Extending the depth of focus using digital image filtering

Two types of image processing methods capable of forming a composite image from a set of image slices which have in-focus as well as out-of-focus segments are discussed. The first type is based on space domain operations and has been discussed in the literature. The second type, to be introduced, is based on the intuitive concept that the spectral energy distribution of a focused object is biased towards lower frequencies after blurring. This approach requires digital image filtering in the spatial frequency domain. A comparison among methods of both types is made using a quantitative uÌ delity criterion.