QTR-Quadtone RIP

Michael - This is a wonderful response - I am still trying to digest
it all. But I am printing a new wedge and will be then working on the
curve values so I will be coming back here with a progress report.
Thank you for the help and the advice to avoid the linearization and
stay with the grey curve
Sean

--- In QuadtoneRIP@yahoogroups.com, Michael Mutmansky <michael@...> wrote:
>
> 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
>