Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Steve Kale
<stevekale@b...> wrote:
...
> We are really talking about the same thing.  A straight Relcol has
no black
> point mapping so Adobe introduced BPC to plug the gap.  Perceptual
requires
> black point mapping but how you do it is not specified.  In a colour
world
> there are very real differences between these two intents because of how
> non-greyscale out-of-gamut colours are managed (ie shrink the entire
gamut
> to fit, perceptual, or render the next best in-gamut colour,
relcol).  In a
> greyscale world, though, there aren't any out-of-gamut colours remaining
> once you have mapped the black and white points.  So if you were
approaching
> the issue purely from a greyscale world perspective then you'd be
facing an
> identical technical issue.

I don't think so, and that was the point of my first reply.
The whole point of RelCol is to map in gamut colors as closely as
possible to the LAB equivalent in the destination space. In gray,
everything is IN GAMUT except the extremes, white point is taken care
of, then everything down to media/ink dmax is in gamut.
Therefore in the majority of the scale there is little compression,
and Adobe then came up with some math to compress shadows
porportionally more, to bring back shadow detail.

In fact, this is why one would select that rendering over perceptual
if apropriate. It's how most of the profiles I have here work, from
various creators.
Put up a gray step wedge, do a perceptual vrs relcol conversion- in
perceptual everything lightens, in RelCol it does not, but the blacks
clip. Now with Relcol hit BPC, mid tones lighten little, but shadow
detail returns.

That is how I would expect it to perform, based on the definitions of
the intents and BPC, and that is indeed how it seems to perform here.
Of course it's not 100% consistant because of the lack of relevant
standards, but mostly.
Tyler