Image coder and image coding method, and image decoder and image decoding method, and quantization control method and inverse quantization control method, and data recording medium

A method of coding images in which not only pixel value signals indicating a pixel value of an image but transparency signals indicating a composite ratio of pixel value for compositing the image and another image are coded, said method comprising the steps of:

• coding the pixel value signals on the basis of a pixel value coding parameter indicating control information on coding process for the pixel value signals;
• deciding a transparency coding parameter indicating control information on coding process for the transparency signals on the basis of the pixel value coding parameter;
• and
• coding the transparency signals on the basis of the transparency coding parameter.

An image decoding apparatus which receives, as input signals, not only coded pixel value signals resulting from coding pixel value signals indicating a pixel value of an image and coded transparency signals resulting from coding transparency signals indicating a composite ratio of pixel value for compositing the image and another image, but a pixel value coding parameter indicating control information on coding process for the pixel value signals and transparency coding control signals indicating a relation between the pixel value coding parameter and a transparency coding parameter indicating control information on coding process for the transparency signals, and performs decoding to the coded pixel value signals and the coded transparency signals, said apparatus comprising:

• a pixel value decoder for performing decoding to the coded pixel value signals in accordance with the pixel value coding parameter and outputting decoded pixel value signals;
• a decoding controller for generating the transparency coding parameter on the basis of the pixel value coding parameter and the transparency coding control signals to output the transparency coding parameter;
• and
• a transparency decoder for decoding the coded transparency signals in accordance with the transparency coding parameter to output decoded transparency signals.

A method of decoding images in which coded pixel value signals resulting from coding pixel value signals indicating a pixel value of an image and coded transparency signals resulting from coding transparency signals indicating a composite ratio of pixel value for compositing the image and another image are decoded, said method comprising the steps of:

• generating a transparency coding parameter indicating control information on coding process for the coded transparency signals on the basis of a pixel value coding parameter indicating control information on coding process for the coded pixel value signals and transparency coding control signals indicating a relation between the pixel value coding parameter and the transparency coding parameter;
• decoding the coded pixel value signals in accordance with the pixel value coding parameter;
• and
• decoding the coded transparency signals in accordance with the transparency coding parameter.

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, said image coding apparatus comprising:

• 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 transparency encoder for coding the transparency signals to output coded transparency signals, and outputting a transparency coding parameter indicating control information on coding process for the transparency signals;
• and
• a parameter encoder for performing coding process to signals obtained on the basis of the pixel value coding parameter and the transparency coding parameter, to output coded parameter signals corresponding to the two coding parameters.

An image decoding apparatus which receives, as input signals, not only coded pixel value signals resulting from coding pixel value signals indicating a pixel value of an image and coded transparency signals resulting from coding transparency signals indicating a composite ratio of pixel value for compositing the image and another image, but coded parameter signals resulting from coding the signals obtained from two types of parameters, that is, a pixel value coding parameter indicating control information on coding process for the pixel value signals and a transparency coding parameter indicating control information on coding process for the transparency signals, and performs decoding to the coded pixel value signals and the coded transparency signals, said apparatus comprising:

• a parameter decoder for decoding the coded parameter signals to regenerate the pixel value coding parameter and the transparency coding parameter;
• a pixel value decoder for decoding the coded pixel value signals in accordance with the pixel value coding parameter to output decoded pixel value signals;
• and
• a transparency decoder for decoding the coded transparency signals in accordance with the transparency coding parameter to output decoded transparency signals.