VIDEO CODING

Pictures are coded using a coding algorithm with a variable parameter QP so that the quality of the coding varies. First (100), a target value T iMOS is specified for a quality measurement parameter. Then, for each picture (or part of a picture) to be coded, one estimates, independently of the other pictures, a value for the variable parameter QP based on a) the target value for that picture area and b) a masking measure C that depends on the picture content of that picture area. The picture is then coded 112 using the estimated value. The masking measure may be compensated 108, 122 to allow for the effect of the coding quality upon the masking effect.