Digital BW, The Print

Steve,

I thought maybe my, in my view too-compressed, low values might just be an
artifact of a bad un-adjusted distribution and too few points.  So, I tried
the Create ICC and Print with Preview workflow with a printing setup that
had a reasonably smooth low end.  I took readings at every 1% point between
100% and 95%, then at 5% to 80%, and then at 10% intervals.  I was also
curious if the program needed even distributions of input data.

The results were not much different than my previous attempts.  Whereas the
un-adjusted printing setup separated all the 95% - 100% points reasonably,
the output adjusted with the Create ICC compressed the dark tones and
posterized the 95% - 100% range.

I don't know what caused this, but it's not, in my view, an output that
efficiently utilizes the grayscale file information.

Paul
www.PaulRoark.com 




> 
> this is the response I received from Phil Green at the London College of
> Communication - the same Phil Green whose names appears at the top of the
> www.color.org International Color Consortium site:
> 
> "Two points: the operation may be defined in XYZ but that does not mean
> it has to be implemented in XYZ; and a scaling operation will have the
> same effect whether it is implemented in XYZ or CIELAB, the only
> difference being a slight shift in the low XYZ values close to the
> threshold where the cube root function is replaced by a linear scaling."
> 
> FYI the points I quoted below were from Bruce Fraser's Real World Color
> Management (pg 41 and 42).
> 
> ...
> >To quote Bruce Fraser, Lab originated out of an 
> > ³attempt to create a
> > space that is perceptually uniform ­ in other words, distances between
> > points in the space predict how different the two colours will be to the
> > human observer.²  L* is ³approximately the cube root of the 
> > luminance value
> > Y (which is a rough approximation of our logarithmic response to
> > luminance).²  The bit in parentheses is critical.  Again from Bruce
³the
> > primary Y doubles as the average luminance function of the 
> > [eye¹s] cones.²
> > The eye sees luminance as described by XYZ_Y not L*.  It makes sense
> then to
> > scale for white point and black point in XYZ_Y.
> >
> > It is this Y that we use when talking about density = -log10(XYZ_Y).
> Logs
> > are nice because they turn non-linear responses such as the eye¹s
> > sensitivity to light into straight lines.
> >
> >
> > Cheers
> >
> > Steve
> 
> 
> 
> 
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