Digital BW, The Print

Tyler Boley wrote:

> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, Ernst Dinkla
> <E.Dinkla@c...> wrote:
> 
>>Amadou Diallo wrote:
>>
>>
>>>With StudioPrint at least, it's a two-step process. To grossly
> 
> simplify, the function of 
> 
>>>linearization is to map a straight line of input to output
> 
> (linear). Following that is a dot 
> 
>>>gain adjustment curve setting. This value chosen for this setting
> 
> adds a non-linear 
> 
>>>gamma-type curve which is better suited to human perception, as we
> 
> don't "see" in a 
> 
>>>linear fahion.
>>>
>>>amadou diallo
>>
>>Amadou,
>>
>>That extra step is only applied in B&W calibration I guess ?
>>
>>Any data available of that gamma curve ?
>>
>>When Roy uses Lab's linear greyscale isn't he getting the same 
>>necessary deviation from strict linearity ?  A perceptive greyscale.
>>
>>Ernst
> 
> 
> Ernst, I'm not Amadou but I can reply to that. The last step is in any
> mode, including the individual colors for CMYK, overall for quad mode.
> It's a dot gain slider. Obviously 0 dot gain is extremely light by
> anyone's standard. This entire issue has been a bit of a mystery for a
> long time. What is perceptually linear? Is LAB? Probably much closer
> than 0 dot gain. What percent dot gain corresponds to linear L values?
> I've heard IJC has output gamma setting for the user to select.
> Obviously StudioPrint leaves it up to the user to select.
> I've put this issue before some pretty extreme geeks, and no
> definitive answer came up. LAB has been suggested as a good "probable"
> enough times to buy into. But I have yet to correspond a particular
> dot gain selection in SP to linear LAB output and I wonder if one
> found a setting that gave equivalent 50% density, if they would also
> be equivalent throughout the rest of the scale. This is a little
> outside my color geek range, so for now I've settled on 20%, and work
> in a 20% dot gain space, so far so good. I'm curious what Amadou and
> others are using.
> Tyler

Tyler,

I'm not a colour guru or geek either. On the Wasatch SoftRip that 
I have I can linearise and build a profile on top of that.
I assumed that the profile actually takes care of the human eye 
responsiveness to grey levels etc. As good as the color 
management works (see below). In absence of a ICC profile in quad 
profiling I can imagine a curve is needed that takes care of that 
human grey level response.

The Wasatch allows me to add correction curves on top of the 
linearisation curve for ink limitation etc.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.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. 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.

On thin ice now and in my own words.... Lab is "more or less" 
perceptually linear.  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. See the density dot maths at the bottom of 
this page:

http://www.brucelindbloom.com/index.html?UPLab.html

Ernst