While you try to change the background to transparent- the filter "color to alpha" is not selectable. How to get that changed.
asked Aug 4, 2018 at 11:13
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2 Answers
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
answered Aug 4, 2018 at 11:24
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1Hmm. True in 2.10, but 2.8 doesn't care and adds the alpha channel automatically.– xenoidCommented Aug 4, 2018 at 12:37
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1Thanks for your feedback on the versions. Yes, I meant for 2.10. Commented Aug 4, 2018 at 17:44
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1Adding an alpha channel alone will not permit usage of the "Color to Alpha" function if the image is in Grayscale mode.– OhmlessCommented Apr 9, 2020 at 14:55
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 2.8 you can also paint (bucket-fill, usually) in Color Erase mode for nearly identical results.
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.
In 2.10, color-to-alpha doesn't produce the same result as in 2.8 (it is normally better (the 2.8 version can produce a dark rim in some cases); but the 2.8 behavior is kept by the Color-erase paint mode. In addition there is also a new Color erase layer blend mode.
