Video Framerate, Resolution and Grayscale Tradeoffs for Undersea Telemanipulator Control

Summary form only given. The high costs associated with a human diver working at ocean depths greater than 100m makes the use of remotely controlled visual inspection and manipulation attractive. However, long coaxial cables from the surface to the remote teleoperator cause additional difficulties. Therefore, sound communication without a tether is desirable. This form of telemetry, however, poses severe bandwidth restrictions so that its use for image transmission is in question. The product of Frame Rate (F) in frames per second, Resolution (R) in total pixels and grayscale in bits (G) equals the transmission baud rate in bits per second. Thus for a fixed channel capacity there are tradeoffs between F, R and G in the actual sampling of the picture for a particular manual control task in the present case remote undersea manipulation. A manipulator was used in the MASTER/SLAVE mode to study these tradeoffs. Images were systematically degreaded from 28 frames per second, 128 × 128 pizels and 16 levels (4 bits) grayscale, with various FRG combinations constructed from a real-time digitized (charge- injection) video camera. When subjects first saw the video pictures with which they had to perform remote manipulation tasks, they refused to believe that they could succeed. Much to their surprise, however, they discovered that they were able to perform with a considerably degraded picture. It was found that frame rate, resolution and grayscale could be independently reduced without pre- venting the operator from accomplishing his/her task. Threshold points -were found beyond which degradation would prevent any successful performance. It was observed that frame rate and grayscale could be de- graded considerably more than resolution before teleoperation became impossible. Isoperformance curves (curves of constant performance) were found for two subjects for various combinations of frame rage, resolution, and grayscale. These results were found to correlate closely - - with isotransmission curves (curves along which the information transmission rate is the same). A general conclusion is that a well trained operator can perform familiar remote manipulator tasks with a considerably degraded picture, down to 50 K bits/ sec, well below the several m bits/sec (5 MHz) normally used for broadcsat video.