Television – Image signal processing circuitry specific to television – Transition or edge sharpeners
Reexamination Certificate
2000-02-23
2001-08-21
Eisenzopf, Reinhard J. (Department: 2614)
Television
Image signal processing circuitry specific to television
Transition or edge sharpeners
C348S606000, C348S627000, C382S266000, C382S263000
Reexamination Certificate
active
06278494
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device and method for emphasizing an edge of a video signal and, more particularly, to a device which can prevent deterioration of image quality by suppressing overshoot and undershoot.
BACKGROUND OF THE INVENTION
Sharpness is one important factor that determines image quality. An edge emphasis circuit is used to improve the sharpness.
FIG. 4
is a circuit diagram for explaining a conventional edge emphasis circuit. Referring to
FIG. 4
, reference numeral
1001
denotes a video input terminal;
1002
and
1003
, delay circuits connected in series to the video input terminal
1001
in the order named;
1004
,
1005
, and
1006
, multipliers respectively connected to the video input terminal
1001
, and the outputs of the delay circuits
1002
and
1003
;
1007
, an adder for adding the outputs from the multipliers
1004
to
1006
;
1008
, a multiplier connected to the output of the adder
1007
;
1009
, an adder for adding the outputs from the multiplier
1008
and delay circuit
1003
; and
1010
, a video output terminal connected to the output of the adder
1009
. Also, reference numerals sl to s
6
denote signals at respective circuits.
FIG. 5
shows the waveforms of these signals.
In this arrangement, a video signal sl input from the video input terminal
1001
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 s
2
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 sl, s
2
, and s
3
are as shown in FIG.
5
. That is, these signals are delayed one pixel each.
These signals sl, 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 sl and s
3
are inverted, and the inverted signals sl 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.
5
.
Furthermore, the multiplier
1008
amplifies the signal s
4
to obtain a signal s
5
. The signal s
5
is an edge-emphasizing signal. The adder
1009
adds the signal s
2
output from the delay circuit
1002
to the edge-emphasizing signal s
5
, thus generating an edge-emphasized video signal s
6
. In
FIG. 5
, the edge-emphasized signal s
6
is indicated by the solid curve, and the original signal s
2
is indicated by the broken curve to overlap the signal s
6
.
However, in the conventional edge emphasis circuit described above, the leading edge of an edge portion of the signal can be improved, while overshot and undershot portions are produced, as shown in FIG.
5
. 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 considerable overshoot and undershoot result 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 suppress the aforementioned overshoot and undershoot while maintaining the improvement effect of the leading edge of an edge portion.
In order to achieve the above object, an edge emphasis device according to the first aspect of the present invention is an edge emphasis device which comprises first delay means for delaying an input signal a predetermined time, second delay means for further delaying an output signal from the first delay means a predetermined time, and second derivative signal generation means for outputting a second derivative signal of the input signal on the basis of the input signal and the output signals from the first and second delay means, characterized by comprising edge-emphasizing signal generation means for generating an edge-emphasizing signal by assigning a sign of the second derivative signal to a minimum absolute value of a difference between the input signal and the output signal from the first delay means, a difference between the output signals from the first and second delay means, and the second derivative signal, and delay addition means for outputting a signal obtained by emphasizing an edge of the input signal by adding the input signal and a corresponding edge-emphasizing signal in correspondence with each other.
According to this aspect, since the aforementioned edge-emphasizing signal generation means is provided, and an input signal is emphasized by an edge-emphasizing signal generated by that means, overshoot or undershoot produced upon emphasizing the input signal by directly adding a second derivative signal thereto can be suppressed.
An edge emphasis device according to the second aspect of the present invention is an edge emphasis device for emphasizing an edge of an image signal, characterized by comprising a second derivative signal generation circuit for outputting a second derivative signal of a target signal on the basis of a target signal, a lead signal that leads ahead of the target signal a predetermined time, and a lag signal that lags behind the target signal a predetermined time, and an edge-emphasizing signal generation circuit for generating an edge-emphasizing signal by assigning a sign of the second derivative signal to a minimum value of an absolute value of a difference between the target signal and the lead signal, an absolute value of a difference between the target signal and the lag signal, and an absolute value of the second derivative signal.
Note that the second derivative signal can use a signal obtained by subtracting the average value of the lead and lag signals from the target signal. Also, the predetermined time the lead signal leads ahead of the target signal is preferably equal to the predetermined time the lag signal lags behind the target signal. Furthermore, the predetermined time the lead signal leads ahead of the target signal and/or the predetermined time the lag signal lags behind the target signal is preferably equal to the interval between signals corresponding to neighboring pixels in the input signal upon image formation.
The respective circuits can have various patterns. Also, the respective circuits may be integrated to build an integrated circuit. When the lead signal, target signal, and lag signal are digital signals, the aforementioned functions may be implemented by a microprocessor.
In this aspect, the edge-emphasizing signal becomes the one corresponding to the target signal. Therefore, a circuit for generating an edge-emphasized signal using the edge-emphasizing signal as a compensation signal corresponding to the target signal can obtain the edge-emphasized signal. More specifically, by adding the edge-emphasizing signal to a signal to be emphasized, the edge-emphasized signal can be obtained. Especially, the edge-emphasizing signal often has a delay that cannot be ignored with respect to the signal to which the edge-emphasizing signal is added. In such case, these signals can be added in correspondence with each other. That is, as will be described later in the following embodiment, an arrangement for delaying the target signal in correspondence with the timing of the edge-emphasizing signal corresponding to the target signal is prefer
Inamura Kohei
Kanai Izumi
Masuda Yukio
Canon Kabushiki Kaisha
Eisenzopf Reinhard J.
Fitzpatrick ,Cella, Harper & Scinto
Tran Trang U.
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