Particle depth measurement based on depth-from-defocus

An optical and digital method has been developed for the detection of the depth of small particles distributed in 3D space and its performance has been examined in numerical simulations and experiments. The present method is based on depth-from-defocus in which the depth of particle is detected from the image blur of the particle. The results of numerical simulations show that low-pass filtering is effective for the reduction of error. In the experiments with a single 3CCD color camera, it is found that the RMS error of the present method is 1.81 mm for the depth range of 40 mm.