Image processing apparatus and method, recording medium, and program

Abstract

A normalized activity calculating unit calculates a normalized activity that is calculated from luminescence component pixel values of an original image on the basis of information from an information buffer such as bit rate, an amount of bits generated in each frame, and an amount of bits generated and quantization step size in each macroblock. The normalized activity calculating unit then outputs the normalized activity to a code amount control unit. The code amount control unit calculates a quantization scale code corresponding to a target bit rate which quantization scale code matches visual characteristics, using the normalized activity inputted from the normalized activity calculating unit, and then outputs the quantization scale code to a quantizing unit. The quantizing unit quantizes discrete cosine transform coefficients inputted from a band limiting unit on the basis of the quantization scale code inputted to the quantizing unit.

1 . An image processing apparatus for converting image data coded at a first bit rate into image data coded at a second bit rate, the image processing apparatus comprising: 
 a first quantization scale code calculating unit for calculating a first quantization scale code required to code the image data at the first bit rate on the basis of the image data coded at the first bit rate;    a second quantization scale code calculating unit for calculating a second quantization scale code obtained by subjecting the first quantization scale code to adaptive quantization on the basis of the image data coded at the first bit rate;    a normalized activity calculating unit for calculating a normalized activity on the basis of the first quantization scale code and the second quantization scale code;    a decoding unit for decoding image data coded at the first bit rate;    a band limiting unit for performing a band limiting in the decoded image data at the first bit rate;    a third quantization scale code calculating unit for calculating a third quantization scale code required to code the image data at the second bit rate; and    a fourth quantization scale code calculating unit for calculating a fourth quantization scale code obtained by the basis of the third quantization scale code and the normalized activity; and    an encoding unit for encoding the band limited image data at the first bit rate based on the fourth quantization scale code.    
     
     
         2 . The image processing apparatus according to  claim 1 , wherein the band limiting unit cuts high-frequency component coefficients in a horizontal direction in the decoded image data.  
     
     
         3 . The image processing apparatus according to  claim 1 , wherein the coded image data is image data compressed by an MPEG method.  
     
     
         4 . The image processing apparatus according to  claim 1 , wherein the image data coded at the first bit rate includes an amount of codes of the image data itself, an amount of bits generated in each frame, an amount of bits generated in each macroblock, and a quantization step size in each macroblock.  
     
     
         5 . The image processing apparatus according to  claim 4 , wherein the first quantization scale code calculating unit calculates the first quantization scale code on the basis of the amount of codes, the amount of bits generated in each frame, and the amount of bits generated in each macroblock.  
     
     
         6 . The image processing apparatus according to  claim 1 , wherein the normalized activity calculating unit calculates the normalized activity by dividing the second quantization scale code by the first quantization scale code.  
     
     
         7 . An image processing method for converting image data coded at a first bit rate into image data coded at a second bit rate, the image processing method comprising: 
 calculating a first quantization scale code required to code the image data at the first bit rate on the basis of the image data coded at the first bit rate;    calculating a second quantization scale code obtained by subjecting the first quantization scale code to adaptive quantization on the basis of the image data coded at the first bit rate;    calculating a normalized activity on the basis of the first quantization scale code and the second quantization scale code;    decoding image data coded at the first bit rate;    performing a band limiting in the decoded image data at the first bit rate;    calculating a third quantization scale code required to code the image data at the second bit rate;    calculating a fourth quantization scale code obtained by the basis of the third quantization scale code and the normalized activity; and    encoding the band limited image data at the first bit rate based on the fourth quantization scale code.    
     
     
         8 . The image processing method according to  claim 7 , wherein the band limiting cuts high-frequency component coefficients in a horizontal direction in the decoded image data.  
     
     
         9 . The image processing method according to  claim 7 , wherein the coded image data is image data compressed by an MPEG method.  
     
     
         10 . The image processing method according to  claim 7 , wherein the image data coded at the first bit rate includes an amount of codes of the image data itself, an amount of bits generated in each frame, an amount of bits generated in each macroblock, and a quantization step size in each macroblock.  
     
     
         11 . The image processing method according to  claim 10 , wherein the first quantization scale code calculating calculates the first quantization scale code on the basis of the amount of codes, the amount of bits generated in each frame, and the amount of bits generated in each macroblock.  
     
     
         12 . The image processing method according to  claim 7 , wherein the normalized activity calculating calculates the normalized activity by dividing the second quantization scale code by the first quantization scale code.  
     
     
         13 . A computer program product, for converting image data coded at a first bit rate into image data coded at a second bit rate, the computer program product stored on a computer readable medium and adapted to perform operations comprising: 
 calculating a first quantization scale code required to code the image data at the first bit rate on the basis of the image data coded at the first bit rate;    calculating a second quantization scale code obtained by subjecting the first quantization scale code to adaptive quantization on the basis of the image data coded at the first bit rate;    calculating a normalized activity on the basis of the first quantization scale code and the second quantization scale code;    decoding image data coded at the first bit rate;    performing a band limiting in the decoded image data at the first bit rate;    calculating a third quantization scale code required to code the image data at the second bit rate;    calculating a fourth quantization scale code obtained by the basis of the third quantization scale code and the normalized activity; and    encoding the band limited image data at the first bit rate based on the fourth quantization scale code.    
     
     
         14 . The computer program product according to  claim 13 , wherein the band limiting cuts high-frequency component coefficients in a horizontal direction in the decoded image data.  
     
     
         15 . The computer program product according to  claim 13 , wherein the coded image data is image data compressed by an MPEG method.  
     
     
         16 . The computer program product according to  claim 13 , wherein the image data coded at the first bit rate includes an amount of codes of the image data itself, an amount of bits generated in each frame, an amount of bits generated in each macroblock, and a quantization step size in each macroblock.  
     
     
         17 . The computer program product according to  claim 16 , wherein the first quantization scale code calculating calculates the first quantization scale code on the basis of the amount of codes, the amount of bits generated in each frame, and the amount of bits generated in each macroblock.  
     
     
         18 . The computer program product according to  claim 13 , wherein the normalized activity calculating calculates the normalized activity by dividing the second quantization scale code by the first quantization scale code.