Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Steve Kale
<stevekale@b...> wrote:
...
> I can only think that the reason why Epson has built black point
> compensation directly into their profiles is because either (a) they
don't
> want to highlight how bad the black point can be, (2) they don't believe
> that simulating black ink is useful, (3) they don't like the way
Adobe PS
> does black point compensation and prefer their own algorithm, or (4)
some
> mix of these.

I think it has more to do with the fact that few, if any, average
Epson users would ever need shadow information from a file clipped
below the ink black point, and therefore a normal colormetric
conversion is nearly useless and would probably lead to more tech
support calls. Believe it or not a great many decisions in this
industry are driven by their potential consequences on tech support.
I can think of a few reasons to need a straight colormetric conversion
once in a great while, but I can't imagine many others needing it for
normal printing. Under most circimstances with a tonally full file, it
will clip.

>  It's also interesting to note the difference in a soft proof
> using a GM i1 profile between perceptual (which has built-in BPC) and
> relative colormetric which does not.  In a B&W world, one would
generally
> expect these two to be the same.  The only explanation that I can see is
> that GM uses a different BPC algorithm to Adobe PS.

I don't think they've ever been the same nor should be. BPC is not
"built in" to perceptual rendering. Something similar to it is an
natural consequence of remapping/compression to the destination gamut.
RelCol with BPC, in theory and in my experience, is supposed to leave
much of the scale alone, and simply begin to compress at some point in
the shadows eventually reaching an in gamut black point at the end.
You will see middle gray shift much more in a perceptual conversion
than a RelCol with BPC conversion. If I recall from months ago,
maintaining the middle gray value in your conversions was desirable to
you, therefore perceptual may not be useful.
You will also see, strangely, with CMYK profiles, a DIFFERENT black
value (CMYK ink combo) resulting from the two different kinds of
conversions, with some profiles.
Of course, since profile builders can make perceptual tables however
they like, and BPC is not an icc standard, but an Adobe implemetation,
many of these issues are not cast in stone.
Tyler