JP5315783B2 - Video display device - Google Patents

Description

  The present invention relates to a video display device, and more particularly to a video display device that adjusts the contrast of a display video and the light emission luminance of a backlight.

  2. Description of the Related Art Conventionally, there has been proposed an image display device that improves the visual contrast by adjusting the contrast and the light source so as to have a correlation with each other.

Specific processing of the video display device will be described. In the video display device, the feature detection unit has a maximum luminance level (hereinafter referred to as MAX), a minimum luminance level (hereinafter described as MIN), and an average luminance level (hereinafter referred to as APL) for the input video signal. Is detected. The control data generation unit amplifies the difference between the detected MAX and MIN to the dynamic range width, and the DC level at which the input video signal amplified by the amplification rate falls within the output dynamic range of the DC level adjustment unit An offset value giving the shift amount is obtained. The signal amplitude adjustment unit amplifies the input video signal according to the amplification factor with reference to APL. The DC level adjustment unit shifts the level of the amplified input video signal according to the offset value. The light source control unit controls the light source based on the offset value so that the visual luminance level on the screen is equal to the luminance level of the input video signal (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2001-27890

  However, in the above video display device, the luminance of the light source (backlight) is controlled so that the average visual luminance level does not change. There is a problem that it is difficult to see the contents of the video displayed on the screen, and the contrast is rather lowered.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a video display device capable of obtaining an appropriate contrast feeling.

In order to achieve the above object, one aspect of the present invention is an image display device capable of adjusting a contrast of a display image and a light emission luminance of a backlight, and a determination unit that determines the intensity of external light, and an input A video signal processing unit that performs processing for correcting the video signal; and a backlight control unit that adjusts the light emission luminance of the backlight; and when the determination unit determines that external light is strong, the backlight control unit The light emission luminance of the backlight is fixed to a constant value, the video signal processing unit corrects the input video signal by changing a correction amount according to the brightness of the scene, and the correction performed by the video signal processing unit is the input This is a correction that improves the average luminance level of the video signal.

  According to one aspect of the present invention, when the external light is strong, specific examples include contrast gain, brightness, and gamma value so as to improve the visual average luminance level while fixing the luminance of the backlight. Since the video signal can be corrected, it is possible to increase the contrast feeling of the displayed video while ensuring the visibility during external light irradiation.

  Also, when the external light is weak, the backlight luminance is dynamically controlled so that the visual average luminance level does not change with the process of correcting the contrast of the input video signal. Even so, it is possible to provide a display image with a higher contrast.

  As described above, according to one aspect of the present invention, an appropriate contrast feeling can be obtained regardless of the intensity of external light.

  FIG. 1 is a block diagram showing an overall configuration of a video display device 1 according to an embodiment of the present invention and its peripheral configuration. In FIG. 1, the video display device 1 is connected to a video source 2 such as a DVD player 2 </ b> A, for example, and includes an external light detection unit 11, a video processing LSI 12, a display 13, and a CPU 14.

  The external light detection unit 11 is, for example, an illuminance sensor 11A. The illuminance sensor 11A is attached around the display 13 and detects the illuminance i of the incident light. The illuminance sensor 11 </ b> A outputs a signal indicating the detected illuminance i to the CPU 14. In the following description, for convenience, the output signal of the illuminance sensor 11A is simply referred to as illuminance i.

  The video processing LSI 12 performs predetermined processing on the video signal A output from the DVD player 2A, and outputs the processed video signal A1 to the display 13. For this purpose, the video processing LSI 12 includes at least a feature detection unit 121 and a video signal processing unit 122.

  The feature detection unit 121 calculates a feature amount group F of the video represented by the input video signal A, and outputs the calculated feature amount group F to the CPU 12 and the video signal processing unit 122. Here, the feature amount group F is the minimum luminance, the average luminance, and the maximum luminance. The feature detection unit 121 also outputs the input video signal A to the video signal processing unit 122 at the subsequent stage. Hereinafter, for convenience of description, the minimum luminance is described as MIN, the average luminance is described as APL, and the maximum luminance is described as MAX.

  The video signal processing unit 122 uses the correction amount group C sent from the CPU 14 and the feature amount group F sent from the feature detection unit 121 to receive the video signal A sent from the feature detection unit 121. to correct. The processed video signal A1 generated by this correction is output to the display 13.

  Here, FIG. 2 is a schematic diagram showing functional blocks of the video processing unit 122. In FIG. 2, the video signal processing unit 122 includes an amplifying unit 1221, a DC level adjusting unit 1222, a contrast correcting unit 1223, a brightness correcting unit 1224, and a gamma correcting unit 1226. Each process of the configuration shown in FIG. 2 will be described later together with a process description of the CPU 14.

  Refer to FIG. 1 again. The display 13 is a liquid crystal display and includes at least a screen 131, a backlight control unit 132, and a backlight 133. Video is displayed on the screen 131 according to the video signal A1 sent from the video signal processing unit 122.

  The backlight control unit 132 controls light emission of the backlight 133 based on the luminance control signal (Lmax, L) sent from the CPU 14.

  The backlight 133 is provided behind the screen 131, emits light under the control of the backlight control unit 132, and gives light to the screen 131 for video display.

  The CPU 14 executes a program stored in advance in a ROM (not shown) using a RAM (not shown) as a work area.

  FIG. 3 is a flowchart showing the operation of the CPU 14. Hereinafter, the operation of the CPU 14 will be described with reference to FIG.

  In FIG. 3, the CPU 14 receives the illuminance i from the illuminance sensor 11A (step S31). The received illuminance i is used as the illuminance of external light incident on the display 13. The CPU 14 compares such illuminance i with a predetermined reference value, and determines whether or not the received illuminance i is equal to or less than the reference value (step S32). Here, the reference value is set to, for example, 3000 lux.

  When the reference value is less than or equal to the reference value, the CPU 14 considers that the ambient light around the display 13 is weak at the present time and the visibility of the display 13 is not deteriorated. In this case, the CPU 14 executes the first processing mode for enlarging the contrast of the display image on the screen 131 while performing the luminance control of the backlight 132 (step S33).

  On the other hand, when the reference value is exceeded, the CPU 14 considers that the ambient light around the display 13 is strong at the present time and the visibility of the display 13 deteriorates. In this case, the CPU 14 selects the second processing mode in which the contrast feeling of the display image on the screen 131 is enlarged while the luminance of the backlight 132 is fixed (step S34).

  FIG. 4 is a flowchart showing step S33, that is, the first processing mode. In FIG. 4, the CPU 14 first divides the signal processable range, that is, the dynamic range of the DC level adjustment unit 1222 by the difference between MAX and MIN sent from the feature detection unit 121 (see the following equation (1)). ), An amplification factor G for amplifying the maximum amplitude of the input video signal A to the dynamic range width is obtained. The amplification factor G obtained in this way is output to the amplification unit 1221 (see FIG. 2) of the video signal processing unit 122 as one of the correction amounts C (step S41).

G = dynamic range / (MAX-MIN) (1)
For example, as shown in FIG. 5A, when the maximum amplitude of the input video signal A is 67% with respect to the dynamic range width, the amplification factor G obtained by the CPU 14 is as shown in FIG. It becomes about 1.5 times.

  After step S41, the CPU 14 obtains a DC level shift amount (offset amount) S such that the video signal A amplified with the amplification factor G falls within the dynamic range. This corresponds to the case where the video signal processing unit 122 performs amplification with the APL as a reference, that is, with the DC level of the APL fixed, so that the amplitude of the amplified video signal A falls within the dynamic range. Then, the DC level of the amplified video signal A is changed. For example, as shown in FIG. 5C, when the amplitude of the amplified video signal A is 0.5 V lower than the lower limit of the dynamic range, the CPU 14 obtains 0.5 V as the shift amount S. The shift amount S is output to the DC level adjustment unit 1222 (see FIG. 2) of the video signal processing unit 122 as another one of the correction amounts, and further output to the backlight control unit 132 as a luminance control signal L. (Step S42).

  Through the processing as described above, the video signal A and APL from the feature detection unit 121 and the amplification factor G from the CPU 14 are input to the amplification unit 1221. The amplifying unit 1221 amplifies the input video signal A with an input amplification factor G with reference to the input APL (see FIG. 5B).

  The video signal A amplified in this way is output to the DC level adjustment unit 1222. Since the output dynamic range of the amplifying unit 1221 is sufficiently wider than the output dynamic range of the DC level adjusting unit 1222, for example, a signal portion exceeding the lower limit of the dynamic range in FIG. Given in.

  The DC level adjustment unit 1222 receives the video signal A from the amplification unit 1221 and the shift amount S from the CPU 14. The DC level adjustment unit 1222 shifts the DC level of the input video signal A by the value of the input shift amount S (see FIG. 5C). The video signal after the level shift is given to the display 13 as the corrected video signal A1.

  In addition, the luminance control signal L from the CPU 14 is input to the backlight control unit 132. The backlight 132 control unit 132 reduces the light emission luminance of the backlight 133 from the reference luminance value of the backlight 133 by the shift amount S represented by the luminance control signal L. Thus, the light emission luminance of the backlight 133 is adjusted so that the visual luminance level of the video represented by the corrected video signal A1 on the screen 131 is equal to the luminance level of the video represented by the input video signal A. That is, the luminance of the backlight 133 is adjusted so that the APL of the video displayed on the screen 131 is the same as the APL of the video represented by the input video signal A (see FIG. 5D).

  As described above, when the luminance of the backlight 133 is decreased with respect to the black level by absorbing the variation of the APL generated in the DC level adjustment unit 1222, the visual luminance level is relatively decreased. A feeling of contrast is improved (see FIG. 5D). As for the white level, when the luminance of the backlight 133 is increased, the visual white peak is relatively high. As a result, the bright part is more conspicuous, and the contrast is improved.

  As described above, according to the first processing mode, the video display device 1 adjusts the luminance of the backlight so that the visual average luminance level does not change while amplifying the video signal when the illuminance i is small. . Thereby, even when external light is weak, a visual contrast feeling can be improved.

  It should be noted that in order to prevent fluttering due to changes in the gain G and the shift amount S for each frame, a low-pass filter having such characteristics that the gain G and the shift amount S change gently may be applied. It doesn't matter.

  In the present embodiment, the amplification unit 1221 performs amplification with the APL as a reference, that is, with the DC level of the APL fixed, but the amplification unit 1221 simply gains a video as shown in FIG. Amplification may be performed by applying. Specifically, first, as shown in FIG. 6A, the input video signal A is multiplied by an amplification factor G for amplifying the maximum amplitude of the input video signal A to the dynamic range width. Next, the DC level is adjusted so that the amplified video signal falls within the dynamic range, thereby generating the video signal A1 (see FIG. 6B). Further, the light emission luminance of the backlight 133 is adjusted so that the APL of the video displayed on the screen 131 is the same as the APL of the video represented by the input video signal A (see FIG. 6C). Even if the video signal is corrected and the backlight luminance is controlled in this way, the same effect as the above-described example can be obtained.

  Next, details of step S34 in FIG. 3 will be described. FIG. 7 is a flowchart showing the second processing mode. In FIG. 7, the CPU 14 first compares the APL sent from the feature detection unit 121 with a predetermined reference value to determine whether or not the received APL is equal to or less than the reference value (step S61). Here, the reference value is set to, for example, an 8-bit luminance gradation value of 100.

  If it is equal to or smaller than the reference value, the CPU 14 regards the currently input video signal A as representing a dark scene, and corrects the contrast correction amount cd, the brightness correction amount bd, and the gamma value correction for the dark scene. The amount γd is selected (step S62). The CPU 14 outputs these four types of correction amounts cd, bd, and γd to the video signal processing unit 122 as correction amounts C for dark scenes in the second processing mode.

  Next, the CPU 14 outputs a luminance control signal for setting the luminance of the backlight 132 to the maximum value Lmax to the backlight control unit 132 (step S63). Hereinafter, for convenience, this control signal is referred to as Lmax.

  On the other hand, if it is determined in step S61 that the input video signal A is not less than the reference value, the CPU 14 considers that the input video signal A represents a bright scene, and for the bright scene, the contrast correction amount cb and the brightness correction amount. bb and a gamma value correction amount γb are selected (step S64). The CPU 14 outputs these four types of correction amounts cb, bb and γb to the video signal processing unit 122 as correction amounts Cb for bright scenes.

  Next, the CPU 14 outputs the luminance control signal Lmax to the backlight control unit 132 as in step S63 (step S65).

  The contrast correction amounts cd and cb are contrast gains to be multiplied with the video signal A, and are set to a value of 1.0 or more. For example, cd = 1.2 times and cb = 1.0 times are set.

  The brightness correction amounts bd and bb are values indicating how much the gradation is improved with respect to the video signal A, and are set to a value of 0 gradation or more. For example, bd = 10 gradation and bb = 0 gradation are set.

  The gamma value correction amounts γd and γb are values indicating what multiplier gamma curve is applied to the video signal A, and are set to values smaller than 2.2. For example, γd = 1.4 and γb = 2.2 are set.

  Through the processing described above, the contrast correction unit 1223 receives the contrast correction amount cd and the input video signal A when the input video signal A represents a dark scene. In this case, the contrast correction unit 1223 corrects the contrast of the video represented by the input video signal A with the correction amount cd.

  In the dark scene, the brightness correction unit 1224 receives the brightness correction amount bd and the output video signal A from the contrast correction unit 1223. In this case, the brightness correction unit 1224 corrects the brightness of the video represented by the input video signal A with the correction amount bd.

  Further, in the case of a dark scene, the gamma correction unit 1226 receives the gamma correction amount γd and the output video signal A of the brightness correction unit 1224. In this case, the gamma correction unit 1226 performs gamma correction on the video represented by the input video signal A with the input correction amount γd.

  Further, Lmax from the CPU 14 is input to the backlight control unit 132. The backlight control unit 132 causes the backlight 133 to emit light with the maximum luminance in response to the luminance control signal Lmax.

  In the case of a bright scene, the contrast correction unit 1223 uses the correction amount cb instead of the correction amount cd, the brightness correction unit 1224 uses the correction amount bb instead of the correction amount bd, and the gamma correction unit 1226 Since only the correction amount γb is used instead of the correction amount γd, detailed description of each is omitted. Further, since the light emission control of the backlight 133 is the same as that in the case of a dark scene, this description is also omitted.

  The reason for changing the correction amount between dark scenes and bright scenes in this way is that the contrast ratio of dark scenes is significantly lower than that of bright scenes due to the influence of external light. This is to apply a large correction.

  The contrast gain, brightness, and gamma value are corrected to improve the average brightness level of the video, and the backlight is set to a fixed value, so that the visual average brightness level is improved and the external light is strong. Can also ensure visibility. In addition, by correcting the image with nonlinear characteristics using contrast gain, brightness, and gamma value, it is possible to perform correction with reduced white contact and black float unlike simply increasing the brightness level of the image. Therefore, it is possible to improve the contrast of the image when the external light is irradiated.

  In this embodiment, two types of correction amounts are used, a dark scene and a bright scene. However, the brightness of the scene is further divided into, for example, 32 types of correction amounts. It doesn't matter.

  Also, in order to prevent fluttering due to changes in contrast gain, brightness, and gamma value from frame to frame, a low-pass filter having characteristics that gradually change contrast gain, brightness, and gamma value may be applied. It doesn't matter.

  As described above, in the video display device 1, when the illuminance i is small, the first processing mode is executed. However, if the first processing mode is applied even when the external light is strong (that is, when the illuminance i is large), the first processing mode is configured so that the visual average luminance level is constant. Since the luminance of 133 is controlled, there is a problem that the visibility of the display image on the screen 131 is lowered. However, visibility can be ensured by fixing the brightness of the backlight 133 and correcting the contrast gain, brightness, and gamma value so as to improve the average brightness level of the video as in the second processing mode. Furthermore, it is possible to increase the contrast of the displayed image.

  On the other hand, if the second processing mode is applied even when the outside light is weak, there is a problem in that the display image has a sense of contrast because black floating occurs in the display image. However, as in the first processing mode, by dynamically controlling the luminance of the backlight 133 together with the amplitude control of the video signal A, it is possible to provide a display image with a higher contrast feeling.

  In the above description, the CPU 14 selects the first processing mode and the second processing mode based on the illuminance i detected by the illuminance sensor 11A. However, the present invention is not limited to this. For example, when the small lamp (width lamp) of the vehicle is turned on, the CPU 14 may select the second processing mode on the assumption that the outside light is strong.

  Further, the CPU 14 may select either the first processing mode or the second processing mode based on the time information. In this case, for example, in the time zone from sunrise to sunset, the second processing mode is selected on the assumption that the outside light is strong.

  Moreover, in the above embodiment, the processing content of the video signal processing part 122 was demonstrated using the typical functional block diagram like FIG. 2 for convenience of explanation. The actual video signal processing unit 122 performs processing based on an input / output characteristic curve as shown in FIG. 8 so that the first processing mode and the second processing mode can be executed with a smaller circuit scale.

  Specifically, FIG. 8 is an input / output characteristic curve of the luminance of the output video signal (that is, the processed video signal A1) with respect to the luminance of the input video signal A to the video signal processing unit 122. In FIG. 8, the horizontal axis represents the luminance Lin of the input video signal A, and the vertical axis represents the luminance Lout of the processed video signal A1. The entire numerical value range of the luminance Lin is divided into a plurality of regions having continuous numerical ranges that do not overlap each other. In the example shown in the figure, the area A is divided into eight areas A to H, and the area A is assigned to the lowest numerical value range of the luminance Lin, and the area H is assigned to the highest numerical value range of the luminance Lin.

  Here, the characteristic curve is defined by nine points ah when divided into eight regions AH. Points a and b are both ends of the region A, points b and c are both ends of the region B, and each point is determined in the same manner.

  The CPU 14 receives MIN, APL, and MAX as the feature amount group F from the feature detection unit 121 when the first processing mode is executed, that is, when step S33 is executed. The gain G and the shift amount S are obtained from these three values. calculate. Next, the CPU 14 calculates an input / output characteristic curve when the gain G and the shift amount S are applied to the video signal, and calculates a combination of points a-i defining the calculated input / output characteristic curve. Then, the calculated combination of points a-i is given as a correction amount C to the video signal processing unit 122. The point a-i obtained in step S33 defines an input / output characteristic curve such that the DC level is shifted after the input video signal A is amplified. The video signal processing unit 122 corrects the luminance Lin of each pixel in the input video signal A so as to become the luminance Lout using the input / output characteristic curve defined by the received point a-i. As a result, a video signal A1 similar to the processing results of steps S41 and S42 is obtained.

  Further, when executing the second processing mode, that is, when executing step S62 or S64, the CPU 14 receives the APL as the feature amount group F from the feature detection unit 121, and based on this APL, the contrast gain, brightness, and gamma value are received. Select. Next, the CPU 14 calculates an input / output characteristic curve when the contrast gain, brightness, and gamma value are applied to the input video signal, and calculates a combination of points a-i defining the input / output characteristic curve. Then, the calculated combination of points a-i is given as a correction amount C to the video signal processing unit 122. The point a-i obtained in step S62 or S64 defines an input / output characteristic curve such that the contrast, brightness, and gamma value of the input video signal A are corrected. The video signal processing unit 122 corrects the luminance Lin of each pixel in the input video signal A to the luminance Lout using the input / output characteristic curve defined by the received point a-i. As a result, the same video signal A1 as the processing results of steps S62 and S64 is obtained.

  As described above, the video signal processing circuit 122 performs the first processing mode and the second processing mode in the same integrated circuit. In other words, the process of correcting the video so that the average luminance level of the input video signal is improved and the process of correcting the contrast of the input video signal are performed by the same integrated circuit. As a result, the video signal processing circuit 122 can be realized with a smaller circuit scale.

  The video display device according to the present invention is suitable for a vehicle-mounted navigation device or a vehicle-mounted television receiver that is required to obtain an appropriate contrast feeling according to the intensity of external light.

1 is a block diagram showing an overall configuration of a video display device 1 according to an embodiment of the present invention. Functional block diagram of the video processing unit 122 shown in FIG. The flowchart which shows operation | movement of CPU14 shown in FIG. The flowchart which shows the detailed process of step S33 shown in FIG. Schematic diagram showing the processing content shown in FIG. Schematic diagram showing an alternative example of the processing content shown in FIG. The flowchart which shows the detailed process of step S34 shown in FIG. The graph which shows the brightness | luminance of an output video signal with respect to the brightness | luminance of the input video signal to the video signal processing part 122 shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image display apparatus 11 External light detection part 11A Illuminance sensor 12 Image processing LSI
121 Feature Detection Unit 122 Video Signal Processing Unit 1221 Amplification Unit 1222 DC Adjustment Unit 1223 Contrast Correction Unit 1224 Brightness Correction Unit 1226 Gamma Correction Unit 13 Display 131 Screen 132 Backlight Control Unit 133 Backlight 14 CPU
2 Video source 2A DVD player

Claims (8)

An image display device capable of adjusting a contrast of a display image and a light emission luminance of a backlight,
A determination unit that determines the intensity of external light, a video signal processing unit that performs a process of correcting an input video signal, and a backlight control unit that adjusts the light emission luminance of the backlight,
If the determination unit determines that the external light is strong, the backlight control unit fixes the light emission luminance of the backlight to a constant value, and the video signal processing unit changes the correction amount according to the brightness of the scene. wherein correcting the input video signal, said correction image signal processing unit performs a correction Ru improve the average luminance level of the input video signal, the video display device.   2. The video according to claim 1, wherein the video signal processing unit performs processing for correcting video so that an average luminance level of the input video signal is improved and processing for correcting contrast of the input video signal in the same integrated circuit. Display device. A feature detector for detecting a feature amount of the input video signal;
When receiving the feature amount detected by the feature detection unit, further comprising a calculation unit that calculates a point defining an input / output characteristic curve based on the received feature amount,
The video display device according to claim 2, wherein the video signal processing unit processes an input video signal based on an input / output characteristic curve defined by the points calculated by the calculation unit.   When the determination unit determines that the external light is strong, the video signal processing unit may improve the average luminance level with respect to the input video signal by using one or a combination of contrast gain, brightness, and gamma value. The video display apparatus according to claim 1, wherein the input video signal is amplified at a predetermined amplification factor when the external light is weak by the determination unit.   The video display device according to claim 2, wherein the backlight control unit fixes the light emission luminance of the backlight to a maximum value when the determination unit determines that external light is strong. It further includes an illumination sensor that detects lighting of a small lamp of the vehicle,
The video display device according to claim 1, wherein the determination unit determines the strength of external light based on a detection result of the illumination sensor. It further includes a time detection unit that detects the current time,
The video display device according to claim 1, wherein the determination unit determines the intensity of external light based on a detection result of the time detection unit. An illuminance sensor that detects the illuminance of incident light is further provided,
The video display device according to claim 1, wherein the determination unit determines the strength of external light based on a detection result of the illuminance sensor.