Television – Image signal processing circuitry specific to television – Color television signal processing
Reexamination Certificate
1997-10-29
2001-09-11
Eisenzopf, Reinhard J. (Department: 2614)
Television
Image signal processing circuitry specific to television
Color television signal processing
C348S536000, C348S711000, C348S655000, C348S656000, C348S657000, C348S687000
Reexamination Certificate
active
06288756
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of luminance correction circuits for correcting unevenness in the luminance level and color of video images displayed on video display monitors.
BACKGROUND OF THE INVENTION
As projection display screens become larger, uneven luminance in each red, green, and blue color (hereafter referred to as R, G, B) and color impurity in the combinations of R, G, B occur because of i) deviation in the characteristics of the light source and video display elements, ii) light reduction at the periphery of the projection lens, and iii) projection angles subtending to the screen. Accordingly, the need has increased to incorporate circuits for correcting uneven luminance and color impurity. One example is disclosed in Japanese Laid-open Patent A61-243495.
An example of the prior art is explained with reference to FIG.
4
.
The video signal input from a video signal input terminal
41
is converted to R, G, B video signals by a signal processor
48
. An adder
49
adds a correction signal (described later) to the R, G, B video signals. After the correction signal is added, the R, G, B video signals pass through a drive circuit
50
and are output at video output terminal
51
to drive the video display element (not illustrated) thereby projecting the video image on the screen (not illustrated).
To generate the correction signal, the video signal with a specified amplitude is input to the video input terminal
41
. A video image is expected to be displayed on the screen at a uniform luminance level by employing this video signal with a specified amplitude. However, because of the aforementioned reasons, the luminance level on the screen may not be uniform in some cases.
Correction data for maintaining a uniform luminance level on the screen is therefore created as follows.
A projection screen is divided into squares. The luminance level of the video image in each divided square on the screen is measured using a video camera. The difference between the measured luminance level and a specified luminance level is stored in a memory
46
as correction data for each divided area.
The video signal input to the video signal input terminal
41
is also input to a synchronizing separator
42
. The synchronizing separator
42
outputs a horizontal synchronizing signal H and a vertical synchronizing signal V. The horizontal synchronizing signal H is input to a phase synchronizing circuit
43
. The phase synchronizing circuit
43
produces a horizontal synchronizing clock signal CLK in accordance with the horizontal synchronizing signal H to an address counter
45
. At the same time, the synchronizing separator
42
also outputs the vertical synchronizing signal V to the address counter
45
.
In practical operation, for reading the correction data previously stored in the memory
46
, the horizontal synchronizing clock signal CLK and the vertical synchronizing signal V control the address counter
45
for calculating an address in the memory
46
corresponding to each divided area made at creating the correction data.
A D/A converter
47
converts the correction data read from the memory
46
into an analog correction signal. This analog correction signal is input to the adder
49
.
As mentioned above, unevenness in the luminance or color of the video image displayed on the screen is corrected by adding the correction signal to the input video signal at the adder
49
and driving the video display element through the driver
50
.
However, since unevenness of the luminance or color of the video image is corrected for each divided area, a gap in correction between the correction data for each area may be obvious.
The gap in horizontal direction can be smoothed relatively easily by the use of a low pass filter. However, for smoothing the gap in vertical direction, an expensive circuit such as a field memory may be required. Consequently, smoothing in the vertical direction is not always easy in the prior art.
SUMMARY OF THE INVENTION
The present invention offers a highly accurate and inexpensive way of smoothing the gap between each area in both horizontal and vertical directions when unevenness of the video image displayed is corrected for each divided area. A video display monitor of the present invention comprises a correction data generator for generating correction data to correct unevenness in the luminance or color of the video image in at least one of the R, G, B primary colors of the video signal, a timing generator for controlling the timing to read out the correction data from the correction data generator, and a processor for correcting the video signal based on the correction data output from the correction data generator. The timing generator shifts an area to apply correction to the video signal using the correction data by controlling the timing to output the correction data from the correction data generator so that the boundary between correction blocks can be smoothed.
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patent: 4722005 (1988-01-01), Ledenbach
patent: 4788601 (1988-11-01), Kawasaki
patent: 4825201 (1989-04-01), Watanabe et al.
patent: 4941186 (1990-07-01), Massmann et al.
patent: 5179438 (1993-01-01), Morimoto
patent: 5196923 (1993-03-01), Ueda et al.
patent: 5359342 (1994-10-01), Nakai et al.
patent: 5359366 (1994-10-01), Ubukata et al.
patent: 5396257 (1995-03-01), Someya et al.
patent: 5546134 (1996-08-01), Lee
patent: 5838396 (1998-11-01), Shiota et al.
patent: 0 462 333 (1991-12-01), None
patent: 0 702 347 (1996-03-01), None
patent: 61061569 (1986-03-01), None
patent: 61-243495 (1986-10-01), None
patent: 6394782 (1988-04-01), None
Miyai Hiroshi
Shiota Tetsuro
Eisenzopf Reinhard J.
Lo Linus H.
Matsushita Electric - Industrial Co., Ltd.
Ratner & Prestia
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