I have a spectrogram of a sound
Darker colors mean quieter parts, brighter colors - louder ones. I need to erase all "quiet" parts from an image and keep all "loud" ones. Loudest parts are represented by shades of yellow. I'm only interested in partly keeping the spots marked by white rectangles.
How do I erase everything that's not bright yellow from an image using Gimp?
P.S. Unfortunately, it's not an option for me to do it analyzing the actual sound. This needs to be done through analyzing the image.