From: lmccullo@nyx.cs.du.edu (Michael McCulloch)
Subject: Re: Lack of color brilliance in GIF pictures?
Organization: University of Denver, Dept. of Math & Comp. Sci.
Date: Wed, 23 Dec 92 21:23:31 GMT

I previously wrote in <1992Dec23.071448.20157@mnemosyne.cs.du.edu>:

>The previous post by William Shipley <1992Dec18.084848.433@u.washington.edu>
>was an excellent explanation of this. However, he wrote:
>
>>PS: PostScript also gives you dithering, which allows you to simulate having  
>>more colors by drawing two (or more) colors right beside each other and  
>>trusting your eye to blur them together as if they were one pixel.  Thus, if  
>>your GIFs look washed out, one solution is to magnify them and back away from  
>>your monitor.  (Another would be to buy a 24-bit true color board, like the
>>NeXTdimension, but the former seems cheaper.)
>
>There's another option. Change the way the GIF is converted. I've noticed
>this 'washed out' appearance of GIFs on my nice Sony monitor -- even with
>images that look fine on other machines. My solution?
>
>I use the gif2tiff converter in Sam Lefler's TIFF utilities library. It is
>available on the sgi.com anonymous ftp site under graphics/tiff. But, before
>you rush to get it, you must compile the package to use it. Although I
>hesitate since this is not my software, I have considered posting just the
>executable for gif2tiff on the NeXT -- since most people are probably only
>interested in that conversion. This may make it to the Purdue ftp site by
>the first of the year.
>
>Sam applies what appears to be a gamma correction (I think -- I'm not an
>expert in image processing) to the color palette of converted GIFs. The
>result is a much more brilliant converted image in which the PS dithering is
>_significantly_ subdued. I have been told that the same 'correction' degrades
>image quality on an ND. This makes sense, since the ND doesn't have to dither
>to display paletted images. I made a slight modification to Sam's gif2tiff
>converter that allows the user to specify the value of the 'correction'
>factor on the command line. Also, he uses the Class P type of TIFF which is
>slightly different from the apparent preferred TIFF formats on the NeXT,
>however, I've had no trouble opening converted files in Preview or Icon
>Builder.
>

Folks, I'm sorry, but for some reason the results when the above package is
compiled on the NeXT are not the same. Why? I don't know -- I've wasted an
afternoon trying to discover the reason with no luck. I have been using the
library on an SGI (IRIX 4.0.5) and the results of gif2tiff are superior when
executed on the SGI and then displayed on the NeXT. So, in summary,

1. Converted 256 color GIFs can look 'washed out' on a NS color using the 
   currently available PD and commercial converters.
2. Sam Lefler's gif2tiff code doesn't help when compiled on the NeXT.
3. To my eyes, Sam's gif2tiff does a superior job when executed on an SGI,
   and the results are then displayed on a NS color machine.

This is a far as I plan to go with this. If someone wants to investigate this
more thoroughly, I can provide example converted GIFs from the SGI if you can
accept 200-300k NeXTmail.

Michael McCulloch
Huntsville, AL