Commodore 64

Color palette

The C64’s VIC-II chip has a fixed palette of 16 colors. These are not RGB values but are generated internally by the chip’s luma/chroma circuitry, which means the exact colors vary between VIC-II revisions (6567, 6569, 8562, 8565) and between NTSC and PAL systems.

The Pepto palette (Philip “Pepto” Timmermann, 2001) is the most widely accepted set of measurements and has become the de facto standard in the C64 community:

The key constraint: per-cell color limits

The C64’s VIC-II chip supports two bitmap graphics modes, each with different color constraints:

Hires mode (320x200)

Each 8x8 character cell can use only 2 colors — one foreground and one background, both chosen freely from the 16-color palette. This gives the full 320x200 resolution but severely limits color variety within each cell. When color boundaries don’t align to the 8x8 grid, the constraint solver must choose which pair of colors best represents each cell, producing the characteristic “attribute clash” artifacts familiar to anyone who used a C64 or ZX Spectrum.

Multicolor mode (160x200)

Each 4x8 cell can use up to 4 colors:

• 1 shared background color (global, the same for every cell on screen)
• 1 shared auxiliary color (also global across the screen)
• 2 cell-specific colors (unique per 4x8 cell)

The tradeoff is horizontal resolution: pixels are double-wide (160 logical pixels stretched to fill the 320-pixel display width), giving a chunkier look but significantly more color variety per cell. Most C64 game graphics used multicolor mode for this reason.

Interactive demo

Code example

Basic usage with the Pepto palette

import { process } from 'bitmapped';
import { getPreset } from 'bitmapped/presets';
 
const c64 = getPreset('c64-pepto')!;
 
const result = process(imageData, {
  blockSize: 1,
  palette: c64.palette!,
  dithering: 'floyd-steinberg',
  distanceAlgorithm: 'redmean',
});

Multicolor mode with constraints

import { process } from 'bitmapped';
import { getPreset } from 'bitmapped/presets';
 
const c64mc = getPreset('c64-multicolor')!;
 
const result = process(imageData, {
  blockSize: 1,
  palette: c64mc.palette!,
  dithering: 'none',
  distanceAlgorithm: 'redmean',
  targetResolution: { width: 160, height: 200 },
  constraintType: 'attribute-block',
  attributeBlockConfig: {
    width: 4,
    height: 8,
    maxColors: 4,
    globalBackground: 0,
  },
});

Note globalBackground: 0 — this tells the constraint solver that palette index 0 (Black) is the shared background color and must appear in every cell.

Available presets