Image encoding apparatus and image encoding method

An image encoding apparatus comprising:

• input means arranged to input image data;
• first compression encoding means arranged to execute compression encoding on the image data input by said input means by a first encoding method including an orthogonal transform process where the image data is transformed into frequency components and a quantization process where the frequency components obtained by the orthogonal transform process are quantized;
• second compression encoding means arranged to execute compression encoding on the image data input by said input means by a second encoding method including a predictive encoding process where a differential value between a reference pixel data and a target pixel data in the image data is encoded by a variable-length encoding;
• correlation detection means arranged to detect a degree of correlation between pixels in the image data input by said input means on the basis of a result of the compression encoding by said second compression encoding means;
• and
• encode parameter determination means arranged to determine an encode parameter for the quantization process of said first compression encoding means according to the degree of correlation detected by said correlation detection means.

An image encoding method comprising:

• an input step of inputting image data;
• a first compression encoding step of executing compression encoding on the image data input in said input step by a first encoding method including an orthogonal transform process where the image data is transformed into frequency components;
• a second compression encoding step of executing compression encoding on the image data input in said input step by a second encoding method including a predictive encoding process where a differential value between a reference pixel data and a target pixel data in the image data is encoded by a variable-length encoding;
• a correlation detection step of detecting a degree of correlation between pixels in the image data input in said input step on the basis of a result of the compression encoding in said first compression encoding step;
• and
• an encode parameter determination step of determining an encode parameter for the variable-length encoding of said second compression encoding step according to the degree of correlation detected in said correlation detection step.

An image encoding method comprising:

• an input step of inputting image data;
• a first compression encoding step of executing compression encoding on the image data input in said input step by a first encoding method including an orthogonal transform process where the image data is transformed into frequency components and a quantization process where the frequency components obtained by the orthogonal transform process are quantized;
• a second compression encoding step of executing compression encoding on the image data input in said input step by a second encoding method including a predictive encoding process where a differential value between a reference pixel data and a target pixel data in the image data is encoded by a variable-length encoding;
• a correlation detection step of detecting a degree of correlation between pixels in the image data input in said input step on the basis of a result of the compression encoding in said second compression encoding step;
• and
• an encode parameter determination step of determining an encode parameter for the quantization process of said first compression encoding step according to the degree of correlation detected in said correlation detection step.