Let user preview channel layer mask selection
@Beep6581
Submitted by Beep6581 Link to original bug (#758497)
Description
"Add a mask to the layer" allows you to select a channel to use as the mask, but you have to click "Add" to see the effects of your choice, and if you need to change the channel used, it takes considerable time to delete the mask and apply a new one, and more importantly it doesn't let you instantly switch from using one channel as a mask to another. Please add a feature (many filters already have a "Preview" checkbox) to let the user preview the effects of adding the chosen layer mask before clicking "Add".
Why is this so important? Luminosity masks are the most powerful tool in the advanced photographer's toolbox. Many of the best landscape photographers absolutely rely on them, as they offer an incredibly easy way of adjusting light tones in a halo-free and realistic way. Using the luminosity mask technique is already perfectly possible in GIMP even though we don't have adjustment layers, however the bottleneck is choosing the right channel to use as a mask. This choice is one you have to make many times during a single image editing session, and having to "guess" which one to use because there is no preview makes it a tedious process. Please add a mask preview functionality to eliminate this bottleneck.
Version: git master