JPH0440188A - Quantizer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a quantizer for a moving image encoding device such as a video telephone or a video conference system.

Conventional technology The development of coding technology has been remarkable, coupled with the development of digital communication lines, and international standardization activities are actively being carried out. ! 5J89 Image Coding Lecture pp
, 43-48, pX 64kb
The ps (p=1-30) video encoding system is well known. Such a video encoding method performs discrete cosine transform (hereinafter, discrete cosine transform is abbreviated as DCT) on the inter-frame difference obtained by motion compensation prediction in block units of M pixels x N lines, and then encodes it. The DcT coefficients are quantized by a quantizer based on a quantization width determined by the bit rate of the transmission buffer, the amount of buffer remaining in the transmission buffer, and the like. The quantized transform coefficients, quantization width, block attribute information, etc. are variable-length encoded to generate a code string to be transmitted. At this time, the quantized transform coefficients are encoded by run-length encoding in which the quantized transform coefficients are scanned in a zigzag scan order and a 00 run length is transmitted.

Hereinafter, the conventional technology of the quantizer will be explained using FIG. 3 showing the quantization characteristics of the quantizer.

In FIG. 3, the horizontal axis is the DCT coefficient before quantization, the vertical axis is the DOT coefficient after quantization, and g is the quantization width. Overall, quantization errors are reduced by dividing the DOT coefficients into g units and using the central value as the quantization representative value. −
The area g-g is called the dead zone, and the DOT
The quantization representative value for the coefficient is set to 0. Minute O
By quantizing the T coefficient to a value of 0, the number of quantized transform coefficients having a value of 0 is increased, and encoding efficiency is improved.

Therefore, the remaining buffer amount becomes low level, and the value of the quantization width g for subsequent blocks can be reduced, leading to improvement in image quality. When the quantization representative value is decomposed into the product of the quantization width and the coefficient i, and the value obtained by rounding off the coefficient i is called the quantization index, the quantizer is
The DCT coefficient and quantization width are input, the quantization representative value or the quantization index is output, and the configuration can be easily configured by having a ROM internally storing the conversion table shown in FIG. 3.

Problems to be Solved by the Invention In a video encoding method that combines motion compensation prediction and DCT, minute noise called mosquito noise occurs in the boundary area between a moving region and a still region, degrading the image quality of the reproduced image. Sometimes. This mosquito noise largely depends on the mid-range component of the DCT coefficient, and when the mid-range component of the DOT coefficient is lost, the mosquito noise becomes noticeable. Moreover, most of the mid-range components of the DCT coefficient are around 10, which is 64
This is not large compared to the average quantization width when encoding a moving image at a low pictorate such as kbps. Therefore, in the prior art, there is a problem in that the mid-range component of the DOT coefficient is included in the dead zone and quantized to a value of 0, and mosquito noise appears in the reproduced image depending on the degree of quantization.

In view of the above-mentioned problems, the present invention reduces mosquito noise by changing the quantization width to a small value to make it difficult to be quantized to 0 when quantizing mid-range components of DCT coefficients. This is an attempt to suppress the outbreak.

Means for Solving the Problems To achieve this object, the present invention provides quantization means with a dead zone that quantizes with an externally given quantization width, and subtraction means that subtracts an offset value from the quantization width. and,
A selection means is provided for selecting a quantization width obtained by subtracting the quantization width and offset value.

Effects According to the present invention, when the mid-range component of the DOT coefficient is quantized with the above configuration, the mid-range component of the DOT coefficient is quantized with a smaller quantization width than a given quantization width. It prevents quantization to 0 and acts to suppress the generation of mosquito noise.

Embodiment FIG. 1 is a block diagram showing an embodiment of a quantizer according to the present invention.

In FIG. 1, 1 is an input terminal for inputting the quantization width, 2
is an input terminal to input the DOT coefficient according to the order of zigzag scan, 3 is a switch to set the value 0, 4 is DOT
A switch that sets the offset value of the quantization width for the mid-range component of the coefficient, 6 is a selector that receives the output of switch 3 and switch 4 as input, and 6 is a difference device that receives the output of input terminal 1 and selector 6 as input. , 7 is a selector control circuit that outputs a selection signal to the selector 6, and 8 is a conversion ROM whose address inputs are the output of the differentiator 6 and the output of the input terminal 2.

The operation of the above configuration will be explained below.

A value of 0 is set in the switch 3 as an offset of the quantization width for DOT coefficients other than mid-range components. switch 4
, an offset value t of the quantization width for the mid-range component is set, but the value depends on the encoding bit rate and the like.

The selector control circuit 7 receives the DOT input from the input terminal 2.
Determine whether the coefficient is a mid-range component or not, and send the result to selector 6
to notify. Its specific configuration can be easily realized using two types of counters that count clocks associated with DOT coefficients, and a flip 70 knob that is set/reset at the timing when the two types of counters finish counting.

Here, when one block is made up of 8 pixels x 8 lines, the mid-range component of the DOT coefficient is approximately the 8th to 20th area in the zigzag scan order. The selector 6 selects the output of the switch 3 or the switch 4 based on the control signal output by the selector control circuit A, and outputs the selected output as an offset value S to the differentiator 6. The differentiator 6 is
The offset value S is subtracted from the quantization width input from the input terminal 1, and the calculation result is output to the conversion ROMB.

The conversion ROMB stores a conversion table based on the characteristics shown in FIG. 3, as in the prior art, and uses the output of the differentiator 6 and the DOT coefficient input from the input terminal 2 as address inputs to convert the quantized representative value or quantum output index.

The video encoding/decoding device outputs the quantization index from the conversion ROMB, and reproduces the quantization representative value by calculating the product of the quantization width input from input terminal 1 and the quantization index in subsequent processing. When configured, the quantization characteristics for the mid-range components of the DOT coefficients are as shown in FIG.

In Figure 2, the horizontal axis is the DCT coefficient before quantization, the vertical axis is the DCT coefficient after quantization, g is the quantization width input from input terminal 1, and f is the quantization from g to the mid-range component of the DCT coefficient. This is the value obtained by subtracting the width offset value t. As shown in FIG. 2, as the DOT coefficient before quantization becomes larger, the quantization error becomes larger. However, since most of the mid-range components of the DCT coefficients have a value of about 10, no new noise is generated due to the quantization error, which can have a very large value.

Effects of the Invention According to the present invention, a quantization means with a dead zone that quantizes with an externally given quantization width, a subtraction means that subtracts an offset value from the quantization width, and a subtraction means that subtracts the quantization width and the offset value. Since the configuration is provided with a selection means for selecting the quantization width, when quantizing the mid-range component of the DCT coefficient, the quantization width is changed to a small value to make it difficult to be quantized to 0. , generation of mosquito noise can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a quantizer according to the present invention, FIG. 2 is a characteristic diagram showing quantization characteristics of an embodiment of a quantizer according to the present invention, and FIG. 3 is a diagram showing a conventional quantizer. FIG. 3 is a characteristic diagram showing quantization characteristics of a quantizer and a quantizer according to the present invention. 6...Selector, 6...Differentiator, 7...Selector control circuit, 8...Conversion ROM. Name of agent: Patent attorney Shigetaka Awano and 1 other person 2nd
Figure / Diagram

Claims (1)

[Claims] A quantization unit with a dead zone that quantizes with an externally given quantization width, a subtraction unit that subtracts an offset value from the quantization width, and a quantization width that is obtained by subtracting the quantization width and the offset value. A quantizer characterized by comprising a selection means for selecting.