In this work we present three spatial filters that perform isotropic edge enhancement or recognition. Their design is based on first determining a convolution kernel that performs the desired operation and then, by Fourier transforming, obtaining the filter function. To the authors' best knowledge, these filters have not been proposed in the past. We present numerical simulations that corroborate our proposal. For the optical implementation of one of the proposed filters, a holographic technique capable of representing complex transmittances is required. In this case, the filter is simulated using a double-phase holographic code.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.