Neo Geo

Color palette

The Neo Geo uses a unique 16-bit color format. Each color word encodes 5 bits per channel for red, green, and blue, plus a shared “dark bit” that halves the brightness of all three channels simultaneously. This gives each of the 32,768 base RGB555 colors a normal and dark variant, totaling 65,536 unique colors.

The bit layout of a 16-bit color word is:

D R0 G0 B0 R4R3R2R1 G4G3G2G1 B4B3B2B1

Where D is the dark bit (bit 15), R0/G0/B0 are the least significant bits of each channel (bits 14-12), and the upper nibbles hold bits 4-1 of each channel. The dark bit acts as a shared LSB appended to each channel’s 5-bit value, effectively producing 6-bit precision per channel.

The key constraint: per-sprite palette

Colors are organized into 256 palettes of 16 colors each, for a maximum of 4,096 simultaneous colors on screen. Each sprite selects one of these 256 palettes.

The generous 256-palette count is far more than most contemporary systems offered (the SNES had 8 sprite palettes, the Genesis had 4). This abundance is why Neo Geo games are known for their rich, vibrant artwork with smooth gradients and detailed shading. Artists could dedicate entire palettes to individual characters or background elements without the palette-sharing compromises required on other hardware.

However, the 16-color-per-palette limit still shapes how graphics are structured. Large characters with many color needs are assembled from multiple sprites, each potentially using a different palette, carefully aligned to avoid visible seams.

Interactive demo

Code example

import { process } from 'bitmapped';
import { getPreset, enumerateColorSpace } from 'bitmapped/presets';
 
const neoGeo = getPreset('neo-geo')!;
 
// Generate the full palette from the color space definition
const fullPalette = enumerateColorSpace(neoGeo.colorSpace!);
 
const result = process(imageData, {
  blockSize: 4,
  palette: fullPalette,
  dithering: 'floyd-steinberg',
  distanceAlgorithm: 'ciede2000',
});

bitmapped also exposes low-level utilities for working with Neo Geo color words directly:

import {
  decodeNeoGeoColor,
  encodeNeoGeoColor,
} from 'bitmapped';
 
// Decode a 16-bit Neo Geo color word to RGB
const rgb = decodeNeoGeoColor(0b1_1_0_0_1111_0000_0111);
// { r: 255, g: 4, b: 60 }
 
// Encode an RGB color back to a 16-bit Neo Geo color word
const word = encodeNeoGeoColor(255, 0, 60);
// Quantizes to 6-bit per channel, packs into Neo Geo bit layout

Presets

bitmapped includes one Neo Geo preset:

• neo-geo — RGB555 + dark bit color space (65,536 possible colors), 4,096 simultaneous, 320x224 resolution, CRT RGB output with scanline effects