JP6261240B2 - Image processing apparatus and control method thereof - Google Patents

Description

  The present invention relates to an image processing apparatus that performs luminance control using a backlight and a control method therefor.

  As an image display device, a combination of a transmissive liquid crystal panel and a backlight is becoming mainstream. However, the response speed of the liquid crystal is slow and an afterimage may occur. Therefore, there is a technique for reducing the afterimage feeling by turning off the backlight in accordance with the frame frequency. Such a technique is described in Patent Document 1, for example.

JP 2012-155059 A

However, in the related art disclosed in Patent Document 1 described above, the afterimage feeling is reduced, but flicker may be conspicuous because there is a period during which the backlight is turned off in accordance with the frame frequency.
Therefore, a method of reducing flicker by turning on and off the backlight at a frequency higher than the frame frequency of the image can be considered. However, if the backlight is turned on and off at a high frequency, the effect of reducing the afterimage feeling is reduced.

  Therefore, an object of the present invention is to achieve both suppression of flicker and suppression of afterimage in an image display device including a transmissive display panel and a backlight.

The first aspect of the present invention is a light emitting means;
Display means for transmitting light from the light emitting means at a transmittance based on an image signal;
The light emission means is controlled to turn on and off at a frequency higher than the frame frequency of the image signal, and the light emission means is controlled to control the light emission period and the light emission period according to the image signal. Control means for controlling the light emission amount of the means;
With
The control means is determined according to an image of a second frame after the first frame rather than a first light emission amount of the light emitting means determined according to an image of the first frame of the image signal. When an image signal for increasing the second light emission amount of the light emitting means is input , at least the first one turn on and off of the light emitting means within a frame period for displaying the image of the second frame The image display device is characterized in that a lighting period and a lighting period determined according to the image of the first frame are applied .
A second aspect of the present invention comprises a light emitting means,
Display means for transmitting light from the light emitting means at a transmittance based on an image signal;
The light emission means is controlled to turn on and off at a frequency higher than the frame frequency of the image signal, and the light emission means is controlled to control the light emission period and the light emission period according to the image signal. Control means for controlling the light emission amount of the means;
With
The display means is a liquid crystal panel;
The control means is determined according to an image of a second frame after the first frame rather than a first light emission amount of the light emitting means determined according to an image of the first frame of the image signal. When an image signal that increases the second light emission amount of the light emitting means is input, for a predetermined number of times of lighting and extinction from the initial lighting and extinction within the frame period for displaying the image of the second frame, Apply the lighting period and extinguishing period determined according to the image of the first frame,
The image display apparatus according to claim 1, wherein the predetermined number of times is determined according to a response speed defined based on a time from a response start to a completion when the liquid crystal transmittance of the liquid crystal panel changes.

A third aspect of the present invention is a light emitting means;
Display means for transmitting light from the light emitting means at a transmittance based on an image signal;
An image display apparatus control method comprising:
The light emission means is controlled to turn on and off at a frequency higher than the frame frequency of the image signal, and the light emission means is controlled to control the light emission period and the light emission period according to the image signal. Having a control step of controlling the light emission amount of the means,
In the control step, it is determined according to an image of a second frame after the first frame rather than a first light emission amount of the light emitting means determined according to an image of the first frame of the image signal. When an image signal for increasing the second light emission amount of the light emitting means is input , at least the first one turn on and off of the light emitting means within a frame period for displaying the image of the second frame A control method for an image display device , wherein a lighting period and a lighting period determined according to the image of the first frame are applied .
A fourth aspect of the present invention is a light emitting means;
Display means for transmitting light from the light emitting means at a transmittance based on an image signal;
An image display apparatus control method comprising:
The light emission means is controlled to turn on and off at a frequency higher than the frame frequency of the image signal, and the light emission means is controlled to control the light emission period and the light emission period according to the image signal. Having a control step of controlling the light emission amount of the means,
The display means is a liquid crystal panel;
In the control step, it is determined according to an image of a second frame after the first frame rather than a first light emission amount of the light emitting means determined according to an image of the first frame of the image signal. When an image signal that increases the second light emission amount of the light emitting means is input, for a predetermined number of times of lighting and extinction from the initial lighting and extinction within the frame period for displaying the image of the second frame, Apply the lighting period and extinguishing period determined according to the image of the first frame,
The predetermined number of times is determined according to a response speed defined based on a time from the start of response to completion when the liquid crystal transmittance of the liquid crystal panel changes. is there.

  According to the present invention, it is possible to achieve both suppression of flicker and suppression of afterimage in an image display device including a transmissive display panel and a backlight.

1 is a block diagram illustrating a schematic configuration of an image processing apparatus according to a first embodiment. The figure explaining the timing which applies the backlight control value which concerns on Example 1. FIG. Circuit block diagram of the statistic detection unit 104 according to the first embodiment. Flowchart of processing of the backlight control value creation unit 106 according to the first embodiment. The figure which shows the characteristic of the dark part area in Example 1, and a backlight control value Diagram explaining how to turn off the backlight according to the frame frequency Diagram explaining how to turn on the backlight at a frequency higher than the frame frequency The figure explaining the method of performing backlight control in Example 1 FIG. 7 is a block diagram illustrating a schematic configuration of an image processing apparatus according to a second embodiment. Circuit block diagram of the statistic detection unit 204 according to the second embodiment. FIG. 6 is a diagram illustrating an image area according to the second embodiment. Flowchart of processing of the divided backlight control value creation unit 206 according to the second embodiment. FIG. 6 is a diagram for explaining a backlight module 208 according to the second embodiment. FIG. 9 is a block diagram illustrating a schematic configuration of an image processing apparatus according to a third embodiment. The figure explaining the backlight control when the liquid crystal response is fast in the third embodiment The figure explaining the backlight control when the liquid crystal response is slow in the third embodiment

Example 1
Embodiments of an image display apparatus and its control method according to the present invention will be described below with reference to the drawings.
FIG. 1 is a functional block diagram of the image display apparatus according to the first embodiment. An image processing apparatus 100 shown in FIG. 1 includes an image delay unit 101, a liquid crystal drive circuit unit 102, a display panel 103, a statistic detection unit 104, a scene change amount calculation unit 105, a backlight control value creation unit 106, and a backlight control unit. 107 and a backlight module 108.
The operation of the image display apparatus of the present embodiment configured as described above will be described below.

The image delay unit 101 stores image data (image signal) for two frames in a memory (storage device), and outputs the image data delayed by two frames to the liquid crystal drive circuit unit 102.
In this embodiment, as shown in FIG. 2, the statistic of the input image is acquired, and a backlight control value is created according to the statistic.
For example, when the backlight control value is created from the statistic of frame N, the backlight control value is created during the period in which frame N + 1 is input.

Therefore, the image delay unit 101 can apply the backlight control value created from the statistics of the frame N when displaying the frame N by delaying by two frames. The delay amount may be a value to which the backlight control value created from the statistics amount can be applied when the frame for which the statistics amount is acquired is displayed. For example, when the statistic of frame N is acquired and the backlight control value can be created during the period until frame N + 1 is input, the delay amount may be 1.
The liquid crystal drive circuit unit 102 outputs data for driving the liquid crystal elements of the display panel 103 to the display panel 103 according to the input image. In this embodiment, the frame rate (frame frequency) of image display is 60 frames / second. The display panel 103 is an apparatus that displays an image by modulating light from a backlight based on image data, and is a liquid crystal panel in this embodiment.

FIG. 3 shows a circuit block diagram of the statistic detection unit 104. The statistic detection unit 104 includes a full screen luminance histogram detection unit 11 and an APL (average picture level) detection unit 12.
The full screen luminance histogram detection unit 11 acquires a full screen luminance histogram Ha from the input image. The full-screen luminance histogram Ha is obtained by counting the number of pixels for each gradation of 0 to 255 gradations. The acquired full-screen brightness histogram Ha is output to the backlight control value creation unit 106.

  The APL detection unit 12 acquires an APL value a as an index of brightness of the input image (frame image). The APL value a is obtained by integrating the luminance value of the image data by the total number of pixels and dividing by the total number of pixels. The APL value a is calculated with an 8-bit accuracy of 0 to 255. The acquired APL value a is output to the scene change amount calculation unit 105.

The scene change amount calculation unit 105 includes an APL value a of the input image (second frame image) obtained by the APL detection unit 12, an APL value a_old of the input image (first frame image) one frame before, From this, the scene change amount a_diff is obtained. The scene change amount a_diff is output to the backlight control value creation unit 106. The scene change amount a_diff is a value representing how the input image has changed. The scene change amount a_diff is obtained by the following formula 1.

a_diff = a-a_old (Formula 1)

  In this embodiment, the backlight control value creating unit 106 creates a backlight control value according to how the input image has changed. A scene change amount a_diff is calculated as an index indicating how the input image has changed. The scene change amount a_diff takes a large value when changing from a dark scene to a bright scene. Further, when the brightness of the scene does not change much, the value is close to 0, and the value becomes smaller when the scene changes from a bright scene to a dark scene (a negative value and an absolute value increases).

  The backlight control value creation unit 106 obtains a backlight control value bl_g from the full-screen luminance histogram Ha, the scene change amount a_diff, and the backlight control value bl_g_old one frame before. The full screen brightness histogram Ha is acquired by the full screen brightness histogram detection unit 11. The scene change amount a_diff is calculated by the scene change amount calculation unit 105.

  The calculated backlight control value bl_g is output to the backlight control unit 107. The backlight control value bl_g is a value for controlling the ratio (duty ratio) between the backlight lighting period and the light extinguishing period. The larger the backlight control value bl_g, the longer the backlight lighting period (the luminance increases). .

The processing flow of the backlight control value creation unit 106 is shown in FIG.
In step S101, the backlight control value creation unit 106 calculates the dark area Sd from the full screen luminance histogram Ha. Further, the backlight control value creation unit 106 calculates the backlight control value bl_g from the dark area Sd based on the conversion characteristics as shown in FIG. 5, and proceeds to step S102.

The dark area Sd is calculated from the full screen luminance histogram Ha by the following formula 2. The dark area Sd is a value representing the area of a dark part in the image.
In Equation 2, Hd is a value obtained by integrating the number of pixels of gradations smaller than the black level threshold th_b in the full screen luminance histogram Ha, and Hs is the total number of pixels of the full screen luminance histogram Ha. Black level threshold th_b
Is a parameter that can be arbitrarily adjusted.

Sd = Hd / Hs (Formula 2)

  The conversion characteristic of FIG. In this embodiment, the backlight is darkened as the dark area is larger, and the backlight is brightened as the dark area is smaller. Therefore, the larger the dark area Sd, the smaller the backlight control value bl_g, and the smaller the dark area Sd, the larger the backlight control value bl_g.

In Expression 3, th_Sd1 and th_Sd2 are thresholds for adjustment, g_min is the minimum value of the backlight control value bl_g, and g_max is the maximum value of the backlight control value bl_g, which are parameters that can be adjusted arbitrarily.

(A) When Sd <th_Sd1
bl_g = g_max
(B) When Sd ≧ th_Sd1 and Sd <th_Sd2
bl_g = (g_min-g_max) × (Sd-th_Sd1) / (th_Sd2-th_Sd1) + g_max
(C) When Sd ≧ th_Sd2
bl_g = g_min
... (Formula 3)

In step S102, the backlight control value creation unit 106 determines whether the scene change amount a_diff is smaller than the threshold value diff_th. When the scene change amount a_diff is smaller than the threshold diff_th (yes
), Go to step S103. If the scene change amount a_diff is equal to or greater than the threshold value diff_th (no), that is, if the current frame is brighter than the previous frame by a threshold value, the process proceeds to step S104. The threshold diff_th is a parameter that can be arbitrarily adjusted.

In step S103, the value is updated to bl_g_old = bl_g, and the process ends. That is, the backlight control value obtained from the current frame is applied to the display of the current frame, and the backlight control value obtained from the current frame is retained for use as the “backlight control value of the previous frame” in the next flow. .
In step S104, the value is updated to bl_g = bl_g_old, and the process proceeds to step S103. That is, the stored backlight control value of the previous frame is used as the backlight control value of the current frame and applied to the display of the current frame.

In this embodiment, when a dark scene changes to a bright scene, the backlight control value bl_g_old created from the statistics of the dark scene one frame before is used as the backlight control value bl_g in the first frame of the bright scene.
By this method, even if the frequency of turning on and off the backlight is higher than the frame frequency so as not to cause flicker, it is possible to suppress a decrease in the effect of reducing the afterimage feeling. This will be described below.

6, 7, and 8 are examples of changing from a dark scene to a bright scene from frame N to frame N + 1 and from a bright scene to a dark scene at frame N + 4.
First, as a reference, FIG. 6 shows a case where a method of turning off the backlight in accordance with the frame frequency as in the prior art is applied.

A graph h in FIG. 6 represents the liquid crystal response. The height of the graph h represents the transmittance of the liquid crystal element. When changing from a dark scene to a bright scene, it gradually becomes brighter over a period of about one frame period, and when changing from a bright scene to a dark scene, it gradually becomes darker over a period of about one frame period. Is shown.

A graph b1 in FIG. 6 represents a lighting waveform of the backlight, and shows that lighting and extinguishing are repeated in accordance with the frame frequency. The height of the graph b1 represents the backlight luminance.
A graph o1 in FIG. 6 represents the brightness of an image displayed on the liquid crystal, and is obtained by multiplying h by b1. It can be seen that frame N has a period during which a dark image is displayed and a period during which nothing is displayed, and frame N + 1 includes a period during which a bright image is displayed and a period during which nothing is displayed.

  In the conventional method of FIG. 6, since the transmittance of the liquid crystal gradually increases during the period when the backlight is turned off in the frame N + 1, even if the response speed of the liquid crystal is slow as shown in the graph h, an afterimage feeling is obtained. It is reduced. However, since the backlight is turned off in accordance with the frame frequency, flicker may occur.

Next, FIG. 7 shows a case where a method of lighting a backlight at a frequency higher than the frame frequency is applied using the conventional technology as a reference. In FIG. 7, it is assumed that backlight control is performed at 180 Hz, which is a frequency higher than the frame frequency 60 Hz, in order to reduce flicker.
A graph b2 in FIG. 7 represents a backlight lighting waveform, and shows that the backlight lighting period is shortened in a dark scene and the backlight lighting period is lengthened in a bright scene. .

  A graph o2 in FIG. 7 represents an image displayed on the liquid crystal, and is obtained by multiplying h and b2. In a dark scene, there are a period in which a dark image is displayed and a period in which nothing is displayed, and in a bright scene, there are a period in which a gradually bright image is displayed and a period in which nothing is displayed.

  In the conventional method of FIG. 7, since the lighting frequency of the backlight is higher than that of the method of FIG. 6, flicker is less likely to occur. However, in the response period of the liquid crystal in which the transmittance gradually increases in the frame N + 1, the period during which the backlight is lit is longer than that in the method of FIG. For this reason, the response of the liquid crystal that becomes gradually brighter is easily recognized, and an afterimage may occur.

  FIG. 8 is a diagram illustrating a case where the present embodiment is applied. In the present embodiment, the backlight control value bl_g of the frame N before the change is applied to the frame N + 1 changed to a bright scene.

  A graph b3 in FIG. 8 represents the lighting waveform of the backlight. Similarly to the graph b2 in FIG. 7, the period during which the backlight is lit is shortened in a dark scene, and the period during which the backlight is lit in a bright scene. It shows that it is long. Similarly to FIG. 7, the backlight control is performed at a frequency of 180 Hz, which is higher than the frame frequency of 60 Hz. However, in this embodiment, in the frame period in which the frame N + 1 changed from the dark scene to the bright scene is displayed, the backlight control value bl_g similar to that of the frame N that is a dark scene one frame before is used for all lighting and extinguishing. Apply.

A graph o3 in FIG. 8 represents an image displayed on the liquid crystal, and is obtained by multiplying h by b3. In the present embodiment, in the liquid crystal response period in which the transmittance gradually increases in the frame N + 1, the period during which the backlight is lit is shorter than the method of FIG. Therefore, it becomes difficult to see the response of the liquid crystal that becomes gradually brighter, and the afterimage feeling can be reduced. Furthermore, since the backlight control frequency is higher than the frame frequency, the interval of turning off the backlight is short, and flicker is less likely to occur.

  In the frame N + 1, since the backlight is turned on for a short period, the frame N + 1 is displayed darker than the original display brightness. However, since only one frame is darker than the original, it is hardly visually recognized by human eyes.

Further, when the scene changes from a bright scene to a dark scene, the scene change amount a_diff becomes a small value, and therefore it is determined in step S102 that the scene change amount a_diff is smaller than the threshold value diff_th. for that reason,
The backlight control value bl_g created from the statistic of the dark scene image in the current frame is directly applied to the backlight control in the current frame. In this case, in the frame N + 4, the period during which the backlight is turned on is set to be short according to the dark scene, so that the response of the liquid crystal that gradually becomes dark is not easily recognized and the afterimage does not increase.

The backlight control unit 107 sets the backlight control value calculated by the backlight control value creation unit 106 in the backlight module 108.
In this embodiment, the backlight control frequency is 180 Hz. The backlight control frequency is not limited to this example as long as it is higher than the frame control frequency.
The backlight module 108 turns on the backlight according to the control of the backlight control unit 107.

  As described above, according to this embodiment, when the dark scene changes to the bright scene, the backlight control value applied to the dark scene is also applied when the first frame of the bright scene is displayed. As described above, in the backlight control according to the brightness of the frame image, the timing for increasing the backlight luminance according to the bright frame image is delayed with respect to the timing for displaying the bright frame image. As a result, the afterimage can be reduced while the backlight is lit at a high frequency so as not to cause flicker.

(Example 2)
In this embodiment, a case will be described in which the backlight is composed of a plurality of blocks whose luminance can be individually controlled.
FIG. 9 shows a functional block diagram of the image display apparatus of the present embodiment. The image processing apparatus 200 includes an image delay unit 101, a liquid crystal drive circuit unit 102, a display panel 103, a statistic detection unit 204, a divided scene change amount calculation unit 205, a divided backlight control value creation unit 206, and a divided backlight control unit 207. , And a backlight module 208.
The same blocks as those in FIG. 1 used in Example 1 are denoted by the same reference numerals. Hereinafter, description of blocks that perform the same processing as in the first embodiment will be omitted.
FIG. 10 is a circuit block diagram of the statistic detection unit 204. The statistic detection unit 204 includes a divided luminance histogram detection unit 21 and a divided APL detection unit 22.

The divided luminance histogram detection unit 21 divides the input image I into a plurality of image areas, and acquires a luminance histogram for each image area. Let Hd (i) be the luminance histogram of the i-th image region (referred to as a divided luminance histogram). In this embodiment, it is assumed that the input image I is divided into horizontal 5 × vertical 3 = 15 image areas d0 to d14 as shown in FIG. Therefore, the divided luminance histogram detection unit 21 acquires 15 divided luminance histograms Hd (0) to Hd (14). The divided luminance histogram Hd (i) is obtained by counting the number of pixels for each gradation of 0 to 255 gradations. The acquired divided luminance histograms Hd (0) to Hd (14) are output to the divided backlight control value creating unit 206.

Similar to the divided luminance histogram detector 21, the divided APL detector 22 divides the input image I into a plurality of image areas, and detects a divided APL value ad (i) for each image area. Therefore, divided AP
The L detection unit 22 acquires 15 divided APL values ad (0) to ad (14). The divided APL value ad (i) is obtained by integrating the luminance values of the pixels in each image area di and dividing by the total number of pixels in each image area di. Further, the divided APL value ad (i) is acquired with an 8-bit accuracy of 0 to 255. The acquired divided APL value ad (i) is output to the divided scene change amount calculation unit 205.

The divided scene change amount calculation unit 205 calculates the divided scene change amount a_diff (i) from the divided APL value ad (i) of the input image obtained by the divided APL detection unit 22 and the divided APL value ad_old (i) one frame before.
Ask for. The divided scene change amount ad_diff (i) is output to the divided backlight control value creation unit 206. The divided scene change amount ad_diff (i) is a value representing how the input image has changed in each image region. The divided scene change amount ad_diff (i) is obtained by the following equation 4.

ad_diff (i) = ad (i) -ad_old (i) (Formula 4)

  In this embodiment, the divided backlight control value creation unit 206 creates divided backlight control values according to how the input image has changed in each image area. ad_diff (i) is calculated.

The divided backlight control value creating unit 206 generates a divided backlight control value bl_g_d () from the divided luminance histogram Hd (i), the divided scene change amount ad_diff (i), and the divided backlight control value bl_g_old_d (i) one frame before. i). The divided luminance histogram Hd (i) is detected by the divided luminance histogram detection unit 21. The divided scene change amount ad_diff (i) is calculated by the divided scene change amount calculation unit 205.
The divided backlight control value bl_g_d (i) may be obtained for each image area by the backlight control value creation unit 106 according to the first embodiment.

The processing flow of the divided backlight control value creation unit 206 is shown in FIG.
In step S201, the divided backlight control value creating unit 206 initializes the variable i with 0, and proceeds to step S202.
In step S202, the divided backlight control value creating unit 206 calculates the divided backlight control value bl_g (i) using the following formulas 5 and 6, and the process proceeds to step S203.

Sd_d (i) = Hd_d (i) / Hs_d (i) (Formula 5)

The divided dark area Sd_d (i) is obtained from Equation 5. The divided dark part area Sd_d (i) is a value representing the area of the dark part in the image region. Hd_d (i) is a value obtained by integrating the number of pixels with gradations smaller than the black level threshold th_b in the divided luminance histogram Hd (i), and Hs_d (i) is the total number of pixels in the divided luminance histogram Hd (i) of each image area. is there. The black level threshold th_b is a parameter that can be arbitrarily adjusted.

(A) When Sd_d (i) <th_Sd1
bl_g = g_max
(B) When Sd_d (i) ≥th_Sd1 and Sd_d (i) <th_Sd2
bl_g = (g_min-g_max) × (Sd_d (i) -th_Sd1) / (th_Sd2-th_Sd1) + g_max
(C) When Sd_d (i) ≥ th_Sd2
bl_g = g_min
... (Formula 6)

Expression 6 is the same as Expression 3 in the first embodiment, and the divided backlight control value bl_g_d (i) for each image region is obtained using the divided dark area Sd_d (i) instead of the dark area Sd.
In Equation 6, th_Sd1 and th_Sd2 are thresholds for adjustment, and g_min and g_max are the minimum and maximum values of the divided backlight control value bl_g_d (i), respectively, and are parameters that can be arbitrarily adjusted.

In step S203, the divided backlight control value creation unit 206 determines whether the divided scene change amount ad_diff (i) is smaller than the threshold value diff_th. When the divided scene change amount ad_diff (i) is smaller than the threshold diff_th (yes), the process proceeds to step S204. If the divided scene change amount ad_diff (i) is greater than or equal to the threshold diff_th (no), the process proceeds to step S206. The threshold diff_th is a parameter that can be arbitrarily adjusted.

  In step S204, the divided backlight control value creation unit 206 updates the value to bl_g_old_d (i) = bl_g_d (i), and proceeds to step S205. That is, the backlight control value of the current frame is stored as the backlight control value of the previous frame in order to be used as the “backlight control value of the previous frame” in the next flow.

In step S205, the divided backlight control value creation unit 206 determines whether the creation processing of the backlight control value has been completed for all image regions. Here, the divided backlight control value creation unit 206 determines whether i = 14. If i = 14 (yes), that is, if the process of creating the backlight control value for all image areas is completed, the process ends. If i is not 14 (no), that is, if the backlight control value creation processing has not been completed for all image regions, the process proceeds to step S207.

  In step S206, the divided backlight control value creation unit 206 updates the value to bl_g_d (i) = bl_g_old_d (i), and proceeds to step S204. That is, the stored backlight control value of the previous frame is used as the backlight control value of the current frame and applied to the display of the current frame.

In step S207, the divided backlight control value creation unit 206 updates the value to i = i + 1, and proceeds to step S203.
The divided backlight control unit 207 sets the divided backlight control value bl_g_d (i) calculated by the divided backlight control value creation unit 206 in the backlight module 208. Example 1
The same processing as that of the backlight control unit 107 is performed for each image area. That is, the divided backlight control unit 207 sets the divided backlight control value bl_g_d (i) for each image area instead of the backlight control value bl_g.

The backlight module 208 turns on the backlight according to the control of the divided backlight control unit 207.
As shown in FIG. 13, the backlight module 208 has a plurality of light sources, and can control the amount of light emission independently of each other.
In this embodiment, the backlight module 208 has light sources 10 × 6 in length = 60, and four light sources are used as one control block as shown in FIG. The light emission amount is controlled for every 15 control blocks. Each control block corresponds to each image area described above.
For example, the backlight control value bl_g_d (0) is applied to control four light sources included in the control block 31 of FIG. 13, and the backlight control value bl_g_d (1) is 4 included in the control block 32 of FIG. Applies to the control of individual light sources.

When the backlight module is composed of, for example, a red LED, a blue LED, and a green LED, the backlight control of this embodiment may be applied for each color of the light source (for each LED of each color).
As described above, according to the present embodiment, the backlight control value is set according to the change of each block of the input image, so that flicker is not generated for each block and the afterimage feeling can be reduced. it can.

(Example 3)
In this embodiment, an example in which backlight control is performed with higher accuracy by controlling a backlight control value in accordance with the response speed of the liquid crystal will be described.
FIG. 14 shows a functional block diagram of the image display apparatus of the present embodiment. 14 includes an image delay unit 101, a liquid crystal drive circuit unit 102, a display panel 103, a statistic detection unit 104, a scene change amount calculation unit 105, a backlight control value creation unit 306, and a backlight control unit. 307 and a backlight module 208.
The same blocks as those in FIGS. 1 and 9 used in the first and second embodiments are denoted by the same reference numerals. Hereinafter, description of blocks that perform the same processing as in the first and second embodiments will be omitted.

The backlight control value creating unit 306 divides the divided backlight control value bl_g_d from the divided luminance histogram Hd (i), the divided scene change amount ad_diff (i), and the divided backlight control value bl_g_old_d (i) one frame before. Find (i). The divided luminance histogram Hd (i) is detected by the divided luminance histogram detection unit 21. The divided scene change amount ad_diff (i) is calculated by the divided scene change amount calculation unit 205.

In this embodiment, the backlight control unit 307 determines the divided backlight control value bl_g_d (i) corresponding to the current frame or the divided backlight control value bl_g_old_d (i) corresponding to the previous frame according to the response speed v of the liquid crystal. Apply either of The response speed v of the liquid crystal is a response speed of modulation of light from the backlight of the display panel with respect to a change in image data. Therefore, the divided backlight control value creation unit 306 outputs the divided backlight control values bl_g_d (i) and bl_g_old_d (i) to the backlight control unit 307.
The backlight control unit 307 sets the divided backlight control value bl_g_d (i) or bl_g_old_d (i) calculated by the divided backlight control value creation unit 306 in the backlight module 208.

Unlike the split backlight control unit 207 of the second embodiment, the backlight control unit 307 uses either the split backlight control value bl_g_d (i) or bl_g_old_d (i) as a backlight module according to the response speed v of the liquid crystal. Set to 208.
In the first and second embodiments, when the dark scene is changed to the bright scene, the backlight control value created from the statistics of the dark scene one frame before is applied to the first frame of the bright scene.

  For example, in the case of FIG. 8, in the frame N + 1 that has changed from a dark scene to a bright scene, the backlight control value created from the statistics of the frame N, which is a dark scene, is used for all backlight control ( 3 times). In contrast, in this embodiment, as shown in the liquid crystal response graph h1 in FIG. 15, when the liquid crystal response speed v1 is fast, the liquid crystal response is completed at the time point t1 within the frame period of the frame N + 1. Therefore, even when the backlight control value created from the frame N + 1 is applied at the time point t1 within the frame period of the frame N + 1, no afterimage feeling is generated.

Accordingly, when the response speed of the liquid crystal is fast as shown in FIG. 15, in this embodiment, the backlight created from the frame N + 1 of the bright scene at the time point t1 in the frame period of the first frame (N + 1) changed to the bright scene. Apply control value bl_g_d (i). As a result of such processing, in the frame N + 1 changed to a bright scene, the period during which the backlight is turned on becomes longer than in the case of the first and second embodiments, and the frame N + 1 has a brightness close to the brightness desired to be displayed. Can be displayed.

On the other hand, as shown in the liquid crystal response graph h2 in FIG. 16, when the liquid crystal response speed v2 is slow, the liquid crystal response is not completed within the frame period of the frame N + 1. Therefore, the backlight control value bl_g_d (i) created from the frame N + 2 at the frame N + 2 next to the frame N + 1
When is applied, an afterimage may occur.
Therefore, when the response speed of the liquid crystal is slow as shown in FIG. 16, in this embodiment, the backlight created from the frame N of the dark scene at the time point t2 in the frame period of the second frame (N + 2) changed to the bright scene. Apply control value bl_g_old_d (i). By such processing, it is possible to suppress the occurrence of afterimage even when the response speed of the liquid crystal is slow.

The backlight control unit 307 applies the divided backlight control value bl_g_old_d (i) created from the dark scene frame for a predetermined number of delays after the bright scene is changed. Thereafter, the backlight control value bl_g_d (i) created from the frame of the bright scene is applied. Here, the number of delays is the number of times nt to apply the divided backlight control value bl_g_old_d (i) created from the dark scene frame. The number of delays nt is calculated from the response speed v and the backlight control frequency bl_f by the following equation (7). In this equation, the response speed v is a quantity having a time dimension, and is defined as the time from when the liquid crystal starts to respond until the response is completed.

nt = 1 + v / (1 / bl_f) (Expression 7)

In Equation 7, the decimal point of the calculation result is discarded.
Since the delay number nt is determined by the response speed v and the backlight control frequency bl_f, it is not necessary to obtain it for each frame, and it may be obtained in advance. In the case of an image display device in which the backlight control frequency is variable by switching the display mode or the like, an appropriate number of delays may be obtained in advance for each backlight control frequency and used in accordance with the display mode.

For example, as shown in FIG. 15, when the backlight control frequency bl_f is 180 Hz and the liquid crystal response speed v is 10 msec, the number of delays nt is 2. Therefore, the divided backlight control value bl_g_old_d (i) is applied twice in the frame period of the frame N + 1, and the frame N + 1
The divided backlight control value bl_g_d (i) is applied once in the remaining frame period.

Further, as shown in FIG. 16, when the backlight control frequency bl_f is 180 Hz and the liquid crystal response speed v is 20 msec, the number of delays nt is 4. Therefore, the divided backlight control value bl_g_old_d (i) is applied three times within the frame period of the frame N + 1. Then, the divided backlight control value bl_g_old_d (i) is applied once in the frame period of the frame N + 2, and the backlight control value bl_g_d (i) is applied twice.
As described above, according to the present embodiment, the backlight control value is controlled according to the response speed of the liquid crystal, so that the backlight can be controlled with higher accuracy, and both flicker suppression and afterimage feeling are reduced. can do.

  In the above-described embodiment, the backlight control value is determined according to the dark area in the frame image. However, the backlight control value may be determined according to the highest luminance in the frame image. good. Further, the determination method of the backlight control value according to the frame image may be a determination method in which the backlight luminance increases as the frame image becomes brighter.

103: Display panel, 106: Backlight control value creation unit, 107: Backlight control unit, 108: Backlight module

Claims (14)

Light emitting means;
Display means for transmitting light from the light emitting means at a transmittance based on an image signal;
The light emission means is controlled to turn on and off at a frequency higher than the frame frequency of the image signal, and the light emission means is controlled to control the light emission period and the light emission period according to the image signal. Control means for controlling the light emission amount of the means;
With
The control means is determined according to an image of a second frame after the first frame rather than a first light emission amount of the light emitting means determined according to an image of the first frame of the image signal. When an image signal for increasing the second light emission amount of the light emitting means is input , at least the first one turn on and off of the light emitting means within a frame period for displaying the image of the second frame An image display device characterized by applying a lighting period and an extinguishing period determined according to the image of the first frame . Light emitting means;
Display means for transmitting light from the light emitting means at a transmittance based on an image signal;
The light emission means is controlled to turn on and off at a frequency higher than the frame frequency of the image signal, and the light emission means is controlled to control the light emission period and the light emission period according to the image signal. Control means for controlling the light emission amount of the means;
With
The display means is a liquid crystal panel;
The control means is determined according to an image of a second frame after the first frame rather than a first light emission amount of the light emitting means determined according to an image of the first frame of the image signal. When an image signal that increases the second light emission amount of the light emitting means is input, for a predetermined number of times of lighting and extinction from the initial lighting and extinction within the frame period for displaying the image of the second frame, Apply the lighting period and extinguishing period determined according to the image of the first frame,
Wherein the predetermined number of times, an image display apparatus, characterized by being determined according to the response rate defined based on the time between the beginning and the end of the response when the transmittance of the liquid crystal of the liquid crystal panel is changed. The image display device according to claim 2 , wherein the predetermined number of times increases as the response speed becomes slower. The image display device according to claim 2 or 3 , wherein the predetermined number of times is determined according to the response speed and a frequency of turning on and off the light emitting means. The image display device according to claim 4 , wherein the predetermined number of times increases as the frequency of turning on and off the light emitting means increases. When the predetermined number of times is greater than the number of times the light emitting unit is turned on and off in one frame period, the control unit is configured to turn on the light emitting unit after the frame period for displaying the image of the second frame. for even off, the image display apparatus according to any one of claims 2-5 for applying a turn-off period with the determined lighting period in accordance with the image of the first frame. The light emitting means comprises a plurality of control blocks capable of independently controlling the light emission amount,
The control means, in accordance with the image of the region corresponding to each control block, the image display apparatus according to any one of claims 1 to 6 for controlling the light emission amount of the light emitting means for each control block. Light emitting means;
Display means for transmitting light from the light emitting means at a transmittance based on an image signal;
An image display apparatus control method comprising:
The light emission means is controlled to turn on and off at a frequency higher than the frame frequency of the image signal, and the light emission means is controlled to control the light emission period and the light emission period according to the image signal. Having a control step of controlling the light emission amount of the means,
In the control step, it is determined according to an image of a second frame after the first frame rather than a first light emission amount of the light emitting means determined according to an image of the first frame of the image signal. When an image signal for increasing the second light emission amount of the light emitting means is input , at least the first one turn on and off of the light emitting means within a frame period for displaying the image of the second frame A control method for an image display device , wherein a lighting period and a lighting period determined according to the image of the first frame are applied . Light emitting means;
Display means for transmitting light from the light emitting means at a transmittance based on an image signal;
An image display apparatus control method comprising:
The light emission means is controlled to turn on and off at a frequency higher than the frame frequency of the image signal, and the light emission means is controlled to control the light emission period and the light emission period according to the image signal. Having a control step of controlling the light emission amount of the means,
The display means is a liquid crystal panel;
In the control step, it is determined according to an image of a second frame after the first frame rather than a first light emission amount of the light emitting means determined according to an image of the first frame of the image signal. When an image signal that increases the second light emission amount of the light emitting means is input, for a predetermined number of times of lighting and extinction from the initial lighting and extinction within the frame period for displaying the image of the second frame, Apply the lighting period and extinguishing period determined according to the image of the first frame,
The control method of an image display device, wherein the predetermined number of times is determined according to a response speed defined based on a time from a response start to a completion when a liquid crystal transmittance of the liquid crystal panel changes. The method for controlling an image display device according to claim 9 , wherein the predetermined number of times is increased as the response speed is lower. The control method of the image display device according to claim 9 or 10 , wherein the predetermined number of times is determined according to the response speed and a frequency of turning on and off the light emitting means. The method of controlling an image display device according to claim 11 , wherein the predetermined number of times increases as the frequency of turning on and off the light emitting means increases. When the predetermined number of times is greater than the number of times the light emitting means is turned on and off in one frame period, the control step includes turning on the light emitting means after the frame period for displaying the image of the second frame. The method for controlling an image display device according to any one of claims 9 to 12 , wherein a lighting period and a lighting period determined in accordance with the image of the first frame are also applied to the lighting. The light emitting means comprises a plurality of control blocks capable of independently controlling the light emission amount,
The method for controlling an image display device according to any one of claims 8 to 13 , wherein, in the control step, the light emission amount of the light emitting unit is controlled for each control block in accordance with an image of a region corresponding to each control block. .

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