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What is Indexed Color?

Indexed color stores each pixel as a reference to an entry in a finite color palette rather than as full channel values. Its capacity is limited by the number of palette entries available to the image.

How Indexed Color works

An indexed raster separates image samples into an index plane and a color table. Quantization chooses representative palette entries and assigns every pixel to one of them; optional dithering distributes the resulting approximation error. Palette order is part of the encoded data because pixel values refer to positions, not colors directly. This model is selected during export for graphics with limited colors, compact archival assets, or formats and devices built around palettes.

Key facts

  1. GIF color tables contain at most 256 entries, and transparency identifies a palette index rather than storing a separate alpha value for every pixel.
  2. Indexed PNG uses a PLTE chunk for colors and can add per-entry transparency through tRNS; decoders expand these references when producing display pixels.
  3. Editing a palette entry changes every pixel that references that index, which enables cheap recoloring but prevents two such pixels from diverging without reassignment.

When Indexed Color matters

Choose indexed color for palette-based GIF or PNG-8 assets when compact size matters more than full color fidelity. Photographs and smooth gradients may show banding or dithering because many source colors must share palette entries.

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