A method is presented to measure the intensity of the blocking artefact in compressed pictures or video frames.
First, a way is devised to artificially introduce pure blocking, which closely resembles the real one subsequent
to JPEG compression. Then a modified no-reference measurement is proposed that requires less computations
than other formerly presented methods, permits to take into account the whole image or frame area, and is
not affected by interlaced video. Some first experiments indicate that the measured values relate closely to the
introduced blockiness effect. The robustness of the metric to the influence of other typical JPEG artefacts is
also checked. Further, the effect on blockiness of some enhancement strategies is measured. Pictures enhanced
with methods introducing the most severe blockiness are found to have the highest value of the proposed metric.
Finally the problem of blockiness measurement in video sequences is addressed. In this case the blocking grid is
no longer regular. In fact, blocks of different size could be used in encoding, and single blocks could be shifted
in referenced (P and B) frames due to motion compensation. A method is devised for grid detection.