[APML]: Useful photoshop info

[Alfredo Zanazzo <alferd@mbox.lol.it>]

Re possibility of reducing film grain with photoshop, I had suggested
to use the integration-printing method, scanning two or more negatives
(prints) of the same subject (possibly taken the same night) and 
stacking them with photoshop, but I did not know how to control a 
perfect register as during rotation option, photoshop does not show you
the image until it goes to the new position.
Thrichromy would introduce the same problem.
Jerry Lodriguss has the solution to this problem, and I thought it was
worth while to republish his answer adding also why I had asked it.
I would like some of you to try this method and report results.
Bravo Jerry!

Alfredo, try this method in Photoshop v 3.05:

Copy one photo, and paste it as a layer into the other one, but select
DIFFERENCE in the paste layer dialog box.  Click on the top layer in the
Layers Pallette so that it is active and SELECT ALL.   Now you can 
rotate
and move that layer (it has to be selected to rotate separately from the
background layer) and its really easy to see when they are in register.

Open three windows on the same composite image, and zoom in on the left 
top
corner of one, the center of another, and the lower right corner of the
third.  When you move the top layer, you will see it move in all three 
windows.

Now get the stars in register in the exact center of the photo. Next use 
the
ROTATE: ARBITRARY and experiment through trial and error until you get 
the
corners in registration.

Then after they are registered, go to the Layers Pallette, and change 
the
method that they are combined to MULTIPLY (or overlay... you get 
different
histograms, multiply has a greater range of pixels on the histogram, but 
it
depends on the original scan). Then FLATTEN the image to combine the two
layers (flatten command is under the small right pointing arrow at the 
top
right of the layers pallette).

Beware that LOTS of things can conspire to make two negatives not 
exactly
the same, even though they were shot with the same instrument on the 
same
night, such as focal length change due to temperature change, emulsion
swelling due to high humidity, etc.  This can also be a problem with
tri-color on techpan, you may even have slightly different focal lengths 
due
to the different wavelengths of the filters (not totally sure how much
difference this will make).

Jerry







-- 

--
Regards, Alfredo Zanazzo ( alferd@mbox.lol.it )

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