JPH0469477B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color decoder for separating a luminance signal and two color difference signals from a composite color video signal, and more particularly to a color decoder having an adaptively controlled color separation filter. Regarding decoders.

"Background Art and Its Problems" FIG. 1 shows a conventional digital NTSC color decoder. Digital from input terminal 1
The NTSC composite color video signal is fed to a color separation filter 2 to separate the carrier color signals.
In the subtraction circuit 4, the carrier color signal is subtracted from the input color video signal via the delay circuit 3, thereby separating the luminance signal Y. The carrier color signal is
The signals are supplied to multipliers 5 and 6, where they are multiplied by the color subcarrier from the color subcarrier generator 7 for demodulation and the color subcarrier whose phase is shifted by 90° by the 90° phase shifter 8, and are demodulated. The color subcarrier for demodulation is a digital sinusoidal signal synchronized with the input color video signal at frequency sc. The respective outputs of multipliers 5 and 6 are supplied to digital low-pass filters 9 and 10, from which color difference signals I and Q are extracted, respectively. The luminance signal Y and the color difference signals I, Q are supplied to the matrix circuit 12 via the delay circuit 11, and the three primary color signals R,
G and B are obtained.

The color separation filter 2 mentioned above has a frequency sc
A two-dimensional filter is used in which a digital bandpass filter for extracting components and a comb filter are connected in cascade. However, the comb filter assumes that there is signal correlation between multiple consecutive lines, and in areas where there is no correlation between lines,
Accurate Y/C separation cannot be performed, resulting in deterioration of image quality. Therefore, it is possible to detect the presence or absence of correlation between lines and avoid using a comb filter in areas where there is no correlation, or to prepare several types of comb filters and switch between them depending on the state of correlation. Controlled Y/C separation circuits have been proposed.

As an example, three consecutive lines of signals T,
A Y/C separation circuit that determines the line correlation between the signals of two lines M and B and switches the comb filter based on the result will be described.

This Y/C separation circuit has the same level of chroma signals on adjacent lines in the same field, 180°
If the states are different, it is determined that there is a correlation; otherwise, it is determined that there is no correlation. Figure 2 shows a means of determining the presence or absence of this correlation, and shows that the absolute value of the sum (or difference) of signals on adjacent lines is almost 0 (ε
≒0), and if so,
It is determined that there is a correlation, and if not, it is determined that there is no correlation. As shown in Fig. 2, the signals that become high level when each judgment is established are a,,b,
b, the following decision is made depending on which of these signal combinations is at a high level.

...There is a correlation among the signals T, M, and B of the three lines.

b... There is a correlation between signals M and T.

a... There is a correlation between signals M and B.

ab... There is no correlation between the signals T, M, and B of the three lines.

Based on these judgments, the following Y/C separation processing is performed.

When b becomes a high level, C=1/2 [M-1/2 (T+B)], Y=1/2 [M+1/2 (T+B)]... When b becomes a high level, C=1/2 ( M-T), Y=1/2 (M+T)... When a becomes a high level C=1/2 (M-B), Y=1/2 (M+B)... When ab becomes a high level (a) When the sample data of the color carrier in signal M that is separated by one period has approximately the same value, it is considered as a color difference signal transient. C=M, Y=0... (b) Color in signal M When the sample data separated by one carrier period are not nearly equal, it is regarded as a luminance signal transient. C=0, Y=M . . .

The above-described adaptively controlled Y/C separation circuit has a drawback that discontinuous portions are generated in the data when switching the Y/C separation process according to the judgment. This discontinuity will be explained with reference to FIG.

As an example, consider an image in which the upper left half is a single color (for example, red) and the lower right half is gray, with the diagonal line of the screen as the boundary. The color video signal corresponding to this image is a sine wave that is inverted line by line in the upper left half, and a DC signal in the lower right half. FIG. 3A shows the waveform of each line near the boundary in the vicinity of the n-th line of this image. nth and (n+
1) In the second line, the color changes from red to gray in the middle of the line. Due to color signal filters used when encoding composite color video signals, band limiting filters for composite color video signals, etc., at the transition point from red to gray, the envelope of the carrier color signal is changes smoothly.

When such a composite color video signal is input to a color decoder, it is first supplied to an adaptively controlled color separation filter. As described above, this color separation filter examines whether or not there is a correlation between signals of two adjacent lines. FIG. 3B shows the strength of the correlation between two lines, and the higher the level, the weaker the line correlation is. Now, focusing on the n-th line and assuming that its signal is M, the color separation processing in each of the horizontally divided areas 15, 16, and 17 is performed as follows.

Area 15: There is a line correlation between the three lines of signals T, M, and B, and color separation is performed using these three lines of signals.

Region 16...There is a correlation between signals M and T,
Color separation is performed using these two lines of signals.

Area 17: There is a correlation between signals M and B, and color separation is performed using these two lines of signals.

Therefore, by the above-described processing, the carrier color signal of the nth line becomes as shown in FIG. 3C, and the color signal after color demodulation becomes as shown in FIG. 3D. Furthermore, by subtracting the carrier color signal shown in FIG. 3C from the composite color video signal, the luminance signal shown in FIG. 3E is separated.

As is clear from Figures 3D and 3E,
Between area 15 and area 16 and between area 16 and area 1
7, a signal discontinuity occurs. This discontinuity may be slight on the waveform, but on the screen it may be
It will stand out. In order to prevent such discontinuity in the signal waveform, it is sufficient if the waveform of the demodulated color signal is as shown in FIG. 3F.

``Object of the Invention'' Therefore, an object of the present invention is to provide an improved color decoder that prevents signal waveform discontinuity from occurring even when the color separation filter processing of an adaptively controlled color separation filter is switched. The purpose is to provide the following.

"Summary of the Invention" The present invention determines the signal correlation between lines from the signals of a plurality of consecutive lines of an input composite color video signal, and based on this determination, switches the color separation processing in the vertical direction. An adaptively controlled color separation filter that generates a control signal indicating a sample point, a demodulation circuit that demodulates the carrier color signal from the color separation filter, and a color difference signal from the demodulation circuit are supplied and switched by the control signal. The color decoder includes an interpolation filter for interpolating sample points before and after the sample points, and means for subtracting a carrier color signal separated from an input composite color video signal to generate a luminance signal.

"Embodiment" An embodiment of the present invention will be described below with reference to the drawings. In FIG. 4, a digital NTSC color video signal sampled at a sampling frequency of 4 _SC and converted into a digital signal of 8 bits per sample is supplied from an input terminal 21. This input color video signal is supplied to an adaptively controlled color separation filter 22, which is shown surrounded by a dashed line.

The adaptively controlled color separation filter 22 includes a color separation filter 23 and a line correlation determination circuit 24. The line correlation determination circuit 24 determines whether there is a correlation between the signals of the upper and lower lines and the signal of the line of interest, and generates a control signal for switching the color separation filter 23. The color separation filter 23 has the above-mentioned formula, formula, formula,
Separation of the color signal designated by the control signal is performed in the formula or among the color signals shown in the formula.

The carrier color signal separated by color separation filter 23 is supplied to multipliers 25 and 26. 27 is
A color subcarrier generation circuit that generates a color subcarrier whose phase is synchronized with the color subcarrier of the carrier color signal. 26. Multipliers 25 and 2
The respective outputs of 6 are low pass filters 29 and 30.
The color difference signals I and Q extracted from the outputs of low-pass filters 29 and 30 are supplied to interpolation filters 31 and 32, respectively.
The interpolation filters 31 and 32 include a delay circuit 3
A control signal from the line correlation determination circuit 24 is supplied through the line correlation determination circuit 3. When switching from the line correlation determination circuit 24 to the color separation filter 23, this control signal is, for example, a high level signal in several sample periods before and after the sample point at which this switching is performed, and is a low level signal in other periods.

The interpolation filters 31 and 32 perform an interpolation operation during the high level period of the control signal, and output the input signal as it is without modifying it during the low level period of the control signal. No matter which operation is performed, the group delay caused by the interpolation filters 31 and 32 is set to a predetermined value. Interpolation filters 31, 32
The method interpolates a plurality of sample points before and after the sample point during which the control signal is at a high level, that is, the color separation filter is switched, using the color difference signals of the sample points before and after the sample point. As this interpolation, average value interpolation, linear approximation interpolation, etc. can be used. At the outputs of the interpolation filters 31 and 32, respectively, color difference signals I and Q with the discontinuity of the switching point corrected are obtained, and these color difference signals are supplied to the matrix circuit 34.

In order to separate the luminance signal Y, an interpolation filter 3
Color difference signals I and Q taken out to the outputs of 1 and 32
A carrier color signal is formed from. Color difference signals I and Q are supplied to multipliers 35 and 36, and color subcarriers with different 90° phase shifts are supplied to multipliers 35 and 36 through delay circuits 37 and 38, respectively. The output is provided to adder 39. The delay circuit 37 has an amount of delay equal to the amount of delay caused by both the low-pass filter 29 and the interpolation filter 31. Similarly, the delay circuit 38 has an amount of delay equal to the amount of delay caused by both the low-pass filter 30 and the interpolation filter 32. The carrier color signal from adder 39 is supplied to subtracter 40, which subtracts the carrier color signal from the phase-aligned composite color video signal by delay circuit 41. The luminance signal Y from the subtracter 40 is supplied to the matrix circuit 34, and the three primary color signals R,
G and B are taken out. Since the luminance signal Y is obtained by subtracting the discontinuity-corrected carrier color signal from the composite color video signal, it does not include the discontinuity caused by switching of the color separation filter 23.

FIG. 5 shows an example of the adaptively controlled color separation filter 22. As shown in FIG. A digital NTSC color video signal from the input terminal 21 is supplied to a bandpass filter 51, where color separation is performed in the horizontal direction. The output of this bandpass filter 51 is supplied to the vertically connected 1H delay circuits 52 and 53. 1H
Three consecutive lines of signals B, M, and T are taken out by delay circuits 52 and 53. The signals B and M are supplied to a subtraction circuit 54, and the signals T and M are supplied to a subtraction circuit 55. Subtraction circuits 54 and 5
The respective outputs of 5 are supplied to 1/2 divider circuits 56 and 57 (consisting of shift registers).

From each of the divider circuits 56 and 57, 1/2
(MB) and 1/2 (MT) outputs are taken out. These two color separated outputs are supplied to AND gates 58 and 59, respectively, and also to an adder 62. The output of this adder 62 is supplied to a 1/2 divider (consisting of a shift register) 63, and the output of 1/2 [M-1/2 (T+B)] is taken out from the divider 63. , this output signal is supplied to an AND gate 60.

Also, the signal M appearing at the output of the 1H delay circuit 52
is supplied to the AND gate 61 and also to the delay circuit 64 and the arithmetic circuit 65. Letting the output of this delay circuit 64 be M', an arithmetic circuit 65 calculates lM-M'l, and its output is supplied to a level comparison circuit 66 and compared with a reference signal R from a terminal 67. The delay circuit 64 has a delay amount of one cycle of the color subcarrier,
M' is a signal before M period. This signal M and
A comparison output is generated from the level comparison circuit 66, which is high level when the levels of M' are almost equal (when lM-M'l<R) and low level otherwise, and is supplied to the AND gate 68. Ru. The output of this AND gate 68 is supplied to AND gate 61.

The above-mentioned AND gates 58, 59, 60, 68 are
Depending on the determination output from the correlation determination circuit 24, one of them is turned on, and the separated carrier color signal C is
It is taken out to the output terminal 70 via the OR gate 69. The correlation determination circuit 24 performs the determination shown in FIG. The signals M and NT are supplied to the arithmetic circuit 71 of the correlation determination circuit 24, and the arithmetic circuit 72
Signals M and B are supplied to the terminals.

The arithmetic circuit 71 of the correlation determination circuit 24 calculates |M+T
The calculation circuit 72 sequentially performs the calculation of |M+B| for each sample. These hydrochloric acid outputs are supplied to level comparison circuits 74 and 75 and compared with a reference value ε (≈0) from terminal 73. The comparison outputs a, b, of the level comparison circuits 74 and 75 are as follows:
This corresponds to the one shown in the flowchart of FIG. 2, and the AND gates 76, 77, 78, 79 of the next stage
As a result, four judgment outputs ab, , a, and b are formed. The meaning of each of these judgment outputs is that a is the output that is high level when |M+T|>ε is true, and a is the output that is high level when |M+B|>ε is true. The output that is at a high level at times is designated as b, and the output that is at a high level at other times is designated as b, so that the outputs are as shown below.

ab... There is no correlation among the signals T, M, and B of the three lines.

...There is a correlation among all of the signals T, M, and B.

a... There is a correlation between signals M and B.

b... There is a correlation between signals M and T.

The above judgment output is output from AND gates 58, 59, 6
0,68. The output of AND gate 68 is supplied to AND gate 61 and
The signals passed through 8, 59, 60, and 61 are supplied to an OR gate 69, from which a chroma signal C appears.

Judgment output ab obtained at the output of AND gate 76
When it is determined that there is no correlation between the three signals at a high level, and when the levels of M and M' are approximately equal, the signal M is sent to the output terminal 70 via the AND gate 61 and the OR gate 69. taken out. Similarly, when it is determined that there is no correlation between the three signals and the levels of M and M' are not approximately equal, the AND gate 61 is turned off and the chroma signal C is set to 0.

Furthermore, when the output of the judgment circuit 24 is at a high level, the output of the division circuit 63 is selected as the chroma signal, and when the judgment output a is at a high level, the output of the division circuit 56 is selected as the chroma signal, and the judgment The output of the divider circuit 57 is selected when the output b is at a high level.

AND gate 7 of line correlation determination detection circuit 24
The judgment outputs obtained at the respective outputs of 6, 77, 78, and 79 are supplied to a register 80, and taken into the register 80 by a clock pulse from a terminal 81. The current judgment output and the previous judgment output stored in the register 80 are supplied to a comparison circuit 82. The comparison circuit 82 is at a low level when the current judgment output and the previous judgment output match;
When the two do not match, a control signal that becomes high level is output. This control signal is taken out to the output terminal 83. As described above, this control signal is supplied to the interpolation filters 31 and 32, and the interpolation operation is performed while the control signal is at a high level. register 8
The clock supplied to 0 is set to 1/N of the sampling frequency, and coincidence detection is performed every N pieces of sample data (approximately 5 to 10 pieces), and the control signal is kept at a high level for a period of N sampling periods. is held. When the frequency of the clock supplied to register 80 is made equal to the sampling frequency, it is necessary to provide a circuit for holding the comparison output of comparison circuit 82 for a period of N sample data.

The present invention is applicable to an adaptive control type color separation filter having a configuration other than that described above, for example, the absolute value of the signal of three lines |T
It can also be applied when using a color separation filter that detects the presence or absence of correlation using |M||B|.

In the embodiment of the invention described above, the demodulated color difference signals are supplied to interpolation filters 31 and 32 via low-pass filters 29 and 30, respectively. These low-pass filters 29, 30 and interpolation filter 3
1 and 32, when the interpolation filters 31 and 32 are configured as low-pass filters, their arithmetic units can have a common configuration. FIG. 6 shows an example of a digital low-pass filter whose characteristics are switched between demodulation and interpolation by a control signal.

The demodulated color difference signal is supplied to cascaded registers 84, 85, 86, 87, 88 as unit delay elements, and the outputs of these registers 84 to 88 are supplied to multipliers 89, 90, 91, 92, 93. Multipliers 89 to 93 include selectors 9
Filter coefficients (impulse responses) from 4, 95, 96, 97, 98 are supplied to multipliers 89-9.
The output of 3 is supplied to an adder 99, and this adder 9
An output signal is taken from 9. The selector 94 is supplied with filter coefficients h ₁ and h ₁ ', and similarly,
Filter coefficients (h ₂ , h ₂ ′) (h ₃ , h ₃ ′) (h ₄ , h ₄ ′) (h ₅ ,
h ₅ ′) is supplied. Selectors 94 to 98 select filter coefficients h 1 ′ to h 5 ′ during a period of several samples before and after the sample point at which the color separation filter is switched, that is, during a period in which the control signal is at a high level, and select filter coefficients h ₁ ′ to _{h 5} ′ during other periods. Select filter coefficients _h1 to _h5 . When filter coefficients h ₁ to _{h 5} are selected, the digital low-pass filter operates as a low-pass filter for demodulation, and when filter coefficients h ₁ ′ to h ₅ ′ are selected,
A digital low-pass filter operates as a low-pass filter for interpolation.

[Effects of the Invention] According to the present invention, it is possible to prevent waveform discontinuity from occurring in demodulated color difference signals when the color separation operation is switched in an adaptively controlled color separation filter. In this invention, since the color difference signal after demodulation is modified, the modification can be performed more easily than when the modification is performed at the stage of the carrier color signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional color decoder to which the present invention can be applied, and FIGS.
The figure is a flowchart and waveform diagram used to explain the adaptively controlled Y/C separation filter, FIG. 4 is a block diagram of an embodiment of the present invention, and FIG. 5 is an adaptively controlled color separation that can be used in the present invention. A block diagram of an example of a filter, FIG. 6 is a block diagram used to explain another embodiment of the present invention. 21... Input terminal for digital composite color video signal, 22... Adaptive control type color separation filter, 25, 26... Multiplier for demodulation, 31,
32... Interpolation filter, 34, 35... Multiplier for modulation.

Claims (1)

[Claims] 1 Determines the correlation between signals between lines from the signals of a plurality of consecutive lines of the input composite color video signal, switches the vertical color separation processing based on this determination, and generates a control signal indicating the sample point at which this switching is performed. an adaptively controlled color separation filter that generates the color difference, a demodulation circuit that demodulates the carrier color signal from the color separation filter, and a sample point to which the color difference signal from the demodulation circuit is supplied and the switching is performed by the control signal. and an interpolation filter for interpolating sample points before and after the input composite color video signal, and means for subtracting a carrier color signal separated from the input composite color video signal to generate a luminance signal.