JPS63224569A - Conversion coding device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a restored picture by providing a movement detection circuit detecting the movement between two blocks included respectively in two frames of an input digital picture signal being timewise consecutive. CONSTITUTION:The absolute value of a difference of frames of picture element data at a position corresponding between two consecutive frames respectively is formed by a subtraction circuit 6 and an absolute value processing circuit 13 in a movement detection circuit 2. The absolute value of the frame difference is fed to a comparator 14, where it is compared with a threshold level from a terminal 15, and a binary comparison output corresponding to the relation of level of the absolute value of the frame difference and the threshold level data is fed to a deciding circuit 16. The circuit 16 decides it as a standstill section when the absolute value of the frame difference relating to all picture data included in each block is a threshold data or below. Then a reset pulse is fed to the circuit 16 at every block from a terminal 17, where the movement detection is applied at every block.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is based on cosine transform (Discrete Co
The present invention relates to a bumpering device in transform encoding such as Co51neTransform.

[Summary of the invention]

In the present invention, in a transform encoding device such as a cosine transform, a motion detection circuit that performs motion detection between two corresponding blocks included in two temporally consecutive frames of an input digital image signal; Depending on the detection signal of the motion detection circuit, in the case of a moving image block, the input digital image signal is supplied as is to the encoder of the orthogonal transform code, and in the case of a still image block, the digital image signal of one block formed from two blocks is A circuit is provided to supply the image signal to an encoder of an orthogonal transform code so that the original image is compressed to the target bit rate without visually severe distortion.

C. Prior art] In order to suppress the redundancy of image signals, the screen is divided into blocks each consisting of a predetermined number of pixels, and each block is subjected to linear transformation using a transformation axis that matches the characteristics of the original image signal. It has been known. Hadamard transform, cosine transform, etc. are known as transform encoding. For example, ““IEEE T
RANSACTIONS ON COMMLINICA
TIONS” VOL, COF2-32.NO, 3, M
ARCH, 1984, pages 225-231, the two-dimensional cosine transformation performs the process shown by the following equation. However, the original data is two-dimensional data f (j, k) in which one block is (MXN) samples.
(j, k・0,1...N-1).

The information at is reduced by thresholding on the coefficient values obtained by the conversion of the above equation, and buffering is performed.

Cosine transformation compresses the data amount of the digital image signal, and the bit rate after compression is, for example, 25 (
Mbps) or 12.5 (Mbps).

When compressing up to 12.5 (Mbps), the high compression rate causes problems such as an increase in background noise, block distortion due to missing frequency components, and noticeable blurring of the image.
There was a problem with significant image quality deterioration.

Therefore, an object of the present invention is to provide a transform encoding device that can reduce image quality deterioration when obtaining a high compression rate through transform encoding.

[Means for solving problems]

In this invention, in a transform encoding device that divides a screen into blocks each consisting of a predetermined number of pixels and orthogonally transforms pixel data for each block, at least two temporally consecutive frames of an input digital image signal are processed. A motion detection circuit 1 that performs motion detection between two corresponding blocks included in each block.
2 and the detection signal of the motion detection circuit 12, in the case of a moving picture block, the input digital image signal is supplied as it is to the encoder 10 of the orthogonal transform code, and in the case of a still picture block, the input digital image signal is supplied as it is to the encoder 10 of the orthogonal transformation code, and in the case of a still picture block, the means 9 for supplying the digital image signals of the blocks to the orthogonal transform code encoder 10.

[Effect]

In the case of still image blocks, the contents of the block images are almost the same. Therefore, two blocks included in at least two temporally consecutive frames can be represented by one block.

In a television image, the proportion of still blocks in one screen is relatively high, and as described above, the number of blocks to be transform coded is reduced by the process of representing a plurality of blocks into one block. Since the amount of data can be compressed before transform encoding, a target bit rate can be obtained without increasing the compression rate of transform codes such as DCT so much. Therefore, significant deterioration in image quality of the restored image can be prevented.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, a digital television signal is supplied to an input terminal indicated by 1, and is converted into a signal in the order of blocks, which is a unit of conversion coding, in a blocking circuit 2.

The output signal of the blocking circuit 2 is transmitted to the delay circuit 3 and the adder circuit 4.
, the frame memory 5 and the subtraction circuit 6. The digital television signal of the previous frame is supplied from the frame memory 5 as another input signal to the adder circuit 4. The output signal of the adder circuit 4 is supplied to the doubler circuit 7, and the output signal of the doubler circuit 7 is supplied to the delay circuit 8. The output signal of the delay circuit 3 is supplied to one input terminal a of the switch circuit 9, and the output signal of the delay circuit 8 is supplied to the other input terminal a of the switch circuit 9.

The output signal from the output terminal C of the switch circuit 9 is DCT.
(Cosine transform) is supplied to the encoder 10, and DCT calculation is performed on a block-by-block basis to obtain a DCT table.
The amount of information is reduced using this DCT table. D.C.
A transmission signal is obtained at the output terminal 11 of the T encoder 10.

FIG. 3 shows an example of the DCT encoder lO. A digital video signal f(j, k) is supplied to an input terminal indicated by 31 in FIG. be done. In the cosine transformation circuit 32, two-dimensional cosine transformation is performed by processing similar to conventional processing. The coefficient values P(u,v) from the cosine transform circuit 32 are supplied to the thresholding circuit 33 to reduce the amount of information. The coefficient value Fr(u,v) from the thresholding circuit 33 is supplied to a quantization circuit 34, and the output of the quantization circuit 34 is supplied to a coding circuit 35, where it is converted into a code signal of a predetermined number of bits.

A code signal from coding circuit 35 is supplied to buffer memory 36. The buffer memory 36 is provided to convert the transmission rate of the code signal from the coding circuit 35 to a constant biso rate within a range that does not exceed the rate of the transmission line. The data rate on the input side of the buffer memory 36 is variable;
The data rate on the output side of 6 is constant. Output data at a constant bit rate from the buffer memory 36 is sent to the terminal 37.
It is taken out. In this buffer memory 36, a constant value is determined for each screen. This value is given to the thresholding circuit 33 and used to determine the threshold value.

The switch circuit 9 is connected to a motion detection circuit 12 surrounded by a broken line.
In the case of a moving image block, the input terminal a and the output terminal C are connected, and in the case of a still image block, the input terminal A and the output terminal C are connected. In the case of a moving image block, the input digital image signal passed through the delay circuit 3 is supplied to the DCT encoder 10 as is. As shown in FIG. 4A, when the motion detection circuit 12 determines that blocks Bn and Bn+1 included in temporally consecutive frames Fn and Fn+1, respectively, of the input digital video signal are moving picture blocks, these blocks A DCT table corresponding to each of Bn and Bn** is calculated in the DCT encoder IO.

Further, in the case of a still image block, the signal passed through the adder circuit 4, the A multiplier circuit 7, and the delay circuit 8 is selected by the switch circuit 9. The adder circuit 4 is supplied with the output signal of the blocking circuit 2 and the previous frame signal from the frame memory 5. That is, as shown in FIG. 4B, blocks Bn and B included in frames Fn and Fn□, respectively
The corresponding pixel data of n, etc. are added together by the adding circuit 4. For example, pixel data aO of block Bn and pixel data bo of block Bn++ are added and supplied to the A multiplier circuit 7 to obtain an output signal of y, (ao' + bO).

Therefore, the two blocks Bn and Bn+1 are converted into one representative block Bn'' consisting of the average value of each pixel data of both blocks. The DCT encoder lO processes the pixel data included in this representative block Bn'. Instead of forming an average value, one block may simply be deleted.The delay circuits 3 and 8 are provided to delay the data by the time required for the motion detection circuit 12 to determine the motion.

The motion detection circuit 12 includes a subtraction circuit 6, an absolute value conversion circuit 13,
It is composed of a comparison circuit 14 and a determination circuit 16.

The subtraction circuit 6 and the absolute value conversion circuit 13 calculate the block B included in each of two consecutive frames FIISFn+1.
The absolute value of the level difference (frame difference) of pixel data at corresponding positions between Bn and Bn is formed. The absolute value of this frame difference is supplied to a comparison circuit 14 and compared with a threshold value from a terminal 15. A binary comparison output corresponding to the level relationship between the absolute value of the frame difference and the threshold data is supplied to the determination circuit 16.

The determination circuit 16 determines that when the absolute value of the frame difference for all the pixel data included in each block Bn and Bn+1 is less than or equal to the threshold data, there is no change between the two, that is,
Determined as a stationary part. A reset pulse for each block is supplied to the determination circuit 16 from a terminal 17, and motion detection is performed for each block. The motion detection signal obtained from the determination circuit 16 is supplied to the switch circuit 9, taken out to the output terminal 18, and transmitted together with the output signal of the DCT encoder 10.

FIG. 2 shows the configuration of the receiving side. Received data from an input terminal indicated by 21 in FIG. 2 is supplied to a DCT decoder 22, and the OCT decoder 22 obtains restored data for each block. The restored data from the DCT decoder 22 is supplied to one input terminal a of the switch circuit 23 and is also supplied to the interpolation circuit 24. The output signal of the interpolation circuit 24 is supplied to the other input terminal of the switch circuit 23. The switch circuit 23 is controlled by a motion detection signal from a terminal 25, and an input terminal a and an output terminal C are connected to each other in a moving image block, and an input terminal A and an output terminal C are connected to each other in a still image block. Interpolation circuit 2
4 is provided to form the same block as one restored block of data.

The output signal of the switch circuit 23 is supplied to a block decomposition circuit 26. In this block decomposition circuit 26, the digital video signal in block order is returned to television scanning order. A restored digital video signal is obtained at the output terminal 27 of the block decomposition circuit 26.

In the above embodiment, the motion adaptive processing is performed on two frames, but the motion adaptive processing may be performed on a period of three frames or more.

〔Effect of the invention〕

In this invention, when one screen is divided into a large number of blocks and transform encoding is performed for each block, a plurality of still blocks are compressed into one representative block in advance.

According to the present invention, since the amount of data to be transmitted can be significantly compressed, the quality of the restored image can be improved without increasing the compression parameters of the transform encoding itself.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a transmitting side according to an embodiment of the present invention, FIG. 2 is a block diagram of a receiving side according to an embodiment of this invention, and FIG.
The figure is a block diagram of an example of a DCT encoder, and FIG. 4 is a route diagram used to explain the operation of an embodiment of the present invention. Explanation of main symbols in the drawings 1 terminal for two people, 5: frame memory, 9: switch circuit, 10: DCT encoder, 11: output terminal, 12: motion detection circuit.

Claims (1)

[Claims] In a transform encoding device that divides a screen into blocks each consisting of a predetermined number of pixels and orthogonally transforms pixel data for each block, 2
Between two corresponding blocks included in each frame,
A motion detection circuit performs motion detection, and a detection signal from the motion detection circuit is used to supply the above-mentioned input digital image signal as it is to an encoder for orthogonal transformation codes in the case of a moving image block, and the above-mentioned two signals in the case of a still image block A transform encoding device comprising: means for supplying one block of digital image signals formed from the blocks to the orthogonal transform code encoder.