Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Ernst Dinkla
<E.Dinkla@c...> wrote:
...
> The Wasatch allows me to add correction curves on top of the
> linearisation curve for ink limitation etc.

SP has a few places to set ink limits, before or after linearizing.
The final dot gain curve one can apply is at the very end of the
process after linearization has been done taking the limiting (new end
point) into account. My assumption is that it amounts to the same
thing in the end as the controls you have in the Wasatch.

> There is however no
> prebaked curve for quads added that should take care of the human
> factor. One improvises a curve that suits one's eyes.

That's what kind of bugs me, we do it to taste instead of an accepted
standard. We can both be linear, but be printing considerably lighter
or darker than each other depending on our eyes. Of course we are
editing our files to suit, but one would think there could be some
widely accepted standard that once we are all linearized to, the same
file would print similarly across the board.
Really outstanding single channel icc profiles would put much of this
to rest, if we both had them, we could print the same file
theoretically identically.

> The Wasatch
> SoftRip isn't very B&W quad aware so that could be the reason but
> on the other hand I find it strange that StudioPrint (ICC
> profiled) has that option for colour as well.

I'm not sure why one would need these controls for color, everyone
advises linearizing to 0 dot gain before color profiling. However this
raises some questions in my mind that would be more appropriate on
some other forums.

>Is this not just
> the same correction facility for ink limitation etc but in this
> case the prebaked quad "human factor" curve has been added as an
> extra service?  Good service by Ergosoft then. But you shouldn't
> use that particular curve when it is for color printing that
> already relies on a custom ICC profile. That's my guess at least.

Mine too.

> On thin ice now and in my own words.... Lab is "more or less"
> perceptually linear.

I'm showing my lack of formal color education here, but I think you
are right. I think LAB was developed over time to come as close as
possible to human visual perception.

>  On top of that the approach by colour
> management applications isn't always in respect of the shape's
> construction. Gamut mapping for instance asks for a more
> complicated approach with (3d?) curved mapping (or tables) to get
> good perceptual hue matches. Most of the time it isn't done like
> that and shifts like the blue > purple hue occur. Similar problem
> with density dot gain.  Some polishing of the original
> mathematical setup of Lab is also needed apparently. All Bruce
> Lindbloom's territory...

Lindbloom to the rescue again. I ran some tests, if we assume LAB is
perceptually uniform from gray values of 0,0,0 to 100,0,0, then middle
gray must be somewhere near 50,0,0. This means a dot gain of something
like 31+%, much more than I would have guessed. Some other tests in
photoshop confirm this. So I'm not sure if that helps at all.
I've come at this problem from every conceivable direction, including
density.
At this point I can only conclude that "linear" simply means that as
tones progress they do so in a mathematically consistent manner. Other
factors thrown in to make it perceptually desirable, like gamma or dot
gain, remain subjective decisions.
But that makes comparisons of systems based on those factors (it
prints too light, or too dark) useless, particularly if it can be
varied easily by the user but remain "linear".
Tyler