JPH0588597B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a luminance signal/chrominance signal separation circuit, more specifically, a luminance signal/chrominance signal separation circuit (hereinafter abbreviated as YC separation) of a composite color television signal. )
In particular, the present invention relates to a separation circuit with high separation accuracy that makes full use of the three-dimensional structure of the signal.

[Background of the invention]

In conventional YC separation circuits for color television signals, there were many methods that used only the horizontal direction and methods that also included the vertical direction (method using a comb filter). Recently, methods including the time direction (between frames) have also been proposed.

For interframe separation circuits, a method has been proposed in which parameters are adaptively changed according to the movement of an image, but the circuit configuration is complicated. Furthermore, in the previous methods, information between fields was not used.

[Purpose of the invention]

An object of the present invention is to provide a circuit that performs more efficient YC separation by using all or part of these circuits.

[Summary of the invention]

In order to achieve the above object, the present invention includes a horizontal filter as well as a filter for extracting a difference signal between scanning lines as required, and a filter for extracting a difference signal between frames, and a filter for extracting a sum signal between fields. The present invention is characterized in that it includes at least one filter for extracting a difference signal, and these filters are connected in series to separate a luminance signal and a chrominance signal of a composite color television signal.

[Embodiments of the invention]

The present invention will be explained below with reference to Examples. First, the principle of the present invention will be explained using the drawings.

FIG. 1 is an explanatory diagram of the structure of a well-known TV signal. The signal consists of 60 fields per second,
Each field has 262,5 scan lines (three or four lines are shown for simplicity in the figure). The scanning lines are shifted by 1/2 from field to field. This is called interlaced scanning.

If you look at this from the right now, it will look like Figure 2. In other words, in the figure, the horizontal axis indicates the time direction,
The vertical axis indicates the vertical direction, and each point indicates the scanning line viewed from the side.

As is well known, in the NTSC signal, a color signal is superimposed on it. The phase of the color subcarrier is written as ,+π. The lines connected by lines are scanning lines of the same phase.

When the relationship shown in FIG. 2 is expressed in a two-dimensional frequency domain, it becomes as shown in FIG. 3. The horizontal axis represents the frequency ∫ in the time direction (interframe direction), and the vertical axis represents the frequency ν in the vertical direction. Here, since the color subcarrier frequency ∫sc is ∫=15 Hz and ν=131 scanning lines, it is located at a place marked as ∫sc in the figure. Furthermore, since the interlaced scanning line can be regarded as a sample, the frequency at this time is located at a place indicated by ∫ _IS .

The purpose of the present invention is to efficiently extract the color signal C at the frequency indicated by ∫sc in the figure and its vicinity.

Usually, a method performed only in the horizontal direction extracts a specific frequency component in the horizontal frequency, that is, the axis extending from the front to the back of the drawing.

Next, considering the frequency in the vertical direction is to extract the component using a filter indicated as "difference between scanning lines" in the figure. The methods used in the horizontal and vertical directions have been well known for a long time (for example, Takahiko Fukinuki, Digital Signal Processing of Images, Nikkan Kogyo Shimbun Publishing Bureau, 1982,
pp106-112).

Next, the method of extracting the difference between frames, that is, extracting the C signal from this difference by utilizing the fact that the phase of the C signal is inverted between frames, is as follows.
This involves extracting the component indicated as "interframe difference" in the figure using a filter.

Conventionally, color (C) signals were often extracted by adaptively switching these filters depending on movement. However, as can be seen from FIG. 3, it is clear that components near ∫sc can be extracted by continuously connecting these filters without adaptive switching.

However, according to this method, in addition to the parts marked as in the figure, components marked as are also extracted. This is undesirable because the Y signal in the section is also regarded as the C signal.

In the present invention, this separation between parts is effectively carried out.

First, when the sum signal of scanning lines of the same phase in adjacent fields (connected by lines in FIG. 2) is determined, the portion indicated as "sum between fields" in the diagram becomes the passband.

Next, when the difference between the signals of opposite-phase scanning lines (adjacent scanning lines) in adjacent fields is determined, the portion marked as "difference between fields" in the figure becomes the pass band of this filter.

Therefore, if some or all of these filters are connected in series, only the components near ∫sc can be efficiently extracted.

FIG. 4 shows the configuration of each filter used in the embodiment of the present invention.

First, considering the well-known case of the difference between scanning lines, the delay time DL is DL=H (one horizontal period). Further, the coefficients a, b, and c are, for example, -1/4, 1/2, -1/4 or 1/2, -1/2, (0). The latter is a case where there is only one delay element.
A method using more delay elements is also possible.
It is well known that with this filter, the area shown as "difference between scanning lines" in FIG. 3 becomes a passband.

Furthermore, in the case of an inter-frame difference, DL=1 frame, and the coefficients are the same as above.

In the case of field-to-field differences, in particular in this case the adjacent scan lines are DL=263H with reference to FIG. In addition, in the case of the sum between fields, DL=
It is 262H.

Note that in the case of a sum, all of the above coefficients are positive.

FIG. 5 shows how the filters obtained as described above are connected in series.

First, the TV signal is filtered through a bandpass filter 11.
Extract only the vicinity of ∫sc in the horizontal direction. Next, a filter 12 that separates based on the difference between scans, a filter 13 that uses the difference between frames, a filter 14 that uses the difference between fields, and a filter 15 that uses the sum of fields are connected in series, and only the components in the vicinity of FIG. 3 are extracted.

Note that, as can be seen from FIG. 3, not all of these are necessary, but some may be used.

In addition, there are several other variations as listed below.

(i) The order in which the filters are connected is arbitrary, as is clear from the principle.

(ii) For example, when performing digital separation, it is necessary to perform horizontal separation at a sampling frequency that is more than twice the horizontal band, for example, 4×∫sc, but subsequent processing is performed using appropriate subsamples. All you have to do is process the sample value.

〔Effect of the invention〕

According to the present invention, the YC separation of a composite color TV signal can be efficiently performed by focusing on the three-dimensional structure, which has an extremely large effect on improving image quality.

In other words, the conventional separation filters are "horizontal", "horizontal-vertical" within a field, and "horizontal-vertical" between frames.
time," or a combination of these. However, by adding processing between fields, it is possible to clearly separate the parts, so that the parts can be efficiently separated as color signals and the parts as luminance signals.

[Brief explanation of the drawing]

FIGS. 1 and 2 are known explanatory diagrams showing the structure of a TV signal, and FIG. 3 is an explanatory diagram showing the well-known frequency spectrum thereof, and is an explanatory diagram showing the pass band of the filter of the present invention. be. FIG. 4 is a configuration diagram showing an example of the configuration of a single filter, and FIG. 5 is an overall configuration diagram of one example. 11...Band pass filter, 12-15...Each filter.

Claims (1)

[Scope of Claims] 1. In a luminance signal/chrominance signal separation circuit that separates color signals from an NTSC composite color television signal, a first filter having a filtering function for extracting frequency components of a carrier color signal in the horizontal direction; A second filter having a filtering function to extract the difference between scanning lines in the same field or a filtering function to extract the difference between frames; Alternatively, an NTSC composite comprising a third filter having a filtering function for extracting a difference component between scanning lines having an opposite phase with respect to a carrier color signal, and characterized in that the first to third filters are connected in cascade. Luminance signal/chrominance signal separation circuit for color television signals.