An image processor is provided which simplifies filter processing and increases the speed when an image is decoded, and is suitable for realizing effective screen effect.In deblocking filter processing, as to a pixel array intersecting a boundary between adjacent blocks, pixel values v.sub.2' to v.sub.7' after filtering are computed by filter arithmetic equations as shown below v.sub.2'=(v.sub.2+v.sub.5)/2+(v.sub.2-v.sub.5)/4 v.sub.3'=(v.sub.3+v.sub.5)/2+(v.sub.3-v.sub.5)/8 v.sub.4'=(v.sub.4+v.sub.5)/2 v.sub.5'=(v.sub.5+v.sub.4)/2+(v.sub.5-v.sub.4)/8 v.sub.6'=(v.sub.6+v.sub.4)/2+(v.sub.6-v.sub.4)/4 v.sub.7'=(v.sub.7-(v.sub.7-v.sub.4)/8.