Photoshop: how can I see both the mask and the masked contents?
When I have a photo with a mask in Photoshop, I want to be able to edit this mask with a brush, e.g. I want to remove the sky from the photo. But as far as I know, I can only view the mask or the photo, but not both. I would like to be able to view them both, so that the mask is an "overlay" of the photo. How can I do that?
I hope that was clear...
You mean like 'quick mask'? Hold Shift + Alt and click on your layer mask. Your mask will be highlighted in red, with your photo still showing.
You can view the mask of a layer overlaid on top of the canvas by pressing \ (backslash, usually the key above return). This toggles it on and off for the currently selected layer. You can also open the channels panel and toggle it from there.
Be careful though. The small box around the layer contents and mask indicates which one you're painting on.
Here's what it looks like when you're painting on the layer itself.
And when you're painting on the mask.
You can change the overlay colour by double clicking the quick mask button in the tool panel (second from the bottom).
Or by right clicking on the mask in the layers panel and choosing Mask Options.
Photoshop CS6 shown, but this stuff hasn't changed for a while. Should be almost identical in all recent versions.