crop an image before treatment

hello all

actually im working on cloud detection on satellite image, i did the detection with F mask, knowing that my satellite file contains image with 11 bands (11 tiff images of different bands), my teacher told me to do a selection of a part of the picture with the mouse , and do the treatment just in this part of the image, so i should apply this to all my 11 bands

do you have an idea how to so that ?

Answer 1

[Zakaria Sadok]

so what i need is to select a part of the image with my mouse, then do the treatment , but this treatment should concern this part of the image in all the tiff files that i have

thank you