Grayscale imbalance correcting method based on fringe normalization in RGB tricolor real-time three-dimensional measurement

Abstract. In real-time phase measuring profilometry based on color-encoded sinusoidal three-step phase-shifting algorithm, three frames of red (R), green (G), and blue (B) individual channel color-encoded sinusoidal gratings with an equivalent shifting phase of 2π/3 are combined to be a color fringe pattern. While this color fringe pattern is projected onto the measured object rapidly and sequentially by a special digital light projector, a high-speed monochrome camera synchronized with the projector signal is used to capture the corresponding deformed patterns in R, G, and B channels. Due to the monochrome camera’s different sensitivity to R, G, and B light, there will be a grayscale imbalance among the captured phase-shifting deformed patterns from R, G, and B channels. So, a grayscale imbalance correcting method based on fringe normalization is proposed. The experimental results verify the feasibility of the proposed method. The three-dimensional (3-D) shape information can be obtained in real-time. It is suitable for real-time 3-D measurement.

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