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filmscanners: Lossless JPEG's? was Hello



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




 




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