Sensitivity analysis and measurement uncertainties of a two-camera depth from defocus imaging system

A two-camera Depth from Defocus imaging system has been previously proposed for the measurement of size and position of particles or drops. It makes use of two images with different degrees of defocus blur captured at different imaging planes. In the present study, the influence of system and particle parameters on the calibration functions and measurement uncertainties of such a system have been comprehensively investigated and experimentally verified. The parameters varied included the distance between the imaging planes, the image bit resolution, pixel resolution and the random image noise. Furthermore, the intensity and position of the backlighting and the type of particle and its relative refractive index have been varied. Experimental verification was conducted using calibration dot targets, polystyrene latex spheres, and pulverized coal powders. A sensitivity analysis was performed using relative errors or differences for the three quantities - calibration function, particle size and particle position. The study concludes with explicit recommendations on which quantities are most influential in determining measurement accuracy and therefore, must be carefully controlled.

Automated summary

This study comprehensively investigated the impact of system and particle parameters on the calibration functions and measurement uncertainties of a two-camera Depth from Defocus imaging system, with experimental verification. It provides explicit recommendations on which quantities are most influential in determining measurement accuracy and must be carefully controlled.