Re: Interlaced vs. Non-interlaced GIFs

Chris Lilley, Computer Graphics Unit (
Tue, 22 Nov 1994 15:18:24 +0100

John Lewis writes:

[attributions deleted]
>>>> Frame -> postscript @ 150 dpi -> scale 50% -> GIF
>>>> This results in an nice anti-aliased image.

>>Yes. I wish more people would do this.

> Perhaps someone could go into this in a little more detail?

> What do you mean by "Frame"?

Many DTP programs put figures in frames which can then be anchored to the text
flow, a particular point on the page, or whatever.

> Do you mean save it (the random image) as a
> postscript file at 150dpi, then scale that image by 50% and save as a gif?


It is a program doing this, not the user. The program saves out each figure -
not an image, a line drawing or diagram - and converts it to an image at 150
dpi. By scaling down (this is called resampling in Photoshop) an antialiased
image at 75dpi results, so that, say, a diagonal black line on a white
background comes out as black pixels with grey ones at the edge. You would
imagine this would make the image fuzzier - infact it removes annoying jaggies
so the image looks higher resolution than it is.