JS9 allows you to set the opacity of all pixels in an image and/or specify
a floor opacity to use if the image pixel is less than or equal to a floor
value. It also supports three types of image masks, which can be used to
assign opacity or overlay colorsx:
mask: image pixel opacity depends on whether the corresponding
mask pixel value is less than or equal to 0.
opacity: image pixel opacity is assigned the corresponding mask
pixel value (0 to 255).
overlay: if the mask pixel has a non-zero alpha, its color
is blended with the image pixel using source-atop composition.
Left demo: Load the opacity mask image, then the Chandra file.
Change default to mask in the Color mode menu
(3rd column in bottom row of Color plugin), then choose the mask
file and change the opacity value to, say, 0.25 or 0.5. Or
change mask mode to opacity to assign opacity
directly from the mask values. You can also choose floor in
the Color mode menu and set the floor opacity and/or
the global opacity directly.
Right demo: Load the LSST test file, then click to display
extension #2 of that file separately. Note the use of a
user-defined static colormap to assign colors to different areas
of the extension. Switch back to the test file, then choose
overlay in the Color mode menu (3rd column in
bottom row of Color plugin), and choose extension #2 as the overlay.