Interlacing Interlacing is something that can be done with GIF89a images. Interlacing allows the browser to display the image as it is being loaded. The image displays first as a VERY blocky representation of itself, and as more data is received, it slowly resolves to its highest quality. For large images, this can give the illusion of faster loading time for the page, as the viewer is able to see something much sooner than if he or she had to wait until the whole image had been received. However, there is a tradeoff.
Interlaced images have a very small amount of overhead.
Therefore, most interlaced images will be slightly larger than their non-interlaced cousins. For large or even medium-sized images, this difference is negligible. For small images, the difference is slight, but it can build up, and the benefit of interlacing is nearly nonexistant. Doing so can cause problems with the display of the image in some browsers. Transparency Transparency is a nice feature of GIF89a images that allows you to specify one color in the image as being transparent.