Message-Id: <mailto:199409140517.AAA26010@library.wustl.edu> Date: Tue, 13 Sep 1994 13:48:36 -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 Tue, 13 Sep 1994, Nick Cahill wrote:> Although an 8-bit color file is only 1/3 the size of a 24-bit file, only
> 24-bit color images can be compressed using JPEG. A JPEG-compressed 24-bit
> file is considerably smaller than an 8-bit image -- by a factor of three to
> five. And it looks just as good if not better, IMHO. If file size is an
> issue (and when isn't it?) then I'd go with compressed 24-bit images every
> time.
>
> Nick Cahill
> Dept. of Art History
> Univ. of Wisconsin-Madison
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) 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)
As soon as you zoom in on the GIF file in comparison with the JPEG file, the quality difference is dramatic (GIF does not handle this well), but the TIFF 8-bit, JPEG, and LZW compressed 24-bit color all appear about the same. With the JPEG, however, you've retained the 24-bit color characteristics. Naturally, this is not an archival quality image. That will be retained for all the usual reasons.
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 |
| Phone: (301) 504-6813 | 10301 Baltimore Blvd. |
| Phone: (301) 504-7473 | Beltsville, MD 20705-2351 |
*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*