Sega Master System

Color palette

The Master System VDP uses 6-bit RGB (2 bits per channel), producing a palette of 64 possible colors. Each channel has 4 intensity levels (0, 85, 170, 255), yielding a 4×4×4 color cube. Colors are written to the VDP’s color RAM as a single byte with the format --BBGGRR.

The 64 colors are selected into two independent 16-color palettes: one for background tiles and one for sprites. This gives up to 32 simultaneous colors on screen.

The key constraint: per-tile palette

All background tiles share a single 16-color palette. Unlike the Genesis with its 4 selectable background palettes, the Master System has just one — every 8×8 background tile draws from the same 16 colors. Sprites use a separate 16-color palette.

This is a significant limitation that gives SMS games their characteristic look. Developers had to carefully choose a single set of 16 background colors that worked for the entire screen. Techniques like palette swaps between frames or mid-screen palette changes (raster effects) were used to work around this constraint, but the hardware itself enforces a single background palette per frame.

bitmapped’s per-tile-palette constraint solver selects the optimal 16-color subpalette from the full 64-color space, then maps every background tile to that palette. Because there is only one subpalette for all tiles, the solver effectively performs global palette optimization — choosing the 16 colors that minimize total error across the entire image.

Interactive demo

Code example

import { process } from 'bitmapped';
import { getPreset, enumerateColorSpace } from 'bitmapped/presets';
 
const preset = getPreset('master-system');
const palette = enumerateColorSpace(preset.colorSpace)
  .map((c) => ({ color: c }));
 
const result = process(imageData, {
  blockSize: Math.floor(imageData.width / 256),
  palette,
  dithering: 'floyd-steinberg',
  distanceAlgorithm: 'redmean',
  constraintType: 'per-tile-palette',
  tilePaletteConfig: {
    tileWidth: 8,
    tileHeight: 8,
    colorsPerSubpalette: 16,
    sharedTransparent: false,
  },
});

Presets

bitmapped includes one Master System preset:

• master-system — 256×192 resolution, 6-bit RGB color space (64 colors), 32 simultaneous