JP3024465B2 - Inter-frame luminance signal / color signal separation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for separating a composite video signal into a luminance signal and a carrier chrominance signal.

[0002]

2. Description of the Related Art A luminance signal / color signal for separating a composite video signal obtained by frequency-multiplexing a luminance signal (hereinafter referred to as Y) and a color signal (hereinafter referred to as C) into an original luminance signal and a color signal. Separation processing (hereinafter referred to as Y / C separation) is conventionally referred to as one-dimensional processing because it is processing only in the horizontal scanning direction.
It has been performed using a low-pass filter or a high-pass filter. In the case of this configuration, complete separation cannot be performed, and there is a problem of image quality deterioration due to occurrence of cross color or dot disturbance.

[0003] Accordingly, since the processing is performed in the horizontal scanning direction and the vertical scanning direction, two-dimensional processing is used. This is improved by processing using a line-to-line comb filter that utilizes inter-line correlation of a composite video signal. Improvements have been made by adaptive processing that uses a comb filter and a one-dimensional filter to adaptively select them.

However, even with such processing, there is a problem that the resolution in the oblique direction is reduced due to the limitation of the frequency characteristic by the calculation in the horizontal and vertical directions.
Complete separation could not be performed.

In order to improve such problems, in recent years,
There is a so-called three-dimensional processing method in which processing is performed in the time axis direction using inter-frame correlation of a composite video signal. This method can completely separate a still image into a luminance signal and a chrominance signal.

FIG. 10 is a schematic view of an NTSC composite video signal viewed in a time axis direction and a vertical direction. In FIG. 10, a vertical line indicates a field, and a circle on the vertical line indicates a line. Y means a luminance signal, and C means a color signal. Y + C means a composite video signal whose color signal has a positive polarity, and Y-C means a composite video signal whose color signal has a negative polarity.

As shown in FIG. 10, the composite video signal of the NTSC system has a feature that the phase of the color signal is inverted between lines and between frames. Therefore, the relationship between the signal content at the point of interest a and the point b that is one frame period away from that point is as follows, where Y is the luminance signal and C is the chrominance signal.
a and Yb-Cb.

For a completely still image, Ya
And Yb are equal, and Ca and Cb are equal.
It can be seen that this is the relationship between Y + C and Y−C.

In this case, a complete color signal can be separated by subtracting the signal at the point b from the signal at the point a, attenuating the amplitude to half and returning it to the original amplitude.

The above processing is represented by the following equation (Equation 1).

[0011]

(Equation 1)

Then, the Y signal can be obtained by subtracting the C signal obtained in this manner from the original Y + C signal.

According to this method, when the image is a still image, a complete separation process can be performed without deteriorating the image quality. This method is called inter-frame Y / C separation processing, and has the configuration shown in FIG.

In FIG. 11, reference numeral 21 denotes an input terminal.
A composite video signal is provided. Reference numeral 22 denotes a frame memory, which supplies the composite video signal input from the input terminal 21 to the subtracter 23 after delaying it by one frame period. The subtracter 23 subtracts the composite video signal delayed by one frame period by the frame memory 22 from the composite video signal input to the input terminal 21 and supplies the result of the subtraction to the multiplier 24. The multiplier 24 multiplies the amplitude of the signal input from the subtractor 23 by half, calculates a color signal returned to the original amplitude, and uses the result as a color signal separated from the output terminal 25. The output is supplied to the subtractor 26. The subtracter 26 subtracts the signal from the multiplier 24 from the signal supplied from the input terminal 21 through the delay circuit 27 to the composite video signal to calculate a luminance signal. This luminance signal is output from the output terminal 28 as a separated luminance signal.

The delay circuit 27 is inserted to match the time axes of the color signal from the multiplier 24 and the composite video signal from the input terminal 21.

As described above, in the Y / C separation between frames, a complete separation process can be performed on a still image, but a frame memory is required to realize the separation. This frame memory has a large capacity of 4 Mbits for a signal sampled at 4 fsc, for example. For this reason, there is a problem that the circuit scale becomes large and the cost increases.

[0017]

As described above, the separation of a luminance signal and a chrominance signal using the inter-frame correlation of a composite video signal can achieve complete separation of a still image.
This requires a memory capacity sufficient to hold at least one frame's worth of signals, which causes a problem that the circuit scale becomes large.

Accordingly, the present invention is to provide an inter-frame luminance signal / color signal separation apparatus which has the same performance as the conventional inter-frame luminance signal / color signal separation performance and can reduce the memory capacity by half. Aim.

[0019]

In order to achieve the above object, an inter-frame luminance signal / chrominance signal separation apparatus according to the present invention comprises a composite signal sampled at a frequency of 4n times (n is a positive integer) the color subcarrier frequency. Sub-sampling means for sub-sampling 2n pixels in the horizontal direction every 2n pixels in the horizontal direction in accordance with the pixel period and the scanning line period; and a first delay for delaying the sub-sampling result as an input by one frame period Means for calculating the color signal component by inputting the composite video signal and the output result of the delay means, and calculating the values of both, and the signal phase missing by the sub-sampling means with the color signal component as input. A horizontal interpolation means for interpolating and calculating a color signal component in a horizontal direction, and the color signal component being input and missing by the sub-sampling means A vertical interpolation means for interpolating and calculating the color signal component in the signal phase in the vertical direction, and which of the horizontal correlation and the vertical correlation in the signal phase missing by the sub-sampling means has a stronger correlation Correlation detection means for detecting whether the color signal component, the horizontal interpolation color signal component and the vertical interpolation color signal component as input, the presence or absence of a signal missing in the sub-sampling means and the output result of the correlation detection means Selecting means for selecting and outputting one of the three input signals to obtain a color separation signal, and second delay means for delaying the composite video signal by a specific period.
Subtracting means for subtracting the color separation signal from the output signal of the second delay means to obtain a luminance separation signal.

[0020]

According to the present invention, the number of data in a composite video signal is reduced by sub-sampling by the above-described configuration, and the lack of a signal caused by the sub-sampling is compensated for by horizontal interpolation processing and vertical interpolation processing. Accordingly, it is possible to reduce the used memory capacity while securing the same inter-frame luminance signal / color signal separation performance as that of the related art.

[0021]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an apparatus for separating a luminance signal and a chrominance signal according to an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes an input terminal to which an NTSC composite video signal sampled at four times the frequency of the color subcarrier is supplied.

This composite video signal is input to the sub-sampling circuit 2 and is sub-sampled in accordance with the cycle of the color subcarrier of the input composite video signal. Reference numeral 3 denotes a first delay circuit, which writes a signal to the input of the sub-sampled signal only when the signal exists, holds the signal for one frame period, and outputs it after one frame period has elapsed. The output of the delay circuit 3 is input to one of the subtraction circuits 4. The composite video signal input to the input terminal 1 is input to the other input of the subtraction circuit 4. The subtraction circuit 4 calculates a color signal by subtracting the output signal of the delay circuit 3 from the composite video signal input to the input terminal 1.

The horizontal interpolation circuit 5 and the vertical interpolation circuit 6 take the output signal of the subtraction circuit 4 as an input and interpolate and calculate the color signal at the signal phase missing by the sub-sampling.

The correlation detection circuit 7 receives the composite video signal input from the input terminal 1 and the color signal output from the subtraction circuit 4 as inputs, and outputs the signal in the horizontal and vertical directions at the signal phase missing in the sub-sampling circuit 2. Detect which is stronger in correlation.

A selection circuit 8 receives the output signal of the subtraction circuit 4 and the output signals of the horizontal interpolation circuit 5 and the vertical sampling circuit 6 and correlates with a timing pulse synchronized with the sub-sampling timing of the sub-sampling circuit 2. Under the control based on the output result of the detection circuit 7, one of the input signals is output. In this way, the output of the selection circuit 8 becomes a color signal with no loss, is output from the output terminal 9 as a separated color signal, and is input to the subtraction circuit 11.
The composite video signal from the input terminal 1 is input to the other input of the subtraction circuit 11 via the second delay circuit 10. The subtraction circuit 11 calculates a luminance signal by subtracting the color signal input from the selection circuit 8 from the composite video signal input from the second delay circuit 10, and outputs the luminance signal.
2 is output as a separated luminance signal.

The second delay circuit 10 includes a selection circuit 8
This is inserted in order to match the time axes of the color signal from the input terminal 1 and the composite video signal from the input terminal 1.

While the overall configuration of the embodiment has been described above, the operation thereof will be described below.

FIG. 2 is a schematic diagram showing signal components of pixels in a field when sampling is performed at four times the frequency of the color subcarrier, and FIG. 3 is a schematic diagram showing an example of a signal form in the sub-sampling process of the present invention. FIG.

For example, if the sampling phase is synchronized with the I- and Q-axis phases of the color signal in the composite video signal, the signal content is as shown in FIG. 2,..., Y + I, Y + Q,
The signal is such that the I-axis component and the Q-axis component such as YI, YQ,.

In this embodiment, for example,..., Y + I, Y
A sub-sampling output that includes a positive I-axis component and a Q-axis component such as + Q, none, none, Y + I, Y + Q,.

In this sub-sampling, as shown in FIG. 3, when two pixels continuous in the horizontal direction of an input signal are viewed as a group as a group, the sub-sampling is alternately present and non-existent in the horizontal and vertical directions. It becomes something.

The output result of the sub-sampling circuit 2 is input to the first delay circuit 3 and output to the subtraction circuit 4 after a delay of one frame period. With respect to the delay circuit 3, the input signal has only half the number of pixels. For this reason, if the input is limited to only when a pixel is present, the capacity of the delay circuit 3 can be set to one field, which is half the original value.

The subtraction circuit 4 subtracts the input signal from the delay circuit 3 from the composite video signal from the input terminal 1. Since the two input signals of the subtraction circuit 4 are separated from each other by one frame period, the result of the subtraction is the same as the result of inter-frame color separation using the fact that the phase of the color signal of the composite video signal is inverted between frames. Become.

However, the color signals separated between the frames exist only at the signal phase selected by the sub-sampling. In other words, for the signal phase missing by the sub-sampling circuit 2, there is no signal necessary for the color signal separation processing between frames of the composite video signal, so the color signal obtained by the above calculation is Only at the time of the signal phase, a missing signal phase exists in the separated color signal.

Explaining the state of the existence of the color signal, in the sequence of signal intervals of four times the frequency of the color subcarrier (hereinafter, referred to as 4 fsc), when the presence is represented by ○ and the absence is represented by ×, ... ・ ・ ・ ○○ ×× ○○ × ・ ・ ・ ・ ・ ・ and in the vertical direction of the screen in the field ... ○ × ○ ×
...

FIG. 3 shows the color signal components when this color signal is regarded as a combination of the I-axis component and the Q-axis component.

Therefore, the components of the color signal are originally..., I, Q, -I, -Q, I, Q,-
For what is I, -Q, ..., I, Q,
×, ×, I, Q, ×, ×,..., And in the vertical direction of the screen within the field, originally,.
I, I, -I, ... or ..., Q, -Q, Q,-
, I, ×, I,
×, ··· or ···, Q, ×, Q, ×, ···, or depending on the subsampling phase ···, ×,-
I, x, -I, ... or ..., x, -Q, x,-
.. Exist as Q,.

In other words, focusing on each color axis component, a signal sequence in which positive and negative signals originally exist alternately becomes a signal sequence in which only positive or negative signals exist due to the sub-sampling.

Taking this relationship into account, the horizontal interpolation circuit 5 and the vertical interpolation circuit 6 interpolate and calculate the color signal components at the signal missing point of the color signal calculation result having the missing as follows.

First, the horizontal interpolation circuit 5 calculates an average value between two pixels having the same color axis component as the missing point and separated from the missing point by two pixels to the left and right, and inverts the sign. Get the interpolation result. FIG. 4 shows the positional relationship of the signals in this case, and FIG. 5 shows the pass frequency band of the signal to be interpolated.

The vertical interpolation circuit 6 calculates an average value between two pixels having the same horizontal position on one line and one line below the missing point in a field having the same color axis component as the missing point. Is obtained by inverting the sign. FIG. 6 shows the positional relationship of the signals in this case, and FIG. 7 shows the pass frequency band of the signal to be interpolated.

The above-described interpolation processing has the following advantages and disadvantages in the performance of the processing results. That is, in the horizontal interpolation processing, dot interference occurs in the case of a pattern having non-correlation in the horizontal direction such as the color boundary part in the horizontal direction of the color bar, and in the vertical interpolation processing, the color boundary in the vertical direction In the case of a pattern having a non-correlation in the vertical direction such as a portion, dot interference occurs.

This is due to the deterioration of the frequency characteristic due to the pass band limitation of the interpolation processing in the interpolation direction.

For example, in the case of a picture having a non-correlation in the horizontal direction and a correlation in the vertical direction, such as a color boundary portion of the color bar in the horizontal direction, the frequency component of the color signal is calculated as shown in FIG.
As shown in the figure, the horizontal frequency is large and the vertical frequency is small.

In such a picture state, if interpolation processing in the vertical direction is performed as in the vertical interpolation circuit 6 of the present embodiment, the color signal components can be calculated without omission, and the occurrence of dot disturbance will not occur. Absent.

Also, in the case of a picture having a correlation in the horizontal direction and a non-correlation in the vertical direction such as a color boundary in the vertical direction, the frequency component of the color signal has a horizontal frequency as shown in FIG. Side, and expands greatly on the vertical frequency side.

In such a picture state, if the interpolation processing in the horizontal direction is performed as in the horizontal interpolation circuit 5 of the present embodiment, the color signal components can be calculated without omission, so that the occurrence of dot disturbance is prevented. Absent.

Therefore, in the present invention, the strength of the correlation between the horizontal and vertical directions is detected, and the result of the interpolation processing in the direction with the stronger correlation is selected. Make up for each other's performance problems and take advantage of only the benefits.

As a method of detecting the correlation, in this embodiment, a difference value between data used for horizontal interpolation and a difference value between data used for vertical interpolation are calculated. Then, by comparing the two, it is determined that there is a stronger correlation in the direction in which the difference value is smaller, and the magnitude of each difference value indicates that if the difference value is larger, the non-correlation is stronger. Both judgments are used to determine the overall correlation. Then, based on the comprehensive correlation, the interpolation processing in the direction determined to be stronger is selected, and the optimal processing is adaptively performed on the picture.

As described above, in this embodiment, the composite video signal is sub-sampled and supplied to the delay circuit, and the sub-sampling is performed between the input and output signals of the delay circuit in the color signal output by the inter-frame processing. In the missing portion of the signal due to the above, interpolation is performed by using a nearby signal, and the interpolation is performed by adaptive processing using a picture in consideration of frequency characteristics in the horizontal and vertical directions.

With such a configuration, the capacity of the first delay circuit 3 can be reduced by half the number of pixels by sub-sampling.
Since it is only necessary to be able to store the reduced signal, the number can be reduced to one half of the conventional one.

In this embodiment, the lack of a signal due to the sub-sampling is compensated by the interpolation processing of the horizontal sampling circuit 5 and the vertical sampling circuit 6, so that the number of pixels is reduced by the sub-sampling. As a result, it is possible to obtain almost the same separation performance as the conventional one.

Various modifications can be made in addition to this embodiment without departing from the gist of the present invention.

[0056]

As described above, according to the present invention, while maintaining the performance equivalent to that of the conventional device using the memory capacity for one frame, the required memory capacity is reduced to the conventional one.
It is possible to realize an inter-frame luminance signal / chrominance signal separation apparatus that is one-half the number of the frames.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a luminance signal / color signal separation device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing signal components of pixels in a field when an NTSC composite video signal is sampled at 4 fsc.

FIG. 3 is a schematic diagram showing an example of a signal form in a sub-sampling process according to the present invention.

FIG. 4 is a schematic diagram showing a positional relationship between signals in a horizontal interpolation process according to the present invention.

FIG. 5 is a characteristic diagram showing a pass band in a two-dimensional frequency domain in the horizontal interpolation processing according to the present invention.

FIG. 6 is a schematic diagram showing a positional relationship between signals in the vertical interpolation processing according to the present invention.

FIG. 7 is a characteristic diagram showing a pass band in a two-dimensional frequency domain in the vertical interpolation processing according to the present invention.

FIG. 8 is a characteristic diagram showing a band in a two-dimensional frequency domain of a pattern having decorrelation in a horizontal direction.

FIG. 9 is a characteristic diagram showing a band in a two-dimensional frequency domain of a pattern having non-correlation in the vertical direction.

FIG. 10 is a schematic diagram showing characteristics of a composite video signal.

FIG. 11 is a block diagram showing a configuration of a conventional inter-frame luminance signal / color signal separating apparatus.

[Explanation of symbols]

 Reference Signs List 1 input terminal 2 sub-sampling circuit 3, 10 delay circuit 4, 11 subtraction circuit 5 horizontal interpolation circuit 6 vertical interpolation circuit 7 correlation detection circuit 8 selection circuit 9 color signal output terminal 12 luminance signal output terminal

Continuation of the front page (56) References JP-A-1-174088 (JP, A) JP-A-63-245087 (JP, A) JP-A-4-170891 (JP, A) (58) Fields studied (Int .Cl. ⁷ , DB name) H04N 9/78 H04N 11/14

Claims (1)

(57) [Claims] 1. For a composite video signal sampled at a frequency of 4n times (n is a positive integer) a frequency of a color subcarrier frequency, 2n pixels continuous every 2n pixels in the horizontal direction are subdivided according to a pixel period and a scanning line period. Sub-sampling means for performing sampling; first delay means for delaying one frame period with the sub-sampling result as an input; color signal by calculating the values of the composite video signal and the output result of the delay means; Calculating means for obtaining the component; horizontal interpolation means for interpolating and calculating in the horizontal direction a color signal component having a signal phase missing by the sub-sampling means by using the color signal component as input; Vertical interpolation means for vertically interpolating and calculating a color signal component at a signal phase missing by the means; Correlation detection means for detecting which of the horizontal correlation and the vertical correlation in the signal phase missing by the stage has a stronger correlation, the color signal component, the horizontal interpolation color signal component and Selecting means for selecting and outputting one of the three input signals to obtain a color separation signal based on the presence / absence of a signal loss in the sub-sampling means and inputting a vertical interpolation color signal component as an input and the output result of the correlation detecting means; A second delay unit that delays the composite video signal by a specific period; and a subtraction unit that subtracts the color separation signal from an output signal of the second delay unit to obtain a luminance separation signal. Inter-frame luminance signal / color signal separation device.