Web graphics: Interlacing samples

On this page: Samples of how interlaced GIF files display over a slow connection.

There is (or used to be) a very large GIF image with no interlacing on Lynda Weinman's site, and in the good old days of universally slow dial-up connections, you could see it download in horizontal strips.

Back in 2001, I located a copy of this image in my browser cache and saved it with interlacing *, just so you can see the effect here:

The small image far right is part of the same thing, but done as a progressive JPEG. Much faster to display, so more difficult to capture! As you can see, JPEGs go from fuzzy to crisp, rather than blocky to fine, but the principle is the same - give the reader something to look at while he/she waits.

PNG files use a more sophisticated (2D) kind of interlacing than GIFs, which gives a better result earlier on in the download process.

* Of course, I subsequently deleted the amended copies from my PC once I'd taken the necessary screen shots, as it isn't my copyright.