Layer mask fun with GIMP

Layer masks can be simply described as The Greatest Way Of Mucking With Your Alpha Channel. Layer masks simply rule. That's why there are so many layer mask based tutorials out there - so this is kind of redundant. But, I will tell you here about some of the techniques I have found to be quite amusing.

Alpha channel, in case you were not aware of this, is the representation of opaqueness of the pixels of the layer. Layer mask is a grayscale bitmap that represents the modification of the alpha channel - if the corresponding pixel in layer mask is black, the layer pixel will be completely transparent, if white, completely opaque, and gray means something between. It is easy to understand, but it's harder to see at first glance how useful they can be.

Pluginning the layer mask

Here's one trick on how to make feathered borders with layer masks:


  1. Add alpha channel, then add white layer mask to the image
  2. Select all, Select | Shrink by some nice value
  3. Feather selection by at least twice as much as you shrunk
  4. Invert selection
  5. Select layer mask, and fill with black

See the results in right.

Okay. That was trivial. But what about doing something a bit more sinister - Something you just can't do without the layer masks?

I recently got a book called Web Pages That Suck. It listed square edges for non-square images as something kind of unprofessional. I found it quite amusing, considering that just a few days before that, I had discovered one very cool technique for making images not that rectangular.

In fact, by manipulating the alpha channel, you can do all sorts of interesting transformations for the image. The technique I found is kind of simple. I used IWarp on the above layer mask to generate this image. (Well, you can't see this image - you should, if you're 
	  following the tutorial.) On the left, you can see my IWarped layer mask - and on the right, in an image you obviously can't see, is the resulting image. As you can see, the image edges are no longer boringly feathered, the feathering is now more random.

This looks particularly interesting if you add another layer behind this one and fill it with a pattern - if you're making web pages, the web page background picture will do fine.

But why stop here? IWarping the layer mask is cool, but doing something even more interesting is cooler! IWarp is just one way among many in doing interesting layer mask tricks - there are tons and tons of ways to make life with the layer masks very interesting.

Here's one way. Now we have the kewl iwarped layer mask - how about adding some degeneration to the image? Simple. Very simple.

Random noise will do fine, as well, if you Shift it a lot to different directions. Here's the trick...

Drawing directly on the layer mask - for the Real Men and Women

Drawing directly to the layer mask is another cool technique. Here's one picture I got - not too fancy, but shows what you can do.
Hmm. Well, draw on the layer mask
	with black and white and you'll see.

In this last image, the layer mask was then Convolved by hand, and the results look a bit more interesting. Another way would be to use the airbrush tool - a fine example of that technique can be seen in the page title.

...make that *would* look more
	interesting... =)

Have fun with the layer masks!

- WWWWolf

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Last modified: Sat Aug 7 16:18:22 EEST 1999