JPS6285588A - System and device for encoding moving picture signal - Google Patents

Abstract

PURPOSE:To correct an unnatural screen at the time of changing a scene by evaluating a change in the contents of a picture between screens and controlling the dynamic range of an output from a quantizer. CONSTITUTION:When picture contents between screens substantially change to detect a scene change in terms of an input moving picture signal, a scene change detector 1 supplies a detection signal to the quantizier 3. A subtractor 2 subtracts the input moving picture signal from a forecast signal out of a frame memory 5 and supplies a difference signal to the quantizer 3. When a scene change signal is given to the quantizer 3, it makes the maximum value of the amplitude of an output smaller, then larger slightly, changes it into a normal value and supplies it to an adder and a variable length encoder 6. The adder 4 reproduces a partial encoding signal with the aid of the difference signal and the forecast signal, and gives said encoding signal to the memory 5. The encoder 6 encodes the given signal into a variable length code through the use of Huffman code, fits the code to a transmission line and transmits the code.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a video signal encoding method and an apparatus thereof.

(Prior art) Usually, in interframe encoding using interframe correlation, the second
As shown in the figure, the output of the interframe code 5xooo is variable-length encoded by a variable-length encoder 6, and is temporarily stored in a buffer memory that matches the output speed of the variable-length code in the variable-length encoder 6 with the speed of the transmission path. It will be done. However, when the screen content changes significantly, a large amount of information is generated in encoding using the correlation between screens. In conventional interframe encoders, when a large amount of information is generated and the buffer memory is about to overflow, a stop message is given to the interframe encoder to stop encoding.

(Problems to be Solved by the Invention) In conventional interframe encoding using interframe correlation, excessive information is generated when the screen content changes significantly (hereinafter referred to as a scene change). When this occurs and the buffer memory is about to overflow, encoding is stopped even if the screen is halfway through, so the previous screen and the new screen that is being encoded may appear unnaturally overlapped within one screen, or The movement of the moving image becomes discontinuous, resulting in a picture-story show-like movement, which is very annoying to the eyes. SUMMARY OF THE INVENTION An object of the present invention is to provide a video signal encoding method and an apparatus therefor, which eliminates the need to present such an unnatural screen even when a scene changes.

(Means for Solving the Problem) According to the present invention, when performing predictive encoding or transform encoding of a moving image signal, changes in image content between screens are evaluated, and the image content changes significantly between screens. When it is determined that a change has occurred, the dynamic range of the quantizer output for the prediction error or transform coefficient is limited to a small value, and this is gradually expanded over time to return to the predetermined original dynamic range. A video signal encoding method characterized by the following is obtained.

Further, according to the present invention, there is provided a device for predictively encoding an input moving image signal, including means for evaluating whether or not a significant change has occurred in the content of an image between screens; means for generating a difference signal; means for quantizing the difference signal; and when performing the quantization, if the output of the evaluation means indicates that there has been a significant change in screen content, the quantization is performed once; A stitching control means that limits the dynamic range of the output to a small value and gradually expands the dynamic range of the output over time to return to a predetermined original dynamic range; the output of the quantization means and the predicted signal; means for generating a locally decoded signal by;
A moving picture signal encoding apparatus is obtained, comprising means for generating the predicted signal using the locally decoded signal, and means for variable length encoding the output of the quantization means. Furthermore, according to the present invention, there is provided an encoding device that encodes an input moving image signal using transform encoding, and a means for evaluating whether or not a significant change has occurred in the content of an image between screens. , means for generating a difference signal between the input signal and the predicted signal; means for performing orthogonal transformation on the difference signal; means for quantizing the output of the orthogonal transformation means; When the output of the means indicates that there has been a significant change in the screen content, the dynamic range of the output is temporarily limited to a small value, and the dynamic range of the output is gradually expanded over time to a predetermined value. Stitching control means for restoring the original dynamic range; means for orthogonal inverse transformation of the output of the quantization means;
means for generating a locally decoded signal using the output of the orthogonal inverse transformer and the predicted signal; means for generating the predicted signal using the locally decoded signal; and means for variable length encoding the output of the quantizing means. There is obtained a moving image signal encoding device characterized by comprising the following.

(Operation) As shown in FIG. 1, in the encoding control system of the present invention, the scene change detector 1 first detects a scene change in which the content of an image changes significantly between screens from an input moving image signal. Although the method of detecting scene changes is not the subject of the present invention, for example, see the paper by Miyahara [Measurement and Study of Frame Difference Signal Characteristics Targeting Bandwidth Compression J].
Theory of faith (A).

VOL56-A, No. 8. P.P., 456-46
3. August 1973) can be used. This method detects a significant change in the content of an image by determining the number of significant frame differences and the inter-frame correlation of this number.

The scene change detector provides a signal indicating a scene change (scene change detection signal) to the interframe encoder when a scene change occurs. When a scene change occurs and a scene change detection signal is provided, the interframe encoder temporarily limits the dynamic range of the quantizer output to a small value, and gradually expands it over time.
Return to normal quantization. For example, when a scene change occurs in a certain frame as shown in Figure 3, the maximum value of the dynamic range of the quantizer output is limited to the width A in Figure 4 for a period of N frames from that frame. , during the next M frames, the amplitude of the output of the quantizer is expanded a little more than during the N frame time, and the dynamic range is limited as shown in FIG. 4B. After a further time, in the time domain P, the dynamic range of the output of the quantizer is further expanded and normal quantization is performed.

During a scene change, a large amount of large output is generated, and in variable length coding such as ordinary Huffman codes, a large amount of long codes are used. Therefore, an excessive amount of code is generated instantaneously. Limiting the quantization output to a small value at the time of scene change corresponds to not generating long codes. In this way, by gradually expanding the output dynamic range of the quantization characteristic from small to normal, it is possible to suppress excessive information generated at the time of scene change and perform smooth encoding.

(Example) An example of the present invention will be described in detail with reference to FIGS. 5, 6, and 7. FIG. 5 is a diagram showing an example of the configuration of an encoder according to the present invention. An input moving image signal is supplied to a scene change detector 1 and a subtractor 2 via a line 101. The scene change detector 1 supplies a scene change signal to the quantizer S3 via a line 102 when the input moving image signal changes significantly in image content between screens and a scene change is detected. The subtracter 2 subtracts the input moving image signal and the prediction signal supplied from the frame memory 5, and supplies a difference signal as an output to the quantizer 3 via a line 201. The quantizer 3 quantizes the difference signal supplied from the subtracter 2, but when a scene change occurs and a scene change signal is provided from the scene change detector 1, the maximum amplitude of the output is For example, limit the value to a small value as shown in A in Fig. 4, and after a while, slightly expand the maximum value of the output amplitude to obtain B in Fig. 4.
Do like this. Then, after a further period of time, the maximum value of the output amplitude is returned to the normal value. Details of the quantizer 3 will be described later. The output of the quantizer 3 is supplied to an adder 4 and a variable length code 56. Adder 4 uses the difference signal supplied from quantizer 3 and the prediction signal supplied from frame memory 5 to reproduce the locally decoded signal.

The locally decoded signal, which is the output of adder 4, is supplied to frame memory 5. Frame memory 5 delays the locally decoded signal by one frame time and supplies the predicted signal to subtracter 2 and adder 4 as output. The variable length encoder 6 performs variable length encoding on the difference signal supplied from the quantizer 3 using an efficient code such as a Huffman code, matches the encoding speed and the transmission path speed, and outputs a line 601. The variable length code is supplied to the transmission path through the transmission line.

Next, the decoder of the present invention will be explained with reference to FIG. Variable length decoding is supplied from the transmission path to variable length decoder 7 via line 701. The variable length decoder 7 performs variable length decoding while matching the speed of the transmission path and the speed of decoding.

The differential signal reproduced by variable length decoding of the output of the variable length decoder 7 is supplied to the - adder 8 . The adder 8 is supplied with the difference signal supplied from the variable length decoder 7 and from the frame memory 9. Decoding is performed using the predicted signal,
Regenerate the original video signal. The decoded signal output from adder 8 is supplied to frame memory 9 . Also line 801
is used as the output of the decoder. Frame memory 9 delays the decoded signal supplied from adder 8 by one frame time, and supplies the predicted signal to adder 8 as an output.

Next, the quantizer 3 will be explained in detail with reference to FIG. The quantizer 3 stores the difference signal supplied from the subtracter 2 via the line 201 into a read-only memory (Read 0
nly Memory: ROM ) ROM-P 301
．． ROM-N 302 and ROM-M 303 are used for quantization. In the ROM-P 301, basic quantization characteristics are stored in advance.

The ROM-N 302 stores in advance a quantization characteristic such as A in FIG. 4 in which the maximum value of the output amplitude is limited to a small value. The ROM-M2O3 stores in advance a quantization characteristic such as B in FIG. Note that these ROMs provide the address input with the differential signal supplied by line 201, so the value of the quantized output is stored in correspondence with the address (and the output of each ROM, that is, the quantized output, can be changed by switching timer 30.
5 is a control circuit 304 for controlling a timing signal indicating a frame.
supply to. The control circuit 304 is normally a ROM-P
A control signal is given to the switch 306 to select 301, and normal quantization is performed. However, when a scene change occurs and a scene change signal is given via the line 102, the timing signal supplied from the timer 305 is Based on this, immediately after a scene change occurs, a control signal is sent to select ROM-N 302, which limits the output amplitude to a small value, and after a predetermined time, a control signal is sent to select ROM-N 302, which increases the output amplitude slightly. ROM-P2O3 which performs normal quantization on the control signal to be selected after further time.
A control signal is given to the switch 306 to select. The switch 306 selects the quantization ROM based on the control signal supplied from the control circuit 304, and selects the quantization ROM from the quantizer 3.
Let the output be Also, if the output level of the quantization characteristic is made common as shown in Figure 4, and only the dynamic range is changed, and the normal characteristic>characteristic B>characteristic A, then characteristic A or characteristic B
Even when is selected, a common variable length encoding can be used and there is no need to send a code switching signal to the receiving side.

Next, a coding device that combines orthogonal transform and predictive coding will be described as another embodiment with reference to FIG. An input moving image signal is supplied to a scene change detector 1 and a subtractor 2 via a line 101. The scene change detection S1 supplies a scene change signal to the quantizer 3 via a line 102 when the input moving image signal changes significantly in image content between screens and a scene change is detected. The subtracter 2 subtracts the input moving image signal and the prediction signal supplied from the frame memory 5, and supplies a difference signal to the orthogonal transformer 202 as an output. Orthogonal transform G202 performs orthogonal transform such as discrete cosine transform or Hadamard transform on the difference signal and converts the transform coefficients into line 20.
1 to the quantizer S3. The quantizer 3 quantizes the transform coefficients supplied from the orthogonal transformer 202, but when a scene change occurs and a scene change signal is given from the scene change detector 1,
For example, the maximum value of the output amplitude is limited to a small value as shown in A in FIG. 4, and after a while, the maximum value of the output amplitude is slightly enlarged to become as shown in B in FIG. Then, after a further period of time, the maximum value of the output amplitude is returned to the normal value. The output of the quantizer 3 is supplied to the orthogonal inverse transformer 203 and the variable length decoder 6. The orthogonal inverse transformer 203 inversely transforms the quantized transform coefficients by orthogonal inverse transform corresponding to the previously performed orthogonal transform, and supplies the reproduced difference signal to the adder 4 . The adder 4 reproduces the locally decoded signal using the difference signal supplied from the orthogonal inverse transformer 203 and the prediction signal supplied from the frame memory 5.

The locally decoded signal output from the adder 4 is stored in the frame memory 17-
5. Frame memory 5 delays the locally decoded signal by one frame time and supplies the predicted signal to subtracter 2 and adder 4 as output. The variable-length decoder 6 performs variable-length encoding on the transform coefficients supplied from the quantizer 3 using an efficient code such as a Huffman code, and matches the encoding speed with the transmission path speed. The compressed variable-length code is supplied to the transmission path via. The decoder includes an orthogonal inverse transformer 203 between the variable length decoder 7 and the adder 8 in FIG.
An orthogonal inverse transformer with the same configuration as is added. The variable length code supplied from the transmission path is variable length decoded while matching the speed of the transmission path and the decoding speed, and the decoded transform coefficients are supplied to the orthogonal inverse transformer. The orthogonal inverse transformer reproduces the original difference signal from the transform coefficients supplied from the variable length decoder 7 and supplies it to the adder 8 . Thereafter, adder 8 and frame memory 9 perform operations similar to those described above.

(Effects of the Invention) As explained in detail above, immediately after a scene change occurs, the dynamic range of the output of the quantizer 3 is limited to a small value, and then expanded a little after a while, and then Perform normal quantization. In this way, immediately after a scene change, the output amplitude of the quantizer is limited to a small value, and by gradually increasing it over time, the generation of excessive information at the time of a scene change is suppressed, and smooth movement without discontinuous movement is achieved. encoding can be performed.

As described above, when the present invention is put into practical use, the effect of improving image quality in video encoding is extremely large.

[Brief explanation of drawings]

FIG. 1, FIG. 3, and FIG. 4 are diagrams for explaining the present invention in detail, and FIG. 2 is a diagram for explaining the conventional method.
FIG. 5, FIG. 6, FIG. 7, and FIG. 8 are diagrams for explaining the present invention in detail. In the figure, 1...Scene change detector, 2...Subtractor, 3
...Quantizer, 4...Adder,
5...Frame memory, 6...Variable length encoder, 7...Variable length decoder, 8...Adder, 9...Frame memory. 202...Orthogonal transformer 203...Orthogonal inverse transformer 301...-ROMP 302-
・・ROMN303・・−ROMM 3
04...Control circuit 305...Timer
306...Switching device.

Claims (1)

[Claims] 1. When performing predictive encoding or transform encoding of a moving image signal, changes in image content between screens are evaluated, and it is determined that the image content has changed significantly between screens. A moving image characterized in that when a prediction error or a transformation coefficient occurs, the dynamic range of the output of a quantizer with respect to a prediction error or a transform coefficient is limited to a small value, and this is gradually expanded over time to return to a predetermined original dynamic range. Signal encoding method. 2. A device that predictively encodes an input moving image signal,
means for evaluating whether or not a significant change has occurred in image content between screens; means for generating a difference signal between the input signal and the predicted signal; means for quantizing the difference signal; and means for quantizing the difference signal. In doing so, when the output of the evaluation means indicates that there has been a significant change in screen content, the dynamic range of the quantized output is temporarily limited to a small value, and the dynamic range of the output is gradually expanded over time. quantization control means for restoring the original dynamic range to a predetermined original dynamic range; means for generating a locally decoded signal using the output of the quantization means and the predicted signal; and generating the predicted signal using the locally decoded signal. An encoding device for a moving image signal, comprising: means for variable length encoding the output of the quantization means. 3. An encoding device that encodes an input moving image signal using transform encoding, a means for evaluating whether or not a significant change has occurred in the content of an image between screens, and a means for evaluating the input signal and prediction. means for generating a differential signal with respect to the signal; means for performing orthogonal transformation on the differential signal; means for quantizing the output of the orthogonal transforming means; When it indicates that there has been a significant change in the output, the dynamic range of the quantized output is temporarily limited to a small value, and the dynamic range of the output is gradually expanded over time to return to the predetermined original dynamic range. quantization control means, means for orthogonally inversely transforming the output of the quantizing means, means for generating a locally decoded signal using the output of the orthogonally inversely transforming means and the predicted signal, and generating the predicted signal using the locally decoded signal. 1. An encoding device for a moving image signal, comprising: means for generating a quantization means; and means for variable-length encoding the output of the quantization means.