Perceiving Colour

Perceiving Colour

Chapter 9
Key Themes and Concepts

  • Color Emotion Guide Themes:

    • Power

    • Sophistication

    • Mystery

    • Death

    • Hope

    • Simplicity

    • Cleanliness

    • Goodness

    • Purity

    • Love

    • Passion

    • Romance

    • Danger

    • Energy

    • Intellect

    • Peace

    • Authority

    • Friendliness

    • Sincerity

    • Maturity

    • Warmth

    • Confidence

    • Security

    • Caution

    • Integrity

    • Stability

    • Cowardice

    • Tranquility

    • Life

    • Growth

    • Nature

    • Innovation

    • Royalty

    • Creativity

    • Luxury

    • Thinking

    • Wisdom

    • Money

    • Ideas

    • Dignity

    • Freshness

Functions of Color Vision

  • Perceptual Classification:

    • Color signals assist in classifying and identifying a variety of objects.

  • Perceptual Organization:

    • Color enhances the organization of visual elements into cohesive objects.

  • Evolutionary Advantage:

    • Color vision may have provided survival benefits for foraging food.

Components of Color

  • Value:

  • Hue:

  • Saturation:

  • Munsell Color System Example:

    • Purple, Red, Orange, Yellow, Green, Blue, White, Black with respective values ranging from lowest to highest.

Light and Colour

  • Visible Light:

    • Ranges in the electromagnetic spectrum from approximately 400-700 nm.

  • Wavelength Color Correlation:

    • 400-450 nm = Violet

    • 450-490 nm = Blue

    • 500-575 nm = Green

    • 575-590 nm = Yellow

    • 590-620 nm = Orange

    • 620-700 nm = Red

Color Perception Statistics

  • Wavelength Discrimination: 200 Just Noticeable Differences (JNDs)

  • Saturation: 20 JNDs

  • Intensity: 500 JNDs

  • Total Color Range Calculation:

    • Total possible colors = 200imes20imes500=2,000,000200 imes 20 imes 500 = 2,000,000

Selective Reflection and Transmission

  • Selective Reflection: [Detailed explanation pending]

  • Selective Transmission: [Detailed explanation pending]

Color Mixing

  • Additive vs. Subtractive Color Mixing

  • Components by Wavelength:

    • Short wavelengths, medium wavelengths, long wavelengths.

  • Color Mixing Examples:

    • Blue paint mixed with yellow paint.

Theories of Color Vision

  • Trichromatic Theory of Color Vision:

    • Proposed by Young and Helmholtz in the 1800s.

    • Asserts that three receptor mechanisms account for color vision.

    • Behavioural Evidence:

    • Color-matching experiments demonstrate the necessity of three wavelengths for color matching.

  • Physiological Evidence for Trichromatic Theory:

    • Conducted in the 1960s, researchers identified visual pigments responding maximally to:

    • Short wavelengths (419 nm)

    • Medium wavelengths (531 nm)

    • Long wavelengths (558 nm)

  • Opponent-Process Theory of Color Vision:

    • Proposed by Hering in the late 1800s.

    • States that color vision operates via opposing responses:

    • Blue vs. Yellow, Red vs. Green, and White vs. Black.

  • Combining Theories:

    • Each theory details mechanisms of color processing in distinct ways:

    • Trichromatic theory relates to retinal cones,

    • Opponent-Process theory relates to neural responses in the brain.

Color Processing in the Brain

  • Cerebral Achromatopsia:

    • Describes how certain cortical areas respond to different wavelengths.

    • There is no singular module for color perception.

    • Cortical cells in V1 and V4 manage responses to wavelengths while also addressing forms and orientations.

Color Deficiencies

  • Monochromats:

    • Extremely rare, occurring in 1 in 1 million, typically lacking functional cones, resulting in true color blindness.

  • Dichromats:

    • Protanopia:

      • Affecting 1% of males and 0.02% of females; neutral point at 492 nm.

      • Above this point, colors appear yellow due to missing long-wavelength pigment.

    • Deuteranopia:

      • Affecting 1% of males and 0.01% of females; neutral point at 498 nm, sees short wavelengths as blue.

    • Tritanopia:

      • Affecting 0.002% of males and 0.001% of females; neutral point at 570 nm, above which red is perceived due to loss of short-wavelength pigment.

Color Constancy Mechanisms

  • Color Constancy:

    • The perception of constant color across various lighting conditions.

  • Chromatic Adaptation:

    • Prolonged exposure to color stimuli can lead receptors to adapt, decreasing sensitivity to that particular color.

    • This adaptation assists in maintaining color constancy.

  • Effect of Surroundings on Color Constancy:

    • The surrounding environment significantly impacts color perception, adjusting visual processing accordingly.

Lightness Constancy

  • Achromatic Colors:

    • Achromatic colors appear relatively constant in light despite variations in illumination.

    • Illustrated by the Ratio Principle, which states that two areas reflecting different amounts of light will look the same if their intensity ratios are consistent.

  • Visual Complications Due to Light Distribution:

    • Consideration must be given to uneven lighting, which can create reflectance and illumination edges affecting perceived color and lightness.

Summary of Studies and Authors

  • Key Studies:

  • Notable Authors:

    • Bruce Goldstein

    • Cengage Learning (2014)

    • Uchikawa et al. (1989) documenting color perception adaptations and shift based on stimuli.

Concluding Thoughts

  • Understanding color perception encompasses a blend of physiological, psychological, and contextual factors, fostering an intricate comprehension of vision and interpretation of color in the world around us.