Image decoding apparatus and image decoding method

An image decoding apparatus comprising:

• circuitry configured to
• extract coded image data and additional information on a scaling amount of the Max-shift method from a bit stream coded by using wavelet transformation;
• generate quantized image data constituted of a plurality of quantized wavelet coefficients by decoding said coded image data;
• generate an ROI (Region Of Interest) mask corresponding to a decomposition level of said quantized image data, by determining whether each of said plurality of quantized wavelet coefficients is associated with an ROI or a non-ROI in an original image on the basis of said scaling amount;
• generate first image data constituted of a plurality of wavelet coefficients by performing inverse quantization on said quantized image data after being scaled down on the basis of said scaling amount;
• generate second image data having a specified decomposition level by performing inverse wavelet transformation on said first image data;
• generate a restored ROI mask having the same decomposition level as that of said second image data by performing a predetermined mask restoration process on said ROI mask once or a plurality of times;
• generate masked image data by applying said restored ROI mask to said second image data;
• and
• generate decoded image data by performing said inverse wavelet transformation on said masked image data until a decomposition level becomes zero.