Image coding apparatus using pixel values from at least three reference pixels

An image coding apparatus for successively coding, block by block, each block comprising a prescribed number of pixels, pixel values constituting an image signal on the basis of pixel values of plural peripheral pixels positioned in the vicinity of a coding target pixel, comprising:

• blocking means for blocking an image signal comprising plural pixels into blocks, each block having a square form and comprising N×N pixels;
• pixel value replacing means for replacing a pixel value of an uncoded pixel not yet subjected to coding among plural peripheral pixels positioned in the vicinity of the coding target pixel, said peripheral pixels including at least three lines of pixels and the target pixel is in the third line, with a replacement pixel value that is obtained on the basis of a pixel value of a coded pixel previously subjected to coding among the plural peripheral pixels;
• wherein the pixel value replacing means employs, as the replacement pixel value of the uncoded pixel, a pixel value of a coded pixel which is positioned at the shortest distance from the uncoded pixel and on the same horizontal scanning line among said three lines of pixels;
• and
• coding means for performing, block by block, a coding process in which the respective pixel values are successively coded on the basis of the pixel value of the coded pixel and the replacement pixel value of the uncoded pixel among the peripheral pixels, and outputting an coded image signal corresponding to each block;
• wherein the coding means selects a probability table corresponding to a code for arithmetically coding the pixel value of the coding target pixel, on the basis of the pixel values and the replacement pixel values of the peripheral pixels corresponding to the coding target pixel, and performs an arithmetic coding process for the coding target pixel on the basis of the selected probability table.