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Layer Masks: Making Masks Permanent

by levyj413

Have you ever used the lasso or other "marching ant" tools to make selections? How about quick mask? Wouldn't it be nice to keep those selections? That's what Photoshop's layer masks do. Instead of marking out some selection and then actually deleting the rest, you tell Photoshop to only show what you want. But the rest of it stays there, so you can edit it the mask later if you want, adding and deleting as much as you like.

I'm going to go through several steps as explanation, and then give you suggested learning projects at the end.

The first way we'll do this is using quick mask. So starting with the squirrel, I'm going to duplicate the original layer and then turn it off. It's always best to work on a duplicate.

Then using quick mask, I'll roughly mask it out (remember that I like to paint what I'm selecting, as opposed to what I'm masking - you can do it either way, but if you paint out the masked area, remember to invert the selection).



Next, I'll exit quick mask so you can see the selection:



I then create the layer mask using the layer menu. The exact location probably varies with the PS version, but here's how it looks in CS2:



Note that I can choose to reveal or hide the selection, so be sure you do what you intend. You'll see that whatever I didn't select disappears. But it's not really deleted - it's all still there, available to be added back in if you like.

Look at the layers tab. You'll see that next to the active image layer thumbnail is a new black and white box. That's the layer mask thumbnail:



In the layer mask thumbnail, the white shows the area that's visible and the black shows what's masked out:



So far, this is just like quick mask. The big difference is that the layer mask is completely editable. To edit the actual image, click on the thumbnail of that layer. But to edit the mask, click on the B&W mask box. For example, if I want to add a bit of the rocks in the upper left, I click on the mask and just paint in some white:



To remove some of the mask instead, I'd paint in black.

Three of the most powerful things to me about layer masks are that you can:

1. edit them
2. see them full size, and
3. temporarily turn them off

It's often good to see the mask full-size, esp. to make sure you really painted it in as solidly as you like. To do that, alt-click on the mask thumbnail in the layers tab:



Alt-click again or just click on the normal image thumbnail to exit full-size mask view.

You can see that I didn't quite paint in solid white across the whole squirrel.

You also sometimes want to temporarily turn off the layer mask (for example, to make sure you didn't mask out something you really wanted to include). To toggle the layer mask on and off, use shift-click on the mask thumbnail. Note that while you're seeing the whole layer, the mask is still there, and can be turned back on again by shift-clicking on the mask thumbnail.



Now that you've seen how to create, edit, and toggle on and off layer masks, it's time for you to try it!

Layer Mask Assignment Part 1: Using the original squirrel image, create a duplicate layer. Turn off the original layer so all you see is the copy. Now create a layer mask following the steps above.

Layer Mask Assignment Part 2: Click on the layer mask thumbnail and edit it. Use the brushes, marquee and other tools, and other methods just like you did to tweak a quick mask. Try black, white, and grays to introduce various levels of transparency.

You can even apply gradients to the mask, which will apply smoothly varying transparency.

Layer Mask Assignment Part 3: Now that you've created a layer mask beginning from a selection, try creating a blank layer mask using the layer menu - you can either reveal the entire layer or hide it, and then start painting in the mask as you see fit.

Extra Credit: in DPC challenges that allow you to make selections, I use layer masks on adjustment layers much more than on the image data themselves. So create some adjustment layers and then some layer masks and see how they affect the adjustments. Adjustment layers automatically come with all-white layer masks (ever wonder what that white box was over to the right in the layers tab?) You can also create a selection first, and then when you then create the adjustment layer, the selection will be applied automatically as a layer mask.

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