Methods and modules for spatial decorrelation and recorrelation are described. A block of data values can be spatially decorrelated in two dimensions efficiently by processing rows of the data values in a particular order such that if the results of spatially decorrelating a first row will be used for column-wise spatial decorrelation of a second row then the data values of the first row are processed in an earlier iteration to that in which the data values of the second row are processed. This allows for highly parallelised processing of the block of data values. Spatial recorrelation can be performed as an inverse process to the spatial decorrelation.