Television – Image signal processing circuitry specific to television – Hue control
Reexamination Certificate
2001-06-12
2004-06-22
Lee, Michael H. (Department: 2614)
Television
Image signal processing circuitry specific to television
Hue control
C348S612000, C348S645000, C348S675000, C348S659000, C382S167000, C358S518000
Reexamination Certificate
active
06753930
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color correction circuit for color representation and a color display comprising such a color correction circuit. More particularly, the present invention relates to a color correction circuit appropriate to use in such digital display devices as a plasma display panel (PDP) and a digital micro-mirror device (DMD) in which primary color light sources, different from fluorescent materials of a CRT, are used and the relation between the applied signal strength and the intensity of display is linear because the intensity of display is digitally controlled.
A color television receiver widely used at the present time uses fluorescent materials of three primary colors, which are specified by the EBU (European Broadcasting Union), and the chromaticity values of x and y of the fluorescent materials of three primary colors (red, green, blue) are different from those of the fluorescent materials (NTSC-compliant fluorescent materials) specified by the NTSC system. Since the color reproduction area of a color television receiver is narrower than that of the NTSC-compliant fluorescent materials, it is known that a distortion in color reproduction characteristics of a color television receiver is caused to occur when color video signals of the NTSC system are displayed on a color television receiver. This phenomenon is described using the UCS chromaticity diagram in FIG.
1
.
FIG. 1
illustrates a distortion in color reproduction caused by the difference in the chromaticity values of x and y between the three primary color fluorescent materials (red, green, blue) of a currently used color television receiver and the NTSC-compliant fluorescent materials. In the figure, reference number
1
refers to the color reproduction area of the NTSC-compliant fluorescent materials and reference number
2
refers to the color reproduction area of a currently used color television receiver. Each circle g, yg, s, r, c, p, and b in the figure indicates green, yellow-green, ocher, red, cyan, pink, and blue, respectively, in the color reproduction area
1
of the NTSC-compliant fluorescent materials, and each bullet dot pointed by the arrow indicates a color when the NTSC signal corresponding to the color is displayed on a currently used color television receiver, in other words, the reproduced color in the color reproduction area
2
. The arrow indicates the shift in position in the UCS chromaticity diagram between a reproduced color in the color reproduction area
1
and that in the color reproduction area
2
due to the distortion in color reproduction. The double circles yg and b indicate that the reproduced colors are not influenced by the distortion.
As shown in the figure, there exists a difference between the color reproduction area
1
of the NTSC-compliant fluorescent materials and the color reproduction area
2
of a currently used color television receiver. The distortion of the color reproduction characteristics in a color television receiver caused by this difference occurs in the way that the distortion causes most reproduced colors to move toward the axis line
16
that connects yellow-green yg and blue b, and for example, green g or ocher s is compressed to yellow-green yg by the distortion in color. As described above, the distortion in color reproduction does not occur irregularly, instead occurs in the way that the distortion causes the position of a color reproduced by the NTSC-compliant fluorescent materials to move from both sides of an axis line (axis line
16
in
FIG. 1
) of some hues toward the axis line. In this way, the color reproduction characteristics of a color television receiver are degraded.
An example of the conventional art that solves this problem is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 57-23478. This disclosed conventional art is briefly described below.
As mentioned above, a distortion in color reproduction occurs in the direction toward an axis line in a currently used color television receiver. The conventional art corrects the distortion and improves the color reproduction characteristics by enlarging the amount of the change in the color so that the position of the color deviates from the axis line. In other words, as shown in
FIG. 1
, the conventional art corrects the compression in the direction toward the axis line
16
and cancels the distortion of color reproduction by enlarging the amount of the change in the color so that the position of the color deviates from the axis line
16
, that is, in the directions shown by the arrows
17
and
18
.
This correction method is described using FIG.
2
. In the figure, the horizontal axis is marked with phases of input chromatic signals of a color television receiver and the vertical axis is marked with phases of the corrected chromatic signals. When not corrected, the relation in phase of these chromatic signals is as shown by a dotted line, on the other hand, when corrected by the above-mentioned conventional art, the relation in phases of these chromatic signals is as shown by a solid line. By this correction, the color change is caused in the directions shown by the arrows
17
and
18
in
FIG. 1
as mentioned above.
FIG. 3
shows a block diagram that illustrates an example of a conventional color reproduction correction device that corrects the distortion in color reproduction by adjusting the hue in the direct current control method, as mentioned above. In the figure, reference number
3
refers to a band amplifier, number
4
, a reference color carrier oscillator, number
5
, a phase shifter, number
6
, a 90° phase advancer (+90°), number
7
, a hue adjuster, number
8
, a limiter, numbers
9
and
10
, phase detectors (P.D.), number
11
, a clipper, number
12
a multiplier, number
13
a direct current power source for hue adjustment, number
14
, an adder, and number
15
, a color demodulator circuit.
In
FIG. 3
, the chromatic signals of the received color video signals are limited in bandwidth by the band amplifier
3
and are supplied to the phase detectors
9
and
10
via the limiter
8
, as well as to the color demodulator circuit
15
. The burst signals taken from the band amplifier
3
are supplied to the reference color carrier oscillator
4
and a reference color carrier synchronized with these burst signals in phase is obtained. After being shifted in phase in the phase shifter
5
, the reference color carrier is supplied directly to the phase detector
9
, and at the same time supplied to the phase detector
10
after the phase is advanced in the 90° phase advancer
6
. If the characteristics of the phase shifter
5
are appropriately selected so that the phase of the output reference color carrier is yellow green, that is, 5° with respect to the phase of the burst signal of the input chromatic signal, the phase detector
9
is a phase detector for yellow green, and the phase detector
10
, a phase detector for the axis perpendicular to the yellow green signal. If we assume that the phase of yellow green signal is the reference phase, and the phase of the chromatic signal with respect to the reference phase is &thgr;, the voltage level of the output signal V
1
of the phase detector
9
will change with respect to phase &thgr; as shown by the curve V
1
in
FIG. 4A
, and that of the output signal V
2
of the phase detector
10
, as shown by the curve V
2
in FIG.
4
B. The output signal V
1
of the phase detector
9
is clipped by the clipper
11
at a specified clip level, and signal V
3
, which has the voltage characteristic with respect to phase &thgr; as shown by the curve V
3
in
FIG. 4C
, is obtained. Thus the output signal of the clipper
11
is adjusted appropriately so that the corrections
17
and
18
in the vicinity of yellow green as shown in
FIG. 1
are obtained. Here, for example, the clipping level of the clipper
11
is selected so that the range is between −60 and +60°. The output signal V
3
of the clipper
11
is multiplied by the output signal V
2
of the phase detec
Kumakura Ken
Ohki Hideaki
Ohtaka Hiroshi
Ueda Toshio
Yamada Kazuyoshi
Desir Jean W.
Fujitsu Hitachi Plasma Display Limited
Lee Michael H.
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