Interpretation of high resolution electron microscope (HREM) images of small hydroxyapatite (OHAp) crystals with image processing using Fourier filtration techniques has been performed. The effects of digitizing filter parameters in relation to the extent of possible artefacts -like crystal bleeding -which limit the correct image interpretation have been tested. Image processing for OHAp crystallites was applied in two different cases : (i) crystal inhomogeneities (void boundaries) where image provides a good test for the extension of the bleeding in reconstructed images; (ii) beam-induced domains with different crystal structure (or different orientation) than the OHAp matrix where processing provides a test on the precise location and contrast enhancement of those secondary structures.