The FIM setup.

(A) Image of 10 larvae (arrow) imaged in a conventional setup. The asterisks denote scratches and reflections in the tracking surface. (B) Image of 10 larvae (arrow) imaged in the FIM setup. Note the high contrast. (C) The principle of frustrated total internal reflection. n1 to n3 indicate different refractory indices, an acrylic glass plate is flooded with infrared light (indicated by red lines). The camera is mounted below the tracking table. (D) Schematic drawing of the setup. (E) Image of the tracking table. (F) Histogram of the image shown in (b). (G) Comparison of Weber contrast (Wc) obtained in the conventional and the FIM setup. The pulse-width modulation (PWM) is plotted against the Weber contrast. (H–J) Histogram taken at different PWM values as indicated.