HELP: GIF question

[JQ Johnson]

Diane Madrigal writes:

>(I'm still not sure *why* Netscape was treating the same image
differently
> in the two different contexts, but now that it's no longer happening,
I'm
> not going to lose any sleep over it.)

I do lose sleep over this sort of thing.  In fact, many of your viewers
will see dithering, though as Thomas Dowling notes the proportion is
decreasing and at some point it won't be an issue.

The GVU 9th survey (1 year old) has data at
http://www.gvu.gatech.edu/user_surveys/survey-1998-04/graphs/technology/q8
8.htm suggesting that at least 70% of web surfers have 16 bit or 24 bit
color support (there's a big "don't know" category).  On our campus, I
suspect that more than 30% of web surfers still use 8 bit color, though.
I know that I personally still use 8 bit color sometimes (my display
driver supports only 8 bit at 1600x1200, though I usually use 16 bit color
at 1280x1024).

In understanding why there's a difference between viewing an image
directly versus in an HTML page, you need to realize that as Netscape is
allocating the color palette to display an HTML document it needs to deal
with potentially multiple images (each with different palettes), plus
colors specified in BODY and FONT tags all on the same page (plus some
palette entries reserved by the system).  Suppose it has a 256-color
display and must thus select which colors to include in its palette.
Rather than attempting to optimize, most versions of Netscape always use
the Netscape 216-color palette in this case.  On the other hand,
optimization is easier if Netscape is directly displaying a single GIF
image, and in that case it can use the palette from the image without
modification (maybe only if the palette has fewer than 236 distinct
entries?).

Note that MSIE does things a bit differently and that Macs are different
from PCs.

My own plan for the next six months or so is to continue to use only the
NS 216 palette for all my colored GIF images and all colors I specify
directly in my HTML or CSS.  I plan to reevaluate that decision this
summer and perhaps relax my discipline if the proportion of 8-bit users
sinks below about 15% or if MSIE market share continues to grow rapidly.

JQ Johnson                      Office: 115F Knight Library
Academic Education Coordinator  mailto:jqj at darkwing.uoregon.edu
1299 University of Oregon       phone: 1-541-346-1746; -3485 fax
Eugene, OR  97403-1299          http://darkwing.uoregon.edu/~jqj/