Digital BW, The Print

> 
> >So the new way we see the difference between 95 and 100
> > on the screen as well as on the print.
> > 
> > The bottom line is that you should Assign to the new space NOT Convert to it.
> > 
> 
> I am still not convinced of this but let me think about it.  I agree that
> the file that gets sent to QTR (via Same as Source) needs to be LAB or
> LAB-grey.  But if I took a photograph such that a portion of the subject is
> Kodak middle grey (L=50) and this successfully makes it through to my B&W
> image on screen (ie is still L=50) before going to LAB-grey, if I ASSIGN
> LAB-grey the L value of this portion of the image will change.
> 
> (As an example, pull up a grey gamma 2.2 step wedge.  The 50% step is L=54.
> Assign LAB-Grey and the 50% step changes colour and becomes L=50.  What was
> L=50 also moves to something less than that.  My image has changed and I
> have lost my reference point that I noted at the time of exposure.)
> 

This is exactly as is should be.  If you have a gg2.2 50% step, it reads K=50 and
the internal pixel value is 127 = 255*.50  if you look at the Info and see L=54
what you are seeing is a CONVERSION of  50 gg2.2 to Lab and the value comes
out 54.  If you were to convert-to-profile the file the pixel value would change from
127 to about 138 = 255*.54.   However if you assign-profile the pixel value
stays at 127 and now when you see the Info L=50 because thats the pixel value.

When you Assign the actual pixel numbers don't change, just the meaning of the
numbers.  Convert changes the pixel numbers so that the new number with the
new meaning is the same gray value as the old number with the old meaning.

If you've already got a file that prints well before you don't want to change all the
pixel numbers because then your print will change.  We're changing just the meanings
so that the display gives a better match to the print.

Of course if you are coming from the other side and like your image on the monitor 
but not the print.  Converting may get the print closer to the monitor.


> > 
> > You are right that absolute values will vary based on dMin, dMax, the kind
> > of display you use, the lighting etc...  I lean toward the everything relative
> > point of view though.   With color management there are the different
> > renderings and Perceptual is usually the one of choice.   This corresponds to
> > the compressing the gamut mode.  The Absolute Colormetric is more like
> > your view but seems rarely used.
> > 
> 
> Not quite.  In my methodology there has been no "compression of gamut" per
> se at the point of "calibrating" the printer - merely a recognition of what
> the range is.  This is important.  I make no judgement call at this point as
> to how out-of-gamut values should be treated.  I recognise that the printer
> can print a good portion of the LAB-grey space and I simply require that it
> do so for the portion it can and I note down the portion that it can't.
> 
> With the recognition that the printer can only render say that portion of
> the LAB-grey space defined by 16<=L=>96, I then look at my image.  How the
> image is then compressed with a simple curve to 16<=L=>96 has an infinite
> number of possibilities - all of which I control simply with one neat PS
> curve.  It is actually better than colorsync in that you have an infinite
> number of possible curves rather than 4 options.  For example, if I chose to
> clip certain values I am in effect using a mix of Absolute Colormetric and
> Perceptual.
> 
> OK you could say that I make the call at the time of calibration that IF I
> don't do anything else, out-of-gamut values will be clipped to dMax or dMin
> respectively!  But you gotta take the package in the same way I must take
> the current package of a transformation function embedded in the RIP and the
> transformation function I must manually do during soft proofing to get the
> image to "look right" again.  If I do nothing with the current setup I don't
> get a satisfactory image - I have to go back and rejigger it with a
> softproof in hand.  Worse yet, if my image is fully in gamut (eg my
> photography class example) at the moment I still have to go back and
> rejigger it to get the image right.

I get what you are saying, I just don't think its as desireable.  I think the
relationship between values is much more important to overall effect rather
than the absolute densities.  I think with your scheme you'd always have this
extra step of trying to find and match up your dmin and dmax.

Roy

> 
> Cheers
> 
> Steve