Television – Image signal processing circuitry specific to television – Transition or edge sharpeners
Reexamination Certificate
2000-02-22
2003-07-08
Brier, Jeffery (Department: 2672)
Television
Image signal processing circuitry specific to television
Transition or edge sharpeners
C345S589000, C345S611000, C382S263000, C382S266000, C382S267000, C382S268000, C382S269000, C348S606000, C348S627000, C348S628000, C327S170000
Reexamination Certificate
active
06590617
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device for emphasizing an edge of a video signal.
BACKGROUND OF THE INVENTION
Sharpness is one important factor that determines image quality. An edge emphasis circuit is used to improve the sharpness.
FIG. 6
shows a conventional edge emphasis circuit. Referring to
FIG. 6
, reference numeral
1001
denotes a video input terminal;
1002
and
1003
, delay circuits;
1004
,
1005
, and
1006
, multipliers;
1007
, an adder;
1008
, a multiplier;
1009
, an adder; and
1010
, a video output terminal. Also, reference numerals s
1
to s
6
denote signals at respective circuits.
FIG. 7
shows the waveforms of these signals.
An input video signal s
1
is input to the multiplier
1004
and first delay circuit
1002
. The first delay circuit
1002
delays the input signal one pixel, and outputs a signal s
2
. The signal s
2
is input to the multiplier
1005
, second delay circuit
1003
, and adder
1009
. The signal input to the second delay circuit
1003
is further delayed one pixel, and is output as a signal s
3
. The waveforms of these three signals s
1
, s
2
, and s
3
are as shown in FIG.
7
. That is, these signals are delayed one pixel each.
These signals s
1
, s
2
, and s
3
are respectively input to the multipliers
1004
,
1005
, and
1006
, and are respectively multiplied by ½, 1, and ½. The signs of the signals s
1
and s
3
are inverted, and the inverted signals s
1
and s
3
, and non-inverted signal s
2
are input to the adder
1007
. The adder
1007
adds these signals, and outputs a sum signal s
4
. That is, the signal s
4
assumes a value obtained by subtracting the average value of the previous and next image data from an image data value at a given point, i.e., a second derivative value at that point. The waveform of the signal s
4
is as shown in FIG.
7
.
Furthermore, the multiplier
1008
amplifies the signal s
4
to obtain a signal s
5
. The signal s
5
is an edge-emphasized signal. The adder
1009
adds the signal s
2
output from the delay circuit
1002
to the edge-emphasized signal s
5
, thus generating an edge-emphasized video signal s
6
. A signal indicated by the solid curve in the signal s
6
in
FIG. 7
is the edge-emphasized signal, and a signal indicated by the broken curve is the original signal s
2
.
However, in the conventional edge emphasis circuit described above, as indicated by the solid curve in the signal s
6
in
FIG. 7
, the leading edge of an edge portion of the signal can be improved, while overshot and undershot portions are produced. If such overshoot and undershoot are considerable, the image quality deteriorates due to a fringe formed at the boundary. When the coefficient of the multiplier
1008
is decreased to eliminate such overshoot and undershoot, the edge emphasis amount decreases in turn, and the improvement effect of the leading edge of the edge portion becomes small.
As described above, in the conventional edge emphasis circuit, the leading or trailing edge of the edge portion can be improved to obtain a sufficient edge emphasis effect, while overshoot and undershoot tend to increase, resulting in deterioration of image quality.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation, and has as its object to provide an edge emphasis device which can maintain the improvement effect of the leading edge of an edge portion while suppressing overshoot and undershoot.
The present invention also provides a device which can set the overshoot/undershoot suppression level.
In order to achieve the above object, an edge emphasis device of the present invention comprises the following arrangement. That is, there is provided an edge emphasis device comprising:
extraction means for extracting signals for three pixels including a pixel of interest and two neighboring pixels, from a time-serially input video signal;
first computation means for computing absolute values of differences between the extracted pixel of interest and the two neighboring pixels;
means for selecting a smaller one of the two absolute values obtained by the first computation means, and outputting the selected value as a first signal;
second computation means for computing a second derivative on the basis of the signal for three pixels extracted by the extraction means, and outputting the second derivative signal as a second signal;
third computation means for computing an absolute value of the second signal, comparing the absolute value with a predetermined threshold value, selecting a smaller one of the absolute value and threshold value, and outputting the selected value as a third signal;
sign checking means for checking a sign of the second signal, and outputting a checking result as a fourth signal;
fourth computation means for generating an edge-emphasizing signal on the basis of the first, third and fourth signals; and
addition means for adding the edge-emphasizing signal obtained by the fourth computation means to the signal of the pixel of interest, and outputting the sum signal as an edge-emphasized signal.
Also, according to a preferred embodiment of the present invention, the edge emphasis device comprises the following arrangement.
That is, an edge emphasis device comprises delay means for delaying an input first signal a predetermined period time to generate a second signal, delay means for further delaying the second signal the predetermined time to generate a third signal, three multiplication means for respectively multiplying the first, second, and third signals by predetermined coefficients to generate fourth, fifth, and sixth signals, computation means for computing the fourth, fifth, and sixth signals to output a seventh signal as a second derivative signal, minimum value selection means for comparing the absolute value of the seventh signal and a given adjustable value, selecting a smaller one, and outputting the selected signal as an eighth signal, sign checking means for checking the sign of the seventh signal, and outputting a ninth signal, minimum value selection means for comparing the absolute value of the difference between the first and second signals, and that of the difference between the second and third signals, selecting a smaller one, and outputting the selected signals as a tenth signal, multiplication means for multiplying the eighth and tenth signals, and determining the sign of the product based on the ninth signal to generate an eleventh signal, and addition means for adding the eleventh signal and a signal obtained by delaying the second signal the predetermined time.
Alternatively, the edge emphasis device the following arrangement.
That is, an edge emphasis device comprises delay means for delaying an input first signal a predetermined period time to generate a second signal, delay means for further delaying the second signal the predetermined time to generate a third signal, three multiplication means for respectively multiplying the first, second, and third signals by predetermined coefficients to generate fourth, fifth, and sixth signals, computation means for computing the fourth, fifth, and sixth signals to output a seventh signal as a second derivative signal, means for suppressing the seventh signal to have a value within a given range, and outputting the suppressed signal as an eighth signal, minimum value selection means for comparing the absolute value of the difference between the first and second signals, and that of the difference between the second and third signals, selecting a smaller one, and outputting the selected signals as a tenth signal, multiplication means for multiplying the eighth and tenth signals to generate an eleventh signal, and addition means for adding the eleventh signal and a signal obtained by delaying the second signal the predetermined time.
The present application includes the following invention.
That is, one of the inventions of an edge emphasis device associated with the present application is an edge emphasis device for emphasizing an edge of an image signal, compr
Hiraki Yukio
Inamura Kohei
Kanai Izumi
Amini Javid
Brier Jeffery
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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