Research on Improved Method of Schlick Model Based on BRDF Measurement

基于BRDF测量的Schlick模型改进方法研究

¹ School of Astronautics, Northwestern Polytechnical University, Xi'an 710072 China
² Shanghai Academy of Spaceflight Technology, Shanghai 210009, China
³ Key Laboratory of Electro-Optical Countermeasures Test & Evaluation Technology, Luoyang 471003, China

Received: 28 December 2017

Abstract

In simulating an infrared scene, the Schlick model uses a commonly-used bidirectional reflection distributional function(BRDF) model. Through simulation and BRDF measurement, this paper points out that the Schlick model is in better agreement with the actual output when the emerging zenith angle is smaller than the incident zenith angle. But when the emerging zenith angle is a certain angle larger than the incident zenith angle, the output of the function value may increase with the increasing emerging zenith angle and may not be in agreement with the actual output. In this paper, a new improved Schlick model is proposed, and a cosine compensation function is designed based on Lambert reflection principle. When the zenith angle is larger than the incident zenith angle, which guarantees the monotonous decreasing of the output of the function through the compensation function when the emerging zenith angle is larger than the incident zenith angle. The results on comparison with experimental data show that the improved Schlick model is basically in agreement with experimental results. The results on comparison with the heightened illumination effect of the fighters model show that the heightened illumination effect produced with the improved Schlick model is superior to that produced with the original Schlick model.

摘要

在红外场景仿真中Schlick模型是常用的双向反射分布函数（BRDF）模型，通过BRDF测量试验与Schlick模型计算结果比较发现该模型在出射天顶角小于入射天顶角时能够较好地与实际输出吻合，但是当出射天顶角大于入射天顶角一定角度的情况下，其函数值输出会随着出射天顶角的增大而逐渐增大，与实际现象不一致，为此，提出了一种新的Schlick改进模型，基于朗伯反射原理设计了一种余弦补偿函数，当出射天顶角大于入射天顶角时该函数与原Schlick模型结合，能够更好地表现大出射天顶角时的光照反射效果，通过与实验数据对比，表明改进后的Schlick模型与实验结果吻合，并针对两种飞机模型开展光照渲染效果对比，结果表明基于改进后的Schlick模型生成的光照渲染效果优于原Schlick模型生成的渲染效果。