Digital BW, The Print

Hi Roy

Ok so I have it up now - well done, just the L channel - cool!  That saves
us a lot of storage space should we choose to work in LAB rather than Grey
Gamma 2.2 and like I had said before LAB is hard for colour but easy for
B&W.  

A couple of points:

1.  I suspect most of us will still start either with a Gray Gamma 2.2 file
(scanning B&W film) or an sRGB/Adobe RGB/scanner RGB file (shooting
digitally or scanning colour film).  Once this is in grey scale we should
CONVERT to LAB else all the tonal values will shift (where we had one shade
of grey will now become another and if we exposed a part of the image to
Kodak grey it will no longer be so).  Not a problem, of course, and better
than converting to LAB because at least with this Grey LAB we strip off the
a and b that aren't needed. Very very cool.

(I am very intrigued as to how you did this by the way.)

2.  Now that we have our image in LAB-lite we still have the issue of this
space not being the same as the printer space.  For starters, an image using
the full tonal range (such as an ordinary step wedge) has deeper blacks than
we can print and hence we don't have WYSIWYG.)  So no "built-in" proofing
:-(  See my last post to Keith in the other thread which I will reproduce
here:

"Even if the printer RIP automatically spaces LAB values from
dMin to dMax, ie 0 gets mapped to 16, 5 to 20 etc, you still end up with the
same result: the mid-point shifts.

(By the way, take a look at this sequence of co-ordinates, and their density
equivalents, and look how all print values are shifted.  Plot the step vs
density figures of the two papers and overlay LAB.  Even if the RIP doesn't
make this linear, as I believe was suggested, but curved in equal increments
of LAB, each paper has a different gamma and non have the same value or
curvature as LAB. Only as paper white moves closer to perfect white and ink
dMax approaches perfect black do the curves begin to converge and have the
same gamma.)"

Cheers

Steve

> From: Roy Harrington <roy@...>

> 
>  Alternatively you can use it
> as a
> proofing space.   You can also Assign the profile to your grayscale files --
> they
> will inherently display just as they print with QTR -- builtin proofing!
> 
> Roy
>