Digital BW, The Print

I guess I am not sure what you mean by "-4 down curve".  The idea is that
you linearize the printer or it is done for you as part of the ABW driver,
as one step, and then you profile this output.  For example, Black Only
output is far from linear (terrible in fact) but we can still profile it.
Then colour management is used to manage the difference between file values
and the print "space".  In essence, for B&W this amounts to just tone
compression due to the different black and white points.  In the current
incarnation of the Grey ICC profile generator, Roy is doing the black point
compensation rather than leaving it to PS (this is why you can't proof for
the weaker print black at the moment).  All the data is adjusted for white
point (ie it is media white point relative).  In essence Roy has created a
file that scales input data (file values) according to the media black and
white points.  A Same as Source workflow just takes file data and maps it
directly to the (linear or, in the case of Black Only, non-linear printer
output).  If the printer is perfectly linear there is a straight line in L*
from dMax to dMin and hence the vast majority of pixels are printed lighter
than one would prefer.  What the CM does with the profile I do not fully
understand (it is very hard to get clear answers from colour people when you
ask them to think in terms of just greyscale ICC profiles).  I think it is
in essence simply a transfer curve which has been scaled as I described
above.  So the file data gets adjusted by this curve before hitting the
linear output table of the printer (in lay terms).  Open up your grey ICC
profile in Colorsync and take a look at the various tags.


> From: bwbonkers <PeterDLevis@aol.com>
> Reply-To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Date: Wed, 03 Aug 2005 14:46:39 -0000
> To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Subject: Re: [Digital BW] QTR ICC Profile + R2400 ABW
> 
> Steve
> 
> Many thanks for the reply. As far as I can see printing using a
> custom grey icc profile instead of Same As Source seems to linearise
> the printer. I tried the following experiment:
> 
> I printed the IJC 21 step file first with Same As Source as print
> space profile in PS CS and then with my own custom grey icc profile.
> I then measured both and saved the L values as a text file. I then
> imported them into IJC linearisation page (MAC version) just to see
> what the values looked like. Result the grey icc profile values
> produced a virtually perfect -4 down curve. The Same As Source values
> were not as accurate.
> 
> Form this it seems that using a custom grey profile instead of Same
> As Source is certainly beneficial.
> 
> Any comments.
> 
> Peter.
> 
> 
> 
> 
> 
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