What is the minimum number of colors a GIF image can have?

The minimum number of colors a GIF image can have is 2 colors. GIF color tables are restricted to powers of two, and the smallest permitted table contains 2 entries.

Both GIF87a and GIF89a support color tables with 2^N entries, where N ranges from 1 through 8. That produces possible table sizes such as 2, 4, 8, 16, and ultimately 256 colors. A simple black-and-white icon can therefore be stored as a two-color GIF.

This does not mean every GIF uses a large palette. Small images often need only a few colors, which can reduce file size. At the other extreme, a GIF frame can use up to 256 palette entries, even though the underlying RGB color space contains millions of possible shades.

Another common mix-up concerns bit depth. GIF image data uses LZW codes, and the encoded-symbol bit width must be at least 2 bits even for a two-color image. That technical rule is separate from the palette itself, whose minimum size is two colors.