Dithering
More colours from fewer
Dithering created the illusion of additional colours by interleaving pixels of different shades, expanding limited palettes through optical mixing.
Overview
When your palette has sixteen colours but your image needs thousands, dithering provides the illusion. By carefully placing pixels of different colours adjacent to each other, artists created apparent gradients and shades that didn’t exist in the palette. The eye blends neighbouring pixels, perceiving colours the hardware cannot display.
The principle
| Technique | Result |
|---|---|
| Alternating pixels | Apparent mixed colour |
| Pattern density | Perceived brightness |
| Colour adjacency | Blended perception |
Common patterns
Ordered dithering
Regular patterns:
Checkerboard: Bayer matrix:
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█ █ █ █ █Error diffusion
Spread quantisation error to neighbours:
- Floyd-Steinberg algorithm
- Smoother gradients
- More computation required
Platform applications
Commodore 64
| Mode | Colours | Dithering use |
|---|---|---|
| Multicolour | 4 per cell | Essential |
| Hi-res | 2 per cell | Very common |
ZX Spectrum
Attribute limitations:
- 2 colours per 8×8 block
- Dithering within blocks
- Colour clash mitigation
Amiga
HAM mode alternative:
- Standard modes: dithering for gradients
- EHB mode: 64 colours, still dithered
- Quality vs performance tradeoff
PC (CGA/EGA)
| Mode | Colours | Dithering |
|---|---|---|
| CGA | 4 | Essential |
| EGA | 16 | Common |
| VGA | 256 | Less needed |
Artist techniques
Gradient creation
Steps to fake smooth gradients:
- Solid colour A
- 75% A / 25% B dither
- 50% A / 50% B dither
- 25% A / 75% B dither
- Solid colour B
Texture simulation
Dithering creates:
- Metal surfaces
- Fabric textures
- Skin tones
- Natural surfaces
Tools
| Software | Platform |
|---|---|
| Deluxe Paint | Amiga |
| Brilliance | Amiga |
| Art Studio | C64 |
| OCP Art Studio | Spectrum |
Display considerations
| Display | Dithering appearance |
|---|---|
| CRT | Blends naturally |
| LCD | More visible pattern |
| Emulator | Depends on filtering |
CRTs’ natural blur helped dithering succeed.
Famous examples
| Game | Dithering use |
|---|---|
| Deluxe Paint art | Showcase pieces |
| Sierra adventures | Background gradients |
| Bitmap Brothers | Metallic surfaces |