Television – Image signal processing circuitry specific to television – Chrominance-luminance signal separation
Reexamination Certificate
2001-07-10
2004-10-26
Kostak, Victor R. (Department: 2614)
Television
Image signal processing circuitry specific to television
Chrominance-luminance signal separation
C348S670000
Reexamination Certificate
active
06809778
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus and method for YC separation and three-line correlation detection providing luminance (often represented as Y) signals with high accuracy in luminance and chrominance signals separation, i.e., YC separation using between-lines correlation found in composite video signals.
BACKGROUND OF THE INVENTION
In recent years, three-line correlation detection has received much attention for its luminance and chrominance signals separation (YC separation) with high accuracy, which is effectively used in a cost-valued television-set having no three-dimensional YC separator with frame memory.
Now will be described an example of the prior-art three-line correlation detecting apparatus, referencing to the accompanying drawings.
FIG. 8
shows a block diagram of an YC separator employing the correlation detecting apparatus disclosed in Japanese Patent Laid-Open No. 8-65706. In the figure, receiving composite video signals as an input, three-line signal separator (three-line comb filter)
1
outputs a separated chrominance signal C′. Band-pass filter (BPF)
3
isolates high-band components from the composite video signals to output a chrominance signal C″.
According to the output from correlation detector
2
, i.e., the output from OR circuit
9
, selector
11
chooses either the signal C′ fed from three-line comb filter
1
, or the signal C″ fed from BPF
3
filtering chrominance signals. Selector
11
then passes the selected signal CC to one end of subtractor
15
as the chrominance signal.
The composite video signal are also fed into delay circuit
13
, which controls output timing by providing the signal with a delay, and then passed to the other end of subtractor
15
. Receiving the delayed composite video signal from delay circuit
13
, subtractor
15
subtracts signal CC from the delayed signal to generate luminance (Y) signal.
Here will be described the object of correlation detector
2
and the structure of the three-line correlation detecting apparatus both of which are introduced in the prior-art.
Suppose that processing the composite video signal having a high correlation in a direction perpendicular to the horizontal lines—the signal with a high vertical correlation with respect to the screen—for example, an image showing vertical stripes. In this case, allowing selector
11
to output signal C′ fed from three-line C separator (three-line comb filter)
1
as signal CC to subtractor
15
can generate a Y signal with a good quality.
Now suppose that processing the composite video signal with a low vertical correlation with respect to the screen—for example, an image showing one horizontal red scanning lines against a white background. If a Y signal is generated from output signal C′ determined as signal CC, dot interference caused by chrominance signals occurs at the horizontal red lines on the screen—a structural weak point of three-line comb filter
1
. That is, because the chrominance level of output signal C′ at the horizontal red lines is decreased to half its normal value, subtractor
15
cannot completely cancel out the chrominance signal. As a result, the residual chrominance signals in the Y signal cause dot interference. In such a screen with a low vertical correlation, allowing selector
11
to output signal C″ fed from BPF
3
as signal CC can generate a Y signal, with dot interference from the chrominance signal suppressed. In this case, however, the high band characteristics of the Y signal are deteriorated.
As described above, the YC separator using the correlation detecting apparatus can properly switch between output signal C′ and output signal C″ according to the level of the detected vertical correlation with respect to the screen, which can generate a good Y signal.
FIG. 9
is a block diagram of the YC separation circuit that is embodied in Japanese Patent Laid-Open No. 8-65706. In the figure, frame
66
surrounded by the dotted lines represents the three-line correlation detecting apparatus, the rest in the figure shows the YC separator.
FIG. 10
shows a block diagram indicating the vertical impulse detector of three-line correlation detecting apparatus
66
.
In
FIG. 9
, the composite video signals are separated into the
0
H signal, the
1
H signal (delayed by delayed element
21
for one horizontal scanning period), and the
2
H signal (delayed by delayed elements
21
and
23
for two horizontal scanning periods), each of which is filtered by low-pass filters (LPFs)
41
,
43
, and
45
, respectively. The filtered signals f, g, and h—the low-band components (luminance signals) of the composite video signal passed through LPFs
41
,
43
, and
45
, respectively—are fed into low-band vertical impulse detector
47
. On the other hand, high-band components (chrominance signals) of the composite video signal, which have passed through band-pass filters (BPFs)
49
,
51
, and
53
, have opposite phases by
1
H. Inverters
55
and
57
process the signals having different phases into in-phase chrominance signals i, j, and k, all of which are fed into high-band vertical impulse detector
59
.
FIG. 10
shows the structure of the vertical impulse detector, which is employed for detector
47
for low-band and detector
59
for high-band. In the figure, accepting signals f, g, and h, subtractors
71
and
73
calculate differential signals by subtracting signal f from signal g, and by subtracting signal h from signal g, respectively. Absolute-value calculators (ABSs)
75
and
77
obtain each absolute value of respective differential signals. Receiving the two values, comparators
79
and
81
compare each value with respective predetermined reference values REFs, which are predetermined by comparators
79
and
81
. The two outputs from comparators
79
and
81
are applied to AND circuit
83
.
To provide the detection through the process above with accuracy, exclusive NOR circuit
85
is placed between the subtractor and ABS. If circuit
85
detects that the two differential signals have same signs, the output from circuit
85
and the output from AND circuit
83
are further applied to AND circuit
87
, with the final output in
FIG. 10
obtained.
High-band vertical impulse detector
59
shown in
FIG. 9
can be the same as the structure illustrated in FIG.
10
.
The output from detector
47
and the output from detector
59
are applied to OR circuit
61
, and the result is determined as the output of three-line correlation detector
66
. If vertical impulse is detected either detector
47
or
59
, detector
66
determines that the correlation is low. The output from detector
66
takes the form of “1” or “0”: “1” indicating low correlation, “0” indicating the presence of the correlation.
As described above, the prior-art three-line correlation detecting apparatus detects correlation between the lines carrying the chrominance signal and the luminance signal of the composite video signal, and then outputs “0” or “1” depending on the presence or absence of the correlation.
According to the output from the correlation detecting apparatus, YC separator switches the filter used in separation; when accepted the output that represents the presence of the correlation, the separator uses three-line comb filter (5 tap median filter), otherwise uses BPF. In the case that a screen shows one horizontal red scanning lines against a white background described earlier, the correlation detector determines that the correlation is low, thereby uses BPF to generate the Y signal. This therefore suppresses dot interference in the Y signal. It still has, however, room for improvement in performance—a series of noises vertically generated on the screen.
The vertically generated in-series noises may occur between adjacent video processing devices. Compared to a noise occurred randomly, the noise spoils the view due to its occurrence in series on a regularly basis.
The frequency spectrum of such a noise is distributed over the range from the lower-middle band to h
Shibutani Ryuichi
Taketani Nobuo
Kostak Victor R.
RatnerPrestia
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