Re: Interlaced vs. Non-interlaced GIFs

David Koblas (
Sat, 19 Nov 1994 18:52:23 +0100

> I'm working on a software package that produces HTML documents and
> GIFs (and other files) from a variety of input formats. Currently,
> all GIFs produced by the package are interlaced, so viewers that have
> the capability (e.g. netscape) can get the incremental display that is
> nice to have over slow connections.
> My question is this: is there any downside to always producing
> interlaced images, or should I make it a user preference? For
> example, are there viewers that would choke on interlaced gifs?
> (Mosaic doesn't). Any other issues I should be aware of?

Speaking as one very biased individual, who claims to know something
about GIF images...

Interlaced images are good for two things:
Slow links between client and server
Cool fade in effect

I dislike them for these reasons:
They have a better chance of compressing to a larger file size
They are the _worst_ way you could think of to load images
for an X windows display. You have to scan convert
line at a time and copy to the server, thus adding
another client<->server interaction for every scanline.

The best thing to do is make it an option, since any time I produce
document for a Internal Information System, the server<->client
throughput is 10Mb/s or more and interlaced images are the last
thing that I wan to ship around.

Just my 0.02 cents..


ps. On this product of yours, are we going to get the option
of specifing what DPI resolution we would like the images
generated for? Since on of the things that I do a lot of
is when I rasterize line drawings is the following process:
Frame -> postscript @ 150 dpi -> scale 50% -> GIF
This results in an nice anti-aliased image.