Palettes

A palette is, at its simplest, a lookup-table of colors with their corresponding index that is utilized when display's computer graphics. Palettes are often hardware defined (i.e. the palette used by the graphics hardware of the NES) or specific to the file-format or software (such as a palette embedded within a GIF or 8-bit PNG). Whilst palettes are common across all media, they are particularly relevant in games.

Game palettes

Early game formats would often make use of a palette for two primary reasons:

• The historical limits of graphics hardware meant that a full-spectrum of colors was not feasible or necessary.
• Palette's allow for greater compression of in-game assets and less processing-time when loading assets.

Structure

Game palettes often comprise a the following chunks of data:

• The palette itself, usually containing 256 swatches and 768 bytes in length. The palette size of 256 swatches allows each index to be represented by a single byte and corresponds to 8bpp mode (or 256 color mode) limitations of personal computers of the time.
• Any number of Blending tables, which store pre-computed transformations on a palette, such as shading or blending. The results refer back to an index in the palette itself.

The palette:

• Palettes are often stored as tuples (1 byte for the red, green and blue channel in sequence) or in planes (1 byte for the red component for each swatch, then 1 byte for the green, then 1 byte for the blue).
• Whilst RGB component ordering is conventional, the components are sometimes ordered differently.
• If the palette appears dimmer than expected, it might be using less bits per byte in one or all components. It was common to store components using 6-bits (0-63). These would need to be multiplied by 4 to map the components back to the expected range of 0-255.
• Often, the palette is the first chunk of data within the file.