A method of k*k subsampling, where k is an integer greater than one, a full frame readout on a plurality of pixels arranged in rows and columns, each pixel belonging to one of at least two sets, a first set configured to sense a first value of an image parameter and a second set configured to sense a second value of the image parameter, the method including sampling signals of k pixels of at least one set in a first row to output subsampled signals, converting the subsampled signals into digital signals having a lower resolution than the full frame readout, repeating sampling and converting for k rows, and adding digital signals for the first to kth rows within the at least one set.