Digital BW, The Print

Steve,

I think you kind of have this backwards.  All your Converts are changing the
file values.  By Converting you no longer have an even stepwedge.  What you see
with the K and Lab values are the actual values.  K is calculated by (255-gray)/2.55
and L is the actual calculated Luminosity based on the grayscale profile.

BTW, if you are looking at RGB values throughout this exercise they will absolutely
confuse the situation to no end.  You would be seeing another profile conversion to
the working RGB space.  The numbers are fairly removed from what's in the data.

The one feature of PS that shows what's really there is the Histogram.  A stepwedge
should have nice even combs there.

You need to Assign profiles to try the different grayspaces.

Roy

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Steve Kale <stevekale@b...> 
wrote:
>
> 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@h...>
> > 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@...m, "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
>