Eraser Genuine modifies image transparency according to two criteria: a colour you wish to erase and a colour you wish to protect. So, this plugin is particulary suitable for images where two colours oppose clearly.
Select with the eyedropper the colours you wish from the current application (background colour to erase, foreground colour to protect). Launch the plugin and the greatest part of the work is done!
The plugin retrieve automatically the background and foreground colour, from the host application. However, you can modify them from the plugin's dialog, to optimize result. Press Reset to restore the two colours.
The Opacity box re-scales the transparency:
Increase minimum parameter "to clean" the background.
Decrease maximum parameter "to get back" certain erased parts.
Auto option allow to adjust automatically minimum and maximum parameters.
The sophisticated algorithm of this plugin, can be useful for subtle replacements of colour. So, in the example below, reflections on the water became red.