Re: Palettes and bad rendering

Murray Altheim (murray@spyglass.com)
Sat, 4 May 1996 12:53:22 -0500


Message-Id: <v02110109adb146abe7c3@[140.186.34.50]>
Date: Sat, 4 May 1996 12:53:22 -0500
To: Chuck Norris <chuck@spinnet.com>
From: murray@spyglass.com (Murray Altheim)
Subject: Re: Palettes and bad rendering
Cc: www-html@w3.org, lee@piclab.com

Chuck Norris <chuck@spinnet.com> writes:
>Lee Daniel Crocker <lee@piclab.com> said:
>>As I see it, then, the issue is not one of lack of information--
>>sending more information, therefore, won't help.  The issue is
>>that browsers are getting the information and doing a lousy job
>>displaying it.  Each image already contains complete information
>>about how it wants to be displayed.  The page itself contains
>>complete information on how it wants to be displayed.  Browsers
>>just aren't listening.  Complain to Netscape, not www-html.
>
>Amen.  Exactly correct.  Graphics software in general has long used color
>>information from the image it's displaying to "tune" the colortable for
>the >best look.  Anyone who uses Photoshop on a 256 color system has
>experienced >this.  Lean on Netscape and Microsoft to implement this
>feature if it's really >what you want.

It won't do any good leaning on them; not that they wouldn't listen, you're
just not approaching the problem. To a great degree, browsers already
attempt to handle the multiple palettes encountered; this isn't a problem
with browsers understanding the specific palette of an individual image.
If you assume a particular GIF is created in PhotoShop, where converting
from RGB to an 'indexed' mode one chooses the palette, a first image might
be 134 colors, the next one 67 colors, the next 199, etc. You can see that
256 gets used up pretty quickly. How would a browser display a document
containing twenty images, all with different, conflicting palettes?
Dithering. Which is what most do.

If you want better color handling, design for 256 colors (since you'll find
that most color displays can handle it) and (IMPORTANT!) use the
_same_palette_ for all of the images that will appear together on that
document. Limiting the number of colors helps, of course, but you'll find
using the same palette to be the big secret. Photoshop allows custom
palettes, or you can simply map RGB to the System palette each time.

In the future, you'll be able to set up your server to handle content
negotiation based on image quality, but that is not currently an available
method.

Murray

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     Murray Altheim, Program Manager
     Spyglass, Inc., Cambridge, Massachusetts
     email: <mailto:murray@spyglass.com>
     http:  <http://www.stonehand.com/murray/murray.html>