Television – Image signal processing circuitry specific to television – Gray scale transformation
Reexamination Certificate
1999-10-05
2002-01-22
Hsia, Sherrie (Department: 2614)
Television
Image signal processing circuitry specific to television
Gray scale transformation
C348S674000
Reexamination Certificate
active
06340996
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital signal processing for such displays as a liquid crystal display and plasma display, and more particularly to a y correction circuit and a &ggr; correction method where the &ggr; correction of digital video signals is executed by line graph approximation.
2. Description of the Related Art
The relationship of the luminance value (X) of the video signal to be input to the display to the output luminance (Z) of the display is called the “&ggr; characteristic”, and the characteristic of a cathode ray tube display, which now dominates the market, is approximated as Z=k·X{circumflex over ( )}&ggr; (&ggr;th power of X). Therefore in NTSC type television broadcasting, the &ggr; characteristic of a cathode ray tube display as an image receiver is considered and video signals are transmitted after executing reverse &ggr; correction at &ggr;=2.2.
In the case of a liquid crystal display, on the other hand, the &ggr; characteristic is different from that of a cathode ray tube display, so if the television images and computer images created by a cathode ray tube display are displayed on a liquid crystal display, luminance reproduction will be distorted. To control the distortion of luminance, it is necessary to include a &ggr; correction circuit in the display so as to execute &ggr; correction on the input video signals at an optimum &ggr; value before displaying. However, a &ggr; value optimum for video signals is generally not always the same where &ggr;=2.2 is used in the case of a television, and &ggr;=1.0 is used to expressed the fine difference of gradation and colors when images are created by a personal computer. Also the &ggr; value is different depending on the cathode ray tube display, so in order to reproduce ideal luminance for computer images, it is necessary to execute &ggr; correction based on the &ggr; characteristic of the display used for image creation.
Therefore in order to display these input images with an optimum &ggr; characteristic, a line graph &ggr; correction circuit, which approximates the &ggr; characteristic curve with a plurality of straight lines and executes non-linear processing on digital video signals, is used, as stated in the Japanese Patent Laid-Open No. 8-18826.
Also as a &ggr; correction circuit control method, a display stated in Japanese Patent Laid-Open No. 7-152347 exists, where a plurality of sets of &ggr; correction data, such as slopes and intercepts, are prepared and a switching operation is executed by input signals.
Also as Japanese Patent Laid-Open No. 10-145806 states, there is a display which holds the plurality of &ggr; correction data separately for each R, G and B, and white balance adjustment is executed by the &ggr; correction circuit at the same time as &ggr; correction.
A conventional type &ggr; correction method will now be explained with reference to FIG.
2
. In
FIG. 2
,
220
is a storage device for storing &ggr; correction data corresponding to n number of &ggr; values, such as a first &ggr; correction data
221
, a second &ggr; correction data
222
and so on until the nth &ggr; correction data
223
.
230
is a line graph &ggr; correction circuit. In the line graph &ggr; correction circuit
230
,
231
is a decoder which outputs a signal to the line graph block for the input video signal data.
232
is a slope data selector which outputs a slope data,
233
is an intercept data selector which outputs an intercept data,
234
is a multiplier,
235
is an adder and
236
is a limiter which executes limiter processing on the video data.
210
is a &ggr; conversion section. A &ggr; correction selection section
211
reads one data from the n number of re-&ggr; corrected data in the storage device
220
based on the &ggr;1 value which was input. The calculation section
212
calculates the slope and intercept of each straight line of the line graph in
FIG. 3
using the re-&ggr; corrected data which was read.
By storing &ggr; correction data having a target &ggr; characteristic in the storage device
220
in advance, optimum &ggr; correction is possible for a video signal having a plurality of &ggr; characteristics. White balance can also be adjusted by preparing the configuration in
FIG. 2
for three colors: R, G and B.
With the conventional method, however, the correction data must be stored in the storage device for the assumed number of &ggr; characteristics and white balances, so an increase in the capacity of the storage device is indispensable to support the subtle changes of &ggr; values and white balance.
With the foregoing in view, it is an object of the present invention to provide a display which implements subtle &ggr; correction, and digital white balance adjustment, as well as black level and contrast adjustment by digital signal processing using the above line graph &ggr; correction circuit and a small capacity storage device.
SUMMARY OF THE INVENTION
To solve the above problems, the display of the present invention has a &ggr; correction circuit for correcting digital video signals by line graph approximation, where the storage device holds a &ggr; characteristics of the display device, and video signals being input are displayed at the desired &ggr; characteristics, black level, contrast and white balance using a micro-controller, which calculates the slope and intercept of the line graph by the &ggr; characteristic of the display device, data which was input by the &ggr; value input means, white balance input means, black level input means, and contrast value input means, and the ideal &ggr; curve, and sets the slope and intercept of the line graph to the &ggr; correction circuit.
A first aspect of the present invention is a &ggr; correction circuit for executing reverse &ggr;1 correction on pre-&ggr;1 corrected input video data and then executing &ggr;2 correction, comprising: means for setting a representative luminance value; primary conversion means for executing reverse &ggr;1 correction on the representative luminance value so as to generate a primary conversion value; secondary conversion means for executing &ggr;2 correction on the primary conversion value so as to generate a secondary conversion value; means for generating a slope and intercept of each straight line of a line graph which pole is the secondary conversion value; and line graph &ggr; correction means for executing &ggr; correction on the input video data by the line graph.
A second aspect is a &ggr; correction circuit according to the first aspect, wherein the above mentioned primary conversion means receives a &ggr;1 value.
A third aspect is a &ggr; correction circuit according to the first aspect, wherein the above mentioned primary conversion means receives a &ggr;1 value and a black level value.
A fourth aspect is a &ggr; correction circuit according to the first aspect, wherein the above mentioned primary conversion means receives a &ggr;1 value and a contrast value.
A fifth aspect is a &ggr; correction circuit according to the first aspect, wherein the above mentioned primary conversion means receives a &ggr;1 value, a red adjustment value, a green adjustment value and a blue adjustment value.
A sixth aspect is a &ggr; correction circuit according to the first aspect, wherein the above mentioned secondary conversion means has a table denoting a relationship between pre- &ggr;2 correction and post &ggr;2 correction.
A seventh aspect is a &ggr; correction circuit according to the first aspect, wherein the above mentioned y
1
value is a &ggr; correction value for a cathode ray tube display.
An eighth aspect is a &ggr; correction circuit according to the first aspect, wherein the above mentioned &ggr;2 correction is a &ggr; correction for a liquid crystal display.
A ninth aspect is a &ggr; correction circuit according to the first aspect, wherein the above mentioned &ggr;2 correction is a &ggr; correction for a plasma display.
A tenth aspect is a &ggr; correction method for executing reverse &ggr;1 correction
Greenblum & Bernstein P.L.C.
Hsia Sherrie
Matsushita Electric - Industrial Co., Ltd.
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