Image coding apparatus

An image coding apparatus which encodes multi-level image data on image density at pixels, the apparatus comprising:

• a block extractor which extracts first blocks and second blocks based on image data, each of the first blocks comprising a plurality of pixels to be encoded, each of the second blocks including the plurality of pixels in one of the first blocks;
• a calculator which calculates feature quantities based on image data of all the pixels included in each of the second block extracted by said block extractor;
• and
• an encoder which encodes image data of the pixels in one of the first blocks according to correlation of the image data with the feature quantities of one of the second blocks including said one of the first blocks calculated by said calculator;
• wherein said block extractor extracts the first blocks over an entire image area by shifting the first block sequentially in the entire image area and when one of the second blocks includes pixels not existing in the image area, it adds image data derived from image data of pixels existing in the image area to the pixels not existing in the image area.

An image coding method for encoding multi-level image data which expresses image density at a pixel, the method comprising the steps of:

• extracting a first block and a second block in image data, the first block comprising a plurality of pixels to be encoded, the second block including the plurality of pixels in the first block;
• calculating feature quantities based on image data of all the pixels included in the second block;
• and
• encoding image data of the pixels in the first block according to correlation of the image data in the first block with the feature quantities calculated on the second block;
• wherein said extracting, calculating and encoding steps are repeated over an entire image area.