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function: imim2op <opnum> -- 2Dcol edit
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keyboard equivalents: none

The "OP" button (lower right on the F3, lower
middle on F4 panel) makes a popup to run a 2D
color operation (edit if inside or outside 2D
color ellipse) using the data currently in the
main/editable buffer (im) and the second/compare
(im2) buffer.

Before doing this, it can help to plan the
truncation by viewing what will be selected as a
transparent green overlay using another popup
available from a left-click of the bold "im2:"
label.

N.B.: the result is applied to the editable
buffer (im).  To undo, alt/cmd-z after clicking
the image window (or tools window).

The number in the entry next to the OP button
selects the operation (currently 0 or 1).  The
ellipse center and radii are set using the
"im:cent,rad:" and "im2:cent,rad:" entries on the
bottom mid-right of the the F4 panel.

This operation is also available from the TRUNC
R-click buttonbar from the smaller interfaces.

The current operations are:

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0:  edit ellipse *inside* im,im2 space to OFF
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   (x-m)^2      (y-n)^2
   --------  +  --------   <   1
     w^2           h^2

where (x,y) is current color, (m,n) is center
color, and (w,h) are color radii.  If < 1, edit.

TODO:
  x' = x*cos(th) + y*sin(th)
  y' = y*cos(th) - x*sin(th)

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1:  edit ellipse *outside* im,im2 space to OFF
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Same as 0, but save 2D colors inside ellipse.

To save the edits, set the desired output name in
the "im:" field and use "W".

N.B.: using SAVEIMG will save the edited images
over the originally-read-in set of images
(probably not wanted).

