Study On 3-D Profile Measurement Methods Based On RGB Color Model

Three dimensional (3-D) profile measurement techniques have been used extensively in various fields, such as automated manufacturing, on-line inspection, reverse engineering, medical diagnosis, machining vision, etc. In recent years, optical 3-D profile measurement techniques have become the research focus due to their non-contact, high resolution, non-destructive nature and fast data acquisition. Because that color image has more information and recognition feature compared with gray image, using the color information of light to do the 3-D measurement has become a new method. In this dissertation, fringe projection 3-D profile measurement methods based on RGB color model were researched. The main contents of this paper are:(1) On the basic of deep analysis and comparison of the various 3-D measurement theories, this paper adopted the non-constraint active vision system structure to design the corresponding measurement system platform, also introduced the calibration methods of CCD camera and projection. Two kinds feature extraction algorithms of symmetric cross centers and X-corners were researched, and the feature extraction accuracy reached the sub-pixel level.(2) Based on three-step phase-shifting algorithm, through replacing the third fringe pattern with a uniform flat image, we developed an improved two-plus-one phase-shifting algorithm and a color phase-shifting technique combining with RGB color space model. The 2+1 phase-shifting algorithm is not sensitive to noise, and can obtain the high quality texture mapping image. Color phase-shifting algorithm used only one color sinusoidal fringe pattern to realize measurement. It reduced the measuring time greatly compared with gray phase-shifting algorithms.(3) For shortcoming of traditional spatial unwrapping method's phase error accumulation and spreading on the surface, using a RGB color-encoded pattern to obtain the absolute phase was proposed. This method imitates the human eyes' vision process, only needs to extract the period boundary line, the processing data amount is less, and because of choosing the three element color to code pattern, it can reduce the sensitivity to noise, so it can improve the unwrapping's accuracy and speed.(4) Combining the frequency variation fringe projection technique with the color phase-shifting technique, a color frequency variation fringe projection technique was developed. The use of color phase-shifting fringe patterns simplifies the measuring process, and the independent phase unwrapping on time domain makes phase error not to accumulate and spread.(5) The spatial color self-normalizing gray code based on RGB color model was designed. The code not only reserves the characteristics of gray code, and by means of the combination of the RGB channels' code, it can generate more codewords which are unambiguous and different between any two adjacent codewords can be used to measure the larger free surface and steep objects. Adaptive threshold method is used to get the binary color image when decoding the code patterns. The method has strong anti-interference ability, so it is possible to measure the color objects.