Method for automating fish-size measurement and camera calibration using a three-dimensional structure and an optical character recognition technique

This study developed a method for automatically measuring fish-body sizes with a stereo-vision system calibrated using a three-dimensional frame for accuracy and precision. The three-dimensional frame was installed in a water tank and photographed using a stereo camera to obtain the parameters for calibration. An optical character recognition technique was used to detect the feature points on the frame. All the feature points could be detected, and the correct combinations of the points were matched automatically in the stereo images. To obtain the fish-body size, the snouts and tails of goldfish in the tank were detected in the stereo video sequences using the Faster R-CNN image recognition technique, and the fish-body lengths were calculated automatically. The accuracy and precision of the automatic calibration system were equivalent to the manual calibration, whereas those of the automatic fish-body size measurements were lower than the manual measurement. The automatic processes of the calibration and the fish body-size measurement were about 96% and 90% faster than those in the manual process. The issues of the accuracy and precision of fish-body size measurements can be resolved in the future by improving the image recognition accuracy.