Digital BW, The Print

On Monday, Dec 13, 2004, at 10:41 US/Pacific, 
DigitalBlackandWhiteThePrint@yahoogroups.com wrote:

> Message: 5
>    Date: Mon, 13 Dec 2004 16:46:09 -0000
>    From: "Steve Kale" <stevekale@...>
> Subject: Re: LAB Step Wedge -- a grayscape Lab space
>
>
> Bruce
>
> Rather than messing with the QTR curves you are better off using an 
> Excel spreadsheet to
> compute a PS curve that, together with the curve in the RIP, gives you 
> the "net curve" you
> want.  I gave you the way QTR will remap input to output.  If you 
> layout a sheet with the
> same calcs but add a column for your target curve (graphing this is 
> useful so you can see
> its shape as you alter the numbers) you can then solve for the curve 
> which will remap the
> file values so that when the adjusted values are then remapped by QTR 
> you will get the
> curve you want.  All without a densimeter.
>
> Steve


Thanks Steve, but unfortunately this is now going over my head a bit.  
My curves are made by eye using QTR without linearization so they are 
done, I think, using ink percentages. Of course dot gain makes the 
steps uneven over part of the output, so I don't use those ink 
percentages in my curves by limiting the maximum ink out put in each 
ink to where there are clear and even (visually) steps from darkest to 
white. My "raw" or 1st trial profiles come out with near gamma 1.8 
(differs on different papers). I then create a temporary photoshop 
levels adjustment layer to match my test image and step wedge (in gamma 
2.2 working space, viewed on calibrated monitor) to the first trial 
curve print. I then create another temp levels adjustment layer to 
bring the monitor image back to the original look using the levels 
gamma adjustment ( I use the eye dropper to make sure I'm accurate to 
the original file). I then type this gamma adjustment into the ink 
descriptor file and create a new curve. Turning off the temporary 
levels layers, I compare the new curve printout to the original file. 
The match will be quite good. So I've now created a QTR curve for 
gamma2.2 greyscale working space.

To add a little more punch (if I desire) to the QTR curve I create a 
curve adjustment layer temporary layer to add a little punch to my 
original. I save this curve and open and apply it to QTR supplied 
"grayscale-16.psd" file. This is a miniature (pixel wise) grey wedge in 
16bit gamma 2.2 space. I save this file with a new name with the curve 
applied and create a new QTR curve by adding the name of this new 
greyscale file in the curve descriptor line in the ink descriptor text. 
(yea this is going over someones' head!) When the new QTR curve is 
made, my photoshop "s" curve made by eye is now built in to the new QTR 
curve on top of the accurate gamma 2.2 QTR curve. No need for Excel. 
Photoshop provides the graph. It's a mystery how exactly this works as 
the instructions with QTR have "a style all their own" and it took me a 
while to figure out that I needed to actually apply the curve to the 
greywedge and save it under a new name. I guess the QTR curve making 
script examines the contents of this greyscale, notes the changes in 
tonal values and applies these changes to a new QTR curve. It's kind of 
neat actually and very cleaver of Roy I think. How the QTR curve making 
software finds this file is a mystery to me as the instructions don't 
say where (which folder) to save the file in. I saved it in the folder 
with the other curve descriptor files I think.  ***I am using an older 
version of the QTR. If the curve making aspects have changed, then no 
one will understand what I'm saying here!

I would encourage the curious who use QTR on the Mac to try making 
their own curves for quadtone ink sets. It is very educational about 
the way the different inks are laid down and the way a good transition 
works from one density ink to the next. What's really amazing is how 
well the curve making software (ink partitioning) works after one has 
identified the maximum amount of each color ink to lay down. The 
transition is so smooth, with no posterization. If you print 
photographs of people, this is really important. When I used the old 
piezo plug-in, it looked fine on landscapes, but faces always showed 
the poor partitioning of the old plug-in from cone/R9. What I mean by 
this is that if I print a grey gradient from white to black, under an 
8x lupe, I cannot see when one inks stops and the next lighter ink 
starts. Very cool.

enough blabbing...
-bruce