Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!elroy.jpl.nasa.gov!decwrl!mcnc!rti!bcw
From: bcw@rti.rti.org (Bruce Wright)
Newsgroups: comp.windows.ms
Subject: Re: How do I get large BMPs as desktops?
Summary: GIFs and context
Keywords: BMP desktop
Message-ID: <1991Apr21.190836.9744@rti.rti.org>
Date: 21 Apr 91 19:08:36 GMT
References: <1991Apr13.125238.17769@uniwa.uwa.oz> <1991Apr21.183828.9406@rti.rti.org>
Organization: Research Triangle Institute, RTP, NC
Lines: 23

I think I ought to clarify something in my previous article about
GIF format.

In article <1991Apr21.183828.9406@rti.rti.org>, bcw@rti.rti.org (Bruce Wright) writes:
>   1)  The GIF format does not have an easy way to find "scan line
> 	n" in an image without reading through the entire image until
> 	you find the beginning of that line - in other words, there's
> 	no way to index to a position, or to jump into the middle and
> 	find the proper reading frame and find the beginning of the
> 	desired line.  Even if you find the proper reading frame you
> 	still have no way to know what line number you're looking at
> 	without having interpreted the entire image preceeding it.

Before anyone unfamiliar with GIF internals jumps in with the
suggestion that Windows could simply keep a table of indices
into the GIF which pointed to the beginning of each line, I
should hasten to point out that you need more context than just
the scan line number.  The additional context is sufficiently
large that this strategy would require significant amounts of
RAM - largely offsetting the benefit of using GIF in the first
place.

					Bruce C. Wright