Development of a System for Pig Weight Measurement by Image Analysis

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To estimate pig weight by a hand-off method, we made a device composed of a video camera and a mesh imaged slide projector.Analysis proceeded from the image of a pig in a pen, when projecting shadow lines of lattice pattern on the pig from above with the slide projector placed at the ceiling above the waterer and taking image of the pig with the video camera fixed beside the projector. From the image of the pig, the gap in pixel of a shadow line at the border between the shoulder and the floor of the booth was measured and related with height. The specified projected image area of the pig, which lacked the image area of ears and a tail, was also measured. Then pig weight was estimated from an exponential function of the area and the height and was compared with the measured one. For the litter of 12 growing pigs in the pen, experiments to estimate pig weight were done at five times during an age of 81 days to that of 98 days. The device set at the ceiling provided a clear image of a pig standing in a normal posture while drinking water.A mean relative error of 2.1% with 1.8% in standard deviation was obtained when estimate each pig weight. The fluctuation of error to estimate pig weight was remained, however, the device had a good prediction for the group weight of the pigs. The difference between estimated and measured mean group weights was only +0.3 kg, or 0.8% in relative error. Despite overestimating in positive side, it indicates a practical accuracy. Although a limitation in reliability to estimate pig weight remains, the method allows for rapid estimation of the weight