Restore transparency to a part of an image

Question

I have this image:

Downloadable here.

I need to isolate the libellula and "restore" the transparency of its wings, the areas highlighted here:

I haven't problems to isolate it but how can I restore the transparency?

The image must be saved as PNG with alpha channel, without the background.

I haven't enough knowledge about GIMP and image manipulation, I already tried with the rubber tool adjusting the opacity but the result is very bad.

Thanks a lot!

Answer 1

You can try GIMP's Color > Color to alpha. You must combine with layer masks

• one version which is otherwise well separated from the background but the wings are still green

• another version where the wings are transparent as wanted but something else green has also vanished

Hopefully you have a high resolution photo. The shown version in the question is inferior, the fine structures need much more. I didn't try the link.

This is one click version. Color to alpha is applied once by clicking green and trimming the treshold sliders in color to alpha dialog.

NOTE after you have combined two versions to one, it probably has green reflections. When the green background is removed, all its reflections are irrational. You must apply selective hue & saturation adjustment to convert the green to insects own color or at least to less offensive. This is normal when backgrounds are removed from photos. Strong color from the nonexistent environment looks wrong.

Answer 2

Possible solution for Gimp 2.10:

• Put your image in a group
• Add a layer above it, set layer mode to Color erase (this mode is new in 2.10)
• Paint the layer with the color you want to make transparent
• Use additional layers for additional colors (you could use several shades of green...)
• You can put a layer outside and below the group to check transparency over a specific background (you don't need a group if you don't need this layer).

As you can see this technique can also be used to extract the rest of the subject.