G'day Mark--
Phil Lippincot recently posted about the existence of lossless JPEG
and is the one who first mentioned that quality level 12 in Photoshop
6 invokes JPEG's lossless mode. He produces drum scanner software
and says his software supports lossless JPEG as a way of making those
huge scans a bit more manageable with no image degradation. Phil
suggests that you can prove it to yourself my saving an image in both
uncompressed TIFF and JPEG quality 12 (in Photoshop), then re-opening
both files, then merging them into one file with two layers, then
setting the blend mode to difference.
JPEG LS is part of the next-generation JPEG standard and it's not
clear whether it's been finalized or not.
--Bill
At 10:55 PM +0930 21-10-01, Mark T. wrote:
>At 04:06 AM 21/10/01 -0600, Bill wrote:
>>...
>>o The JPEG standard includes a lossless setting. Photoshop 6
>>supports it: set the quality level to 12. it will compress to, say,
>>1/3 of the original size. JPEG only supports 24-bit images.
>
>G'day Bill.
>
>I had never heard of a lossless JPG, so I checked the JPEG FAQ,
>which basically says that there *was* an early version of a lossless
>JPEG, but it never took off. They also referred to a new standard
>called JPEG-LS - is this what you meant? I couldn't see anything
>about it in the PS Help file, but I only took a quick look. I would
>be most interested if PS6 really does supprt a lossless JPG.. As
>far as I knew, the main players were/are:
>
>TIFF
>- 48-bit, lossless, large files
>
>TIFF with LZ compression
>- As above but files can be much smaller (esp if image is not grainy
>or detailed), eg typically 1/2 to 1/5 original size
>
>JPEG
>- 24-bit, lossy but adjustable. File sizes often less than 1/5 of
>the uncompressed TIFF (depending on quality setting and image
>content)
>
>PNG
>- 24-bit, lossless. File sizes usually a bit smaller than
>compressed TIFF, but not as small as JPEG.
>(PNG's are also readable by most browsers, which makes them useful
>for 'critical' web-display.)
>
>FWIW, I always use TIFF without compression if in any doubt (I have
>had quite a few problems with lack of portability of LZ'd TIFs), and
>I am now moving over to PNG's for my own file storage in order to
>save CD space. The lack of 48-bit quality hasn't yet been an issue
>for me..
>
>mt
--
======================================================================
Bill Fernandez * User Interface Architect * Bill Fernandez Design
(505) 346-3080 * bill@billfernandez.com *
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