JPH07177511A - Picture coder - Google Patents

Abstract

PURPOSE:To suppress sudden increase in an information quantity, to decrease a delay due to coding and to improve the fineness even regardless of a predetermined information quantity. CONSTITUTION:A difference detector 17 detects a difference between an input digital picture signal 18 and a picture signal delayed by one frame period from a frame memory 16 to produce a difference signal 19. The difference signal 19 is used to control a pass band of a 2-dimension low pass filter 20 passing through low frequency components of signals in the horizontal direction and the vertical direction of a picture represented by the picture signal 18 to be narrower toward a lower frequency when the difference is large. Through the constitution above, a sudden increase in the information quantity due to a scene change or the processing of a moving picture is suppressed and a buffer quantity after DCT (discrete cosine transformation) coding are reduced, then a delay due to coding is reduced. Furthermore, since the pass band of the 2-dimensional low pass filter 20 is controlled wider with respect to a still picture causing a small difference to improve the fineness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image coding apparatus for compressing and coding an input digital image signal representing a continuous image into a coded signal, and particularly to a high-efficiency image transmission by wire or wireless. The present invention relates to an image coding device used for high density image recording on a recording medium.

[0002]

2. Description of the Related Art A conventional image encoding apparatus of this type encodes an input image signal with a compression encoder such as a two-dimensional DCT (discrete cosine transform) encoder in order to control the amount of information, and then buffers it. The compression rate of the compression encoder is controlled by storing the data in a memory and increasing or decreasing the amount of data on the buffer memory. FIG. 2 shows the basic configuration. The input analog image signal 10 is converted into a digital image signal by the A / D converter 11, encoded by the two-dimensional DCT encoder 12, and stored in the buffer memory 13. The data in the buffer memory 13 is read from the buffer memory 13 at regular intervals and becomes a coded signal (output data) 14.
The buffer memory 13 gives the compression rate control signal 15 to the DCT encoder 12 to the DCT encoder 12 depending on the amount of information (data amount) stored therein. This is to prevent information from being generated beyond the capacity of the buffer memory 13 and to prevent the buffer memory 13 from becoming empty due to less information generation than the reading speed from the buffer memory 13.

[0003]

SUMMARY OF THE INVENTION With such a configuration,
In order to cope with a sudden increase in the amount of information, the capacity of the buffer memory 13 is increased or the compression rate is constantly set to a high value for encoding. However, buffer memory 1
The increase in the capacity of 3 causes an increase in the delay time between input and output,
Higher compression ratio settings lead to lower image quality.

An object of the present invention is to provide an image coding apparatus which suppresses a sudden increase in the amount of information, shortens the coding delay, and causes no deterioration in image quality.

[0005]

According to the present invention, in an image coding apparatus for compressing and coding an input digital image signal representing a continuous image into an encoded signal, the input digital image signal is input to the input digital image signal. A frame memory that delays the digital image signal by one frame; a difference detector that detects a difference between the input digital image signal and an output signal of the frame memory and outputs a difference signal representing the difference; the input digital A two-dimensional low-pass filter that passes low-frequency components in the horizontal and vertical signal components of the image of the image; compression-encodes the signal component that has passed through the two-dimensional low-pass filter, and encodes the signal component. A two-dimensional low-pass filter receives the difference signal, and the difference represented by the difference signal is located in the two-dimensional low-pass filter. When the difference is larger than the difference, the pass band of the two-dimensional low-pass filter is narrowed, and when the difference represented by the difference signal is less than or equal to the predetermined difference, the pass band of the two-dimensional low-pass filter is reduced. An image encoding device characterized by widening is obtained.

According to the present invention, there is provided an image coding apparatus characterized in that the compression encoder is a two-dimensional discrete cosine transform encoder.

[0007]

Embodiments of the present invention will now be described with reference to the drawings.

Referring to FIG. 1, an image encoding apparatus according to an embodiment of the present invention compresses and encodes an input analog image signal 10 representing a continuous image into an encoded signal 14. The image encoding apparatus has an A / D (analog-digital) converter 11 that converts an input analog image signal 10 into an input digital image signal 18.

The frame memory 16 gives the input digital image signal 18 a delay of one frame of the input digital image signal 18. The difference detector 17 detects a difference between the input digital image signal 18 and the output signal of the frame memory 16 and outputs a difference signal 19 representing the difference.

Two-dimensional low pass filter (D2-LPF)
Reference numeral 20 allows low frequency components of the signal components of the input digital image signal 18 in the horizontal and vertical directions of the image to pass therethrough. At this time, the two-dimensional low-pass filter 20 receives the difference signal 19 and narrows the pass band of the two-dimensional low-pass filter 20 when the difference represented by the difference signal 19 is larger than a predetermined difference. However, when the difference represented by the difference signal 19 is less than or equal to the predetermined difference, the pass band of the two-dimensional low-pass filter 20 is widened. As described above, the two-dimensional low-pass filter 20 receives the input digital image signal 1
8 operates as a low-pass filter that limits the horizontal and vertical bands on the image, but by using the difference signal 19 to control the pass band, an image with a large difference between frames, that is, a motion The operation is performed so that the pass band is narrowed for an image having a certain value and the pass band is widened for an image having no difference between frames, that is, a still image.

A two-dimensional DCT (discrete cosine transform) encoder 12 acts as a compression encoder which compression-encodes the signal component passed through the two-dimensional low-pass filter 20 and outputs an encoded signal 14. To do.

[0012]

As described above, according to the present invention, it is possible to suppress a sudden increase in the amount of information, and the buffer memory after encoding can be minimized. Further, it is not necessary to constantly set a high compression rate, and the image quality can be improved. In particular, for a static image, the passband of the two-dimensional low-pass filter is widened to improve the definition, and when the image is moving or the screen is switched, the passband is narrowed to reduce the amount of information. You can As described above, even with a certain amount of information, the amount of information can be allocated so that the increase in the definition of the still image portion can be suppressed while suppressing the increase in the amount of information due to the moving image, so that the image quality can be improved from the visual effect.

[Brief description of drawings]

FIG. 1 is a block diagram of an image coding apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional image encoding device.

[Explanation of symbols]

 10 input analog image signal 11 A / D converter 12 DCT encoder 13 buffer memory 14 encoded signal 15 compression ratio control signal 16 frame memory 17 difference detector 18 input digital image signal 19 difference signal 20 two-dimensional low pass filter

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Claims (2)

[Claims] 1. An image encoding apparatus for compression-encoding an input digital image signal representing a continuous image into an encoded signal, wherein the input digital image signal is delayed by one frame of the input digital image signal. A frame memory for giving; a difference detector for detecting a difference between the input digital image signal and an output signal of the frame memory and outputting a difference signal representing the difference; horizontal and vertical directions of the image of the input digital image signal A two-dimensional low-pass filter that passes a low-frequency component in a directional signal component; a compression encoder that compresses and encodes the signal component that has passed through the two-dimensional low-pass filter, and outputs the encoded signal; The two-dimensional low-pass filter receives the difference signal,
When the difference represented by the difference signal is larger than a predetermined difference, the pass band of the two-dimensional low-pass filter is narrowed, and when the difference represented by the difference signal is less than or equal to the predetermined difference. An image coding apparatus, characterized in that a pass band of the two-dimensional low-pass filter is widened. 2. The image encoding apparatus according to claim 1, wherein the compression encoder is a two-dimensional discrete cosine transform encoder.