To provide an image data filtering method and an image data filtering apparatus for reducing blocking effect and ringing noise.

It is preferable that, a signal adaptation filtering method for reducing blocking effect and ringing noise in the image data, when one frame contains blocks of a predetermined size; if the frame is an intra frame when a bit stream image data is disassembled to be inverse quantized, it includes a step to generate the blocking information for reducing the blocking effect and the ringing information for reducing the ringing noise from the coefficient of predetermined pixels in the upper boundary region and the left-side boundary region of a data block and a step to filter the inverse quantized image data and subjected to inverse discrete-cosine transformation for the block adaptively, according to the generated blocking information and the ringing information.