Application of Direct Phase Gradients Extraction in Image Distinction of Photodynamic Patterns

摘要

In order to overcome the basic deficiencies associated with the use of an arctangent operation in the calculation of optical phase, an approach to compute pixel-by-pixel gradients of optical phase directly from digitally encoded Fourier-transform or phase-stepped fringe patterns is used in the information recognition of photodynamic fringe patterns. This approach can be classified as a sine-cosine demodulation technique that finds its roots in the differential cross-multiplier phase-demodulation technique commonly used by the optical fiber sensor community. The technique is algorithmically simple and does not rely on a computation of the arctangent, therefore, it is not subject to some of the limitations of the standard phase-unwrapping methodologies. Based on this method, the requisite forms of sine and cosine aiming at Phase-stepping and Fourier-transform have been obtained respectively. The proposed phase-gradient technique is demonstrated by two examples, one is the calculation of the stress field of three point bending model using Isodyne method combined with Fourier transform fringe interpretation, the other is the calculation of the contact stress of a plate by using phase-stepping Isodyne method of four maps. Experimental results indicate that this technique does not propagate localized noise events and is very significant for the image processing of photodynamic fringe patterns.