JPS6156590A - Forecaster/encoder - Google Patents

Abstract

PURPOSE:To forecast and to encode the forecasted coded signals of sampled PAL television signals efficiently by sampling the frequency so that number of samples per several lines is an integer, by forecasting and encoding the samples by means of forecaster containing forecasting circuit in which the forecasting function within the Z-zone is represented by Z<->N{(2/3)Z<-1>-1/3+(2/3)Z}. CONSTITUTION:The signal having the sign of transmission line and received from the input terminal 10 to the forecaster/encoder is inverted to reversed sign through sign changer 11 to regenerate contized forecast error signal (i.e. quantized output signal) depending on the transmitted sign to be supplied to adder 12. Forecasters 6, 13 are composed of digital filers having forecasting function of P2(Z) characteristic within Z-zone of Z<-1>=e<-j.2pif/fs> where sampling frequency f2 3fsc and fs=(N/2)fH, N being an integer).

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a predictive decoding device used for data compression encoding of PAL color television signals.

[Prior art]

Conventionally, two types of methods for data compression encoding (bandwidth compression encoding) of video television signals have been studied. Compared to a separation method that restores the carrier color signal to a baseband signal and encodes the luminance signal and color signal separately, the method that directly predictively encodes a composite color television signal requires processing of separation, demodulation, and modulation of the carrier color signal. Since there is no hardware, high-quality encoding can be performed with simple hardware. However, since the single color signal is frequency multiplexed, efficient encoding cannot be performed using the prediction function used for the monochrome signal.

On the other hand, as a method for efficiently direct predictive coding of composite color television signals, the IEEE Trans
actions on communication
s) Vol, COM-22No, 8 August 1
974.

Pages 1106-1113 and the same Vol. COM-25
No.

1111, 1977, 1349-1385, the relationship between sampling frequency f11 and subcarrier frequency j"sc is expressed as fs=t/m" fsc (L
It is known that if z m is a positive integer), efficient predictive coding can be performed by making predictions using sampling points where subcarriers are in phase. On the other hand, the number of samples per line is: In the case of an NTSC television signal, the relationship between subcarrier f8c and horizontal synchronization frequency fu is c=455. , so.

If t=4 and m=1, the number of samples for one line is 91.
It becomes 0 and an integer.

However, in the case of PAL television signals.

fsc=C"royu+")fu, so the number of samples per several lines could not be easily made into an integer value. For this reason, when encoding a PAL television signal in units synchronized with a horizontal synchronizing signal, special processing must be performed on half-sized samples, which has the disadvantage of complicating the hardware.

Also, since the relationship between pfBc and fu is not simple, PAL
In cases where both a television signal and a monochrome signal without subcarriers can be encoded with the same sampling frequency, or when subcarrier f is used for signals from a VTR, etc.

If there is jitter in the sampling frequency oscillator (VCO
) had the disadvantage of being complicated. Also.

Also when connecting to other encoding devices in the form of digital television signals, it is convenient for the number of samples in the equation 2 in ab to be an integer value.

[Purpose of the invention]

An object of the present invention is to provide a decoding device that can predictively decode a signal obtained by efficiently predictively encoding a PAL television signal sampled at a sampling frequency such that the number of samples per several lines is an integer. .

[Structure of the invention]

According to the present invention, a signal obtained by predictively encoding a PAL television signal sampled at a sampling frequency that is approximately three times the subcarrier frequency and seven times the horizontal synchronization frequency (N is an integer) is received and decoded. , the prediction function in the z domain is z
-N(iZ-1-8+42) A predictive decoding device is obtained that includes means for performing predictive decoding using a predictor including a prediction circuit of -N(iZ-1-8+42).

[Principle and operation]

The sampling frequency f8 is set to be approximately three times the subcarrier frequency fsc and seven times the horizontal synchronization frequency fu.

By performing sampling, efficient prediction can be performed using three consecutive samples two lines before. The arrangement of the sample points at this time is shown in Figure 2 of the seventh stand, f, middle 3f8
It should be 0, three consecutive samples S, , S, ,
The sum of S1 is almost only the luminance signal Y.

3Y out of s, +s, +s3 ・・・・・・(
1) If the signal at the current sample point

Ignoring -625-fH of fsc=(+)fH, S, key y -c -9,-(
2). Therefore, Sl r 821 S
The predicted value of X using Equation (1) and (2) is as follows:

Even if fs is set so that the number of samples per two lines is an integer value N, an image with strong vertical correlation can be efficiently predicted using three sample points two lines before.

〔Example〕

FIG. 6 is a diagram showing the configuration of a conventional predictive encoding device and predictive decoding device for PAL television signals.

The sampling frequency is generally f3=4·f8°.

In this example, t=3. It is assumed that m=1. That is, fs”
3 fsc, and the arrangement of sample points at this time is shown in FIG. The locations marked with ■ are the locations where the subcarriers are in phase, but since the ■ signal is inverted for each line, the phase of the carrier color signal differs between even and odd lines. The predictor 66 of the predictive encoding device and the predictor 73 of the predictive decoding device perform two-dimensional prediction using sample points including two lines before the phase matching. Furthermore, if one of the sampling points is measured along the U axis, prediction using the previous line becomes possible. Further, by correcting the color signal by performing phase conversion and filtering processing on the color signal, it becomes possible to perform prediction using the previous line. However, with these methods, it is not easy to make efficient predictions by setting the number of samples per several lines to an integer number.

FIG. 1 is a block diagram showing an embodiment of the present invention.

A PAL television signal applied to an input terminal 1 of the predictive encoding device is sent to an A/D converter 2 and/or an pulse signal generator 3. The pulse signal generator 3 uses a horizontal synchronization signal to the frequency obtained by synchronous separation.

A value close to three times the subcarrier frequency faC and f s
” 2 fn (N is an integer) (4)
A sampling frequency f is generated and supplied to the A/D converter 2. Note that N=1702 is taken as a specific example of the value of N. The PAL television signal converted into a digital signal by the A/D converter 2 at a sampling frequency of j' s =2 fu is supplied to the subtracter 4 . A prediction signal is output from the predictor 6 and supplied to the subtracter 4 and adder 7. The prediction error signal output from the subtracter 4 is supplied to the quantizer 5 and quantized according to predetermined quantization characteristics, resulting in a quantized prediction error signal, or in other words, a quantized output signal. is output and supplied to the adder 7 and code conversion circuit 8.

In the adder 7, the predicted signal and the quantized output signal are added, and a (locally) decoded signal is obtained as an output.

The (local) decoded signal is supplied to a predictor 6, where a predicted signal is determined according to the prediction characteristics and output as a predicted value for the next sample time. The code conversion circuit 8 converts the quantized prediction error signal into a transmission line code signal according to predetermined conversion characteristics and outputs the signal, and outputs the signal to the output terminal 9 of the predictive coding device.
supply to.

On the receiving side, the transmission line code signal input from the input terminal 10 of the predictive decoding device is subjected to code inverse conversion in the code inverse conversion circuit 11, and the prediction error is quantized according to the transmitted code. Regenerate and output the signal (quantized output signal),
It is supplied to the adder 12. The adder 12 adds the reproduced quantized output signal and the prediction signal from the predictor 13 to obtain a decoded signal, outputs it, and supplies it to the D/A converter 14 and the predictor 13 . The predictor 13 has the same prediction characteristics as the predictor 6 of the predictive encoding device, and calculates and outputs a prediction signal for the next sample time according to the prediction characteristics. The D/A converter 14 converts the decoded digital PAL television signal into an analog signal, outputs it, and supplies it to one output terminal of the predictive decoding device.

FIG. 3 is a diagram showing a first specific example of the predictors 6 and 13. The predictor in this example is the sampling te, z−1=
e-j2rcf/fs o Z area+7) Predictor a
The circuit is configured as a digital filter prediction circuit with characteristics expressed by the Pg(Z) order equation.

Pg(Z)=z-N(zz-'-1+zz)/3
(5) 21 is a shift register that delays an input signal by (N-1) sampling clock periods and outputs the same; 22 and 23 are registers 1 and 23 that delay an input signal by one sampling period.

FIG. 4 is a diagram showing a second specific example of the predictors 6 and 13. There is a one-dimensional prediction function p s (z) that can efficiently perform predictive coding in the case of 18K3 fsc as shown by the following equation.

P, (Z)=0.52 +Z -0,52-'
(6) The prediction circuit 31 is constituted by a digital filter with a prediction function P□(Z) expressed by equation (6).

The prediction circuit 32 is composed of a digital filter having a prediction function P 2 (Z) expressed by equation (5).

The coefficients A1 and A2 of multipliers 33 and 34 are 2 usually A1+
It is set to be 1 in A2, but 1 For example, A1 = 0
．． 5 Let A2=0.5. The output terminal 36 has the predicted function power P(Z)=A, -P, (Z)+A, -P2(
A predicted signal determined by the predicted filter characteristic is obtained.

FIG. 5 is a diagram showing a third specific example of the predictors 6 and 13. Adaptive prediction is used in which two prediction characteristics are switched for each sample. How to switch?

Determine which prediction function had a closer value to the predicted signal to the decoded signal at the previous sample time,
A predicted signal for the next sample time is obtained using the closer prediction function. The prediction circuits 41 and 42 are configured with digital filters shown by equations (6) and (5), respectively,
The predicted signal portion and the predicted signal portion and the portion 2 are respectively output. The comparator circuit 43 determines the arrows of 1x-ptl and lX-1'21 from the input signal Delayed output.

It is supplied to the switching circuit 45. In the switching circuit 45, if lX-pH is small in the previous sample, the prediction signal □ for the current sample from the prediction circuit 41 is selected and output;
If Ixpzl was small in the previous sample, prediction circuit 4
The predicted signal portion 2 for the current sample from 2 is selected and output and provided to output terminal 46.

〔Effect of the invention〕

As is clear from the above description, according to the predictive decoding device of the present invention, 2.
K fs ” so that the number of samples in lie/in is an integer
2 fn, it is possible to receive and predictively decode a signal that has been subjected to efficient secondary predictive coding using a simple prediction function, and it is possible to perform high-quality PAL even for images with strong correlation in the vertical direction. Can play TV signals.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a predictive coding device and a predictive decoding device of the present invention that decodes signals encoded by the device, and FIG. 2 shows an arrangement of sample points according to the present invention. Figures 3, 4 and 5 show the predictor 6'J? and 13th 1st. Diagram showing the second and third specific examples, No. 6
The figure shows an example of a conventional predictive encoding device and predictive decoding device, and FIG. 7 is a diagram showing an arrangement of sample points in the conventional embodiment. 1... Input terminal, 2... A/D converter, 3... Pulse signal generator, 4... Subtractor, 5... Quantizer,
6... Predictor, 7... Adder, 8... Code conversion circuit, 9... Output terminal, 10... Input terminal, 11...
・Sign inversion circuit. 12...Adder, 13...Predictor, 14...D
/ A converter, 15... Output terminal, 20... Input terminal, 21... Shift register, 22.23... Register, 24° 25.26... Multiplier, 27... Addition 28...output terminal, 30...input terminal, 31.
32...Prediction circuit. 33.34... Multiplier, 35... Adder, 36...
- Output terminal, 40... Input terminal, 41.42... Prediction circuit. 43... Comparison circuit, 44... Register, 45...
Switching Kani 2 figure 3 figure 4 ward misfortune 7L + 1. 51 -11

Claims (1)

[Claims] 1. A device that receives and decodes a signal obtained by predictively encoding a PAL television signal sampled at a sampling frequency that is approximately three times the subcarrier frequency and N/2 times the horizontal synchronization frequency (N is an integer). , and the prediction function in the Z domain is Z^−^N
A predictive decoding device comprising means for performing predictive decoding using a predictor including a prediction circuit of {2/3Z^-^1-1/3+2/3Z}.