Three-dimensional measurement systems of high precision have been widely applied in high-technology industries and bio-medical areas, especially for microscale accuracy measurement. However, due to their bulky volume, most of the current surface profilometers cannot perform 3D measurement within a space-restricted inspection environment. To overcome this drawback, a novel 3D surface profilometer with a miniaturized probe was developed according to the digital fringe projection (DFP) principle. Measurement of small objects within a limited space can be made by the profilometer which comprises a digital fringe projection system, coherent image fibres and optical lenses. Using phase shifting and an accurate calibration method, the proposed system can analyse the phase fringe and reconstruct clouds of surface points accurately. An example of 3D intra-oral dental measurement was provided to verify the feasibility and performance of the developed system and techniques. The experimental results indicate that the spatial and vertical measurement resolution can reach 25 µm and 5 µm, respectively, and the accuracy can be controlled within 25 µm, less than 1% of full measurement range.
An innovative mura defect detection methodology for a thin-film transistor liquid crystal display (TFT-LCD) is developed for automatic inspection of mura defects using the discrete cosine transform (DCT) principle and background image filtering strategy. Efficient and accurate surface defect detection on flat panel display (FPD) panels has never been so important in achieving a high yield rate of FPD manufacturing. Detecting blob-mura defects in an LCD panel can be difficult due to non-uniform brightness background and slightly different brightness levels between the defect region and the background. To overcome this problem, a DCT-based background reconstruction algorithm was developed to establish the background image separated from the defects. The significant level of mura defects can be rationally quantified using the just noticeable difference (JND) definition. Actual performance of the developed method was evaluated on industrial LCD panels containing natural mura defects. Results of experimental tests verified that the proposed algorithm has a superior capability for detecting mura defects efficiently and accurately.
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