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A New Colorimetrically-Calibrated Automated Video-Imaging Protocol for Day-Night Fish Counting at the OBSEA Coastal Cabled Observatory
SARTI Research Group, Electronics Department, Universitat Politècnica de Catalunya (UPC), Rambla de la Exposición 24, Vilanova i la Geltrú-Barcelona 08800, Spain
Instituto de Ciencias del Mar (ICM-CSIC), Paseo Maritimo de la Barceloneta, 37-49, Barcelona 08003, Spain
Consiglio per la Ricerca e la Sperimentazione in Agricoltura, Via della Pascolare, Monterotondo Scalo 16-00015, Rome, Italy
* Authors to whom correspondence should be addressed.
Received: 30 August 2013; in revised form: 22 October 2013 / Accepted: 22 October 2013 / Published: 30 October 2013
Abstract: Field measurements of the swimming activity rhythms of fishes are scant due to the difficulty of counting individuals at a high frequency over a long period of time. Cabled observatory video monitoring allows such a sampling at a high frequency over unlimited periods of time. Unfortunately, automation for the extraction of biological information (i.e., animals’ visual counts per unit of time) is still a major bottleneck. In this study, we describe a new automated video-imaging protocol for the 24-h continuous counting of fishes in colorimetrically calibrated time-lapse photographic outputs, taken by a shallow water (20 m depth) cabled video-platform, the OBSEA. The spectral reflectance value for each patch was measured between 400 to 700 nm and then converted into standard RGB, used as a reference for all subsequent calibrations. All the images were acquired within a standardized Region Of Interest (ROI), represented by a 2 × 2 m methacrylate panel, endowed with a 9-colour calibration chart, and calibrated using the recently implemented “3D Thin-Plate Spline” warping approach in order to numerically define color by its coordinates in n-dimensional space. That operation was repeated on a subset of images, 500 images as a training set, manually selected since acquired under optimum visibility conditions. All images plus those for the training set were ordered together through Principal Component Analysis allowing the selection of 614 images (67.6%) out of 908 as a total corresponding to 18 days (at 30 min frequency). The Roberts operator (used in image processing and computer vision for edge detection) was used to highlights regions of high spatial colour gradient corresponding to fishes’ bodies. Time series in manual and visual counts were compared together for efficiency evaluation. Periodogram and waveform analysis outputs provided very similar results, although quantified parameters in relation to the strength of respective rhythms were different. Results indicate that automation efficiency is limited by optimum visibility conditions. Data sets from manual counting present the larger day-night fluctuations in comparison to those derived from automation. This comparison indicates that the automation protocol subestimate fish numbers but it is anyway suitable for the study of community activity rhythms.
Keywords: coastal fishes; cables observatories; OBSEA; automated video-imaging; colorimetric calibration; swimming rhythms; 3D Thin-Plate Spline warping
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del Río, J.; Aguzzi, J.; Costa, C.; Menesatti, P.; Sbragaglia, V.; Nogueras, M.; Sarda, F.; Manuèl, A. A New Colorimetrically-Calibrated Automated Video-Imaging Protocol for Day-Night Fish Counting at the OBSEA Coastal Cabled Observatory. Sensors 2013, 13, 14740-14753.
del Río J, Aguzzi J, Costa C, Menesatti P, Sbragaglia V, Nogueras M, Sarda F, Manuèl A. A New Colorimetrically-Calibrated Automated Video-Imaging Protocol for Day-Night Fish Counting at the OBSEA Coastal Cabled Observatory. Sensors. 2013; 13(11):14740-14753.
del Río, Joaquín; Aguzzi, Jacopo; Costa, Corrado; Menesatti, Paolo; Sbragaglia, Valerio; Nogueras, Marc; Sarda, Francesc; Manuèl, Antoni. 2013. "A New Colorimetrically-Calibrated Automated Video-Imaging Protocol for Day-Night Fish Counting at the OBSEA Coastal Cabled Observatory." Sensors 13, no. 11: 14740-14753.