JP2506737B2 - Digital color decoder - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the synthesis of a digital composite color television signal from a digital color television signal in which a luminance signal and a color signal are separated, and vice versa. The present invention relates to a digital color decoder of a digital color television which requires separation of a luminance signal and a color signal from a television signal.

2. Description of the Related Art As a conventional digital color encoder and digital color decoder, for example, the former is disclosed in JP-A-50-114123 and the latter is disclosed in JP-A-60-226292.
Figure 3 is shows the conventional digital encoder, 30 controls the gate circuits 31 and 32 according to a clock of four times the sub-carrier frequency _SC of NTSC television signal (hereinafter abbreviated as 4 _SC) Control circuit, 31 and 32 input control circuit
A gate circuit which passes positive / negative inversion according to the output of 30 to pass / block, and 33 is an adder. This conventional example is 4 _SC
Although the target is a sampled NTSC composite color television signal, it can be applied to other composite color television signals such as PAL with the same operating principle.
The operation of FIG. 3 will be described with reference to FIG. FIG. 5 corresponds to a television screen, and squares represent pixels. Each pixel is given a number in order from the beginning in the line, and the following is the j-th line on line i (O ≦ i, O
The luminance signal of the pixel of ≦ j) is represented by Y _{i, j} , and the two color difference signals are represented by I _{i, j} , Q _{i, j} . In the analog signal, the chrominance signal is obtained by quadrature balance modulation of the subcarrier, so in the case of this conventional example, if the phase is selected so that Q _{i, j} becomes zero, the pixel (i, j) is on the same line as the first line. The color signal components of the four pixels are represented by a series of I _{i, j,} Q _{i, j + 1,} −I _{i, j + 2,} −Q _{i, j + 3} . Therefore, the composite color television signal to be synthesized is Y _{i, j} + I _{i, j,} Y _{i, j + 1} + Q _{i, j + 1,} Y _{i, j + 2,} −I
_{i, j + 2} Y _{i, j + 3} −Q _{i, j + 3} , and other pixels are similarly repeated in units of 4 pixels. The subscripts shown below the pixels in FIG. 5 indicate the relationship between the Y signal and the color difference signals I and Q. As described above, according to the color encoder shown as the conventional example, the frequency multiplexing of the color difference signals, that is, the composite color television can be combined by a simple calculation between the sampled values without depending on the analog method. Next, FIG. 4 shows a digital color decoder of this conventional example. The digital color decoder of the present conventional example was devised independently of the digital color encoder of the above conventional example and should not necessarily be a pair, but even if a pair does not lose generality as a conventional example. This is a conventional example of the present invention. In FIG. 4, 22 and 23 are delay units that delay input data by 1H-2D, 24 and 25 are delay units that delay input data by 2D, 26 is a vertical operation circuit, 27
Is a horizontal operation circuit, 28 is a comparison circuit, and 29 is a switcher for selecting one of the outputs of 26 and 27. Here, H is the number of delay stages of pixels for one line, and D is a delay unit for one pixel, and this expression will be used below. Now, the output of the delay circuit 24 is set to N
_{i, j} (i is the line number and j is the pixel number on the line). At this time, the input of the delay device 22 is N _{i + 1, j} and the output is N _{i
i, j + 2} , the output of the delay device 25 is N _{i, j−2} , and the output of the delay device 23 is N _{i−1, j} . Receiving the above data, the vertical direction operation circuit 26 causes YV _{i, j} = {N _{i, j} + (N _{i−1, j} + N _{i + 1, j} ) / 2} / 2 ...
(1) CV _{i, j} = {N _{i, j} − (N _{i−1, j} + N _{i + 1, j} ) / 2} / 2 ...
(2) In the horizontal direction operation circuit 27, YH _{i, j} = {N _{i, j} + (N _{i, j−2} + N _{i, j + 2} ) / 2} / 2 ...
(3) CH _{i, j} = {N _{i, j} − (N _{i, j−2} + N _{i, j + 2} ) / 2} / 2 ...
(4) The following calculation is performed. Assuming that the input N _{i, j} is Y _{i, j} + I _{i, j} , equations (1), (2), (3) and (4) are transformed as follows.

YV _{i, j} = {Y _{i, j} + (Y _{i−1, j} + Y _{i + 1, j} ) / 2 + I _{i, j} − (I _{i−1, j} + I _{i + 1, j} ) / 2} / 2 (5 ) CV _{i, j} = {Y _{i, j} + (Y _{i-1, j} + Y _{i + 1, j} ) / 2 + I _{i, j} + (I _{i-1, j} + I _{i + 1, j} ) / 2} / 2 ( 6) YH _{i, j} = {Y _{i, j} + (Y _{i, j−2} + Y _{i, j + 2} ) / 2 + I _{i, j} − (I _{i−2, j} + I _{i + 2, j} ) / 2} / 2 ... (7) CH _{i, j} = {Y _{i, j} − (Y _{i, j−2} + Y _{i, j + 2} ) / 2 + I _{i, j} + (I _{i, j −2} + I _{i, j + 2} ) / 2} / 2 (8) According to equations (5), (6), (7) and (8), Y _{i, j} ≈
(Y _{i−1, j} + Y _{i + 1, j} ) / 2 and I _{i, j} ≈ (I _{i−1, j} +
_{I i + 1, j) /} 2 if _{YV i, j ≒ Y i,} j and _{CV i, j ≒ I i,} j is established, also _{Y i, j ≒ (Y i} , j-2 + Y i, j + 2) / 2 and I _{i, j} ≈ (I _{i, j-2} + I _{i, j +2} ) / 2, then YH _{i, j} ≈Y
_{i, j} and CH _{i, j} ≈I _{i, j} hold. That is, according to the digital color decoder of the present embodiment, the horizontal on the two-dimensional screen,
Correlation of neighboring pixels in either vertical direction guarantees good separation of NTSC color television signals. The selection of the direction of correlation is evaluated by the absolute value of the difference in each direction of | N _{i−1, j} −N _{i + 1, j} | and | N _{i, j−2} −N _{i, j + 2} | As described above, the calculated value in the direction of the pair having a small value is output by operating the switch 29.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the configuration of the digital color decoder as described above, the selector 29 selects the horizontal and vertical directional arithmetic circuits by the difference between pixels in each directional direction. There was a problem that the selection error of the correlation direction could not be avoided in principle in the frequency space where there is an image that can be transmitted, such as thin lines and characters, observed above. This is a function that expresses the absolute value of the difference in frequency space, for example, the function | sin (π / _SC ) | that corresponds to the absolute value of the difference between two pixels separated by four pixels in the horizontal direction is This can be explained by the fact that there is no monotonic increase with respect to the spatial frequency.

It is an object of the present invention to provide a digital color decoder that realizes good YC separation in a composite digital transmission system.

Means for Solving the Problems The digital color decoder of the present invention receives as input a coded composite color television signal on which codewords having N (N> 1) codes which are correlation codewords are superimposed. Delaying means for outputting pixel information to be decoded and neighboring pixel information, and a plurality of calculating means for outputting a color television signal composed of a luminance signal and a color signal independent of the output of the delaying means, Decoding means for receiving the output of the delay means, separating and decoding the correlation codeword and outputting the same, and selecting means for receiving the output of the decoding means and selecting one of the outputs of the plurality of arithmetic means .

The present invention has the above-described configuration, and the selection of the results of the plurality of calculation means in the digital color decoder is determined by the superimposed correlation code word. This superimposed codeword is determined by the evaluation means of the digital color encoder, and thus the output at the digital color decoder is determined by the evaluation of the correlation pattern at the digital color encoder.

Example 1 FIG. 1 shows a luminance signal Y sampled by 4 _SC of the present invention,
FIG. 6 is a block diagram of a digital color encoder in an embodiment in which the color difference signals I and Q are NTSC signals. In FIG. 1, 1 and 2 are delay units that delay input data by 1H-2D, 3 and 4 are delay units that delay input data by 2D, 5 is a vertical correlation circuit that outputs a vertical correlation value, and 6 is a horizontal direction. horizontal correlation circuit for outputting a correlation value, 7 correlation determination circuit for outputting the output received by 2-bit determination words of the horizontal correlation circuit and the vertical correlation circuit, 8 I, clock Q color difference signals 4 _SC , A gate circuit for inverting and outputting positive and negative in a cycle of 2 _SC , 9 is a delay device for delaying input data by 1H, 10 is an adder for superimposing a Y signal and a color difference signal, 11 is a composite of the adder output A superimposing circuit that superimposes a correlation code word on a color signal, 12 is a delay device that delays the output of the superimposing circuit by 2D, and 13 is a control circuit that controls the superimposing circuit. The operation of the digital color encoder of this embodiment constructed as above will be described below. Delay device 3 now
_Is Y _{i, j} , and the output of the delay device 9 is I _{i, j} . At the same time, the output of the adder 10 is Y _{i, j} + I _{i, j} , and in the following order, Y _{i, j + 1} + Q _{i, j + 1} , Y _{i, j + 2-} I _{i, j + 2} , Y _{i, j + 3 for} each clock in the same manner as in the conventional example.
−Q _{i, j + 3} . If this data series is output as it is, it will be digital as in the conventional digital color encoder.
Although it becomes an NTSC color television signal, in the present embodiment, the correlation code word is superposed on it in the superposing circuit 11 as follows and output.

Hereinafter, in this specification, pixel data to be superimposed is N ′ _{i, j} , and the result of superimposition is N _{i, j} . The least significant bit of these data is abbreviated as LSB. ) Horizontal correlation >> Vertical correlation If the LSB of N'i _{, j-2} is 0, the LSB of N _{i, j} is set to 0.

If the LSB of N'i _{, j-2} is 1, the LSB of N _{i, j} is set to 1.

Horizontal correlation << vertical correlation If the LSB of N'i _{, j-2} is 0, the LSB of N _{i, j} is set to 1.

If the LSB of N'i _{, j-2} is 1, the LSB of N _{i, j} is set to 0.

When the horizontal correlation is approximately equal to the vertical correlation, nothing is done, that is, the correlation codeword is not superimposed.

The correlation determination required for the above superposition is performed using the luminance signals Y of the pixel to be encoded and the neighboring pixels. That is, similarly to the above, when the output of the delay device 3 is Y _{i, j} , the input of the vertical correlation circuit 5 is Y _{i−1, j} , Y _{i, j,} Y _{i + 1, j} , and the input of the horizontal correlation circuit 6 is Y _{i, j−2} , Y _{i, j} , Y _{i, j + 2} , and the following calculations are performed respectively.

Vertical correlation circuit V _{i, j} = | 2Y _{i, j} − (Y _{i−1, j} + Y _{i + 1, j} ) | (9) Horizontal correlation circuit H _{i, j} = | 2Y _{i, j} − (Y _{i, j -2} + Y _{i, j +2} ) | (10) The above V _{i, j} and H _{i, j} are output to the correlation determination circuit 7.

If the correlation determination circuit 7 is | V _{i, j} −H _{i, j} | <(predetermined threshold value S) (11), the determination code “00” is not satisfied in the expression (11) and V _{i, j} >. If H _{i, j} , the determination code of “01” is not satisfied and if V _{i, j} > H _{i, j} , the determination code of “10” is output to the control circuit 13. The operation of the superposition circuit 11 is such that the input is N ′.
_{If the i, j} output is N _{i, j} , it is expressed by the following equation.

N _{i, j} = N ′ _{i, j} + D _{i, j} (d _{i, j} = −1,0, + 1) (12) D _{i, j} in the equation (12) is determined by the control circuit 13. The operation of the control circuit 13 is represented in FIG. In FIG. 6, when the output of the correlation judgment circuit 7 is "00", it indicates that the correlation in the vicinity of the target pixel is not biased horizontally and vertically, and "01".
Indicates horizontal correlation and “10” indicates vertical correlation. D
_{i, j-2} is a control circuit 13 for the pixel data two data before
D _{i, j} is the addition value (that is, the past processing content) of Equation 12
As shown in, the added value with respect to the output of the adder 10 is meant. Here, as shown in FIG. 6, the control circuit 13 outputs the output of the correlation determination circuit 7, the output of the adder 10, the output of the delay device 12,
The operation differs depending on the past (two pixels before) processing result. When the correlation determination circuit 7 outputs "00", that is, when the correlation in the vicinity of the pixel is not biased in the horizontal and vertical directions, any correlation may be used for the signal separation of the NTSC color television signal. Therefore, D _{i, j} in Expression 12 is “0”. Next, consider a case where the output of the correlation determination circuit 7 is "01", indicating horizontal correlation. In this case, the delay device 12 output
The exclusive OR of the LSB and the LSB of the output of the superimposing circuit 11 must be "0". Therefore, adder 10 output LS
The combination of B and the LSB of the delay device 12 output is (0,0) or (1,
In the case of 1) (the case of lines 2 to 3 in FIG. 6), D _{i, j} may be “0”. However, in other cases (in the case of lines 4 to 7 in FIG. 6), D _{i, j} must take +1 or -1 in order to set the exclusive OR to "0". +
Which one of 1 and -1 is added depends on the processing content D _{i, j-2} of two data before, and in this embodiment, it is determined so that the average luminance level of the entire screen does not change as much as possible. ing. For example, the past processing result N _{i, j−2} is performed by adding +1 and the current processing content is +1 or −1.
If it needs to be, then -1 is selected. When the output of the correlation judgment circuit 7 is “10”, the delay 12 output
D _{i, j} is added to the output of the adder 10 so that the exclusive OR of the LSB and the LSB of the output of the superimposing circuit 11 becomes “1”.

Depending on the case, the direction of the correlation between neighboring pixels is superimposed on the least significant 1 bit of the output of the digital color encoder configured as described above. Next, the digital color decoder of this embodiment will be described. FIG. 2 is a block diagram of the digital color decoder of this embodiment.
4, 15 is a delay device that delays input data by 1H-2D, 16 and 17 is a delay device that delays input data by 2D, 18 is a vertical operation circuit, 19 is a horizontal operation circuit, and 20 is a pixel to be decoded. And a circuit for decoding a correlation code from each data of the pixel two data before, 21 is a digital color decoder for receiving one of the output of the vertical direction arithmetic circuit 18 and the output of the horizontal direction arithmetic circuit 19 under the control of the correlation code decoding circuit. It is a switching device that outputs as. The operation of the digital color decoder of this embodiment constructed as above will be described below.

The conventional digital color decoder shown in FIG. 4 differs from the digital decoder of this embodiment in that the comparison circuit 28 is replaced with a correlation code decoding circuit 20. The operation of the other blocks is exactly the same. In FIG. 2, assuming that the output of the delay device 16 is N _{i, j} and the output of the delay device 17 is N _{i, j-2} , the correlation code decoding circuit 20 outputs the LSB of N _{i, j-2} and N _{i, j . If} the exclusive OR of the LSBs of _j is 0, the output of the horizontal operation circuit 19 is controlled, and if it is 1, the output of the horizontal operation circuit 18 is controlled to be the output of the switch 21.

The digital color encoder and digital color decoder of this embodiment have been described above. According to the present embodiment, the NTSC in which the 2-bit correlation code represented by the least significant bit of the pixel data to be encoded and decoded and the pixel data two data before is sampled at the sampling frequency of 4 _SC.
By superimposing it on the signal, the selection error of the horizontal and vertical decoding means used at the time of separating the luminance signal and the color difference signal is prevented, and the luminance signal Y is completely transmitted in the two horizontal and vertical directions in the transmittable frequency range of the NTSC signal. Color difference signal I,
It can be guaranteed that Q is separated.

In the present embodiment in which the pixel data is represented by 8 bits, the least significant 1 bit is assigned to the correlation code, which may reduce the amplitude resolution. However, this is when the equation (11) is not satisfied, that is, the correlation of the pixels. Occurs only in one of the horizontal and vertical directions, and 8-bit resolution is guaranteed in the lower part of the spatial frequency. In this embodiment, the delay amounts of the delay units 1, 2, 14, and 15 are set to 1H-2D, but it is also possible to use the inter-pixel correlation between fields as 263H-2D. Although the Y signal at the time of encoding is used for the correlation determination in this embodiment, it is also possible to use other color difference signals.

In the present embodiment, the NTSC signal sampled at the sampling frequency of 4 _SC was used as the object of encoding and decoding.
In principle, it is easy to realize as a PAL signal, and 3
_The same applies to sampling frequencies such as _SC . In addition, even if the output of the digital encoder of this embodiment is analog-transmitted, reproduction can be performed as usual in a general receiver, and this is also true of a system in which digital transmission is performed and reproduction is performed by another digital color decoder.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to realize an adaptive luminance signal / color difference signal separation function without selection error, and obtain an image quality that cannot be realized by a conventional adaptive digital color decoder. It is possible and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of a digital color encoder of one embodiment, FIG. 2 is a block diagram of a digital color decoder corresponding to the encoder, FIG. 3 is a block diagram of a conventional digital color encoder, and FIG. FIG. 5 is a block diagram of a digital color decoder, FIG. 5 is an explanatory diagram of an NTSC signal sampled by 4 _SC , and FIG. 6 is an explanatory diagram of the operation of the present digital color encoder. 11 …… Superposition circuit, 8,31,32 …… Gate circuit.

Claims (5)

(57) [Claims] 1. Pixel information to be decoded and neighboring pixels by inputting a coded composite color television signal on which code words having N (N> 1) codes as correlation code words are superimposed. A delay means for outputting information, and a plurality of calculating means for outputting a color television signal composed of a luminance signal and a color signal independent of the output of the delay means,
Decoding means for receiving the output of the delay means, separating and decoding the correlation codewords and outputting the same, and selecting means for receiving one of the outputs of the plurality of arithmetic means by receiving the output of the decoding means. A digital color decoder characterized by the following. 2. A digital color decoder as set forth in claim 1, wherein the plurality of arithmetic means are two, one utilizing horizontal correlation between pixels and one utilizing vertical correlation. 3. A correlation code word of an encoded composite color television signal on which a correlation code word to be an input is superimposed is superimposed on the pixel to be decoded and its neighboring pixel by the relationship of the least significant bit. The digital color decoder according to claim 1, wherein 4. A correlation code word of an encoded composite color television signal on which a correlation code word to be an input is superimposed is superimposed on the pixel to be decoded and its neighboring pixel in the relationship of the least significant bit. The digital color decoder according to claim 2, wherein 5. The digital color decoder according to claim 1, wherein the digital composite color signal to be decoded is an NTSC signal or a PAL signal.