US Patent RE41909 Method of determining a pixel value

A method and apparatus to remove a block effect and a ring effect appearing in a compression-coded image is disclosed. The present invention is especially applicable to an image compression-coded at a low bit rate. In particular, the present invention includes a variety of masks for the removal of the block/ring effect. Thus, one mask is select for a pixel to be filtered. Moreover, candidate pixels to be averaged with the pixel to be filtered is selected from the pixels of the selected mask to better maintain the details of the image, and a weight is applied to improve the calculation speed of the averaging operation. More particularly, the masks according to the present invention have longer tabs toward adjacent blocks at boundaries of the given block to remove the block and ring effect. In the method, a value of a pixel of an image is determined according to a filtering methodology. The filtering methodology includes selecting a filtering mask including eight pixels based on a position of the pixel of the image, and applying an averaging operation to a number of the eight pixels included in the filtering mask.