GIMP (or others): How to remove background (by color) of several images in one step?

Question

I have a set of about 200 PNG-images in like that:

Only black and white, no colors, no grey.

I need the background color (white) to be removed and tried to do so in macOS Preview (with that Instant alpha tool), but the problem is that it just lets me remove connected white areas. But I also want to remove white between the lines and inside the note circle.

In short: every black pixel should stay black, every white pixel should be transparent. How can I do this without selecting every white area? I have mac Preview and GIMP, but other Freeware is possible too.

And the other thing: It is not a single image, but about 200 of that kind. Is there any way to automate the operation? E.g. with the GIMP Batch mode? (I have got no clue how to use it.)

PS: Is that question right on graphicdesign? I had no idea where to look else...

Answer 1

GIMP hasn't "action recording" like Photoshop. A programmer is needed to create a script for this. To process one image you should open the image, go to the interesting layer if there's more than one, insert alpha channel if there's not one present already, change the current foreground color to white and apply Layer > Transparency > Color to Alpha. The result has your black image against transparent background and ready to export as PNG.

Unfortunately I cannot write any properly working code to automate this. The same is true for other freeware. For example free or actually "pay what you like" web service Photopea could do your job. There one image needs inserting the image itself to the layer mask and inverting the mask. Then the result could be exported as PNG. Repeating the same automatically needs a programmed script, there's no "record the sequence" functionality.