Patent Publication Number: US-8531383-B2

Title: Display device with luminance variation control unit

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese application JP2009-101137 filed on Apr. 17, 2009, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a display device, and more particularly, to a display device suited to displaying a moving image. 
     2. Description of the Related Art 
     Heretofore, a backlight using a cold cathode fluorescent lamp (CCFL) has been mainly used for a backlight of a liquid crystal display device. However, in recent years, further research has been conducted on a backlight using a light emitting diode (LED) device. JP 2001-142409 A (hereinafter, referred to as Patent Document 1) discloses a representative example of such a backlight using an LED device. 
     Patent Document 1 discloses the following method. At least one LED, which serves as a light source for emitting illuminating light irradiating a liquid crystal panel, is arranged for each of a plurality of divided areas. The LED is controlled in the unit of divided areas so as to irradiate at least only an area requiring the illuminating light, in accordance with an image to be displayed. An area which does not require the illuminating light is not irradiated basically. In this manner, the power consumption required for illumination may be reduced. 
     According to the technology disclosed in Patent Document 1, the LED devices vary in light emission luminance for each divided display area, and the variation in light emission luminance results in flicker. One of the representative exemplary methods to solve the problem is disclosed in JP 2008-299145 A (hereinafter, referred to as Patent Document 2). 
     Patent Document 2 relates to a technology of controlling LEDs. According to the technology, it is determined whether an input video is a still image or a moving image, and in the case where the input video is a still image, the LED devices are constantly turned on, to thereby avoid flicker. 
     SUMMARY OF THE INVENTION 
     The technology disclosed in Patent Document 2 aims to avoid flicker in a still image, and hence there may be expected no effect therefrom of avoiding flicker in a moving image. 
     Under the circumstances, the inventors of the present invention have made a study on a method of controlling LEDs so as to avoid flicker even in displaying a moving image. In the course of the study, the inventors have discovered that flicker becomes more noticeable in a display where an object in the video moves at lower velocity (for example, a display in which the foreground scrolls at lower velocity), while luminance substantially reduces in a display in which an object in the video moves at higher velocity (for example, a display in which the foreground scrolls at higher velocity). 
     It is an object of the present invention to provide a display device capable of producing an image of excellent quality with reduced flicker and little reduction in luminance, the display device including a backlight having a plurality of light sources (for example, a plurality of LED devices) arranged two-dimensionally, each of which may be individually modulated in luminance. 
     The display device according to the present invention, which includes the backlight having the plurality of light sources (for example, the plurality of LED devices) arranged two-dimensionally, and is capable of modulating the luminance for each light source, further includes means for detecting a moving velocity of an object in a video (for example, moving velocity of a foreground), and means for automatically controlling luminance variations of the light sources for each light source, in accordance with the moving velocity of the object in the video. 
     The present invention may thus provide the display device, which includes the backlight having the plurality of light sources (for example, the plurality of LED devices) arranged two-dimensionally, each of which may be individually modulated in luminance, and which is capable of producing an image of excellent quality with reduced flicker and little reduction in luminance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a diagram illustrating a display device according to a first embodiment of the present invention; 
         FIG. 2  is a diagram for illustrating a moving velocity of an object in a video according to the first embodiment; 
         FIG. 3A  is a graph illustrating a relation between the moving velocity of an object in a video and a luminance variation of a backlight LED according to the first embodiment; 
         FIG. 3B  is a graph illustrating a relation between the moving velocity of an object in a video and the luminance variation of the backlight LED according to the first embodiment; 
         FIG. 4A  is a diagram for illustrating an LED lighting pattern in a backlight according to a second embodiment of the present invention; 
         FIG. 4B  is a diagram for illustrating another LED lighting pattern in the backlight according to the second embodiment; 
         FIG. 4C  is a diagram for illustrating further another LED lighting pattern in the backlight according to the second embodiment; 
         FIG. 5  is a diagram illustrating a display device according to the second embodiment; 
         FIG. 6A  is a diagram for illustrating an operating principle according to a third embodiment of the present invention; 
         FIG. 6B  is a diagram for illustrating the operating principle according to the third embodiment; 
         FIG. 7  is a diagram illustrating a display device according to the third embodiment; 
         FIG. 8A  is a diagram illustrating a first configuration example of a moving velocity detection unit according to the third embodiment; 
         FIG. 8B  is a diagram illustrating the first configuration example of the moving velocity detection unit according to the third embodiment; and 
         FIG. 9  is diagram illustrating a second configuration example of the moving velocity detection unit according to the third embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Subsequently, examples of a configuration of a display device according to the present invention are described. 
     [First Embodiment] 
     A first embodiment of the present invention is described with reference to  FIGS. 1 to 3 . 
     In the display device according to the first embodiment, it is detected whether a display in which an object in a video corresponding to an input video moves at higher velocity (for example, a display in which the foreground moves at higher velocity) is provided or a display in which the object moves at lower velocity (for example, a display in which the foreground moves at lower velocity) is provided, and the luminance variations in one frame of the LED devices forming a backlight is automatically controlled for each LED device according to the detection result. 
       FIG. 1  is a diagram illustrating an example of the liquid crystal display device according to the first embodiment. 
     A display panel  100  includes, for example, a liquid crystal display panel in which display elements are arranged as pixels (display units) in a matrix of S columns and T rows (S and T each are an integer equal to or larger than 2). In the display panel  100 , each of the pixels are applied with a gradation voltage so that the pixels are individually controlled in transmittance (modulation degree of light passing through the liquid crystal). 
     A backlight  101  serves a function of illuminating the display panel  100 , and has a plurality of light sources. Each of the light sources may employ, for example, a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent lamp (HCFL), or a light emitting diode (LED) device. In the backlight  101 , a plurality of illumination areas are arranged in P columns and Q rows, and the luminance and turn-on/turn-off timing of the light sources may be controlled for each of the illumination areas (P and Q each are an integer equal to or larger than 2.  FIG. 1  illustrates an exemplary case where LEDs are used for the backlight  101  and P=9 and Q=5). 
     In the display device, a display luminance to be finally obtained for each pixel may be determined by multiplying a transmittance of each pixel of the display panel  100  with a luminance of each area of the backlight  101  corresponding to the pixel. 
     The gradation voltage to be applied to the display panel  100  may be controlled by blocks  102  to  107  described below. 
     The display data selection unit  102  is a block for sequentially selecting input display data for each area of the display panel  100 , and transferring the display data to a display data expansion unit  104 , a maximum value selection unit  111 , and display data use frame memory  108 , which are described later. 
     An expansion coefficient calculation unit  103  is a block for calculating an expansion coefficient e (e is a value equal to or larger than 1) for use in expanding display data, in accordance with an LED light emission luminance data value transferred from a light emission luminance calculation unit  113  to be described later, and transferring the expansion coefficient e to the display data expansion unit  104  to be described later. 
     The display data expansion unit  104  is a block for multiplying the expansion coefficient e transferred from the expansion coefficient calculation unit  103  with display data transferred from the display data selection unit  102 , and transferring the result to a source driver  106  to be described later. 
     With the use of the expansion coefficient calculation unit  103  and the data display expansion unit  104 , the power consumption and flicker may be reduced. 
     For example, a case is assumed where a certain luminance B 1  is displayed under a reference state where the backlight  101  has a luminance B 11  and a display panel has a transmittance Tr 1 . In this case, a relation of B 1 =B 11 ×Tr 1  is established. Meanwhile, the expansion coefficient calculation unit  103  and the display data expansion unit  104  reduce a luminance of the backlight to 1/e of the reference state while expanding the display data so that the transmittance of the display panel is increased e times larger than usual. The luminance observed in this case is obtained as B 2 =(B 11 ×1/e)×(Tr 1 ×e). In other words, when the transmittance Tr 1  is expanded, an observation luminance obtained with a smaller backlight luminance B 12  becomes equal to the observation luminance obtained with a backlight luminance B 11  in the reference state (that is, B 1 =B 2  is attained). 
     Further, even if the luminance of the backlight varies, the observation luminance is maintained, which may alleviate flicker resulting from a variation in the backlight luminance. 
     A timing signal generation unit  105  is a block for generating a timing signal to be used by the source driver  106  and a gate driver  107 , and transferring the timing signal to the source driver  106  and the gate driver  107 . 
     The source driver  106  is a block for selecting, according to the timing signal transferred from the timing signal generation unit  105 , a gradation voltage appropriate to display data which has been subjected to expansion calculation and transferred from the display data expansion unit  104 , and applying the gradation voltage to the pixels of the display panel  100  in accordance with the timing signal transferred from the gate driver  107 . 
     The gate driver  107  is a block for generating, in accordance with the timing signal transferred from the timing signal generation unit  105 , a timing signal indicating a timing at which the source driver  106  applies the gradation voltage to the pixels of the display panel  100 . 
     The LED devices of the backlight  101  may be controlled in light emission luminance by blocks  108  to  115  described below. 
     The display data use frame memory  108  is a block for holding display data for the past N frames transferred from the display data selection unit  102 , and transferring the display data to a moving velocity detection unit VD 1   109  to be described later. 
     The moving velocity detection unit VD 1   109  is a block for detecting a moving velocity (for example, a velocity at which the foreground scrolls) by calculating a luminance histogram or a motion vector based on the display data transferred from the display data use frame memory  108 , and transferring the moving velocity (Mv) to a light emission luminance variation LUT  110  to be described later. Specifically, the moving velocity detection unit VD 1   109  outputs the moving velocity (Mv)=1 for a display  200  illustrated in  FIG. 2  where a bright foreground moves at higher velocity in a dark background, while outputs the moving velocity (Mv)=0 for a display  201  illustrated in  FIG. 2  where a bright foreground moves at lower velocity in a dark background. 
     It should be noted that, in the first embodiment, the method of detecting a moving velocity employs, for example, a luminance histogram or a motion vector. However, any other method may also be employed as long as the method is capable of detecting a moving velocity. Further, the moving velocity is detected at two stages of high velocity and low velocity, which may also be detected at H stages (H is equal to or larger than 3). 
     The light emission luminance variation LUT  110  is a block provided with a look-up table (LUT) storing a luminance variation per one frame when the light emission luminance of LED devices forming the backlight  101  increases or decreases, for selecting a luminance variation (A) from the look-up table (LUT) in accordance with the moving velocity (Mv) transferred from the moving velocity detection unit VD 1   109 , and transferring the luminance variation (A) to a light emission luminance calculation unit  113  to be described later. 
     For example, when a moving velocity (Mv) is 1, a large luminance variation is selected. In this case, the light emission luminance  300  of the LED devices forming the backlight  101  precipitously increases to reach a target luminance as illustrated in  FIG. 3A . As illustrated in  FIG. 3A , the luminance  300  of the LED devices changes from 0% to 100% in one frame period, and therefore the luminance variation per one frame is 100%. On the other hand, when the moving velocity (Mv) is 0, a small luminance variation is selected. In this case, the light emission luminance  301  of the LED devices forming the backlight  101  gradually reaches a target value as illustrated in  FIG. 3B . As illustrated in  FIG. 3B , the luminance  301  of the LED devices changes from 0% to 100% over three frame periods, and therefore the luminance variation per one frame is 33.3%. 
     It should be noted that in the first embodiment, the luminance variation is defined by two stages including cases of a sudden change and a gradual change. However, the luminance variation may be defined by L stages (L is equal to or larger than 3). 
     Further, values stored in the look-up table (LUT) may be changed by a register adjustable from outside. Further, the number of smaller values stored in the look-up table (LUT) may preferably be larger than the number of larger values stored therein. With this configuration, in the case of a low velocity movement display, a luminance variation (A) may be selected with higher accuracy, with the result that flicker in the low velocity movement display may be avoided with more ease. 
     The maximum value selection unit  111  is a block for selecting a maximum value from the display data transferred from the display data selection unit  102 , and transferring the maximum value to a target light emission luminance LUT  112  to be described later. 
     The target light emission luminance LUT  112  is a block provided with a look-up table storing luminance values of light emitting devices, for selecting a target light emission luminance from the look-up table in accordance with the data transferred from the maximum value selection unit  111 , and transferring the target light emission luminance to a light emission luminance calculation unit  113  to be described later. 
     The light emission luminance calculation unit  113  is a block for comparing the target light emission luminance transferred from the target light emission luminance LUT  112  with a previous frame light emission luminance transferred from a light emission luminance use frame memory  114  to be described later, calculating, based on the comparison result, a light emission luminance, and transferring the light emission luminance to the expansion coefficient e calculation unit  103 , to the light emission luminance use frame memory  114  to be described later, and to a light emitting device selection unit  115  to be described later. A specific process of calculating the light emission luminance is as follows. When the target light emission luminance value is larger than the light emission luminance value of the previous frame, the luminance variation (A) transferred from the light emission luminance variation LUT  110  is added to the light emission luminance value of the previous frame. When the target light emission luminance value is smaller than the light emission luminance value of the previous frame, the luminance variation (A) is subtracted from the light emission luminance value of the previous frame. In the manner as described above, the light emission luminance calculation unit  113  controls the luminance variation for each light emitting device in accordance with the result detected by the moving velocity detection unit VD 1   109 . 
     The light emission luminance use frame memory  114  is a block for transferring the luminance data value transferred from the light emission luminance calculation unit  113 , to the light emission luminance calculation unit  113 , after holding the luminance data value for one frame period. 
     The light emitting device selection unit  115  is a block for applying a voltage corresponding to the light emission luminance, to the light emitting devices forming the backlight  101 , under the control of the light emission luminance calculation unit  113 . 
     In the above, the first embodiment has been described in detail. The display device according to the first embodiment includes the backlight  101  having a plurality of light sources and is capable of controlling a luminance for each light source, and the display device may further include the moving velocity detection unit VD 1   109  for detecting a moving velocity of an object in a video and a luminance variation control unit (corresponding to the light emission luminance variation LUT  110  and the light emission luminance calculation unit  113  of  FIG. 1 ) for controlling a luminance variation of each of the light sources in accordance with the result detected by the moving velocity detection unit VD 1   109 . The luminance variation control unit sets, for example, the luminance variation to a first value when the moving velocity of an object in a video is high, while sets the luminance variation to a second value when the moving velocity of an object in a video is low. Here, the first value is larger than the second value. In the examples of  FIGS. 3A and 3B , the first value is 100% and the second value is 33.3%. Further, when the second value may be adjustable in smaller units as compared with the first value, the luminance variation in a low velocity movement display may be selected with higher accuracy, with the result that flicker in a low velocity movement display may be avoided with more ease. 
     According to the first embodiment of the present invention, a moving velocity of an object in a video may be detected, and luminance variations of the LED devices may be adjusted in accordance with the moving velocity, to thereby obtain a display in excellent quality with reduced flicker and little reduction in luminance in displaying the video. 
     Specifically, in a case of a display in which an object in a video moves at lower velocity (for example, a display in which the foreground moves at lower velocity), the luminance variations in the LED devices may be controlled to be small so as to gradually increase or decrease the luminance, to thereby obtain a display in excellent quality with reduced flicker. 
     On the other hand, in a case of a display in which an object in a video moves at higher velocity (for example, a display in which the foreground moves at higher velocity), the luminance variations in the LED devices may be controlled to be large so as to precipitously increase or decrease the luminance, to thereby obtain a display in excellent quality with little reduction in luminance. 
     [Second Embodiment] 
     A second embodiment of the present invention is described with reference to  FIGS. 4 and 5 . In the first embodiment, when a displayed object in a video moves at lower velocity, the luminance variation of the LED backlight is controlled to be small, which has a negative side that it takes time for the LED backlight to reach a target luminance, with the result that the display luminance reduces until the target luminance is reached. In order to work around the problem, in a display device according to the second embodiment, a move destination of a display object is estimated, and the LED luminance in the area of the move destination is increased in advance to around the target value. In other words, as compared with the display device according to the first embodiment in which only an LED  400  for irradiating a foreground is turned on as illustrated in  FIG. 4A , in the display device according to the second embodiment, the luminance of an LED  401  in the moving direction of the foreground is increased in advance as illustrated in  FIG. 4B .  FIG. 4B  illustrates an example where the LED  400  is turned on at 100% and the LED  401  is turned on at X %. X is defined as 0&lt;X&lt;100. Alternatively, as illustrated in  FIG. 4C , LEDs  402  surrounding the LED  400  may all be increased in luminance so as to cover any moving direction to the right, left, upward, or downward.  FIG. 4C  illustrates an example where the LED  400  is turned on at 100% while the LEDs  401  and  402  are turned on at X %. 
       FIG. 5  is a diagram illustrating an example of the display device according to the second embodiment. As illustrated in  FIG. 5 , the display device includes the constituent elements  100  to  115  similarly to the first embodiment. The display device according to the second embodiment further includes an object moving direction detection unit  500  and the move destination area irradiation computing unit  501 . 
     The object moving direction detection unit  500  is a block for detecting, based on data for a plurality of frames input from the display data use frame memory  108 , a move destination direction, and transferring a signal indicating any one of upward, downward, rightward, leftward, and diagonal directions, to the move destination area irradiation computing unit  501 . The moving direction may be detected by using an optical flow or the like which is generally employed in a video processing technology. However, any other method may be employed, without being limited to the method, as long as the method is capable of detecting or estimating the moving direction. 
     The move destination area irradiation computing unit  501  is a block for performing a computation on the data transferred from the maximum value selection unit  111 , based on the signal from the object moving direction detection unit  500 , so as to irradiate the moving direction of the moving object, and transferring the data obtained from the computation to the target light emission luminance LUT  112 . 
     In the case where the LEDs of the adjacent areas are all increased in luminance beforehand as illustrated  FIG. 4C , the object moving direction detection unit  500  may be omitted. The move destination area irradiation computing unit  501  may perform a computation so as to increase in advance the luminances of the LEDs of all the adjacent areas. 
     In the above, the second embodiment has been described in detail. The display device according to the second embodiment may include, in addition to the configuration of the first embodiment, an adjacent area irradiation computing unit (corresponding to the move destination area irradiation computing unit  501  of  FIG. 5 ) for computing luminances of the light sources in at least one or all areas adjacent in upward, downward, rightward, leftward, and diagonal directions to the display area of an object in a video, so that the at least one or all adjacent areas may be irradiated in advance, in which a luminance variation control unit (corresponding to the light emission luminance calculation unit  113  of  FIG. 5 ) controls, as well as controlling the luminance variation of the light sources of the display area in accordance with the result detected in the moving velocity detection unit VD 1   109 , the luminances of the light sources in the adjacent areas in accordance with the result of a computation performed by the adjacent area irradiation computing unit. Further, the display device according to the second embodiment further includes the object moving direction detection unit  500  for detecting a moving direction of an object in a video, in which the adjacent area irradiation computing unit (move destination area irradiation computing unit  501 ) may compute the luminance of a light source in the adjacent area that is the move destination of an object in a video, so that the adjacent area may be irradiated in advance. 
     According to the second embodiment of the present invention, the negative side of the first embodiment may be alleviated. Specifically, in the first embodiment, it takes time for the LED backlight to reach a target luminance because the luminance variation of the LED backlight is controlled to be small, with the result that the display luminance reduces until the target luminance is reached. According to the second embodiment, however, the move destination of a display object is estimated and the LED luminance in the area of the move destination is increased in advance to around the target value, to thereby suppress the above-mentioned reduction in luminance. 
     [Third Embodiment] 
     A third embodiment of the present invention is described with reference to  FIGS. 6 to 9 . The first embodiment requires the display data use frame memory  108  for determining the moving velocity of an object in an input video, which increases the cost. In view of the above, the third embodiment is capable of producing an effect similar to that of the first embodiment, without the need for the display data use frame memory  108  of the first embodiment. 
     An operating principle of the third embodiment is described with reference to  FIGS. 6A and 6B .  FIG. 6A  is a diagram illustrating, by taking a display unit in which the foreground moves at higher velocity as an example, a display before and after the movement of the foreground, and a backlight unit in which the LED device corresponding to the foreground is turned on at 100% and LED devices surrounding the LED device are turned on at X %. X is defined as 0&lt;X&lt;100. 
       FIG. 6B  is a diagram illustrating, by taking a display unit in which the foreground moves at lower velocity as an example, a display before and after the movement of the foreground, and a backlight unit in which the LED device corresponding to the foreground is turned on at 100% and LED devices surrounding the LED device are turned on at X %. 
     In  FIG. 6A , the difference in luminance of the LED device (P) before and after the movement of the foreground is 100%, which is (100-X) % in  FIG. 6B . The difference in luminance may allow easy determination as to whether the moving velocity of the foreground is low or high. 
     In other words, the difference between the LED luminance of the previous frame and the LED luminance of the current frame is calculated, and when the difference is large, it is determined that the moving velocity of an object in a video is high in the display (for example, the foreground moves at higher velocity in the display). On the other hand, when the difference is small, it is determined that the moving velocity is low in the display (for example, the foreground moves at lower velocity in the display). 
       FIG. 7  is a diagram illustrating an example of a liquid crystal display device according to the third embodiment. In  FIG. 7 , the display device includes the constituent elements  100  to  107  and  110  to  115  similarly to the first embodiment. The display device according to the third embodiment includes a moving velocity detection unit VD 2   700  in place of the moving velocity detection unit VD 1   109 , and further includes an adjacent area irradiation computing unit  701 . 
     The moving velocity detection unit VD 2   700  is a block for comparing an LED light emission luminance value of the previous frame transferred from the light emission luminance use frame memory  114  with an LED target luminance value of the current frame transferred from the target light emission luminance LUT  112 , determining a moving velocity (Mv) based on the difference therebetween, and transferring the moving velocity (Mv) thus determined to the light emission luminance variation LUT  110 . 
     The internal operation of the moving velocity detection unit VD 2   700  is described with reference to  FIGS. 8A and 8B .  FIG. 8A  is a block diagram illustrating an inside of the moving velocity detection unit VD 2   700 . The block includes a circuit for calculating a difference (Sub) between the LED light emission luminance value of the previous frame and the LED target luminance value of the current frame, and an LUT  800  for selecting a moving velocity (Mv) appropriate to the difference (Sub). 
     An operation of the LUT  800  is described with reference to  FIG. 8B .  FIG. 8B  is a diagram illustrating a relation between the difference (Sub) and the moving velocity (Mv). When the difference (Sub) is larger than an arbitrary reference value Su, the LUT  800  determines that the display is of high velocity and selects a moving velocity Mv of 1. When the difference (Sub) is smaller than the arbitrary reference value Su, the LUT determines that the display is of low velocity and selects a moving velocity Mv of 0. 
     In the third embodiment, the difference (Sub) between the LED light emission luminance value of the previous frame and the LED target luminance value of the current frame is employed. It should be noted that, however, a mean squared error (MSE) between the LED light emission luminance value of the previous frame and the LED target luminance value of the current frame may be calculated as illustrated in  FIG. 9 , and the moving velocity My may be selected based on the MSE. 
     The adjacent area irradiation computing unit  701  is a block for performing a computation on data transferred from the maximum value selection unit  111  so as to turn on LEDs for irradiating the surrounding area, and transferring the data obtained from the computation to the target light emission luminance LUT  112 . The adjacent area irradiation computing unit  701  may include an external register capable of changing a range of adjacent areas to be irradiated, so that the range of adjacent areas to be irradiated may be adjusted. Alternatively, the adjacent area irradiation computing unit  701  may include an external register capable of changing a lighting luminance of a light source corresponding to the adjacent area to be irradiated, so that the lighting luminance (value of X) of the light source corresponding to the adjacent area may be adjusted. 
     In the above, the third embodiment has been described in detail. The display device of the third embodiment includes the backlight  101  having a plurality of light sources and is capable of controlling a luminance for each light source, and the display device may further include the adjacent area irradiation computing unit  701  for computing luminances of the light sources in at least one or all areas adjacent in upward, downward, rightward, leftward, and diagonal directions to the display area of an object in a video, so that the at least one or all adjacent areas may be irradiated in advance, a comparing unit (corresponding to the moving velocity detection unit VD 2   700  of  FIG. 7 ) for comparing the light emission luminance value of the previous frame and the light emission luminance value of the display frame, and a luminance variation control unit (light emission luminance variation LUT  110  and the light emission luminance calculation unit  113  of  FIG. 7 ) for controlling, as well as controlling the luminance variation of the light source in the display area based on the comparison result of the comparing unit, the luminances of the light sources in the adjacent areas based on the result of the computation performed by the adjacent area irradiation computing unit  701 . Further, for example, the comparing unit calculates a difference or an MSE between the light emission luminance value of the previous frame and the light emission luminance value of the display frame, sets the luminance variation to a third value when the difference or the MSE is large, and sets the luminance variation to a fourth value when the difference or the MSE is small. Here, the third value is larger than the fourth value. A register capable of externally adjusting the third value and the fourth value may also be provided. Further, when the fourth value may be made adjustable in smaller units as compared with the third value, the luminance variation in a low velocity movement display may be selected with higher accuracy, with the result that flicker in a low velocity movement display may be avoided with more ease. 
     According to third embodiment of the present invention, the moving velocity of an object in a video may be detected similarly to the first embodiment and the second embodiment, without the need for a complicated circuit for a motion vector analysis or a histogram analysis on display data, and hence the detection may be performed at low cost. 
     While there have been described what are at present considered to be certain embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover all such modifications as fall within the true spirit and scope of the invention.