What technique approximates more colors using a limited GIF palette?

Dithering approximates more colors in an image that uses a limited GIF palette.

Instead of assigning every pixel the exact color from a source image, dithering places nearby pixels of available colors in patterns. At normal viewing distance, the eye blends those colors and perceives an approximate intermediate shade. This lets a palette-based image suggest more tonal variety than its stored colors alone would provide.

GIF itself supports at most 256 colors per image or frame, so converting a photograph or other true-color artwork can produce banding, harsh transitions, and lost detail. Dithering reduces some of the visible banding by distributing quantization errors spatially. Floyd–Steinberg dithering is one well-known error-diffusion method, while ordered and patterned dithering use more regular arrangements.

Dithering does not add extra colors to the GIF palette and is not the same as interlacing. It can also make files less compressible because the added pixel patterns create more variation. For simple logos, diagrams, and flat illustrations, avoiding dithering may produce cleaner edges and smaller files.