KR19980050957A - Multiple Codeword Transmission Method for Video Signal Vector Quantizer - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

Multiple codeword transmission method for video signal vector quantizer.

2. The technical problem to be solved by the invention

We want to improve the performance of vector quantization by assigning one or more codewords to input images that are different from the training data and statistical characteristics, and interpolating them on the receiving side.

3. Summary of Solution to Invention

The present invention improves the performance of vector quantization by using a plurality of codewords to encode one input data pattern and reconstructing the original pattern by using the plurality of codewords received at the receiver.

4. Important uses of the invention

Applied to vector quantizer for compression and transmission of video signal.

Description

Multiple Codeword Transmission Method for Video Signal Vector Quantizer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multiple codeword transmission method as a method for improving performance in vector quantization, which is one of the important element techniques used to compress a video signal.

In general, the purpose of image data compression is to reduce the number of bits required to transmit or store an image without losing visual information. Coding techniques for image compression are based on information theory, and the first generation of image coding techniques that effectively reduce the image data by using time or space redundancy in the image data and the human visual characteristics or pattern recognition techniques. It can be classified as a second generation video encoding technique.

Most of the classical data compression methods belonging to the first generation image coding scheme are largely divided into two types, a prediction method and a transform method. The prediction method removes mutual redundancy between consecutive samples and quantizes only error information. Redundancy refers to a property in which a current sample value can be predicted by a previous sample value.

Therefore, instead of directly quantizing a pixel, the prediction method quantizes the difference between a prediction value obtained from each pixel and a previously encoded pixel. In coding by the transform method, first, a given image is transformed so that information is concentrated in a small number of samples, and the transform coefficient is quantized. In general, various image data compression methods in the form of generalizing or combining these two methods have been proposed and studied. Second-generation image coding techniques use the characteristics of the human visual system (HUNS visual system (HVS), and include pyramid coding, directional decomposition-based, and segmentation-based coding. A common drawback of this coding method is that quantization is done in a scalar fashion on individual real values of waveforms or image pixels.

Vector quantization is a method of encoding an input block using a codebook composed of prototype patterns, which may be referred to as a pattern matching technique. According to Shannon's rate-distortion theory, vector quantization always has better performance than scalar quantization, and between conventional sub-optimal techniques and theoretical limitations of source coding presented by rate-distortion theory Fill in spaces.

When the vector quantization is applied to video compression on a line having a low data rate, the codebook is small in size, and thus, it is difficult to prevent a significant deterioration in image quality of an input image having different statistical characteristics from training data.

In other words, in vector quantization, the input data pattern is represented by a codeword, which is a prototype pattern included in the codebook, where the reproduction quality is determined by the codebook and has input data having statistical characteristics similar to the training data used to learn the codebook. Only patterns can be properly represented. Therefore, in high compression coding where the size of the codebook should be small, information such as edges, which occupy a relatively small portion of the input image, cannot be properly represented.

An object of the present invention is to provide a multiple codeword transmission method for improving performance of vector quantization by allocating one or more codewords to an input image having different statistical characteristics from those of training data, and interpolating them.

1 is a vector quantization system block diagram,

2 is a conceptual diagram of an image vector quantization according to the present invention;

3 is a conceptual diagram of a multiple codeword transmission method according to the present invention;

4 is a process flowchart of a multiple codeword transmission method according to the present invention;

In order to achieve the above object, the present invention provides a first step of selecting a codeword having a minimum distortion by searching a codebook when an input vector is input, and having a next smaller distortion when the distortion is larger than a predetermined threshold. A second step of selecting two codewords and interpolating them by an average and calculating the distortion between the interpolated result vector and the input vector; and three if the distortion error value is smaller than the distortion error between the first codeword selected. A third step of transmitting all the indexes of the codeword, and only the index of the first selected codeword; and a fourth step of restoring the information transmitted from the receiving side.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention;

1 and 2 show a block diagram and a conceptual diagram of a vector quantization system.

In a vector quantization system, encoders and decoders must store the same codebook in advance.

Vector quantization encoding first calculates the distortion between the N codewords stored in the codebook and the k-dimensional input vector, and selects a codeword for which the distortion is minimized. This process is called exhaustive codebook search. In the global codebook search, find the best matched codeword and send the index. The decoder of vector quantization also stores a codebook and only requires a table look-up process. At this time, the output index of the received encoding is used as an address for extracting the corresponding codevector from the same codebook. This simple decoding process is useful for applications such as broadcasting, where the cost of the receiver must be lower than the transmitter.

In vector quantization, the input data pattern is represented by a codeword, which is a prototype pattern included in the codebook. In this case, only the input data pattern having a statistical characteristic similar to the training data used for learning the codebook may be properly represented. Therefore, information such as edges, which occupy a relatively small portion of the input image, is difficult to be properly represented in high compression coding that requires a small size of the codebook.

The multiple codeword approach overcomes this problem by using multiple codewords to encode one input data pattern. The receiving side restores the original pattern using the plurality of received codewords.

3 shows a block diagram of an encoding and decoding process of an input vector by a multiple codeword method.

In the drawing P _i is given input data _{vector, Wi = [W i1, W} i2 ... W iM] is encoded codeword, R _i is a reproduction pattern on the receiving side. On the receiving side, R _i is calculated as in Equation 1.

Where α _ij is the weight vector for interpolation.

The reproduced pattern R _i thus reproduced is a new prototype pattern not included in the codebook. However, this method has to transmit the weight vector aij for interpolation together with the selected codeword, resulting in a decrease in the compression rate by increasing the amount of transmitted information. Therefore, there is a need to find a suitable compromise between reproduction quality and compression ratio. The simplest method is to select three codewords (M = 3) and apply the method of interpolation by the average of the codewords at the receiving side instead of using the weight vector aij. In this case, the weight vectors α _ij are all 1 / M.

When the neural network learning algorithm is used for the training of the codebook, it is very advantageous for adaptive vector quantization that learns and updates the codebook whenever both sides of the transmission and reception are needed. The receiving side restores a single codeword or multiple coders according to the indes information sent from the transmitting side.

An internal processing procedure, that is, the encoding and decoding procedures of the multiple codeword method is shown in FIG. 4.

When an input vector comes in (1), the codebook is first searched (2) to select the codeword with the least distortion. If the distortion at this time is larger than a predetermined threshold value, two codewords having the next smaller distortion are selected, interpolated by the average, and the distortion between the interpolated result vector and the input vector is calculated (4 to 7). . If the value of the distortion error is smaller than the distortion error with the first selected codeword, all indexes of the three codewords are transmitted (8, 9). Otherwise, only the index of the first selected codeword is transmitted (8, 10). At this time, the transmitted index needs to be added with information indicating how it is encoded.

The receiver simply reads this information and restores the receiving index as an address if it is encoded by a single codeword, obtains three transmission vectors using the receiving index as an address if it is encoded by multiple codewords, and then interpolates them Restore (11-14).

The present invention described above is capable of various substitutions, modifications, and changes within the scope without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains, and thus is limited to the above-described embodiments and drawings. It is not.

Accordingly, the present invention can improve the performance of vector quantization by using a plurality of codewords to encode one input data pattern and reconstructing the original pattern by using a plurality of received codewords at the receiving end. In addition, this method has the advantage that it can be operated in a variable bit rate method in the situation that the characteristics of the line changes with time.

Claims (3)

The first step is to select a codeword with the least distortion by searching the codebook when the input vector comes in; and, if the distortion is greater than a predetermined threshold, select the next two codewords with the smallest distortion and add them to the average. The second step of calculating the distortion between the interpolated and interpolated result vector and the input vector, and if the distortion error value is smaller than the distortion error between the first selected codeword, all three codeword indices are transmitted. And a fourth step of transmitting only the index of the first selected codeword and a fourth step of restoring information transmitted from the receiving side. The method of claim 1, wherein the fourth step is to simply read the encoding scheme indication information added to the transmitted index to restore the information. 2. The method of claim 1, wherein the fourth step restores the reception index to the address when the information from the transmitter is encoded by a single codeword, and sets the reception index as an address when encoded by multiple codewords. A method of transmitting multiple codewords for video signal vector quantization, wherein three transmission vectors are obtained and then interpolated and reconstructed.