Colour Paerception

  1. Definition of Colour: Colour differentiates surfaces of the same brightness. It results from differences in light wavelength absorption and reflection.

  2. Sensation Properties:

    • Hue (colour)

    • Saturation (purity of the colour)

    • Brightness (light intensity)

  3. Function of Colour: Essential for signaling and detection (e.g., spotting food, determining ripeness, and recognizing traffic signals).

  4. Physical Properties of Light:

    • Wavelength determines colour.

    • White = all wavelengths; Black = absence of light.

  5. Mixing Colours:

    • Additive Mixing: Light waves combine to create new colours (e.g., blue + green = cyan).

    • Subtractive Mixing: Mixing pigments absorbs more wavelengths, reducing reflected light (e.g., blue + yellow = green).

  6. Cone Photoreceptors:

    • S-Type: Sensitive to short wavelengths (blue).

    • M-Type: Sensitive to medium wavelengths (green).

    • L-Type: Sensitive to long wavelengths (red).

    • Most cones are concentrated in the fovea.

  7. Theories of Colour Vision:

    • Trichromatic Theory: Colour vision based on three cone types.

    • Opponent Process Theory: Colour perception arises from opposing signals (e.g., blue vs. yellow, red vs. green).

  8. Colour Deficiencies:

    • Types: Protanope (red), Deuteranope (green), Tritanope (blue).

    • Detected using Ishihara tests.

  9. Colour Constancy: Perception of consistent colour despite changing lighting conditions.