JP6180135B2 - Image display apparatus and control method thereof - Google Patents

Description

  The present invention relates to an image display device and a control method thereof.

Conventionally, in a liquid crystal display device, the light emission luminance of the backlight (light emitting unit) and the transmittance of the liquid crystal panel (display unit) are controlled according to the luminance feature amount (maximum luminance value, etc.) of the input image signal (input image data). There was a technique to do (patent document 1). By using such a technique, it is possible to suppress the black floating of the display image (image displayed on the screen) in a dark scene and to increase the contrast of the display image.
When determining the backlight luminance according to the maximum luminance value of the input image signal for each frame, if the maximum luminance value changes abruptly due to the influence of noise etc., the backlight luminance also abruptly changes accordingly. It changes and flicker is perceived. In order to suppress the occurrence of such flicker, there has been proposed a technique for performing a smoothing process that suppresses a change in the backlight emission luminance in the time direction (Patent Document 2). Further, by performing smoothing processing that suppresses changes in the luminance feature amount of the input image signal in the time direction, it is possible to suppress a rapid change in the luminance feature amount and, in turn, an abrupt change in the light emission luminance of the backlight. In the following, the smoothing process for suppressing the change in the luminance feature amount of the input image signal in the time direction is the first smoothing process, and the smoothing process for suppressing the change in the backlight emission luminance in the time direction is the second smoothing process. It describes.

However, if the degree of suppression by the second smoothing process (the degree of suppression of the change in the light emission luminance of the backlight) is low, flicker is perceived because the backlight repeats light and dark due to noise (noise superimposed on the image signal). .
If the degree of suppression by the second smoothing process is increased, the occurrence of flicker due to noise can be suppressed. However, when the degree of suppression by the second smoothing process is increased, pixel value saturation occurs when the maximum luminance value of the input image signal monotonously increases as indicated by reference numeral 201 in FIG. Specifically, when a compensation process for compensating for a decrease in luminance of the display image due to a decrease in emission luminance is performed on the input image signal, the emission luminance of the backlight is insufficient and pixel value saturation occurs.
Further, if the first smoothing process is performed, the occurrence of flicker due to noise can be suppressed. However, when the first smoothing process is performed when the maximum luminance value of the input image signal monotonously increases as indicated by the thin line 201 in FIG. 2, the maximum luminance value of the input image signal is increased as indicated by the thick line 202 in FIG. Temporal changes will be suppressed. For this reason, a temporal change in the issued luminance of the backlight is also suppressed. When the compensation process is performed on the input image signal, the light emission luminance of the backlight is insufficient, and the pixel value is saturated.

JP 2002-251171 A JP 2010-169768 A

  The present invention suppresses both the occurrence of flicker and the saturation of pixel values in an image display device that increases the contrast of a display image by controlling the light emission luminance of the light emitting unit and the transmittance of the display unit. An object is to provide a technique capable of increasing the contrast.

The first aspect of the present invention is:
An image display device that sequentially displays a plurality of images respectively corresponding to a plurality of frames,
Light emitting means;
Display means for displaying an image corresponding to the frame on the screen by transmitting the light emitted by the light emitting means with a transmittance corresponding to the frame for each frame;
For each frame, an acquisition means for acquiring a luminance feature amount related to the luminance of the frame;
A first smoothing unit that performs a first smoothing process for acquiring a smooth feature amount that suppresses a temporal change in luminance feature amount acquired by the acquisition unit for each frame;
For each frame, based on the smooth feature amount, control means for controlling the light emission luminance of the light emitting means,
Correction means for applying correction processing to each frame to suppress a decrease in luminance of the image displayed on the screen due to a decrease in emission luminance of the light emitting means;
Have
The first smoothing unit is configured such that the difference between the luminance feature amount of the frame displayed by the display unit and the smooth feature amount of the frame is equal to or greater than a predetermined threshold in two or more predetermined numbers of frames. In such a case, the first smoothing process is performed so that the difference between the luminance feature amount of the frame displayed by the display unit and the smooth feature amount of the frame is smaller than the case where it is not. An image display device characterized by the above.

The second aspect of the present invention is:
An image display device that sequentially displays a plurality of images respectively corresponding to a plurality of frames,
Light emitting means;
Display means for transmitting light emitted from the light emitting means based on a target frame of the plurality of frames and displaying an image corresponding to the target frame on a screen;
For each frame, whether or not the difference between the feature value related to the brightness of the frame and the feature value of the frame and the average value of the feature values of one or more frames preceding the frame is equal to or greater than a predetermined threshold value. Determination means for determining;
Control means for controlling light emission of the light emitting means;
Have
The control means includes
When it is determined that the difference is equal to or greater than the predetermined threshold in a predetermined number of consecutive frames before the target frame, the light emission of the light emitting unit is controlled by the light emission amount based on the feature amount of the target frame. ,
Otherwise, the light emission of the light emitting means is controlled by a light emission amount based on an average value of the feature amount of the target frame and the feature amount of one or more frames before the target frame. An image display device.

The third aspect of the present invention is:
A method for controlling an image display device that sequentially displays a plurality of images respectively corresponding to a plurality of frames,
The image display device includes:
Light emitting means;
Display means for displaying an image corresponding to the frame on the screen by transmitting the light emitted by the light-emitting means at a transmittance corresponding to the frame for each frame;
The control method is:
For each frame, an acquisition step for acquiring a luminance feature amount related to the luminance of the frame;
For each frame, a smoothing step for performing a smoothing process for acquiring a smooth feature amount that suppresses a temporal change in the luminance feature amount acquired in the acquisition step;
For each frame, a control step of controlling the light emission luminance of the light emitting means based on the smooth feature amount;
A correction step for applying correction processing to each frame to suppress a decrease in luminance of the image displayed on the screen due to a decrease in emission luminance of the light emitting means;
Have
In the smoothing step, when the difference between the luminance feature amount of the frame displayed by the display means and the smooth feature amount of the frame is equal to or greater than a predetermined threshold value in two or more predetermined number of frames In addition, the smoothing process is performed so that a difference between a luminance feature amount of a frame displayed by the display unit and a smooth feature amount of the frame is smaller than that in a case where it is not. This is a method for controlling the image display apparatus.

The fourth aspect of the present invention is:
A method for controlling an image display device that sequentially displays a plurality of images respectively corresponding to a plurality of frames,
The image display device includes:
Light emitting means;
Display means for transmitting light emitted from the light emitting means based on a target frame of the plurality of frames and displaying an image corresponding to the target frame on a screen;
Have
The control method is:
For each frame, whether or not the difference between the feature value related to the brightness of the frame and the feature value of the frame and the average value of the feature values of one or more frames preceding the frame is equal to or greater than a predetermined threshold value. A determination step for determining;
A control step for controlling light emission of the light emitting means;
Have
In the control step,
When it is determined that the difference is equal to or greater than the predetermined threshold in a predetermined number of consecutive frames before the target frame, the light emission of the light emitting unit is controlled by the light emission amount based on the feature amount of the target frame. ,
Otherwise, the light emission of the light emitting means is controlled by a light emission amount based on an average value of the feature amount of the target frame and the feature amount of one or more frames before the target frame. This is a control method of the image display apparatus.

  According to the present invention, in an image display device that increases the contrast of a display image by controlling the light emission luminance of the light emitting unit and the transmittance of the display unit, both occurrence of flicker and occurrence of saturation of the pixel value are suppressed. The contrast can be increased.

1 is a diagram illustrating an example of a functional configuration of a liquid crystal display device according to Embodiment 1. FIG. The figure which shows an example of the change of the maximum luminance value by which the smoothing process was performed The figure which shows an example of the change of the maximum luminance value of an input image signal The figure which shows an example of the processing flow of the scene change determination part which concerns on Example 1. FIG. The figure which shows an example of the determination result of the scene change determination part which concerns on Example 1. FIG. The figure which shows an example of the processing flow of the deviation determination part which concerns on Example 1. FIG. The figure which shows an example of the processing flow of the smoothing process part which concerns on Example 1. FIG. The figure which shows an example of the determination result of the deviation determination part which concerns on Example 1. FIG. The figure which shows an example of the change of the maximum luminance value after a 1st smoothing process. The figure which shows an example of the change of luminescence brightness The figure which shows an example of the change of a correction coefficient The figure which shows an example of the change of the maximum luminance value after correction coefficient multiplication The figure which shows an example of the change of the maximum luminance value after a 1st smoothing process. FIG. 10 is a diagram illustrating an example of a functional configuration of a liquid crystal display device according to the second embodiment. The figure which shows an example of the change of the light emission luminance after a 2nd smoothing process. The figure which shows an example of the change of the maximum luminance value after correction coefficient multiplication FIG. 10 is a diagram illustrating an example of a functional configuration of a liquid crystal display device according to the third embodiment.

<Example 1>
Hereinafter, an image display apparatus and a control method thereof according to Embodiment 1 of the present invention will be described. In this embodiment, an example in which the image display device is a liquid crystal display device will be described. However, the image display device according to this embodiment is not limited to a liquid crystal display device. The image display apparatus according to the present embodiment is an apparatus including a light emitting unit and a display unit that displays an image on a screen by transmitting light emitted from the light emitting unit with a transmittance according to an image signal (image data). Any device can be used.

  FIG. 1 is a block diagram illustrating an example of a functional configuration of the liquid crystal display device according to the present embodiment. As shown in FIG. 1, the liquid crystal display device according to this embodiment includes a maximum luminance value detection unit 101, a maximum luminance value storage unit 102, a scene change determination unit 103, a deviation determination unit 104, a smoothing processing unit 105, a light emission luminance. A determination unit 106, a backlight module 107, a correction coefficient calculation unit 108, a correction coefficient multiplication unit 109, a liquid crystal panel 110, and the like are included. Although FIG. 1 shows an example in which an RGB signal is input as an input image signal (input image data), the input image signal is not limited to an RGB signal. For example, the input image signal may be a YCbCr signal.

  The maximum brightness value detection unit 101 acquires a brightness feature amount (a brightness statistic value indicating a brightness statistical value) representing the brightness of an input image signal (an image signal input to the liquid crystal display device). In the present embodiment, the input image signal is input in units of frames, and the maximum luminance value detection unit 101 determines the maximum luminance value (each value of the input image signal) as a luminance feature amount from the luminance value of each pixel of the input image signal of the current frame. The maximum luminance value of the pixel) is detected. The acquired (detected) maximum luminance value is output to the maximum luminance value storage unit 102. Note that the luminance feature amount may be acquired from the outside. For example, the luminance feature amount may be input to the liquid crystal display device together with the input image signal as metadata of the input image signal. Further, the luminance feature amount is not limited to the maximum luminance value. The luminance feature amount may be a luminance histogram or a representative value (average value, mode value, intermediate value, minimum value, maximum value) of the luminance value of each pixel.

  The maximum luminance value storage unit 102 stores the maximum luminance value of a plurality of frames (the maximum luminance value detected by the maximum luminance value detection unit 101). In this embodiment, the maximum luminance value of Q frame (Q is an integer of 2 or more) is stored. When the number of maximum luminance values exceeds Q (when the maximum luminance value of the current frame is already stored when the maximum luminance value of the current frame is input), the stored Q maximum Of the luminance values, the maximum luminance value of the earliest frame is rewritten to the maximum luminance value of the current frame. The stored maximum luminance value is output to the scene change determination unit 103, the deviation determination unit 104, and the smoothing processing unit 105. Specifically, the maximum luminance values of a plurality of frames including the current frame and the frame immediately before the current frame (previous frame) are output to the scene change determination unit 103. Maximum luminance values of a plurality of frames including at least L frames (L is an integer of 2 or more) up to the current frame are output to divergence determination unit 104. Then, the maximum luminance values of a plurality of frames including at least N frames (N is an integer of 2 or more) up to the current frame are output to the smoothing processing unit 105. In this embodiment, L = N = Q. However, Q may be larger than N or L. L may be larger or smaller than N.

The scene change determination unit 103 detects a scene change in the input image signal. Specifically, the scene change determination unit 103 calculates the absolute value of the difference between the maximum luminance value of the current frame and the maximum luminance value of the previous frame. Then, the scene change determination unit 103 determines that the scene has been switched from the previous frame to the current frame when the absolute value of the difference is equal to or greater than a threshold value ScnChTh (a threshold for scene change determination). In addition, the scene change determination unit 103 determines that the previous frame and the current frame are the same scene frame when the absolute value of the difference is smaller than or equal to the threshold value ScnChTh (the scene is switched from the previous frame to the current frame). No). The determination result (scene change determination result) is output to the deviation determination unit 104 and the smoothing processing unit 105.

  The deviation determination unit 104 determines whether or not the luminance of the input image signal continues to increase for a predetermined time at a speed equal to or higher than a predetermined value based on the maximum luminance value detected by the maximum luminance value detection unit 101. In this embodiment, a state in which the luminance of the input image signal continues to increase for a predetermined time at a speed equal to or higher than a predetermined value is referred to as a “deviation state”. In the present embodiment, the divergence determination unit 104 calculates the average value of the maximum luminance values of the L frame described above, and the difference value obtained by subtracting the average value from the maximum luminance value of the current frame is equal to or greater than a threshold value (threshold value SepTh or more). It is determined whether or not there is. The divergence determination unit 104 determines that the current value is in a divergence state when it is determined that the difference value is equal to or greater than the threshold SepTh for M frames (M is an integer equal to or greater than 2). The determination result (deviation determination result) is output to the smoothing processing unit 105.

  The smoothing processing unit 105 performs the first smoothing process on the maximum luminance value of the current frame, and outputs the maximum luminance value subjected to the first smoothing process to the light emission luminance determining unit 106. The first smoothing process is a process for suppressing a change in the maximum luminance value in the time direction. In the present embodiment, the smoothing processing unit 105 calculates and outputs the average value of the maximum luminance values of the N frames as the maximum luminance value subjected to the first smoothing processing. In addition, when a scene change is detected or when it is determined that the scene is in a divergence state, the smoothing processing unit 105 reduces the degree of suppression of the change in luminance feature amount due to the first smoothing process. Specifically, when a scene change is detected or when it is determined that the scene is in a divergence state, the smoothing processing unit 105 selects the earliest frame among the stored maximum luminance values of the N frames. To P frame (P is an integer not smaller than 1 and not larger than N-1) is rewritten with the luminance characteristic amount of the current frame. Thereafter, the average value of the maximum luminance values of the N frames after rewriting is calculated and output.

The light emission luminance determination unit 106 determines the light emission luminance of the backlight module 107 based on the maximum luminance value output from the smoothing processing unit 105 (the maximum luminance value of the current frame or the average value of the maximum luminance values of N frames). Control (emission luminance control). In this embodiment, the light emission luminance determining unit 106 controls the light emission luminance (the light emission luminance of the entire screen) so that the higher the luminance of the input image signal in the current frame, the higher the value. Specifically, the light emission luminance determination unit 106 determines the light emission luminance of the entire screen according to the maximum luminance value output from the smoothing processing unit 105, and sets the value representing the determined light emission luminance to the backlight module 107 and the correction coefficient. It outputs to the calculation part 108.
The backlight module 107 emits light with the light emission luminance determined by the light emission luminance determination unit 106.

The correction coefficient calculation unit 108 calculates a correction coefficient used in the compensation process according to the light emission luminance determined by the light emission luminance determination unit 106. The compensation process is a process for compensating for a decrease in luminance of a display image (image displayed on the screen) due to a decrease in emission luminance of the backlight module 107. The calculated correction coefficient is output to the correction coefficient multiplier 109.
The correction coefficient multiplication unit 109 performs compensation processing on the input image signal and outputs the image signal subjected to the compensation processing to the liquid crystal panel 110. Specifically, the correction coefficient multiplication unit 109 multiplies the input image signal by the correction coefficient calculated by the correction coefficient calculation unit 108. Then, the correction coefficient multiplier 109 outputs the image signal multiplied by the correction coefficient to the liquid crystal panel 110.
The liquid crystal panel 110 displays an image on a screen by transmitting light emitted from the backlight module 107 with a transmittance according to an image signal (an image signal after correction coefficient multiplication). Specifically, the liquid crystal panel 110 includes a plurality of liquid crystal elements, and the transmittance (open ratio of the liquid crystal) of each liquid crystal element is changed according to the gradation value of the image signal. Each liquid crystal element transmits the light emitted from the backlight module 107 with the changed transmittance, so that an image is displayed on the screen.

  Hereinafter, the processing flow of the liquid crystal display device according to the present embodiment will be described in detail. In the following, an example in which the maximum luminance value detected by the maximum luminance value detection unit 101 changes as shown in FIG. 3 will be described. In the following, it is assumed that the number of stored frames Q (= N = L) = 4 in the maximum luminance value storage unit 102.

A process flow of the scene change determination unit 103 will be described. The scene change determination unit 103 detects a scene change according to the flowchart shown in FIG.
First, in S101, the absolute value DiffFrameMax of the difference between the maximum luminance value of the current frame and the maximum luminance value of the previous frame is calculated. Then, the process proceeds to S102.
In S102, the absolute value DiffFrameMax of the difference is compared with the threshold value ScnChTh. If the absolute value DiffFrameMax of the difference is greater than or equal to the threshold value ScnChTh, it is determined that the scene has been switched, and the process transitions to S103. If the absolute value DiffFrameMax of the difference is less than the threshold value ScnChTh, it is determined that the scene has not been switched, and the process transitions to S104.
In S103, 1 is set to the flag ScnChFlg indicating whether or not the scene is switched. ScnChFlg = 1 indicates that there is a scene change.
In S104, 0 is set to ScnChFlg. ScnChFlg = 0 indicates that there was no scene change.
The scene change determination unit 103 performs the above process for each frame.
The processing flow of the scene change determination unit 103 has been described above. When the threshold value ScnChTh = 60 and the maximum luminance value changes as shown in FIG. 3, it is determined that the scene has not changed for each of all the frames as shown in FIG.

A processing flow of the deviation determination unit 104 will be described. The deviation determination unit 104 determines whether or not the deviation state is in accordance with the flowchart shown in FIG.
First, in S201, an average value AveMax of the maximum luminance values of four frames (L frame described above) up to the current frame stored in the maximum luminance value storage unit 102 is calculated. Then, the process transitions to S202.
In S202, a difference value DiffValue obtained by subtracting the average value AveMax from the maximum luminance value of the current frame is calculated. Then, the process proceeds to S203.
In S203, the difference value DiffValue and the threshold value SepTh are compared. If the difference value DiffValue is greater than or equal to the threshold SepTh, the process proceeds to S204. If the difference value DiffValue is less than the threshold SepTh, the process proceeds to S208.
In S204, 1 is added to the number (the number of frames; the count value) SepFrame that is continuously determined that the difference value DiffValue is equal to or greater than the threshold value SepTh. Then, the process proceeds to S205.
In S205, the count value SepFrame is compared with a threshold value SepFrameTh (= M). If the count value SepFrame is greater than or equal to the threshold SepFrameTh, the process proceeds to S206. If the count value SepFrame is less than the threshold SepFrameTh, the process proceeds to S207.
In S206, 1 is set to the flag SepFlg indicating whether or not the vehicle is in a divergence state. SepFlg = 1 indicates a divergence state.
In S207, 0 is set in SepFlg. SepFlg = 0 indicates that there is no divergence state. Also, the count value SepFrame is reset to 0.
As described above, if the difference value DiffValue is less than the threshold SepTh in S203, the process proceeds to S208. When the difference value DiffValue is less than the threshold value SepTh, it is not a divergence state, and thus the count value SepFrame is reset to 0 in S208. Then, the process proceeds to S209.
In S209, 0 is set in SepFlg.
The processing flow of the deviation determination unit 104 has been described above. In this embodiment, the threshold SepTh = 25 and the threshold SepFrameTh (= M) = 2.

A processing flow of the smoothing processing unit 105 will be described. The smoothing processing unit 105 performs the first smoothing process on the maximum luminance value of the current frame according to the flowchart shown in FIG.
First, in S301, the determination result (ScnChFlg) of the scene change determination unit 103 and the determination result (SepFlg) of the deviation determination unit 104 are confirmed. If a scene change is not detected (ScnChFlg = 0) and not in a divergence state (SepFlg = 0), the process proceeds to S302. If a scene change is detected (ScnChFlg = 1) or is in a divergence state (SepFlg = 1), the process proceeds to S303.
In S302, the first smoothing process is turned on. Specifically, in S302, it is determined that the process of reducing the degree of suppression of the first smoothing process (the degree of suppression of change in the maximum luminance value due to the first smoothing process) is not performed. Then, the process proceeds to S304.
In S303, the first smoothing process is turned off. Specifically, in S303, it is determined that a process of reducing the degree of suppression of the first smoothing process is performed. Then, among the maximum luminance values of four frames (N frames described above) up to the current frame stored in the maximum luminance value storage unit 102, the maximum luminance values of three frames (P frames described above) from the first frame are the current luminance values. It is rewritten to the maximum luminance value of the frame. Then, the process proceeds to S304.
In S304, the average value of the maximum luminance values of the four frames up to the current frame is calculated and output as the maximum luminance value subjected to the first smoothing process.
The processing flow of the smoothing processing unit 105 has been described above. In this embodiment, since P = N−1, the maximum luminance value of the four frames up to the current frame becomes the same value as the maximum luminance value of the current frame by the processing of S303. Therefore, in S304, the maximum luminance value of the current frame does not change before and after the first smoothing process. Thus, if P = N−1, the degree of suppression of the first smoothing process can be reduced to zero. As a configuration in which the degree of suppression of the first smoothing process is set to 0, for example, a configuration in which the first smoothing process is omitted and the maximum luminance value of the current frame is output as it is can be considered.

  FIG. 8 shows the determination result of the divergence determination unit 104 described above. When the threshold SepTh = 25, the threshold SepFrameTh = 2, and the maximum luminance value changes as shown in FIG. 3, as shown in FIG. 8, SepFlg = 1 in the frames of frame numbers 6, 8, and 10 It becomes. Then, SepFlg = 0 in the remaining frames. Then, from the determination result of FIG. 5 and the determination result of FIG. 8, the maximum luminance value after the first smoothing process changes as indicated by a solid line 901 in FIG. A thin line 900 in FIG. 9 indicates a change in the maximum luminance value (maximum luminance value before the first smoothing process) of the input image signal. A broken line 902 in FIG. 9 indicates a change in the maximum luminance value after the conventional first smoothing process. As shown in FIG. 9, in the present embodiment, the change period of the maximum luminance value can be shortened as compared with the conventional case by reducing the degree of suppression of the first smoothing process when it is determined as a divergence state.

An example of a method for determining the light emission luminance in the light emission luminance determination unit 106 will be described below. In this embodiment, when the maximum luminance value output from the smoothing processing unit 105 is 255, the emission luminance is set to 100%, and when the maximum luminance value is 16, the emission luminance is set to 6%. . When the maximum luminance value is a value between 16 and 255, the emission luminance is obtained by linearly interpolating (maximum luminance value, emission luminance) = (255, 100) and (16, 6). When the maximum luminance value is less than 16, the same light emission luminance (6%) as that when the maximum luminance value is 16 is set. When the maximum luminance value changes as indicated by a solid line 901 in FIG. 9, the light emission luminance changes as indicated by a solid line 1001 in FIG. A thin line 1000 in FIG. 10 indicates a change in light emission luminance determined from the maximum luminance value of the input image signal (maximum luminance value before the first smoothing process). A broken line 1002 in FIG. 10 indicates a change in light emission luminance determined from the maximum luminance value after the first smoothing process (the maximum luminance value indicated by the broken line 902 in FIG. 9). As shown in FIG. 10, in this embodiment, the emission luminance change period can be shortened compared to the conventional case by reducing the degree of suppression of the first smoothing process when it is determined that the state is a deviation state.

  An example of a correction coefficient calculation method in the correction coefficient calculation unit 108 will be described below. In this embodiment, the reciprocal of the light emission luminance output from the light emission luminance determination unit 106 is calculated as a correction coefficient. When the light emission luminance changes as indicated by a solid line 1001 in FIG. 10, the correction coefficient changes as indicated by a solid line 1101 in FIG. A thin line 1100 in FIG. 11 indicates a change in a correction coefficient calculated based on the maximum luminance value of the input image signal (a correction coefficient calculated using the light emission luminance indicated by the thin line 1000 in FIG. 10). A broken line 1102 in FIG. 11 indicates a change in a correction coefficient (a correction coefficient calculated using the light emission luminance indicated by the broken line 1002 in FIG. 10) calculated based on the maximum luminance value after the conventional first smoothing process. . As shown in FIG. 11, in the present embodiment, the correction coefficient change period can be shortened as compared with the prior art by reducing the degree of suppression of the first smoothing process when it is determined that the state is a deviation state.

  As described above, the correction coefficient multiplier 109 multiplies the input image signal by the correction coefficient output from the correction coefficient calculator 108. In this embodiment, the upper limit value of the gradation value (luminance gradation value) is 255, and the value of the image signal exceeds 255 (the value of the image signal is saturated) by multiplying the correction coefficient. ), The value of the image signal is limited to 255. When the correction coefficient changes as shown by the solid line 1101 in FIG. 11 and the maximum luminance value of the input image signal changes as shown in FIG. 3, the maximum luminance value after multiplication of the correction coefficient is the solid line 1201 in FIG. It changes as shown in. A thin line 1200 in FIG. 12 indicates a change in the maximum luminance value obtained by multiplying the input image signal by a correction coefficient based on the maximum luminance value of the input image signal (a correction coefficient indicated by the thin line 1100 in FIG. 11). A broken line 1202 in FIG. 12 indicates a change in the maximum luminance value obtained by multiplying the input image signal by a correction coefficient (correction coefficient indicated by the broken line 1102 in FIG. 11) based on the maximum luminance value after the conventional first smoothing process. Show. As shown in FIG. 12, in this embodiment, when it is determined that there is a divergence state, the degree of suppression of the first smoothing process is reduced, so that the saturation period (the period during which the value of the image signal is saturated) is reduced. ) Can be shortened.

  As described above, according to the present embodiment, in the image display device that increases the contrast of the display image by controlling the light emission luminance of the light emitting unit and the transmittance of the display unit, the occurrence of flicker and the saturation of the pixel value are performed. Contrast can be enhanced by suppressing both occurrences of the above-mentioned. Specifically, the occurrence of flicker can be suppressed by suppressing the change in the luminance feature amount by the first smoothing process. Further, when it is determined that the luminance of the input image signal continues to increase for a predetermined time at a speed equal to or higher than a predetermined value (when it is determined that the state is a divergence state), a change in luminance feature amount due to the first smoothing process By reducing the degree of suppression, the saturation period can be shortened.

  Further, according to the present embodiment, when a scene change is detected, the degree of suppression of the change in the luminance feature amount due to the first smoothing process is reduced. FIG. 13 shows an example of a change in the maximum luminance value after the first smoothing process at the time of scene switching. A solid line 1301 in FIG. 13 shows a change in the maximum luminance value after the first smoothing process according to the present embodiment, and a broken line 1302 shows a change in the maximum luminance value after the conventional first smoothing process. As shown in FIG. 13, in the present embodiment, when the scene change is detected, the change period of the maximum luminance value can be shortened as compared with the conventional case by reducing the degree of suppression of the first smoothing process. . As a result, the saturation period at the time of scene switching can be shortened.

  In the present embodiment, an example is shown in which the degree of suppression of the first smoothing process is set to 0 when it is determined that the state is a divergence or when a scene change is detected. Not limited to. The degree of suppression of the first smoothing process when it is determined that the state is a deviation state or when a scene change is detected may be lower than the degree of suppression of the first smoothing process in other cases. It can be large. In addition, the degree of suppression of the first smoothing process may be different between a case where it is determined that the state is a divergence state and a case where a scene change is detected. However, the saturation period can be shortened as the degree of suppression in the case where it is determined that the state is a divergence state or when a scene change is detected.

  In this embodiment, it is determined whether or not the difference value DiffValue obtained by subtracting the average value of the maximum luminance value of the L frame from the maximum luminance value of the current frame is equal to or larger than the threshold value SepTh. Then, when it is continuously determined that the difference value DiffValue is equal to or greater than the threshold SepTh, the frame is determined to be in a divergence state. However, the determination method of whether it is a deviation state is not restricted to this. For example, a linear expression representing a change in luminance feature amount with respect to time may be calculated using luminance feature amounts of a plurality of frames. Then, when the state in which the inclination of the approximate expression is equal to or greater than a predetermined value continues for a predetermined time (a plurality of frames) or more, it may be determined that the state is a deviation state. In addition, the difference value DiffValue may be a value obtained by subtracting the maximum luminance value subjected to the first smoothing process from the maximum luminance value of the current frame.

  In the present embodiment, the average value of the luminance feature values of the N frames is output as the luminance feature value subjected to the first smoothing process, and a part of the luminance feature values of the N frame is used as the luminance feature value of the current frame. The degree of suppression of the first smoothing process is reduced by rewriting with. However, the first smoothing process and the method for reducing the degree of suppression of the first smoothing process are not limited to this. In the first smoothing process, it is only necessary to suppress a change in the luminance feature amount from the previous frame. For example, the average value of the luminance feature amount of the previous frame and the luminance feature amount of the current frame may be output as the luminance feature amount subjected to the first smoothing process. The degree of suppression of the first smoothing process is, for example, when calculating the average value of the luminance feature amount of the previous frame and the luminance feature amount of the current frame, and assigning the weight of the luminance feature amount of the previous frame to the luminance feature amount of the current frame. The weighted average may be calculated by making it larger than the weight.

  In this embodiment, it is determined whether or not the scene has been switched based on the absolute value of the difference between the luminance feature value of the current frame and the luminance feature value of the previous frame. However, the method for detecting a scene change is not limited to this. For example, scene switching may be detected using three or more frames including a frame before the current frame and a frame after the current frame. Specifically, a linear expression representing a change in luminance feature amount with respect to time may be calculated for each before and after the current frame. Then, when the slopes of the linear expressions are all less than the threshold value and the absolute value of the difference between the intercepts of the linear expressions is equal to or greater than the threshold value, it may be determined that the scene has been switched.

  In the present embodiment, an example in which the threshold SepTh and the threshold SepFrameTh are fixed values has been described, but the present invention is not limited to this. At least one of the threshold SepTh and the threshold SepFrameTh may be determined based on the luminance of the input image signal. For example, a larger value may be set as the threshold SepTh as the luminance of the current frame is higher, and a larger value may be set as the threshold SepFrameTh as the luminance of the current frame is higher. Further, when it is determined that there is a divergence state in the previous frame and the luminance increases from the previous frame to the current frame, the threshold value SepTh and the threshold value SepFrameTh may be reduced to determine the current frame. . By determining the threshold value based on the luminance of the input image signal, more accurate determination can be performed.

In addition, although the present Example showed the example which reduces the suppression degree of a 1st smoothing process only in the period determined to be a deviation state, it is not restricted to this. For example, when the luminance of the input image signal continues to increase after it is determined that the state is a divergence state, there is a high possibility that the increase in luminance is not due to noise. Therefore, the degree of suppression of the change in the luminance feature amount due to the first smoothing process may be reduced until the increase in the luminance of the input image signal stops after it is determined that the state is a divergence state. By adopting such a configuration, the saturation period can be further shortened.

<Example 2>
In Example 1, when it determined with it being a deviation state, the suppression degree of the 1st smoothing processing was reduced. In the first embodiment, the light emission luminance of the backlight module is determined according to the luminance feature amount subjected to the first smoothing process. However, in such a configuration, when the luminance feature amount changes abruptly by reducing the degree of suppression of the first smoothing process, the light emission luminance of the backlight module also changes abruptly, and flicker is perceived. End up. Therefore, in the second embodiment, in addition to the processing described in the first embodiment, a smoothing process (second smoothing process) for the determined light emission luminance is further performed. The second smoothing process is a process for suppressing a change in light emission luminance in the time direction.

  FIG. 14 is a block diagram illustrating an example of a functional configuration of the liquid crystal display device according to the present embodiment. As illustrated in FIG. 14, the liquid crystal display device according to the present embodiment further includes a light emission luminance fluctuation suppressing unit 111 in addition to the functional unit described in the first embodiment (the functional unit illustrated in FIG. 1). In addition, about the same function part as Example 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  The light emission luminance fluctuation suppressing unit 111 performs the second smoothing process on the light emission luminance determined by the light emission luminance determining unit 106 (the light emission luminance of the current frame). Then, the light emission luminance fluctuation suppressing unit 111 controls the light emission luminance of the backlight module 107 to the light emission luminance subjected to the second smoothing process. Specifically, the light emission luminance fluctuation suppressing unit 111 stores a value representing the light emission luminance of the previous frame, and the light emission luminance (of the current frame) subjected to the second smoothing process from the light emission luminance of the previous frame and the current frame. Emission luminance) is calculated.

  In this embodiment, when a scene change is detected, the light emission luminance fluctuation suppressing unit 111 reduces the degree of suppression of the light emission luminance change due to the second luminance smoothing process. Specifically, in this embodiment, when a scene change is detected, the degree of suppression of the change in luminance feature amount by the first smoothing process is set to 0, and the change in emission luminance by the second smoothing process is reduced. The degree of suppression is also set to zero. That is, when a scene change is detected, the backlight module 107 emits light with the light emission luminance determined by the light emission luminance determination unit 106 as in the first embodiment.

In the present embodiment, the light emission luminance after the second smoothing process is calculated using the following formula 1. In Equation 1, BLIn is a value representing the light emission luminance of the current frame, BLInPre is a value representing the light emission luminance of the previous frame, α is a coefficient (a variation rate with respect to the light emission luminance of the previous frame), and BLOut is the light emission after the second smoothing process. It is a value representing luminance.

BLOut = BLInPre + α {BLIn−BLInPre} (Formula 1)

In this embodiment, it is assumed that α = 0.3 is set when the scene is not switched, and α = 1 is set when the scene is switched. Therefore, when BLIn = 80 and BLInPre = 20, BLOut = 38 when the scene is not switched, and BLOut = 80 when the scene is switched. With the above calculation method, the degree of suppression of the second smoothing process can be increased when the scene is not switched, and the degree of suppression of the second smoothing process can be reduced (set to 0) when the scene is switched.

FIG. 15 shows an example of a change in light emission luminance after the second smoothing process according to the present embodiment. When the maximum luminance value changes as indicated by the solid line 901 in FIG. 9, the light emission luminance after the second smoothing process changes as indicated by the solid line 1501 in FIG. A thin line 1500 in FIG. 15 indicates a change in light emission luminance after the second smoothing process calculated from the maximum luminance value of the input image signal (the maximum luminance value before the first smoothing process). A broken line 1502 in FIG. 15 indicates a change in emission luminance after the second smoothing process calculated from the maximum luminance value after the first smoothing process (the maximum luminance value indicated by the broken line 902 in FIG. 9).

  FIG. 16 shows an example of a change in the maximum luminance value after multiplication by the correction coefficient according to the present embodiment. When the maximum luminance value of the input image signal changes as shown in FIG. 3 and the light emission luminance changes as shown by the solid line 1501 in FIG. 15, the maximum luminance value after multiplication of the correction coefficient is shown by the solid line 1601 in FIG. To change. A thin line 1600 in FIG. 16 shows the maximum luminance value after multiplication of the correction coefficient when the maximum luminance value of the input image signal changes as shown in FIG. 3 and the emission luminance changes as shown by the thin line 1500 in FIG. Showing change. A broken line 1602 in FIG. 16 indicates the maximum luminance value after multiplication of the correction coefficient when the maximum luminance value of the input image signal changes as shown in FIG. 3 and the emission luminance changes as shown by the broken line 1502 in FIG. Showing change.

  As is apparent from FIG. 16, according to the present embodiment, when the deviation state is determined, the degree of suppression of the first smoothing process is reduced, so that the saturation period (the value of the image signal is more saturated than before). Period). Further, according to the present embodiment, the occurrence of flicker can be further suppressed by further performing the second smoothing process.

  Further, if the second smoothing process is performed at the time of switching scenes, the saturation period may become longer. According to the present embodiment, when a scene change is detected, the degree of suppression of the change in light emission luminance by the second luminance smoothing process is reduced. Thereby, the saturation period at the time of scene switching can be shortened.

  In this embodiment, when a scene change is detected, the degree of suppression of the change in luminance feature amount by the first smoothing process is set to 0, and the degree of suppression of the change in light emission luminance by the second smoothing process is also 0. Although the example to make was shown, it is not restricted to this. The degree of suppression of the first smoothing process and the second smoothing process when a scene change is detected may be greater than zero. However, if the smoothing process is performed at the time of scene switching, the saturation period may occur or become longer, so the smoothing process is not performed at the time of scene switching (the degree of suppression of the smoothing process is set to 0). Is preferable.

  In the present embodiment, an example in which the light emission luminance after the second smoothing process is calculated using Expression 1, but the method for calculating the light emission luminance after the second smoothing process is not limited thereto. For example, as in the first embodiment, the average value of the emission luminance of N frames may be calculated as the emission luminance after the second smoothing process. Then, the degree of suppression of the second smoothing process may be reduced by rewriting the light emission luminance of the P frame to the light emission luminance of the current frame (light emission luminance before the second smoothing process).

<Example 3>
In the first and second embodiments, the example in which the first smoothing process is performed has been described. In the third embodiment, an example in which only the second smoothing process is performed will be described.

  FIG. 17 is a block diagram illustrating an example of a functional configuration of the liquid crystal display device according to the present embodiment. As shown in FIG. 17, the liquid crystal display device according to the present embodiment includes a maximum luminance value detection unit 101, a maximum luminance value storage unit 102, a scene change determination unit 103, a light emission luminance determination unit 201, a light emission luminance fluctuation suppression unit 202, A deviation determination unit 203, a backlight module 107, a correction coefficient calculation unit 108, a correction coefficient multiplication unit 109, a liquid crystal panel 110, and the like are included. In addition, about the same function part as Example 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  The light emission luminance determination unit 201 determines (temporarily determines) the light emission luminance of the backlight module 107 based on the maximum luminance value (the maximum luminance value of the current frame) detected by the maximum luminance value detection unit 101. The method for determining the light emission luminance is the same as that in the first embodiment.

  Similar to the light emission luminance fluctuation suppressing unit 111 of the second embodiment, the light emission luminance fluctuation suppressing unit 202 performs the second smoothing process on the light emission luminance determined by the light emission luminance determining unit 201 and the light emission luminance of the backlight module 107. Is controlled to the light emission luminance subjected to the second smoothing process. However, in this embodiment, the light emission luminance fluctuation suppressing unit 202 performs the second smoothing process not only when the scene change is detected but also when the divergence determining unit 203 determines that it is in the divergence state. The degree of suppression of the change in light emission luminance is reduced. The method for reducing the degree of suppression of the change in emission luminance by the second smoothing process is the same as in the second embodiment.

  The deviation determination unit 203 determines whether or not the deviation state is based on the light emission luminance determined by the light emission luminance determination unit 201. The light emission luminance determined by the light emission luminance determination unit 201 corresponds to the maximum luminance value detected by the maximum luminance value detection unit 101. Therefore, by using the light emission luminance determined by the light emission luminance determination unit 201 as the maximum luminance value detected by the maximum luminance value detection unit 101, it is determined whether or not the state is a deviation state in the same manner as in the first embodiment. be able to. In the present embodiment, it is determined whether or not a difference value obtained by subtracting the light emission luminance subjected to the second smoothing process from the light emission luminance determined by the light emission luminance determination unit 201 is equal to or greater than a threshold value. When it is determined that the difference value is equal to or greater than the threshold value for M frames or more, it is determined that the current frame is in a divergence state.

  As described above, according to the present embodiment, in the image display device that increases the contrast of the display image by controlling the light emission luminance of the light emitting unit and the transmittance of the display unit, the occurrence of flicker and the saturation of the pixel value are performed. Contrast can be enhanced by suppressing both occurrences of the above-mentioned. Specifically, the occurrence of flicker can be suppressed by suppressing the change in emission luminance by the second smoothing process. In addition, when it is determined that the luminance of the input image signal continues to increase for a predetermined time at a speed equal to or higher than a predetermined value (when it is determined that the input image signal is in a divergence state), a change in luminance feature amount due to the second smoothing process By reducing the degree of suppression, the saturation period can be shortened. Since the basic principle for obtaining the above effect is the same as that of the first embodiment, the description thereof is omitted.

  The configuration of the present embodiment and the configuration of the second embodiment may be combined. That is, if both the first smoothing process and the second smoothing process are performed and it is determined that the state is a divergence state, the degree of suppression of both the first smoothing process and the second smoothing process may be reduced. Good. Further, both the first smoothing process and the second smoothing process may be performed, and the degree of suppression of the second smoothing process may be reduced when it is determined that the state is a divergence state.

DESCRIPTION OF SYMBOLS 101 Maximum brightness value detection part 104 Deviation determination part 105 Smoothing process part 106 Light emission brightness determination part 107 Backlight module 109 Correction coefficient multiplication part 110 Liquid crystal panel

Claims (15)

An image display device that sequentially displays a plurality of images respectively corresponding to a plurality of frames,
Light emitting means;
For each frame, by transmitting the light said light emitting means is emitted with a transmission rate corresponding to the frame, and a table Shimesuru display means an image corresponding to the frame on the screen,
For each frame, an acquisition means for acquiring a luminance feature amount related to the luminance of the frame ;
A first smoothing unit that performs a first smoothing process for acquiring a smooth feature amount that suppresses a temporal change in luminance feature amount acquired by the acquisition unit for each frame ;
For each frame, based on the smoothing feature quantity, and a control to that control means the emission luminance of the light emitting means,
And correcting means for performing inhibit correction the decrease in brightness of the outgoing light intensity of the screen on the display image due to the decrease of the light emitting means in each frame,
Have
The first smoothing unit is configured such that the difference between the luminance feature amount of the frame displayed by the display unit and the smooth feature amount of the frame is equal to or greater than a predetermined threshold in two or more predetermined numbers of frames. In such a case, the first smoothing process is performed so that the difference between the luminance feature amount of the frame displayed by the display unit and the smooth feature amount of the frame is smaller than the case where it is not. An image display device characterized by that. When the state in which the difference is equal to or greater than the predetermined threshold is continued in the predetermined number of frames, the first smoothing unit converts the luminance feature amount of the frame displayed by the display unit to the smoothing of the frame. The image display device according to claim 1, wherein the image display device is a feature amount . Detecting means for detecting a scene change between two consecutive frames ;
When the detection unit detects a scene change, the first smoothing unit calculates a difference between a luminance feature amount of the frame displayed by the display unit and a smooth feature amount of the frame by the detection unit. The image display device according to claim 1 or 2 , wherein the first smoothing process is performed so as to be smaller than a case where a scene change is not detected . The said 1st smoothing means uses the brightness | luminance feature-value of the flame | frame displayed by the said display means as the smoothing feature-value of the said frame, when the switching of a scene is detected by the said detection means. 4. The image display device according to 3. Before Symbol control means,
Determining means for determining light emission luminance according to the smooth feature amount;
Second smoothing is performed to perform second smoothing processing that suppresses temporal changes in the light emission luminance determined by the determining means, and to control the light emission luminance of the light emitting means to the light emission luminance subjected to the second smoothing processing. Means,
The image display device according to claim 1, further comprising: To any one of claims 1 to 5, characterized in that said state said difference is greater than or equal to the predetermined threshold further comprises a determining means determines whether or not continuous in the predetermined number of frames The image display device described. The determination means includes
From the luminance feature amount of the frame to be displayed by said display means, a difference value by subtracting the average value of the luminance feature amount of L frames up to the frame to be displayed (L is an integer of 2 or more) by the display means of the predetermined Determine whether it is above the threshold,
The image display according to claim 6 , wherein it is determined whether or not the state where the difference value is determined to be equal to or greater than the predetermined threshold is continued in M frames (M is an integer equal to or greater than 2) . apparatus. The determination means includes
As the predetermined threshold, a larger value is used as the luminance of the frame displayed by the display means is lower,
The image display apparatus according to claim 7 , wherein a larger value is used as the value of M as the luminance of the frame displayed by the display unit is lower. The determination unit determines that the state in which the difference is equal to or greater than the predetermined threshold is continued in the predetermined number of frames in a frame immediately before the frame displayed by the display unit ; and , when the luminance over the preceding frame to be displayed from the frame by said display means is increased, by reducing the value of the said predetermined threshold M, the determination for a frame to be displayed by the display means The image display device according to claim 7 , wherein the image display device is performed. Storage means for storing luminance feature quantities of two or more frames including a frame displayed by the display means ;
The first smoothing means includes
The average value of the luminance feature quantities of N frames (N is an integer of 2 or more) up to the frame displayed by the display means stored in the storage means is the smoothed feature quantity of the frames displayed by the display means. And
When the state in which the difference is greater than or equal to the predetermined threshold continues in the predetermined number of frames, the P frame from the earliest frame among the luminance feature quantities of the N frames stored in the storage unit (P is one or more N-1 an integer) luminance feature amount of, according to any one of claims 1 to 9, characterized in that rewriting the luminance feature amount of the frame to be displayed by the display means Image display device. The luminance feature amount of the frame, the image display apparatus according to any one of claims 1 to 10, characterized in that the maximum value of the luminance value of each pixel of the frame.   The first smoothing process for the frame is a process of averaging luminance feature amounts of L frames (L is an integer of 2 or more) including the frame.
The image display device according to claim 1, wherein: A method for controlling an image display device that sequentially displays a plurality of images respectively corresponding to a plurality of frames,
The image display device includes:
Light emitting means;
For each frame, by transmitting the light said light emitting means is emitted with a transmission rate corresponding to the frame, possess a table Shimesuru display means, the image corresponding to the frame on the screen,
The control method is :
For each frame, an acquisition step for acquiring a luminance feature amount related to the luminance of the frame ;
For each frame, a smoothing step for performing a smoothing process for acquiring a smooth feature amount that suppresses a temporal change in the luminance feature amount acquired in the acquisition step;
For each frame, based on the smoothing feature quantity, and your step system that controls the light emission luminance of the light emitting means,
A correction step of performing suppressing correction the decrease in brightness of the outgoing light intensity of the screen on the display image due to the decrease of the light emitting means in each frame,
Have
In the smoothing step, when the difference between the luminance feature amount of the frame displayed by the display means and the smooth feature amount of the frame is equal to or greater than a predetermined threshold value in two or more predetermined number of frames In addition, the smoothing process is performed so that a difference between a luminance feature amount of a frame displayed by the display unit and a smooth feature amount of the frame is smaller than that in a case where it is not. For controlling an image display apparatus.   An image display device that sequentially displays a plurality of images respectively corresponding to a plurality of frames,
  A light emitting means;
  Display means for transmitting light emitted from the light emitting means based on a target frame of the plurality of frames and displaying an image corresponding to the target frame on a screen;
  For each frame, whether or not the difference between the feature value related to the brightness of the frame and the feature value of the frame and the average value of the feature values of one or more frames preceding the frame is equal to or greater than a predetermined threshold value. Determination means for determining;
  Control means for controlling light emission of the light emitting means;
Have
  The control means includes
    When it is determined that the difference is equal to or greater than the predetermined threshold in a predetermined number of consecutive frames before the target frame, the light emission of the light emitting unit is controlled by the light emission amount based on the feature amount of the target frame. ,
    Otherwise, the light emission of the light emitting means is controlled by the light emission amount based on the feature value of the target frame and the average value of the feature values of one or more frames before the target frame.
An image display device characterized by that.   A method for controlling an image display device that sequentially displays a plurality of images respectively corresponding to a plurality of frames,
  The image display device includes:
  A light emitting means;
  Display means for transmitting light emitted from the light emitting means based on a target frame of the plurality of frames and displaying an image corresponding to the target frame on a screen;
Have
  The control method is:
  For each frame, whether or not the difference between the feature value related to the brightness of the frame and the feature value of the frame and the average value of the feature values of one or more frames preceding the frame is equal to or greater than a predetermined threshold value. A determination step for determining;
  A control step for controlling light emission of the light emitting means;
Have
  In the control step,
    When it is determined that the difference is equal to or greater than the predetermined threshold in a predetermined number of consecutive frames before the target frame, the light emission of the light emitting unit is controlled by the light emission amount based on the feature amount of the target frame. ,
    Otherwise, the light emission of the light emitting means is controlled by the light emission amount based on the feature value of the target frame and the average value of the feature values of one or more frames before the target frame.
And a control method for the image display device.

Images