Image encoding apparatus and image decoding apparatus

Abstract

A coefficient conversion unit obtains a conversion coefficient for each image region by performing coefficient conversion for each image region. A luminance distribution extraction unit generates luminance distribution information indicating a luminance of each image region. A correction coefficient determination unit determines a correction coefficient based on the luminance distribution information for each image region. A quantization width correction unit obtains a corrected quantization width for each image region by correcting a quantization width with use of a correction coefficient of an image region for each image region. A scalar quantization unit obtains a quantized conversion coefficient for each image region by quantizing a conversion coefficient of an image region with use of a corrected quantization width for each image region. An entropy encoding unit obtains an encoded conversion coefficient for each image region by performing entropy encoding on a quantized conversion coefficient for each image region.

1 - 24 . (canceled) 
     
     
         25 . An image encoding apparatus comprising:
 processing circuitry   to obtain a conversion coefficient by performing coefficient conversion on an image for each image region that is a part of the image,   to determine a correction coefficient to be used for correction of a conversion coefficient of an image region, based on a luminance of an image region for each image region,   to obtain a corrected conversion coefficient for each image region by correcting a conversion coefficient of an image region with use of a correction coefficient of an image region for each image region,   to obtain an encoded conversion coefficient by performing entropy encoding on corrected conversion coefficients, and   to obtain quantized conversion coefficients by quantizing encoded conversion coefficients.   
     
     
         26 . The image encoding apparatus according to  claim 25 , wherein
 a corrected conversion coefficient is smaller as the image region is brighter and larger as the image region is darker.   
     
     
         27 . The image encoding apparatus according to  claim 26 , wherein
 each correction coefficient is a value to divide a conversion coefficient of the image region, and is larger as the image region is brighter and smaller as the image region is darker.   
     
     
         28 . The image encoding apparatus according to  claim 27 , wherein
 each correction coefficient is proportional to a luminance of the image region.   
     
     
         29 . The image encoding apparatus according to  claim 27 , wherein
 each correction coefficient is proportional to a one-half power of a luminance of the image region.   
     
     
         30 . The image encoding apparatus according to  claim 25 , wherein the processing circuitry
 obtains discrete wavelet conversion coefficients of the image by performing discrete wavelet conversion on the image,   generates luminance distribution information indicating a luminance of each image region with use of a discrete wavelet conversion coefficient of the image as a luminance of each image region, and   determines a correction coefficient for each image region with use of the luminance distribution information.   
     
     
         31 . An image decoding apparatus comprising:
 processing circuitry   to determine a correction coefficient to be used for correction of a conversion coefficient of an image region, based on a luminance of an image region for each image region that is a part of an image,   to obtain decoded conversion coefficients of the image by performing entropy decoding on quantized conversion coefficients,   to obtain conversion coefficients of the image by inversely correcting a decoded conversion coefficient of the image with use of a correction coefficient of an image region for each image region, and   to perform coefficient inverse conversion on conversion coefficients of the image.   
     
     
         32 . An image encoding apparatus comprising:
 processing circuitry   to determine a correction coefficient to be used for correction of a quantization width, based on a luminance of an image region for each image region that is a part of an image,   to obtain a discrete cosine transformation coefficient for each image region by performing discrete cosine transformation for each image region,   to generate luminance distribution information indicating a luminance of each image region with use of a direct current component included in a discrete cosine transformation coefficient of an image region for each image region as a luminance of an image region, and   to obtain inversely quantized luminance distribution information by performing quantization on the luminance distribution information and performing inverse quantization on quantized luminance distribution information, wherein   the processing circuitry determines a correction coefficient for each image region with use of inversely quantized luminance distribution information.   
     
     
         33 . An image encoding apparatus comprising:
 processing circuitry   to determine a correction coefficient to be used for correction of a conversion coefficient of an image region, based on a luminance of an image region for each image region that is a part of an image,   to obtain discrete wavelet conversion coefficients of the image by performing discrete wavelet conversion on the image,   to generate luminance distribution information indicating a luminance of each image region with use of a discrete wavelet conversion coefficient of the image as a luminance of each image region, and   to obtain inversely quantized luminance distribution information by performing quantization on the luminance distribution information and performing inverse quantization on quantized luminance distribution information, wherein   the processing circuitry determines a correction coefficient for each image region with use of inversely quantized luminance distribution information.