Image processing apparatus and method, recording medium, and program

An image processing method of an image processing apparatus, said image processing apparatus converting image data coded at a first bit rate into image data coded at a second bit rate, said image processing method comprising:

• a first quantization scale code calculating step for calculating a first quantization scale code required to code said image data at said first bit rate on the basis of said image data coded at said first bit rate;
• a second quantization scale code calculating step for calculating a second quantization scale code obtained by subjecting said first quantization scale code to adaptive quantization according to visual characteristics on the basis of said image data coded at said first bit rate;
• a normalized activity calculating step for calculating a normalized activity on the basis of said first quantization scale code and said second quantization scale code;
• a third quantization scale code calculating step for calculating a third quantization scale code required to code said image data at said second bit rate;
• a fourth quantization scale code calculating step for calculating a fourth quantization scale code obtained by subjecting said third quantization scale code to adaptive quantization according to visual characteristics on the basis of said third quantization scale code and said normalized activity;
• providing a determined quantization scale code from the second quantization scale code and the fourth quantization scale code;
• and
• using the determined quantization scale code to provide image data coded at the second bit rate.

A recording medium on which a computer readable program for controlling an image processing apparatus is recorded, said image processing apparatus converting image data coded at a first bit rate into image data coded at a second bit rate, said program including:

• a first quantization scale code calculation control step for controlling calculation of a first quantization scale code required to code said image data at said first bit rate on the basis of said image data coded at said first bit rate;
• a second quantization scale code calculation control step for controlling calculation of a second quantization scale code obtained by subjecting said first quantization scale code to adaptive quantization according to visual characteristics on the basis of said image data coded at said first bit rate;
• a normalized activity calculation control step for controlling calculation of a normalized activity on the basis of said first quantization scale code and said second quantization scale code;
• a third quantization scale code calculation control step for controlling calculation of a third quantization scale code required to code said image data at said second bit rate;
• a fourth quantization scale code calculation control step for controlling calculation of a fourth quantization scale code obtained by subjecting said third quantization scale code to adaptive quantization according to visual characteristics on the basis of said third quantization scale code and said normalized activity;
• providing a determined quantization scale code from the second quantization scale code and the fourth quantization scale code;
• and
• using the determined quantization scale code to provide image data coded at the second bit rate.

A transcoder apparatus for converting image data coded at a first bit rate into image data coded at a second bit rate, said program comprising:

• a normalized activity calculating unit, which controls calculation of a first quantization scale code required to code said image data at said first bit rate on the basis of said image data coded at said first bit rate, calculation of a second quantization scale code obtained by subjecting said first quantization scale code to adaptive quantization according to visual characteristics on the basis of said image data coded at said first bit rate, and calculation of a normalized activity on the basis of said first quantization scale code and said second quantization scale code;
• a code amount control unit, in operative communication with the normalized activity calculating unit, which controls calculation of a third quantization scale code required to code said image data at said second bit rate, and calculation of a fourth quantization scale code obtained by subjecting said third quantization scale code to adaptive quantization according to visual characteristics on the basis of said third quantization scale code and said normalized activity, wherein the code amount control unit provides a determined quantization scale code from the second quantization scale code and the fourth quantization scale code;
• and
• means for using the determined quantization scale code to provide image data coded at the second bit rate.