Datacolor User to User Support Group.

>>1) I understand that the 8 bit vs. 16 bit refers to the bit depth of
the LUT, but don't understand what the practical significance of this
is in terms of the profile precision.  Why would one choose 8 bit
only in some circumstances?

Saving space or time would be the only reasons, and with fast computers 
and large drives, its really not an issue. If you were to send profiles 
via low speed connections to other locations, that might be a reason... 
but printer profiles are not tagged to images for distribution, as they 
are printer specific. So there isn't a lot of reason to build low bit 
profiles.

>>What advantage to 16 bit?  Does this
have anything to do with the bit depth of the target printed to make
the profile?

None at all, it just specifies the number of digits each value is 
calculated to.

>>2) When looking at profiles in Colorthink, those made with GMB
Profilemaker (with Atkinson 1728 patch target) show:

16 bit table, 33 grid points
16 bit table, 33 grid points

while those produced by Canon for the IPF5000 show:

8 bit table, 9 grid points
8 bit table, 33 grid points

>>What does the number of grid points mean, and how does it relate to
bit depth (if at all) and number of patches in the target used to
make the profile (if at all)?

No direct relation to bit depth, a coarser grid on the return side of 
the profile (used only for previewing, not printing in most 
circumstances) is just a space saver... the grid is how many 
measurements there are, the bit depth is how many digits in each 
measurement, so you would ideally want more in both... within reason.

>> I haven't seen any of the printfix
profiles, but wonder how they compare here.

Our low bit profiles also contain a coarser grid return table, on the 
theory that those wishing to save space will want to save it there as 
well, like the Canon profiles.  Our high bit profiles are fine grid in 
both directions, like the Atkinson profiles.

>>Any help appreciated on this confusing topic.

I think that covers it; you would have to look very closely to see any 
difference, but we added the highbit/fine return grid option to PFP for 
those who would prefer the larger, and at least theoretically more 
accurate, option.

C. David Tobie
Product Technology Manager
ColorVision, Inc.
CDTobie@...
www.colorvision.com

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