Re: 8 bit vs 16 bit profiling -- does anyone gives a hoot?
Re: 8 bit vs 16 bit profiling -- does anyone gives a hoot?
- Subject: Re: 8 bit vs 16 bit profiling -- does anyone gives a hoot?
- From: Graeme Gill <email@hidden>
- Date: Thu, 07 Jul 2005 14:17:21 +1000
- Organization: Argyll CMS
Roger Breton wrote:
So I heard, that ACE is internally implemented as 16 bit.
I understand that it actually uses 32 bits or more internally.
You mean ACE could interpolate the LUTs in 16-bit instead of 8 bit?
No, I'm pointing out that there is a difference between how the numbers
that determine a transform are stored, and how they are represented
during calculations. Of course an 8 bit ICC profile has sacrificed some
precision in the name of smaller files, but that doesn't automatically
imply that all input, output and intermediate calculations in the transform
are 8 bit.
Gotta back to icclib for further testing of my theory, I guess. But the
problem I'm seeing is that InDesign, Illustrator and maybe Photoshop too (I
stand corrected) are all using 8-bit conversions. In that context, I wonder
what the value of using "Large" or 16-bit profiles in the first place? When
everything will be dumbed down to 8 bit with the possible artifacts I
discussed above. Does an 8 bit profile by design offers less grid points?
Will result in the the CMM doing larger interpolations?
I'd be kind of surprised if this was the case. Most of the time you
are linking two profiles, even if you are only going to use the linked
result to transform 8 bit files, so extra precision in the
individual tables (input, clut, output, *2) will help prevent
accumulating rounding errors at each stage.
Apart from a minor point (the input & output tables are fixed at
256 entries, but remember entries are interpolated between),
the actual clut resolution can be the same as 16 bit profiles.
What is lost is the precision of the numbers in the tables.
I have the impression that actually 16 bit profiles are the norm,
and that 8 bit profiles are rather rare.
Graeme Gill.
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