Machine vision system has great significance for the automatic inspection to enhance unclear defects. For the improvement of the recognition accuracy in the automation inspection, in addition to development of image-processing technology, the optical technology is also required to emphasize the contrast of defects difficult to find in a camera. Here, we develop both the optical-engineering and image-processing technology with high throughput to enhance defects in transparent material, using the phase-shift illumination method with striped structured illumination. We succeeded in the enhancement of shape defects difficult to visualize in a bright-field observation with our approach to construct the composite image from a few pictures. Our challenge of development has been the discrimination of actual defects from dark fringes due to the artificial and periodic structures which is prepared for the improvement of optical performance or design, such as embossing film or micro-lens array. To overcome this issue, we suggested that artificial textures with the gentler slope should be more insensitive than actual defects by providing the illumination pattern with finite-width dark regions. We extended theoretical model for the transmissive phase-shift illumination approach in the case of a rectangular wave as the typical illumination pattern as the illumination pattern with finite-width dark regions and established the novel inspection method to discriminate defects with artificial textures. We confirmed that the rectangular-wave illumination enables us to selectively distinguish between defects and artificial textures.
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