Changing this image to be transparent

[tm2383]

I work as a teacher for the visually impaired (VI) and I need to make this image of a special protractor transparent, leaving the black lines and numbers, so that I can demonstrate it being used to measure angles on an interactive screen. The protractors which come with the screen software aren't VI ones. 
I have looked at tutorials, but haven't successfully managed to do this. How would I go about doing this?

[rich2005]

There are a few ways. You could try this way

The image is a jpeg, which does not support transparency.

1. Layer -> Transparency -> Add Alpha Channel
2. Make it all black and white Colors -> Threshold
3. Remove the white Colors -> Color-to-Alpha
4. Optional if you want: Image -> Zealous Crop to trim to size
5. Export as a png to keep the transparency.

...and that as a 40 second animation https://i.imgur.com/i2vQhmg.mp4

[tm2383]

Thanks so much for your help. It works perfectly in Powerpoint, but when I use it with ActivInspire board software, the background is still white for some reason, although I should be able to work with that, unless you have any other suggestions. I assume its just the fact that the image is a jpg format. Thanks again!

[rich2005]

(01-06-2024, 11:27 PM)tm2383 Wrote: Thanks so much for your help. It works perfectly in Powerpoint, but when I use it with ActivInspire board software, the background is still white for some reason, although I should be able to work with that, unless you have any other suggestions.  I assume its just the fact that the image is a jpg format. Thanks again!

Jpeg does not support transparency, Usually the format to use is png but there are others gif or tif or psd can be exported by Gimp.

Some software ignores the Alpha Channel which provides the transparency mask and will display with a white background, sometimes a black background. Nothing you can do about that.