近年来,对物体的颜色显现力、光源光谱功率分布和自身表面反射光谱三者的定量关系方面的研究备受大家关注.在三维扫描测量领域,由于颜色特征具有反映物体材料和纹理等丰富信息的优势,提出了一种主要由彩色相机、投点光源和PC机组成的色度自适应投点仪结构,其中数字微镜(DMD)作为投点光源的核心元件用于调制R,G,B 三个LED光源的光谱功率分布.然而主动式标记点的颜色显现力因受未知反射光谱投影接受面的影响,其颜色特征往往难以识别和区分.为了提高投影标记点与不同反射光谱的投影接收面作为背景的分辨力,描述了一种色度自适应投影标记点的选取方法.在高维线性反射光谱建模的基础上,用光谱响应的方法对彩色投点仪设备特征化,以解决三通道彩色相机设备特征化精度低的问题.并通过样本训练为高维线性反射光谱的求解提供条件约束.继而,在CIE1931色度坐标空间下,选取与投影接收面背景色度坐标欧氏矩最大的色度坐标点.根据投点仪设备特征化结果,推导其LED最优设定值.最后,采用24孟塞尔色卡作为被投影对象,主动标记点与色块的色差作为其颜色显现力的评价参数,通过与激光二极管投点仪做对比性实验.实验结果表明对各不同色度的投点接受面,提出的色度自适应投影标记点的选取方法均有较好表现.

The authors designed a self-adaptive projection system which is composed of color camera,projector and PC.In detail,digital micro-mirror device (DMD) as a spatial light modulator for the projector was introduced in the optical path to modulate the illuminant spectrum based on red,green and blue light emitting diodes (LED).However,the color visibility of active markers is affected by the screen which has unknown reflective spectrum as well.Here active markers are projected spot array.And chromaticity feature of markers is sometimes submerged in similar spectral screen.In order to enhance the color visibility of active markers relative to screen,a method for selecting self-adaptive chromaticity of the projected markers in 3D scanning metrology is described.Color camera with 3 channels limits the accuracy of device characterization.For achieving interconversion of device-independent color space and device-dependent color space,high-dimensional linear model of reflective spectrum was built.Prior training samples provide additional constraints to yield high-dimensional linear model with more than three degrees of freedom.Meanwhile,spectral power distribution of ambient light was estimated.Subsequently,markers’ chromaticity in CIE color spaces was selected via maximization principle of Euclidean distance.The setting values of RGB were easily estimated via inverse transform.Finally,we implemented a typical experiment to show the performance of the proposed approach.An 24 Munsell Color Checker was used as projective screen.Color difference in the chromaticity coordinates between the active marker and the color patch was utilized to evaluate the color visibility of active markers relative to the screen.The result comparison between self-adaptive projection system and traditional diode-laser light projector was listed and discussed to highlight advantage of our proposed method.