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Does anyone know how to make a selection by value in GIMP 2.9?

I'm trying to "cut out" saturated stars (values of 64k) in an astrophotograph. "Select By Color" should be able to do it, but the slider only goes to 256 (8-bit). I'd like to select pixels that are above, say, 40k.

Can anyone suggest a tool that is not PS assuming Gimp's devel 16-bit support isn't sufficient?

  • Does the slider for threshold go high enough? – Peter Taylor Jul 11 '17 at 6:55
  • I haven't worked on images other than 8-bit... But is it possible to make an 8-bit copy to create a mask and copy the mask back to the 16-bit image? – Roflo Jul 11 '17 at 15:41
  • Color select sort of works, but it isn't obvious to me if it is only working on the 8bit image on screen vs. the underlying 16-bit channel values. The fact that the threshold slider only spans 1-255 suggests that it is just working on 8-bit values. – mittimithai Jul 12 '17 at 6:53
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The way to do this in gimp 2.9, as suggested by a post on the gimp users mailing list here is to threshold on a grayscale duplicate (or channel depending on how you want to do it); then that can be turned into a selection or mask.

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