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tickbox variable: $imim2elloverlayflag -- 2D colmask
popup entry variable: imcolcent       => im target color
popup entry varibale: imcolrad        => im2 col radius
popup entry variable: im2colcent     => im2 target color
popup entry variable: im2colrad       => im2 col radius
popup entry variable: overlayalpha  => overlay transparency
-------------------------------------------
keyboard equiv: <none>

Color Conjunction Overlay

A left-click on the "im2:" label brings up a
popup panel for testing 2D color space
conjunction masking.  To use color space
conjunction as a mask, see below.

To mark regions (with a transparent overlay) that
fall within an elliptical region of (im,im2)
color space, first read in a second image set
with different contrast than the first.

Then set the variables on the popup to control
whether the overlay is active, the center and
size of the ellipse, and the overlay
transparency:

  imim2elloverlayflag
  imcolcent     => im target color
  imcolrad
  im2colcent   => im2 target color
  im2colrad
  overlayalpha

The variables $imcolcent and $im2colcent control
the position of the target color in each of the
images.  The dimensions of the ellipse are set by
$imcolrad and $im2colrad.

Units for all 4 are are grayscale colors (0-255).
Any voxel whose pair of colors lie within that
ellipse will be given a transparent green
overlay.

The transparent overlay is always displayed over
the first image set.  To toggle the visibility of
the overlay, use the $imim2elloverlayflag
checkbutton.

Use $overlayalpha to adjust the transparency of
the green acceptance mark (255 is opaque):

Equivalent/redundant F4 interface

The popup variables are also available on the
large interface (fn-F4) as two pairs of entries
just to the right of the COMPARE button:

    im:cent,rad:  ____   ____
  im2:cent,rad:  ____   ____

On that panel, $imim2elloverlayflag is
abbreviated "2Dcol".

Using the Color Conjunction As Mask

To use the areas detected by 2D color conjunction
to mask the editable data set, R-click the TRUNC
button and select the last button on the button
bar:

  Truncate Using 2D Color Space Ellipse

This make a popup that allows truncating editable
buffer colors that are either inside or outside
of the color space ellipse.  This operation is
also available (more opaquely) on the F3
interface using the lower right "OP" button right
(0=trunc-inside, 1=trunc-outside).

