Originally Posted by
Monroe
Actually interlacing images is still useful, particularly in web design. It saves the data of the image differently, so that the entire shape and size of the image will appear at a low resolution, and then get more clear as it finishes downloading. If you don't interlace the images, then they have to start downloading from the top of the image and it increases to its full size as it finishes downloading. So if you interlace the images of you website say, the layout won't jump around as you wait for the images to download, they'll all appear at their normal size and just get clearer. That's why it makes more sense to use it with larger images because with a smaller image it downloads so quick there's no point, since interlacing an image increases the file size.