Image analysis – Image compression or coding
Reexamination Certificate
1997-01-09
2001-11-13
Couso, Jose L. (Department: 2624)
Image analysis
Image compression or coding
C382S236000, C382S238000, C375S240130
Reexamination Certificate
active
06317518
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image coding apparatus and, more particularly, to an image coding apparatus for coding an image signal by adaptively switching coding based on an inter-mode (interframe (or interfield) prediction coding) and coding based on an intra-mode (intraframe (or intrafield) coding).
2. Related Background Art
Various coding schemes have been proposed to reduce the data quantity in coding a motion image signal.
According to one of the proposed coding schemes, coding is performed by switching coding based on the intra-mode (intraframe coding) and coding based on the inter-mode (interframe prediction coding).
A motion image can be regarded as a continuous display of independent images along a time axis.
Intraframe coding is a compression coding scheme suitable for an image having a low correlation in the direction of time, e.g., an image exhibiting quick movement, or an image having no correlation in the direction of time, e.g., an image having undergone a scene change. That is, intraframe coding is designed to perform compression coding by using similarities between adjacent pixels.
Interframe prediction coding is a compression coding scheme suitable for an image exhibiting a small movement. That is, interframe prediction coding is based on the fact that the correlation between frames of an image exhibiting a small movement is high in the direction of time. In interframe prediction coding, therefore, compression coding is performed by calculating prediction values of image data to be coded from an adjacent image, calculating differences between the calculated prediction values and the image data to be coded, and coding the calculated differences.
It is known that in a conventional coding apparatus, when an error occurs in data in coding based on the inter-mode, the error generally propagates.
Coding based on the intra-mode is, therefore, forcibly performed at predetermined time intervals (e.g., one sec) to eliminate the influences of errors mixed in data at the predetermined time intervals. That is, refresh processing is performed.
Assume that coding based on the intra-mode is periodically performed for refresh processing, and for example, refresh processing is performed for a high-resolution image or an image exhibiting a low correlation between frames. In this case, since the quantization step for a reduction in data quantity in coding is abruptly coarsened, a deterioration in image quality become conspicuous. In addition, if images like the above images continuously appear, a deterioration in image quality caused by refresh processing occurs at every refresh period, making the deterioration in image quality even more conspicuous.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation, and has as its object to provide an image coding apparatus which executes refresh processing inconspicuously to prevent the propagation of an error in the image-coded data.
In order to achieve the above object, according to an aspect of the present invention, there is provided an image coding apparatus which includes input means for inputting an image signal, coding means for coding the image signal by adaptively switching a first coding mode for performing intraframe coding and a second coding mode for performing interframe coding, and command means for outputting a command to the coding means to forcibly execute the first coding mode, the command means outputting a command at the intervals controlled in accordance with the quantity of coded data generated when the image signal is coded.
In addition, according to another aspect of the present invention, there is provided an image coding apparatus which includes input means for inputting an image signal, detection means for detecting the activity of the image signal input by the input means, coding means for coding the image signal by adaptively switching a first coding mode for performing intraframe coding and a second coding mode for performing interframe coding, and command means for outputting a command to the coding means to forcibly execute the first coding mode, the command means outputting a command at the intervals controlled in accordance with an output from the detection means.
Other objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.
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patent: 5333013 (1994-07-01), Enari et al.
patent: 5351086 (1994-09-01), Park
patent: 5379356 (1995-01-01), Purcell et al.
patent: 5400075 (1995-03-01), Savatier
patent: 5459517 (1995-10-01), Kunitake et al.
Canon Kabushiki Kaisha
Couso Jose L.
Do Anh Hong
Fitzpatrick ,Cella, Harper & Scinto
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