Abstract: ：This paper briefly introduced the experimental environment of Epinephelus malabaricus’s image acquisition, brief description of the setting of three kinds of light intensities, also introduced the steps to acquisition images by Matlab. Described the steps that how to use the gray histogram concavity analysis, OTSU threshold selection method, iterative threshold selection method, maximum entropy selection method to segment images which obtained under different light intensities. Finally, the results were analyzed and discussed. The results shown as follows: light intensity had different influence on the results of the image segmentation, iterative threshold selection method could separate the fish body from the background better and kept the fish body characteristics with the maximum retention.

Key words: light intensity, Epinephelus malabaricus, image segmentation