随机散斑投影粗粒反光表面图像采集方法

Random Speckle Projection Image Acquisition Method for Coarsegrained Reflective Surface

针对粗粒反光表面在一般光源照明条件下产生的局部反光问题,提出一种基于随机散斑投影的图像采集方法。以主动投影照明的方式在工件表面形成系列随机散斑图案,利用组图冗余信息抑制反光,生成光强均匀且高信噪比的融合图像。给出了随机散斑图畸变矫正方法,实现高效的密度均匀散斑投影。实验结果表明,所提方法很好地抑制了工件表面局部反光问题,显著提升了图像对比度与清晰度,为后续图像检测算法设计打下良好基础。

As a fundamental procedure of machine vision inspection,whether high-quality images can be acquired directly affects the difficulty of subsequent detection algorithm design and the object recognition ability.The light source and illumination mode are critical components of image acquisition.Common illumination modes with fixed light sources include backlighting,vertical lighting,coaxial lighting,etc.,which are not suitable for surfaces with subtle targets,highlights,complex textures and embossed printing in special inspection scenes.For coarse-grained reflective surfaces,there is a local reflection phenomenon directly utilizing a general light source.To solve this problem,this paper proposes a novel image acquisition method based on random speckle projection to avoid fixing the light field direction.A series of random speckle patterns are designed to project on the coarse-grained reflective surface through active projection illumination,and a set of images with random light field distribution are obtained by a camera.The abundant information of the acquired images is used to suppress the reflection,and a fused image with uniform light intensity and a high signal-to-noise ratio is generated according to the mean fusion method.Aiming at the problem of perspective distortion during speckle projection,a perspective distortion correction method of the random speckle image is proposed to achieve efficient speckle projection with uniform density.Specifically,an oblique projection geometric model along the perspective distortion direction is established by introducing a projection distortion factor and projection image scale ratio and analyzing the relationship of two parameters and the projector inclined angle and its throw ratio.Compared with the traditional perspective distortion correction method of the projection transformation matrix,the proposed method does not need to rely on feature point calibration,and it is simpler and more practical.This paper takes the surface of zinc oxide resistors as an example to verify the effectiveness of the proposed method.We design and build an image acquisition system that involves a programmable structured light projector,a camera matched lens,detection supports and a computer,which can realize the rapid cycling of image projection and image acquisition.The experimental results show that our method suppresses the local reflection on the surface of the workpiece to a large extent,and the details of the surface texture and scratches of the workpiece are recorded more abundantly in the fusion image.Compared with the general ring light source,the image gray histogram and contrast show an advantage of our method during image quality evaluation,which significantly improves the image contrast by 1.33~2.75 times and lays a good foundation for the subsequent image detection algorithm design.