JP2865801B2 - Video coding transmission equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving picture coded transmission apparatus for compressing and transmitting a video signal of a moving picture and transmitting it.

[Conventional technology]

FIG. 8 shows a conventional moving image shown in, for example, a paper "TV conference system" published on pages 38 to 41 of Mitsubishi Electric Technical Report Vol. 60, No. 10 (published by Mitsubishi Electric Corporation, 1986). It is a block diagram which shows an encoding transmission apparatus. In the figure, reference numeral 1 denotes a transmitting apparatus for encoding and transmitting a video signal of an input moving image for each encoded video frame, and 2 denotes a receiving apparatus for receiving and decoding the encoded video signal. Is a transmission line connecting the transmitting device 1 and the receiving device 2.

Reference numeral 4 denotes a video signal input terminal for inputting an input video signal to the transmission device 1. Reference numeral 5 denotes an analog input unit which digitizes the video signal input from the video signal input terminal 4 and performs a luminance / color difference component separation process. is there. Reference numeral 6 denotes a transmission frame memory for storing video data of one frame processed by the analog input unit 5, and reference numeral 7 denotes a frame memory for storing video data of one frame before. Reference numeral 8 denotes a subtracter that calculates a difference between the video data of the current frame read from the transmission frame memory 6 and the video data of one frame before read from the frame memory 7.

Reference numeral 9 denotes an encoder for compression-encoding the inter-frame difference signal from the subtracter 8 according to a predetermined algorithm. Reference numeral 10 denotes a transmission buffer for temporarily storing the encoded data from the encoder 9. Reference numeral 11 denotes a transmission interface unit for transmitting the encoded data stored in the transmission buffer 10 in accordance with the transmission speed of the transmission line 3. Reference numeral 12 denotes encoded data to the transmission line 3 output from the transmission interface unit 11. Coded data output terminal.

Reference numeral 13 denotes the encoded data from the encoder 9
Is a decoder that decodes in the reverse procedure to reproduce the inter-frame difference signal. Numeral 14 adds the video data of the previous frame stored in the frame memory 7 to the inter-frame difference signal reproduced by the decoder 13 to generate video data of the current frame, and generates the video data of the next frame. Is an adder that re-stores the data in the frame memory 7 for calculating the inter-frame difference signal.

Numeral 15 denotes the receiving device 2 which receives the encoded data from the transmission line 3
Is a coded data input terminal, and 16 is a receiving interface unit for receiving the coded data in accordance with the transmission speed of the transmission line 3. 17 is the receiving interface
Reference numeral 18 denotes a reception buffer for temporarily storing the encoded data received, and 18 decodes the encoded data stored in the reception buffer 17 in a reverse procedure of the encoder 9 of the transmission device 1.
This is a decoder for restoring the inter-frame difference signal.

Reference numeral 19 denotes a frame memory in which the video data of the previous frame is stored. Reference numeral 20 denotes a frame memory for storing the video data of the previous frame stored in the frame memory 19 in the inter-frame difference signal restored by the decoder 18. This is an adder that restores the video data of the current frame by adding. The video data restored by the adder 20 is restored to the frame memory 19 to restore the data of the next frame.

Reference numeral 21 denotes a reception frame memory for storing the video data of the current frame restored by the adder 20, and reference numeral 22 sequentially reads the video data stored in the reception frame memory 21 at a speed according to the video rate of the video signal. This is an analog output unit that converts the data to analog. Reference numeral 23 denotes a video signal output terminal to which a video signal from the analog output section 22 is output.

Next, the operation will be described. A video signal input from the video signal input terminal 4 to the transmission device 1 is converted from an analog signal to a digital signal by an analog input unit 5,
After being separated into a luminance component and a chrominance component, it is written into the transmission frame memory 6. The transmission frame memory 6 absorbs the difference between the video rate of the input video signal (for example, 30 frames per second in the case of the NTSC color television system) and the coded video rate in the encoder 9 at the subsequent stage, and performs raster scanning. Scan conversion to a format suitable for encoding is performed.

Thereafter, the video data of the current frame read from the transmission frame memory 6 and the video data of one frame before read from the frame memory 7 are sent to the subtracter 8 to calculate the difference between them, and the difference between the frames is calculated. Output as a signal. Since the inter-frame difference signal is a change component between the video data of one frame before and the video data of the current frame, its absolute value is much smaller than the video data of the current frame itself, and the amount of information is reduced. .

This inter-frame difference signal is input to the encoder 9 and is compression-coded based on a predetermined coding algorithm, thereby further reducing the amount of information. This encoding result is temporarily stored in the transmission buffer 10 as encoded data,
In accordance with the transmission rate determined by the transmission line 3, via the transmission interface unit 11, the encoded data output terminal 12
Is transmitted to the transmission line 3.

On the other hand, the coded data coded by the coder 9 undergoes a decoding process according to a procedure reverse to the coding in the decoder 13 in preparation for a coding operation of the next frame, and becomes an inter-frame difference signal. Will be played. The reproduced inter-frame difference signal is added to the video data of the previous frame output from the frame memory 7 by the adder 14, and stored again in the frame memory 7 as the video data of the current frame. This video data is used as the video data of the previous frame at the time of encoding in the next frame for encoding in the above-described procedure.

 The transmitting device 1 operates as described above.

Next, the encoded data transmitted via the transmission line 3 is input to the receiving device 2 from the encoded data input terminal 15,
The data is written to the reception buffer 17 via the reception interface unit 16 according to the transmission speed determined by the transmission line 3. Thereafter, the received encoded data undergoes a decoding process in a decoder 18 having the same configuration as the decoder 13 of the transmission device 1,
It is restored as an inter-frame difference signal. The restored inter-frame difference signal is added by the adder 20 to the video data of the previous frame output from the frame memory 19, and is restored as the video data of the current frame.

The restored video data is temporarily written into the reception frame memory 21, sequentially read out at a speed according to the video rate of the video signal, and sent to the analog output unit 22. The analog output section converts the signal into an analog signal, reproduces the signal as a video signal, and outputs the video signal from the video signal output terminal 23.

On the other hand, the video data of the current frame restored by the adder 20 is written again to the frame memory 19, and is used as the video data of one frame before in the decoding operation of the next frame.

 The receiving device 2 operates as described above.

Next, the operation of the encoder 9 will be described. The inter-frame difference signal input to the encoder 9 has a value much smaller than the video data of the current frame itself as described above. However, if all information is to be transmitted, the reproduction information amount is The capacity of the line 3 will be exceeded.

For example, consider a case where a vector quantization method is used as an encoding method and one screen is composed of 336 pixels × 240 lines. Here, for example, spectrum Vol.01, NO.05,1
As shown in FIG. 13 of 988-05P99, a conversion pattern is obtained from a code book in a block of 4 pixels × 4 lines, and the number of patterns stored in the code book in advance is calculated.
In the case of a 4096 pattern, 4096 = 2 ¹² , so that 12 bits are required to represent one block. The block group consisting of 4 pixels × 4 lines in one block includes, in the 336 pixels × 240 lines, That is, if one block is represented by 12 bits, data of 5040 × 12 = 60,480 bits will be generated.

When the data of 60,480 bits is transmitted, for example, on the transmission line 3 of 64 Kbps, the number of transmission frames per second is And it is no longer a state that can be called a movie.

For this reason, the encoder 9 preferentially encodes a portion where the change is more severe (a portion where the inter-frame difference signal is large) within one screen, and uses the value of the video data of the previous frame as it is in a portion where the change is small. By performing encoding operation of, for example, only 500 blocks out of the above 5,000 blocks, the number of transmission frames per second is increased, and control is performed so as to approach a more natural moving image. That is, if only 500 blocks out of 5040 blocks are encoded, Becomes

However, since the input video signal changes every moment, the magnitude of the inter-frame difference signal input to the encoder 9 also changes every frame. In order to select a certain number of blocks from among these, the threshold for determination to determine whether or not to encode is also changed for each frame, and when the change is severe, the threshold is increased, and when the change is small, the threshold is decreased. By controlling as described above, the variation in the number of transmission frames per second is suppressed.

[Problems to be solved by the invention]

Since the conventional moving picture coding transmission apparatus is configured as described above, it is possible to secure a fixed number of transmission frames even when the input video signal changes, and to transmit and reproduce a moving picture having more natural motion. However, when the threshold value for determining whether or not to perform encoding changes, the image quality of the reproduced image also changes for each video frame. When the determination threshold value is high, that is, when the change of the input image is large, Since, as a result, a portion where a certain degree of change has occurred but is not enough to reach the determination threshold is not encoded, the final encoding distortion increases, and in particular, the above-described vector quantization is used. In this case, since the coding distortion of the high-frequency component that is easily recognized tends to occur, the determination threshold cannot be increased unnecessarily,
There is a problem that the final number of transmission frames must be limited to a certain value or less.

The present invention has been made in order to solve the above-described problem, and a large change in an input image indicates a high threshold value for determining whether or not to perform encoding. Even if the high-band coding distortion increases, the high-band distortion component in the video signal finally output from the device is removed, and a more natural moving image is obtained. It is an object of the present invention to obtain a moving picture coded transmission device that operates to output an original high-frequency signal in a video signal.

[Means for solving the problem]

The video encoding and transmitting apparatus according to the present invention includes a transmitting apparatus,
A distortion value signal generation unit that generates an encoding distortion value signal indicating an amount of encoding distortion generated when encoding the video signal, and a multiplexing unit that multiplexes the encoding distortion value signal into an encoded video signal. In the receiving device, a separation unit that separates the multiplexed encoded distortion value signal and the encoded video signal, and the cutoff frequency is controlled by the separated encoded distortion value signal,
It has a low-pass filter for filtering the decoded video signal.

[Action]

The receiving device according to the present invention includes a low-pass filter capable of controlling a cutoff frequency for filtering a decoded video signal, and includes a coding device that is transmitted from the transmitting device and indicates an amount of coding distortion generated during coding. Based on the distortion value signal, the cut-off frequency of this low-pass filter is controlled, and when the coding distortion is large, the cut-off frequency is lowered to remove high-frequency distortion components. By returning the value to the original value and reproducing the original high-frequency signal component, a moving picture coding and transmitting apparatus capable of obtaining a more natural moving picture is realized.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a transmitting device, 2 is a receiving device, 3 is a transmission line, 4 is a video signal input terminal, 5 is an analog input unit,
6 is a transmission frame memory, 7 is a frame memory, 8 is a subtractor, 11 is a transmission interface unit, 12 is an encoded data output terminal, 13 is a decoder, 14 is an adder, 15 is an encoded data input terminal, and 16 is an encoded data input terminal. Is a receiving interface unit, 18 is a decoder,
19 is a frame memory, 20 is an adder, 21 is a reception frame memory, 22 is an analog output unit, and 23 is a video signal output terminal, which are the same as those of the prior art which are denoted by the same reference numerals in FIG.
Or, since it is a substantial part, detailed description is omitted.

Reference numeral 24 denotes an encoder for compression-encoding the inter-frame difference signal from the subtractor 8 in accordance with a predetermined algorithm. Reference numeral 25 denotes a built-in encoder 24, which indicates the amount of encoding distortion generated during the encoding. This is a distortion value signal generation unit that generates an encoding distortion value signal, and the encoder 24 differs from the conventional encoder 9 shown in FIG. 8 in that the encoder 24 incorporates the distortion value signal generation unit 25. ing. 26 is the encoded data from the encoder 24,
This is a transmission buffer as a multiplexing unit that multiplexes and temporarily stores the encoded distortion value signal generated by the distortion value signal generation unit 25.

Reference numeral 27 denotes a reception buffer serving as a separation unit that temporarily stores the multiplexed coded data and the coding distortion value signal received by the reception interface unit 16 and separates and outputs them. 28, the cut-off frequency of which is controlled according to the coding distortion value signal separated by the reception buffer 27,
A low-pass filter that performs filtering of the video data restored based on the inter-frame difference signal decoded by 18.

Next, the operation will be described. Here, FIG. 2 is a characteristic diagram showing the frequency characteristics of the low-pass filter 28, FIG. 3 is an explanatory diagram showing the frequency components of the video signal when encoding distortion occurs, and FIG. FIG. 4 is an explanatory diagram showing frequency components of a signal obtained by passing a video signal having a frequency component shown in FIG.

In the transmitting device 1, the input video signal is digitized by the analog input unit 5, and then compression-coded in each subsequent process. In the receiving device 2, the transmission video signal is transmitted from the transmission line 3 through the receiving interface unit 16. The operation until the received encoded data is sequentially restored and output as video data from the adder 20 is the same as the conventional case.

Here, in the course of encoding, the encoder 24 performs a determination operation for preferentially encoding a portion having a large change from among the encoding target pixels in one screen, as in the conventional case. The distortion value signal generation unit 25 outputs information on a determination threshold for determining whether or not to perform encoding in the encoder 24 as an encoding distortion value signal. The encoded distortion value signal is sent to the transmission buffer 26, multiplexed and temporarily stored with the encoded data from the encoder 24, and is transmitted from the encoded data output terminal 12 via the transmission interface unit 11 to the transmission line. 3 is output.

On the other hand, the receiving device 2 temporarily stores the multiplexed coded data and the coded distortion value signal received by the receiving interface unit 16 in the receiving buffer 27, separates them and separates the coded data into a decoder. At 18, the coding distortion value signal is sent to the low-pass filter 28. The coded data input to the decoder 18 is restored to an inter-frame difference signal in the same manner as in the conventional case, as described above. Further, the coding distortion value signal input to the low-pass filter 28 acts as control information of the low-pass filter 28 to change its cutoff frequency.

Figure 2 is for a cutoff frequency of the low-pass filter 28 is showing how to change, usually has a low-pass characteristic of a cutoff frequency a frequency ₀ as indicated by the solid line, ₀ [HZ] Attenuate frequency components above. When the input coding distortion value signal shows a large value, the cutoff frequency is changed to ₁ ( ₁ < ₀ ),
₁ Attenuate frequency components above [HZ].

Next, the operation of the low-pass filter 28 will be described, paying attention to the property of the restored video data input to the low-pass filter 28. FIG. 3 shows the distribution of the frequency components of the restored video data input from the adder 20 to the low-pass filter 28.

In the transmitting apparatus 1, when there is a large change between frames of the input video signal, as described above, the threshold value for determining whether or not to perform encoding is increased in order to suppress an increase in the amount of encoded information as in the conventional case. As a result, an area in which there is actually a change but is not coded increases in the screen, and as a result, a large amount of error from the original image occurs as coding distortion. The frequency component of the coding distortion at this time is
When vector quantization similar to the conventional case is used as an encoding method, noticeable distortion tends to occur in a high-frequency portion in a video signal. FIG. 3 shows that this high-frequency distortion component exists in the range of ₁ to ₀ .

The signal having the spectrum shown in FIG.
When passing through a low-pass filter 28 having the characteristics shown in the figure, if the cutoff frequency is changed to ₁ , no more than ₁ [HZ] frequency components will not pass, and as a result, as shown in FIG. A signal in which the high-frequency component of the chemical distortion is attenuated is obtained.
The signal from which the high-frequency distortion component has been removed is sent to the reception frame memory 21.
And is converted into an analog signal by an analog output section 22 and output from a video signal output terminal 23. Therefore, a reproduced moving image with improved image quality can be obtained.

In the above-described embodiment, the cutoff frequency of the low-pass filter 28 is changed by switching between ₀ and ₁ , but the configuration is such that the value of the coding distortion value signal changes continuously. The type of cutoff frequency may be switched according to the value of the encoding distortion value signal. In this case, there is an effect that a sudden change in image quality for each frame can be prevented.

Further, in the above-described embodiment, the case has been described in which the determination threshold value for determining whether or not to perform the encoding in the encoder 24 is used as the encoding distortion value signal. An error between the inter-frame difference signal that has been dynamically decoded and the inter-frame difference signal input to the encoder 24 may be determined, and the accumulated value of the error signal per video frame may be used as the encoding distortion value signal. .

FIG. 5 is a block diagram showing a configuration example of the transmission device 1 in such an embodiment. In the figure, 29 is a decoder
13 is a subtractor for detecting an error between the inter-frame difference signal locally decoded in 13 and the inter-frame difference signal input to the encoder 9. This is an accumulator for accumulating frames. Distortion signal generator 25
Is formed by the subtractor 29 and the accumulator 30.

In the transmission device 1 configured as above, the decoder
Since the inter-frame difference signal locally decoded in 13 includes coding distortion, when the difference between the inter-frame difference signal input to the subtractor 29 and input to the encoder 9 is obtained,
The subtractor 29 outputs only the encoding distortion component. By accumulating the coding distortion component for one video frame in the accumulator 30, it is possible to directly determine the degree of coding distortion in the video frame. The distortion value signal generation unit 25 notifies the transmission buffer 26 of this as an encoding distortion value signal. Subsequent operations in the transmitting device 1 and the receiving device 2 are the same as those in the embodiment shown in FIG.

In the embodiment shown in FIG. 1, the low-pass filter 28 whose cutoff frequency is controllable is arranged at the preceding stage of the reception frame memory 21. However, between the reception frame memory 21 and the analog output unit 22, It may be arranged, or may be arranged inside the analog output unit 22.

FIG. 6 shows the low-pass filter 28 connected to an analog output section.
Analog output section 22 in the embodiment when arranged inside 22
FIG. 3 is a block diagram illustrating a configuration example of FIG. In the figure, 31 is a DA converter for converting received video data into analog, 32 is a low-pass type individual filter arranged in parallel with different cutoff frequencies, and 33 is a coding distortion filter. A switch for selecting one of the outputs of the individual filters 32 based on the signal. The low-pass filter 28 whose cut-off frequency can be changed includes the plurality of individual filters 32 and the switch 33.
It is composed of

In the analog output unit 22 configured as described above, when the video data from the reception frame memory 21 is input to the DA converter 31, it is converted into an analog signal, and each of the individual filters 32 of the low-pass filter 28 is converted. Input in parallel. Each individual filter 32 performs its filtering at a different cutoff frequency, and removes frequency components higher than the cutoff frequency. On the other hand, the switch 33 selects the output from the individual filter 32 having a low cutoff frequency when the coding distortion value signal indicates a large value, and selects the output from the individual filter 32 having a high cutoff frequency when the coding distortion value signal indicates a small value. Its action is set to select the output. Therefore, the same operation as the embodiment shown in FIG. 1 is performed, and a reproduced moving image with improved image quality can be obtained.

In FIG. 6, a plurality of individual filters 32 are arranged in parallel and one of them is selected by the switch 33. However, the output of the individual filters 32 arranged in series as shown in FIG. The configuration may be such that:

〔The invention's effect〕

As described above, according to the present invention, an encoding distortion value signal indicating the amount of encoding distortion generated during encoding is transmitted from a transmitting apparatus, and a receiving apparatus filters a decoded video signal. The cutoff frequency of the controllable low-pass filter is controlled by this coding distortion value signal, and when the coding distortion is large, the cutoff frequency is lowered to remove high-frequency distortion components, and when the coding distortion is small, the cutoff is cut off. Since the frequency is returned to the normal value and the original high-frequency signal component is reproduced, even if the input video signal changes greatly and the high-frequency distortion component in the encoded data increases, it is reproduced and output Does not appear in this, it is possible to change the determination threshold of whether to perform encoding to a higher value, it is possible to increase the number of transmission frames,
There is an effect that a moving picture coded transmission apparatus capable of reproducing a more natural moving picture with smooth movement and little distortion can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a moving picture coding transmission apparatus according to an embodiment of the present invention, FIG. 2 is a characteristic chart showing frequency characteristics of the low-pass filter, and FIG. FIG. 4 is an explanatory diagram showing frequency components of a signal, FIG. 4 is an explanatory diagram showing frequency components of a signal obtained by passing a video signal having the frequency components shown in FIG. 3 through a low-pass filter, and FIG. FIGS. 6 and 7 are block diagrams showing a configuration of an analog output unit according to still another embodiment of the present invention.
FIG. 8 is a block diagram showing a conventional moving picture coding transmission apparatus. 1 is a transmitting device, 2 is a receiving device, 3 is a transmission line, 9 and 24 are encoders, 18 is a decoder, 25 is a distortion value signal generator, 26 is a multiplexing unit (transmission buffer), and 27 is a demultiplexer. (Receive buffer),
28 is a low-pass filter. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] A transmitting device for encoding an input video signal of a moving image for each encoded video frame by an encoder and transmitting the encoded video signal to a transmission line; and the encoded video signal received from the transmission line. In a moving picture coded transmission device comprising a receiving device for decoding and outputting a video signal by a decoder, the video signal is generated when the input video signal is coded by the coder to the transmitting device. A distortion value signal generation unit that generates an encoding distortion value signal indicating an amount of encoding distortion; and the video signal encoded by the encoder, the encoding distortion value signal generated by the distortion value signal generation unit. A multiplexing unit for multiplexing, the receiving device, multiplexed by the multiplexing unit, a separation unit that separates the encoded distortion value signal and the encoded video signal, Before separation at the separation unit Its cut-off frequency is controlled according to the coding distortion value signal, the video encoding transmission apparatus, characterized in that which gave the low-pass filter for filtering the decoded said video signal by said decoder.