JPH02177684A - Inter-frame encoder for television signal - Google Patents

Abstract

PURPOSE:To suppress the deterioration of picture quality even for a part having the different statistical character of a predicted error by switching an encoding table according to the character of the coefficients of an orthogonal transformation. CONSTITUTION:When an input picture and the reproduced picture of the preceding frame are inputted to a scene change detecting circuit 113, and a scene change is detected in the circuit 113, a detected signal is outputted, the detected signal is sent to a table switching circuit 103, and an encoding table 2 and a decoding table 2 for a first frame are selected in the table switching circuit 103. While the encoding table adaptive to the processing of the first frame is used when the scene change is detected by the scene change detecting circuit 113 in this manner, a conventional encoding table is used in any other case. Thus, the deterioration of the picture quality accompanying the scene change can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an interframe encoding device for television signals used in video conference systems, video telephones, monitoring systems, and the like.

2. Description of the Related Art A conventional interframe coding device for television signals performs motion compensated interframe prediction to calculate a prediction error, then performs orthogonal transformation on a block that is a set of multiple prediction errors, and calculates the coefficients. There is a device that uses an encoding method. FIG. 2 is a block diagram of a conventional television signal interframe encoding device. In Figure 2, 4
01 is an input terminal, 402 is an A/D converter, and subtracter 4
04 and the motion vector detection circuit 421.

Further, a prediction circuit 419 is connected to the subtracter 404, and the subtracted result is input to the orthogonal transform circuit 406. The output of orthogonal transform circuit 406 is connected to coefficient encoding circuit 408, and the output of coefficient encoding circuit 408 is connected to coefficient decoding circuit 410 and line encoding circuit 425. The coefficient decoding circuit 410 is connected to an orthogonal inverse transform circuit 412, which is further connected to an adder 414.

A prediction circuit 419 is also connected to the adder 414, and the addition result is input to the frame memory 417. The frame memory 417 is connected to a prediction circuit 419 and a motion vector detection circuit 421. Motion vector detection circuit 421
The output of is connected to a prediction circuit 419 and a line encoding circuit 425.

Line encoding circuit 425 is connected to the line.

Next, the operation of the above conventional example will be explained. At the *th time, an analog image signal is input to the A/D converter 402 through the input terminal 401, converted to a digital image, and then input to the motion vector detection circuit 421 and the subtracter 404. The motion vector detection circuit 421 uses the above input digital original image and the pixel values of the previous frame read out from the frame memory 417 to detect a motion vector in units of blocks, which are sets of a plurality of pixels. The detected motion vector is input to the prediction circuit 419 and output to the line encoding circuit 425. Motion compensated interframe prediction is performed using this motion vector and the pixel value of the previous frame, and the calculated predicted value is sent to the subtracter 404 and the adder 4.
14. The subtracter 404 calculates a prediction error value for the pixel value of the input image using the predicted value, and the orthogonal transform circuit 406 performs orthogonal transform on a block that is a set of a plurality of prediction errors. The coefficients calculated at this time are encoded in coefficient encoding circuit 408 and sent to line encoding circuit 425. At this time, in accordance with the statistical properties of the prediction error signal, in the coefficient encoding circuit 408, many bits are assigned to coefficients corresponding to frequency bands where a lot of energy is concentrated, and frequencies where energy is not concentrated yet. Fewer bits are allocated to coefficients corresponding to bands. Further, the encoded coefficients are locally decoded in a coefficient decoding circuit 410, a prediction error is reproduced in an orthogonal inverse transform circuit 412, and a pixel value is reproduced by adding the predicted value to this in an adder 414. , writes the result to the frame memory 417. The locally reproduced value obtained in the encoder in this way is used for prediction at the next stage and subsequent stages. The motion vector information and orthogonal transform coefficient information input to the line encoding circuit 425 are encoded here and output to the line through 426.

In this way, the conventional interframe compression encoding device described above also performs orthogonal transformation on the prediction error signal, and changes the number of bits allocated to the coefficient corresponding to that frequency band depending on the energy contained in each frequency band. This allows highly efficient image compression.

Problems to be Solved by the Invention However, in the conventional interframe encoding device described above, the number of bits allocated to the coefficients after orthogonal transformation is fixed, so the image quality may deteriorate in areas where the statistical properties of prediction errors are different. There was a problem with deterioration.

In particular, in the first frame of the encoding process, since there is no previous frame necessary for interframe prediction, there are two methods: (i) formally assuming an image with all 128 values as the previous frame, (ii) input There are processing methods such as dividing an image into blocks consisting of multiple pixels, calculating the average value for each block, transmitting this, taking all the pixel values in that block as the average value, and treating this as the previous frame. It is done. However, in this case, since there is little formal correlation between the previous frame and the input frame, its statistical properties are significantly different from the steady-state prediction error, and a lot of information is generated, resulting in poor image quality. It will deteriorate.

The present invention is intended to solve such problems, and aims to provide an interframe coding device that can suppress image quality deterioration even in parts where the statistical properties of prediction errors are different. .

Means for Solving the Problems In order to achieve the above object, the present invention has a plurality of encoding tables for orthogonal transform coefficients, is provided with the above-mentioned chifur switching circuit, and is configured to change the above-mentioned plurality of coding tables according to the nature of the input image. The deterioration of image quality can be suppressed by switching the tables.

Operation The present invention has the following effects due to the above-described configuration. In other words, since the encoding table of orthogonal transform coefficients is adaptively switched according to the characteristics of the input image, it is possible to suppress image quality deterioration even for images with any statistical characteristics, and to improve image efficiency. It can be compressed. In particular, for the first frame of the encoding process, since the statistical properties of the prediction error are different from those in the steady state, the present invention can improve the image quality of the first frame.

Embodiment FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In FIG. 1, the same numbers as those in FIG. 2 indicate the same contents, and the different numbers from the conventional example in FIG. 2 will be explained below.

In FIG. 1, 113 is a scene change detection circuit, which compares the input image output from the A/D converter 402 and the previous image from the frame memory 417, and as a result detects that a scene change has occurred. Outputs a detection signal.

Reference numeral 103 denotes a table switching circuit which switches between an encoding table and a decoding table, which will be described below, depending on the presence or absence of the scene change detection signal.

106 and 110 are encoding table 1 and decoding table 1, respectively, and the encoding (
Tables 107 and 111 are encoding table 2 and decoding table 2, respectively, which define the focus allocation method when performing orthogonal transformation of the first frame. This is a table that defines how to allocate bits during (or decoding).

Next, the operation of the above embodiment will be explained. In the above embodiment, the input image and the reproduced image of the previous frame are input to the scene change detection circuit 113, and when a scene change is detected there, a detection signal is output, which is sent to the table switching circuit 103. In this step, encoding table 2 and decoding table 2 for the first frame are selected. In addition, scene change detection circuit 1
When no scene change is detected in step 13, the full switching circuit 103 selects encoding table 1 and decoding table 1 for normal frames.

On the other hand, the prediction error signal of the input image is orthogonally transformed in an orthogonal transform circuit 406, and then in a coefficient encoding circuit 408 and a coefficient decoding circuit 410.
Encoding and decoding are performed using the data of the encoding table and decoding table selected in . The encoded signal is then sent out via line encoding circuit 425.

According to the above embodiment, when a scene change is detected by the scene change detection circuit 113, the first
Since a coding table adapted to frame processing can be used, and a conventional coding table can be used at other times, it has the advantage of eliminating image quality deterioration due to scene changes.

Here - as an example, we will detect a scene change in an image,
A case will be described in which this signal is used to switch the encoding table of orthogonal transform coefficients. However, the present invention is not limited to this case; it is also possible to use a signal other than the scene change detection signal as the table switching signal, and it is also possible to have not only two but a plurality of encoding tables.

Effects of the Invention As is clear from the above embodiments, the present invention is capable of switching the encoding table depending on the properties of the orthogonal transform coefficients, and it does not matter what kind of statistical properties the part has. This also has the effect of suppressing deterioration in image quality and transmitting images with high efficiency.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of an interframe compression encoding apparatus for television signals according to an embodiment of the present invention, and FIG. 2 is a schematic block diagram of a conventional interframe compression encoding apparatus for television signals. 103...Table switching circuit, 106.107...
・Encoding tape notebook 110.111・Decoding table, 113・・Scene change detection circuit, 401・・Input terminal, 402・A/D converter, 404・・Subtractor,
406...Orthogonal transform circuit, 408...Coefficient encoding circuit, 410...Coefficient decoding circuit, 412...Orthogonal inverse transform circuit, 414...Adder, 417 Frame memory, 41
9...Prediction circuit, 421...Moving vector detection circuit, 425...Line encoding circuit, 426...Output terminal.

Claims (2)

[Claims] (1) A means for performing motion compensated interframe prediction and orthogonally transforming the prediction error, a plurality of tables for encoding or decoding transform coefficients of the orthogonally transformed image, and and means for switching between a plurality of tables. (2) The table switching means corresponds to when a scene change occurs and when a scene change does not occur.
2. The interframe encoding apparatus for television signals according to claim 1, wherein a set of encoding tables and decoding tables is switched.