JPH03836B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for separating chrominance components and luminance components from a composite video signal, and particularly to a circuit for separating chrominance components and luminance components from a composite video signal.
This invention relates to a comb filter that utilizes field delay and is equipped with a circuit that compensates for motion inducers.

[Background of the invention]

The use of comb filters to separate luminance and chrominance components is well known in the field of video processing, but its cost has limited its use to relatively simple interline comb filters. Ta. An explanation of this interline comb filter can be found, for example, in the article by DHPritchard, published in RCA Review, Vol. 41, No. 1, pp. 3-28, March 1980. CCD comb filter for image enhancement.

Although interline comb filters efficiently separate chrominance and luminance components, they can produce some unwanted effects. These effects include loss of diagonal resolution, reduction of vertical resolution, and the creation of "hanging dots" due to vertical transitions.

An interframe comb filter, acting on each signal separated by a complete video frame period, separates the chrominance and luminance components without any of the unwanted effects described above, but can be extremely unsightly around the edges of moving objects. This may occur.
The use of adaptive comb filters has been proposed to eliminate this drawback. One of these adaptive filters is a combination of line-comb and frame-comb filters, in which separated luminance and chrominance components are transferred from the line-comb filter during image motion and from the line-comb filter when there is no motion. is obtained from a frame comb filter. Adaptive schemes generally produce improved signals, but are relatively expensive and come with performance limitations.

The invention is generally superior to interline comb filters or adaptive interframe comb filters;
It includes a comb filter scheme that requires significantly less hardware than an interframe comb filter.

[Summary of the invention]

The invention consists of an apparatus for separating a luminance signal from a composite video signal using an interfield comb filter and an interline comb filter. A compensation signal is extracted and combined with the comb-filtered luminance signal to produce a luminance signal without significant motion effects and with minimal hanging dots.

[Detailed explanation]

In FIG. 1A, the center of the figure shows the scan lines of an interlaced raster scan image, with the solid horizontal lines being the scan lines for odd fields and the dashed lines therebetween being the scan lines for even fields. At the left end of the diagram are three columns of numbers representing the scan lines of three consecutive fields. The (±) symbol attached to this line number indicates the relative phase of the chrominance signal associated with each line. As is well known in the field of video formats, one field of a normal NTSC signal consists of 262.5 lines, each second field starts with 1/2 line (second half), and the fields sandwiched between them are line 1. /Ends with 2 pieces (first half). Signals delayed by 1 field plus or minus 1/2 line period correspond to vertically coincident samples and lie on adjacent interpolated lines. In the MTSC system, signal samples separated by 262 lines have an in-phase chrominance subcarrier relationship, and signal samples separated by 263 lines have an in-phase chrominance subcarrier relationship.
It has a chrominance subcarrier relationship with a degree of phase separation.

To the right of the figure is shown a waveform representing a chrominance amplitude change showing a vertical transition across the image width, ie, the horizontal color edge of the displayed image. This transition represents the fastest chrominance signal change caused by the effective sampling rate (in the vertical direction) of a conventional raster scan video camera.

Curved arrows along vertical line a indicate horizontal lines of signals that are additively combined to produce a line-comb filtered luminance signal. The curved arrows to the left of line a indicate the lines of the odd fields that are combined, and the curved arrows to the right of column a indicate the lines of the even fields that are combined. For example, in an odd field, line 1 is added to line 2 to generate a luminance signal corresponding to displayed line 2, and line 2 is added to line 3 to generate a luminance signal corresponding to displayed line 3. etc.

During vertical chrominance transitions, the chrominance signal is not completely erased from the line-comb filtered luminance signal, and the remaining chrominance signal creates a phenomenon known as "hanging dots" along the horizontal edges. If we average lines 264 and 265 from Figure 1A, the result is Y+ΔC/2. where Y is the luminance signal and ΔC is the change in the chrominance signal between these two lines. The term ΔC/2 is the useless residual chrominance signal. Similarly, by adding lines 2 and 3 and dividing the sum by 2, the signal obtained is Y
+ΔC, where the term ΔC is the useless residual chrominance signal. This residual chrominance value is illustrated by a horizontal arrow along the vertical dashed line b, the length of which indicates the relative amplitude of the residual chrominance signal associated with each line of the comb-filtered signal. The arrow on the right shows the residual chrominance signal with the same relative polarity as the chrominance transition, and the arrow on the left shows one of the opposite polarity.

The vertical dashed line b' passes through a point at a distance corresponding to half a cycle of the chrominance subcarrier from point b. point
The chrominance signal at b' is 180° out of phase with the chrominance signal at point b. Thus, the polarity of the residual chrominance signal in the comb-filtered luminance signal (for a similar chrominance transition) along vertical line b' is the opposite of that along dashed line b. This residual chrominance signal is linearly added to and subtracted from the luminance signal so that along the horizontal edges of the color image, the residual chrominance signal changes the amplitude of the luminance signal alternately between white and black levels every half cycle of the chrominance signal. It will be pulled towards. It can be seen that for a color transition that occurs between two lines, residual chrominance signals are found in three lines of the line comb-filtered luminance signal.

Consider now FIG. 1B, which is similar to FIG. 1A except that it shows adjacent interlaced lines in a comb filter system. The curved arrow to the left of the vertical dashed line C indicates the line of signal to be combined into the first field of the field-comb-filtered luminance signal, and the curved arrow to the right of the dashed line C indicates the line of signal to be combined into the next field of the comb-filtered luminance signal. Indicates the horizontal line used. The luminance comb filter sample is the average of samples from two consecutive fields.

This sample is spatially separated by 1/2 line.
That is, they are separated by 1/2 the vertical distance that the samples combined in the line comb filter are separated. Due to inherent bandwidth limitations, the amplitude of the chrominance change is always less than the amplitude of the chrominance transition between each line in a field. This causes the maximum amplitude of the residual chrominance signal contaminating the comb-filtered luminance signal to be smaller for the interfield comb-filtered signal than for the interline comb-filtered signal for the same chrominance transition.

The arrows along the vertical lines d, d' represent the residual chrominance signal in the field comb filtered luminance signal relative to the chrominance signal shown on the right side of the figure.
The generation of this residual chrominance signal is limited to two lines, the maximum amplitude of which is 1/2 of the maximum amplitude exhibited by the line comb filtered signal. Moreover, the polarity of this residual chrominance signal is opposite to that of the adjacent line. These three properties result in a dramatic reduction in the visibility of the "hanging dots" in the field comb filtered luminance signal. A residual chrominance signal of one polarity on one line will increase the brightness of the image, a residual chrominance signal of the opposite polarity on the next line will decrease the brightness of that image, and the very small distance between these two points will cause the brightness of that image area to decrease. It is integrated by the eye and the hanging dots become indistinguishable.

Field comb filtered luminance signals have an inherent vertical detail loss as in line comb filters. That is, the luminance signal for any comb-shaped filter line is, for example, the average luminance signal over two lines. Therefore, if the luminance signal Y changes by ΔY from line 2 of field 1 to line 265 of field 2, the effective change in the field comb-filtered luminance signal is ΔY/2. To recover the comb-filtered signal, it is necessary to add back the value ΔY/2 to create a true luminance transition.

If we look at the left side of Figure 1B and assume that the comb-filtered luminance signal is derived by adding lines 2 and 265 and that luminance transitions occur vertically in these lines, then the same transition between lines 265 and 527 It turns out that this happens. Since the chrominance signals on lines 265 and 527 are in phase, subtracting one from the other produces a signal that corresponds to a luminance transition. Dividing this signal into two provides the required vertical detail signal which is added back to create the comb-filtered luminance signal.
However, in order to generate a comb-filtered signal, lines 2, 26
It should be noted that a device operating 5,527 simultaneously requires two storage fields.

According to the principles of this invention, the accumulation field is 1
Only one is needed. This is accomplished by combining the closest in-phase lines adjacent to the lines utilized in the comb filter. When lines 2 and 265 are averaged to produce a comb-filtered chrominance signal, the appropriate in-phase lines to produce different signals are lines 265 and 3. This difference signal is accurate and will generally be the case when the luminance transition is generally monotonic over several lines. It should also be noted that when there is image movement between fields, information about this movement will be included in the difference signal. Adding this motion information to the comb-filtered luminance signal corrects for the phenomenon that occurs in the field-comb-filtered image.

It is understood by those skilled in the art of comb filtering video signals that the difference signal includes not only luminance vertical and motion detail information, but also chrominance vertical and motion detail information, so the difference signal is referred to as a comb-filtered luminance signal. It may be desirable to low-pass filter the chrominance component before adding it to the chrominance component. In reality, certain compromises need to be made. Removing the chrominance component from the difference signal makes the "hanging dot" less visible, but it also makes it harder to distinguish the edges of objects that are moving quickly horizontally. Therefore,
It may be necessary to choose between hanging dots and horizontal movement details. Referring again to FIG. 1B, the arrow along vertical line e represents the residual chrominance signal in the comb-filtered luminance signal to which the broadband difference signal has been added. This residual chrominance signal has a tendency to produce "hanging dots";
It is extremely inconspicuous for interline comb filtered signals. This residual chrominance signal is only bad for sharp chrominance transitions, but generally improves for transitions that span several lines.

FIG. 2 is a block diagram of a circuit that performs the field comb filtering described above to separate the motion corrected luminance signal from the composite video signal. This circuit may be a digital or analog device depending on the signal to be processed.

In FIG. 2, the baseband composite video signal applied to the input terminal 10 is transmitted through a 262H delay element 20,
It is led to each input terminal of a signal adder 40 and a signal subtracter 50. Delay element 20 delays the applied signal by 262 times the horizontal deflection period H, and this delayed signal is further applied to delay element 30 and delayed by 1H. The delayed signal from element 20 is also applied to each input terminal of a signal subtractor 50, 60 and
The delayed signal from 0 is applied to each input of signal adder 40 and signal subtractor 60. Finally, the signal sum from adder 40 and the signal difference from subtracter 50 are applied to both inputs of signal adder 70. The output 80 of this summer 70 is a comb-filtered, motion-corrected luminance signal.

If the signal from the nth horizontal line is at the output of delay element 30, the signal at the input of that element 30 corresponds to the n+1th line. line n and line n+1
are consecutive lines, and their chrominance components are separated by 180°. When the subtracter 60 subtracts the line n from the line n+1, the luminance component of the applied video signal is canceled and a chrominance signal with double amplitude is generated.
This signal is then split in half for subsequent chrominance processing.

If the output signal of the delay element 20 is line n+1,
Its input is line n+263. This line n+263 is added to line n from delay element 30 in adder 40. Note that if n is an odd number, then n+263 is an even number.In an NTSC signal, each odd numbered line has a color subcarrier in the same phase, and each corner numbered line has a color subcarrier in opposite phase. n and n+263 are 263H
That is, since they are separated by one field period plus H/2, when the adder adds the odd and even lines, the chrominance component is eliminated and a luminance signal is generated separately. This luminance signal contains residual chrominance signal at chrominance transitions, lacks some of the vertical luminance detail information, and contains anomalous effects due to field-to-field motion.

Line n+1 and line n+263 from delay element 20 are applied to subtracter 50, and since these lines are both odd or both even, the chrominance signals are in phase. The two lines are separated by one field period minus H/2 periods. Line n+1 is subtracted from line n+263 to produce a difference signal containing vertical detail and motion information, which is applied to one input of adder 70 to combine with the luminance signal separated from adder 40; Reinsert vertical detail and motion information.

Regarding the luminance signal, the operation performed in the circuit of FIG. 2 can be expressed by the following equation.

Y=S _o+263 +S _o (S _o+263 −S _o+1 ) (1) where Y is the signal appearing at the output terminal 80 and S _o is the signal appearing on the line n
, where n is an integer.

As mentioned above, it may be advantageous to low-pass filter the difference signal before reinserting it into the luminance signal. This is the element 10 virtually coupled between the elements 50 and 70.
Indicated by 0. When this element 100 is put into a circuit, a delay element is inserted between elements 40 and 70, and the element 100
It may be necessary to compensate for the inherent signal delay of

For convenience, the illustrated interline chrominance comb filter uses a 1H delay element 30, but some also include a subtracter 110, as shown in phantom. In this case, the signal delayed by 1H is sent to delay element 2.
0 and subtracted from the signal applied to terminal 10 in subtractor 110. With this modified chrominance comb filter, both the difference signal and the comb-filtered chrominance signal all receive contributions from line n+263.

[Brief explanation of the drawing]

1A and 1B are schematic representations of reconstructed images showing particular horizontal lines associated with line comb filters and field comb filters, respectively, and FIG. 2 is an interfield luminance comb filter embodying the invention. FIG. 20, 30, 40...first means, 50...second means, 70...third means.

Claims (1)

[Scope of Claims] 1. A device for separating a luminance signal from a composite video signal containing both chrominance signal and luminance signal components, the device delaying the composite video signal so as to separate the luminance signal from the composite video signal by substantially one field period. a first means for generating a comb-filtered luminance signal by combining said composite video signal and said composite video signal delayed by one horizontal line period shorter than said substantially one field period; a second means for subtractively combining the difference signal and the comb-filtered luminance signal to produce a difference signal; and additively combining the difference signal and the comb-filtered luminance signal to produce at its output the separated luminance signal. and a third means.