The imaging of underwater objects illuminated by artificial light has been of long-standing interest to investigators working in oceanographic environments. Pulsed lasers together with range-gated technology have been widely used for underwater optical imaging applications. In order to describe the formation of underwater range-gated images, a pulsed laser underwater imaging model based on pulse spatial and temporal broadening is proposed. Experiments based on a self-assembled laser range-gated imaging system were implemented in our laboratory. Results show good agreements between experiments and simulations. Both results also confirm higher image contrast toward the tail region of the target-reflected light. Furthermore, experiments on underwater image blur and restoration are also implemented and show good image recovery results. The modulation transfer function-based restoration mechanism also implies a way to eliminate the blur effect caused by light forward scattering.
In this paper, we propose a method to deduce the dynamic modulation transfer function (DMTF) of a space-variant sampling retina-like sensor and demonstrate its utilization in the forward motion imaging process. With the analysis of sampling and the motion imaging property of the sensor, DMTF has been derived. Next, the performance of DMTF between a retina-like sensor and a rectilinear sensor is compared, and the results show that the degradation of DMTF in forward motion is less than that of a rectilinear sensor. Then, the output images are obtained through simulation based on DMTF, and they are compared with that obtained from a CMOS camera with the same forward motion conditions. The Pearson correlation coefficients between the two kinds of images are all larger than 0.85. Thus, the effectiveness of DMTF is shown.
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