Enhancement of the Shadow-Moire Method Through Digital Image Processing

Surface topography can be conveniently investigated by a well-known shadow-moire technique. It is relatively free from stringent requirements on stability of instrumentation and quality of the light source. The main unresolved problem of the shadow moire is its relatively low resolution. The digital-image-analysis enhanced shadow-moire technique described here is based on the marriage of two well-known and developed methods: classical shadow moire and contemporary digital image analysis. This combination allows a significant increase of the sensitivity of the classical shadow moire by utilizing the ability of the digital-image-analysis system to acquire whole-field light-intensity information and process this information to yield the related displacement field. The suggested approach was utilized for a three-dimensional curved surface (made of aluminum). The obtained topography of the three-dimensional specimen was compared to the one measured by a high precision dial gage and the differences were on average < 3% between the two sets of data. The described combination of the shadow moire and digital image analysis may prove a useful tool for on-line quality control in a variety of manufacturing processes.