Hello, everyone. Recently I performed an experiment to investigate the dynamics of stomatal movement, guard cells on the intact leaf were applied with ABA (Abscisic acid) and monitored the stomatal aperture by the camera. The stomata started to close after the treatment. I obtained the stack containing 100 images. Now I want to analyze the stomatal aperture by Fiji/imageJ. General speaking, most of people use the “straight line” function to measure it. But the stomatal aperture changed all the time, from large to small when the guard cells are given ABA. That means we need to adjust the length of the straight line by hand all the time. It is inevitable to make an error that leading to an unreliable result. So, does anyone know how to measure the dynamics of stomatal aperture automatically by Fiji/ImageJ?