bucket fill tool to make transparent

Is there any way to use the bucket fill tool to change a color to be transparent instead of color?

update: I want to take some b&w calligraphy image and then superimpose that on a ‘parchment’ image background.

I am not sure that this is possible. But the way I would tackle your problem is to select either the calligraphy or the background and create a layer mask from selection. This will either let the parchment layer underneath show through where the calligraphy or the background is. I do this a lot and it is very easy to turn text into letters made of images.

This was my first foray into using layer masks. I sort of get it, but I had a few glitches:

  1. as the underlayer is exposed, the top layer (calligraphy) is lightened. I wish to keep the calligraphy dark.
  2. I was not able to expose the bottom layer evenly

But I was able to stumble onto a solution that was what I was looking for. With calligraphy on top layer (and selected) and parchment below:
action bar → Colors → Color to Alpha

The result is that all of the white is turned to transparency.

Is there any way to use the bucket fill tool to change a color to be transparent instead of color?

This is exactly what the Color erase mode of the paint tools is for.

image

An alternative solution is to stack a layer above, set to Color erase blend mode, and of course fill it with the color to erase.

Thanks for answering the question!