Message-Id: <mailto:199607122140.QAA09605@library.wustl.edu> Date: Fri, 12 Jul 1996 17:41:45 -0500 From: Sandeep Somaiya <mailto:root@SANDEEP.VTLS.COM> Subject: Re: Lossless JPEG? To: Multiple recipients of list IMAGELIB
> From: Pamela Mason <mailto:pmason@ENH.NIST.GOV> Is it possible
> to have a lossless JPEG file? If so, what would the
> compression be vs. a typical original with no compression?
According to the JPEG standard and JPEG FAQ's:
The JPEG standard does include a truly lossless compression algorithm, i.e., one that guarantees its decompressed output is bit-for-bit identical to the original input. However, this lossless mode has almost nothing in common with the regular lossy JPEG algorithm, and it offers much less compression.
Lossless JPEG typically compresses full-color data by around 2:1. Lossless JPEG works well only on continuous-tone images; it does not provide useful compression of palette-color images or low-bit-depth images. There are very few implementations of true lossless JPEG: The PVRG code and an implementation available from [ftp.cs.cornell.edu in /pub/multimed/ljpg.tar.Z]
Cranking a regular JPEG implementation up to its maximum quality setting does not get you lossless storage; lossless JPEG is a fundamentally different method. Even at the maximum possible quality setting, regular JPEG cannot be lossless because it is subject to roundoff errors in various calculations. The roundoff errors are nearly always too small to be seen, but they will accumulate if you put the image through multiple cycles of compression.
Best Sandeep Somaiya
* Sandeep Somaiya * Manager Multimedia Systems * VTLS Inc.* * Tel: (540) 231 3605 * Fax: (540) 231 3648 * * Email: mailto:sandeep@sandeep.vtls.com * http://sandeep.vtls.com * *"Look Learn Listen Libraries change Lives"*