Last modified: Tue Feb 12 11:40:36 UTC+0100 2019 © A. Tarpai

Interlaced GIF: progressive display

Nearly all image compression method has a technique for browsers to display an approximate image while the file is loading.

GIF calls it interlaced: when this bit in the Image Descriptor is set, there are four sub-images coded after each other and each sub-image contains only a portion of the final image: every eighth, fourth, etc. lines.

Without interlace the image would look like this:

This type of storage makes it possible to display the image progressively:

The GIF-decoder in RAINBOW Library decodes the whole image as if non-interlaced.