Message-Id: <mailto:199409181037.FAA10209@library.wustl.edu> Date: Fri, 16 Sep 1994 11:25:08 -0400 From: Pamela Mason <mailto:pmason@NALUSDA.GOV> Subject: Re: 8-bit vs. 24-bit color To: Multiple recipients of list IMAGELIB <mailto:IMAGELIB@ARIZVM1.BITNET>
On Fri, 16 Sep 1994, Frank Dunn wrote: (quoting me)> >I agree, Nick. I've been weighing what to use on the CD version of an
> >imaging project, and I 've pretty much decided to go with JPEG for just
> >that reason. The image file sizes I was comparing were:
> >*1.8 MB Original 24-bit color TIFF image (512x768)*
>
> At that spacial resolution it would be worthwhile considering
> fractal image transform compression ( AKA .FIF ). The downside is that it
> really requires hardware compression but decompression is fast in software
> and the files are generally a lot smaller than JPEG at Q2.
>
Well, as I understand it, fractal is a proprietary scheme. I needed something which would work with off-the-shelf software people were likely to have. Do you know of any which supports fractals other than the originator's POEM?
> >857K Compressed (Lossless LZW) 24-bit color file
> >404K Tiff 8-bit color (uncompressed)
> >268K Tiff 8-bit color compressed with LZW
> >205K JPEG (JFIF type) 24-bit color, compressed at quality level 2 (highest)
> >89K GIF (which is 8-bit color and uses a variant of LZW compression)
>
> GIF's LZW isn't as good as run length encoding (RLE) for 8 bit (paletted)
> files, it will result in larger files.
Can you recommend some software which would generate RLE compression? In fact, can you recommend some reading in this area (I'm always looking for material which goes beyond the "This is JPEG" level of discussion but is understandable without a degree in optics!)?
> >Pamela
>
> IMHO its quite feasible to tell the difference between a 24 bit TIFF and
> the same file JPEGed at a high Q level, the DCT algorithm in JPEG tends to
> enhance edges for one without considering the possible changes in the
> images colour gamut.
Interestingly, the images I was looking at had very sharp edges, so I tended to focus on that. I'll have to have another look. Thanks for your comments, Frank!
Pamela *ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ* | Pamela Mason, Project Manager | National Agricultural Library |
| mailto:pmason@nalusda.gov | Information Systems Division |
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> Frank.
> Library Manager (Images).
>
>
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