1. An imaging module, comprising: a matrix of detector elements formed on a single semiconductor substrate and configured to output electrical signals in response to optical radiation that is incident on the detector elements; and a filter layer, which is disposed over the detector elements and comprises multiple filter zones overlying different, respective, convex rectangular regions of the matrix and having different, respective passbands, each of the rectangular regions comprising multiple rows and columns of the detector elements, wherein the filter zones and the respective convex regions share a common aspect ratio, while the filter zones comprise at least first and second zones of different, respective, first and second sizes that share the common aspect ratio.