Question #3

Graded by: Toli Lerios

The following questions concen the representation of color used in computer graphics.

A. (10 points) Briefly, what do the terms hue, saturation, and value refer to?

Answer:

Hue: The "intrinsic color", or the dominant wavelength.

Saturation: The "purity", or how "washed out" a color is, or how much/far the color/dominant wavelength is from a gray of same value.

Value: The "brightness" or "intensity", how dark the color is, how close to black the color is.

B. (10 points) When drawing a polygon, colors at vertices are often interpolated so that the colors in the interior of the polygon are smoothly graded across the polygon. Is it better to interpolate the colors in an RGB coordinate system, or a HSV coordinate system. Explain your reasoning.

Answer:
  1. Linearly interpolating R,G,B values moves result along a line joining endpoints (ie. colors at vertices). RGB is a linear, additive color space.
  2. RGB accurately represents mixing of lights (linear, additive space), and lit-to-shadow transtitions. Shading has to take place in RGB.
  3. No need to convert for display since framebuffers are RGB.
  4. HSV interpolation yields psychadelic colors when interpolated hues are far apart (Try it).
Copyright © 1996 Pat Hanrahan