JP2012078589A - Image display device and control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the display quality for displaying a motion image in a liquid crystal display device.SOLUTION: An image display device comprises a liquid crystal panel, a backlight, and a control portion for controlling the light emission of the backlight. The control portion sets the light emission time of the backlight by analyzing an input image signal and detecting the motion of the image, so that the light emission time is short when the detected motion is at constant speed or constant acceleration, and the light emission time is long when the detected motion is not at constant speed or constant acceleration. Further, the control portion preferably changes the light emission intensity of the backlight in accordance with the set light emission time so that the light emission intensity is higher as the light emission time is shorter.

Description

  The present invention relates to an image display device and a control method thereof, and more particularly to a control method of a backlight of a liquid crystal display device.

  Conventionally, various methods for improving the display quality of a liquid crystal display (LCD) have been proposed. For example, in Patent Document 1, in order to improve moving image blur (hold blur) unique to a hold-type display such as a liquid crystal display device, a black frame having a black signal level corresponding to a difference amount between frames is inserted between video frames. Insertion is disclosed. Note that flicker may occur due to the insertion of a black frame. Therefore, in Patent Document 1, flicker is reduced by controlling the luminance of the backlight to high / low according to the high / low of the black signal level. is doing. Patent Document 2 discloses that a vivid video display can be obtained by controlling the light emission intensity of the backlight based on the histogram of the video signal in units of frames.

JP 2008-096521 A JP 2008-134664 A

  Black frame insertion as in Patent Document 1 realizes display similar to an impulse-type display in a liquid crystal display device, and is effective in improving hold blur in an image with large movement. However, as a result of studies by the present inventors, it has been found that some images with large movements are not suitable for impulse-type display. For example, if a black frame is inserted into an image where the object is moving in various directions and speeds, the continuity of the object's movement will not be visually felt, and the object will appear and disappear at random positions. It may look like Such a feeling of interference is referred to as a random feeling in this specification. In the conventional method, such a random feeling cannot be avoided.

  The present invention has been made in view of the above circumstances, and an object thereof is to further improve the display quality when a moving image is displayed on a liquid crystal display device.

  A first aspect of the present invention includes a liquid crystal panel, a backlight, and a control unit that controls the light emission of the backlight, and the control unit analyzes an input video signal to determine a motion of the video. The backlight is configured so that the light emission time when the detected motion is a constant velocity or constant acceleration motion is short, and the light emission time when the detected motion is not a constant velocity or constant acceleration motion is long. Provided is an image display device for setting the light emission time.

  According to a second aspect of the present invention, there is provided a control method for an image display device including a liquid crystal panel and a backlight, the step of analyzing an input video signal to detect the motion of the video, and the detected motion A step of setting the light emission time of the backlight so that the light emission time is short when the movement is constant velocity or constant acceleration, and the light emission time is long when the detected movement is not constant velocity or constant acceleration. And a method for controlling the image display apparatus.

  ADVANTAGE OF THE INVENTION According to this invention, the display quality at the time of displaying the image | video with a motion in a liquid crystal display device can be improved further.

1 is a block diagram of an image display device according to a first embodiment of the present invention. The block diagram of the image display apparatus of the 2nd Embodiment of this invention. The block diagram of the image display apparatus of the 3rd Embodiment of this invention. The block diagram explaining the structure of AM-LCD. FIG. 9 is a timing chart illustrating the operation of an AM-LCD. The timing diagram explaining the lighting operation of the backlight of AM-LCD. The figure which shows the relationship between the suitable light emission time and light emission intensity of a backlight. The figure which shows an example of the calculation method of the motion vector of a main target object. The figure for demonstrating the evaluation of a uniform velocity motion and the evaluation of a uniform acceleration motion. The graph which shows an example of the characteristic of the light emission time of the backlight with respect to the shift coefficient K. The figure which shows the structure of the light emission time calculation part which evaluates equal speed. 6 is a graph showing an example of a characteristic of a backlight emission time with respect to a deviation coefficient L. The figure which shows the structure of the light emission time calculation part which evaluates equal acceleration. The graph which shows an example of the relationship between the weight of V1, V2, and light emission time.

  The present invention can be suitably applied to a transmissive or reflective liquid crystal display (LCD) having a backlight in a display device. The embodiment of the present invention will be described using a transmissive LCD that is directly viewed by an observer, but the present invention can also be suitably applied to a transmissive or reflective LCD that projects onto a screen or the like.

(Principle of LCD)
First, an outline of the operating principle of an LCD suitable for the present invention will be described. LCDs are roughly classified into active matrix types and simple matrix types. In the following embodiments, an active matrix type that is currently widely used in TV sets, PC monitors, and the like will be described. However, the present invention can be similarly applied to a simple matrix type LCD.

  FIG. 4 schematically shows a partial configuration of a liquid crystal panel of an active matrix type LCD (AM-LCD). In FIG. 4, 101 is a source wiring, 102 is a gate wiring, 103 is a thin film transistor formed for each display element, 104 is a capacitor formed for each display element, and 105 is a liquid crystal formed for each display element. is there. Arrows 106 and 107 indicate wirings from the electrodes of the capacitor 104 and the liquid crystal 105, and these wirings 106 and 107 are commonly connected to a counter electrode (not shown). In FIG. 4, the number of source wirings 101 and gate wirings 102 corresponds to the required number of pixels of the display device. Here, in order to simplify the description, an example of a display device having 240 × 320 pixels will be described as an example. In a 240 × 320 pixel display device, the number of source lines 101 is 960 (320 × 3 (RGB)), and the number of gate lines 102 is 240.

Next, the operation of the AM-LCD shown in FIG. 4 will be described using the timing chart of FIG. In FIG. 5, the horizontal axis schematically represents time, and the vertical axis schematically represents voltage or light emission intensity. 5, waveforms G1, G2,... G240 are voltages applied to the gate wiring 102, and are signals for scanning the voltage applied to the liquid crystal 105. In FIG. 5, the waveforms of S1,..., S960 are voltages applied to the source wiring 101. When the voltage applied to the gate line 102 is, for example, +10 V, the channel of the thin film transistor 103 formed for each display element becomes conductive, and the voltage of the source line 101 corresponds to the capacitor 104 and the liquid crystal 10 of the corresponding display element.
5 is applied. When the voltage applied to the gate wiring 102 changes from, for example, +10 V to −10 V, the channel of the thin film transistor 103 is turned off, and the voltages of the capacitor 104 and the liquid crystal 105 are held. For example, the voltage applied to the gate wiring 102 is sequentially scanned downward from the top of the display screen, and the voltage of the corresponding source wiring 101 is controlled to a desired voltage. As a result, a voltage that is the difference between the voltage of the corresponding source line 101 and the voltage of the counter electrode is charged and held in the capacitor 104 and the liquid crystal 105 formed for each corresponding display element. The transmittance of the liquid crystal 105 (and a polarizing plate (not shown)) to which a desired voltage is applied is determined after the response time of the liquid crystal. The luminance of the light emitted from the backlight is modulated by the transmittance of the liquid crystal 105 (and a polarizing plate (not shown)) determined for each display element, and an image is formed.

  Although the backlight can be always turned on, as shown in the BL waveform in FIG. 5, the backlight is turned on only after the response time of the liquid crystal 105 until the gate voltage is applied to the gate wiring 102 in the next field. preferable. Thereby, it is possible to prevent display during the time when the transmittance of the liquid crystal 105 (and a polarizing plate (not shown)) is not fixed, and thus the image quality is improved.

  Further, if a DC voltage is continuously applied to the liquid crystal itself, the liquid crystal substance is deteriorated and burned. In order to avoid this deterioration and burn-in, driving is performed to periodically invert the polarity of the voltage applied to the liquid crystal. In the field indicated by A in FIG. 5, the voltage of the source wiring 101 is −5 V to +5 V and the voltage of the counter electrode is −5 V. In the field indicated by B, the voltage of the source wiring 101 is from +5 V. The voltage of −5V and the counter electrode is + 5V. As a result, the voltage applied to the liquid crystal is inverted for each field. The inversion driving method includes a line unit and a dot unit. However, since the essential configuration of the present invention is not affected, detailed description thereof is omitted.

(Backlight)
As shown in the waveform of BL in FIG. 5, when the light is turned on only after the response time of the liquid crystal 105 until the gate voltage is applied to the gate wiring 102 in the next field, the liquid crystal 105 (and a polarizing plate (not shown)) is transmitted. Since the display is not performed at a time when the rate is not fixed, the image quality is improved. In a display device with a small number of display elements, the scanning time is short with respect to one field period, and thus such backlight control is possible. However, a display device with a large number of display elements requires a long scanning time and a short backlight emission time, and the backlight control method of FIG. 5 reduces the luminance of the display device.

  The explanation will be further supplemented by using FIG. 6A and FIG. 6A and 6B, the horizontal axis represents time, and the vertical axis represents gate wiring. A thick line 201 indicates a time when a selection potential is applied to the gate wiring. A portion indicated by hatching 202 indicates the response time of the liquid crystal, and a vertical hatching portion 203 indicates the light emission time of the backlight. A dotted line 204 indicates a time centroid (center in the time axis direction) of the light emission time weighted by the light emission intensity of the light source of the backlight.

  FIG. 6A shows a display device having the same number of display elements (number of gate lines) as FIG. On the other hand, FIG. 6B shows an example of a display device having the number of display elements of full high vision, for example, the number of gate wirings is 1080, and the scanning time required to apply a selection potential to all the gate wirings is very high. It will be long. Therefore, the light emission time of the backlight indicated by 203 is shortened and the luminance is decreased. As a countermeasure against the reduction in the light emission time of the backlight and the decrease in luminance, the method shown in FIG. 6C is performed. In FIG.6 (c), the meaning shown by 201-203 is as having mentioned above. A dotted line 204a indicates the time center of light emission time weighted by the light emission intensity of the light source of the backlight.

In the LCD that performs driving shown in the timing chart of FIG. 6C, although not shown, the backlight is divided into 10 blocks in the scanning direction (vertical direction), and the light emission time can be controlled respectively. ing. Then, the backlights are individually controlled to light after the required liquid crystal response time has elapsed for each of the ten blocks. As shown in FIG. 6C, the backlight lighting is started after the liquid crystal response time elapses for each block, and the backlight is turned off immediately before the scanning period of the next field. It can be made longer than b). The time centroid 204a of the light emission time weighted with the light emission intensity of the light source of the backlight is different for each block.

(Hold blur)
The hold blur that causes a problem in the AM-LCD will be described. Hold blur occurs when a moving object on the screen is tracked. Tracking vision refers to observing a moving object while keeping the line of sight following the movement of the object.

In impulse-type displays such as CRT, line-sequential FED and SED (Surface-conduction Electron-emitter Display), the display time (light emission time) in each frame (or field) is very short. Therefore, no blur occurs even when the moving object is viewed.
On the other hand, in a hold-type display such as an AM-LCD, the light emission intensity is maintained for one frame. Therefore, when the moving object is viewed, the object spreads in the moving direction and is connected to the retina. Imaged. This is observed as a hold blur. The hold blur always occurs in the hold-type display when the moving object is tracked. In order to avoid this hold blur, it is preferable to display the object like a impulse display by controlling the backlight emission time to be short when displaying a moving object on the hold display.

  On the other hand, in the case of an image that cannot clearly follow the moving object, the impulse display makes it impossible for the observer to visually sense the continuity of the object's movement, and the object appears and disappears at random positions. It looks like an unnatural display (random feeling). When a similar image is displayed on the hold-type display, the movement of the object is blurred, and thus an image with less unnaturalness can be observed. Examples of images that are difficult to follow are, for example, images of waterfalls and fountains. Drops of waterfalls and fountains are scattered in many directions at various speeds, making it impossible to follow. Further, even if one or a small number of objects are moving in various directions and velocities, the movement cannot be predicted, and tracking is difficult.

(Control of backlight emission time)
Next, control of the light emission time of the backlight, which is one of the characteristic configurations of the image display apparatus of the present embodiment, will be described. In the present embodiment, the display time of the backlight is changed depending on the quality of the displayed video (whether the movement is easy to follow). Further, at this time, the light emission intensity of the backlight is changed according to the length of the display time so that the brightness (luminance) felt by the observer does not change.

  FIG. 7 is a timing chart showing the relationship between the light emission time and the light emission intensity. In FIG. 7, 201 indicates a selection potential of the gate wiring, 202 indicates the response time of the liquid crystal, hatched portion 203 indicates the backlight emission time, 203 indicates the backlight emission time, and 204 indicates the backlight light source emission. The time centroid of the emission time weighted by intensity is shown. The vertical axis of 203, 203a, 203b, 203c indicates the emission intensity. In addition, although 203, 203a, 203b, and 203c are the light emission times in different frames, in FIG. 7, these are shown side by side on the same time axis for comparison.

As shown in FIG. 7, in this embodiment, the light emission intensity of the light source is controlled so that the luminance (brightness felt by the observer) does not change with the length of the light emission time. That is, if the light emission time is long (
In 203a), the emission intensity is lowered, and when the emission time is short (203c), the emission intensity is increased and control is performed so that the luminance does not change with the emission time. If it is assumed that the light emission intensity and the luminance are proportional, the light emission intensity may be controlled so that the time integral of the light emission intensity (the areas of the waveforms 203a, 203b, and 203c in FIG. 7) is equal.

  The light emission time is controlled so that the position (timing) of the time center of gravity 204 of the light emission time weighted by the light emission intensity of the light source of the backlight does not change between frames. When the light emission intensity within the light emission time is constant as shown in FIG. 7, the timing of the light emission start and the light emission end may be determined simply so that the center of the light emission time does not change. The reason why the time center of gravity 204 is not changed is as follows. Changing the time centroid 204 for each frame is equivalent to making the display (light emission) intervals of the frames uneven. For example, when each frame of an image in which an object moves at a constant speed is displayed at unequal intervals, the movement of the object looks unnatural or motion blur is observed. This is a problem that occurs because the imaging position on the retina of the observer varies as a result of the shift of the observer's line of sight (predicted position) and the display position of the object. Therefore, as shown in FIG. 7, by controlling the light emission time so that the time centroid 204 does not change (that is, the time centroid 204 is the same in all frames), unnatural movement and blurring are prevented. Can be suppressed.

(Bokeh during imaging)
Next, blur at the time of imaging will be described. The blur at the time of imaging occurs when an object that is a subject moves within the imaging time of the imaging device, and is also called motion blur. In order to reduce blur at the time of imaging, there is a method of imaging an object in an imaging time shorter than the frame time by controlling the electronic shutter of the imaging plate.
When an object photographed in such a short imaging time using such an electronic shutter is observed with an impulse display, the object that can be followed can be clearly seen without blurring.

  On the other hand, when an image obtained by photographing an object that is difficult to follow is captured in a short imaging time on an impulse display, a random feeling is generated. In order to solve this problem, it has been found by studying the present inventor that a random feeling can be removed by setting a long imaging time and intentionally adding a blur at the time of imaging. Even when an object that is difficult to follow is shot in a short imaging time, a low-frequency component corresponding to blur at the time of imaging is added to the video signal itself by signal processing, or a display that causes hold blur is generated randomly. It was found that the feeling can be reduced.

(Flicker)
Flicker often becomes a problem with impulse-type displays when the display frame rate is low. Even at the same frame rate, the hold-type display has less change in luminance in the time direction, and therefore the feeling of interference due to flicker is smaller than that of the impulse-type display. However, even with a hold-type display, flicker may occur if the backlight emission time is shortened and a non-light emission time is provided between successive frames.

<First Embodiment>
In the present embodiment, the backlight and video signal of the AM-LCD, which is a hold-type display, are optimally controlled to reduce the above-mentioned hold blur, flicker interference, etc. A method for suppressing the generation of feeling will be described. Specifically, in the image display device of the present embodiment, in the case of an image that is easy to follow, the emission time is shortened and the emission intensity is increased, and in the case of an image that is difficult to follow, the emission time is increased. The backlight is controlled so as to reduce the emission intensity.

FIG. 1 shows a block diagram of main parts of the image display apparatus according to the first embodiment of the present invention.
In FIG. 1, reference numeral 1 denotes a liquid crystal panel shown in FIG. 4, for example, 2 denotes a backlight having a light source such as a light emitting diode (LED) installed behind the liquid crystal panel 1. Reference numeral 3 is a video input terminal, and 4 is a motion detection unit that detects video motion by analyzing a video signal. Reference numeral 8 denotes a main object movement calculation unit that calculates the movement of the main object that the observer can expect to follow. 5 is a light emission time calculation unit that calculates the light emission time and light emission intensity of the backlight 2 based on the output of the required object motion calculation unit 8, and 6 is a light emission time and light emission intensity of the LED according to the output of the light emission time calculation unit 5. It is the backlight control part to control. In the present embodiment, the motion detection unit 4, the main object motion calculation unit 8, the light emission time calculation unit 5, and the backlight control unit 6 constitute a control unit that controls light emission of the backlight 2. Reference numeral 7 denotes a frame delay unit that delays the video signal by a time corresponding to the processing of the motion detection unit 4, the main object motion calculation unit 8, and the light emission time calculation unit 5. Reference numeral 90 denotes an object that is a subject, and reference numeral 91 denotes a video camera that images the object.

  In the configuration of FIG. 1, the video output of the video camera 91 that images the object 90 is input to the video input terminal 3 of the image display device. For the video signal input to the video input terminal 3, a motion vector for each frame is calculated by the motion detection unit 4.

  The motion detection unit 4 performs a local motion vector calculation process in a plurality of areas (motion vector detection areas) on the video, for example, as follows. A motion vector detection unit area is set for each of the currently input frame (current frame) and the previous frame (previous frame). The correlation value between the image of the previous frame and the image of the current frame is obtained while moving the motion vector detection unit area of the previous frame within a predetermined search range. Then, the movement amount having a high correlation value is determined as the motion vector of the motion vector detection unit area. This process is performed for each of a plurality of motion vector detection unit areas on the current frame. The motion vector is expressed in (x, y) coordinates as a distance indicating how the motion vector detection unit area has moved in one frame time.

  The size of the motion vector detection unit area may be set in any way. If the area is made finer, the accuracy of motion vector detection increases, but the amount of calculation increases and the problem of increased hardware (circuit) costs may arise. Therefore, it is usually preferable to divide the video into motion vector detection unit areas of about several tens of several tens to several hundreds of several hundreds. In order to reduce the calculation amount of the motion vector of the motion detection unit 4, it is preferable to calculate after reducing the number of pixels by thinning out or averaging the pixels in advance.

  The main object motion calculation unit 8 calculates a representative motion vector of the entire video from the local motion vector for each area calculated by the motion detection unit 4. At this time, it is preferable to calculate the motion vector of the target object (main target object) in the video that the observer can expect to follow as a representative motion vector. The motion vector of the main object can be calculated by the following method, for example.

  In the first method, the main object motion calculation unit 8 calculates the average of the entire video of the local motion vectors calculated by the motion detection unit 4, and outputs the average value as the motion vector of the main object. Is the method. When the entire image is moving in the same direction and at the same speed as when the camera is panned, the motion of the tracking vision and the motion vector output from the main object motion calculation unit 8 are in good agreement. The first method is advantageous in that the processing contents are simple and hardware implementation is easy.

In the second method, the main object motion calculation unit 8 calculates an average of only local motion vectors having a magnitude equal to or larger than a preset threshold value, and outputs the average value as a motion vector of the main object. It is a method to do. The threshold TH1 used here may be set as appropriate according to the size (resolution), frame rate, size of the motion detection unit area, and the like of the video. For example, the threshold TH1 can be set to about several pixels to several tens of pixels. Similar to the first method, the second method is also effective for images such as when the camera is panned. Further, the second method has an advantage that the motion vector of the object can be calculated more accurately than the first method in the case of an image where the background is stationary or hardly moving and only the object is moving. There is. Note that the second method also has a relatively simple processing content and is easy to implement in hardware.

The third method is the most preferable calculation method. For example, consider an image in which the main object in the image (the object that the observer follows) is not so large and there is a moving object in the background. When the motion of the background portion is small, the motion vector of the main object can be calculated with high accuracy also by the second method. However, if the background part contains many moving objects, the background part moves greatly, or moves in a random direction, the error in the calculation result of the motion vector of the main object may increase. There is.
Therefore, in the third method, a plurality of adjacent motion detection unit areas that have the same or similar local motion vectors and whose total area is equal to or greater than the threshold value TH2 are selected as main objects. At this time, as in the second method, it is better to exclude the area of the motion vector smaller than the threshold value TH1. When a plurality of main object candidates are detected, the one with the largest movement among them may be selected as the main object. The threshold value TH2 may be appropriately set according to the size (resolution), frame rate, size of the motion detection unit area, etc. of the video. it can. Note that the same motion vector refers to a motion vector having the same direction and size, and the similar motion vector refers to a motion vector having a very small difference in direction and difference in size. For example, when the direction difference is smaller than a threshold value TH3 (for example, about several degrees to several tens of degrees) and the size difference is smaller than a threshold value TH4 (for example, about several pixels to about a dozen pixels), similar movement is performed. It can be determined as a vector.

  After selecting the area corresponding to the main object by the above method, the main object motion calculation unit 8 calculates the average of local motion vectors of the selected area, and uses the average value as the motion vector of the main object. Output as. Thereby, the motion vector of the main object can be obtained with high accuracy.

  The algorithm of the third method will be specifically described with reference to FIG. In FIG. 8, each rectangular area 801 is a motion vector detection unit area, and in this example, 40 motion vector detection unit areas 801 of 5 × 8 are shown. Reference numeral 802 denotes an arrow schematically showing a local motion vector calculated for each motion vector detection unit area 801. A black circle represents a motion vector of zero size. A region 803 hatched with diagonal lines is a region determined by the main object motion calculation unit 8 as a plurality of adjacent motion vector detection unit areas having the same or similar motion vectors. It is assumed that the threshold value TH2 is set to 5% of the area S of the entire video, for example. In this case, if the total area of the region 803 is 0.05 × S or more, the main object motion calculation unit 8 regards the region 803 as a main object, and motion vectors of 11 areas 801 in the region 803. Is output as a vector of main objects.

  The motion vector output from the main object motion calculation unit 8 is input to the light emission time calculation unit 5. The light emission time calculation unit 5 generates and outputs data for controlling the light emission time and light emission intensity of a backlight composed of a light source such as an LED from the input motion vector. The detailed operation of the light emission time calculation unit 5 will be described later.

The backlight control unit 6 controls the light emission time and light emission intensity of a light source such as an LED according to the output of the light emission time calculation unit 5. For example, the backlight control unit 6 may be configured by a circuit that performs analog control of the light emission intensity of the LED by negative feedback using an operational amplifier, or controls the light emission intensity by performing PWM modulation in a cycle shorter than one frame time. It can also be configured from a circuit that The configuration for performing PWM control has an advantage of less power loss compared to analog control.

  The configuration of the backlight 2 includes a type that uniformly controls the entire light emission time and light emission intensity, and a type that is divided into a plurality of blocks that can independently control the light emission time and light emission intensity. Any type of backlight 2 may be used in the present invention. In the former case, the light sources of the liquid crystal panel 1 and the backlight 2 are controlled at the timing shown in FIGS. In the latter case, as shown in FIG. 6C, the light sources of the respective blocks are caused to emit light at different timings. However, although the light emission start time is different for each block, the light emission time and light emission intensity are controlled to be the same for all blocks.

  In FIG. 1, a frame delay unit 7 is composed of a frame memory, and delays a video signal output to the liquid crystal panel 1. The amount of delay is preferably matched with the delay time of the backlight control by the calculation time of the motion detection unit 4, the main object motion calculation unit 8, and the light emission time calculation unit 5. Since the frame delay unit 7 requires a frame memory, the amount of hardware is large and the cost is relatively high. When the frame delay unit 7 is omitted, there is a time lag between the display on the liquid crystal panel 1 and the light emission from the backlight 2, but since there is little discomfort in normal video, the frame delay unit 7 is omitted to reduce costs. Is possible. In the liquid crystal panel 1, the transmittance of each pixel is set based on the input video signal as described above. Although not shown, the information on the light emission time and the light emission intensity calculated by the light emission time calculation unit 5 is also input to the liquid crystal panel 1 and used for controlling the transmittance of the display element in the liquid crystal panel 1 as necessary. .

(Backlight control method)
Before describing the configuration and operation of the light emission time calculation unit 5, a concept for controlling the backlight in the present embodiment will be described.

  As described above, in the impulse-type display, a sense of disturbance called random feeling occurs for an object that cannot be followed. Since there is no continuity of movement and the object appears to appear or disappear at random, the display is more unnatural than the hold blur that occurs in the hold-type display.

  The backlight control method in the first embodiment is a method for improving such unnatural display. In other words, the quality of the movement of the main object (whether it is easy to follow or not) is evaluated from the video signal. To reduce hold blur. On the other hand, for a video that is difficult to follow, the original drive of the hold type display (longening the light emission time of the backlight) is performed to suppress the occurrence of random feeling. Further, for a difficult movement of a still image and follow-up vision, flicker can be reduced by lengthening the light emission time of the backlight.

  Next, the movement of the object that can be followed and viewed will be described. When the inventor observed the movement of an object that can be followed, the human eye can follow the object moving at a constant speed such as a telop or the object moving at a constant acceleration. I understood.

For this reason, in the case of an object that moves at a constant velocity or a constant acceleration, the light emission time of the backlight is shortened to approach the driving of the impulse display. Thereby, hold blur can be prevented. Furthermore, since an object that moves at a constant velocity or a constant acceleration can be followed, a random feeling does not occur. For other movements, it is difficult to follow, so the light emission time of the backlight is long so that randomness does not occur, and the original drive of the hold type display is performed. Thereby, although hold blur occurs, generation | occurrence | production of a random feeling can be suppressed.

(Evaluation of constant speed)
First, an example of evaluating constant speed will be described.
FIG. 9A shows a graph for explaining the evaluation of constant velocity motion. In FIG. 9A, the vertical axis represents time, and the horizontal axis represents the position in the x direction. T _n-2 , T _n−1 , T _n , and T _{n + 1} indicate the time for each frame. Although the horizontal axis is described as the x direction, it is preferable to evaluate the positions of both the x and y axes. In FIG. 9 (a) 401a, 401b, 401c, 401d each time _{T n-2, T n-} 1, T n, a line of sight that tracks the motion when _{T n + 1} shown schematically. Reference numerals 402a, 402b, 402c, and 402d are moving objects that are moving at approximately equal speed. The observer cannot adjust the line of sight to the movement of the object for each frame, and follows the average movement of the object and moves the line of sight at a constant speed. That is, a deviation (ΔX) from the line of sight 401c occurs for an object that deviates from the constant velocity, such as the object 402c. This shift is blurred on the retina. Due to this blur, a random feeling is generated in the impulse display.

  In this specification, the degree of blurring, that is, the ratio of how much the object is deviated with respect to the line of sight following at a constant speed is defined as “deviation coefficient: K”. If the deviation coefficient K is a small value, randomness is unlikely to occur. Therefore, the light emission time of the backlight is shortened, and display without hold blur that is close to an impulse-type display is performed.

  As described above, the main target object motion calculation unit 8 outputs a distance indicating how the main target object that the observer can expect to follow is moved per frame as a motion vector (x, y). The object described in FIG. 9A may be considered as the movement of the main object calculated by the main object movement calculation unit 8.

ずれ係数Ｋは図９（ａ）に示したように、主要対象物の位置と視線の位置の差（ΔＸ）を１フレームあたりの視線の移動距離（Ｘａｖｅ）で割った値で定義する。 The movement amount per frame in the m-th frame obtained from the motion vector of the main object that is the output from the main object motion calculation unit 8 is Xm, and the average movement amount per frame of the observer's line of sight is Xave. To do. The deviation coefficient K in the nth frame that is the current time is defined by Equation 1).

As shown in FIG. 9A, the deviation coefficient K is defined by a value obtained by dividing the difference (ΔX) between the position of the main object and the position of the line of sight by the movement distance (Xave) of the line of sight per frame.

  If the deviation coefficient K is, for example, 0, the position of the line of sight and the position of the main object are not displaced, so that even when the backlight emission time is shortened as in the impulse display, randomness does not occur. On the other hand, when the deviation coefficient K is 0.5 or more, the main object is displaced by a distance that is half of the moving distance in one frame period when the follow-up view is performed, and the feeling of interference starts to become noticeable. Therefore, the light emission time of the backlight is controlled according to the value of the deviation coefficient K. Specifically, for a video signal with a small deviation coefficient K that can be followed, the backlight emission time is controlled to be short to reduce hold blur. On the other hand, in the case of a video signal in which randomness may occur when the deviation coefficient K is viewed large, the backlight emission time is controlled to be long to suppress the occurrence of randomness.

と、変形できる。現時刻ｎより前までは追従視できている（すなわち、視線の位置と主要対象物の位置がずれていない）と仮定する。式で示すと、

となる。
式２）に式３）を代入し、
K=|Xn-Xave|/|Xave| ・・・・式４）
が求まる。
式１）あるいは、式２）により、ずれ係数Ｋを求め追従視可能かを判断すると好適である。 In order to simplify the definition formula of the deviation coefficient K, it is also preferable to obtain the deviation coefficient by modifying the following expression. That is, Equation 1) is

And can be transformed. It is assumed that a follow-up view is possible before the current time n (that is, the position of the line of sight is not shifted from the position of the main object). In terms of the formula:

It becomes.
Substituting Equation 3) into Equation 2)
K = | Xn-Xave | / | Xave |
Is obtained.
It is preferable that the deviation coefficient K is obtained by the equation 1) or the equation 2) to determine whether the follow-up view is possible.

と、求めることができる。 Next, the moving distance of the line of sight per frame (the speed of line of sight) is the average value of the moving distance of the main object per frame before the current time n.

And can be asked.

  In the present embodiment, Equation 5) is substituted into Equation 1) or Equation 4) to calculate the deviation coefficient K, and the backlight emission time is determined based on the magnitude of the deviation coefficient K. The start time of Expression 5) may be calculated from the past, for example, when the scene changes.

  When Xave is 0 in the video signal of the stationary main object, the denominators of Equation 1) and Equation 4) are 0. Since the follow-up view is possible when the main object is stationary, in this case, the calculation of Equations 1) and 4) is not performed, and a small value (for example, K = 0) is output as the value of K.

These calculations are easy to implement when processed by software, but there is a concern about an increase in hardware when implemented as hardware. Therefore, when realized by hardware, the calculation of Expression 5) may be performed by calculating the line-of-sight movement distance (line-of-sight speed) Xave by a calculation weighted according to the current time (cyclic filter). As a result, the amount of hardware can be reduced, and a value close to the actual observer's tracking speed can be obtained. Assuming that the speed of follow-up vision at the frame of time _n is Xave _n , the equation for obtaining Xave _n is:
Xave _n = S1 · X _n-1 + S2 · Xave _n-1 ··· Equation 6)
However,
S1 + S2 = 1 ・ ・ ・ ・ Equation 7)
It becomes. By S1 and S2, the weight of the line-of-sight speed one frame before and the speed of the main object speed one frame before can be changed. Usually, S1 and S2 should be set so that S2 is larger than S1.

Further, in order to calculate the gaze speed easily, it is preferable to perform the following calculation. The amount of calculation can be reduced when the line-of-sight speed Xave _n in the frame at time n is obtained from the average value of the speeds of the main objects in the previous two frames. That is,
Xave _n = (1/2) · X _n-2 + (1/2) · X _n-1 ··· Equation 8)
Ask for.
Further, in order to more easily calculate the line-of-sight speed, the line-of-sight speed Xaven in the frame at time _n may be simply obtained from the speed of the main object in the immediately preceding frame. That is,
Xave _n = X _n-1 ... Equation 9)
Ask for.
The calculation of the line-of-sight speed of Equation 8) and Equation 9) has a great advantage that the amount of calculation in hardware or software can be reduced, although the error is somewhat larger.

  Substituting Equation 5), Equation 6), Equation 8) or Equation 9) into Equation 1) or Equation 4) to calculate the deviation coefficient K, and determining the backlight emission time according to the magnitude of the deviation coefficient K. Control the light emission time of the backlight. If the value of the deviation coefficient K is large, a deviation between the line of sight and the main object occurs. Therefore, the light emission time is long. If the value of the deviation coefficient K is small, the deviation between the line of sight and the main object is small. Set and reduce hold blur as much as possible. FIGS. 10A, 10B, and 10C show an example of the relationship between the preferable backlight emission time and the deviation coefficient K. FIG. In any of the conversion methods, when constant velocity motion is detected (the deviation coefficient K is zero or sufficiently small), the light emission time becomes the minimum value Tmin, and movement that is not constant velocity movement is detected (the deviation coefficient K is somewhat large). ), The light emission time becomes the maximum value Tmax. Between Tmin and Tmax, the emission time monotonously increases stepwise or continuously in accordance with the amount of deviation from the constant velocity motion (the value of the deviation coefficient K). In the conversion table of FIG. 10A, the first light emission time Tmax is selected if the deviation coefficient K is larger than a predetermined threshold (for example, 0.5), and the short second light emission if the deviation coefficient K is equal to or less than the threshold. The time Tmin is selected. Although this method can also suppress the generation of random feeling, there is a risk that an uncomfortable feeling may occur when switching the light emission time. Therefore, as shown in FIGS. 10B and 10C, a method in which the light emission time is continuously changed with respect to the amount of deviation from the uniform motion is more preferable. FIGS. 10A, 10B, and 10C are examples. For example, the light emission time may be increased in multiple steps from Tmin to Tmax.

(Luminescence time calculation unit that evaluates constant speed)
FIG. 11 shows a configuration example of a light emission time calculation unit that evaluates constant speed. In FIG. 11, reference numeral 501 denotes an input terminal for inputting a motion vector that is an output of the main object motion calculation unit 8. Reference numeral 510 denotes a follow-up visual speed calculation unit that calculates the visual line speed (Xave) by any one of the above formulas 5), 6), 8), and 9). Reference numeral 511 denotes a K calculation unit that calculates a shift coefficient K from the input line-of-sight speed (Xave) and a motion vector. A conversion table 508 stores the characteristics shown in FIGS. 10A, 10B, and 10C in a look-up table format, and outputs a light emission time with respect to the shift coefficient K. Reference numeral 509 denotes a low-pass filter that cuts high-frequency components in the time direction with respect to the output of the conversion table 508.

  504 is a timing generation unit that generates a light emission timing from the light emission time that is the output of the low-pass filter 509, and 505 is a light emission intensity calculation unit that determines the light emission intensity from the light emission time that is the output of the low-pass filter 509 as shown in FIG. is there. Reference numeral 506 denotes an output terminal that outputs a light emission time to the backlight control unit 6, and reference numeral 507 denotes an output terminal that outputs a voltage indicating the light emission intensity to the backlight control unit 6.

  The light emission time data that is the output of the conversion table 508 may be directly input to the timing generation unit 504 and the light emission intensity calculation unit 505, but more preferably is input to the low-pass filter 509 as shown in FIG. By attaching the low-pass filter 509, the change in the light emission time in the time direction becomes gradual, and the sense of incongruity due to the change in the length of the light emission time over time is reduced.

In FIG. 11, the tracking visual velocity detection unit 510 determines the tracking visual velocity of the main object by using the method of any one of Equation 5), Equation 6), Equation 8), or Equation 9) as a frame-based motion vector (x, y). Output as. The K calculation unit 511 calculates a deviation coefficient K from the tracking visual speed that is the output of the tracking visual speed detection unit 510 and the motion vector of the main object. Then, the shift coefficient K is converted into the light emission time by the conversion table 508.

  The light emission time that is the output of the conversion table 508 is input to the timing generation unit 504 via the low-pass filter 509. The timing generation unit 504 determines the light emission start timing so that the time centroid 204 is not shifted, and outputs the light emission start and end timing signals from the output terminal 506. Further, the light emission intensity calculator 505 calculates the light emission intensity so that the luminance does not change regardless of the length of the light emission time. The emission intensity calculation unit 505 is preferably configured with a table realized by a memory or the like, for example. The calculated emission intensity is converted into a voltage by a D / A converter (not shown) and output.

  In the LCD having the configuration shown in FIG. 6C, the timing generation unit 504 determines the light emission start timing for each of the plurality of blocks of the backlight 2, and outputs the timing signal of each block from the output terminal 506. To do. In the present embodiment, the light emission times of all blocks are controlled to be the same. Further, the light emission intensity calculation unit 505 calculates the light emission intensity so that the luminance does not change regardless of the length of the light emission time.

  In order to make the explanation easy to understand, only the deviation coefficient in the X direction has been described, but it is preferable to perform the same evaluation in the Y direction. When evaluating in the X direction and the Y direction, it is preferable to shorten the light emission time only when the deviation coefficient in both directions is zero or sufficiently small. For example, after obtaining the light emission times in the X and Y directions, respectively, it is preferable to select a longer light emission time from among the light emission times calculated in the X and Y directions and use it for controlling the backlight. Actually, in FIG. 11, the processing up to the conversion table 508 is processed by two systems of X and Y, the magnitude of the light emission time that is the output of the conversion table 508 is compared, and a larger value is input to the low-pass filter 509. This process is preferably performed by one system.

  Further, the deviation coefficient K obtained by Equations 1) and 4) was determined to be 0 when Xave was 0. However, when both the speeds of follow-up vision in the X direction and the Y direction (Xave, Yave) are 0, it is nothing but a standstill, and it is clear that hold blur does not occur even if the light emission time is long. In this case, it is preferable to increase the light emission time in order to reduce flicker. Actually, the value of Xave + Yave is calculated, and if it is equal to or less than the threshold value, it is determined that the camera is stationary, and the light emission time that is the output of the conversion table 508 is preferably set to the maximum value.

(Evaluation of equal acceleration)
Next, an example of evaluating the uniform acceleration will be described.

FIG. 9B shows a graph for explaining the evaluation of the uniform acceleration motion. In FIG. 9B, the vertical axis represents time, and the horizontal axis represents speed in the x direction. T _n-2 , T _n−1 , T _n , and T _{n + 1} indicate the time for each frame. Although the horizontal axis is described as the velocity in the x direction, it is preferable to evaluate the velocity in both the x and y axes. In FIG. 9 (b) 401a, 401b, 401c, 401d each time _{T n-2, T n-} 1, T n, a line of sight that tracks the motion when _{T n + 1} shown schematically. Reference numerals 402a, 402b, 402c, and 402d are moving objects, and are approximately moving at an equal acceleration. The observer cannot adjust the line of sight to the movement of the object for each frame, and follows the average movement of the object and moves the line of sight with equal acceleration. That is, for an object that deviates from the constant acceleration, such as the object 402c, a speed deviation (ΔV) from the line of sight 401c occurs. This difference in speed (ΔV) is blurred on the retina for an observer who follows at a constant acceleration. Due to this blur, a random feeling is generated in the impulse display.

  In this specification, the degree of blurring, that is, the ratio of how much the acceleration of the object is deviated from the line of sight following with constant acceleration is defined as “deviation coefficient: L”. If this deviation coefficient L is a small value, randomness is unlikely to occur. Therefore, the light emission time of the backlight is shortened, and display without hold blur that is close to an impulse-type display is performed.

  As described above, the main target object motion calculation unit 8 outputs a distance indicating how the main target object that the observer can expect to follow is moved per frame as a motion vector (x, y). The object described with reference to FIG. 9A may be replaced with the main object calculated by the main object motion calculation unit 8 in the following description.

When An is the acceleration of the main object in the nth frame and Aave is the average acceleration of the main object (that is, the average acceleration of the line of sight that the observer follows), the deviation coefficient L is defined by Equation 10).
L = | An-Aave | / | Aave |
That is, the deviation coefficient L is the difference between the acceleration at the current time and the average acceleration of the observer's line of sight.
It is the ratio to the average acceleration of the line of sight. If this ratio is 0, the movement of the observer's line of sight and the movement of the main object are the same. Therefore, even if the backlight emission time is shortened as in the impulse display, randomness does not occur. On the other hand, when the deviation coefficient L is 0.5 or more, the distance corresponding to half the speed that changes in one frame period when following is viewed, the main object is displaced, and the feeling of interference starts to become noticeable. Therefore, the light emission time of the backlight is controlled by the value of the deviation coefficient L. Specifically, for a video signal that has a small deviation coefficient L and can be followed, the backlight emission time is controlled to be short and hold blur is reduced. On the other hand, in a video signal in which randomness may occur when the deviation coefficient L is large and followed, the backlight emission time is controlled to be long to suppress the occurrence of randomness.

でもとめることができる。 Since the motion vector output from the main object motion calculation unit 8 is the amount of movement per frame time, that is, the speed, the acceleration at the current time can be obtained from the difference in the output of the main object motion calculation unit 8. . Equation 10) is
L = | {X _n -X _n-1 } -Aave | / | Aave |
It becomes.
Average acceleration is

But you can stop.

By substituting Equation 12) into Equation 11), the deviation coefficient L is calculated, and the backlight emission time is determined by the magnitude of the deviation coefficient L. The start time of Equation 12) may be calculated from the past, for example, when the scene changes.
In the video signal of the main object moving at a constant speed, Aave is 0, and the denominators of Equations 10) and 11) are 0. Since the observer can follow when the main object is moving at a constant velocity, in this case, the calculation of Expressions 10) and 11) is not performed, and a small value (for example, L = 0) is used as the value of L. ) Is output.

These calculations are easy to implement when processed by software, but there is a concern about an increase in hardware when implemented as hardware. Therefore, when realized by hardware, the calculation of Equation 12) may be performed by calculating the average acceleration Aave of the line of sight by calculation weighted according to the current time (cyclic filter). This can reduce the amount of hardware, and
A value close to the acceleration of the actual observer's tracking vision can be obtained. When the acceleration of the tracking vision at the time n frame is Aave _n , the equation for calculating Aave _n is as follows:
Aave _n = S1 ・ (X _n-1 -X _n-2 ) + S2 ・ Aave _n-1・ ・ ・ ・ Equation 13)
However,
S1 + S2 = 1 ・ ・ ・ ・ Formula 14)
It becomes. By S1 and S2, the weight of the acceleration of the line of sight one frame before and the acceleration of the main object one frame before can be changed. Usually, S1 and S2 should be set so that S2 is larger than S1.

Furthermore, in order to simply calculate the gaze acceleration, it is preferable to perform the following calculation. The line-of-sight acceleration Aave _n in the frame at time n may be obtained from an average value of accelerations of the main objects in the immediately preceding two frames. That is,
Aave _n = {(X _n-2 -X _n-3 ) + (X _n-1 -X _n-2 )} / 2 (Equation 15)
Ask for.

Furthermore, in order to calculate the acceleration of tracking vision more simply, the acceleration Aave _n of tracking vision in the frame at time n may be obtained simply from the acceleration of the main object in the immediately preceding two frames. That is,
Aave _n = (X _n-1 -X _n-2 ) (16)
Ask for.
The calculation of the line-of-sight acceleration obtained by Equation 15) and Equation 16) has a great advantage that the amount of calculation in hardware or software can be reduced, although the error is somewhat larger.

  The deviation coefficient L is calculated by substituting the expression 12), the expression 13), the expression 15), or the expression 16) into the expression 11), and the light emission time of the backlight is controlled by the magnitude of the deviation coefficient L. If the value of the deviation coefficient L is large, a deviation between the line of sight and the main object occurs. Therefore, the light emission time is long. If the value of the deviation coefficient L is small, the deviation between the line of sight and the main object is small. Set and reduce hold blur as much as possible. FIGS. 12A, 12B, and 12C show an example of the relationship between the preferable backlight emission time and the deviation coefficient L. FIG. In any conversion method, when a uniform acceleration motion is detected (the deviation coefficient L is zero or sufficiently small), the light emission time becomes the minimum value Tmin, and a movement that is not a uniform acceleration movement is detected (the deviation coefficient L is somewhat large). ), The light emission time becomes the maximum value Tmax. Between Tmin and Tmax, the emission time monotonously increases stepwise or continuously in accordance with the amount of deviation from the constant velocity motion (the value of the deviation coefficient L). In the conversion table of FIG. 12A, the first light emission time Tmax is selected if the deviation coefficient L is larger than a predetermined threshold (for example, 0.5), and the short second light emission if the deviation coefficient K is equal to or less than the threshold. The time Tmin is selected. Although this method can also suppress the generation of random feeling, there is a risk that an uncomfortable feeling may occur when switching the light emission time. Therefore, as shown in FIGS. 12B and 12C, a method in which the light emission time is continuously changed with respect to the amount of deviation from the uniform acceleration motion is more preferable. FIGS. 12A, 12B, and 12C are examples. For example, the light emission time may be increased in multiple steps from Tmin to Tmax.

(Light emission time calculation unit that evaluates equal acceleration)
FIG. 13 shows a configuration example of a light emission time calculation unit that evaluates equal acceleration. In FIG. 13, the description of the same constituent blocks as those in FIG. 11 is omitted. In FIG. 13, reference numeral 512 denotes a follow-up visual acceleration calculation unit, which calculates the line-of-sight acceleration (Aave) by any one of the above-described equations 12), 13), 15), and 16). Reference numeral 513 denotes an L calculation unit that calculates a deviation coefficient L from the input gaze acceleration (Aave) and a motion vector. A conversion table 508 stores the characteristics shown in FIGS. 12A, 12B, and 12C in a look-up table format, and outputs a light emission time with respect to the deviation coefficient L. The configurations and processing contents of the low-pass filter 509, the timing generation unit 504, and the emission intensity calculation unit 505 are the same as those in FIG.

  In order to make the explanation easy to understand, only the deviation coefficient in the X direction has been described, but it is preferable to perform the same evaluation in the Y direction. When evaluating in the X direction and the Y direction, it is preferable to shorten the light emission time only when the deviation coefficient in both directions is zero or sufficiently small. For example, after obtaining the light emission times in the X and Y directions, respectively, it is preferable to select a longer light emission time from among the light emission times calculated in the X and Y directions and use it for controlling the backlight. Actually, in FIG. 13, the conversion table 508 is processed by two systems of X and Y, the magnitude of the light emission time that is the output of the conversion table 508 is compared, and a larger value is input to the low-pass filter 509. This process is preferably performed by one system.

  As described above, the method for determining the light emission time of the backlight 2 by the evaluation of the constant velocity and the evaluation of the constant acceleration has been described. These methods for determining the light emission time are effective even if performed alone. Even if the two methods are combined, a good effect can be obtained. When combining both methods, it is preferable to calculate the light emission time independently and control the backlight 2 using the longer light emission time among the calculated light emission times. In addition, for the evaluation of constant velocity and the evaluation of constant acceleration, the effect of controlling the backlight emission time by the constant velocity evaluation is greater than the effect of controlling the backlight emission time by the constant acceleration evaluation. It is also preferable to perform only the evaluation.

(Advantages of the first embodiment)
According to the first embodiment, the ease of follow-up of the main object is evaluated based on the video signal, and in the video signal with easy follow-up, the backlight emission time is shortened to reduce the impulse display. By performing such display, it is possible to realize high-quality moving image reproduction with less hold blur. On the other hand, in a video signal that is difficult to follow, it is possible to prevent the occurrence of a sense of interference called random feeling by increasing the backlight emission time and generating hold blur. In addition, for a still image, it is possible to follow-up, but since the light emission time is set long, the occurrence of flicker can be suppressed.

  In this embodiment, since the light emission intensity is controlled according to the length of the light emission time so that the luminance is constant regardless of the length of the light emission time, the variation in luminance in the time direction due to the fluctuation of the light emission time. Can be reduced. Further, in the present embodiment, the light emission start timing and the light emission end timing are controlled so that the time center of gravity does not change from a predetermined position regardless of the length of the light emission time. Thereby, the display interval (light emission interval) of the frames can be apparently made uniform, and the movement of the object can be prevented from becoming unnatural or blurred.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. When the imaging time of the video camera is long (when the shutter speed is slow), blurring during imaging occurs as described above. When displaying a video signal including blur at the time of imaging, the blur at the time of imaging is not improved even if the light emission time of the backlight is shortened. In the second embodiment, a method for improving blurring during imaging is proposed.

Similarly to the image display device of the first embodiment, the image display device of the second embodiment also evaluates the quality of video motion (ease of following vision) and determines the backlight emission time. That is, for a video signal in which the movement of the main object is easy to follow, the light emission time is controlled to be short and the hold blur is reduced. In addition, for a video signal in which the movement of the main object is difficult to follow, the light emission time is controlled to be long to prevent the occurrence of randomness. In the second embodiment, the video signal is further subjected to high-frequency emphasis processing with respect to the direction of the motion vector output from the motion detector 4. As a result, blurring at the time of imaging of a moving object is improved, so that both hold blur and blurring at the time of imaging can be reduced.

  FIG. 2 shows a block diagram of the main part of the drive circuit according to the second embodiment of the present invention. In FIG. 2, the description of the same numbers as those in FIG. 1 of the first embodiment is omitted. In FIG. 2, 11 is a motion direction high-frequency emphasis filter (blur reduction unit), 12 is a video control unit, 13 is a switch, and the other parts perform the same operation as the configuration of FIG. 1 of the first embodiment.

  The motion detection unit 4 calculates a local motion vector for each motion vector detection unit area. The local motion vector is input to the main object motion calculation unit 8. Similar to the first embodiment, the main object motion calculation unit 8 calculates a representative motion vector (motion vector of the main object) from the local motion vector and outputs it to the light emission time calculation unit 5. As described above, the light emission time calculation unit 5 controls to shorten the light emission time of the video signal in which the motion of constant velocity or constant acceleration is detected. The video control unit 12 controls the switch 13 according to the light emission time calculated by the light emission time calculation unit 5, and switches to the signal V2 when the light emission time is short and to the signal V1 when the light emission time is long. The video signal input to the input terminal 3 is delayed for a necessary time by the frame delay unit 7. The video signal input to the input terminal 3 is input to the motion direction high-frequency emphasis filter 11 and subjected to high-frequency emphasis processing regarding the motion direction based on the motion vector output from the motion detection unit 4. This filtering process reduces blurring during imaging. The processing of the motion direction high-frequency emphasis filter 11 is preferably performed by controlling the characteristics of the filter according to the magnitude and direction of the motion vector. In other words, it is preferable to select a spatial filter corresponding to the direction of the motion vector and change the way of raising the spatial frequency of the high frequency of the filter according to the magnitude of the motion vector. When the motion vector is large, blurring at the time of imaging is large, and thus the motion direction high-frequency emphasis filter 11 is preferably enhanced from a lower frequency. The motion direction high-frequency emphasis filter 11 preferably has a delay time equivalent to that of the frame delay unit 7. In the present embodiment, the filter to be applied is changed according to the direction of movement of the object, but the same filter (filter having no direction dependency) may be used regardless of the direction of movement.

  The switch 13 switches the signal V1 and the signal V2 according to the backlight emission time. When an easy movement of following vision is detected (in the case of a short light emission time Tmin), a signal V2 in which blurring during imaging is canceled is selected and input to the liquid crystal panel 1. Then, the display element (liquid crystal) is driven based on the signal V2, whereby a display without blur is obtained. On the other hand, when no motion is detected or when a motion difficult to follow is detected (in the case of a long light emission time Tmax), the signal V1 is selected and input to the liquid crystal panel 1. By driving the display element based on the signal V1, a display faithful to the original (input video) can be obtained.

  Note that when the signals V1 and V2 are switched, the video image may become discontinuous and give the observer a sense of discomfort. Therefore, it is preferable to continuously change the signals V1 and V2 from the signals V1 to V2 (or V2 to V1) instead of switching the signals V1 and V2 alternatively. For example, as shown in FIGS. 14A, 14B, and 14C, weights corresponding to the light emission times are set for the signals V1 and V2, and the signals V1 and V2 are weighted and added and output. At this time, when the sum of the weights of the signals V1 and V2 is 1, it is preferable because the luminance does not change.

  The signals V1 and V2 are preferably data having a value proportional to the luminance. When a video signal that has been subjected to gamma conversion is input, it is preferable to perform the above processing after performing inverse gamma conversion on the input video signal to convert it to data proportional to luminance.

According to the second embodiment of the present invention described above, as with the first embodiment, high-quality video playback with less hold blur can be realized by shortening the light emission time for video signals that are easy to follow. In video signals that are difficult to follow, it is possible to prevent the occurrence of a disturbing feeling called random feeling. In addition, when the light emission time is short, the liquid crystal panel is driven using the signal V2 with reduced blurring or the synthesized signal of the original signal V1 and the signal V2, so that the video signal includes blurring during imaging. However, it is possible to display high-quality moving images with less blur. In addition, for a still image, it is possible to follow-up, but since the light emission time is set long, the occurrence of flicker can be suppressed.

<Third Embodiment>
In the third embodiment, an example is shown in which a video signal is displayed when the imaging time of a video camera that images an object is short (when a high-speed electronic shutter is used in combination). When the imaging time of the video camera is short, no blur occurs during imaging. However, when such a blur-free image is displayed on a normal liquid crystal display device (with a long backlight emission time), the movement of the object may appear jerky and awkward. In the embodiment of the present invention, in the case of a video signal that is difficult to follow, such a jerky movement may appear because the light emission time of the backlight is lengthened. The third embodiment proposes a method for solving such a problem.

  Similarly to the image display apparatus of the first embodiment, the image display apparatus of the third embodiment also determines the backlight emission time by evaluating the quality of motion of the video signal (ease of follow-up viewing). That is, for a video signal in which the movement of the main object is difficult to follow, the backlight emission time is lengthened to generate hold blur. In the third embodiment, the video signal is further subjected to low-pass filter processing with respect to the direction of the motion vector output from the motion detection unit 4. As a result, it is possible to prevent a moving object from appearing awkward when a long light emission time is set.

  FIG. 3 shows a block diagram of the main part of the drive circuit according to the third embodiment of the present invention. In FIG. 3, the description of the same numbers as those in FIG. 1 of the first embodiment is omitted. In FIG. 3, 12 is a video control unit, 13 is a switch, 14 is a motion direction low-pass filter (blur addition unit), and the other parts perform the same operation as the configuration of FIG. 1 of the first embodiment.

  The motion detection unit 4 calculates a local motion vector for each motion vector detection unit area. The local motion vector is input to the main object motion calculation unit 8. Similar to the first embodiment, the main object motion calculation unit 8 calculates a representative motion vector (motion vector of the main object) from the local motion vector and outputs it to the light emission time calculation unit 5. As described above, the light emission time calculation unit 5 controls to shorten the light emission time of the video signal in which the motion of constant velocity or constant acceleration is detected. The video control unit 12 controls the switch 13 according to the light emission time calculated by the light emission time calculation unit 5, and switches to the signal V1 when the light emission time is short and to the signal V3 when the light emission time is long. The video signal input to the input terminal 3 is delayed for a necessary time by the frame delay unit 7. Also, the video signal input to the input terminal 3 is input to the motion direction low-pass filter 14, and motion direction blur is added by the low-pass filter processing related to the motion direction based on the motion vector output from the motion detection unit 4. . The processing of the motion direction low-pass filter 14 is preferably performed by controlling the filter characteristics according to the magnitude and direction of the motion vector. That is, it is preferable to select a spatial filter corresponding to the direction of the motion vector and change the way of lowering the spatial frequency in the high frequency according to the magnitude of the motion vector. When the motion vector is large, blurring at the time of imaging should be large. Therefore, the motion direction low-pass filter 14 may attenuate a high-frequency signal from a lower frequency. The moving direction low-pass filter 14 preferably has a delay time equivalent to that of the frame delay unit 7. In the present embodiment, the filter to be applied is changed according to the direction of movement of the object, but the same filter (filter having no direction dependency) may be used regardless of the direction of movement.

The switch 13 switches the signals V1 and V3 according to the backlight emission time. When an easy movement of following vision is detected (in the case of a short light emission time Tmin), the signal V1 is selected and input to the liquid crystal panel 1. When the display element is driven by the signal V1, a display with less blur can be obtained. When no movement is detected or a movement that is difficult to follow is detected (in the case of a long light emission time Tmax), the movement direction low-pass filter 14 selects the signal V3 to which the movement direction blur is added, and the liquid crystal panel 1 is input. When the display element is driven by the signal V3, a display in which a blur at the time of imaging is added to a moving object is obtained. In order to eliminate the uncomfortable feeling at the time of switching between the signals V1 and V3, a signal obtained by synthesizing the signals V1 and V3 with a weight corresponding to the light emission time is output in the same manner as described in FIG. 14 of the second embodiment. Is preferred. The signals V1 and V3 are preferably data having a value proportional to the luminance.

  According to the third embodiment of the present invention described above, as with the first embodiment, high-quality video playback with less hold blur can be realized by shortening the light emission time for video signals that are easy to follow. In video signals that are difficult to follow, it is possible to prevent the occurrence of a disturbing feeling called random feeling. When the light emission time is long, the signal V3 to which blur is added or the combined signal of the original signal V1 and the signal V3 is used for driving the liquid crystal panel. Therefore, it is possible to suppress the occurrence of awkward and awkward movements seen in a video signal imaged in a short imaging time.

<Other embodiments>
In the above embodiment, an example of an image display device using a transmissive direct-view AM-LCD has been described. However, similar effects can be expected even with a transmissive projection AM-LCD or a reflective projection AM-LCD.
In the above-described embodiment, the example in which the light emission intensity is controlled so that the luminance (feeling of brightness) does not change depending on the length of the light emission time has been described. However, it is also preferable to combine a technique for changing the light emission time of the backlight in accordance with the motion of the image with a technique for controlling the light emission intensity of the block backlight by an image signal developed in recent years.

  1: liquid crystal panel, 2: backlight, 4: motion detector, 5: light emission time calculator, 6: backlight controller, 8: main object motion calculator

Claims (10)

LCD panel,
With backlight,
A control unit for controlling light emission of the backlight;
With
The controller is
Analyzing the input video signal to detect the movement of the video,
The light emission time of the backlight is such that the light emission time is short when the detected motion is a constant velocity or constant acceleration motion, and the light emission time is long when the detected motion is not a constant velocity or constant acceleration motion. An image display device characterized by setting. The controller is
Calculate the difference between the detected motion and the constant velocity or constant acceleration,
If the deviation is greater than the threshold, set the longest first emission time,
When there is no deviation, set the shortest second flash time,
2. The image display device according to claim 1, wherein between the first light emission time and the second light emission time, the light emission time is increased stepwise or continuously in accordance with the magnitude of the shift. . The controller is
The image display device according to claim 1, wherein the light emission intensity of the backlight is changed according to the set light emission time so that the light emission intensity increases as the light emission time decreases. The controller is
The timing of the light emission start and light emission end of the backlight is set so that the time centroid of the light emission time weighted by the light emission intensity does not change between frames. The image display device according to item. The controller is
Analyzing the input video signal and calculating local motion vectors in multiple areas on the video,
Calculate a representative motion vector of the video from local motion vectors of the plurality of areas,
5. The method according to claim 1, wherein the calculated representative motion vector is used to evaluate whether or not the motion of the video is a constant velocity or a constant acceleration motion. Image display device. The controller is
By averaging the local motion vectors of the plurality of areas, or by averaging vectors having a magnitude greater than or equal to a threshold among the local motion vectors of the plurality of areas, the representative motion vector is The image display device according to claim 5, wherein the image display device is calculated. The controller is
From the plurality of areas, a plurality of adjacent areas having the same or similar local motion vector and having a total area equal to or larger than a threshold value are selected, and the local areas of the selected plurality of areas are selected. The image display device according to claim 5, wherein the representative motion vector is calculated by averaging various motion vectors. It further has a blur reduction unit that reduces blur on the video signal,
When a short light emission time is set, the liquid crystal panel is driven using a video signal with reduced blur, or a video signal in which an input video signal and a video signal with reduced blur are combined. The image display device according to claim 1, wherein the image display device is an image display device. A blur adding unit for adding blur to the video signal;
When a long light emission time is set, the liquid crystal panel is driven using a video signal to which blur is added or a video signal obtained by combining an input video signal and a video signal to which blur is added. The image display device according to claim 1, wherein the image display device is an image display device. A control method for an image display device comprising a liquid crystal panel and a backlight,
Analyzing the input video signal and detecting the motion of the video;
The light emission time of the backlight is such that the light emission time is short when the detected motion is a constant velocity or constant acceleration motion, and the light emission time is long when the detected motion is not a constant velocity or constant acceleration motion. Steps to set
A control method for an image display device, comprising:

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