JPH06197333A - Picture compression system providing weight onto pattern - Google Patents

Abstract

PURPOSE:To obtain a highly accurate pattern just after a camera comes to a standstill state by detecting the presence of the motion of an image pickup camera so as to quantize the pattern while the camera is moving with rough accuracy. CONSTITUTION:Sent picture data are divided by pattern division and an orthogonal transformation circuit 5 applies discrete cosine transformation (DCT) to difference data for each block. A quantization circuit 6 quantizes data from the orthogonal transformation circuit 5 in a step width represented by a quantization step width calculation circuit 10. A coding circuit 7 applies variable length coding to the quantized value and the motion vector and stores the result to a transmission buffer circuit 8. Picture data part when the camera is not moving are sent from the transmission buffer circuit 8 to a line with high accuracy, and picture data part when the camera is moving are sent with rough accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects the presence or absence of motion of a photographing camera, and the screen with motion has a very large quantization step width, so that the screen immediately after motion stops is a high-definition screen. The present invention relates to an image compression method for providing a video conference, more specifically, to an image compression method suitable for image transmission of a TV conference system or a TV phone.

[0002]

2. Description of the Related Art Image quality in a TV conference system or a TV phone depends on how faithfully a person in a conversation is reproduced.

FIG. 3 is a circuit block diagram showing an example of a conventional image compression method. An image taken in via the image pickup system is divided into n × n by the screen division circuit 1, stored in the frame memory 2 and sent to the motion prediction circuit 3.

The frame memory 2 is delayed by one frame and then input to the motion prediction circuit 3. Motion prediction circuit 3
Compares each block of the frame input from the screen division circuit 1 with the block at the same position in the previous frame from the frame memory 2 and the blocks around it, thereby detecting the change in the position between the frames and determining the motion vector. And

The inter-frame prediction circuit 4 includes a motion prediction circuit 3
From the value of the motion vector obtained from the above, the position of the block before the movement in the previous frame is detected, the difference data with that value is detected, and the image data is created by combining with the value of the motion vector.

The orthogonal transform circuit 5 performs a discrete cosine (DCT) transform on the difference data for each block.

The quantizing circuit 6 quantizes the data from the orthogonal transform circuit 5 with the step width indicated by the quantizing step width calculating circuit 10.

In the coding circuit 7, the quantized value and the motion vector value are variable-length coded and stored in the transmission buffer circuit 8.

After this, the accumulated data is sent to the line at a constant speed according to the transmission rate.

Here, the amount of data stored in the transmission buffer circuit 8 is detected by the buffer storage amount detection circuit 9 and sent to the quantization step width calculation circuit 10.

[0011]

In this image compression method, when the camera moves such as panning, tilting, and zooming, the correlation with the previous frame is greatly deviated, so that the image data amount is extremely increased. However, there is a drawback that the transmission buffer storage amount is almost full.

Generally, in a video conference system, the movements of the eyes and mouth of the other party when the camera is stationary and the reproducibility of facial expressions are often particularly noted rather than the screen while the camera is moving. How to faithfully reproduce the image quality will greatly affect the image quality evaluation result. Therefore,
The inventor of the present invention wondered whether the person immediately after the camera stopped still could be image-compressed with high definition and transmitted without changing the limited transmission data amount. However, on the other hand, there is an upper limit to the amount of data that can be transmitted as one frame screen depending on the bit rate of the transmission system. Therefore, if the transmission buffer storage amount is full as described above, even if the camera stops moving for a while It takes a long time to obtain a high-definition image quality because the quantization step width has a large value.

An object of the present invention is to solve each of the above-mentioned drawbacks, and an image compression method suitable for a TV conference system or a TV telephone system, which enables transmission of a high-definition screen immediately after the movement of the photographing camera is stopped. To provide.

[0014]

The present invention is intended to solve these problems, and one screen is divided into a plurality of blocks, which are calculated according to the transmission buffer accumulated amount vs. quantization step width characteristic. In the image compression method of quantizing based on the quantizing step width, encoding and accumulating in the transmission buffer, a plurality of characteristics of the transmission buffer accumulation amount vs. the quantizing step width are set and it is determined whether or not there is a movement of the photographing camera. Therefore, a selection unit is provided for selecting the transmission buffer storage amount vs. quantization step width characteristic so that the quantization step width is small when the camera is not moving and is large when the camera is moving. It is configured.

[0015]

According to the above construction, the amount of image data during the operation of the photographing camera is reduced, and as a result, there is a margin in the transmission buffer storage amount. Therefore, the quantization step width is set to a small value immediately after the camera is stopped, that is, High-definition images can be transmitted instantly when the camera is stationary.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a circuit to which an image compression method according to the present invention is applied.

In the figure, the circuit parts given the same reference numerals as those used in FIG. 3 perform similar functions. An operation from the angle-of-view key input 14 notifies the first CPU to electrically control the angle of view of the camera 13, and a command from the first CPU causes the angle of view of the camera 13 to perform a moving operation. The first CPU 15 is notified of the presence / absence of the moving operation of the angle of view, and the first CPU 15 to the second CPU 16
Will be notified.

The function selection unit 17 is set with a plurality of transmission buffer storage amount vs. quantization step width functions, and has functions of g (x) and f (x) as shown in FIG. 2, for example.

The function g (x) is used when there is a moving motion, and since the quantization step width is largely associated with the transmission buffer storage amount, it is quantized with a coarse definition.

Since the function f (x) corresponds to the case where there is no moving motion and the quantization step width is associated with a small amount in the transmission buffer storage amount, the function f (x) is quantized with high precision.

Here, when the movement of the moving operation is large, that is, the angle of view of the camera 13 is greatly moved,
If the buffer storage amount becomes full even if g (x) having a large quantization step width is selected, the frame skip calculation means 11 skips one screen of image data. Then, the switch 12 is switched from a to a by a command from the second CPU 16 so that the image data from the camera 13 is not transferred to the image compression block.

The image data for one screen is not skipped, and the switch 12 is switched from a to a by a command from the second CPU 16 and the image data from the camera 13 is transferred to the image compression block. The sent image data is divided by screen division 1, and the orthogonal transformation circuit 5 transforms the difference data for each block by discrete cosine (DCT).

The quantization circuit 6 quantizes the data from the orthogonal transformation circuit 5 with the step width indicated by the quantization step width calculation circuit 10.

In the coding circuit 7, the quantized value and the motion vector value are variable-length coded and stored in the transmission buffer circuit 8.

Data is transmitted from the transmission buffer circuit 8 to the line with high definition in the image data portion in which the camera is not moving, and in coarse definition in the image data portion in the moving operation. .

From the above, according to the present invention, it is possible to quantize-encode and transmit only image data in a state in which there is no moving operation of the camera with a relatively high image quality, which can contribute to improvement of image quality in a TV conference system or a TV telephone. .

[0027]

As described above, according to the present invention, in the image compression method to which the frame motion prediction method is applied,
By selecting the quantization step size to be small only for the image data in the state where there is no moving operation of the camera and to increase the quantization step size for the image data in the state where there is motion, a high level suitable for a TV conference system or a videophone is selected. There is an effect that image quality can be transmitted and that can be realized by adding a relatively simple processing circuit.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing an embodiment of an image compression system according to the present invention.

FIG. 2 is a diagram showing an example of a quantization step calculation function selected by an image compression method according to the present invention.

FIG. 3 is a circuit block diagram showing an example of a conventional image compression method.

[Explanation of symbols]

 1 Screen Division Circuit 2 Frame Memory 3 Motion Prediction Circuit 4 Inter-frame Prediction Circuit 5 Orthogonal Transform Circuit 6 Quantization Circuit 7 Encoding Circuit 8 Transmission Buffer 9 Buffer Accumulation Detecting Circuit 10 Quantization Step Width Calculation Circuit 11 Frame Skip Calculation Means 12 Switch 13 Camera 14 View angle key input 15 First CPU 16 Second CPU 17 Function selection unit

Claims (1)

[Claims] 1. An image in which one screen is divided into a plurality of blocks, quantized based on a quantization step width calculated according to a transmission buffer storage amount-quantization step width characteristic, coded and stored in a transmission buffer. In the compression method, by setting a plurality of transmission buffer storage amount vs. quantization step width characteristics and determining the presence / absence of movement of the shooting camera, if there is no movement of the camera, the movement is reduced to a small quantization step width. An image compression method in which a screen is weighted, characterized in that selection means is provided for selecting a transmission buffer storage amount vs. quantization step width characteristic that provides a large quantization step width in some cases.