Notes on Human Colour Vision for IDG1004

Course Structure for IDG1004
  • Introduction to Human Colour Vision
    • Importance of understanding how we perceive color.
Introduction to Human Colour Vision

  • What is Colour?

    • Colour is a sensation arising from the interaction among:
    • Source (light)
    • Object (reflective surfaces)
    • Observer (human eye)
    • There are no distinct colors in the electromagnetic spectrum, only wavelengths of light.

  • Historical Perspectives:

    • Isaac Newton (1642-1727): Color is a physical phenomenon created by light striking objects.
    • Johann Wolfgang von Goethe (1749-1832): Emphasized that sensations of color are influenced by the observer's perception.
Key Components of Colour Vision
  • Three Elements:
    • Physics:
    • Light (wavelengths, energy source)
    • Physiology:
    • Eye structure and sensitivity (L, M, S - representing cones)
    • Perception:
    • Brain processing color signals and categorizing colors (e.g., red, green).
Anatomy of the Eye
  • Retina:
    • Acts as the central nervous system's part responsible for visual capture.
    • Contains:
    • Rods:
      • Function in low light (scotopic vision)
      • 100 million rods present per eye, sensitive to single photons.
    • Cones:
      • Function in bright light (photopic vision)
      • 5 million cones per eye, responsible for color vision, concentrated in fovea (approximately 50,000 cones).
      • Types of cones categorized as:
      • L (long, red)
      • M (medium, green)
      • S (short, blue)
Colour Perception Phenomena
  • Purkinje Effect:
    • Shifts peak luminance sensitivity towards blue in low illumination (scotopic) versus bright light (photopic).
  • Young-Helmholtz’s Trichromatic Theory:
    • Suggests that three types of cones correspond to different ranges of visible light (red, green, blue).
Colour Constancy and Surrounding Influence
  • Colour Constancy:
    • Maintains stability in perceived color under different lighting conditions (illumination changes).
  • Simultaneous Contrast:
    • Perception of color influenced by adjacent background colors, causing brightness and chromatic contrasts.
Colour Vision Deficiencies (CVD)
  • Types of CVD:
    • X-linked recessive inheritance affects how certain colors are perceived.
    • Major types include:
    • Protanopia (red deficiency)
    • Deuteranopia (green deficiency)
    • Tritanopia (blue deficiency)
Diagnostic Tests for Colour Vision
  • Ishihara Test: Identifies color perception by using numbers in colored circles (e.g., seeing number "42").
  • Anomaloscope: Measures the ability to perceive colors by mixing red and green light.
  • Lantern Tests: Assess the ability to identify signal lights, historically used in vocational training.
Colour Models and Spaces
  • RGB Model: Additive color model using red, green, blue to create a spectrum of colors.
  • CMY and CMYK Models: Subtractive color models used in printing, starting with white and absorbing light.
  • CIE Colour Systems: Established standard color spaces for consistent color communication across devices.
Conclusion
  • Understanding color vision and its mechanisms is essential in various fields such as art, design, and optometry. Keep the definitions, historical perspectives, anatomical details, and differential factors in mind for a holistic understanding of the topic.