JP2012013858A - Display control device, display device and display control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of controlling a backlight at an early stage with a derived ideal light quantity control value while preventing enlargement of a circuit scale and flickers of a screen.SOLUTION: A display control device limits a light quantity control value before used for light quantity adjustment of a backlight within a limit range based on the light quantity control value used in the past for the light quantity adjustment, and changes the limit range based on differences of brightness of continuous images, so that the limit range can be flexibly set. Consequently, it is possible to prevent the flickers of the screen illuminated by the backlight and to restore early to the ideal light quantity control value before limitation.

Description

  The present invention relates to a technique for controlling a light amount of a backlight that illuminates a display screen.

  There is a technique for preventing wasteful power consumption in the backlight by controlling the backlight that illuminates the screen with the amount of light derived based on the brightness of the image displayed on the screen.

  For example, Patent Document 1 discloses a technique for controlling a backlight using a light amount control value derived based on the brightness of an image input to a circuit such as an ASIC installed in the apparatus.

  In such a circuit, in order to match the timing of outputting the input image to the screen and the timing of controlling the backlight with the light amount control value based on the brightness of the input image as much as possible, the interval between the repeatedly input images In view of the fact that the brightness of the image does not tend to differ unless there is a scene change, when the next input image is displayed on the screen, the amount of light based on the brightness of the image input this time There is a technique for controlling a backlight with a control value.

  In a circuit that employs such a technology, if the brightness of images that are repeatedly input varies greatly, the light amount control value of the backlight that is derived also varies greatly, so the screen flickers and is visible Sexuality will deteriorate. Therefore, there is a technology that allows the backlight to be controlled with the ideal light amount control value derived in the long run while restricting large fluctuations in the light amount control value of the backlight with changes in the image that is repeatedly input. is there.

JP 2009-251331 A

  However, when a scene change occurs in an image that is repeatedly input in the circuit, for example, when a relatively bright image is input from a relatively dark image that has been repeatedly input, the amount of light If the variation limit of the control value is made constant, it takes time to control the backlight with the light amount control value based on the bright image, that is, the ideal light amount control value, and the visibility of the image displayed on the screen is reduced. There is a problem that it can not be improved.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of early backlight control with a derived ideal light amount control value while preventing flickering of the screen.

  In order to solve the above problems, the invention of claim 1 is a display control device for controlling a backlight that illuminates a screen for displaying an image, and the backlight is based on the brightness of the image that is repeatedly input. Deriving means for deriving a light amount control value that regulates the amount of light, limiting means for deriving the derived value derived as the light amount control value by the deriving means to a range based on a limiting range value, Adjusting means for adjusting the light amount of the backlight using an output value as the light amount control value; and changing means for changing the limit range value based on a difference in brightness between successive images. It is characterized by.

  According to a second aspect of the present invention, in the display control apparatus according to the first aspect, the change means increases the limit range value as a difference in brightness between the successive images increases. .

  The display control apparatus according to claim 1, wherein the change unit is configured to change the limit range value from a reference value when a difference in brightness between successive images is equal to or greater than a predetermined value. It is characterized by being enlarged.

  According to a fourth aspect of the present invention, in the display control device according to the second or third aspect, the changing unit increases the limit range from a reference value until the output value reaches the derived value, After the output value reaches the derived value, the limit range is set to the reference value.

  According to a fifth aspect of the present invention, in the display control apparatus according to the first aspect, when the repeatedly input image transitions from a relatively bright image to a relatively dark image, the changing means is invalidated. It further comprises invalidating means.

  According to a sixth aspect of the present invention, in the display control device according to any one of the first to fifth aspects, the screen is selected in accordance with a degree of decrease of the light amount control value used by the adjusting unit from a reference light amount. Image amplification means for amplifying pixel data constituting an image to be displayed on the display, and display control means for displaying the image constituted by the amplified pixel data on the screen. .

  A seventh aspect of the invention includes the display control device according to any one of the first to sixth aspects, the backlight, and the screen.

  The invention of claim 8 is a display control method for controlling a backlight for illuminating a screen for displaying an image, wherein (a) the amount of light of the backlight is based on the brightness of the image repeatedly input. A step of deriving a light amount control value that defines the light amount; (b) a step of adjusting the light amount of the backlight using the light amount control value; and (c) a step of (b) derived in the step (a). A step of limiting the light amount control value before being used in step S to a limit range based on the light amount control value used in the step (b) in the past, and (d) brightness of the image being continuous. And a step of changing based on the difference in height.

  According to the first to eighth aspects of the invention, the display control device derives a light amount control value that defines the light amount of the backlight based on the brightness of the image that is repeatedly input, and is derived as the light amount control value. The value is limited to a range based on the limit range value to be an output value, and the output value is used as a light amount control value to adjust the light amount of the backlight, and the limit range value is based on the difference in brightness between successive images. In order to change, the limit range can be set flexibly. As a result, flickering of the screen illuminated by the backlight can be prevented, and the light amount control value before the limit can be quickly terminated.

  In particular, according to the invention of claim 2, the display control device increases the limit range as the difference in brightness between successive images increases, so that flickering of the screen can be prevented and the ideal light amount before the limit The control value can be terminated earlier.

  In particular, according to the invention of claim 3, the display control device can prevent the screen from flickering because the limit range is larger than the reference range when the brightness difference between successive images is equal to or greater than a predetermined value. It is possible to terminate the ideal light amount control value before the restriction earlier.

  In particular, according to the invention of claim 4, the display control device increases the limit range from the reference range until the limited output value reaches the derived value, and after reaching the limited output value, the display control device Since the range is set to the reference range, it is possible to terminate the ideal light amount control value before the restriction earlier, and to prevent flickering of the screen.

  In particular, according to the invention of claim 5, the display control device is limited in that it is unlikely that halation will occur when an repeatedly input image transitions from a relatively bright image to a relatively dark image. By invalidating the changing means for changing the range, it is possible to efficiently prevent the flickering of the screen.

  In particular, according to the invention of claim 6, the display control device amplifies the pixel data constituting the image in accordance with the degree of reduction of the derived and limited light amount from the reference light amount. Brightness can be made appropriate.

FIG. 1 is a system configuration diagram of an in-vehicle device. FIG. 2 is a system configuration diagram of the in-vehicle device. FIG. 3 is a diagram illustrating the display unit. FIG. 4 shows an image. FIG. 5 is a flowchart showing the contents of the control executed by the in-vehicle device. FIG. 6 is a diagram illustrating pixels in an image. FIG. 7 is a diagram illustrating a histogram of pixel data. FIG. 8 is a flowchart showing the contents of control executed by the in-vehicle device. FIG. 9 is a flowchart showing the contents of the control executed by the in-vehicle device. FIG. 10 is a diagram illustrating limit range value data. FIG. 11 is a diagram illustrating data on the backlight control duty. FIG. 12 is a diagram illustrating the transition of the input image. FIG. 13 is a diagram illustrating the transition of the input image. FIG. 14 is a diagram illustrating the transition of the input image. FIG. 15 is a diagram illustrating a change in the limit range value. FIG. 16 is a diagram illustrating the transition of the input image.

  The display control technology described below is applied to various display devices equipped with a display unit. For convenience, the in-vehicle device that is one of the various display devices will be specifically described. To do. Hereinafter, the in-vehicle device will be described separately with reference to the accompanying drawings by dividing the structure of the display unit mounted in the in-vehicle device, the configuration of the in-vehicle device, and the control of the in-vehicle device.

<Representative embodiment>
<Configuration of display unit mounted on in-vehicle device>
The structure of the display part with which the vehicle-mounted apparatus which is a display apparatus mounted in a vehicle is provided is demonstrated based on FIG. The display unit 7 includes a color filter 1, a liquid crystal layer 2, a TFT (Thin Film Transistor) 3, a backlight 5, and a touch panel 4.

  The color filter 1 is a film on which three primary colors (RGB) are printed for each pixel.

  The liquid crystal layer 2 is a so-called liquid crystal shutter whose molecular arrangement changes when an external voltage or the like is applied.

  The TFT 3 is a thin film transistor composed of electrodes arranged in a matrix. The TFT 3 changes the molecular arrangement of the liquid crystal in the liquid crystal layer 2 corresponding to the cell by generating a voltage to the target cell in a matrix form by controlling the electricity that the TFT control unit flows to the electrode, that is, the backlight. The light is transmitted to the color filter 1 side and the target color is displayed on the liquid crystal screen.

  The backlight 5 has a plurality of LEDs (Light Emitting Diodes) 5 serving as light sources arranged in series. That is, the backlight 5 has a function of illuminating the liquid crystal screen of the display unit constituted by the color filter 1, the liquid crystal layer 2, and the TFT 3.

  The type of the backlight 5 is an edge light type with a simple structure, and it can be said that it is an optimum structure for an in-vehicle device that requires a thin display portion, that is, a small size. In such an edge light type backlight, the LEDs 5 as a plurality of light sources are provided in series in the vicinity of the bottom side (lower base) of the display unit having a rectangular shape, so that the light faces the one side in the display unit 7. A polarizing plate is provided to prevent the light from becoming weaker toward the bottom (upper base), that is, to make the light of the backlight uniform in the display unit 7.

  Moreover, the backlight 5 can change the light quantity of LED5 by changing not only the simple light emission which makes LED5 which comprises comprise light but not light emission, and the duty ratio of the control current which controls LED5 differ.

  The touch panel 4 is a panel composed of transparent electrodes made of a metal thin film having resistance. The touch panel 4 has the electrodes arranged in a matrix, and a voltage is generated in the vicinity of the electrodes corresponding to the position of the liquid crystal screen touched by the user. For this reason, the in-vehicle device can determine that the position where the voltage is generated is the position operated by the user.

  Of the display unit 7 in which the color filter 1, the liquid crystal layer 2, the TFT 3, the backlight 5, the touch panel 4, and the like are stacked, the TFT 3 and the backlight 5 are used as the TFT control unit and backlight adjustment of the in-vehicle device. By controlling the unit, as shown in FIG. 3, an image such as a car navigation image or a TV image can be displayed on the liquid crystal screen of the display unit 7.

<Configuration of in-vehicle device>
Next, the configuration of the in-vehicle device will be described with reference to FIG. The in-vehicle device 27 includes a display unit 7, a volatile storage unit 11, a display control unit 16, an input switching unit 17, a control unit 18, a broadcast receiving unit 19, a camera input unit 20, a disk reading unit 21, and a car navigation unit 22. Are electrically connected to a bus or signal line capable of data communication.

  The control unit 18 is a microcomputer configured by a ROM or the like in which a CPU, a control program, and the like are stored. For example, the control unit 18 receives a user operation from the touch panel 4 and outputs an image corresponding to the user operation to the display control unit 16, so that the broadcast receiving unit 19, the camera input unit 20, the disk reading unit 21, or The input switching unit 17 is switched so that an image output from any of the car navigation units 22 is displayed on the display unit 7.

  The input switching unit 17 receives a switching instruction from the control unit and outputs a broadcast reception unit 19, a camera input unit 20, a disk reading unit 21, or a card so that an image corresponding to the instruction is output to the display control unit 16. This is a hardware circuit that switches the route of an image output from the navigation unit 22 to the display control unit 16.

  The display control unit 16 is an ASIC (Application Specific Integrated Circuit) configured by a logic circuit. For example, as illustrated in FIG. 2, the image adjustment unit 8, the TFT control unit 9, the sampling unit 10, the histogram generation unit 12, the analysis unit 13, the light amount control value deriving unit 14, and the backlight adjustment included in the display control unit 16. The unit 15 performs an image adjustment function, a TFT control function, a sampling function, a histogram generation function, an analysis function, a light amount derivation function, and a backlight adjustment function, respectively. Details of these functions will be described later.

  The light quantity control value deriving unit 14 is a part of the circuit of the display control unit 16 that is an ASIC. For example, the light amount control value calculating unit 30, the light amount control value limiting unit 31, and the limit range changing unit 32 exhibit a light amount control value calculating function, a light amount control value limiting function, and a limit range changing function, respectively. Details of these functions will be described later.

  The volatile storage unit 11 is, for example, an SRAM (Static Random Access Memory). The volatile storage unit 11 temporarily stores results such as derived control values when the display control unit 16 performs the respective functions, that is, it functions as a working area.

  The in-vehicle device 27 derives a light amount control value that defines the light amount based on the brightness of the image input to the display control unit 16 that is an ASIC. In other words, the light quantity control value is derived by analyzing a plurality of pixel data constituting the image. However, in order to perform normal analysis, all the pixel data is stored in the volatile storage unit 11 which is a memory mounted on the ASIC. There must be. For this reason, it is necessary to mount a memory having a capacity corresponding to the number of pixels in the ASIC, and there is a problem that the size of the ASIC increases as the number of pixels of the input image increases. Therefore, in the in-vehicle device 27 that is limited in size when mounted on the vehicle 28 and is packed with various functions, a technique described later is employed so that the size of the display control unit 16 that is an ASIC does not increase.

  In addition, the pixel data means a red (R) value, a green (G) value, and a blue (B) value that each of a plurality of pixels constituting the input image has, and values derived based on these values are also included. means.

  The broadcast receiving unit 19 receives the radio wave by the TV broadcast antenna 23 that directly receives the radio wave of the digital TV broadcast emitted in the air, and extracts a TV image G as shown in FIG. 3 based on the received radio wave. Take on the function. In addition, the broadcast receiving unit 19 transmits the extracted TV image G to the display control unit 16 through a signal line.

  The camera input unit 20 is provided with an image received via the signal line from the vehicle-mounted camera 24 provided in the vehicle 28 with the imaging direction facing the outside of the vehicle, that is, provided so that an image outside the vehicle can be imaged. It performs functions such as AGC (Automatic Gain Control) for adjusting to an image. In addition, the camera input unit 20 transmits the adjusted image outside the vehicle to the display control unit 16 via a signal line.

  The disk reading unit 21 has a function of reading a DVD image recorded on the DVD 25 set by the user. Further, the disk reading unit 21 transmits the DVD image recorded on the read DVD 25 to the display control unit 16 through a signal line.

  The car navigation unit 22 reads a map image corresponding to the calculated vehicle position data based on the GPS signal received by the GPS antenna 26, etc., from a storage device to be mounted, and combines it with data such as the vehicle position mark, Responsible for generating car navigation images. In addition, the car navigation unit 22 transmits a car navigation image to the display control unit 16.

  In addition, each of the broadcast receiving unit 19, the camera input unit 20, the disk reading unit 21, and the car navigation unit 22 displays an image size (for example, vertical width 480) displayed on the display unit 7 as an image generated in each unit. (Pixel, width 800 pixels), and then transmitted to the display control unit 16.

<Control of in-vehicle devices>
When the control unit 18 of the in-vehicle device 27 receives a user operation for setting the image mode outside the vehicle via the touch panel 4 of the display unit 7, the control unit 18 controls the input switching unit 17 to display the vehicle outside image adjusted by the camera input unit 20. And output to the display control unit 16.

  When the control unit 18 receives a user operation for DVD playback mode setting via the touch panel 4 of the display unit 7, the control unit 18 controls the input switching unit 17 so that the DVD image read from the DVD 25 by the disk reading unit 21 is controlled. And output to the display control unit 16.

  In addition, when the control unit 18 receives a user operation for setting the car navigation mode via the touch panel 4 of the display unit 7, the control unit 18 controls the input switching unit 17 to generate the vehicle position mark generated by the car navigation unit 22. The display control unit 16 outputs a car navigation image including a selection mark for accepting execution of a predetermined function and a map image.

  Thereafter, after the user selects the TV image, the in-vehicle camera image, the DVD image, or the car navigation image selected by the touch panel 4 to the display control unit 16 via the input switching unit 17, Processing executed in the display control unit 16 will be described in detail with reference to FIG. The control process shown in FIG. 5 is executed each time an image is input to the display control unit 16 at a predetermined cycle, and the process proceeds to step S1 shown in FIG. 5, and the power to the in-vehicle device 27 is turned off by the user. If finished.

(Sampling process)
In step S1, the sampling unit 10 included in the display control unit 16 samples a predetermined number of predetermined data from the input image.

  Specifically, the input image is divided into regions having a predetermined range as shown in FIG. 6, for example, a region composed of 6 pixels in the vertical width (Y axis) and 7 pixels in the horizontal width (X axis), A part of pixel data in the divided area is extracted. For example, it is data that satisfies a predetermined condition among data of a plurality of pixels constituting each of a plurality of areas. Specifically, the highest pixel data among the plurality of pixel data constituting the area is sampled (extracted) by comparison processing. )

  The sampling part 10 performs this comparison process for every area | region with respect to all the pixels contained in an area | region in predetermined order.

  The predetermined order in which the sampling unit 10 performs the comparison process is to compare for each region, for example, from the upper left region when the input image is viewed from the front among the plurality of regions in the divided input image. The comparison process is executed in order to the area on the right side of the same line, and when the comparison process is completed for the rightmost area in the line, the same line is formed from the leftmost area in the next line. The comparison processing is executed in order to the right adjacent region, and so on until the input processing is repeated in the lower right region when the input image is viewed from the front.

  The comparison performed by the sampling unit 10 in the area is, for example, a volatile storage that is a memory that stores the highest pixel data by executing the comparison of the first line in an area that consists of 7 rows of 6 pixels. The second row is compared, the highest pixel data is stored in the volatile storage unit 11, and the highest pixel data in the second row is compared with the highest pixel data in the first row. Then, the higher pixel data is stored in the volatile storage unit 11. Next, the comparison of the third row is executed to store the highest pixel data in the volatile storage unit 11 and the highest pixel data so far is compared with the highest pixel data of the third row. The same comparison is repeated until the last row such that the pixel data is stored in the volatile storage unit 11 and the highest pixel data in the region is stored in the volatile storage unit 11.

  Each of the plurality of pixels constituting the region has a red (R) value, a green (G) value, and a blue (B) value. In such a configuration, pixel data to be compared with other pixel data Is not the total pixel data of the three data, but the highest pixel data among the three pixel data.

  The sampling unit 10 stores the maximum pixel data in the volatile storage unit 11 having a size of 64 dots in the vertical width (Y axis) and 128 dots in the horizontal width (X axis). That is, the data stored in 11 is smaller than the input image data, and is the minimum necessary data for the histogram generation unit 12 described later to generate a histogram. Next, the process proceeds to step S2.

(Histogram generation processing)
In step S2, the histogram generation unit 12 included in the display control unit 16 causes the light amount control value deriving unit 14 to derive a light amount control value from a plurality of sampled pixel data, that is, from all sampled pixel data. Generate a histogram of

  Specifically, the histogram generation unit 12 generates a histogram H of a plurality of sampled pixel data as shown in FIG. The histogram is data indicating a graph showing a distribution of pixel data of a plurality of pixels constituting an image. Next, the process proceeds to step S3.

(Analysis processing)
In step S3, the analysis unit 13 included in the display control unit 16 analyzes the generated histogram H and extracts pixel data distributed at a predetermined position. This process will be specifically described with reference to FIG.

  In step S31, the analysis unit 13 counts the number of pixels from the pixel with the highest pixel data (255) to the pixel with the lowest pixel data (0) in the histogram H generated by the histogram generation unit 12. In this case, pixel data (for example, 220) when the count value exceeds a predetermined value (for example, 200) is extracted. In other words, the predetermined highest pixel data is extracted from the generated histogram H. Hereinafter, the predetermined highest pixel data is referred to as a histogram position HP. The value of the pixel data at the histogram position HP typically indicates the brightness of the input image.

  Here, the reason why the display control unit 16 derives the light amount control value for controlling the backlight 5 by the histogram H based on the plurality of pixel data constituting the image will be described.

  As will be described later, the display control unit 16 controls a light amount control value based on the extracted pixel data (a light amount control value serving as a reference in order to reduce the power consumed by the backlight, for example, a light amount lower than 100%. Control value) is derived as the light amount control value of the backlight 5, the backlight 5 is controlled with the derived light amount control value, and the backlight is controlled with the light amount control value that is lower than the reference light amount control value. In order to follow the brightness of the image, the pixel data constituting the image is uniformly amplified to make the brightness of the image displayed on the liquid crystal screen appropriate as a whole.

  That is, in applying this technique, the value of the predetermined value in the display control unit 16 is a value that hardly causes saturation when the pixel data constituting the image is uniformly amplified according to the light amount control value. Is set.

  If the display control unit 16 executes the standard for deriving the light amount control value not by the histogram but by the average (data average) of the data of a plurality of pixels constituting the image, a small number of high values are obtained when the data average is relatively low. There is a possibility that the pixel data is saturated when the data of the pixels constituting the image is uniformly amplified.

  Therefore, the display control unit 16 performs the process of deriving the light amount control value of the backlight based on the histogram and amplifying the data of the pixels constituting the image uniformly as described above, so that a part of the image is saturated. The visibility of the image is improved without any problems. Next, the process proceeds to step S32.

  In step S <b> 32, the analysis unit 13 stores the analyzed result value, that is, the pixel data 220 that is the histogram position HP in the volatile storage unit 11. Since this analysis result value is obtained by analyzing the image input to the display control unit 16, this analysis result value is used. Next, the process proceeds to step S33.

  In step S <b> 33, the analysis unit 13 analyzes a result value obtained by analyzing the image input to the display control unit 16 in the past, that is, the previous time, that is, the display control unit 16 performs the control flow illustrated in FIGS. 5 and 8. The previous analysis result value stored in the volatile storage unit 11 in step S32 is read from the result value analyzed at the time of execution in the previous turn.

  Note that the previous analysis result value is initially set to a default value (for example, 150) by the display control unit 16. Next, the process proceeds to step S34.

  In step S34, the analysis unit 13 derives the difference between the result value obtained by analyzing this time and the previous analysis result value read from the volatile storage unit 11 (that is, the difference in brightness between successive input images). It is determined whether or not the difference is a predetermined value (for example, 60) or more. If it is determined that the difference is greater than or equal to the predetermined value, the process proceeds to step S35 (in the case of YES in step S34). If it is not determined that the difference is greater than or equal to the predetermined value, the process proceeds to step S36 (in the case of NO in step S34).

  In step S <b> 35, the analysis unit 13 turns on the flag set in the volatile storage unit 11. Next, the process proceeds to return, and the process returns to the flowchart of FIG. 5 to proceed to step S4.

  In step S <b> 36, the analysis unit 13 turns off the flag set in the volatile storage unit 11. Next, the process proceeds to return, and the process returns to the flowchart of FIG. 5 to proceed to step S4.

  This flag is turned off by the display controller 16 by default.

(Light intensity control value derivation process)
In step S4, the light amount control value deriving unit 14 included in the display control unit 16 derives a light amount control value based on the pixel data extracted after analyzing the histogram H (that is, the brightness of the input image) as a derived value. This process will be specifically described with reference to FIG.

  In step S41, the light amount control value calculation unit 30 of the light amount control value deriving unit 14 conventionally has a fixed light amount control value regardless of the pixel data, that is, the duty of the control current that is the light amount control value for controlling the backlight 5. The ratio is a fixed value (for example, 100%), but in order to reduce the power consumed by the backlight 5, a predetermined process is executed to calculate the duty ratio.

  In other words, the predetermined processing means that the light quantity control value calculation unit 30 extracts pixel data when the above-mentioned count number exceeds a predetermined value (for example, 200th) in the above-described histogram H, that is, the histogram H. The duty ratio is calculated by calculating the ratio of the extracted pixel data in the pixel data range (for example, 256 from 0 to 255). In the processing, a ratio (for example, 100%) to the maximum value (for example, 256) of the pixel data range can be considered as the reference light amount control value.

  Therefore, the light quantity control value calculation unit 30 divides the pixel data obtained by adding 1 to the pixel data when the count number exceeds the predetermined value by the pixel data range 256, and adds 100 to the divided result, thereby obtaining the reference value. A ratio with respect to the light quantity control value is calculated, and the ratio is set as the duty ratio. In the above-described example, 220/256 = 86% is the duty ratio of the control current that is the light amount control value for controlling the backlight 5.

  That is, in the following, the display control unit 16 limits the light amount control value in order to prevent flickering of the screen on which the repeatedly input image is projected, but the light amount control value calculation unit 30 before such restriction is made. It can be said that the light amount control value as derived from the above is the ideal light amount control value for the image projected on the screen.

  Specifically, the light amount control value calculation unit 30 uses pixel data extracted after analysis from a non-volatile storage unit (not shown) in which the light amount control value associated with the pixel data is stored as a search key, and associates it with it. The obtained light quantity control value is searched and extracted. The light amount control value calculation unit 30 calculates the light amount control value when the backlight adjustment unit 15 controls the backlight 5 based on the light amount control value. Next, the process proceeds to step S42.

  In step S <b> 42, the light amount control value limiting unit 31 determines whether or not the flag set in the volatile storage unit 11 is on. When it is determined that the flag is off (when the difference in brightness of the input image is less than a predetermined value), the process proceeds to step S43 (in the case of YES in step S42). If it is determined that the flag is on (if the difference in brightness of the input image is greater than or equal to a predetermined value), the process proceeds to step S45 (in the case of NO in step S42). Then, the light amount control value limiting unit 31 executes a limiting process for limiting the light amount control value derived by the light amount control value calculating unit 30.

  If the difference in brightness of the input images is less than the predetermined value, in step S43, the light amount control value limiting unit 31 reads a fixed limit range value that is a reference range value from a non-volatile storage unit (not shown). Next, the process proceeds to step S44.

  In step S44, the light quantity control value limiting unit 31 applies the limit range value to the light quantity control value derived in step S41 and limits the output value.

  Specifically, the light quantity control value limiting unit 31 uses the light quantity control value used for the control of the backlight 5 last time as a reference control value, and obtains the change amount of the light quantity control value derived this time with respect to this reference control value.

  When the amount of change exceeds the limit range value, the change in the light amount control value is limited to the limit range value as a limit. That is, the light amount control value is limited so that the upper limit is a value obtained by adding the limit range value to the reference control value and the lower limit is a value obtained by subtracting the limit range value. On the contrary, the light amount control value limiter 31 falls within the limit range when the change amount of the light amount control value derived this time relative to the reference control value does not exceed the limit range value. The value is as derived. Next, the process proceeds to step S47.

  On the other hand, when the difference in brightness of the input images is equal to or greater than a predetermined value, the limit range value is set larger than the reference range value. Specifically, in step S45, the limit range changing unit 32 determines the difference between the current analysis result value and the previous analysis result value derived by the analysis unit 13 from a non-volatile storage unit (not shown) (brightness of successive input images). Using the search key as a search key, the limit range value associated therewith is searched and extracted. As shown in FIG. 10, the association is defined such that the limit range value increases as the difference increases, and the extent that the limit range value increases on the side where the difference is small is small, and on the side where the difference is large The degree of increase of the limit range value is related so as to increase. Increasing the limit range value corresponds to increasing the limit range for limiting the light amount control value.

  By such association, the display control unit 16 increases the limit range for the light amount control value for controlling the backlight based on the repeatedly input image as the difference between the current analysis result and the previous analysis result increases. Can do.

  In step S46, the light quantity control value limiting unit 31 applies the limit range value to the light quantity control value derived in step S41, and limits the light quantity control value.

  Specifically, when the change amount of the light amount control value derived this time with respect to the reference control value exceeds the limit range value, the light amount control value limit unit 31 limits the change of the light amount control value to the limit range value. . That is, the light quantity control value is limited so that the upper limit is a value obtained by adding the limit range value to the reference control value, and the lower limit is a value obtained by subtracting the limit range value.

  On the contrary, the light amount control value deriving unit 14 falls within the limit range when the change amount of the light amount control value derived this time relative to the reference control value does not exceed the limit range value. The value is as derived. Next, the process proceeds to step S47.

  In step S <b> 47, the light quantity control value restriction unit 31 stores the light quantity control value subjected to the restriction process in the volatile storage unit 11 as a light quantity control value used for the next control of the backlight 5.

  Here, the reason why the light quantity control value restriction unit 31 stores the light quantity control value subjected to the restriction process in the volatile storage unit 11 as the light quantity control value for the next backlight control will be described.

  The display control unit 16 is devised so that the memory is not mounted as much as possible in order not to increase the size of the display control unit 16 itself.

  In the display control unit 16, it is necessary to match the timing for outputting the input image to the screen and the timing for controlling the backlight so as to obtain the light amount control value derived by analyzing the input image. It is possible to temporarily store the data in the buffer memory and execute the control at the same time when the input image and the light intensity control value corresponding to each other in the buffer memory are aligned. In this case, the buffer memory is installed. Therefore, there is a problem that the display control unit 16 is increased in size.

  Therefore, in order to avoid this problem, the images that are input next time are displayed on the screen in consideration of the fact that there is not much difference between the analysis results of the images unless there is a scene change. When the image is displayed, a technique is adopted in which the backlight is controlled with a light amount control value derived based on the analysis result of the image input this time.

  That is, the reason why the light amount control value limiting unit 31 stores the light amount control value subjected to the restriction process in the volatile storage unit 11 as the light amount control value for the next backlight control is the next time in the display control unit 16. This is because when the input image is displayed on the screen, the backlight is controlled by the light amount control value derived based on the analysis result of the image input this time.

  Next, the process proceeds to return, and the process returns to the flowchart of FIG. 5 and proceeds to step S5.

  In step S <b> 5, the light amount control value derived from the light amount control value deriving unit 14 included in the display control unit 16 (the light amount control value subjected to the restriction process) is transmitted to the image adjusting unit 8. Next, the process proceeds to step S6 and step S7.

  In step S <b> 6, the backlight adjustment unit 15 of the display control unit 16 determines the backlight 5 based on the light amount control value derived from the light amount control value deriving unit 14 (the output value subjected to the restriction process, that is, the light amount control value). The duty factor is controlled for the LED 6 constituting the circuit.

  Specifically, the backlight adjustment unit 15 looks brighter if the duty ratio of the current controlled by the LED 6 is increased, and apparently darker if the duty ratio is decreased. A current for controlling the LED 6 is supplied at a certain duty ratio.

  In step S <b> 7, the image adjustment unit 8 included in the display control unit 16 reads out the pixel data coefficient from the nonvolatile storage unit based on the derived light amount control value, and uses the read out pixel data coefficient as pixel data constituting the input image. Multiply.

  Specifically, the image adjusting unit 8 searches the pixel data coefficient associated with the derived light amount control value from the nonvolatile storage unit using the light amount control value as a search key and searches for the pixel data coefficient associated therewith. Extract and multiply the pixel data of the input image by a pixel data coefficient. As shown in FIG. 11, the association is performed such that the coefficient for correcting the pixel data decreases as the duty for controlling the LED 6 constituting the backlight 5 increases. Next, the process proceeds to step S8.

  In step S8, the TFT control unit 9 included in the display control unit 16 controls the TFT 3 so that an image multiplied by the pixel data coefficient is displayed on the display unit 7.

  That is, in the non-volatile storage unit, the setting for associating the pixel data with the light amount control value is performed by setting the target brightness of the image when the TFT control unit 9 displays the image on the display unit 7 to the brightness based on the pixel data. In order to achieve the total brightness of the backlight controlled by the light quantity control value, the backlight light quantity control value has been lowered below the reference light quantity control value so that the power of the backlight 5 is reduced. The brightness of the image that becomes darker is set in a range that can be amplified and followed by the brightness based on the pixel data. Next, the process proceeds to return.

  Next, problems when the light quantity control value deriving unit 14 does not execute the above-described light quantity control value restriction process will be described with reference to a comparative example shown in FIG. Further, a problem when the light amount control value deriving unit 14 makes the restriction range value constant in the light amount control value restriction process will be described with reference to FIG. Further, the effect of changing the limit range value based on the difference between the current analysis result value and the previous analysis result value (difference in brightness of the input image) will be described with reference to FIGS.

<< Comparative example 1 (in the case of non-execution of restriction processing) >>
First, the problem of the comparative example when the light amount control value deriving unit 14 does not execute the light amount control value restriction process will be described with reference to FIG.

  In FIG. 12, when a plurality of images, for example, image 1G to image 5G are sequentially input to the display control unit 16, the analysis unit 13 analyzes the histogram H generated by the histogram generation unit 12 based on each of the images. Histogram position HP (brightness of the input image) derived in this way, the control duty for controlling the backlight 5, which is the light amount control value derived based on the histogram position HP, and the change in the correction coefficient of the image data. .

  In the example of FIG. 12, the histogram position HP of the image 1G is “20”, the histogram position HP of the image 2G is “80”, the histogram position HP of the image 3G is “15”, the histogram position HP of the image 4G is “40”, The histogram position HP of the image 5G has changed to “30”. When the brightness of each of the plurality of images input in this way varies, the backlight control duty derived by the display control unit 16 and the image data correction coefficient also vary according to the histogram position HP. End up.

  As a result, when the display control unit 16 repeatedly displays a plurality of images on the screen in a short time based on these control values, there arises a problem that the viewer who sees the screen feels flickering.

  In view of this, in the display control unit 16 in the present embodiment, fluctuations in these control values are limited to a certain level so that the viewer does not feel flicker.

<< Comparative Example 2 (When Limit Range Value is Constant) >>
Next, a problem of the comparative example in the case where the light quantity control value deriving unit 14 makes the restriction range value constant in the light quantity control value restriction process will be described with reference to FIG.

  FIG. 13 shows a control for controlling the histogram position HP (brightness of the input image) and the backlight 5 based on images when a plurality of images, for example, the image 1G to the image 5G are sequentially input to the display control unit 16. It represents changes in duty (light quantity control value used for light quantity adjustment), limit range value, and correction coefficient of image data.

  In the example of FIG. 13, the histogram position HP of the image 1G is “20”, the histogram position HP of the image 2G is “240”, the histogram position HP of the image 3G is “230”, the histogram position HP of the image 4G is “230”, The histogram position HP of the image 5G has changed to “230”. In this case, the display control unit 16 does not control the backlight 5 with the ideal backlight control duty derived based on the histogram position HP in accordance with the change of the histogram position HP, but a fixed limit range value. (For example, “5”) is set as a limit value of fluctuation of the backlight control duty (light quantity control value).

  That is, the display control unit 16 does not immediately follow the backlight control duty in accordance with the change in the histogram position HP, but changes the backlight control duty by a value within “5” that is the limit range value. By repeating such a change in the backlight control duty, the backlight 5 is eventually controlled with the ideal backlight control duty.

  As a result, even if the display control unit 16 changes the histogram position HP in a plurality of input images in a short time, the fluctuation of the backlight control duty is limited to a certain limit range. For this reason, there is little fluctuation | variation in the brightness of a screen, and it can prevent making the viewer who sees the screen feel flicker.

  However, on the other hand, as shown in FIG. 13, when the display control unit 16 makes a transition from the input image G1 to the input image G2, the histogram position HP changes rapidly from 20 to 240. That is, when a phenomenon such as a scene change occurs in the display control unit 16 in a short time, that is, when a repetitively input image transitions from a relatively dark image to an extremely bright image, If the fluctuation of the light control duty is limited to a certain limit range, it takes time until the backlight 5 can be controlled with the ideal backlight control duty derived based on the histogram position HP.

  In view of this, in the display control unit 16 of the present embodiment, the limit range value is not constant but variable, so that the viewer does not feel flickering and the ideal backlight control duty is reached early. To be able to end. This technique will be specifically described below.

<< When changing the limit range value >>
Next, an effect when the limit range changing unit 32 of the light amount control value deriving unit 14 changes the limit range value in the light amount control value limiting process as in the present embodiment will be described with reference to FIG. . In the control flow shown in FIG. 9 described above, the processing after step S45 corresponds to part of the processing shown in FIG.

  FIG. 14 is similar to FIG. 13, when a plurality of images, for example, the image 1G to the image 5G, are sequentially input to the display control unit 16, the histogram position HP (brightness of the input image) based on these images, the backlight 5 represents a change in control duty (a light amount control value used for light amount adjustment), a limit range value, and a correction coefficient of image data. Furthermore, the change of the limit range value is also shown.

  In the example of FIG. 14, the histogram position HP of the image 1G is “20”, the histogram position HP of the image 2G is “25”, the histogram position HP of the image 3G is “200”, and the histogram position HP of the image 4G is “200”. The histogram position HP of the image 5G has changed to “200”. Further, the difference between the histogram positions HP of the input images 2G and 3G (the difference in brightness between successive input images) is equal to or greater than a predetermined value (60 in the previous example). In this case, a scene change occurs in which the image repeatedly input suddenly changes from a relatively dark image to a relatively bright image. For this reason, there is a large difference between the ideal backlight control duty of the image 2G and the ideal backlight control duty of the image 3G.

  That is, when the display control unit 16 receives relatively dark images 1G and 2G, the ideal backlight control duty for these images was small, but after the relatively dark image 2G was input, Since bright images 3G, 4G, and 5G are input, the ideal backlight control duty for these images has increased.

  In such a situation, as in the comparative example 2 described above, if the display control unit 16 limits the fluctuation of the backlight control duty only to a certain limited range, the backlight control duty is increased from the small backlight control duty. It takes time to reach the duty.

  Therefore, when the difference between the brightness of the current image and the brightness of the previous image is greater than or equal to a predetermined value, the display control unit 16 varies the limit range value based on the difference. That is, when the difference between the histogram position HP based on the current image and the histogram position HP based on the previous image is greater than or equal to a predetermined value, the display control unit 16 stores the non-illustrated nonvolatile storage unit in FIG. The limit range value is extracted from the map including the relationship between the limit range value and the difference as shown by using the difference as a search key.

  Note that, as described above, the map is defined such that the limit range value increases as the difference increases, as described above, and the extent that the limit range value increases on the smaller difference side is small, On the side where the difference is large, the degree of increase in the limit range value is related to increase. By increasing the limit range value in this way, the limit range of the light quantity control value becomes larger than the reference range based on the reference range value (for example, “5”).

  The display control unit 16 limits the light amount control value derived based on the histogram position HP to a limit range based on the extracted limit range value.

  By such processing, when the image repeatedly input in the display control unit 16 transitions from a relatively dark image to a relatively bright image and when a scene change occurs, the limit range value is set. Increase

  More specifically, as shown in FIG. 15, before the scene change occurs when an image repeatedly input in the display control unit 16 transitions from a relatively dark image to a relatively bright image. Controls the backlight 5 based on the output value applied by the limit range value A having a relatively small derived value. On the other hand, after the scene change occurs, the backlight 5 is controlled based on the output value applied by the limit range value B having a relatively large derived value. For this reason, the display control part 16 can be terminated at an early stage to the ideal light quantity control value before being restricted.

Note that the derived value in this case is a light amount control value that defines the light amount of the backlight 5 derived based on the brightness of the image repeatedly input to the display control unit 16 as described above. Further, the output value in this case is a light amount control value in which the derived value is limited to a range based on the limit range value as described above.
(Light intensity control value that defines the light intensity of the backlight derived based on the brightness of the image),
Further, the display control unit 16 can be prevented from being enlarged by adopting other techniques. For example, as the number of pixels of the input image increases, the capacity of the memory increases and the size of the ASIC increases accordingly. However, the input image is divided into a plurality of regions and the maximum is obtained from each of the plurality of regions. By extracting pixel data and generating a histogram based on the extracted pixel data, it is possible to reduce the memory capacity mounted on the display control unit 16 that is an ASIC. In other words, by installing a small-sized memory, it is possible to prevent an increase in the size of the display control unit 16 that is an ASIC, and to appropriately derive the amount of backlight that illuminates a high-definition liquid crystal screen, which limits the mounting area. It can be mounted on a small vehicle 28.

<Modification>
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible. Below, the modification of the said embodiment is demonstrated. Of course, the modifications described below may be combined as appropriate.

<Modification 1>
In the above representative embodiment, “when the difference between the brightness of the current image and the brightness of the previous image is greater than or equal to a predetermined value, the display control unit 16 varies the limit range value based on the difference”. As described above, when the repeatedly input image transitions from a relatively bright image to a relatively dark image, the function of the limit range changing unit 32 is disabled and the limit range value is made constant. Also good. Details thereof will be described with reference to FIG.

  FIG. 16 is similar to FIG. 14, when a plurality of images, for example, image 1G to image 5G, are sequentially input to the display control unit 16, histogram position HP (brightness of input image) and light amount control based on these images. It represents changes in the control duty (light amount control value used for light amount adjustment), the limit range value, and the correction coefficient of the image data.

  In the example of FIG. 16, the histogram position HP of the image 1G is “200”, the histogram position HP of the image 2G is “200”, the histogram position HP of the image 3G is “25”, the histogram position HP of the image 4G is “20”, The histogram position HP of the image 5G has changed to “20”. Further, the difference between the histogram positions HP of the input images 2G and 3G is equal to or greater than a predetermined value (60 in the previous example). In this case, a scene change occurs in which the image repeatedly input suddenly changes from a relatively bright image to a relatively dark image. For this reason, there is a large difference between the ideal backlight control duty of the image 2G and the ideal backlight control duty of the image 3G.

  That is, in the display control unit 16, when the relatively dark image 1G and the relatively image 2G are input, the ideal backlight control duty for the images is not large, but the relatively dark image 2G is input. Since relatively bright images 3G, 4G, and 5G were input later, the ideal backlight control duty for these images has been reduced.

  In such a situation, as in the representative embodiment, it is conceivable to increase the limit range value in accordance with the difference in brightness between successive input images.

  However, unlike the case where an image that is repeatedly input transitions from a relatively dark image to a relatively light image, the input image transitions from a relatively light image to a relatively dark image, When a dark image is projected on the screen, even if the backlight is controlled with a relatively large duty corresponding to the relatively bright image, the visibility for the viewer watching the screen is not greatly reduced. .

  Therefore, the display control unit 16 is in the case where the difference between the brightness of the current image and the brightness of the previous image is greater than or equal to a predetermined value, and the input image transitions from a relatively bright image to a relatively dark image. The function of the limit range changing unit 32 that varies the limit range value according to the difference is invalidated to make the limit range value constant.

  As a result, even when the input image transitions from a relatively bright image to a relatively dark image and when a scene change occurs, the visibility is not deteriorated by a relatively simple process. Flickering of the screen illuminated by the backlight can be prevented.

<Modification 2>
In step S41 in the above representative embodiment, the fact that “the ideal light amount control value is calculated based on the histogram position HP calculated based on the histogram H” will be described. Further, in steps S45 and S46, “variable restriction” It has been explained that the light quantity control value is limited based on the range value. On the other hand, the display control unit 16 controls the backlight 5 with the limited light quantity control value, and eventually, the limited light quantity control value becomes the light quantity control value before the restriction, that is, the ideal light quantity control value. After reaching the light amount limit value, the limit range value may be returned to a certain limit range value that is the reference range.

  Specifically, the display control unit 16 turns off the flag when the limited light amount control value matches or substantially matches the ideal light amount control value.

  As a result, the ideal light amount control value before the restriction can be terminated earlier and flickering of the screen can be prevented.

<Modification 3>
Further, the limit range value may be increased every time the limit process for limiting the light amount control value is executed. For example, when the control shown in FIGS. 5, 8, and 9 is executed every time an image is repeatedly input, the change range from the reference range value of the limit range value applied in step S <b> 45 and step S <b> 46. Will be increased. The display control unit 16 executes the control for gradually increasing the limit range value in this way until the limited light amount control value reaches the light amount control value before being limited, that is, the ideal light amount limit value. Can do.

  Thereby, the flickering of the screen can be prevented and the ideal light amount control value before the limit can be terminated earlier.

<Modification 4>
In addition, the speed at which the limit range value is increased can be changed. For example,
When a repetitively input image transitions from a relatively dark image to a relatively light image, the speed of increasing the limit range is increased and the repetitively input image transitions from a relatively light image to a relatively dark image. If so, the speed of increasing the limit range can be slowed.

  When a repetitively input image transitions from a dark image to a bright image, there is a high possibility that halation will occur, so by increasing the speed of increasing the limit range, the limited light control value will be The ideal light quantity control value can be quickly terminated. In addition, when an image that is repeatedly input transitions from a bright image to a dark image, it is unlikely that halation will occur, so the speed of increasing the limit range is slowed, and screen flickering can be prevented. .

<Modification 5>
In the above-described representative embodiment, the backlight is described as an LED. However, the backlight may be any light source that can illuminate the liquid crystal screen and adjust the amount of light. For example, a fluorescent lamp may be used.

<Modification 6>
In the above-described representative embodiment, the histogram position HP, which is the analysis result by the analysis unit 13, is used as the brightness of the input image. For example, the average value of a plurality of pixel data constituting the image is used. The value of may be used. Further, as the value of the pixel data, a red (R) value, a green (G) value, a blue (B) value, a luminance value, a color difference value, or the like assigned to each pixel can be used.

<Modification 7>
In the above-described representative embodiment, it has been described that the backlight 5 is uniformly controlled based on the light amount control value derived, but the plurality of LEDs 6 constituting the backlight 5 may be individually controlled.

  In that case, the display control unit 16 does not analyze the generated histogram H, but derives the average luminance in the vertical direction of the image projected on the screen corresponding to the vertical direction of the screen illuminated by each of the plurality of LEDs 5, Each LED 6 is controlled based on each average luminance.

<Modification 8>
In the above-described representative embodiment, “when the limit range value is exceeded, the value obtained by adding the limit range value to the reference control value is the upper limit, and the value obtained by subtracting the limit range value is the lower limit. The reference control value may be a light amount control value, that is, a derived value, or may be a light amount control value, that is, an output value.

DESCRIPTION OF SYMBOLS 10 Sampling part 11 Volatile memory | storage part 12 Histogram generation part 13 Analysis part 14 Light quantity control value derivation part 15 Backlight adjustment part 16 Display control part 30 Light quantity control value calculation part 31 Light quantity control value restriction part 32 Restriction range change part 8 Image adjustment Part H Histogram HP Histogram position

Claims (8)

A display control device that controls a backlight that illuminates a screen that displays an image,
Derivation means for deriving a light amount control value for defining the light amount of the backlight based on the brightness of the image repeatedly input;
Limiting means for limiting the derived value derived as the light amount control value by the deriving means to a range based on the limiting range value and setting it as an output value;
Adjusting means for adjusting the light quantity of the backlight using the output value as the light quantity control value;
Changing means for changing the limit range value based on a difference in brightness between successive images;
A display control apparatus comprising: The display control device according to claim 1,
The display control device, wherein the change unit increases the limit range value as a difference in brightness between successive images increases. The display control device according to claim 1,
The display control device, wherein the changing unit increases the limit range value from a reference value when a difference in brightness between successive images is equal to or greater than a predetermined value. In the display control device according to claim 2 or claim 3,
The changing means is
Until the output value reaches the derived value, the limit range is larger than a reference value,
After the output value reaches the derived value, the limit range is set to the reference value. The display control device according to claim 1,
Invalidating means for invalidating the changing means when the repeatedly input image transitions from a relatively bright image to a relatively dark image;
A display control device further comprising: In the display control device according to any one of claims 1 to 5,
Image amplifying means for amplifying pixel data constituting an image to be displayed on the screen in accordance with the degree of reduction from the reference light quantity of the light quantity control value used by the adjusting means;
Display control means for displaying the image composed of the amplified pixel data on the screen;
A display control device further comprising:   A display control apparatus comprising: the display control apparatus according to claim 1; the backlight; and the screen.   A display control method for controlling a backlight that illuminates a screen for displaying an image, wherein (a) a light amount control value that defines a light amount of the backlight is derived based on the brightness of the image that is repeatedly input. (B) adjusting the amount of light of the backlight using the light amount control value; (c) calculating the light amount control value derived in the step (a) and before being used in the step (b). A step of limiting to the limit range based on the light amount control value used in the step (b) in the past, and (d) a step of changing the limit range based on a difference in brightness of the successive images. A display control method comprising:

Images