Imaging apparatus (2000, 2100, 2200) includes a photosensitive medium (2004, 2204) and an array of pixel circuits (302), which are arranged in a regular grid on a semiconductor substrate (2002) and define respective pixels (2006, 2106) of the apparatus. Pixel electrodes (2012, 2112, 2212) are connected respectively to the pixel circuits in the array and coupled to read out photocharge from respective areas of the photosensitive medium to the pixel circuits. The pixel electrodes in a peripheral region of the array are spatially offset, relative to the regular grid, in respective directions away from a center of the array.