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I have an image where I want all the pixels with a specific color converted to transparent pixels. The operation should not change the color/alpha value of any pixel which don't match the color exactly. How do I do that?

At first I thought I could use Colors->"Color to Alpha" but that don't work because it changes the color of all pixels(It adds an alpha value to all pixels).

Using Gimp 2.6.11 on Linux

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up vote 5 down vote accepted

You do use the Color to Alpha tool, but you also need to isolate the color using the Select by color tool. Here is how I accomplished replacing a specific color to transparent:

  • Create a new, transparent layer at the bottom of the layer stack.
  • Use the Select by Color tool to isolate the color. Be sure to set threshold = 0.0;
  • Now that you have the selection, use the Color to alpha tool, and use the eyedropper (after double clicking the "from" color) to select your color.
  • Click OK (twice).

Let me know if this works for you, or if you need me to clarify any further.

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This was almost right for me. I needed to right click the layer and select Add Alpha Channel. Then I used Select by Color. Then I deleted the selection. After that the Color to Alpha tool wasn't necessary. – bafilius May 16 at 15:25

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