Imaging apparatus includes an image sensor, which is adapted to generate an input image in response to optical radiation. A processing engine is configured to apply a digital filter, having a kernel width greater than five pixels, to the input image to generate a filtered image. An optical assembly is arranged to focus the optical radiation onto the image sensor with a point spread function such that no more than a first threshold percentage of energy emitted from a point object and focused by the optical assembly falls within a first region of the image sensor having a first width five times the pitch of the image sensor, while at least a second threshold percentage of the energy emitted from the point object and focused by the optical assembly falls within a second region, which contains the first region and has a second width corresponding to the kernel width.