Television – Image signal processing circuitry specific to television – Transition or edge sharpeners
Reexamination Certificate
1999-04-05
2003-07-22
Hsia, Sherrie (Department: 2614)
Television
Image signal processing circuitry specific to television
Transition or edge sharpeners
C348S627000, C348S630000
Reexamination Certificate
active
06597407
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a contour correction circuit for displaying a sharp picture free from degrading picture quality regardless of any kinds of scenes supplied to a video display apparatus including a television receiver, and also relates to a contour correction method.
PRIOR ART
The technique to realize sharper pictures has been pursued since the advent of television receivers (TV) in the market. Recently, the screen of TV has become larger and larger, which emphasizes particularly an importance of this technique, i.e. the technique of enhancing sharpness of a reproduced-image on the screen. Further, digital technique introduced in TV allows accurate time control as well as fine control over picture quality, so that further sharper and clearer pictures are demanded.
A conventional contour correction circuit is described hereinafter with reference to the accompanying drawings.
FIG. 7
is a block diagram of a conventional contour correction circuit.
FIG. 8
illustrates an operational concept of the circuit shown in FIG.
7
.
In
FIG. 7
, corrected-waveform-generating-circuit
1
generates contour correction waveform
205
by differentiating video-input-signal
200
in twice. Variable amplifier
2
receives an output signal from generator
1
and controls amplitude of contour correction signal
215
responsive to a size of control signal
210
determined by a picture quality controller. Picture quality controller
3
determines a gain of amplifier
2
. Delay circuit
4
synchronizes contour correction signal
215
tapped off from amplifier
2
with video input signal
200
. Adding circuit
5
adds delayed video input signal
220
tapped off from delay circuit
4
to contour correction signal
215
so that video output signal
225
with sharpness is supplied. The operation of the circuit discussed above is described hereinafter.
Corrected-waveform-generating-circuit
1
receives input video signal
200
. As shown in
FIG. 8
, signal
200
is twice differentiated in generator
1
so that contour corrected waveform
205
is generated. Variable amplifier
2
amplifies corrected waveform
205
responsive to a size of control signal
210
determined by picture quality controller
3
. Contour corrected signal
215
is thus supplied from amplifier
2
. Delay circuit
4
delays the input video signal to be synchronized with signal
215
delayed by generator
1
and amplifier
2
. Adding circuit
5
adds delayed video input signal
220
tapped off from delay circuit
4
to contour correction signal
215
so that video output signal
225
with sharpness due to contour correction is supplied.
However, in the circuit structure discussed above, once the picture quality controller determines a control voltage at a certain level, amount of contour correction stays constant regardless of any input video signals. Therefore, in the case of a blank picture, e.g. when a picture shows only a blue sky, noises are conspicuous.
In order to address this problem, a method for automatically controlling the contour correction amount with regard to a detected amount was proposed. The detected amount corresponds to a fine portion out of an entire picture, e.g. lawn portion in the entire picture, the lawn portion having a little change of the amplitude corresponding to the edge portion of the input video signal.
The Japanese Letters of Patent No. 2532605 teaches the method as discussed above in FIG.
5
and
FIG. 6
illustrating a conventional contour correction circuit.
Input video signal
200
is fed in parallel into delay circuit
4
, first corrected waveform generating circuit
11
, second corrected waveform generating circuit
12
and high pass filter
15
. Delay circuit
4
adjusts the timing of input video signal
200
to meet a delay of the circuit system, and outputs the resultant delayed video signal
200
to adding circuit
10
.
First-corrected-waveform-generating-circuit
11
produces contour-emphasis-signal
230
with regard to a signal having a high contrast ratio, i.e. a large change in amplitude corresponding to a crisp edge portion of signal
200
, and supplies signal
230
to first variable amplifier
13
. A noise component included in input video signal
200
is too little to be carried by signal
230
. Amplifier
13
controls the amplitude of signal
230
responsive to a voltage determined by controller
3
, and outputs the resultant signal to adding circuit
10
as the amplified-contour-emphasis-signal
240
.
Second-corrected-waveform-generating-circuit
12
produces fine-contour-emphasis-signal
235
with regard to a small amplitude portion out of signal
200
, and sends it to second variable amplifier
14
.
Amplifier
14
controls the amplitude of emphasis signal
235
responsive to the sum of output voltages from controller
3
and smoothing circuit
21
. Adding circuit
10
adds signal
240
and signal
245
to signal
220
, then outputs video signal
225
undergone the contour correction process.
A method of obtaining fine-portion-controlling-voltage
280
that controls a gain of second variable amplifier
14
is now described hereinafter.
First, high pass filter
15
extracts high-frequency-portion out of input video signal
200
so that high-band-video signal
250
is formed.
Second, full-wave-rectifying circuit
16
rectifies high band video signal
250
so that rectified high-band-video-signal
255
is formed. First clipping circuit
17
removes subtle signals from signal
255
so that clipped and rectified high-band-video-signal
260
is obtained.
Then, signal
260
is fed into limiting circuit
18
and second clipping circuit
19
respectively. Limiting circuit extracts fine signals only so that fine-portion-video-signal
265
is formed.
Second clipping circuit
19
extracts edge portions having high contrasts so that contour video signal
270
is obtained. Fine-portion-video-signal
265
includes contour-portion besides fine-portion in a strict sense. Therefore, subtracting circuit
20
subtracts signal
270
from signal
265
to obtain an accurate fine-portion-signal-component, and then outputs fine-controlling-pulse-signal
275
.
Smoothing circuit
21
smoothes signal
275
so that a voltage responsive to an amount of fine portions can be obtained. Accordingly, this voltage is lowered at a picture having relatively smaller fine-portion. Since this voltage controls the amplitude of the fine-portion-emphasis-signal
235
, the fine-portion is not so much emphasized, and noises are reduced. On the contrary, when a picture has relatively greater fine-portion signals, the fine-portion is strongly emphasized so that the picture can be sharply enhanced.
The circuit structure discussed above still has the following problem.
Fine-portion-controlling voltage
280
averaged by the smoothing circuit controls the gain of second variable amplifier
14
. Therefore, when a signal having a high contrast ratio such as input video signal
200
shown in
FIG. 6
is adjacent to a signal having a low contrast ratio such as a signal corresponding to vague edge portion where an amplitude changes a little, fine-portion-controlling voltage
280
is corrected only at its average value. Thus the fine-portion-emphasis-signal is also added to output video signal
225
having a high contrast ratio as shown in FIG.
6
.
As a result, a picture port ion having a high contrast is provided with unnecessary edge enhancement, and the noises of this portion are also emphasized.
DISCLOSURE OF THE INVENTION
The present invention addresses the problem discussed above and aims to provide a contour correction circuit having the following structure and also provide a contour correction method using the same circuit.
The contour correction circuit of the present invention comprises the following element:
(a) a delay circuit for delaying an input video signal;
(b) corrected waveform generating circuit for generating a contour correction signal using the input video signal;
(c) a variable amplifier for controlling an amplitude of the contour correction signal;
(d) contour control circuit for su
Kageyama Atsuhisa
Taketani Nobuo
Hsia Sherrie
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
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