Television – Image signal processing circuitry specific to television – Color balance or temperature
Reexamination Certificate
2000-11-27
2003-06-17
Kostak, Victor R. (Department: 2611)
Television
Image signal processing circuitry specific to television
Color balance or temperature
C348S631000, C348S600000
Reexamination Certificate
active
06580464
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a color difference signal correction apparatus which makes a correction for changing color temperatures of brighter whites such as white telop characters in display outputs of digitally driven display devices or the like. More particularly, this invention relates to a color difference signal correction apparatus for making a correction of white characters (hereinafter referred to as white character correction).
BACKGROUND OF THE INVENTION
In recent years, the demand for digitally driven display devices such as PDP (plasma display panel) and LCD (liquid crystal display) is growing, and the demand for image quality is more and more increasing. A color difference signal correction apparatus for particularly correcting color temperatures of white characters, i.e., making the white character correction has become valued as a circuit for changing a balance between primary colors of red, blue and green and correcting the color temperatures to make images more clear.
FIG. 5
is a block diagram illustrating a structure of a prior art color temperature correction apparatus for making the above-mentioned white character correction, disclosed in Japanese Published Patent Application No.2-196588. In this figure, a color signal detection circuit
54
receives color difference signals (R−Y) Sf, (G−Y) Sg and (B−Y) Sd obtained from a color demodulation circuit (not shown) which is provided in a previous stage of the color temperature correction apparatus, and outputs the maximum value among these color difference signals as a color detection signal Sh, thereby detecting a color. An addition circuit
55
adds an input luminance signal Sa and the color detection signal Sh which is output by the color signal detection circuit
54
, and outputs a corrected luminance signal Si. A slice circuit
51
compares a slice level voltage which is output by a slice level voltage generation circuit
52
with the corrected luminance signal Si from the addition circuit
55
, and when the input corrected luminance signal is below the slice level voltage outputs this signal as a correction signal Sc. The slice level voltage generation circuit
52
generates a DC voltage for deciding a level at which the output of the addition circuit
55
is sliced. A subtraction circuit
53
subtracts the correction signal Sc which is output by the slice circuit
51
from the color difference signal (B−Y) Sd, and outputs a corrected color difference signal. A clamping circuit
56
returns the pedestal level of the luminance signal, which has been changed due to the addition to the original level on the basis of a horizontal synchronous pulse Sj.
FIG. 6
is a circuit diagram illustrating the structure of the color signal detection circuit
54
. The color signal detection circuit
54
comprises transistors
61
,
62
and
63
, bases of which receives the color difference signals (R−Y) Sf, (B−Y) Sd and (G−Y) Sg, respectively, and their base resistors
64
,
65
and
66
. Emitters of the transistors
61
,
62
and
63
are commonly connected and constitutes a color detection signal output terminal, and the transistors
61
,
62
and
63
are grounded via a common emitter resistor
67
. In addition,the power voltage +B is supplied to the correctors. The detected color signal is output as the color detection signal Sh from the color detection signal output terminal.
FIGS.
7
(
a
)-
7
(
h
) are diagrams showing waveforms of signals which are obtained in the respective elements of the prior art color temperature correction apparatus. FIG.
7
(
a
) shows the waveform of the input luminance signal Sa. FIGS.
7
(
b
),
7
(
c
) and
7
(
d
) show the waveforms of the color difference signals (R−Y) Sf, (G−Y) Sg and (B−Y) Sd, respectively. FIG.
7
(
e
) shows the waveform of the color detection signal Sh. FIG.
7
(
f
) shows the waveform of the corrected luminance signal Si and the waveform of the slice level signal Sb. FIG.
7
(
g
) shows the waveform of the correction signal Sc, and FIG.
7
(
h
) shows the waveform of the corrected color difference signal Se.
Hereinafter, the operation of the so-constructed color temperature correction apparatus will be described. Initially, the color difference signals (R−Y) Sf, (G−Y) Sg and (B−Y) Sd having the waveforms as shown in FIGS.
7
(
b
)-
7
(
d
), respectively, which are output by the color modulation circuit in the previous stage (not shown) are input to the color signal detection circuit
54
. The color signal detection circuit
54
detects the maximum value among the three input signals and outputs the detected color signal as the color detection signal Sh. Then, the color detection signal Sh and the input luminance signal Sa as shown in FIG.
7
(
a
) are added by the addition circuit
55
and the corrected luminance signal Si is output. In this prior art, assume that a brighter luminance signal has a lower voltage. The corrected luminance signal Si is input to the slice circuit
51
and compared with the slice level voltage Sb from the slice level voltage generation circuit
52
, as shown in FIG.
7
(
f
). Then, a part of the luminance signal, which is lower than the voltage Sb is output as the correction signal Sc as shown in FIG.
7
(
g
). Then, the correction signal Sc is input to the subtraction circuit
53
and subtracted from the input color difference signal (B−Y) Sd, whereby the corrected color difference signal Se which has been corrected to increase the color temperature of the sliced part is obtained.
As described above, in the prior art color temperature correction apparatus, the color signal detection circuit
54
detects the maximum value among the input three color difference signals and outputs the color detection signal Sh. Then, the color detection signal Sh is added to the input luminance signal Sa. Accordingly, the input luminance signal is corrected to increase its level by the color detection signal Sh in a colored part. Consequently, the input luminance signal is not sliced in the colored part and therefore even when the luminance is higher the color temperature correction is not performed to the colored part, i.e., the part which is not white.
However, in the prior art, only the maximum value among the input color difference signals (R−Y), (B−Y) and (G−Y) is extracted by the color signal detection circuit and added to the input luminance signal, whereby the white character correction is hardly performed in the colored parts. Therefore, in some cases, the white character correction may be applied to light colors like flesh tones. In addition, it is impossible to make a fine adjustment to the white character correction with high accuracy so that the white character correction is not applied to the light colors like flesh tones.
In addition, according to the prior art construction, in cases of a picture whose frame is entirely whitish, i.e., a picture having a high brightness level of the whole frame, the color temperature correction is performed to many parts in the frame. Therefore, the sufficient effects of the white character correction cannot be obtained and further the frame becomes generally bluish.
Further, according to the prior art construction, the base resistors and the emitter resistors are used in the color signal detection circuit. The maximum value of the color is adversely varied due to dispersion errors of these resistors. Accordingly, when the luminance signal is to be shifted toward black according to the sizes of the color, there is the possibility that the signal is sliced and then the white character correction is performed with low accuracy.
Furthermore, according to the prior art construction, the fine adjustment to the effects of the white character correction so that an image which is obtained as a result of the white character correction has an optimum image quality for an apparatus which utilizes the color temperature correction apparatus cannot be made.
SUMMARY OF THE INVENTION
It i
Ishikawa Katsuya
Kageyama Atsuhisa
Kunitani Hisao
Kostak Victor R.
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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