A new improved unwrapping algorithm based on the combination of modulation and phase fitting reliability is presented. In a 3-D sensing technology with structured light projection, for the measurement of a surface with complex reflectivity and a quasisanded object, noises such as saturation/cut-off and quasispeckle in the fringe images are important error sources. The phase unwrapping algorithm based only on fringe modulation is not enough to bypass these error points. The characteristics of the phase measurement errors caused by saturation/cut-off are analyzed, and a new phase reliability criterion that is sensitive to both modulation and some intensity noises is defined to reduce the unwrapping errors. With this new reliability criterion and “flood” unwrapping algorithm, the phase unwrapping can be implemented along a more reliable path and errors are limited in the minimum areas. © 2002 Society of Photo-Optical Instrumentation Engineers.