Pixel Bunneh

Alpha masks.  Everyone talks about them, but what the heck are they really?  If you’re looking for the in depth technical answer to that, you’re in the wrong place!  This is my answer to what an alpha mask is:

It is a method of adding elements to another image.

That sounds pretty simple doesn’t it?  Well, it’s a bit more complicated than that, but let’s jump right in to how to create your own and what to do with it once you have.  The instructions below are for GIMP.

If you want to work along, here’s the file I’m making in .psd and .xcf.

I’ve started with an image of a stormy looking sky, and I want to add some lightning to it.  I open the sky pic, and then add a new layer to it (to keep my layers the exact same size).  I then fill it with black.

Sky and Black layer

I then grab a lightning brush, make sure I’m using white, and add a bolt to my black layer.

Making sure my black layer is active (click on the black layer), in the image window I go to Layer > Mask > Add Layer Mask.  I then choose Black – Full Transparency.  Your layers window should look like this:

Mask added

Activate the lightning layer, then go to Edit > Copy.  Activate the mask layer, and do Edit > Paste.  Right click on your new floating layer and choose Anchor. You should then have this:

Picture with Mask

And your sky image should look like this:

Sky with Lightning

Now here’s where the real neat thing about an alpha mask comes in.  In Colors > Levels, experiment with the sliders and see what happens.  You have a great deal of control over how your added element appears.  My final image:

Lightning!

So now when you get a hold of some great textures, and you’re wondering what in the world those black images with some white on them are, you’ll know what to do!