1. An imaging system comprising: an array of elements switchable between two states spatially related to a two-dimensional array of pixel positions; a first site for each of the pixel positions to measure light received by said system to provide values of pixels comprising first image data; a second site for each of the pixel positions to measure light received by said system to provide values of pixels comprising second image data, in which said first site and said second sites for each of the pixel positions operate independently for measuring light received over a common integration time; and wherein for each of said pixel positions when one or more of said switchable elements which are spatially related with the pixel position are switched to a first of said states said first site for the pixel position measures light received by said system, and when one or more of said switchable elements which are spatially related with the pixel position are switched to a second of said states said second site for the pixel position measures light received by said system, wherein said switchable elements are operable to switch between said states faster than the integration time.