Color The main purpose of an OpenGL application is to determine the color of each pixel in the window   Contents of this session: Color Perception Computer Color RGBA vs Color-index Specifying a Color and Shading Model

Color Perception The Human Visual System (HVS) recognizes light in the range from 390 nm (violet) 720 nm (red)   Perceived colors are a combination of light of different frequencies The cone cells in the retena are sensitive to red, green and blue frequencies (the HVS is least sensitive to blue)  A monitor emultates visible colors by lighting pixels with a combination of red/green/blue colors. OpenGL represents color in RGB - other color models (HLS/HSV/CMYK) must be converted to and from RGB.

	Computer Color The hardware causes different amounts of R/G/B light emmision for each pixel  Two ways to encode the color information for the application RGB (or RGBA) Color index  Color index mode stores table entries for each pixel The colormap is not fixed size and can vary between platforms

Colorspace  (image from http://www.swin.edu.au/astronomy/pbourke/colour/colourspace/)   Red, Green, and Blue intensities vary from 0.0 to 1.0   Each axis of the color space represents RGB intensities Examples of OpenGL colors: Red:          glColor3f(1.0, 0.0, 0.0) Yellow:     glColor3f(1.0, 1.0, 0.0) Magenta:  glColor(1.0, 0.0, 1.0) NOTE! other operations (texture/lighting/blending) may affect the final color in the framebuffer

Coloring Early in execution, the color display mode (RGBA or Color Index) is set  The mode cannot be changed after it is set But there are workarounds ... Color is based on several factors: The per-vertex color definition (via glColor3f()) The interaction of the light source(s) with the surface normal and the material properties Rasterization The shading model Blending  Texturing Anti-alising Fog Bit-wise operation (logical ops)

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