THE DEVELOPMENT OF THE MODIFIED SCHLICK MODEL FOR THE SPECULAR COLOR COMPONENT CALCULATION

Abstract

The most common bidirectional reflectance distribution functions (BRDF), among which the Schlick function is included, were analyzed. Compared to Blinn and Phong's BRDF, this function has a smaller degree, which makes it possible to use it in dynamic computer graphics tools. The Schlick function uses the specularity coefficient of the surface and the cosine of the angle between the vector normal to the surface and the median vector for calculation. The disadvantage of the function is the unrealistic reproduction of glare in the attenuation zone. In order to realistically reproduce both the glare epicenter and its blooming, a new modification of the Schlick function using correction coefficients and exponents is proposed. A program for selecting powers and coefficients has been developed. A diagram of the program with a detailed description is given. Mathcad 2001 Professional tools were used to perform a comparative analysis of the Schlick, Blinn BRDFs and modified function. The advantage of the modified function compared to Schlick's BRDF in the fall speed in the attenuation zone is proved. A smaller value of the relative error of approximation of the modified Schlick BRDF at the level of the glare epicenter was proven. Graphs of the dependences of the maximum relative and absolute approximation errors of the modified Schlick's BRDF compared to Blinn's BRDF depending on the specularity coefficient of the surface are plotted. An argument was found in which the modified BRDF reaches the sludge level. The monotonic decrease of the proposed BRDF on the interval of arguments [0, ] is proven. The intervals for calculating the specular color component were calculated for the proposed BRDF, Schlick and Blinn BRDFs. The limit values of the intervals were used when finding the ratio of the size of the glare spots for the modified BRDF and Blinn BRDF, Schlick and Blinn BRDFs. Spot size ratios for BRDFs are illustrated by three-dimensional graphs. It was proven that the blooming zone for the modified BRDF is calculated on a shorter interval than for Schlick's BRDF. The modified BRDF can be used in high-performance rendering systems and provides increased realism in the formation of reflections compared to Schlick's BRDF.