Digital BW, The Print

In a message dated 5/30/07 10:09:17 PM, bob@... writes:


> I keep seeing the mention of ICC's with imbedded curves.  (I don't
> think this is what Jonathan meant, IMO.)  Is an "ICC with imbedded
> curves" an ICC plus a curve or a completely self-contained ICC?  What
> is meant by "ICC with imbedded curves"?
> 
> Thanks, Roy and Tobie, for the very enlightening conversation!
> 

This is the distinction I keep trying to describe, apparently not too 
successfully.

An ICC profile is a three dimensional transform from on space to another, via 
a 3d LUT. It contains other factors, including a set of single dimensional 
"linearization" graphs for each incoming and outgoing channel. So an RGB printer 
profile comes in from Lab, where you can adjust input L*, or a* or b* values 
before they get to the 3d LUT for transformation. In the case of Create ICC, 
what happens here is the a* and b* values are zeroed out in these tables. Then 
the transform occurs. In the case of CreateICC, this is a dummy transform, a 
simple set of zeros and ones that move the date from one space to the other, 
but don't adjust it. Then there are a set of linearization graphs on the other 
side for the output channels. In a CreateICC profile, it is not the 3d LUT that 
is used for corrections, its the linearization graphs sandwiched to it. Thats 
the "just imbedded curves" that he's referring to. 

You could pull this set of curves out of the profile, apply them in 
Photoshop, and not need the profile at all. The reasons (that I'm aware of) for doing 
it in a profile is convenience (you can pick it from a list at print time, and 
don't need to alter your image file) and preview (some CreateICC profiles can 
be used to preview your print results in Photoshop).

On the other hand, a PrintFIX PRO profile uses the 3d LUT transform (a 
different one for each rendering intent, actually) to do its adjustment. If you are 
printing to a "grays only" printing device or driver, thats all you'd get from 
a PrintFIX PRO profile, not because its all it can hold, but because thats 
the only thing being used. So when I build a profile via Canon's "Monochrome 
(Photo)" mode and use the resulting PFP profile to print to that mode, I get only 
linearization out of it, because thats all the mode looks for.   No color 
adjustment allowed on the input side. But that doesn't mean the data is "just 
imbedded curves", in this case its "just a 3d LUT conversion" instead.

What I would like people to realize is that they are effectively wasting two 
dimensions of correction (a* and b*) when they use PrintFIX PRO to lineralize 
a black and white mode. If it were physically a black and white printer, sure, 
why not, there's nothing else you could adjust anyways. But if its a highend 
color graphics printer with two levels of gray ink, plus a full range of 
colors, then you have the opportunity to use it all, via color mode, to get the 
most controlled, neutralized results possible, by using all three dimensions of 
the Lab space: L* (the grayscale linearization part that you can get in B&W 
modes as well) and a*/b* corrections, which improve the neutrality of the output.

Sorry to keep at this, but I didn't feel that I had succeeded in expressing 
it in a way that was getting across yet... so I'll say it one more time:

The only method I know of that is designed to automatically measures 
neutrality of adjustable tint output at dozens of levels, and neutralizes all of them 
on the fly is PrintFIX PRO used with the Color Mode of a recent graphics 
inkjet. It produces amazingly neutral output on a wide range of media, with 
controls for tuning how the gray ramp runs to paper white, how much shadow detail you 
get, and other important factors. It produces gallery quality B&W output, 
plus your choice of tints and crosstones, and full color images, on gloss and 
matte media, all from the same printer; all from the same paper profile for that 
matter (assuming the printer has two levels of gray ink, and both types of 
black ink). Given all of that, I fail to see why people that already have 
PrintFIX PRO at hand still want to work through the B&W mode of such printers, and 
live with whatever wiggles and wabbles the neutrality of that mode produces on 
the paper they are using.

C. David Tobie
Product Technology Manager
ColorVision Business Unit
Datacolor Inc.
CDTobie@...
www.colorvision.com


**************************************
 See what's free at 
http://www.aol.com.


[Non-text portions of this message have been removed]