.[.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..]. .Iadd.In one embodiment, a pixel of an
image is filtered according to a filtering methodology. The filtering
methodology includes selecting at least four pixels of successive pixels
according to a position of a pixel to be filtered. The selected at least
four pixels include the pixel to be filtered, at least one of the
selected at least four pixels is in a first block, and three of the
selected at least four pixels are in a second block adjacent to the first
block. The filtering methodology includes at least one comparison. The
comparison compares a determined value and a threshold. The threshold is
based on a quantization information of at least a portion of the image
including the pixel to be filtered, the determined value is based on a
difference value, and the difference value is based on two of the
successive pixels..Iaddend.