8

This question already has an answer here:

While you try to change the background to transparent- the filter "color to alpha" is not selectable. How to get that changed.

marked as duplicate by Ovaryraptor, Paolo Gibellini, GerardFalla, Luciano, WELZ Mar 27 at 12:22

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

9

Well- this is more of an answer that I wanted to post- but was unable to. This is how you do it-

  • Open the image in GIMP.
  • In the Layers window, right click and select "Add Alpha Channel"
  • From the Colors drop-down menu- select "Color to Alpha"
  • Done- the pop up asks you the preset color, click OK and your image can be saved now as png with transparent background. I thought it would be good to answer how I figured it out. Tania
  • 1
    Hmm. True in 2.10, but 2.8 doesn't care and adds the alpha channel automatically. – xenoid Aug 4 '18 at 12:37
  • 1
    Thanks for your feedback on the versions. Yes, I meant for 2.10. – Tania Chowdhury Aug 4 '18 at 17:44
2

In both v2.8 and v2.10

Color-To-Alpha (as well as many tools in the Color menu) is not available in color-indexed images (typically, GIF, but also some PNG, the image mode in indicate in the title bar).

You have to change the image to RGB mode (Image>Mode>RGB).

However, if you go back to indexed mode, explicitly with Image>Mode>Indexed or implicitly when exporting to GIF, the alpha channel becomes "binary": pixels become either fully opaque or fully transparent, and your image will be pixellated along the edges. You can mitigate this by using Filters>Web>Semi-flatten but that makes your image usable only over a specific background color.

In v2.10

It appears that the new C2A tool in 2.10 won't add an alpha channel automatically like the 2.8 one did. Possibly a fixable oversight. In the mean time, in 2.10, in RGB/Grayscale images, check that you have an alpha-channel first.

Not the answer you're looking for? Browse other questions tagged or ask your own question.