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July 1999
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1999.07.16 17:39 "Re: RGB Gradient Code, adapted from Andreas Neumann", by Eric B Middlecamp
mccoy@pixar.com (Daniel McCoy) on 07/16/99 11:17:00 AM
To: TIFF Mailing List <tiff@olympiakos.com>, Eric B.
Middlecamp/MIPP/Imation@Imation
cc:
Subject: Re: RGB Gradient Code, adapted from Andreas Neumann
> Eric Middlecamp wrote:
> >I made a simple extension to Andreas Neumann's gradient code,
> >(see
>
>http://www.gis.univie.ac.at/strv/strv/leute/andi/computer/graphics/raster-formats/example_tiff_main.html)
> >but the output TIFF image has some odd contamination. Looking at the
> >image, you wouldn't be able to tell -- however a histogram reveals that
> >some levels are omitted and others are doubled.
> >
> >Has anyone else experienced bizarre anomalies like this?
>
> The code looks fine, and Niles was able to run it with no problem.
> But you don't say anything about what type of computer, operating system,
> compiler, image display program, how you produced the histogram or what
> version of libtiff you used in your message.
>
> Dan McCoy Pixar mccoy@pixar.com
>
Ok, here goes.. I am running on a Power Mac 8100/100 under MacOS 8.1, I am
compiling under Codewarrior IDE 2.1, displaying the images in Adobe
Photoshop
5.0, producing the histogram in Photoshop with full data sampling (histogram
not
from cache), and I am using a Mac-compiled version of the old libtiff
"tiff-v3.4beta028," although I have compared the code for libtiff version
"tiff-v3.4beta037" and not found any major differences.
As an update, I just ran a modified version of "tiffinfo," it verified that
the
image I have matches what Niles got when he ran it; the problem must be
related
to the image readers, namely Photoshop. I am also writing some code which
reads
TIFFs, though, and I have gotten some strange results there as well. Is it
possible that I am using a valid, but uncommon/problemmatic, set of tags?
Eric Middlecamp
=========================================================================
sample of modified tiffinfo output on a RGB gradient image:
Strip 0: (00)
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Strip 1: (01)
01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01
Strip 2: (02)
02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02
...
Strip 253: (fd)
fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
Strip 254: (fe)
fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
Strip 255: (ff)
ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
========================================================================