JPH02265328A - Variable length coder - Google Patents

Abstract

PURPOSE:To improve the transmission response at in frame coding mode by providing two kinds of tables optimized to an in-frame coding mode and an inter-frame coding mode as variable length code conversion tables respectively and selecting them with a selector adaptively. CONSTITUTION:Inter-frame variable length code conversion sections 82A-82c and in-frame variable length code conversion sections 82D-82F consist of different variable length code tables. That is, the former decreases the variable length code length with respect to a quantized coding data and the latter decreases a mean code length of the variable length code of the quantized coding data. Selectors 84A-84C switch the outputs of both the conversion sections for each coding mode and send an optimum variable length code to each code mode to a multiplex section 83. The multiplex section 83 applies P/S conversion to the variable length code to apply multiplex and the result is fed to the transmission buffer section of the next stage. Thus, the production of transmission information is optimized independently of the coded mode.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a variable length encoding device applied to a digital information transmission device such as a differential pulse coding modulation (hereinafter referred to as DPCM) video encoding device.

[Conventional technology]

Figure 2 is an example of the Journal of the Television Society Vol. 1.42Nal.
(1988), Section 5-2 “High-efficiency coding technology (
52 is a block diagram showing a DPCM video encoding device using the conventional variable length encoding device shown on pages 52 to 58. FIG. In the figure, 1 is an interframe subtracter that takes the difference between the video data and the predicted signal, 2 is a quantization encoder that quantizes the output of the interframe subtractor 1, and 3 is a quantization encoder that quantizes the output of the interframe subtractor 1. 4 is an interframe adder that adds the output of the quantization decoder 3 and the predicted signal to perform local decoding; 5 is a locally decoded signal output from the interframe adder 4; 6 is an intra-frame prediction data generator for generating a prediction signal (fixed value) in intra-frame coding mode, and 7 is a frame memory 5 and an intra-frame prediction data generator 6 depending on the coding mode. A selector 8 is a variable length encoding device that allocates a variable length code to the quantized encoded data outputted from the quantized encoder 2 and outputs it as encoded data. Also, FIG. 3 shows a variable length encoding device 8 using this conventional technology.
In the figure, 81 is an input section that separates quantization-encoded signal groups and takes them in by type, and 82A to 82C are input sections for each quantization-encoded data separated by the input section 81. A variable-length code converter 83 assigns variable-length codes to variable-length codes, and a variable-length code converter 83 performs parallel-to-serial conversion (hereinafter referred to as P/Fs conversion) to multiplex the variable-length codes allocated by the variable-length code converters 82A to 82C. This is a multiplexing unit that performs Next, the operation will be explained. The difference between the video data input to the DPCM video encoding device and the predicted signal is calculated by the interframe subtracter 1, and the prediction error signal obtained as a result of the subtraction is then subjected to quantization encoding. The reason why the prediction error signal is subjected to quantization encoding is that if the prediction of the input video data is accurate to some extent, the prediction error signal will be concentrated near "0", so high compression efficiency is expected. Because you can. The prediction error signal is processed by the quantization encoder 2 to have an average value,
The signal is converted into a quantization coded signal group such as a quantization parameter and a quantization index, and the quantization coded signal group is sent to a quantization decoder 3 and a variable length coding device 8. The quantization decoder 3 receives the quantization encoded signal group and decodes a prediction error signal in a procedure reverse to that of the quantization encoder 2. Furthermore, the decoded prediction error signal is sent to the interframe subtractor 1.
The input video data is locally decoded by adding the predicted signal input to the interframe adder 4 to the interframe adder 4. The locally decoded input video data is stored in the frame memo +75 to become an interframe prediction signal for the next frame and subsequent frames. Here, the DPCM video encoding device generally uses the video data of the previous frame as its prediction signal by using the interframe correlation of the video data, but in the first frame of encoding, the opening of the previous frame is used. The decoded signal is sent to frame memory 5
The encoding mode that uses the video data of the previous frame as the prediction signal is the interframe encoding mode, and the encoding mode that uses the fixed ill as the prediction signal. Define mode as the encoding mode of a frame. The selector 7 adaptively switches between the interframe prediction signal from the frame memory 5 and the intraframe prediction signal (fixed value) from the intraframe prediction data generator 6 according to each encoding mode and supplies it to the interframe subtraction agricultural engineering. do. Here, the prediction error signal in the intra-frame encoding mode is “O” because the prediction error signal in the inter-frame encoding mode utilizes the strength of the inter-frame correlation of the video data.
, the variance is large and often deviates from the vicinity of "0" because it is a difference with an almost uncorrelated signal. Furthermore, interframe coding accounts for most of the occurrence frequency of each coding mode, whereas intraframe coding occurs only in the first frame of coding, and the probability of occurrence is small. Further, the quantization encoded data group inputted from the quantization encoder 2 to the variable length encoding device 8 is inputted for each type of quantization encoded data at the input section 81, and a variable length code specific to each type is input. The converters 82A to 82C sequentially convert the code into variable length codes. Further, the various variable length codes are subjected to P/S conversion in a multiplexing section 83, multiplexed according to a multiplexing sequence, and sent as encoded data (serial) to a transmission buffer section (not shown). Here, the variable length code converters 82A to 82C convert each quantized encoded data into variable length codes having different bit lengths according to the probability of occurrence of the value. In other words, Fig. 4(a)
As shown in the figure below, codes with short bit lengths are assigned in descending order of probability of occurrence. As a result, the average code length becomes the shortest as shown in Figure 4 (°C). In reality, the variable length code length of quantized coded data distributed near “O” due to the interframe coding mode with a high probability of occurrence is short, and the quantized code that deviates from the “0” neighborhood due to the intraframe coding mode. Variable-length codes for encoded data tend to become longer.

[Problem to be solved by the invention]

Conventional variable-length encoding devices are configured as described above, and can achieve good video transmission in interframe encoding mode, but in intraframe encoding mode, transmission information is generated almost to the maximum value. However, there were problems in that the transmission response of the encoded data of the first frame was poor when the power was turned on or after recovery from a transmission error, and visual characteristics were poor. This invention was made to solve the above problems, and it provides a variable length code that maintains good video transmission characteristics in interframe coding mode and improves transmission response in intraframe coding mode. The purpose is to obtain a conversion device.

[Means to solve the problem]

The variable length encoding device according to the present invention has two types of variable length code conversion tables optimized for each of the intraframe encoding mode and the interframe encoding mode, and uses a selector to switch between them according to the encoding mode. The selection is made adaptively.

[Effect]

The selector in this invention adaptively switches between two types of variable length code conversion tables depending on the encoding mode, thereby transmitting data in the intraframe encoding mode without impairing good video transmission characteristics in the interframe encoding mode. Suppress information generation.

【Example】

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 8 is a variable length encoding device according to an embodiment of the present invention. Further, 81 is an input section, 83 is a multiplexing section,
These are the same or equivalent parts as those in the prior art, which are denoted by the same reference numerals in FIG. 82A to 82C are interframe variable length code conversion units 82D to 8 which allocate variable length codes to each quantized encoded data separated by the input unit 81 in interframe encoding mode;
2F is an intra-frame variable-length code converter that assigns a variable-length code to each quantized coded data separated by the input unit 81 in the intra-frame coding mode, and 84A to 84C convert the variable-length code according to each coding mode. This is a selector that adaptively switches the outputs of the interframe variable length code conversion units 82A to 82C and the intraframe variable length code conversion units 820 to 82F. Next, the operation will be explained. Here, since the DPCM video encoding apparatus as a whole operates in the same manner as in the conventional case, only the operation of the variable length encoding apparatus 8 will be described. A group of quantized encoded data input from the quantized encoder 2 to the variable length encoder 8 is inputted for each type of quantized encoded data at the input section 81, and an interframe variable length code specific to each type of quantized encoded data is input. The signal is supplied to converters 82A to 82C1 and intraframe variable length code converters 82D to 82F. Here, the variable length code tables configuring the interframe variable length code conversion units 82A to 82C and the intraframe variable length code conversion units 82D to 82F are different. In other words, the former shortens the variable length code length for quantized encoded data distributed around "0'', which occurs frequently in the same mode, in order to optimize the interframe encoding mode, and the latter optimizes the interframe encoding mode. In order to optimize the mode, the variable-length code length for the quantized coded data distributed near “0” is made longer than the former, but on the other hand, the quantization code length that is distributed around “0”, which often occurs in the intra-frame coding mode, The average code length of the variable length code of encoded data is shortened.The selectors 84A to 84C select between the interframe variable length code converters 82A to 82C and the intraframe variable length code converters 82D to 82F. Switch output for each encoding mode,
The optimum variable length code for each code mode is sent to the multiplexer 83. In the multiplexing section 83, these selectors 84A to 84G
The variable-length code from the transmitter is P/S converted, multiplexed, and supplied to the next-stage transmission buffer section (not shown). By the above operation, the amount of transmission information generated is optimized regardless of the encoding mote. [Effects of the Invention] As described above, according to the present invention, since the variable length code table to be used is switched for each encoding mode, even in the intraframe encoding mode where a large amount of transmitted information tends to occur, This can be suppressed, resulting in good video responsiveness.
This has the effect of providing a variable length encoding device with a smooth frame display rate and good visual characteristics.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a variable length encoding device according to an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of a DPCM video encoding device to which the same is applied, and FIG. 3 is a block diagram showing a conventional variable length encoding device. FIG. 4 is a block diagram showing a long encoding device, and is an explanatory diagram showing an example of allocation of variable length codes. 8 is a variable length encoding device, 82A to 82G are interframe variable length code converters, 82D to 82F are intraframe variable length code converters, and 84A to 84C are selectors. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A frame with a variable length code table that shortens the average code length of the quantized encoded signal distributed around “0” in order to optimize the interframe encoding mode that uses locally decoded data of the previous frame as the predicted signal. In order to optimize the intra-frame encoding mode in which a fixed value is used for the predicted signal, the inter-frame variable length code conversion unit and the variable length code converter shorten the average code length of the quantized encoded signal that is outside the vicinity of “0”. A variable-length code comprising: an intra-frame variable-length code converter having a long code table; and a selector that adaptively switches between the inter-frame variable-length code converter and the intra-frame variable-length code converter according to each of the encoding modes. conversion device.