amount determining means includes
If the difference value is below a predetermined value, the display control device according to any one of claims 1-4 for the variation, characterized in that a 0 from the current light emission amount. A display control method for controlling a light emission amount of a backlight that irradiates light to a display panel,
A target light emission amount determination step for determining a target light emission amount of the backlight based on the luminance value of the input image data;
A change amount determining step of determining a change amount from the current light emission amount according to a difference value between the target light emission amount determined in the target light emission amount determination step and the current light emission amount of the backlight;
A light emission amount determination step of determining a light emission amount obtained by changing the current light emission amount by the amount of change determined in the change amount determination step, as a light emission amount of the backlight ;
A light emission amount history storage step for storing the light emission amount of the backlight determined in the light emission amount determination step for a predetermined frame;
Only including,
The change amount determining step includes:
It is determined that the screen is blinking when the difference values of the light emission amounts between adjacent frames among the light emission amounts for the predetermined frames stored in the light emission amount history storing step are all equal to or larger than the predetermined value, and the screen When it is determined that is blinking, a change amount from the current light emission amount is reduced as compared with a case where an image is not blinking .

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