1. An apparatus, comprising: a full-reference blocking artifact detector for detecting blocking artifacts in a processed version of a picture based on a blockiness metric, wherein the full-reference blocking artifact detector has at least a first input for receiving the processed version of the picture and a second input for receiving an original version of the picture, and the blockiness metric is determined based on respective local variations in the processed version of the picture and in the original version of the picture, wherein a quantity of blockiness is determined responsive to: a difference between a gradient at a block border in the original version of the picture and a gradient at a co-located block border in the processed version of the picture, a gradient within a block, contiguous to the block border, in the original version of the picture, and a gradient within a co-located block, contiguous to the co-located block border, in the processed version of the picture.