and thank you very much for your comment. I am aware of GIMP’s Color compose function. However, at least in my Mac just opening a single about 10k x 10k pixel image takes very long time. This is one reason why I use Imagemagick (I actually usually also crop the image using IM), it is so much faster. I think in GIMP most of the time is taken to draw image/part of the image. Any idea if this could be made faster? Or should I just upgrade my old Macbook?