Digital BW, The Print

Steve,

> 
> The ICC profiles are of a very specific file type and description as
> outlined by the International Colour Consortium.  You can get the
> specification from www.color.org.  Therefore, subject to spec version
> changes, there is just one type of file and ICC profile capable
> applications
> can use any profile that meets the spec for which they are compliant.

There are a number of ways to make an ICC for different purposes.  For
example, we make ICCs in Photoshop to modify the monitor view (or "soft
proof" it).  QTR can make ICCs.  Are these the same type of file?  Can
either or both be used in the Print with Preview workflow?

> 
> As far as greyscale is concerned, an ICC profile is sort of similar to
> what
> I believe a transfer curve is in the sense that typically a greyscale ICC
> profile comprises the mandatory header information, the paper white point
> (wtpt tag) and a tag called kTRC.

> ... a transfer curve function doesn't typically allow you to
> alter the two end points.  

I agree, but that has not been a problem for most printers (7600 aside).

>  kTRC is a curve describing the stimulus
> response behaviour of the printer/ink/driver/paper combination.

This is probably where the similarity is, but perhaps coded differently.

I call this graph or relationship an input-output curve.

> The data is
> scaled in XYZ to the media white point, ie it is media relative.

Like Lab, is XYZ an absolute luminance scale?

Unless one is using glop, I can't see many situations where I'd want to tell
the printer to put any ink in my 0% highlights.  

I think the loading for the black point may be where there would be more
practical difference, but aside from the 7600, I almost always found an
Epson paper type that worked for controlling loading and gave essentially
the best dmax.  As was noted in a recent thread, most of the good matte
papers seem to be able to handle about the same load.

> Therefore
> the curve runs from the very top right to some point on the left y axis
> equivalent to the black point of the output as scaled for white point.  If
> you build into the ICC profile kTRC tag black point compensation then the
> curve will hit 0,0.


So, does black point compensation mean the curve hits (0,0)?



>  Therefore one can, via a transfer curve, cause the same
> sort of luminance adjustment that an ICC profile can achieve.  
> You just need to know the points for the transfer curve.

Yes, and in that respect, I think there will always need to be a variety of
ways to determine this, including manually and visually.

As long as the loading is set right with the Epson paper type selection, it
would appear a Transfer Function could do essentially the same input-output
mapping function as an ICC or "linearizing" function in another rip. 

> Therefore as I understand it, one could theoretically achieve the same
> thing with either approach.  However, the transfer function in PS 
> (and other apps), if I recall correctly, limits the number of points.

Yes, it uses less than I'd ideally like.  Is there a limit in the ICC
format?

> The old QTR Create ICC app essentially created a kTRC (k for greyscale)
> from the input data.  WTPT scaling was done and, depending on the
> version of QTR Create ICC, BPC scaling was done.  

> So you can go into one of these profiles
> and take a look at the kTRC tag and see the curve I am talking about.

If the ICC files are all the same in the way they deal with a grayscale
curve, is it the interface with the curve or input-output tabel that
distinguishes them?

I note that the section of PS that makes the custom dot gain curves -- which
are saved as ICCs -- does not appear to be able to open the QTR ICCs.

>  For colour ICC profiles ...

Too much information for now and a B&W guy.



> In general terms, though, the TRC (tonal response curve)
> approach is deemed insufficient for most devices and lookup tables are
> preferred, specifically A to B and B to A tables.

Is the QTR Curve Creator Linearization tab a look-up take interface?

Is there a graphical curve system?  

Is there a way to relate a PS curve to this system?



> There is a pair for each rendering intent. 

> One for PCS (Profile Connection Space - currently can
> only be XYZ or CIELab) to device conversion and one for device to PCS
> conversion. 

Can you explain these spaces and where they are used?  

> The new/current QTR Create ICC app takes advantage of this and
> uses A2B0 and B2A0 (perceptual) tags.

Do these tags relate to what you've said above?

>  This allows Roy to have colour
> information one way - for soft proofing - but not the other way - for
> controlling the luminance output of the printer. 

To simplify, I'm really interested only in the luminance end right now.

> (The only issue with the
> current version of QTR Create ICC is that Roy is scaling the soft proofing
> data for luminance only 

Good.

> Hope this helps

Yes, I hope within the limited B&W fine-tuning or linearization, and  also
perhaps monitor matching contexts, I can understand the options.  Probably
dealing with just the printer output end is the place to concentrate
initially.  

My goal is to find the easiest way to fine tune or linearize a basic
monotone inkset -- manually and/or with instruments -- within the normal PS
printing procedures as well as others.  It sounds like ICCs and Transfer
Functions can be used in a Print with Preview workflow in PS almost
interchangeably, but perhaps with the advantage of more points going to the
ICC approach.  Does this sound correct? 

Is there a place that describes the specific ways in which a Windows XP user
can use QTR to make an ICC that can be used in the Print with Preview
workflow and then the Epson driver?


Thanks.

Paul
www.PaulRoark.com