1. A method of processing data comprised in a digital input image, said method comprising the steps of: calculating a first discrete transform ( 31 ) of a first data set ( 13 ), calculating a second discrete transform ( 32 ) of a second data set ( 14 ) adjacent to the first set, calculating an overall discrete transform ( 33 ) of a data set ( 15 ) corresponding to the concatenation ( 30 ) of the first and the second set, determining ( 34 ) a predicted maximum frequency ( 37 ) on the basis of the transformed resulting from the first and the second transform ( 13 ′, 14 ′), said processing method being characterized in that it further comprises a step of determining ( 35 ) a real maximum frequency ( 38 ) on the basis of the transformed data ( 15 ′) resulting from the overall transform, and a step of detecting ( 36 ) a grid ( 39 ) by means of a comparison between the real maximum frequency and the predicted maximum frequency for a portion of the digital input image.