1. What is Color:
Color is a visual perception created by the wavelength of light reflected from an object and sensed by the human eye.
Although color perception is a physiological and psychological process, its physical nature is well understood through science and experiments.
2. Discovery of Spectrum (Newton’s Experiment)
- In 1666, Sir Isaac Newton passed white sunlight through a glass prism.
- He observed that white light splits into a spectrum of colors:
Violet, Blue, Green, Yellow, Orange, Red
(No color ends abruptly — they blend smoothly).
3. Visible Light and Wavelength
- Visible light is a small portion of the electromagnetic spectrum (range: 400–700 nm).
- Example:
- Green objects reflect light mostly in 500–570 nm range.
- Objects reflecting all wavelengths equally appear white.
4. Types of Light
| Type | Meaning | Example |
|---|---|---|
| Achromatic | No color, only intensity | Black & white movies |
| Chromatic | Contains color (400–700nm) | Normal colored image |
5. Three Main Quantities of Light
| Quantity | Description | Measured In |
|---|---|---|
| Radiance | Total energy from a light source | Watts (W) |
| Luminance | Energy perceived by the human eye | Lumens (lm) |
| Brightness | Subjective measure (how bright a color looks) | Not measurable |
6. Role of Human Eye
- Human eye has 6–7 million cones (color sensors), divided into:
- Red cones – 65%
- Green cones – 33%
- Blue cones – 2% (most sensitive)
So, we perceive color using RGB (Red, Green, Blue) system.
7. Primary and Secondary Colors
Primary Colors (Light):
- Red + Green + Blue
Secondary Colors (Light):
- Red + Green = Yellow
- Red + Blue = Magenta
- Green + Blue = Cyan
Mixing all 3 primary colors (light) = White Light
Primary Colors (Pigments/Ink):
- Cyan, Magenta, Yellow (These subtract light)
Secondary Colors (Pigments):
- Red, Green, Blue
Mixing all 3 pigment primaries = Black
8. Display Technologies
| Technology | Working Principle |
|---|---|
| CRT TV | Uses RGB phosphor dots hit by electron guns to produce color |
| LCD | Uses polarized light & color filters with Thin Film Transistors (TFTs) |
| Plasma | Tiny gas cells coated with phosphor emit RGB colors when excited |
All display systems use RGB triads (3 subpixels) to create color pixels.
9. Color Characteristics
| Property | Meaning |
|---|---|
| Brightness | Intensity of color (light or dark) |
| Hue | Dominant color (Red, Green, Blue etc.) |
| Saturation | Purity of color (0% = White, 100% = Pure color) |
Hue + Saturation = Chromaticity
10. Tristimulus Values (X, Y, Z)
- Represent the amount of Red, Green, Blue needed to produce a color.
11. Trichromatic Coefficients
12. CIE Chromaticity Diagram
- A 2D plot of
xandyvalues to represent all visible colors. - Boundary: Pure spectrum colors (fully saturated)
- Center (white point): Equal mix of R, G, B
- Line between two colors: Shows all possible color blends between them
13. Color Gamut (Color Range)
- Triangle in CIE diagram: Represents range of colors an RGB monitor can display.
- Printer Gamut is smaller and irregular due to mixing limitations in ink/pigments.
Final Summary
| Concept | Description |
|---|---|
| Visible Light Range | 400 – 700 nm |
| Primary Colors (Light) | Red, Green, Blue |
| Secondary Colors (Light) | Cyan, Magenta, Yellow |
| Color Properties | Brightness, Hue, Saturation |
| Chromaticity | Hue + Saturation |
| Color Mixing Diagram | CIE Chromaticity Diagram |
| Device Color Range | Called Color Gamut |