Introduction to Shape and Color

Shape

Line 6.5.2
Angle 6.10
- Vertex
- Reference angle
- Terminating side
Circles and arcs 6.5.4
- Center
- Radius
- Diameter
- Circumference
- Chord
- Quadrants
- 3 Point
Polygons 6.12.1
- Regular polygons
- Rectangles
- Triangles
- Irregular polygons
Geometric operations and terms 6.5
- Circumscribe
- Inscribe
- Bisect
- Tangent
- Parallel
- Midpoint
- Endpoint
- Intersect

Perceptual response to visible light wave energy
- The totality of all wavelengths reaching the eye
- 400 nm to 700 nm
Perceptual dimensions - HSV model
- Hue
  - What we normally think of as 'color'
  - Related to wavelength
- Saturation
  - Ratio of dominant hue (wavelength) to others
  - Gray equals no hue
- Value (lightness)
  - Total intensity (luminance) of light
  - Related to 'shading' and 'shadow'
Can be represented at a HSV Hexacone

Representing energy not visible to the eye
- grayscale on an X-ray
- hue coding on a infrared satellite image
Reprenting conceptual data dimensions
- Mapping dimensions of color to ranges of data values
- Assigning specific colors to discrete values
  - Color coding lines on a graph
Representing ideas or concepts
- e.g., red for hot, blue for cold
Representing common uses for color
- e.g., green for go or start

Defined by mixture of three additive primaries
- Red, Green, Blue
- Represents mixture of illuminated light
Can be represented by a RGB cube
Used in definition of color in computer graphics
Subtractive primaries
- CYM - Cyan, Yellow, and Magenta
- Each paired with additive primary
- Represents mixture of reflected light
- Used in pigment definition along with black (CYMK)
- Using in printing - Offest, inkjet, etc.
Projection of RGB cube along lightness axis
- Gives hue hexagon
- Additive and subtractive primaries opposite each other

Define number of available colors
- Infinite number in real world
- Limited number on paper or computer monitor
Computer graphics based on number of colors for each primary color
- 1-bit: Two total colors
  - Usually black and white
- 8-bit: 256 total colors
  - Can be gray (lightness) or color scale
- 24 -bit: 16+ million colors
  - 8 bits per RGB primary
  - Each primary takes a value from 0 to 255
Color assignment
- Each pixel (on screen) can be assigned a value
- Each value is assigned a look-up color
  - Assignments held in look-up table (LUT)
General rules of thumb
- Color is not good for perception of exact numeric values
- Lightness and saturation can be used for ordinal scales
  - Lightness (grayscales) most common
- Hue can be used for nominal scales
  - Only used in ordinal scales with supplied legend