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Just like in Paint, how can I do a "transparent selection"? For example, if red is the background color and I select a part of an image with red in it, I want my selection to consider the the red to be transparent.

Or equivalently : How can I change a specific color inside a selection to transparent?

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up vote 2 down vote accepted

Transparent selection with GIMP

Below are some possible approaches using default GIMP 2.8. without additional plugins.

Color to Alpha:

To make the background color in a selection transparent we may take the following steps:

  1. enter image description here Edit - Copy the selection
  2. enter image description here Edit - Paste the selection
  3. enter image description here Colors - Color to Alpha... choose background color

Note that in the example above the color channel for red is completely made transparent leading to a "transparency" with color shift in the grey area too. Depending on our source this may not be what we wanted.

Select By Color

  1. Edit - Copy the selection
  2. Edit - Paste as - New Image to work on a new image
  3. enter image description here Tools - Selection Tools - By Color Select selects all the background
  4. enter image description here Delete the selection
  5. Select - Invert
  6. Edit - Copy the selection
  7. enter image description here Edit - Paste the selection to our source.

Again, depending on the source image we may find it faster to apply the By Color Select tool directly on the image background, invert this selection, then copy & paste it to the destiny (or as a new image for further processing).

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That is good, but I tried the second method and there is still a small line of red around the selection. – Gradient Jun 10 '13 at 15:06
I think your answer is the closest to what I want to do. – Gradient Jun 10 '13 at 20:55
Thank you - but don't hesitate to unaccept if a better solution comes in - I would love to see that myself ;) – Takkat Jun 10 '13 at 21:08

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