A New Phase Unwrapping Algorithm Based On The Analysis Of Fringe Frequency

Noncontact, high-precision, high-speed optical 3D sensing has been widely used since being presented in the nineteen eighties, in which phase-measurement technology is an important technology. Phase wrapping is a common problem in all phase-measurement techniques. Due to unreliable phase value and under-sampling in practical situation, especially when a complex shape is measured, phase unwrapping is a difficult step. There is no solution suitable to all the problems of phase unwrapping though many algorithms have been presented in the recent 20 years.A new phase unwrapping algorithm is presented and is applied to FTP and PMP in this paper. The new algorithm is one of Quality Guided Path Following Methods, belonging to spatial phase unwrapping methods dependent on path. Its framework consists of digital weighted filtering and modulation ordering. By digital weighted filtering, the analysis of fringe frequency is converted into the analysis of fringe modulation. And based on the correlation between local spatial frequency and the reliability of phase data, the correlation between modulation after digital weighted filtering and the reliability can be set up. Thus modulation ordering at this moment is equal to reliability ordering, resulting in an optimized path. The unreliable pixels are left to the end of the path when phase unwrapping is proceeded along this path, which avoid error propagating. Even in the worse case the error is limited, if three is any. to local minimum areas.With the ability of modulation to mask the unreliable areas such as noise, local shadow, and the ability to deal with under-sampling areas successfully, the newalgorithm can be applied to complex phase unwrapping. Also the new algorithm improves the automatization of phase unwrapping by avoiding complex pole joint.Computer simulation and experiments prove the correctness and effectiveness of the new phase unwrapping algorithm.