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To estimate pig weight by a hands-off method, we developed a device, which consists of a video camera, a slide projector, and a computer. The device measured the height and weight of a standing pig from above by imaging and image analysis. The slide projector was equipped with a clear slide film printed with black mesh lines in an orthogonal lattice pattern. When the shadow lines were projected on a pig with the slide projector, the parallax of a shadow line at the border between the pig and the floor was used for the estimation of the pig height using a regression equation. The weight was derived from the height combined with the projected area of the pig at the floor using a multiple regression equation. However, a difficulty of image analysis was remained when discriminating the pig image from the surroundings and the shadow lines.

In this study, a clear pig image suitable for image analysis was obtained when providing a red slide film printed with yellow cross-lines with the slide projector. A high contrast of the pig image to the surroundings and the shadow lines was achieved because of the spectrum pattern of a halogen lamp formed by increasing red and yellow spectrum and decreasing violet and blue spectrum in visible ray. Semiautomatic software of image analysis was developed and used for the experiment. The device including the red slide film was fixed to the ceiling in a pen and provided a clear image of a pig while drinking water. A litter of seven growing pigs, ages of 87 days and two-crossbreeds of Landrace by Landrace, was used in the experiments. Weight estimation of the pigs, from 40 kg to 70 kg in mean weight, was examined four times in a month. A mean error of 2.1% and a mean group error of 1.3% were achieved. Despite overestimating in the early experiments, these error numbers indicate a practical accuracy. (Download PDF)    (Export to EndNotes)