Computer graphics processing and selective visual display system – Data responsive crt display control – Data responsive intensity control
Reexamination Certificate
2002-09-16
2004-11-23
Chang, Kent (Department: 2673)
Computer graphics processing and selective visual display system
Data responsive crt display control
Data responsive intensity control
C345S690000, C345S611000, C348S470000
Reexamination Certificate
active
06822625
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an image processing apparatus allowing a quality of image of a color cathode-ray tube (color CRT) to be improved when it is used as a picture monitor. More particularly, it relates to the one wherein a high horizontal spatial frequency picture pattern having a peak level and a picture pattern having an edge are extracted respectively, and separate corrections are performed on these picture patterns, thereby improving sharpness of the picture without losing the color saturation.
BACKGROUND ART
It is known that, with a picture display apparatus such as the color CRT used as a picture monitor, the waveform becomes dull by passage through signal transmission system of an input picture signal from a signal input unit to a cathode electrode of the color CRT. Further, it is not possible to ensure a sufficient bandwidth for a high input picture signal because of attenuation of a horizontal spatial frequency bandwidth due to the aperture effect in a color CRT display system.
It is known that the sharpness of the image is not sufficient for these reasons. Therefore, for example, when this picture monitor is used as a computer display or the like, it cannot show a small character clearly, so that small character information tends to become difficult to see. Further, particularly for thin line display, a white vertical line on a black background tends to be darker, and a black vertical line on a white background tends to thicken in the horizontal direction.
For this reason, an attempt has been made to sharpen the picture by using the following means in the art. First, for the dullness of the waveform generated in the signal transmission system, correction is made by using a peaking correction circuit. The peaking correction is a processing for compensating the lacking frequency bandwidth by performing a processing for increasing the gain with respect to a given specific horizontal frequency.
For changing the gain by the horizontal frequency, it is recommendable that the impedance determining the gain is allowed to have a frequency characteristic. A specific example of the peaking correction circuit will be described by reference to
FIG. 1. A
peaking correction circuit
10
is provided between a picture output stage and a cathode electrode of the color CRT, and a grounded emitter amplifier is used as the peaking correction circuit
10
, as shown in FIG.
1
.
An input picture signal such as a monochrome picture signal SR of R is supplied to a base terminal
12
of an NPN transistor Q. A collector thereof is connected to a power source +Vcc via a resistor
14
and an impedance element
16
which is a serial peaking correction element. Further, an emitter peaking circuit
20
of a resistor
20
a
and a capacitor
20
b
may be also connected in parallel to an emitter resistor
18
thereof.
Herein, the high frequency gain of the output picture signal is determined by the impedance element
16
, the resistor
20
a
, and the capacitor
20
b
. Therefore, utilizing the peaking correction circuit
10
allows the gain for the high frequency component of the input signal frequency to increase, thereby compensating for the loss due to the signal transmission system.
The state of correction by peaking is shown in
FIGS. 2A
to
2
C and
FIGS. 3A
to
3
C.
FIGS. 2A
to
2
C show the case of a white image on a black background, while
FIGS. 3A
to
3
C show the case of a black image on a white background.
FIGS. 2A and 3A
show ideal waveforms, and
FIGS. 2B and 3B
respectively show the signal waveforms each deteriorated by passage through the signal transmission system. Then,
FIGS. 2C
and
3
C respectively show the signal waveforms each improved by the peaking processing.
Due to the waveform deterioration in the signal transmission system, for
FIG. 2B
, white information on a black background darkens, and for
FIG. 3B
, the line width of black information on a white background increases, as well as the level of the black display portion of the signal increases, resulting in a deterioration in contrast of the detail (the vertical line of a character, or the like) to be expressed. The reduction in contrast is a serious problem particularly for a computer display. However, it is indicated that the reduction in level and the reduction in contrast are both improved by peaking correction as apparent from the waveform processings of
FIGS. 2C and 3C
.
On the other hand, for the aperture effect of a CRT display system, correction is performed by enhancing the edge of the input picture signal. The edge portion of a picture is enhanced by aperture correction whereby preshoot and overshoot are added to the edge portion, so that the apparent performances of the CRT display system are improved by this enhancement processing.
FIG. 4
shows a specific example of an aperture correction circuit
30
. It has a pair of delay circuits
32
and
34
as well as the delay circuit
32
of the first stage receives an input picture signal from an input terminal
36
. Its delay output is supplied to an adder
50
. Then, an adder
46
adds the ones obtained by multiplying the inputs and outputs of the respective delay circuits
32
and
34
by coefficients ((−1) fold and two fold) as shown by means of coefficient multipliers
40
,
42
, and
44
. The one obtained by multiplying the addition output SRe at a coefficient multiplier
48
is supplied to the adder
50
, which adds it to the output picture signal.
FIGS. 5A
to
5
E are waveform diagrams each showing the operations wherein picture signals SRa and SRc respectively preceding and succeeding an input picture signal serving as a reference such as a monochromatic picture signal SRb by one pixel (
FIGS. 5A
to
5
C) are obtained. These are subjected to coefficient multiplication and then passed to the adder
46
, so that an edge signal SRe as shown in
FIG. 5D
is obtained. The coefficient multiplier
48
appropriately adjusts the gain thereof and the one thus adjusted is added to the reference picture signal SRb, thereby obtaining a picture signal SRo whose leading and trailing edges are respectively enhanced as shown in FIG.
5
E.
Incidentally, if the peaking correction is performed, it is possible to improve the above described state in which white information on a black background darkens, and it is possible to improve the above described state in which the line width of black information on a white background appears to be large. Further, there are a feature that the deterioration in contrast is also eliminated, and other features.
However, if the peaking correction is performed, ringing occurs. Accordingly, particularly for the case as shown in
FIG. 3C
, the black information looks whitely edged, so that the quality of the image is largely impaired.
Further, even if ringing roughly has the amplitude characteristic due to the peaking processing, the group delay characteristic is difficult to flatten, and ringing increases with an increase in peaking amount.
Namely, for the peaking correction, the improvement in edge dullness and the inhibition of ringing are not completely compatible. This is because if the peaking amount is decreased, the improvement of the dullness of the edge is insufficient, but it is possible to inhibit ringing: in contrast, if the peaking amount is increased, it is possible to improve the dullness of the edge, but ringing becomes noticeable.
Peaking correction is performed using the resistor, the capacitor, the impedance element, and the like as described above. However, variations in constants of these elements, and variations in value due to the temperature characteristics occur, and hence stable peaking correction is impossible.
On the other hand, in aperture correction, the following problems are presented.
The width of the edge added by aperture correction equals to the unit delay time of the delay circuits
32
and
34
as apparent from
FIGS. 5A
to
5
E. Essentially, the edge is added to a picture, and hence it is constant with respect to the spatial frequency. Namely, it shou
Tomizawa Hidekazu
Yamashita Hiroshi
Yamazaki Nobuo
Chang Kent
Maioli Jay H.
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