Understanding Human Perception: A Deep Dive into Light, Color, and the Human Eye - Prof. R, Study notes of Computer Science

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Human Perception

CS

Slides from Minglun Gong Tuesday, March 03, 2009 2

Outline

• Light
  • Visible spectrum
• Human eye
  • Intensity perception
  • Color perception

Tuesday, March 03, 2009 3

What is Light

• Light:
  • Electromagnetic radiation that can produce a

visual sensation

• Electromagnetic energy:
  • A wave characterized by variations of electric

and magnetic fields.

• Low frequency - > high frequency
  • Radio waves, Microwaves.
  • Infrared, Visible light, Ultraviolet.
  • X-Rays, Gamma Rays. Tuesday, March 03, 2009 4

Electromagnetic Spectrum

Tuesday, March 03, 2009 7

Light (Cont’d)

• Intensity & Color:
  • Intensity of the light depends on its energy.
  • Color of the light depends on its spectral

distribution.

• The visual effect of light can be described concisely by a triple: - Different spectral energy distribution look the

same to human.

• Mapping between spectral distributions and colors

is many-to-one.

Tuesday, March 03, 2009 8

Human Eye

Eye’s receptors

• Rods and Cones
  • Cones
    • Roughly 6-7 million
    • Concentrated in the fovea
    • Highly sensitive to color
  • Rods
    • 75 - 150 million
    • Not involved in color vision
    • Sensitive to low-level illumination
    • Help give an overall picture of the field of view

Receptor distribution

rods rods

• 80 0 80 Fovea 180 000 90 000 20 000 Degrees from fovea blind spot cones

Optics of the eye

100 m^ 17mm 15m 15 X 100 = 17 X = 2.55mm X = D tan( ) 2 X 2

Human visual acuity

Visual acuity of a normal eye is 1/60 of a degree 2 D^ D’ X X 2 X’

Visual acuity calculations

= D tan( ) 2 X 2 = 1/ Thus, X = 2D tan(1/120 degree) X = 2D*0. X = 0.00029088 * D X = size of object D = distance from object Human acuity How far can we be from an 1mm object and still see it? 1mm = D D = 3.437 meters

Human sampling

fovea

Tuesday, March 03, 2009 19

Chromostereopsis

• Depth effect due to color: - Red appears closer - Blue appears further
• Used to create 3D effect. Tuesday, March 03, 2009 20

Afterimage

• Strong colors create afterimage - Red – > cyan - Blue – > yellow - Green - > magenta

Tuesday, March 03, 2009 21

Color Deficiency

• Europe and North America
  • Male: 8%
  • Female: 1%
• Major form is dichromatism:
  • have difficulty in discriminating colors.
• Avoid using color alone to convey information. Tuesday, March 03, 2009 22

Ishihara Test