Patent ID: 7227901

Claim:
A method of filtering samples to minimise coding artifacts introduced at a block boundary in a block-based video encoder, the method having the steps of: (a) checking content activity on every line of samples said block boundary; (b) determining whether the filtering process will modify the sample values on the line of samples based on content activity thresholds, said content activity thresholds being dependent on an average quantization parameter and a selected filter offset parameter; (c) determining whether a block on either side of the block boundary was coded using either intra or inter prediction; (d) providing a pair of filter modes, i) the first filter mode, a strong filtering mode consisting of a selection of a 3-tap filter sub-mode and an alternative 5-tap filter sub-mode with the selection between these two sub-modes made separately on each side of the block boundary based on the sample values on each line of samples across said block boundary, ii) the second filter mode, a non-recursive default filtering mode; and (e) selecting one of the pair of filter modes for filtering the samples, wherein said content-dependent activity checks include a pair of activity threshold values, ALPHA (α) and BETA (β), to determine whether sample values will be modified, and where the values of said activity thresholds are determined based on a pair of indices that are used to access the tables of these parameter values, these indices being calculated using the average quantization parameter, QP av , used in coding the two blocks that neighbour the block boundary, as well as a pair of encoder-selected offset parameters that can be transmitted in a slice header or other high-level syntax structures of a video bitstream.