| 摘要 |
Spectral transmittance of a dye coating for optical data is determined off line. Light source (28) wavelength is then matched to the wavelengths at which the dye has the least transmission (i.e. maximum absorbance). The method and system of the present invention are provided for detecting local and global defects in the coating whereby the inspection is done at the maximum absorbance wavelengths to produce a maximum change in a transmitted light signal for a given change in physical thickness of the dye coating. Relative change in thickness is determined based on the change in the transmitted light signal through the dye coating. In order to complete detection and measurement of the transmittance changes, a pair of electronic signals are split (32) from a camera signal wherein one of the electronic signals is filtered by a FIR filter (30) to identify local changes in dye thickness against a globally varying background. In order to detect global variations in the dye thickness, the other electronic signal is processed by a simple thresholding circuit.
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