An apparatus includes an array of sub-diffraction limit-sized light receptors formed in a substrate having a light receiving surface. Each receptor is configured to output an n-bit element and to change state based on the absorption of at least one photon (n is an integer >0). The apparatus includes an optical filter structure disposed over the light receiving surface, the structure having an array of filter pixels, each having an associated passband spectral characteristic. A data element obtained from the array of receptors is generated from a combination of a plurality of the n-bit elements output from a plurality of light receptors that underlie filter pixels having at least two different passband spectral characteristics. The filter pixels having at least two different passband spectral characteristics form a gradient filter wherein bandpass regions increase when moving from a central region of the gradient filter towards an edge region.