I use the Lightroom app and on my Chromebook and there is a mask under sharpening however when I hold down ALT and slide the mask nothing happens. On other Lightroom versions the screen will change color and as you move the slider it will show you what's being sharpened. Is there a way to do this that I'm missing? Also, same thing for adjusting whites and blacks. I know on other versions you can also hold shift and double click the whites and blacks sliders to automatically maximize them. That would work too.