How can I select pixels within a tonal range in GIMP?

Question

I want to select pixels in an image based on a specific brightness/intensity range, similar to choosing a range from the histogram. Is there a straightforward way to do this in GIMP, either built in or with a plugin?

user1558 · Accepted Answer

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

Step-by-step

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