JMSE, Vol. 4, Pages 17: Comparison of Human and Camera Visual Acuity—Setting the Benchmark for Shallow Water Autonomous Imaging Platforms

A comparison was made between the underwater visual acuity of human observers and a high-end stills camera as applied to visual surveys of shallow water coral reefs. The human observers had almost double the visual acuity of the camera, recording a Snellen eye test score of 20/8 at 4.3 m depth against 20/15 for the camera. The human observers had a field of view of 7.8 m (horizontal) by 5.8 m at 4.3 m depth while the camera had a field of view of 4.46 m by 2.98 m, or only one-third of the area observed by the snorkelers. The human observers were therefore able to see a three-times-larger field of view at twice the resolution of the camera. This result comes from the observers actively scanning the scene to put the area of interest in the part of the retina with the greatest resolving power (the fovea), increasing the apparent resolving power of their eyes, against the camera which resolved equally across the image. As a result, in actively identifying targets, humans exceeded the camera, but for more passive observation work they may be closer to the performance of the camera. The implications for autonomous platforms are that to match the human observers for target recognition, platforms will need to operate lower (to increase resolution) and longer (to sample the same area) and so issues such as collision avoidance and navigation will be critical to operationalizing autonomous systems.

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