Sean,
You cannot use the linearize tab when doing digital negatives, so if that's
what you are doing, it won't work, as the negative is the opposite of the
final result, and the formulas for linearization are built around the
positive, not the negative.
If you are attempting to linearize in the grey tab, you have to be very
careful about your math, otherwise it is possible to accidentally invert the
math, and double the nonlinearity, making the result even more nonlinear.
First, start with this in the adjustment/linearization data window in the
Grey Curve tab:
"0;0 100;100"
This linearizes the curve and starts you with what should be a linear
starting point for making adjustments.
Then, do a test stepwedge. I would recommend a 51 step tablet, rather than
21, as the steps can be somewhat large for the curve in the highlight
otherwise.
From here, you should be able to follow the Reeder approach very precisely,
and you will get a reasonable starting point for more precise final
adjustments.
The trick is to take all the data readings but don't just apply them, think
about what the mean while doing it. That way, when you are doing the
inversions, etc. you should be able tell if you are making the adjustment in
the right direction.
For example, lets suppose the midtones are too dark, and we have only three
steps to the test; 0, 50, 100. Also, the endpoints are perfect, so no
adjustment will be done there.
If the midtones are too dark in the print, that means that not enough
density is being put down on the negative, so too much light is passing
through to the sensitized paper. So, the mid-value needs to be set to a
higher value than it is now.
Using the Reeder approach, you would subtract the high values from the low
value to obtain the range, and then subtract the mid value and the low value
from the high to get the middle value within the range. Lets say that the
50 value is producing a 70% print density and we want it to be 50%.
So when the printer is being sent a 50% image value, it is resulting in a
70% print value. To lighten the print, we need to darken the negative, so
the value that we need to be in the linearization line at the 50 point will
need to be a lower number than 50 to get it to be darker.
If everything worked in a linear fashion, the proper value would be 30, so
the adjustment curve would look like this:
"0;0 50;30 100;100"
-----
Here's one of the real difficulties of working with QTR...
Image values are from 0-255 from black to light OR from 100 to 0 from black
to white depending on what color space you are working in.
QTR works from 100 to 0 for black to white in the curve creator (or 255 to
0) with QTR translating 0 to mean absolutely no ink being laid down, and
100/255 being all the ink going down.
When working on a negative, however, these values flip, so 100/255 means
absolute paper white, and 0 means the darkest black you can produce
(assuming you have enough density to produce paper white with your process).
So there are a series if math inversions that have to be made to keep the
math working properly, hence the reason Reeder does those inversions to the
charts.
This is complicated by the Yuill-Nielson equations for visual linearity in
the print, and nonlinearity in the inks and receiving film, and lastly, the
response curve of the process you are using. This is the reason the Reeder
approach will get you close to a linear result but not give you an
absolutely linear response even after a few iterations.
Regardless, once you have it working, you will find that you can produce a
negative that is better than can be produced in any other method that I have
seen or used, so it is worth the effort.
---Michael