JPS5927512B2 - Interframe coding device for color television signals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an interframe encoding device for interframe encoding a color television signal, transmitting it, receiving it, and decoding it.

When digitally transmitting television signals, it is known to perform interframe coding as a band compression method to reduce the number of transmission bits as much as possible and improve the efficiency of the transmission path.

This utilizes the frame correlation of television signals, and is a band compression technique that is particularly effective for television signals with little movement. However, conventionally, NTS
When such interframe coding technology is applied to a color television signal in which a luminance signal and a color signal modulated by a subcarrier are frequency multiplexed, such as in the C, PAL, and SECAM systems, the interframe coding for color components is There is a problem that the prediction error increases and effective compression cannot be performed.

In other words, taking an NTSC color television signal as an example, the subcarrier frequency fsc is (455/2) times the horizontal scanning frequency fH, and the horizontal scanning frequency fH is 525 times the frame frequency fF. After all, fs
c becomes an odd multiple of fF, the subcarrier phase differs by 1800 from frame to frame, and the frame difference signal increases approximately twice in terms of color components. For this reason, the above-mentioned effective band compression cannot be performed. Conventionally, in order to solve this subcarrier phase problem, when performing interframe encoding of color television signals, the color signal is first separated and demodulated into baseband signals, then interframe encoded, and then received. On the other hand, the interframe decoded chrominance signal and luminance signal are converted back to the original NTSC signal. A so-called separate encoding technique is employed. However, in such separate encoding, at the transmitting side, NTSC
A signal decoder and a digital Φ (analog/digital) converter that corresponds to each of the luminance and chrominance signals are required, and on the receiving side, a D/A (digital) converter that corresponds to each of the luminance and chrominance signals is required. This method requires an NTSC/analog converter and an NTSC signal encoder, which has the disadvantage of complicating the device configuration.

In addition, there is also a drawback that distortion occurs in the signal waveform during the demodulation and remodulation process of the NTSC signal during transmission and reception, resulting in deterioration of image quality. An object of the present invention is to provide an interframe code for a color television signal that can directly interframe code the color television signal without performing separate coding and suppress the increase in information due to the carrier color signal, in order to eliminate the above-mentioned drawbacks. The objective is to provide a device for converting

That is, the interframe encoding device for a color television signal of the present invention changes the phase of the carrier color signal by providing means on the transmitting side for inverting the positive and negative polarities of the carrier color signal of the color television signal every other frame. By matching the frames, the color television signal is interframe encoded and transmitted, and the receiving side inverts the polarity of the carrier color signal of the interframe decoded color television signal every other frame. It is characterized by converting the phase of the carrier color signal into the original color television signal, which differs by 1800 between frames. In the present invention, the polarity inversion of the carrier color signal is realized by frequency separation and calculation of the carrier color signal, and demodulation of the color signal to the baseband signal is not performed. That is, there is no need for an NTSC signal decoder, encoder, or extra A/D and D/A converter on the transmitting and receiving sides, and since the process of reversing the positive and negative polarities is simple, there is almost no signal waveform distortion. Furthermore, since the phase of the carrier color signal matches between frames due to the polarity inversion signal, the color signal can be efficiently compressed during interframe encoding. Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. A color television signal M to be transmitted is applied to the input terminal 1, and a signal conversion is performed in the preprocessing circuit 100 to invert the positive/negative polarity of the carrier color signal every other frame. N is interframe encoded by the interframe encoder 200 and sent to the transmission path 3. On the receiving side, the signal from the transmission line 3 is decoded by the interframe decoding device 201 to obtain the signal N, which is converted into the original color television signal M by the post-processing circuit 101. A feature of the present invention is that it includes a pre-processing circuit 100 and a post-processing circuit 101 for inverting the polarity of a carrier color signal, and the interframe encoding device and decoding device will be described later. It has the same functions as the conventional one except that it is provided with a function of transmitting and receiving a code to distinguish between even frames and odd frames.

Furthermore, since the pre-processing and post-processing perform conversion operations that are opposite to each other, they will be collectively described in detail below. FIG. 2 is a diagram showing the preprocessing circuit 100 and postprocessing circuit 101 of FIG. 1 in detail.

First, in the preprocessing circuit 100 , the carrier color signal component of the color television signal M is frequency-separated by a bandpass filter (BPF) 110 , the amplitude is doubled by a coefficient multiplier 113 , and the resultant signal is input to the minus side of a subtracter 114 . be done.

The delay circuit 111 is for compensating for the delay of BPFllO, and the delay-compensated color television signal is supplied to the plus side of the subtracter 114 and also applied to one side of the switch circuit 115, and is switched by the switch circuit 115. The output is N. The switch circuit 115 switches between these two signals in response to even frames and odd frames, and the switching signal 116 is generated from the original color television signal M via the control signal generator 112 and converted. It is sent to the interframe encoding device 200 together with the television signal N, and transmitted to the receiving side. The post-processing circuit 101 has almost the same configuration as the pre-processing circuit 100, but the switching signal 116' corresponding to even frames and odd frames is supplied from the interframe decoding device 201. The operation will be explained below using mathematical formulas.

The input color television signal M(t) is the luminance signal Y(t
) and the color signals c1(t) and C2(t). However, Φ1(t)−Sin2πFs
ct, Φ2(t)-COs2πFsct.

Furthermore, the signal M(t-TF) after one frame is Φ1(t
-TF)=-Φ1(t),Φ2(t-TF)=-Φ2(
t), and C2(t - TF)Zc2(t), so the phase of the carrier color signal is 1 for each frame.
They differ by 80°.

A BPF through which the signal M(t) selectively passes the carrier color signal.
After passing through IIO, most of the luminance signal Y(t) is attenuated, so the output M2(t) of the subtracter 114 becomes, and the polarity of the carrier color signal is reversed. The switch circuit 115 outputs the signal M1(t) passed through the delay compensation circuit 111 in odd frames.
), and select the signal M2(t-TF) in the next frame', that is, even frames.
The output N(t) of the switch circuit 115 is as follows, and it is possible to obtain a signal in which the phase of the carrier color signal is almost the same for each frame.

If the screen is stationary, N(t)': - N(t-
TF), the frame difference signal becomes almost zero, and efficient interframe coding can be performed. On the receiving side,
When the frame is an odd number, N(t) is simply given delay compensation and is passed through as is; when the frame is an even number, the positive and negative polarities of the carrier color signal are reversed by the same operation as on the transmitting side, and the post-processing circuit 101 The original color television signal M can be obtained as output.

It is of course possible to concretely implement this embodiment using an analog circuit, but in order to maintain stable calculation accuracy, it is preferable to use a digital circuit.

FIG. 3 is a diagram showing another example of the preprocessing circuit 100 of FIG. 1.

The preprocessing circuit 100 shown in FIG. 2 has the advantage of a simple configuration, but has the disadvantage that the amplitude of the frame difference signal increases with respect to the high frequency component of the luminance signal. That is, since the luminance signal Y of the color television signal M includes a high frequency component that shares the band with the carrier color signal, the output that has passed through the BPFIIO contains the luminance signal Y in addition to the carrier color signal component. A high frequency component YH also appears. Therefore, if we write equation (4) more precisely, we get
The frame difference signal D(t) for a still image is D(t)-M
1(t)-M2(t-TF)'-12YH(t) (6
), the high-frequency luminance signal appears twice.

The configuration of FIG. 3 eliminates this drawback by using a one-line delay line.

In FIG. 3, reference numeral 122 is a one-line delay line, reference numeral 120 is an adder, reference numerals 125 and 126 are a coefficient unit for v and 1/, respectively, and the other components are the same as those used in FIG. 2. is used.

The switch circuit 115 selects the b side for odd frames and the a side for even frames, and the conversion output N for the input color television signal M is as follows.

Here, YL(t)-Y(t)-YH(t) and T
H is one horizontal scanning time. In this conversion, the positive and negative polarities of the negative signal terms are reversed every other frame, and the negative signals of two scanning lines are averaged. Moreover, for the luminance signal, if the vertical correlation of the screen is strong, YH(t)Z
Since YH(t-TH), the high frequency component is attenuated by the comb filter. After performing such conversion, the frame difference signal D(t) for the still image becomes,
This is the line difference between the high frequency components of the luminance signal.

Since there are few line differences in ordinary images, the frame difference signal becomes almost zero, and efficient interframe coding can be realized. As the post-processing circuit 101 on the receiving side, the one shown in FIG. 2 can be used as is. Therefore, as a third example, a sub-Nyquist encoding method in which encoding and transmission is performed at a sampling frequency lower than the Nyquist frequency (twice the frequency of the signal band) is applied to the preprocessing and postprocessing of the present invention. A sub-Nyquist interframe encoding device that is much more effective than the conventional one will be described. In the sub-Nyquist encoding method, the signal is sampled at a time when the subcarrier phase differs by about 180 degrees, and the sampling phase is shifted by 180 hours for each scanning line.
On the receiving side, the intermediate sample points are interpolated from neighboring sample values.

Even with this sub-Nyquist encoding method, the positive and negative polarities of the carrier chrominance signal are still inverted for each frame, so if it is directly applied to interframe encoding, the carrier chrominance signal will be approximately equal to the frame difference signal. This appears to be twice as large, and the effect of band compression by interframe coding is small. Therefore, if the preprocessing circuit 100 of the present invention incorporates an operation of reversing the positive/negative polarity of the carrier color signal every other frame, the frame difference signal becomes almost zero, and efficient interframe coding can be realized. . Regarding the above-mentioned sub-Nyquist encoding method, please refer to the publication "32 Mb/s" Direct Coding (HODPCM) Color Television Transmission System (Communication Method) published by Yamako Institute of Electronics and Communication Engineers on September 10, 1975.
Since this is detailed on pages 10 to 11 of the ``Shiki Research Group Materials (S75-69)'' (Reference 1), further explanation will be omitted. FIG. 4 is a block diagram showing the preprocessing circuit on the transmitting side of the sub-Nyquist interframe encoding device described above.The structure is the same in principle as that shown in FIG. The color signal is averaged with the color signal one scan line later.

Further, FIG. 4 shows a case in which it is constructed using a digital circuit. In FIG. 4, a color television signal M is input to an A/D converter 130 and a pulse generation circuit 136. A pulse generation circuit 136 separates the synchronization signal from the color television signal and generates a sampling pulse 140 for A/D conversion.
, a sub-Nyquist sampling pulse 150, a line switch signal 141, and a frame switch signal 116. A/
The sampling pulse frequency Fp for D conversion is selected to be approximately four times the subcarrier frequency Fsc. When Fp-4fsc,
The sampling time is a position where the subcarrier phase is shifted by 90f. As shown in FIG. 5, if a number is assigned to the sample value A that is the output of the A/D converter 130, the signal delayed by one sample in the register 131 becomes B, and A and B
is switched for each scanning line by the switch circuit 132, and then subsampled by the sub-Nyquist frequency Fs of the sampling pulse frequency Fp(7)% by the register 135.
A sample value of C or D appears at its output. The sample values of C and D each have a subcarrier phase of 180
The phase of the subcarriers between C and D is shifted by 90 degrees. Since the switch circuit 132 switches between A and B for each scanning line, a sub-Nyquist encoded sample value is obtained at the output of the register 135. The 1-line delay line 122 has Fp=4fsc for NTSC signals.
Alternatively, when Fs=2fsc is selected, it is configured with a shift register or memory with a delay of 455 samples.

The multiplexer 133 is a switch that inverts the positive/negative polarity of the carrier color signal every other frame, and the other calculation operations are the same as those shown in FIGS. 2 and 3. The relationship between input M and output N can be easily described using Z transformation. That is, in Z-transform, since z-n represents n-sample delay, one line delay is written as z-0, and BP
The z-transform of the transfer characteristic of FLLO is B(2) me1-B(2)
=A2, the output NOZ transformation NZ) becomes, so the z transformation DΦ of the frame difference signal becomes.

However, z-F represents frame delay. According to the Q test, the first term represents the frame difference of the low frequency component, and the second term represents the frame sum of the line difference of the high frequency component including the carrier color signal. The first term is zero for a still image, the second term is also zero for a carrier signal, and what remains is only the line difference of the high frequency luminance component, similar to equation (7). For example, the concrete implementation method of BPFIlO in digital circuit, Raku is B(Z)
It can be realized by registers and adders/subtractors since it is only necessary to configure it so that it becomes or.

Most of the configuration shown in FIG. 4 is a circuit used for sub-Nyquist encoding using a comb filter, and the circuit required only for polarity inversion of the carrier color signal of the present invention is the subtracter 13.
4 and multiplexer 133, the sub-Nyquist encoding method can be easily applied to the present invention.

FIG. 6 is a block diagram showing a post-processing circuit on the receiving side of the sub-Nyquist interframe encoding device.

Sub-Nyquist decoding is performed by interpolating subsampled pixels on the transmitting side. First, the transmitted sample value is transferred to the BPFIIO' and the delay compensation circuit 111.
1 of the output of the delay correction circuit 111'.
One goes directly to the multiplexer (Mpx) 133b and passes through this multiplexer when the frame is an odd number.
It is multiplexed with the interpolation pixel at l6O, and converted into an analog signal by the D/A converter 165. In this circuit, the signal is processed at the sub-Nyquist sampling frequency Fs up to the input of the multiplexer 160, and the sampling frequency is increased to 2 at the multiplexer.
fs, that is, Fp. At the time of an even frame, the signal whose polarity of the carrier color signal is inverted by the subtracter 134' is MPX.
Selected by l33b. The interpolated pixel is created separately into an interpolated value of the low-range luminance component and an interpolated value of the carrier color signal, and these are combined by an adder 162 and a subtracter 163. First, the low-range luminance component is extracted from the original signal by a subtracter 114'.
The interpolated value is obtained by subtracting the high frequency component including the carrier color signal that has passed through the interpolation circuit 161. As the interpolation circuit 161, for example, a circuit that creates an average value of two adjacent sample values may be used. Since the interpolated value of the carrier color signal is obtained by inverting the polarity of the sample value one scanning line before, the output of the l-line delay line 122' may be used. Therefore, in odd frames, the interpolated values are combined in the subtracter 163, and in even frames, the polarity of the carrier color signal is inverted, so the adder 16
Synthesize in 2. The MPXl 33a switches these interpolation pixels for each frame. Most of the post-processing circuit in FIG. 6 is necessary for sub-Nyquist decoding, and only the subtracter 134', adder 162, and There are only multiplexers 133a and 133b. Next, an example of a specific configuration of the interframe encoding device 200 will be explained as follows.
As shown in the figure.

The output N of the preprocessing circuit 100 in FIG.
Subtractor 2 only for the signal of one frame before that appears at the output of 14.
10, noise components are removed by a non-linear circuit 211, and the signal is transmitted to the next-stage intra-frame predictive coding loop.
The nonlinear circuit 211 is a circuit whose gain is less than 1 when the amplitude of the signal is small, and whose gain is approximately 1 when the amplitude is large. Since the difference signal amplitude is sufficiently suppressed, minute noise can be effectively removed. The subtracter 210, the quantizer 212, the adder 215, and the prediction circuit 213 constitute an intra-frame predictive coding loop, and function to remove the horizontal hole length remaining in the frame difference signal. Here, the intra-frame prediction error signal created based on the frame difference signal by the quantizer 212 is quantized, and is unequal-length coded by the unequal-length code conversion circuit 21T, so that the quantized code has redundancy. is removed. A signal 116 for switching between odd and even frames is encoded by a synchronization code generation circuit 216, multiplexed with the unequal length code together with a synchronization code, a coding mode control code, etc. by a multiplexer 218, and written into a buffer memory 219. . The buffer memory 219 is for temporally equalizing information generated in the interframe coding loop.
9, data is read out at a constant speed and sent to the transmission path. The above-mentioned interframe encoding device 200 (Fig. 7) is based on a publication published by the Institute of Electronics and Communication Engineers in 1975, ``Configuration of 4MTV Telephone Interframe Coding System - Communication System Study Group Materials'' (CS75-1). 68)” (Reference 2)
The structure is almost the same as that shown in detail in FIG. 1 on page 1 and FIG. 6 on page 5, and its operation is also similar, so further detailed description will be omitted. Similarly, the first
Regarding the interframe decoding device 201 on the receiving side in the figure,
It is also possible to simply perform the reverse operation of the interframe encoding device 200 in FIG. Therefore, I will omit the details.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an example of the preprocessing circuit 100 and postprocessing circuit 101 shown in FIG. 1, and FIG. 4 is a diagram showing a third example of the preprocessing circuit 100 in FIG. 1, FIG. 5 is a diagram for explaining the sampling phase, and FIG. A diagram showing a second example of the post-processing circuit 101 in the figure and a block diagram showing an example of the interframe encoding device 200 are shown in FIG. 1 to 7, 100... pre-processing circuit, 101... post-processing circuit, 200...
...Interframe encoding device, 201...Interframe decoding device, 110, 110'...Band pass filter, 111, 111'...Delay compensation circuit, 113 ,113! ...Coefficient unit, 114,1
14... Subtractor, 115, 115'...
・Switch circuit, 112...control signal generator,
122, 122'...1 line delay line, 120
... Adder, 130 ... Analog/digital converter, 131, 135 ... Register, 133, 160, 218 ... Multiplexer, 134, 134'・・・・・・Subtractor, 161...
... Interpolation circuit, 165 ... Digital/analog converter, 212 quantization circuit, 213 ... Prediction circuit, 214 ... Frame memory, 217.
... Unequal length encoder, 216 ... Synchronous code generation circuit, 219 ... Buffer memory, 211
...It is a non-linear circuit.

Claims (1)

[Claims] 1. A composite color television signal obtained by frequency multiplexing a luminance signal and a carrier color signal obtained by modulating a subcarrier with a color signal.A composite color television signal in which the positive and negative polarities of the carrier color signal are reversed every other frame. a means of converting it into
The transmitting side includes a means for interframe-encoding and transmitting the composite color television signal obtained from this means, a means for interframe-decoding the transmitted interframe-encoded signal, and a means for interframe-decoding the interframe-encoded signal thus decoded. Between frames of a color television signal, characterized in that the receiving side is provided with means for inverting the positive and negative polarities of the carrier color signal of the composite color television signal every other frame and converting it into the original composite color television signal. Encoding device.