Re: Quadtone profile for MIS ink & Luminos Preservation paper?

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



>A question for Dan and Tyler: how did you arrive at these curves? Is further
>adjusting them the way to solve this problem? If so, can you give me any
>advice on doing it sensibly? Finally, is my calibration-by-stepped-grayscale
>a realistic approach?

I think the curves posted are Tyler's finessing of my first rough
partitioning curves but the answer does lie in tweaking the curves (as you
suspected).  As for advice -- I think the best thing to do is make the info
pallette visible and set the second color to "total ink."  Then as you
adjust the curves run the cursor over various areas to see if there are any
supposedly smooth areas that drop or raise total ink suddenly.  If look
closely at the info pallette first color (it should be set to "actual"
which becomes CMYK) running the cursor over the same area to see which ink
channel is posterized.  Then tweak the curve for that channel to move the
area of posterization under an area of heavier ink (you may see the
discontinuity bands move as you adjust the channels). Usually you need to
iterate between curves and channel mixer for the best result.   It is best
to work in 16 bit as much as possible since this process *challenges* the
individual 255 level channels of 8 bit.  Of course in 16 bit you can't use
layers so tweaking involves a lot of do and undo and saving and reloading
curves settings.  The channel mixer layer (or adjustment) removes the light
color inks from under the dark color restoring detail to the shadows that
would be lost with heavy ink spreading.  But it is easy to overdo it.  Try
setting the layer opacity lower (or in 16 bit try adjusting the amounts of
ink removed in each channel of the channel mixer adjustment).  It is better
to get a light partitioning of the channels in 16 bit with very
conservative curves and channel mixer adjustments, then convert to 8 bit
and add the adjustment layers for final tweaks.  Did you get my action
which does the first partition automatically in 16 bit?  If not email me
off line and I will send the files.

I'm not sure calibration buys you much since each image is so different and
the channels really are stretched to their limits.  But it will give you a
good start.  Try pasting a narrow step gradient along the top of the image
(per recommendation of Blatner and Fraser for similar types of activities).

Dan Culbertson






-
Turn off HTML mail features. Keep quoted material short. Use accurate
subject lines. http://www.leben.com/lists for list instructions.


[Index of Archives]     [Yosemite News]     [Yosemite Photos]     [Scanners]     [Gimp]     [Gimp Users]
  Powered by Linux