JPH0588596B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a luminance signal/chrominance signal separation circuit, and is particularly suitable for application to a color video signal processing device.

B. Summary of the Invention The present invention provides a luminance signal/chrominance signal separation circuit having a comb filter including a CCD element as a 1H delay element. By providing the comb filter on the output side, it is intended to prevent deterioration of the image quality of the video signal.

C. Prior Art Composite color television signals are
As shown in the figure, the frequency distribution of the luminance signal Y is 3.58
The frequency range extends to the frequency range that is superimposed on the color signal C modulated by a color subcarrier having a carrier frequency of [MHz], and the components of the luminance signal Y that are superimposed on the color signal C are in a frequency interleaved relationship with each other. By filtering the color signal C with a comb filter, the color signal C can be separated from the luminance signal Y.

The comb filter is configured to include a 1H delay element, and thus has a so-called comb characteristic having a passband at every horizontal synchronization frequency _fH . In addition, CCD (charge coupled
device) is known.

D Problems to be solved by the invention However, due to its structure, CCD has a so-called 1/f
There is an unavoidable problem that low frequency noise called noise is generated. This 1/f noise N is thought to be caused by short key noise that occurs when the CCD performs switching operation.
As shown in FIG. 3, the 1/f noise N has a frequency characteristic in which the noise level increases rapidly in a low frequency region.

When this 1/f noise N is mixed into the separated color signal C, it causes a visual disturbance that gives a grainy appearance to the image displayed on the display.
This becomes a problem especially when trying to obtain a clearer image.

The present invention has been made in consideration of the above points, and
This paper attempts to propose a luminance signal/chrominance signal separation circuit that can effectively avoid the effects of 1/f noise when using a comb-shaped filter including a CCD delay element.

E. Means for Solving the Problems In order to solve these problems, the present invention includes a first bandpass filter 1 that passes a frequency component corresponding to a color signal component included in the composite input video signal VDIN; A comb filter 2 includes a CCD element as a 1H delay element that passes a color signal component out of the output of the first bandpass filter 1, and a 1/1/2 output from the CCD element out of the output of this comb filter 2 The output S1 of the first band pass filter 1 is subtracted from the output S3 of the second band pass filter 3 having a cutoff frequency characteristic that does not pass the f noise component, and the subtraction output S4 is obtained. a first subtraction circuit 4 which emits as a separated color signal output, and a composite input video signal VDIN.
A second subtraction circuit 5 that subtracts the output S1 of the first bandpass filter 1 from the subtraction circuit 5 to obtain the subtracted output S5.
and first and second bandpass filters 1 and 3
In response to the outputs S1 and S3, the two outputs S1
and S3, the first bandpass filter 1
A correlator 7 which obtains an output S6 consisting of a luminance signal component having a frequency corresponding to a passband of An adder circuit 6 is provided which emits a signal output S7.

F Function The color signal component C included in the composite input video signal VDIN is filtered in the first bandpass filter 1 together with the luminance signal component Y superimposed thereon, and the color signal component C in a frequency interlaced relationship is filtered. is further filtered in a CCD comb filter 2. As a result, in the output S2 of the CCD comb filter 2, the color signal component located at the frequency interlace position is separated from other signal components. However, in the color signal component C of this output S2, the luminance signal component superimposed at the same frequency position remains without being completely removed. The subtraction is performed so as to cancel each other out, and thus a separated color signal output S4 containing no luminance signal component is obtained at the output end of the first subtraction circuit 4.

On the other hand, in the second subtraction circuit 5, the component in the frequency band of the luminance signal of the composite input video signal VDIN is extracted by subtracting the output S1, so that it does not have a signal component in the frequency band of the chrominance signal. Output S5 is supplied to adder circuit 6.
Among the signal components of this extracted frequency band, the luminance signal component Y is added in the adder circuit 6 as the output S6 obtained from the correlator 7, and thus a separated luminance signal output S7 can be obtained at the output end of the adder circuit 6. .

In addition to the above operations, CCD comb filter 2
In this case, a 1/f noise component, which is a low frequency component generated by a CCD element incorporated as a 1H delay element, is mixed into the output S2. However, this 1/f noise component cannot pass through the second bandpass filter 3 due to its cutoff frequency characteristics and is removed. In this way, it is possible to prevent the 1/f noise component from being mixed into the separated color signal output S4, and thus it is possible to prevent deterioration of image quality.

G. Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 generally shows a luminance signal/chrominance signal separation circuit in which a bandpass filter 1 receives a composite input video signal VDIN having a luminance signal Y and a chrominance signal C superimposed thereon as described above with reference to FIG. As shown in Figure 4, the bandpass filter 1 has a center frequency of 3.58 ± 3.58 [MHz].
It has a cutoff frequency of 0.5 [MHz], and thus an output S1 consisting of a color signal C and a luminance signal Y superimposed thereon is obtained at its output end, and this output S1 is input to a CCD comb filter 2. be done.

As shown in FIG.
Among them, the color signal component C is extracted. As shown in FIG. 6, the CCD comb filter 2 has a pass band at every horizontal synchronization frequency _fH , and thus sends out the color signal component C, which is in a frequency interleaved relationship with the luminance signal component Y, as the output S2. .

However, since the luminance signal component Y is also superimposed on the frequency band of this color signal component, the luminance signal component Y remains without being completely removed. In addition to this
The output S2 of the CCD comb filter 2 contains 1/f noise N generated from the CCD delay element constituting the CCD comb filter 2, which has a frequency lower than the passband of the bandpass filter 1. occurring in the area.

The output S2 of this CCD comb filter 2 is supplied to a bandpass filter 3. As shown in FIG. 7, this bandpass filter 3 has a center frequency of
Cutoff frequency is 3.58± for 3.58 [MHz]
It has a frequency characteristic of 1.0 [MHz], and the signal component within this passband of the output S2 is sent out as the output S3. As a result, the output S3 has only the color signal component C including the luminance signal component Y, with the clock signal in the high band and the 1/f noise N in the low band being removed with respect to the passband of the bandpass filter 3. It turns out.

This output S3 is supplied as an addition input to the subtraction circuit 4, and the output S1 of the bandpass filter 1 is supplied as a subtraction input, whereby the luminance signal component Y of the output S3 is canceled and removed from the subtraction output S4. Ru. Here, the output S3 of the bandpass filter 3 is delayed by a time corresponding to a 1H interval in the CCD comb filter 2 with respect to the output S1 of the bandpass filter 1, and thus the subtraction circuit 4 has a 1H delay. Luminance signal component Y that does not receive a 1H delay with respect to the received luminance signal component Y
will be subtracted. However, since the signal levels of the luminance signals of adjacent scanning lines have a sufficient correlation with each other, the luminance signal components Y cancel each other out in the subtracter 4, while the phases of the adjacent color signals differ by 180°. are being rotated, the subtraction circuit 4 adds the color signals C to each other to obtain a subtracted output S.
Send as 4.

In this way, only the color signal component C is sent out from the subtraction circuit 4 as a separated color signal.

In addition to this, a composite input video signal
VDIN is applied as an addition input to the subtraction circuit 5, and the output S1 of the bandpass filter 1 is applied to the subtraction circuit 5 as a subtraction input. Here, the output S1 includes a color signal component C and a luminance signal component Y superimposed thereon, and this signal component is canceled from the input video signal VDIN to produce a subtracted output S5 as shown in FIG. , and this subtracted output S5 is supplied to the adder circuit 6.

The output S6 of the correlator 7 is applied to the addition circuit 6 as an addition input. The correlator 7 receives the output S3 of the bandpass filter 3 and the output S1 of the bandpass filter 1, adds these inputs and then averages them to obtain an output S6, thus an output whose content is (S1+S3)/2. S6 is added to the output S5 of the subtraction circuit 5 in the addition circuit 6.

Of the two inputs supplied to the correlator 7, the output S1 of the bandpass filter 1 contains the color signal C before being delayed by 1H, whereas the output S3 of the bandpass filter 3 is delayed by 1H. contains the color signal component C whose phase has been rotated by 180° after receiving the signal.
Therefore, the correlator 7 cancels each other out by adding these color signal components having phases different by 180° from each other. On the other hand, since the luminance signal components of adjacent scanning lines have substantially sufficient correlation, only the luminance signal component Y is outputted as the output S6 of the correlator 7.

By the way, the two outputs S3 supplied to the correlator 7
and the luminance signal component Y included in S1 are both the fourth
As described above with reference to the figure, it has a luminance signal component Y band-limited by the bandpass filter 1, and therefore the output S6 of the correlator 7 also has a luminance signal component Y in the same band. On the other hand, the output S5 of the subtraction circuit 5 is a signal lacking the luminance signal component Y band-limited by the bandpass filter 1, as described above with reference to FIG. 8, and therefore the output S7 of the addition circuit 6 is: As shown in FIG. 9, it has a luminance signal component Y that is not subject to frequency band limitations. However, the luminance signal component Y corresponding to the output S6 has a comb-shaped frequency characteristic extracted together with the color signal component by the comb-shaped frequency characteristic of the CCD comb filter 2, as described above with reference to FIG. is different from the luminance signal component Y of the other signal component S5.

In this way, an output S7 consisting of the luminance signal component Y is obtained from the adder circuit 6, and is sent as a separated luminance signal to the luminance signal/chrominance signal separation circuit together with an output S4 consisting of the chrominance signal separated from the input video signal VDIN. .

According to the configuration shown in FIG. 1, the color signal C separated from the composite video signal VDIN is separated using the comb frequency characteristic of the CCD comb filter 2, but the 1/2 color signal generated at that time is The f-noise N (FIG. 5) is removed by the bandpass filter 3 provided at the subsequent stage and is not input to the subtraction circuit 4, and is therefore not included in the output S4. In this way, it is possible to prevent the deterioration of image quality that occurs on the screen due to 1/f noise, which has been a problem in the past.

In the above, a case has been described in which the correlator 7 is configured to send out the average value of the two inputs S3 and S1 as the output S6, but instead of this, the color signals included in two adjacent scanning lines determine whether there is a correlation with each other,
Even if a configuration is used in which the average value is sent out as the output S6 when there is a correlation, but the color signal is not sent out as the output S6 when there is no correlation, the same effect as in the above case can be obtained. Obtainable. In this case, in addition to this effect, it is possible to effectively prevent dot noise from occurring due to vertical non-correlation on the screen.

H. Effects of the Invention As described above, according to the present invention, the bandpass filter 3 is provided after the CCD comb filter 2 to remove 1/f noise, and as a result, compared to the conventional case, A luminance signal/chrominance signal separation circuit that can significantly improve image quality can be easily realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the luminance signal/chrominance signal separation circuit according to the present invention, FIG. 2 is a characteristic curve diagram showing frequency components of the composite input video signal VDIN, and FIG. 3 is a diagram showing the frequency components of the composite input video signal VDIN. FIG. 4 is a characteristic curve diagram showing the 1/f noise generated in the CCD delay element included in the CCD comb filter 2. FIG. 4 is a characteristic curve diagram showing the frequency component of the output S1 of the bandpass filter 1 in FIG. The figure is a characteristic curve diagram showing the frequency components of the output 2 of the CCD comb filter 2, Figure 6 is a characteristic curve diagram showing the frequency characteristics of the CCD comb filter 2 of Figure 1, Figures 7 and 8,
Figure 9 shows the bandpass filter 3 in Figure 1.
output S3 of subtraction circuit 5, output S5 of subtraction circuit 5, addition circuit 6
It is a characteristic curve diagram which shows the frequency component of output S7 of. 2...CCD comb filter, 3...band pass filter, 7...correlator.

Claims (1)

[Scope of Claims] 1(a) a first bandpass filter that passes frequency components corresponding to color signal components included in the composite input video signal; (b) among the outputs of the first bandpass filter; A CCD element (charge
(c) the CCD of the output of the comb filter;
a second bandpass filter having a cutoff frequency characteristic that does not pass the 1/f noise component generated from the element; (d) subtracting the output of the first bandpass filter from the output of the second bandpass filter; death,
(e) a second subtraction circuit that subtracts the output of the first bandpass filter from the composite input video signal and obtains the subtraction output; and (f) receiving the outputs of the first and second bandpass filters and calculating the first bandpass filter from the correlation between the two outputs.
a correlator that obtains an output consisting of a luminance signal component having a frequency corresponding to the passband of a bandpass filter; (g) adding the subtraction output of the second subtraction circuit and the output of the correlator; A luminance signal/chrominance signal separation circuit comprising: an addition circuit that sends out a luminance signal as a separated luminance signal output.