Illumination for Computer Generated Pictures
📜 Abstract
The quality of computer generated images of three-dimensional scenes depends on the shading technique used to paint the objects on the cathode-ray tube screen. The shading algorithm itself depends in part on the method for modeling the object, which also determines the hidden surface algorithm. The various methods of object modeling, shading, and hidden surface removal are thus strongly interconnected. Several shading techniques corresponding to different methods of object modeling and the related hidden surface algorithms are presented here. Human visual perception and the fundamental laws of optics are considered in the development of a shading rule that provides better quality and increased realism in generated images.
✨ Summary
The paper introduced a practical illumination model that combines diffuse reflection, empirically controlled specular reflection, and interpolated surface normals evaluated at individual raster positions. This approach improved upon flat and Gouraud shading by producing smoother curved surfaces and more accurately positioned highlights, while remaining suitable for polygonal models and scan-line rendering. The paper became the basis for the widely used Phong reflection model and Phong shading technique. Later research developed related models, including Blinn’s half-angle formulation, while subsequent graphics research continued to use Phong shading as a reference point for comparing realism and computational cost. (users.cs.northwestern.edu) Its influence also extended into practical graphics systems and patents, which cite Phong’s model as an established method for per-pixel shading of polygonal 3D images. (patents.google.com)