Enhanced Visualization of Scratches on Milled Metal Surface Using Normal Variation Computed by Auxiliary Rays

When machining metal, the machining process often leaves numerous scratches on the milled metal surface, making inspection of its appearance crucial to ensure the quality of the product. Recently, computer graphics techniques have been employed to visualize simulated milled metal surfaces for appearance inspection, as an alternative to creating physical prototypes. Path tracing is a commonly used computer graphics technique for appearance inspection because it can produce photorealistic visualizations of the milled metal surface under realistic illumination. However, because of the influence of illumination, path tracing sometimes fails to clearly visualize scratches, even though the results are physically accurate. In this paper, we propose two computer graphics-based visualization methods that incorporate auxiliary rays into a ray tracing framework to compute normal variations of the milled metal surface. These normal variations are then used to enhance scratch visualization. Experimental results demonstrate that our methods successfully enhance the visibility of scratches, making them more suitable for appearance inspection tasks.