Lecture 2.1: Scalar Techniques

• Color Mapping
• Uses of Color
  • identify
  • represent or imitate reality
  • show value
  • show structure
  • draw attention
  • enliven or decorate
• Mechanism
• colormap / color lookup table; generally:
      array of colors (r, g, b, (a))
      min -- value for first color (lower clamped)
      max -- value for last color (higher clamped)
• mapping
• transfer functions -- mappings can be described as set of functions
• Color Scales
• color model components
  • grey
  • saturation
  • hue
• composites
  • rainbow
  • optimal
  • heated-object
• double-ended
• banded
• cycling
• multivariate
  • color model components
  • Census Bureau
  • complementary
• Design Considerations
• Trumbo's Principles
  • order -- ordered values should be represented by ordered colors
  • separation -- significantly different levels should be represented by distinguishable colors
  • rows & columns -- to preserve univariate information, display parameters should not obscure one another
  • diagonal -- to show positive association, displayed colors should group into three perceptual classes: diagonal, above, below
• Ware's Experiments
  • metric (quantitative) judgements
  • surface (qualitative judgements
  • redundant color scales
• Other Considerations
  • cultural connotations / expectations
  • discrete nature
  • saturated / bright colors draw eye
  • contrast important
• Other Transfer Functions
  • Height Mapping (carpet plots, mountain plots, statistical surface)
        data: 2D topological grid
        derive z coord from scalar value: zi = h(si)
  • Density
  • Opacity
  • Size