[253] in World Wide Web
Images on the web
daemon@ATHENA.MIT.EDU (yandros@MIT.EDU)
Mon May 16 00:38:32 1994
From: yandros@MIT.EDU
Date: Mon, 16 May 94 00:38:14 EDT
To: www@MIT.EDU
I found this on the <a href="news:comp.infosystems.www">net</a> and
thought that people might be interested. There are some problems with
colormap issues and graphics browsers, since the most common type of
color workstation can only display 256 colors at any one time and has
to switch colors around in a table called a `colormap'. Mosaic, by
default, only allows inlined images to take up 50 colors at any one
time, so if you're inlining 256 color images hoping that other mosaic
users will see the fine detail you're (in some senses) wasting your
time.
One good trick to do is to take the GIF you're starting with and
pass it through the pbmplus/netpbm utilities like so:
giftoppm < my.gif | ppmquant 16 | ppmtogif > my.clean.gif
This knocks the image down to 16 colors and does a very clever
job of it, utilizing dithering and other techniques to produce
a high quality result. You might be surprised to learn that the
output is usually highly satisfactory even on rather colorful
images. It falls down only for images with many essential colors
that must be distinguishable in areas of fine detail.
