Applications of Digital Image Enhancement Techniques to the Ultrasonic NDE of Composite Materials
Results of the applications of local and global digital image enhancement techniques to ultrasonic C-scan images of damaged graphite/epoxy composites are presented. The original unenhanced images were generated by using focused ultrasonic transducers with center frequencies between 3.5 and 25 MHz. Small defects were often difficult to detect in the unenhanced images because the relatively small signal amplitude changes resulting from the defects were obscured by the larger signal amplitude changes caused by variations in: (1) surface roughness, (2) material attenuation, and (3) material morphology. Results given in this paper indicate that those enhancement techniques which emphasize the higher spatial frequencies at the expense of the lower spatial frequencies and those techniques which operate on local pixel regions can often remove enough of the undesirable variations to make small defects visible in the enhanced images.
KeywordsVariable Gain Histogram Equalization Matrix Crack Edge Enhancement Grey Level Threshold
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