A transmissive and/or reflective optical filter can receive input light, which can emanate from objects traveling along paths past the filter, e.g. from biological cells, viruses, colored spots or other markings on documents, and so forth. In response, the filter can provide output light in accordance with a combined transmission function that is approximately equal to a superposition or scaled superposition of a set of simpler transmission functions. The set can include two or more non-uniform transmission functions, a subset of which can be different from each other and positioned relative to each other so that the output light has time variation in accordance with each of the functions in the subset. The subset could include, for example, a random function and a periodic function, a chirp function and a periodic function, or any other suitable combination of two or more simpler functions.