Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2002-09-05
2004-06-29
Wu, Xiao (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S089000, C345S604000
Reexamination Certificate
active
06756955
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid-crystal display device employing a liquid-crystal panel and, more particularly, to a liquid-crystal driving circuit and liquid-crystal driving method for improving the response speed of the liquid crystal.
2. Description of the Related Art
Liquid crystals have the drawback of being unable to respond to rapidly changing moving pictures, because their transmissivity changes according to a cumulative response effect. One method of solving this problem is to improve the response speed of the liquid crystal by increasing the liquid-crystal driving voltage above the normal driving voltage when the gray level changes.
FIG. 72
shows an example of a liquid-crystal driving device that drives a liquid crystal by the above method; details are given in, for example, Japanese Unexamined Patent Application Publication No. 6-189232. Reference numeral
100
in
FIG. 72
denotes an A/D conversion circuit,
101
denotes an image memory storing the data for one frame of a picture signal,
102
denotes a comparison circuit that compares the present image data with the image data one frame before and outputs a gray-level change signal,
103
denotes the driving circuit of a liquid-crystal panel, and
104
denotes the liquid-crystal panel.
Next, the operation will be described. The A/D conversion circuit
100
samples the picture signal on a clock having a certain frequency, converts the picture signal to image data in digital form, and outputs the data to the image memory
101
and comparison circuit
102
. The image memory
101
delays the input image data by an interval equivalent to one frame of the picture signal, and outputs the delayed data to the comparison circuit
102
. The comparison circuit
102
compares the present image data output by the A/D conversion circuit
100
with the image data one frame before output by the image memory
101
, and outputs a gray-level change signal, indicating changes in gray level between the two images, to the driving circuit
103
, together with the present image data. The driving circuit
103
drives the display pixels of the liquid-crystal panel
104
, supplying a higher driving voltage than the normal liquid-crystal driving voltage for pixels in which the gray level has increased, and a lower voltage for pixels in which the gray level has decreased, according to the gray-level change signal.
A problem in the image display device shown in
FIG. 72
is that as the number of pixels displayed by the liquid-crystal panel
104
increases, so does the amount of image data written into the image memory
101
for one frame, so the necessary memory size increases. In the image display device described in Japanese Unexamined Patent Application Publication No. 4-204593, one address in the image memory is assigned to four pixels, as shown in
FIG. 73
, to reduce the size of the image memory
101
. The size of the image memory is reduced because the pixel data stored in the image memory are decimated, excluding every other pixel horizontally and vertically; when the image memory is read, the same image data are read for the excluded pixels as for the stored pixel, several times. For example, the data at address 0 are read for pixels (a, B), (b, A), and (b, B).
As described above, the response speed of the liquid crystal can be improved by increasing the liquid-crystal driving voltage above the normal liquid-crystal driving voltage when the gray level changes from the gray level one frame before. Since the liquid-crystal driving voltage is increased or reduced, however, only according to changes in the magnitude relationship between the gray levels, if the gray level increases from the gray level one frame before, the same higher driving voltage than the normal voltage is applied regardless of the size of the increase. Therefore, when the gray level changes only slightly, an overly high voltage is applied to the liquid crystal, causing a degradation of image quality.
If the size of the image memory
101
is reduced by decimation of the image data in the image memory
101
as shown in
FIG. 73
, the problem described below occurs.
FIGS. 74A
to
74
D illustrate the problem caused by decimation.
FIG. 74A
shows image data for frame n+1,
FIG. 74B
shows image data for the image in frame n+1 shown in
FIG. 74A
after decimation,
FIG. 74C
shows the image data read by interpolation of the decimated pixel data, and
FIG. 74D
shows the image data for frame n, one frame before. The image for frame n and the image for frame n+1 are identical, as shown in
FIGS. 74A and 74D
.
If decimation is carried out as shown in
FIG. 74C
, the pixel data at (A, a) are read as the pixel data for (B, a) and (B, b), and the pixel data at (A, c) are read as the pixel data for (B, c) and (B, d). Thus pixel data with gray level
50
are read as pixel data for a gray level that is actually
150
. Therefore, even though the image has not changed from the frame before, pixels (B, a), (B, b), (B, c), and (B, d) in frame n+1 are driven with a higher driving voltage than the normal voltage.
Thus when decimation is carried out, the voltages for the pixels with decimated pixel data are not controlled accurately, and the image quality is degraded by the application of unnecessary voltages.
SUMMARY OF THE INVENTION
The present invention addresses the problem above, with the object of providing a liquid-crystal driving circuit and liquid-crystal driving method capable of accurately controlling the response speed of the liquid crystal in a liquid-crystal display device by appropriately controlling the voltage applied to the liquid crystal.
Another object is to provide a liquid-crystal driving circuit and liquid-crystal driving method capable of accurately controlling the voltage applied to the liquid crystal, even if the capacity of the frame memory for reading the image one frame before is reduced.
The present invention provides a liquid-crystal driving circuit that generates image data from gray-scale values of an input image made up of a series of frames. The image data determine voltages that are applied to a liquid crystal to display the input image.
A first liquid-crystal driving circuit according to the present invention includes:
an encoding unit for encoding a present image corresponding to a frame of the input image and outputting an encoded image corresponding to the present image;
a first decoding unit for decoding the encoded image and outputting a first decoded image corresponding to the present image;
a delay unit for delaying the encoded image for an interval corresponding to one frame;
a second decoding unit for decoding the delayed encoded image and outputting a second decoded image;
a compensation data generator for generating compensation data for adjusting the gray-scale values in the present image according to the first decoded image and the second decoded image; and
a compensation unit for generating the image data according to the present image and the compensation data.
The compensation data preferably adjust the gray-scale values of the present image so that the liquid crystal reaches a transmissivity corresponding to the gray-scale values of the present image within substantially one frame interval.
The compensation data generator may include:
a data conversion unit for reducing the number of bits with which the gray-scale values of the first decoded image and the second decoded image are quantized, thereby generating a third decoded image corresponding to the first decoded image and a fourth decoded image corresponding to the second decoded image; and
a unit for outputting the compensation data according to the third decoded image and the fourth decoded image.
Alternatively, the compensation data generator may include:
a data conversion unit for reducing the number of bits with which the gray-scale values of the first decoded image or the second decoded image are quantized, thereby generating either a third decoded image corresponding to the first decoded im
Someya Jun
Yamakawa Masaki
Birch & Stewart Kolasch & Birch, LLP
Mitsubishi Denki & Kabushiki Kaisha
Wu Xiao
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