There a 16 bit version of JPEG but not too many systems are supporting it yet. It still uses lossy compression though. The advantage of that lossy compression is that the files can be much smaller than they can with lossless compression methods.
--
William Robb wrote:
Thanks Mike. I realize that to be true to the subject, one should learn something of the mathmatics of the compression method, I am really only interested in what JPEGing does to the opened file. IE: If a file has gone through a JPEG phase, will it always be an 8 bit per channel (I undersand this, it's like the Zone system with higher math) image when opened in an imaging program such as Photoshop? Your answer seems to confirm that.
William Robb
----- Original Message ----- From: "Mike Ignatiev"
Subject: Re[2]: JPEG Question
The "reduced" algorithm, from the FAQ is fairly simple:
1. Transform the image into a suitable color space. 2. (Optional -- omitted) 3. Group the pixel values for each component into 8x8 blocks.
Transform each
8x8 block through a discrete cosine transform 4. In each block, divide each of the 64 frequency components by a
separate
"quantization coefficient", and round the results to integers. 5. Encode the reduced coefficients using either Huffman or
arithmetic coding.
6. Tack on appropriate headers, etc, and output the result.
Basically, the 3rd step is where the "pixel" come into play. In
theory,
one can write a codec for an arbitrary color depth. In practice, I
am yet
to see one. Since all "observable" codecs work on 24 bit color,
there's
a good reason to think of JPEG as 24 bit format (if you want to be
able
to read it back, anyway).
BTW, zipped 24 bit tiff would be still a 24 bit format, although <q>the concept of "bits per channel" just doesn't exist inside
a</q>
zip file :)
Mishka
-----Original Message----- From: Steve Jolly Subject: Re: JPEG Question
Sorry to rain on your parade, but JPEG is far more complicated
than
"eight bits per channel". Internally, there is no concept even
of
pixels! Regular JPEGs are usually created from 8-bit-per-channel bitmaps, and there's not much point in converting them back into
bitmaps
of greater depth than that before viewing or printing them, but
there
the concept of "bits per channel" just doesn't exist inside a
JPEG file.
If you want to enter the scary world of lossy compression
techniques, a
good starting place is the comp.compression FAQ at http://www.faqs.org/faqs/compression-faq/. JPEG is described in
section
75, which is in part 2 of the FAQ.
S
-- graywolf http://graywolfphoto.com
"You might as well accept people as they are, you are not going to be able to change them anyway."
