JPS63269883A - Encoder for semi-variable length code dpcm - Google Patents

Abstract

PURPOSE:To effectively use a long code and to improve a transmission quality by providing a predicting circuit for plane predicting a next appearing picture element signal and a semi-variable length quantizing circuit for limiting the long code to a fixed length code and quantizing. CONSTITUTION:The titled encoder is provided with the semi-variable length quantizing circuit 14, the preceding and current line predicting circuits 18, 17, a long code counter 12, a fixed length code selection output block 13, a picture element counter 24, a preceding line predictive stop signal output block 22, a preceding line predictive stop gate 21 and a fixed length code forcing signal output block 23 or the like. The next appearing picture element signal is plane predicted from plural picture elements before the current line and the preceding line of a digitized video signal, the predicted error of a predicted picture element is quantized to the long code or a short code, and when the prescribed number of the long codes is generated in a certain line, it is limited to the fixed length code in the line thereafter and quantized and further, a prediction is controlled so as to change to a current line prediction in the specific area of a screen. A semi-variable length quantization is limited to the fixed length code in the specific area of the screen.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to a DPCM system that encodes and quantizes video signals with high efficiency.
This invention relates to an encoding device.

2. Description of the Related Art FIG. 2 shows a simple example of a semi-variable length code DPCM encoding device. In this configuration, the luminance signal 'I+ of the predicted pixel is composed of the past pixel b2Y+t)Oy, which has already been encoded in the previous line, and the previous value a of the current line, as shown in FIG.
'I +-a2y+ bOy b2y using 2y
It is predicted that the color signal c, has an inverted phase between the previous line and the current line, as shown in FIG. 3(b), so that c,=-b. It is predicted that y. Assuming that the luminance signal and chrominance signal separation is performed using a second-order linear digital filter, the luminance signal is passed through a low-pass filter Z ((1+Z
-')/212, the color signal is passed through a high-pass filter -Z・
+ (1-Z-1> /2 +2), so the final predicted value Xi is
-b])/4 (1), and requires 4 pixels on the previous line and 3 pixels on the current line. This is shown in FIG. 4(a).

In the above, the prediction error is small because the video signal has a two-dimensional correlation, but if the previous value or the correlation between the previous line pixel and the predicted pixel is lost due to an image boundary, etc.
This prediction may not hold true and may cause quality deterioration of the transmitted image. The semi-variable length quantization circuit normally quantizes into short codes, and only when the prediction error of predicted pixels is large, quantizes them into long codes to shorten the average code length. In this case, after a predetermined number of long codes are generated in one line, quantization in that line is limited to fixed length codes. Therefore, it can be said that it is inevitable that the image quality tends to be inferior in the latter half of one line than in the first half.

Problems to be Solved by the Invention Conventionally, no control has been applied to the previous line prediction operation or the long code generation of the quasi-variable length quantization circuit, so the following problems occur. First, in front line prediction, a prediction point is selected as shown in Figure 4(a), but as shown in Figures 4(b) and (c), the prediction point is selected from the front edge, end, or When predicting pixels of the first line of the effective screen, a necessary previous line prediction point may be located in a horizontal blanking period or a vertical blanking period. Since the signals in the horizontal and vertical blanking periods do not have the same correlation with the effective screen, the prediction error at this time is larger than the prediction error due only to the current line. Due to its nature,
This can spread toward the center of the effective screen of subsequent lines and become a major cause of deterioration in transmission quality. Second, depending on the size of the error that occurs at the periphery of the effective screen, there is a high possibility that it will be quantized using a long code by the semi-variable length quantization circuit during transmission; Since it is a peripheral area, the advantages of long code quantization are not visually apparent. Particularly when the number of long codes that can be used is limited depending on the transmission speed, this use of long codes is very disadvantageous.

The present invention solves the above-mentioned problems and provides a DPCM encoding device that makes it possible to effectively use long codes and improve transmission quality.

Means for Solving the Problems The present invention predicts the pixel signal that will appear next from a plurality of pixels before the current line and the previous line of the digitized video signal, and lengthens the prediction error of the predicted pixel. code or short code, and if a predetermined number of long codes occur in a certain line, then quantization is limited to fixed length codes in that line, and the prediction is changed to the current line prediction in a specific area of the screen. In addition, the semi-variable length quantization is limited to fixed length codes in specific areas of the screen.

Operation: The method described above prevents an increase in errors in the periphery of the effective screen of the semi-variable length code DPCM encoding device, and also makes it possible to improve transmission quality by using the limited number of long codes more effectively.

Embodiment Regarding an embodiment of the DPCM encoding device according to the present invention,
That episode with the 1st I21! ? 8f11I formation is shown. This includes a semi-variable length quantum north circuit &'814, previous line/current line prediction circuits 18 and 17, a long code counter 12, a fixed length code selection signal output block 13, a pixel counter 24, and a previous line prediction stop. It consists of a signal output block 22, a previous line prediction stop gate 21, a fixed length code forced signal output block 23, etc. Here, as an example, the sampling frequency is 8.91MHz, so the number of sample points per line is 566, and the number of pixels on the effective screen is 460.
60 pixels. When the transmission speed is 32.06 Mbps, up to 46 pixels (46,060 pixels) can be transmitted as 8-bit long codes, and the rest can be transmitted as 4-bit short codes. The fixed length code selection signal output block 13 outputs a fixed length code (short code) selection signal to the semi-variable length quantization circuit 14 immediately after the long code counter 12 counts 46 long codes.

The prediction formula for this circuit is already shown in formula (1), and the fourth
According to the figure, prediction of the pixel If the signals of three front-end pixels and one rear-end pixel of the effective screen are masked in the front line prediction stop gate 21 as shown in Fig. 3, this can occur if the front line pixels necessary for gt++ belong to the horizontal blanking period. The negative influence on the current line prediction point can be removed.

The previous line prediction result must pass through two delays (in the current line prediction circuit) before reaching the subtracter 11 for error detection with the input PCM signal, and the pixel counter 24 must pass through the semi-variable length quantum north circuit 14 when manually operated. The mask signal that the previous line prediction stop signal output block 22 gives to the previous line prediction stop gate 21 is as shown in FIG. 6 because of the fact that the count is one clock earlier than the pixel signal.

Similarly, if the previous line prediction stop gate 21 masks the prediction signal when the previous line pixel belongs to the vertical blanking period, that is, when predicting the first line of the effective screen, the adverse effects of the previous line prediction can be removed.

FIG. 5 shows the vertical blanking period and the first effective screen.
The line is shown as the predicted stop period of the previous line. If the long code quantization prohibited area, that is, the fixed length code forced area, is the horizontal blanking period and the period of 5 pixels at the front edge of the effective screen as shown in FIG. Since the pixel signal is one clock earlier than the pixel signal in the case of 14 human input, the signal given by the fixed length code forced signal output block 23 to the semi-variable length encoding circuit 14 is as shown in FIG. 6(b).

Effects of the Invention As described above, according to the present invention, in a DPCM encoding device using semi-variable length codes, deterioration in transmission quality due to large prediction errors occurring in the peripheral area of the effective screen can be prevented, and long codes can be effectively used. By using it, transmission quality can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a semi-variable length DPCM encoding device according to an embodiment of the present invention, FIG. 2 is a block diagram showing a simple example of a conventional semi-variable length DPCM encoding device, and FIGS. 4 is a predicted pixel state diagram in the conventional example, FIG. 5 is a predicted pixel state diagram of the device in FIG. 1, and FIG. 6 is an operation waveform diagram of the same device. 10.25.26...Delay device, 11...Subtractor, 1
2...Long code counter, 13...Fixed length code selection signal output block, 14...Semi-variable length quantization circuit, 15
．． 16...Adder, 17...Current line prediction circuit, 1
8... Previous line prediction circuit, 20... AND gate,
21 - Previous line prediction stop gate, 22... Previous line prediction stop signal output block, 23... Fixed length code forced signal output block, 24... Pixel counter, 27...
・NAND gate. Name of agent: Patent attorney Toshio Tsuchinakao 1 person 10 - Rentei 11 - A calculation gain 73 - 1 fixed request & gray signal (゛Siri appearance flow) ri 15.76 - # It is limited Figure 2 Figure 3 (Q) (b) Figure 4 (Q) (b) Figure 5 Figure 6 (b) Front line pre-5 rule stop signal

Claims (1)

[Claims] A prediction circuit predicts the pixel signal that will appear next from a plurality of sample pixels before the current line and the previous line of the digitized video signal, and quantizes the prediction error of this predicted pixel into a long code or short code. , when a predetermined number of long codes are generated in a certain line, the component is a semi-variable length quantization circuit that quantizes only fixed length codes in that line, and the prediction circuit is configured to quantize only fixed length codes in that line. Semi-variable length DPCM encoding characterized in that it has a previous line prediction stop circuit that changes only the current line prediction at a time, and a forcing circuit that forcibly limits the semi-variable length quantization circuit to a fixed length code in a specific area of the screen. Device.