Digital BW, The Print

But the L* separation of Lab vs GG 2.2 is an illusion created by sample.
Convert between the two and your colours remain the same.  So if you are
looking at a 51 step wedge on your display in GG 2.2 then the 90% K patch
reads L* 6.  Convert to Lab and the same patch's colour doesn't change at
all and it's L* is still 6.  Convert to GG 1.8 and yes 90% grey is now 94%
grey but the color is the same and it is still L* 6.  Another way to put
this is that the visual separation you see does not change as you convert
between workspaces.  If your printer could reproduce all the shades of grey
you see on screen then that patch will look the same in print and read the
same when you measure it.  It doesn't matter which space you work in (at
least for B&W - there are other complications for colour).  When you convert
to the printer output profile (you do not assign a printer profile) your
colours will map the same. The only issue is the handling of out-of-gamut
colours and its influence (if any) depending on intent of in-gamut colours.


> From: Roy Harrington <roy@...>
> Reply-To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Date: Thu, 20 Oct 2005 20:30:04 -0000
> To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Subject: Re: [Digital BW] ICC v. Transfer Function in Epson driver
> 
> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Paul Roark"
> <paul.roark@v...> wrote:
>> 
>> I've printed several samples this morning to further explore the flat
>> 95-100% print separation issue.  Consistent with what Roy noted, I've found
> 
> ...
> 
>> 
>> What kind of 100% - 95% print separation (Lab L differences) are others
>> seeing with the Create ICC approach?  Is it just my system?
>> 
>> Paul
>> www.PaulRoark.com
>> 
> 
> There's been a lot of talk about the 95 to 100 range and what separation can
> be
> and ought to be seen there.
> 
> The one thing that I haven't seen emphasized is the issue of what grayspace
> people are using.    100 is always dMax but where 95 falls is dependent on
> what grayscale people are using.   Most often the default grayspace that is
> used
> is GG 2.2.   This defines a very dark 95 step.  Put the eye dropper on it and
> 100 to 95 is L=0 to L=1 a very much lower slope than most of the range.  This
> is
> a definition issue not a matter of any calibration or device quality.   This
> small
> step is often visible with a nicely calibrated monitor but on a matte print
> the
> difference is very small.   Without CMM this can be fudged but as the
> measurements
> get more precise I think this is a builtin side effect.
> 
> This is one of the main reasons I create the Gray Lab space.  With this space
> 100 to 95 shows as L=0 to L=5  -- 5 times the slope.  Note that the only thing
> different is the grayspace used -- you make and use the ICC profiles
> identically.
> 
> Roy