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The other day I was wondering if there is an easy way in GIMP to choose the pixels that are part of a selected range on the histogram.

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Welcome to the site! –  che Nov 11 '10 at 20:29

2 Answers 2

up vote 15 down vote accepted

Yes, it's possible to select by pixels' intensity range.

Step-by-step

  1. Make a copy of the layer (Layer → Duplicate Layer)
  2. Select the duplicate layer, apply threshold (Colors → Threshold) to select the range of intensities.
  3. In Layer → Mask → Add Layer Mask (or right click in the list of layers). Select “Grayscale copy of layer” and “Invert mask”.
  4. idem: Mask to selection.
  5. Hide or remove the layer with mask.

An example:

Original image. I want to select the circle:

Original image

Make a copy of the layer:

Duplicate layer

Apply threshold. Note that the area to be selected is black:

Threshold

Add Layer Mask using the grayscale value of the image:

Add Layer Mask

Now you've obtained an image with the mask. Everything except the black circle is transparent (we can see the bottom layer through it):

Image with the mask

Convert the mask to selection. Switch to the original layer. The circle is selected.

Mask to selection

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+1 This is a very thorough solution –  ltn100 Nov 11 '10 at 16:30

There is a plugin called Adagio Range Selection that does pretty much what you want. You can't select from the histogram directly, but you can select the upper and lower boundaries.

alt text

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¡Gracias por la respuesta! –  huff Nov 12 '10 at 10:39

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