Display device

The display device including: a display panel; a backlight; a memory for converting frame rate of an input video signal and outputting a video signal; an interpolation frame generation unit for generating an interpolation frame based on the video signal output from the memory; a histogram generator for generating a histogram based on the input video signal; and a backlight brightness calculation unit for calculating a backlight control signal, the display device further comprising: wherein image data for display, which is obtained by an N-th frame of the input video signal, and image data of the interpolation frame generated based on the N-th frame and an (N+1)-th frame of the input video signal, is input to the display panel; and wherein the backlight control signal calculated based on the histogram generated based on the image data of the N-th frame is used for displaying the image data for display.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese application JP 2008-258041 filed on Oct. 3, 2008, 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 a driving method therefor. More particularly, the present invention relates to a display device for performing display by synchronizing a video signal with light source brightness control in controlling brightness of a light source according to the video signal.

2. Description of the Related Art

In recent years, non-emissive display devices as typified by liquid crystal display devices have been in widespread use. The non-emissive display device uses a light source and a light modulation device for adjusting the amount of light to be transmitted from the light source. The non-emissive display device has such disadvantages that the light source consumes power and that light leakage from the light source during the black display causes deteriorated contrast. In view of this, in order to make improvement in power consumption and contrast, there have been proposed a plurality of methods of controlling light source brightness according to video signals. As one example of such methods, JP 2008-076755 A proposes an image display device for controlling the light source brightness according to a histogram in which, for each predetermined gray-scale level, gray-scale levels representing the respective level-ranges in an input image are associated with frequencies of pixels included in the respective level-ranges.

Further, in general, the liquid crystal display device is a hold-type display device in which a rendered image is held until an image of the next frame is rendered, instead of an impulse-type display device, such as a display device using a cathode ray tube (CRT), in which strong light is emitted at the moment when an image is rendered. One of the drawbacks of the hold-type display device is so-called motion blur, in which an edge portion of a moving object becomes blurred when a moving picture is displayed. This motion blur is caused by so-called retinal persistence of vision, which occurs when a viewer moves his/her direction of sight along with the movement of an object, interpolating display images before and after the movement with regard to a display image for which the brightness is held. As a solution to such motion blur, a method of making the hold-type display device operate more like the impulse-type display device is known to be effective, such as updating display images with higher frequencies or temporarily canceling the retinal persistence of vision with insertion of a black screen (see “Moving Picture Quality Improvement for Hold-type AM-LCDs”, Taiichiro kurita, SID 01 DIGEST).

As one example of the methods for solving the motion blur, JP 2005-241787 A discloses a system (interpolation frame inserting system) in which an intermediate frame of two adjacent frames is generated as an interpolation frame based on the two adjacent frames, the interpolation frame thus generated is inserted between the two adjacent frames, and a video signal into which the interpolation frame is inserted is output with a higher frame frequency than the frame frequency of the original video signal.

As another example of the methods for solving the motion blur, JP 2006-343706 A discloses a system (light-dark field dividing system) in which a one-frame interval is divided into two field intervals for a light field and a dark field, display of the original video signal is performed using the two fields in a simulated manner, and the retinal persistence of vision is canceled by the dark field.

In both the interpolation frame inserting system and the light-dark field dividing system described above, the frame frequency of the video signal to be output needs to be converted into a higher frame frequency than the frame frequency of the input video signal (frame rate conversion). When the frame rate conversion is performed, a frame memory is used to temporarily hold the video signal.

Description is given of a problem posed when the brightness of the light source is controlled according to the video signal.FIG. 1Ais a diagram for describing a schematic configuration of a liquid crystal display device related to a display device of the present invention. In particular,FIG. 1Ais one example of a block configuration diagram of a display device including a mechanism for controlling light source brightness according to the video signal. The display device illustrated inFIG. 1Aincludes a display image data correction unit108, a histogram generator106, a backlight brightness calculation unit107, and an image display unit109. The image display unit109includes a liquid crystal panel110serving as a light modulation device and a backlight111provided behind the liquid crystal panel, which serves as a light source unit. Specifically, in the liquid crystal display device illustrated inFIG. 1A, the mechanism for controlling the light source brightness is independent of other video processing circuits, and also, an output signal from another video processing circuits is used as a video signal102to be input to the mechanism.

Next, by taking a case in which the video signal is input to the block configuration diagram illustrated inFIG. 1Aat timing illustrated in a timing chart ofFIG. 1B, focus is given to image data D0corresponding to one frame of the video signal102, and a problem therewith is described. For example, in a case of a high-definition TV format of 1,920 dots×1,080 lines with each color of RGB having 8 bits (total of 24 bits), the image data corresponding to one frame represents data constructed of 1,920×1,080×24 bits. The image data D0is input to the histogram generator106and the display image data correction unit108. The histogram generator106generates a histogram104showing a feature amount of the image data D0, which is used by the backlight brightness calculation unit107as an indicator in calculating backlight brightness based on the image data D0. When the histogram104is generated based on image data corresponding to one frame, as illustrated in the timing chart ofFIG. 1B, data HG0, which is the histogram104of the image data D0, is generated with a delay of a one-frame interval T, compared to the image data D0. The histogram104generated as the data HG0is output to the backlight brightness calculation unit107. The backlight brightness calculation unit107uses the data HG0, which is the histogram104obtained by the histogram generator106, to calculate light emission brightness of the backlight, and then outputs data BL0serving as a backlight control signal105to the display image data correction unit108and the backlight111. Here, focus is given to timings at which the image data and the backlight control signal105are input to the display image data correction unit108. There occurs a time lag of the one-frame interval T between the timing at which the image data D0is input to the display image data correction unit108and the timing at which the data BL0is input to the display image data correction unit108. Here, the data BL0is the backlight control signal105obtained based on the data HG0, which is the histogram104generated based on the image data D0. As a result, there occurs a problem that the display image data correction unit108corrects the image data D1by using the data BL0, which is the backlight control signal105obtained based on the image data D0, and then generates data D1′ serving as display image data103.

As a method for solving this problem, JP 2008-076755 A proposes a method of using a frame memory.FIG. 2Ais an exemplary block configuration diagram of a liquid crystal display device obtained by applying the method of using a frame memory to the liquid crystal display device illustrated inFIG. 1A. A frame memory203delays the image data D0by the one-frame interval T, to thereby synchronize the image data D0to be input to the display image data correction unit108with the data BL0, which is the backlight control signal105obtained based on the image data D0, before the image data D0and the data BL0are input to the display image data correction unit108. Therefore, the display image data correction unit108can correct the image data D0by using the data BL0, which is the backlight control signal105obtained based on the image data D0. However, in order to synchronize the image data with the backlight control signal105, a frame memory is required, which prevents reduction in cost of the display device.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problems, the present invention has been made, and it is an object thereof to provide a display device capable of synchronizing image data with a backlight control signal while preventing such a circuit as a frame memory from increasing.

In order to solve the above-mentioned problems, the present invention provides a display device including: a display panel serving as a light modulation device; a backlight provided behind the display panel, for emitting irradiation light; a memory for frame rate conversion for outputting a video signal, which is subjected to frame rate conversion, with a higher frequency than a frequency of an input video signal input from an external system; an interpolation frame generation unit for generating an interpolation frame based on the video signal which is subjected to the frame rate conversion, and outputting a video signal into which the interpolation frame is inserted; a histogram generator for generating a histogram based on the input video signal; and a backlight brightness calculation unit for calculating a backlight control signal for adjusting brightness of the backlight based on the histogram, the display device further comprising: wherein image data for display is input to the display panel, wherein the backlight control signal is input to the backlight, wherein the image data for display is obtained by subjecting image data of an N-th frame of the input video signal to the frame rate conversion, and image data of the interpolation frame generated based on the image data of the N-th frame and image data of an (N+1)-th frame of the input video signal, where N represents a natural number including zero; and wherein the backlight control signal calculated based on the histogram generated based on the image data of the N-th frame is used for displaying the image data for display.

In order to solve the above-mentioned problems, the present invention also provides a display device including: a display panel serving as a light modulation device; a backlight provided behind the display panel, for emitting irradiation light; a memory for frame rate conversion for outputting a video signal, which is subjected to frame rate conversion, with a higher frequency than a frequency of an input video signal input from an external system; a light-dark field generation unit for generating a light field and a dark field based on the video signal which is subjected to the frame rate conversion, and outputting a video signal containing the light field and the dark field; a histogram generator for generating a histogram based on the input video signal; and a backlight brightness calculation unit for calculating a backlight control signal for adjusting brightness of the backlight based on the histogram, the display device further comprising: wherein image data for display is input to the display panel, wherein the backlight control signal is input to the backlight, wherein the image data for display is obtained by image data of the dark field generated based on image data of an N-th frame of the input video signal, and image data of the light field generated based on image data of an (N+1)-th frame of the input video signal; and wherein the backlight control signal calculated based on the histogram generated based on the image data of the N-th frame is used for displaying the image data for display.

In order to solve the above-mentioned problems, the present invention also provides a display device for performing display with gray scale and brightness according to image data input from an external system, the display device including: a display panel including a plurality of pixels arranged in matrix; a backlight for emitting irradiation light to a back side of the display panel; a memory for storing the image data corresponding to at least one frame, which is input from the external system; a generation unit for generating image data having a different value from the image data; and a light emission amount calculation unit for calculating a light emission amount of the backlight based on the image data, wherein: the image data is written into the memory once during a one-frame interval, and the image data is read out from the memory twice with a delay of at least half a length of the one-frame interval after the image data is written; the generation unit uses first image data read out from the memory for a first time and second image data read out from the memory for a second time, to generate first image data for display and second image data for display corresponding to the first image data and the second image data, respectively; the light emission amount calculation unit calculates the light emission amount of the backlight based on the image data input from the external system; and displaying of the first image data for display and the second image data for display on the display panel and irradiation made by the backlight with the calculated light emission amount are performed in synchronization with a frame interval of the image data input from the external system.

According to the present invention, it is possible to provide the display device in which the image data and the backlight control signal are synchronized with each other while preventing such a circuit as a frame memory from increasing.

Other effects of the present invention will become apparent from the following description.

DETAILED DESCRIPTION OF THE INVENTION

Hereinbelow, with reference to the drawings, description is given of a display device according to embodiments of the present invention. It should be noted that, in the following description, like reference numerals and symbols refer to like components to avoid repetitive description.

FIG. 3Ais a diagram for describing a schematic configuration of a liquid crystal display device, which is one example of the display device according to a first embodiment of the present invention. In particular,FIG. 3Ais a block configuration diagram for describing the schematic configuration of the liquid crystal display device according to the first embodiment of the present invention, whereasFIG. 3Bis an operation chart for describing operation of the liquid crystal display device according to the first embodiment of the present invention. The liquid crystal display device according to the first embodiment, which is illustrated inFIG. 3A, is a liquid crystal display device that employs an interpolation frame inserting system and a backlight brightness modulating system. It should be noted that, herein, N represents a natural number including zero.

As illustrated inFIG. 3A, the liquid crystal display device according to the first embodiment of the present invention includes a memory for frame rate conversion306, an interpolation frame generation unit307, a display image data correction unit308, a histogram generator106, a backlight brightness calculation unit309, and an image display unit109. Further, the image display unit109includes a liquid crystal panel (display panel)110serving as a light modulation device and a backlight111provided behind the liquid crystal panel, which serves as a light source unit.

InFIG. 3A, the memory for frame rate conversion306includes a frame memory having a memory capacity for at least one frame. The frame memory may be constructed by any one of an SDRAM, a DRAM, a RAM, a FIFO, and the like, which are all well known. Further, the memory for frame rate conversion306of the first embodiment outputs a video signal (image data), which is stored in the frame memory, as a comparison frame A301and a comparison frame B302with a higher frame frequency than the frame frequency used when a video signal310is input. In the memory for frame rate conversion306of the first embodiment, the frame frequency used when the video signal310is input is 60 Hz, and the frame frequencies of the comparison frame A301and the comparison frame B302are 120 Hz.

The interpolation frame generation unit307includes a well-known intermediate value detection circuit. For example, the intermediate value detection circuit calculates, for each pixel, an intermediate value between image data of an N-th frame input based on the comparison frame A301and image data of an (N+1)-th frame input based on the comparison frame B302. Specifically, for each pair of two image data inputs (comparison frame A301and comparison frame B302) that are sequentially input, the interpolation frame generation unit307of the first embodiment adds values of the respective pixels (pixel values) together on a pixel basis, and then divides the sum by two, which represents the number of added elements, to thereby obtain the intermediate value. The intermediate value thus obtained is output as image data after calculation303for an interpolation frame. Here, the image data is input to the interpolation frame generation unit307with an interval of half the length of one frame (=T/2), and hence an output interval of the interpolation frame corresponding thereto is also half the length of a one-frame interval (T/2). Further, the method of generating an interpolation frame by the interpolation frame generation unit307is not limited to the use of the intermediate value obtained by the intermediate value detection circuit. For example, a well-known motion vector detection circuit employing a matching method may also be used as the method of generating an interpolation frame. Various modifications may be made without departing from the spirit and scope of the present invention.

The histogram generator106is a circuit for generating an indicator to be used for calculating backlight brightness based on the video signal310input from an external system (not shown). Based on the image data input as the video signal310from the external system, the histogram generator106of the first embodiment generates a histogram showing a feature amount of the image data, and then outputs the obtained histogram. On this occasion, because a histogram is generated based on image data corresponding to one frame, the histogram generator106of the first embodiment requires a period of time corresponding to one frame for generating a histogram after input of the image data. In other words, after the input of the image data, a histogram corresponding to that image data is obtained with a delay of a one-frame interval.

The backlight brightness calculation unit309is a circuit for: calculating a backlight control signal305for controlling brightness of the backlight111based on the histogram; controlling a driver circuit (not shown) for the backlight111based on the obtained backlight control signal305; and causing the backlight111to emit light with a desired brightness. It should be noted that the backlight brightness calculation unit309of the first embodiment calculates the backlight control signal305substantially in real time with input of a histogram104.

The display image data correction unit308is a circuit for generating image data in consideration of the brightness of the backlight111based on the image data after calculation303and the backlight control signal305. Specifically, in a case where an image is bright across the entire screen, the backlight brightness calculation unit309causes the backlight111to emit backlight with increased brightness based on the histogram. However, in a case where the entire screen is relatively dark, the backlight brightness calculation unit309causes the backlight111to emit backlight with decreased brightness. Meanwhile, the image data after calculation303to be output from the interpolation frame generation unit307is such image data that is obtained assuming a case in which the backlight is ON with the highest brightness. For this reason, simply decreasing light emission brightness of the backlight111causes an insufficient amount of light of the backlight111passing through the liquid crystal panel110, which results in darker screen display than desired screen display. Accordingly, the display image data correction unit308converts the input image data after calculation303into display image data304according to the amount of light of the backlight111, and then outputs, as display data, the obtained display image data304(image data for display) to a liquid crystal driver circuit (not shown) of the liquid crystal panel110.

Next, with reference to the operation chart illustrated inFIG. 3B, description is given of the operation of the liquid crystal display device according to the first embodiment. Here, in the following description, pieces of image data each corresponding to one frame of the video signal310are respectively denoted by image data D0, D1, D2, . . . . Accordingly, image data of an N-th frame is denoted by DN, and image data of the next frame, that is, image data of an (N+1)-th frame, is denoted by DN+1. Hereinbelow, description is given focusing on timings at which the image data after calculation303and the backlight control signal305are input to the display image data correction unit308.

First, from the external system (not shown), video data (image data) to be displayed according to screen display, such as color tone or gray scale, is input as the video signal310(t0to t1).

The input video signal310is input to the memory for frame rate conversion306and the histogram generator106, respectively.

The input video signal310is sequentially stored in the frame memory (not shown) included in the memory for frame rate conversion306. Next, the video signal310stored in the frame memory is output from the memory for frame rate conversion306as the comparison frame A301and the comparison frame B302with a higher frame frequency (120 Hz) than the frame frequency (60 Hz) used when the video signal310is input. On this occasion, compared to the input video signal310, the comparison frame A301is output with a delay of a 0.5-frame interval (=0.5 T) (t1to t2), and the comparison frame B302is output with a delay of the one-frame interval (=T) (t2to t3).

In the interpolation frame generation unit307to which the pieces of image data denoted by D0and D1have been input based on the input comparison frame A301and comparison frame B302, an interpolation frame, which is an intermediate frame between the comparison frame A301and the comparison frame B302, is generated. In a case where the comparison frame A301is D0and the comparison frame B302is D0, the interpolation frame generation unit307outputs D0as the image data after calculation303(t2to t3). In a case where the comparison frame A301is D1and the comparison frame B302is D0, the interpolation frame generation unit307outputs D0.5as the image data after calculation303representing an interpolation frame between D0and D1(t3to t4). In this manner, compared to the image data D0corresponding to one frame of the input video signal310(for example, t0to t2), the image data after calculation303to be output from the interpolation frame generation unit307is output with a delay of the one-frame interval (=T) (for example, t2to t4). Further, compared to the image data D0, the image data after calculation303(denoted by D0.5) representing the interpolation frame between the image data D0and the image data D1is output with a delay of a 1.5−frame interval (=1.5 T) (t3to t4).

Meanwhile, when the image data D0has been input to the histogram generator106(t0), the histogram generator106generates the histogram104showing the feature amount of the image data D0based on the image data D0. As described above, the histogram104is generated by using image data corresponding to one frame (for example, image data during an interval between t0and t2), and hence the histogram104(denoted by HG0) corresponding to the image data D0is generated with a delay of the one-frame interval (=T), compared to the image data D0(t2to t4).

The backlight brightness calculation unit309calculates the light emission brightness of the backlight111based on the histogram104denoted by HG0, which has been obtained by the histogram generator106, and then outputs a backlight control signal305denoted by BL0to the display image data correction unit308and the backlight111(t2to t4). On this occasion, the backlight control signal305denoted by BL0is output to the display image data correction unit308with a delay of one frame (t2to t4), compared to the originally-input image data D0(t0to t2).

Accordingly, to the display image data correction unit308, with regard to the image data D0input as the video signal310, there are input the image data after calculation303denoted by D0, which is delayed by the one-frame interval, the image data after calculation303denoted by D0.5, which is delayed by the 1.5-frame interval, and the backlight control signal305denoted by BL0, which is delayed by the one-frame interval.

With this configuration, the display image data correction unit308can correct the image data after calculation303denoted by D0and the image data after calculation303denoted by D0.5based on the backlight control signal305denoted by BL0. Here, the image data after calculation303denoted by D0.5is corrected based on the backlight control signal305denoted by BL0. However, because the image data after calculation303denoted by D0.5is an interpolation frame between the originally-input image data D0and the image data D1, there is no problem with correcting the image data after calculation303denoted by D0.5based on the backlight control signal305denoted by BL0.

Further, in the intervals after t4, by repeating the above-mentioned operation, the histogram104is generated based on the image data input as the video signal310, and then, the backlight control signal305is generated. As a result, it becomes possible to reduce the frame memory for synchronizing the image data after calculation303with the backlight control signal305in the display image data correction unit308, enabling synchronization between the image data and the backlight control signal to be realized at low cost.

In the liquid crystal display device according to the first embodiment of the present invention, the histogram104for controlling the backlight is generated based on the video signal310input to a circuit including the memory for frame rate conversion306and the interpolation frame generation unit307, which is a circuit for implementing the interpolation frame inserting system.

As described above, in the liquid crystal display device according to the first embodiment, the video signal310, which is image data input from the external system, is temporarily stored in the memory for frame rate conversion306. The stored image data is then output as the comparison frame A301and the comparison frame B302with a delay of the interval (=T/2) of half the length of one frame and a delay of the one-frame interval (=T), respectively, with a frame frequency of 120 Hz, which is twice as high as that of the input image data. Accordingly, when it is assumed that the interval (t0to t2) during which the video signal310denoted by D0is input corresponds to the N-th frame, uncorrected image data (image data after calculation303) from D0is to be obtained in the next interval (t2to t4), which corresponds to the (N+1)-th frame during which the video signal310denoted by D1is to be input.

On the other hand, the histogram generator106for generating the histogram104based on the video signal310, which is image data input from the external system, requires image data corresponding to one frame. Accordingly, when it is assumed that the interval (t0to t2) during which the video signal310denoted by D0is input corresponds to the N-th frame, a histogram to be obtained based on the video signal310denoted by D0is generated in the next interval (t2to t4), which corresponds to the (N+1)-th frame during which the video signal310denoted by D1is to be input. Then, during the (N+1)-th frame, the backlight control signal305is generated based on the video signal310denoted by D0, and the amount of light emission from the backlight111is controlled.

As described above, in the liquid crystal display device according to the first embodiment, a histogram is directly generated based on a signal input to the memory for frame rate conversion306, which is a circuit for implementing the interpolation frame inserting system in which it takes the one-frame interval to obtain image data after input of the video signal310, that is, based on the video signal310, which is the image data input from the external system. Then, the backlight control signal305is calculated. Therefore, it is possible to synchronize control of the amount of light emission, which is obtained based on the image data of the N-th frame, with the image display to be made based on the image data of the N-th frame during the interval of the (N+1)-th frame (t2to t4).

As a result, it becomes possible to synchronize the image data after calculation303with the backlight control signal305to perform display while preventing such a circuit as a frame memory from increasing.

FIG. 4Ais a diagram for describing a schematic configuration of a liquid crystal display device, which is one example of the display device according to a second embodiment of the present invention. In particular,FIG. 4Ais a block configuration diagram for describing the schematic configuration of the liquid crystal display device according to the second embodiment of the present invention, whereasFIG. 4Bis an operation chart for describing operation of the liquid crystal display device according to the second embodiment of the present invention. The liquid crystal display device according to the second embodiment, which is illustrated inFIG. 4A, is a liquid crystal display device that employs a light-dark field dividing system and a backlight brightness modulating system.

As illustrated inFIG. 4A, the liquid crystal display device according to the second embodiment of the present invention includes a memory for frame rate conversion406, a light-dark field generation unit407, a display image data correction unit408, a histogram generator106, a backlight brightness calculation unit409, and an image display unit109. Further, the image display unit109includes a liquid crystal panel (display panel)110serving as a light modulation device and a backlight111provided behind the liquid crystal panel, which serves as a light source unit.

InFIG. 4A, the memory for frame rate conversion406includes a frame memory having a memory capacity for at least one frame. The frame memory may be constructed by any one of an SDRAM, a DRAM, a RAM, a FIFO, and the like, which are all well known. Further, the memory for frame rate conversion406of the second embodiment outputs a video signal410stored in the frame memory twice in a row with a higher frame frequency than the frame frequency used when the video signal410is input. For example, in the memory for frame rate conversion406of the second embodiment, the frame frequency used when the video signal410is input is 60 Hz, and the frame frequency of memory output image data401, which is the output of the video signal410, is 120 Hz. In this manner, the liquid crystal display device according to the second embodiment outputs, as the memory output image data401, the same image data twice with a frequency twice as high as the frame frequency used when the video signal410is input to the memory for frame rate conversion406, to thereby divide a one-frame interval into two intervals of a first interval (light-field interval) and a second interval (dark-field interval).

Of the same image data that is input twice in a row, based on the image data of the first interval, the light-dark field generation unit407generates image data having a larger brightness value than the brightness of the image data of the first interval, that is, generates a brighter image, and then outputs the obtained image data as image data after calculation402of the light-field interval. Further, based on the image data of the second interval, the light-dark field generation unit407generates image data having a smaller brightness value than the brightness of the image data of the second interval, that is, generates a darker image, and then outputs the obtained image data as image data after calculation402of the dark-field interval. Subsequently, this operation is repeated for the image data input in the first and second intervals.

As a result, the pieces of image data after calculation402of the light field and the dark field are generated for the same image data, and, by using the pieces of image data after calculation402of the two fields, it is possible to obtain the same brightness (visual brightness) as that of the original image data in a simulated manner.

The backlight brightness calculation unit409is a circuit for: calculating a backlight control signal404for controlling brightness of the backlight111based on a histogram104; controlling a driver circuit (not shown) for the backlight111based on the obtained backlight control signal404; and causing the backlight111to emit light with a desired brightness. The backlight brightness calculation unit409of the second embodiment also calculates the backlight control signal404substantially in real time with input of the histogram104.

The display image data correction unit408is a circuit for generating display image data403in consideration of the brightness of the backlight111based on the image data after calculation402and the backlight control signal404. Specifically, in a case where an image is bright across the entire screen, the backlight brightness calculation unit409causes the backlight111to emit backlight with increased brightness based on the histogram. However, in a case where the entire screen is relatively dark, the backlight brightness calculation unit409causes the backlight111to emit backlight with decreased brightness, which is the same manner as the first embodiment.

Next, with reference to the operation chart illustrated inFIG. 4B, description is given of the operation of the liquid crystal display device according to the second embodiment.

First, from the external system (not shown), image data to be displayed according to screen display, such as color tone or gray scale, is input as the video signal410(t0to t2). The input video signal410is subjected to the frame rate conversion by the memory for frame rate conversion406(t1to t3), and then, the light-dark field generation unit407generates the light field and the dark field (t1to t3).

Here, focus is given to image data D0, which is image data corresponding to one frame of the video signal410. Compared to the input image data D0, image data after calculation402denoted by D0−light(D0−L) is delayed by a 0.5-frame interval (=0.5 T) (t1to t2), and image data after calculation402denoted by D0−dark(D0−D) is delayed by the one-frame interval (=T) (t2to t3), which are then output to the display image data correction unit408.

Meanwhile, as for the backlight control signal404, the histogram generator106generates a histogram104denoted by HG0based on the input image data D0(t2to t4), and, based on the histogram104denoted by HG0, the backlight brightness calculation unit409calculates a backlight control signal I404denoted by BL0(t2to t4). Specifically, the backlight control signal I404denoted by

BL0is output to the display image data correction unit408with a delay of the one-frame interval (=T), compared to the input image data D0(t2to t4). In the intervals after t4, the above-mentioned operation is repeated.

Here, the display image data correction unit408uses the backlight control signal I404denoted by BL0to correct the image data after calculation402denoted by D0−-dark (D0−D) (t2to t3) and image data after calculation402denoted by D1−light (D1−-L) (t3to t4). In this case, the light field and the dark field are corrected with the same backlight control signal I404.

It should be noted that the liquid crystal display device of the second embodiment is not limited to the above-mentioned configuration. For example, the following configuration may be employed. That is, by modifying the above-mentioned backlight control signal I404into a backlight control signal II405, a backlight control signal II405for the dark field (denoted by BL0A) (t2to t3) and a backlight control signal II405for the light field (denoted by BL0B) (t3to t4) are calculated based on the histogram104denoted by HG0. With this configuration, the image data after calculation402denoted by D0−dark (D0−D) can be corrected with the backlight control signal II405denoted by BL0A, which is calculated based on the histogram104denoted by HG0(t2to t3). In this case, the image data after calculation402denoted by D1−light (D1−L) is to be corrected with the backlight control signal II405denoted by BL0B, which is calculated based on the histogram104denoted by HG0. However, compared to the light field, the dark field is more likely to contribute to improvement in power consumption by decreasing backlight brightness to enhance the gray scale of image data. Therefore, it is desirable that the image data after calculation402of the dark field is synchronized with the backlight control signal II405.

As described above, the liquid crystal display device of the second embodiment performs calculation by using the light-dark field dividing system, and then corrects the display image data403by using the backlight brightness modulating system. As a result, it becomes possible to reduce the frame memory for synchronizing the image data after calculation402with the backlight control signal404in the display image data correction unit408, enabling synchronization between the image data and the backlight control signal to be realized efficiently at low cost.

As described above, in the liquid crystal display device according to the second embodiment, the video signal410, which is image data input from the external system, is temporarily stored in the memory for frame rate conversion406. Then, the stored image data is output with a delay of the interval of half the length of one frame (=T/2) with the frame frequency of 120 Hz, which is twice as high as that of the input image data. Accordingly, when it is assumed that the interval (t0to t2) during which the video signal410denoted by D0is input corresponds to the N-th frame, D0−light(D0−L), which is uncorrected image data from D0, is to be obtained in the interval between t1and t2, and D0−dark(D0−D) is to be obtained in the interval between t2and t3. Therefore, D0−dark(D0−D) is to be obtained in the (N+1)-th frame, during which the video signal410denoted by D1is to be input.

On the other hand, the histogram generator106for generating the histogram104based on the video signal410, which is image data input from the external system, requires image data corresponding to one frame. Accordingly, when it is assumed that the interval (t0to t2) during which the video signal410denoted by D0is input corresponds to the N-th frame, a histogram to be obtained based on the video signal410denoted by D0is generated in the next interval (t2to t4), which corresponds to the (N+1)-th frame during which the video signal410denoted by D1is to be input. Then, during the (N+1)-th frame, the backlight control signal404is generated based on the video signal410denoted by D0, and the amount of light emission from the backlight111is controlled.

As described above, in the liquid crystal display device according to the second embodiment, a histogram is directly generated based on a signal input to the memory for frame rate conversion406, which is a circuit for implementing the light-dark field dividing system in which it takes half the length (=T/2) of the one-frame interval (=T) to obtain image data after input of the video signal410, that is, based on the video signal410, which is the image data input from the external system. Then, the backlight control signal404is calculated. Therefore, it is possible to synchronize control of the amount of light emission, which is obtained based on the image data of the N-th frame, with the image display to be made based on the image data of the N-th frame during the interval between t2and t3of the (N+1)-th frame.

As a result, it becomes possible to synchronize the image data after calculation402with the backlight control signal404to perform display while preventing such a circuit as a frame memory from increasing.

It should be noted that the present invention is not limited to the liquid crystal display device according to the first and second embodiments. Considering that a circuit for implementing an interlace-progressive (I-P) conversion system includes a frame memory as well, the present invention is also applicable to a liquid crystal display device using the I-P conversion system.

As described above, when the display device according to the first embodiment of the present invention displays the image data of an interpolation frame generated based on the image data of the N-th frame of the input video signal and the image data of the (N+1)-th frame thereof, and the image data obtained by subjecting the image data of the N-th frame of the input video signal to the frame rate conversion, display is performed using the backlight control signal calculated based on a histogram generated from the image data of the N-th frame, which is the same frame as the input video signal that has been input to the memory for frame rate conversion.

On this occasion, the backlight of the (N+1)-th frame is controlled according to light emission amount control based on the histogram obtained from the image data of the N-th frame. Meanwhile, the image display of the (N+1)-th frame on the liquid crystal panel is also based on the image data of the N-th frame.

As a result, it becomes possible to synchronize the image data with the backlight control signal to perform display while preventing such a circuit as a frame memory from increasing.