Comparative analysis of image measurement technology and artificial measurement method based on three kinds of prawns

The measurement of prawns’ morphological parameters was traditionally to use vernier caliper, but the error was great. In order to improve the intelligent level of prawns measurement, this paper first invented image measurement technique based on computer vision technology. Using this technique, we measured body length(BL), carapace length(CL) and carapace width(CW) of Marsupenaeus japonicus, Litopenaeus vannamei and Metapenaeus ensis, then compared these results with those from vernier calipers. We measured 421 prawns and obtained 15 156 data. Based on Bland-Altman mapping method and Intraclass Correlation Coefficient (ICC) to judge the consistency and repeatability. It turned out that: (1) More than 95% of the D-value between image measurement technique and vernier caliper method fell within the scope of LoA, and LoA CI was acceptable in professional sense, which showed that the consistency of the two methods was good. (2) For one individual, the results of identifying one angle by using image measurement technique were the same. The ICC of identifying three different angles were 0.996, 0.973, 0.957, which had no significant difference compared with that of 3 times measurements using vernier caliper by one person (ICC=0.997, 0.980, 0.965), but larger than three different persons (ICC=0.991, 0.952, 0.947). The result indicated that the repeatability of image measurement technique was related to shooting angle, and the same angle was the best. (3) The results of identifying one angle using image measurement technique were the closest to assumed truth value. Meanwhile, the degree of variation was minimal, the relative error was 1.52%, 2.37% and 3.74% respectively. In short, the consistency of image measurement technique and vernier caliper method was good, and the repeatability of the former was superior to the latter, with advantages in non-contact, fast measurement and wide application. Therefore, we could replace vernier caliper with image measurement technique to be applied in prawns morphological parameters measurement.