Study Notes on Color Perception and Trichromatic Theory

Introduction to Color Perception

• Humans possess three types of cones: red, green, and blue.

  • These cones are photoreceptors that help us perceive colors.

  • Despite having only these three types, we can see millions of different colors.

Perception of the Color Yellow

• Humans do not have cones specific to yellow light, yet we can perceive yellow objects, like a banana.

• The key to color perception lies in the relative activation of the red, green, and blue cones.

• Example of the banana:

  • Reflectance Characteristics:

  • Reflects very little in the short wavelengths (blue).

  • Reflects strongly and equally in the medium and long wavelengths (green and red).

  • Activation of the cones:

  • Strong activation of both red and green cones (low blue activation).

  • Resulting Perception: This pattern is interpreted as yellow by the human visual system.

Artificial Light and Color Perception

• An artificial light source can produce the same cone activation pattern to create yellow.

  • A light of a single wavelength that stimulates only red and green cones, and not blue, will also be perceived as yellow.

  • This suggests that perception of yellow is dependent on the pattern of red, green, and blue activation rather than the source of light.

Color Mixing in Technology

• All perceivable colors can be reproduced through combinations of red, green, and blue lights.

  • Devices such as color TVs, computer monitors, cell phones, and video projectors operate using this principle.

  • Pixels are created by blending red, green, and blue lights:

  • Each pixel consists of individual red, green, and blue lights.

  • By varying the intensity of each, a vast array of colors can be produced.

• Example of experimenting with color combinations:

  • Use software such as PowerPoint or websites like htmlcolorcodes.com/color-picker.

  • RGB values typically range from 0 to 255 for each color channel.

  • Example setting for yellow: Red = 255, Green = 255, Blue = 0.

Examples of Colors and RGB Values

• Different colors and their RGB values illustrate how combinations can create various colors:

  • Yellow: (255, 255, 0)

  • Orange: (255, 165, 0)

  • Brown: (165, 42, 42)

  • Magenta: (255, 0, 255)

  • Teal: (0, 128, 128)

  • Gray: (128, 128, 128)

• Suggestion to try creating other colors:

  • Pink, purple, baby blue, and white by adjusting RGB values.

Understanding White Light through RGB

• White light can be generated when red, green, and blue are set to their maximum value:

  • RGB for white: (255, 255, 255)

• Combining yellow light (red and green activation) with blue light results in white:

  • A scenario where overlapping beams from yellow and blue flashlights combine to produce white light.

The Difference Between Light and Paint Mixing

• Mixing colors from light works differently than mixing pigments (paints):

  • Additive Mixing for light:

  • Wavelengths combine to add up to create colors.

  • Example: Mixing lights leads to white.

  • Subtractive Mixing for pigments:

  • Wavelengths absorb certain colors, altering the perception of light.

  • Example: Combining yellow and blue paint results in green.

• For further explanation on the differences, reference material is provided.

Summary of Key Concepts

• Color vision relies on three types of cones, each tuned to different wavelengths:

  • Short wavelengths perceived as blue,

  • Medium wavelengths perceived as green,

  • Long wavelengths perceived as red.

• Trichromatic theory of color perception states that color perception arises from the relative activation of these cones.

  • This theory connects the chemistry of photopigments in the cones with the anatomical structure of the eye.

• Real-world examples demonstrate that perceptions of color can overlap:

  • Different physical objects can be perceived as the same color depending on their wavelength reflectance and the corresponding cone activation patterns.