JPH0630409A - Terminal equipment - Google Patents

Abstract

PURPOSE:To obtain a terminal equipment capable of improving the intra-frame compression rate of a picked-up image at the time of moving a camera and reducing the thinning-out of frames. CONSTITUTION:A control circuit 60 controls a moving board 12 and at the time of moving a TV camera 10, a quantization table to be used by a quantizing circuit 26 is switched and used. Since data are compressed and coded by a high compression rate with a DCT conversion circuit 24 and the circuit 26, a prescribed compression rate can be attained without executing the thinning-out of frames.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terminal device, and more particularly to a terminal device that can be used in a video conference system.

[0002]

2. Description of the Related Art A videophone system and a videoconference system are known in which remote places are connected by a dedicated or public digital line to transmit images and voices for a conversation or a conference. In such a system, since the available communication line capacity is limited, moving images are highly efficiently compressed and encoded for transmission. There are two types of image information compression methods: intraframe compression and interframe compression. In intra-frame compression, the amount of information is compressed by linear transformation such as discrete cosine transformation (DCT) by utilizing the correlation between neighboring pixels in one frame. In the inter-frame compression, the fact that there is a strong correlation between pixels at the same position on the screen in successive frames is used, and the information amount is compressed by substituting the pixels of the already encoded past frame.

A high compression rate can be achieved by using both intra-frame compression and inter-frame compression. However, in the inter-frame compression, the correlation between the frames becomes weak in an image with a lot of motion, so that the compression rate sharply decreases. In that case, the intra-frame compression exclusively depends on the intra-frame compression. Normally, the intra-frame compression alone cannot achieve a predetermined compression rate suitable for the communication line capacity, and in that case, frame thinning is performed.

[0004]

However, in the above-mentioned conventional example, in the case of the videophone, there is no request so far, but in the conventional videoconference system, the TV camera for photographing the conference participants is used as the image. A configuration in which a conference participant or a speaker is tracked according to processing or sound and the direction of the TV camera is changed as the conference participant or the speaker moves, or the image transmitting side and / or the image receiving side A configuration has been proposed in which the position, orientation, zoom, and the like of the camera can be controlled using an operation panel.

In such a case, the compression rate of the inter-frame compression becomes very poor during the movement of the TV camera, the frames are thinned out as described above, and the display screen on the receiving side moves awkwardly. Image is displayed. Further, for example, when the TV camera on the transmission side is operated from the operation panel on the reception side, a non-negligible time difference occurs between the movement of the TV camera and the image displayed on the reception side, and the TV
There was a drawback that it became difficult to align the camera.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a terminal device in which the intra-frame compression ratio of a captured image is increased and the thinning-out of the frame is reduced when the camera is moved. To do.

[0007]

[Means for Solving the Problems] and

In order to achieve the above object, the terminal device of the present invention has the following configuration.

That is, it has a video input means including a movable camera, and a compression coding means for compressing and coding a captured image by the video input means within a frame and between frames.
The compression encoding means increases the compression rate in the intraframe compression encoding when the camera moves.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of a terminal device in the embodiment. However, only the transmission system is shown in order to simplify the description.

In the figure, 10 is a TV camera for photographing the participants of the video conference, 12 is a moving base for changing the position and direction of the TV camera 10, and 14 is A / D conversion for digitizing the output image of the TV camera 10. The output of the A / D converter 14 from the raster format to the CIF (Common Interme
A format conversion circuit for converting an intermediate format for transmission such as diate Format) or QCIF (Quarter CIF), 2
0 is a subtractor for subtracting the prediction value in the prediction differential encoding from the output of the format conversion circuit 16, and 24 is the subtractor 2
A DCT conversion circuit that performs DCT conversion on the output of 0 in block units of 8 × 8 pixels, and 26 is a quantization circuit that quantizes the conversion coefficient of the DCT conversion circuit 24.

28 is an inverse quantization circuit for inversely quantizing the output of the quantization circuit 26, and 30 is an inverse D of the output of the inverse quantization circuit 28.
An inverse DCT conversion circuit for CT conversion, 32 is an adder for adding the predicted value to the output of the inverse DCT conversion circuit 30 by "0" when the TV camera 10 is moving normally, and 34 is an output of the format conversion circuit 16 (current frame). ) And an output (past frame) of the adder 32, and a motion-compensated inter-frame prediction circuit that detects a motion vector and calculates a prediction value by motion-compensated inter-frame prediction.
4 is a motion adaptive filter composed of a low-pass filter that removes the high frequency band of the predicted value according to 4. Motion adaptive filter 36
Is output as a predicted value, the subtracter 20 and the switch 38
Is applied to the adder 32 via. The switch 38 is normally closed and is opened when the TV camera is moved.

With the switch 38 closed, the circuits 20, 24, 26, 28, 30, 34, and 36 function as a predictive differential encoding circuit using the previous frame value as a predictive value. Intra and inter-frame compression is performed.

Reference numeral 40 is a variable length coding circuit for variable length coding the output of the quantizing circuit 26 and the motion vector supplied from the motion compensation inter-frame prediction circuit 34, and 42 is rate-adjusting the output of the circuit 40, if necessary. A transmission buffer for thinning out frames, and a correction coding circuit 44 for adding an error correction code to the output of the transmission buffer 42.

Reference numeral 48 is a microphone for voice input, 50 is an A / D converter for digitizing the output of the microphone 48, and 52 is A.
An audio encoding circuit that compresses and encodes the output of the D / D converter 50, and a delay circuit 54 that delays the output of the audio encoding circuit 52 for a time corresponding to the processing time of the output image of the TV camera 10.

Reference numeral 56 denotes a multiplexing circuit for multiplexing the output of the error correction coding circuit 44 and the output of the delay circuit 54, and 58 denotes I.
A line connection circuit such as a terminal adapter connected to a communication line such as SDN. In this embodiment, the output of the multiplexing circuit 56 is output to the communication line. 60 is a TV camera 1
The control circuit controls the aperture of 0, the zoom of the photographing lens, and the like, and controls the moving table 12 and the switch 38. 62
Is a scanning device for inputting various instructions to the control circuit 60.

First, the operation when the TV camera 10 is stationary or almost stationary will be described. At this time, the control circuit 6
0 closes the switch 38. The output video signal of the TV camera 10 is converted into a digital signal by the A / D converter 14, and the format conversion circuit 16 converts the output of the A / D converter 14 from the raster format to a predetermined intermediate format for transmission. The output of the format conversion circuit 16 is applied to the resolution conversion circuit 18, the subtractor 20, and the motion-guaranteed inter-frame prediction circuit 36.

The subtractor 20 subtracts the prediction value (output of the motion adaptive filter 38) to calculate an error signal for predictive differential encoding. The output of the subtractor 20 is the DCT conversion circuit 2
4, the DCT transform circuit 24 performs DCT transform for each block of 8 × 8 pixels and outputs transform coefficients, and the quantizing circuit 26 quantizes the transform coefficients.

The inverse quantization circuit 28 inversely quantizes the output of the quantization circuit 26, and the inverse DCT conversion circuit 30 inversely quantizes the inverse quantization circuit 2.
The output of 8 is subjected to inverse DCT conversion. The adder 32 adds the predicted value to the output of the inverse DCT conversion circuit 30. The output of the adder 32 is a locally decoded value that is decoded after the output of the format conversion circuit 16 is subjected to predictive differential encoding. The motion-compensated inter-frame prediction circuit 34 includes the format conversion circuit 1
A motion vector is calculated from the current value (current frame) from 6 and the local decoded value (past frame) from the adder 32, and the prediction value of the current frame is calculated by motion compensation inter-frame prediction. The calculated motion vector is applied to the variable length coding circuit 40, and the predicted value is applied to the motion adaptive filter 36. The motion adaptive filter 36 removes a predetermined high frequency component from the predicted value and applies it to the adder 32 via the subtracter 20 and the switch 38.

The circuits 20 to 38 form a predictive differential encoding circuit, which compresses image information between frames and within a frame. The image data compressed by the circuits 20 to 38 is applied from the quantization circuit 26 to the variable length coding circuit 40.

The variable length coding circuit 40 includes a quantization circuit 26.
And the motion vector from the motion-compensated inter-frame prediction circuit 34 are variable-length coded and compressed in a frame. The output of the variable length coding circuit 40 is applied to the error correction coding circuit 44 via the transmission buffer 42. The error correction coding circuit 44 generates and adds error correction coding, and the multiplexing circuit 5
6 is applied.

On the other hand, the audio signal from the microphone 48 is A / D.
It is converted into a digital signal by the converter 50 and encoded by the voice encoding circuit 52. The delay circuit 54 delays the output of the audio encoding circuit 52 by a time corresponding to the delay due to the above-mentioned video signal processing, and supplies it to the multiplexing circuit 56.

The multiplexing circuit 56 includes an error correction coding circuit 4
4 and the data from the delay circuit 54 are multiplexed, and the output is output to the communication line via the line connection circuit 58.

Next, the operation when the TV camera 10 is moved will be described. At this time, the control circuit 60 opens the switch 38. Since the switch 38 is in the open state, the portion composed of the circuits 24 to 36 performs intra-frame compression by DCT conversion and motion vector detection.

The output video signal of the TV camera 10 is A / D.
The signal is converted into a digital signal by the converter 14, and the format conversion circuit 16 converts the output of the A / D converter 14 from the raster format to a predetermined intermediate format for transmission. The output of the format conversion circuit 16 is applied to the subtractor 20 and the motion compensation inter-frame prediction circuit 36. The DCT conversion circuit 24 performs DCT conversion for each block of 8 × 8 pixels and outputs the conversion coefficient, and the quantization circuit 26 quantizes the conversion coefficient. In the quantization circuit 26, the coding quantization table Q _ij (i = 1 to 8, i = 1 to 8, j = 1 to 8) for the transform coefficient S _ij (i = 1 to 8, j = 1 to 8) DCT-transformed for each 8 × 8 pixel. j = 1 to 1
8) and the quantization coefficient F are used for the quantization. Quantization is generally expressed by the following equation.

R _ij = S _ij / (Q _ij × F / 50) where r _ij is the quantized coefficient, S _ij is the DTC transformed transform coefficient, Q _ij is the coded quantization table, and F is The quantized coefficients are respectively shown. As can be seen from the above equation, by increasing the value of the coding quantization table Q _ij or the quantization coefficient F, the compression rate by quantization can be increased.

FIG. 2 and FIG. 3 show examples of the commonly used coding quantization table for luminance and the coding quantization table used when the camera is moved. By switching the normally used encoding quantization table of FIG. 2 to the encoding quantization table of FIG. 3 when the camera is moved, the compression rate of encoding by the quantization circuit 26 is increased.

The inverse quantization circuit 28 inversely quantizes the output of the quantization circuit 26, and the inverse DCT conversion circuit 30 inversely DCT-converts the output of the inverse quantization circuit 28. Since the switch 38 is in the open state, the adder 32 outputs the output of the inverse DCT conversion circuit 30 as it is. The output of the adder 32 is the locally decoded value of the coded code by the DCT conversion circuit 24 and the quantization circuit 26. However, the motion-compensated interframe prediction circuit 34 does not calculate the motion vector under the control of the control circuit 60, so that the motion vector is not supplied to the variable-length coding circuit 40.

The image data is compressed in the frame by the DCT conversion circuit 24 and the quantization circuit 26. The image data compressed in this way is applied from the quantization circuit 26 to the variable length coding circuit 40.

The variable length coding circuit 40 includes a quantization circuit 26.
The output of is variable length coded and compressed in the frame. The output of the variable length coding circuit 40 is applied to the error correction coding circuit 44 via the transmission buffer 42. When the amount of data to be transmitted is too large as compared with the communication line, the transmission buffer 42 thins out the frames. Error correction coding circuit 44
Generates and adds an error correction code and applies it to the multiplexing circuit 56.

The audio signal from the microphone 48 is processed by the A / D converter 50 and the audio encoding circuit 52, and is time-adjusted by the delay circuit 54 and supplied to the multiplexing circuit, as in the case where the TV camera 10 is stationary. It

The multiplexing circuit 56 is an error correction coding circuit 44.
And the data from the delay circuit 54 are multiplexed, and the output is output to the communication line via the line connection circuit 58.

As described above, by switching and using the quantization table used in the quantization circuit 26 when the TV camera is moved, compression coding can be performed at a high compression rate by the DCT conversion circuit 24 and the quantization circuit 26, and the frame It is possible to achieve a predetermined compression ratio without performing thinning.

[0034]

Other Embodiments In the above-described embodiment, the quantizing circuit 26 switches the encoding / quantizing table used when the camera moves to obtain a high compression rate. A high compression rate may be obtained by increasing the value of the quantization coefficient used.

In the above, the case where the TV camera is moved by the operation panel on the receiving side or the transmitting side or by the subject tracking system has been described, but it goes without saying that the invention can be applied to the case where the subject itself moves. The amount of motion is monitored by the motion vector obtained by the motion-compensated inter-frame prediction circuit 34, and when a certain amount of motion is detected, the low-resolution image by the resolution conversion circuit 18 is intra-frame compression encoded and transmitted. Is also good.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of one device.

Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0038]

As can be easily understood from the above description, according to the present invention, since the resolution is reduced when the camera is moved, the intra-frame compression rate can be substantially increased,
The thinning of the frame can be reduced. Therefore, the awkwardness of images due to thinning is improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a terminal device according to the present embodiment.

FIG. 2 is a commonly used coding / quantization table for a luminance signal.

FIG. 3 is an example of a coding and quantization table used when the camera moves.

[Explanation of symbols]

 10 TV camera 12 Mobile platform 14 A / D converter 16 Format conversion circuit 20 Subtractor 24 DCT conversion circuit 26 Quantization circuit 28 Inverse quantization circuit 30 Inverse DCT conversion circuit 32 Adder 34 Motion compensation interframe prediction circuit 36 Motion adaptation Filter 38 Switch 40 Variable length coding circuit 42 Transmission buffer 44 Error correction coding circuit 48 Microphone 50 A / D converter 52 Voice coding circuit 54 Delay circuit 56 Multiplexing circuit 58 Line connection circuit 60 Control circuit 62 Operating device

Claims (4)

[Claims] 1. A video input means including a movable camera, and a compression coding means for compressing and coding a captured image by the video input means within a frame and between frames, the compression coding means comprising: A terminal device, wherein a compression rate in intraframe compression encoding is increased when the camera is moved. 2. The terminal device according to claim 1, wherein the compression encoding means preferentially executes intraframe compression encoding when the camera moves. 3. The compression encoding means variably switches a quantization table used for intraframe compression as means for performing intraframe compression at a high compression rate when the camera moves. The terminal device described. 4. The compression encoding means variably switches a quantizer used for intraframe compression as means for performing intraframe compression at a high compression rate when the camera moves. The terminal device described.