Reef rubble representsthe broken components of the coraland reefstructure which could be in the form of dead,broken or other fragmented coral.The process to estimate the distribution of reef rubble is currently done manually and thus takesa long timeto completeand is laborious. This paper presentsan image-processing-basedmethod to estimate the distribution of reef rubbles in a coral reef environmentfrom a still image. The method is basically a series of image processing steps includingimage complement, image binarization, edgedetection, smoothing by Weiner filter and followed by erosion and dilation process.The experimentalresults showedthat the system wasable to roughly estimate the distribution of reef rubble.