Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-08-11
2001-08-14
Britton, Howard (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240040, C375S240080, C375S240100, C375S240140
Reexamination Certificate
active
06275530
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an image coding apparatus and an image coding method, an image decoding apparatus and an image decoding method, a quantization control method and an inverse quantization control method, and a data recording medium and, more particularly, to coding and decoding processes in which image signals are recorded or transmitted with fewer bits and without degrading an image quality, and a recording medium which stores a program for implementing the coding process or decoding process.
BACKGROUND ART
Conventionally, there are many types of methods of coding image signals including DPCM (Differential Pulse Code Modulation) or DCT (Discrete Cosine Transform) and so forth. In particular, the latter is well known for high efficiency in coding of natural images such as a scenery and adopted in an international standard on multimedia coding such as JPEG (Joint Photographic Coding Experts Group) or MPEG (Moving Picture Experts Group).
Meanwhile, with recent improvement of computer technologies and image processing techniques, composite images resulting from compositing plural images using chroma key processing or computer graphics have been widely used. The composite image includes an edge whose pixel value changes sharply and has characteristics which significantly differ from those of conventional natural image, e.g., high spatial resolution.
In coding of the above-described composite image, if image signals corresponding to images to be composited are coded together with signals indicating a composite ratio for each image, decoding side can perform decoding process for a desired image among plural images constituting a composite image as well as decoding process for the composite image itself. In this case, the resultant composite image is effective in interactive multimedia (interactive processing to plural images related to each other and provided simultaneously), but a special coding process for coding the signals indicating a composite ratio is required.
Signals indicating this ratio of composition represent a degree of transparency of a background with respect to a foreground when a prescribed image and the other image are assumed to be a foreground and a background, respectively, for formation of a composite image. The signals indicating composite ratio are set for each image and referred to as transparency signals to distinguish them from pixel value signals used for color display of images.
More specifically, transparency signals of individual images (objects) constituting a composite image to be displayed on a display screen have a characteristic in which values thereof are almost equal inside the objects and vary greatly around the boundaries thereof, which characteristic is different from that of pixel value signals for displaying natural images; in a prior art coding method, however, coding is performed to transparency signals using the coding method for pixel value signals indicating a pixel value of an image and the same parameters for coding.
In addition, in coding of image signals, image signals of higher image quality require more amount of code to be used for the coding process. In the decoding side, since one image (object) is regenerated by decoding pixel value signals and transparency signals together, an image quality of a regenerated image is degraded if an image quality of a regenerated image formed by one type of signals is high image quality and that of the regenerated image formed by the other type of signals is low.
When performing data coding process, in general, high coding efficiency is not obtained unless a coding method corresponding to a quality of data to be coded is used. However, in the prior art coding method, the coding method and parameters used in coding process for pixel value signals are also used in coding process for transparency signals, which causes problems including an unnecessarily high image quality of transparency signals in comparison with that of pixel value signals and the coding method being not suitable for coding process for transparency signals, resulting in that an enormous amount of code is required for coding process for transparency signals.
The present invention is introduced to resolve the above-described problems, and its object is to provide an image coding apparatus and an image coding method capable of optimally controlling a coding method and a coding parameter for transparency signals according to a coding parameter for pixel value signals or independently of the coding parameter for pixel value signals.
It is another object of the present invention to provide an image decoding apparatus and an image decoding method capable of properly decoding coded transparency signals resulting from optimal coding process for transparency signals in accordance with the coding parameter for pixel value signals or optimal coding process for transparency signals independently of the coding parameter for pixel value signals.
It is still another aspect of the present invention to provide a quantization control method which is suitable for an optimal coding process for transparency signals according to the coding parameter of pixel value signals and an inverse quantization control method which is suitable for a decoding process for the coded transparency signals acquired from the coding process.
It is further object of the present invention to provide a data recording medium which stores a program for implementing in a computer an optimal coding process for transparency signals on the basis of the coding parameter of pixel value signals or independently of the coding parameter of pixel value signals, a decoding process for the coded transparency signals resulting from the coding process, and a quantization process which is suitable for the coding process and an inverse quantization process which is suitable for the decoding process.
DISCLOSURE OF THE INVENTION
According to the present invention, an image coding apparatus which receives pixel value signals indicating a pixel value of an image and transparency signals indicating a composite ratio of pixel value for compositing the image and another image as input signals, and performs coding to the pixel value signals and the transparency signals, and the image coding apparatus comprises: a pixel value encoder for coding the pixel value signals to output coded pixel value signals, and outputting a pixel value coding parameter indicating control information on coding process for the pixel value signals; a coding controller for generating a transparency coding parameter indicating control information on coding process for the transparency signals on the basis of the pixel value coding parameter, and outputting transparency coding control signals indicating a relation between the pixel value coding parameter and the transparency coding parameter; and a transparency encoder for coding the transparency signals in accordance with the transparency coding parameter to output coded transparency signals.
In accordance with the image coding apparatus constructed above, a transparency coding parameter for controlling coding process for transparency signals is generated on the basis of the pixel value coding parameter for controlling coding process for the pixel value signals, and coding process is performed to transparency signals on the basis of the transparency coding parameter; therefore, according to an image quality obtained from the pixel value signals of the individual images of a composite image, it is possible to control an image quality obtained from the transparency signals of the individual images. Thereby, redundant information of the coded transparency signals resulting from coding the transparency signals can be reduced without degrading an image quality of each image, enabling recording or transmission of image signals including pixel value signals and transparency signals with fewer bits and with no degradation of an image quality.
According to the present invention, in the image coding apparatus of the transparency encoder includes: a st
Kadono Shinya
Nishi Takahiro
Britton Howard
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
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