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Lighting CSIS 5838: Graphics and Animation for Gaming Terminology • ϴL: Incident light angle to point on surface • ϴV: Incident viewing angle to point on surface • K: Intensity of light source Image plane Light source (intensity I) Focal point of camera ϴV ϴL Surface in image Reflected Light • Amount of light received by surface proportional to K cos(ϴL) Light source Light concentrated in smallest area at ϴL = 90° Light more “spread out” at smaller ϴL Shape from Shading • Brain reverses this process, interpolating shape from shading across surface – No variation in lighting flat surface – Slow variation in lighting curved surface – Sharp variation in lighting corners Smooth Shading • Can create illusion that non-curved surface is curved – More efficient than adding large number of vertices • Interpolate curve through series of edges – Often done with Bezier curves (built into Blender) • Render image based on interpolated curves, not actual surface Diffuse Reflection • Portion of light “scattered” from surface, reflecting in all directions ϴV Image plane Light source Focal point of camera ϴV ϴL Surface in image Specular Reflection • Portion of light directly reflected from surface, only visible if ϴV = ϴL (Snell’s law) Light source Not visible visible ϴL ϴV Surface in image Specular Reflection in Blender • “Hardness” parameter defines additional angles at which specular light visible • Light intensity function of |ϴL - ϴv|/hardness Intensity Hardness = 2 Hardness = 20 ϴL - ϴ V Lambertian Model • Assumption: Amount of light reflected in direction ϴV = K cos(ϴV) – Most light reflected normal to surface – Less light reflected parallel to surface Lambertian Model • Amount of surface projected to camera inversely proportional to ϴV • = 1/cos(ϴV) Light source Smallest surface at ϴv = 90° More surface at smaller ϴV Lambertian Model • Amount of light received by camera = K cos(ϴV) * 1/cos(ϴV) • Lambertian assumption: Amount of light percieved independent of viewing direction – Simplest to compute – Close to being true for many surfaces (moon)