Image decoding apparatus and image coding apparatus

An image decoding apparatus including a decoding means that decodes a prediction residual signal, a prediction signal and a filter parameter from coded data and a generating means that generates a prediction residual by dequantizing and inverse transforming the prediction residual signal decoded by the decoding means, to decode image data from the prediction residual and the prediction signal, comprising:

• a filtering means that performs a filtering process by adding weight coefficients to reference pixels that are made up of a pixel to be targeted for the filtering process and pixels in a vicinity of the pixel to be targeted;
• an index calculating means that calculates an amount of variation in a pixel value in the vicinity of the pixel to be targeted for the filtering process, and an index by classifying a magnitude of the amount of variation based on a group of predetermined threshold values;
• and
• a weight coefficient calculating means that calculates the filter parameter, as a weight coefficient, that is determined corresponding to positions of the reference pixels with respect to the pixel to be targeted, wherein
• the weight coefficient calculating means comprises a selecting means that selects one filter parameter from a set of filter parameter, in accordance with the calculated index.

An image decoding apparatus including a decoding means that decodes a prediction residual signal and a prediction signal from coded data and a generating means that generates a prediction residual by dequantizing and inverse transforming the prediction residual signal decoded by the decoding means, to decode image data from the prediction residual and the prediction signal, the image decoding apparatus comprising:

• an index calculating means that calculates an amount of variation in a pixel value in a vicinity of a pixel to be targeted for a filtering process, and an index by classifying a magnitude of the amount of variation based on a group of predetermined threshold values;
• and,
• a filtering means that performs the filtering process on the image data, in accordance with the index calculated by the index calculating means, wherein
• the index calculating means calculates an index based on a magnitude of transform coefficients for the block to be targeted for the filtering process, and a magnitude of differences between the filtering target pixel and pixels in a vicinity of the target pixel.

An image coding apparatus including a decoded image generating means for generating a locally decoded image, comprising:

• a gradient value calculating means that calculates a gradient value in a close vicinity of a certain calculating target pixel on the locally decoded image;
• a learning data calculation storing means that calculates learning data from a value of the pixel to be a calculation target, values of pixels in a vicinity of the pixel and a value of a pixel at a same location as the target pixel of the inputted image and stores the calculated learning data for each gradient value;
• and,
• a filter parameter calculating means that calculates a filter parameter for each gradient value, using learning data for each gradient value stored by the learning data calculation storing means.