JPH01303891A - In-field adaptive y/c separating circuit - Google Patents

Abstract

PURPOSE:To simplify the circuit constitution and to make the size small by using a band pass filter provided to the processing system of the comb-line filter separation system and a band pass filter provided to the processing system of the frequency separation system in common. CONSTITUTION:A correlation detection circuit 10 receives a composite video signal to detect line correlation and a chroma signal is outputted from a switch circuit 7 in the presence of correlation and the composite video signal is outputted from the switch circuit 7 in the absence of correlation. A band pass filter circuit 15 filters a signal inputted from the switch circuit 7 and when the input signal is a chroma signal, the undesired component is eliminated and when the input signal is a composite video signal, the chroma signal is outputted while being separated. Then a subtraction circuit 25 subtracts the chroma signal given from the band pass filter circuit 15 from the composite video signal to extract the luminance signal by and to gives and output. Thus, the circuit constitution is simplified and the size is made small.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an intra-field adaptive Y/C separation circuit that adaptively switches between a comb filter separation method and a frequency separation method to obtain a chroma signal and a luminance signal.

[Prior Art] Conventionally, Y/C separation methods include a frequency separation method that uses the frequency spectrum of a composite video signal to separate a luminance signal and a chrominance signal on the frequency axis using, for example, a bandpass filter and a lowpass filter. There is a comb filter separation method that separates a luminance signal and a color signal using the correlation between lines of a video signal.

Each of these re-separation methods has the disadvantage that in screen conditions where the luminance signal contains high-frequency components near the color subcarrier frequency, the color signal leaks into the luminance signal, causing dot interference that flows vertically. The comb filter separation method has the disadvantage that the separation becomes insufficient due to the collapse of the correlation that is the premise of the method, resulting in deterioration of image quality called dot crawl, in which dots flow laterally at the vertical edges of the image.

Therefore, in the past, Y/C separation circuits of both types were provided in parallel, and the separation methods were switched depending on the image content.

[Problems to be Solved by the Invention] By the way, in order to separate the chroma signal from the composite video signal according to the frequency separation method, a bandpass filter is required. Further, after the chroma signal is separated by the comb filter separation method, unnecessary components other than the chroma signal components may be generated due to calculations, etc., so a bandpass filter is used to remove the unnecessary components.

The signal given to the bandpass filter in the comb filter separation method is a chroma signal that has undergone a lot of arithmetic processing, and the signal given to the bandpass filter in the frequency separation method is a composite video signal, and its signal content and data format are Since they are different, they have not been used together in the past.

However, the frequency separation method and the comb filter separation method are alternatively selected in the adaptive case. Therefore, when the frequency separation method is selected, the bandpass filter in the comb filter separation method processing system is not functioning. Conversely, when the comb filter separation method is selected, the bandpass filter in the frequency separation method is not functioning. Considering this point, there is a possibility of using one bandpass filter for both methods.
If a bandpass filter can be used in conjunction with this, Y/C
The configuration of the entire separation circuit can be made simple and compact, which is considered to be a great advantage.

The present invention has been made in consideration of the above points, and allows the band-pass filter to be used in combination with the frequency separation method and the comb filter separation method, and as a result, the overall configuration is simplified and
In-field adaptive Y/ that can be made small
The present invention is intended to provide a C separation circuit.

[Means for Solving the Problem] In order to solve the problem, the present invention provides a chroma signal separation circuit that separates a chroma signal from a digitized composite video signal according to a comb filter separation method, and a chroma signal separation circuit that separates a chroma signal from a digitized composite video signal according to a comb filter separation method; A data conversion circuit that matches the data format of one of the chroma signals separated by the signal separation circuit to the data format of the other signal, inputs the composite video signal and chroma signal whose data formats have been matched, and selects one signal. A switch circuit that inputs a composite video signal, detects line correlation, outputs a chroma signal from the switch circuit when there is a correlation, and outputs a composite video signal from the switch circuit when there is no correlation. It filters the signals input from the correlation detection circuit and the switch circuit, which removes unnecessary components when the input signal is a chroma signal, and filters the chroma signal when the input signal is a composite video signal. It includes a bandpass filter circuit that separates and outputs signals, and a subtraction circuit that subtracts a chroma signal given from the bandpass filter circuit from a composite video signal to collect and output a luminance signal.

[Function] If the composite video signal has line correlation,
The switch circuit provides the bandpass filter circuit with the chroma signal separated by the chroma signal separation circuit according to the comb filter separation method in response to the detection signal from the correlation detection circuit.

The bandpass filter circuit removes unnecessary components of the input chroma signal and outputs the removed chroma signal, and also supplies the chroma signal to the subtraction circuit. The subtraction circuit is supplied with a composite video signal, subtracts the chroma signal from the composite video signal, and extracts and outputs the luminance signal.

On the other hand, if there is no line correlation in the composite video signal, the switch circuit supplies the composite video signal to the bandpass filter circuit in response to the detection signal from the correlation detection circuit. The bandpass filter circuit separates and outputs a chroma signal from the input composite video signal on the frequency axis, and also supplies the chroma signal to a subtraction circuit.

The subtraction circuit subtracts this chroma signal from the composite video signal to extract and output a luminance signal.

Note that the data formats of these signals are made uniform by the data conversion circuit so that the bandpass filter circuit can process both the chroma signal and the composite video signal separated according to the comb filter separation method.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

In the figure, the Y/C separation circuit of this embodiment receives a composite video signal COM having a frequency four times the color subcarrier frequency and digitized by a clock signal synchronized with a horizontal synchronization signal or a subcarrier signal. is input. This composite video signal COM is sequentially applied to two vertically connected one-line delay circuits 1 and 2, and data D1 to D3 of three vertically adjacent pixels are taken out. The pixel data D1 and D3 of the upper and lower horizontal scanning lines are added by an adder circuit 3 and then supplied to a subtractor circuit 4 as a subtraction input. The pixel data D2 of the central horizontal scanning line is doubled via the doubling circuit 5 and then supplied to the subtracting circuit 4 as an input to be subtracted. The subtraction circuit 4 subtracts these inputs, and the subtraction output is 1/4
The signal is multiplied by 1/4 via the multiplier circuit 6 and applied to the switch circuit 7 as a first selection input.

When a composite video signal is converted into a digital signal using the above-mentioned tarok signal, the color difference signal components in the pixel data D1 to D3 of three horizontal scanning lines that are continuous in the vertical direction are converted into one color difference signal component (R-Y or B -Y), and appears with the sign reversed for each horizontal scanning line.

Therefore, by performing the above calculation on the pixel data D1 to D3 of the three horizontal scanning lines, if there is a line correlation, the luminance signal component is canceled out, and the color difference signal component of the pixel data of the central horizontal scanning line is taken out.

That is, a chroma signal is extracted.

The pixel data D2 of the central horizontal scanning line is also converted into data via the data conversion circuit 8 and supplied to the switch circuit 7 as a second selection input. Here, the data conversion circuit 8 converts the incoming pixel data in accordance with the data format (the number of bits and the presence or absence of a sign bit) of the other signal applied to the switch circuit 7. The two inputs given to will follow the same data format.

This switch circuit 7 is switched by a detection signal from a line correlation detection circuit 10. Line correlation detection circuit 1
0, pixel data D1 and D3 of the upper and lower horizontal scanning lines are given, and the difference between these data D1 and D3 is obtained by the subtraction circuit 11. As mentioned above, the color difference signal components of the same type and the same sign appear in the upper and lower horizontal scanning lines, and of course also include the luminance signal component, so if these are correlated, the difference obtained from the subtraction circuit 11 will be very small, and if there is no correlation, it will take a somewhat large value.

Therefore, after converting this difference into an absolute value via the absolute value circuit 12, the comparison circuit 13 compares it with a reference value to determine whether there is a line correlation.

The comparison circuit 13 selects the data (chroma signal) separated according to the comb filter separation method via the 1/4 multiplier circuit 6 when there is line correlation, and selects the data conversion circuit 8 when there is no line correlation. The switch circuit 7 is switched so as to select the data (composite video signal) that has not been separated by Y/C.

The data selected by the switch circuit 7 is given to the bandpass filter circuit 15. The bandpass filter circuit 15 receives input data in one of four one-sampling period delay circuits 16 connected in series. These one sampling period delay circuits 16 to 19 take out data of five consecutive pixels in the horizontal direction, and pixel data D4 and D6, which are different from the center pixel by two pixels before and after, are supplied to an adder circuit 20 and added. The output signal from the adder circuit 20 is given to the subtractor circuit 21 as a subtraction input. The center pixel data D5 is doubled via the doubling circuit 22 and then supplied to the subtraction circuit 21 as an input to be subtracted. The subtraction circuit 21 subtracts these inputs, and the subtracted output is multiplied by 1/4 via the 1/4 multiplier circuit 23 and output as a separated chroma signal.

When a composite video signal is converted into a digital signal using the above-mentioned clock signal, the color difference signal component appears with the sign reversed every two pixels.

Even if the data for this bandpass filter circuit 15 is a chroma signal that has already been separated according to the comb filter separation method, noise components can be removed by appropriately calculating the same color difference signal components adjacent in the horizontal scanning direction as described above. It is possible to cancel the chroma signal and output a chroma signal from which unnecessary components have been removed.

On the other hand, if the data given to this bandpass filter circuit 15 is a composite video signal containing a luminance signal component, the luminance signal component can be canceled out by executing the above-mentioned operation, and the chroma signal component can be extracted. I can do it,
Output the extracted chroma signal.

The chroma signal output from this bandpass filter circuit 15 is output to the next stage and is also given to the subtraction circuit 25 as a subtraction input. Pixel data (composite video signal) D2 that has passed through the one-line delay circuit 1 is phase-aligned via a delay compensation circuit 26 and is supplied to the subtraction circuit 25 as an input to be subtracted. The subtraction circuit 25 subtracts the chroma signal from the video signal to extract the luminance signal,
This is output as a separated luminance signal.

Therefore, according to the above embodiment, in the adaptive Y/C separation circuit that switches between the comb filter separation method and the frequency separation method depending on the presence or absence of line correlation, the bandpass filter circuit provided in the processing system of the comb filter separation method and the frequency A bandpass filter circuit for separating according to the separation method can be used in combination, and the circuit can be made smaller and simpler than conventional circuits. In this way, small size,
By simplifying the structure, power consumption can be reduced, making it suitable for forming a gate array.

In the above-described embodiment, a so-called 2H type comb filter separation method is shown, but an IH type can also be applied.

Furthermore, in the above description, the data format provided to the bandpass filter circuit 15 is made uniform by the data conversion circuit 8 inserted in the frequency separation type processing system.
The data conversion circuit may be inserted into a processing system using a comb filter separation method.

[Effects of the Invention] As described above, according to the present invention, the bandpass filter circuit provided in the processing system of the comb filter separation method and the bandpass filter circuit provided in the processing system of the frequency separation method are shared. Therefore, the circuit configuration can be made simpler and smaller than the conventional circuit, power consumption can be reduced, and a Y/C separation circuit suitable for forming into a gate array can be realized.

[Brief explanation of the drawing]

The figure is a block diagram showing an embodiment of an intra-field adaptive Y/C separation circuit according to the present invention. 1.2...1 line delay circuit, 3...addition circuit, 4
．． 25... Subtraction circuit, 7... Switch circuit, 8...
・Data conversion circuit, 10... Correlation detection circuit, 15...
・Band pass filter circuit.

Claims (1)

[Claims] A chroma signal separation circuit that separates a chroma signal from a digitized composite video signal according to a comb filter separation method, and a data format of either the composite video signal or the chroma signal separated by the chroma signal separation means. a data conversion circuit that matches the data format of the other signal with the data format of the other signal; a switch circuit that inputs the composite video signal and the chroma signal whose data formats have been matched and selects and outputs one of the signals; and the composite video signal. a correlation detection circuit that detects line correlation by inputting a line correlation, and outputs the chroma signal from the switch circuit when there is a correlation, and outputs the composite video signal from the switch circuit when there is no correlation; It filters the signal input from the switch circuit, and removes unnecessary components when the input signal is the chroma signal, and separates the chroma signal when the input signal is the composite video signal. and a subtraction circuit that extracts and outputs a luminance signal by subtracting a chroma signal given from the bandpass filter circuit from the composite video signal. Type Y/C separation circuit.