Tuesday, June 25, 2013

Using Photoshop Alpha Channels To Control Composition

Today’s image demonstrates what happens when you screw around with an image too much.  I was trying to get rid of the people in the background but give a hint of people “in the stands”.  The fact that it didn’t work out well doesn’t subtract from the point of today’s discussion.  Typically when I do something like today’s image the mask is one big thing with all the elements selected.  The ball, the batter and the catcher picked out as one Alpha Channel.  Today’s image has four separate Alpha Channels.  In this case, an Alpha Channel is a Saved Selection.  The Selection process is not important.  Make your Selections any way you’re comfortable with.  If you’re reading this and using Adobe Photoshop Elements, keep reading.  PSE has the ability to save Alpha Channels.  The big difference between Adobe Photoshop whatever and PSE is the fact that PS gives you access to the Alpha Channels and PSE doesn’t.  The question would be: “do you really need to have that access?”  Hit the “Read More” to find my thoughts on the subject.

If you have access to the Alphas Channels you can mark them up as a separate piece of your work.  If you don’t have access (are using PSE) you would have to load the Alpha Channel as a Selection (Select/Load Selection) and work with it as a Selection.  You can make changes to the Selection and then resave it as another (or possibly the same) Alpha Channel.

So, what are Alpha Channels used for?  In the case of today’s image it’s so the individual pieces of the puzzle can be worked on one at a time.  There’s the ball, the bat, the batter and the catcher.  The and the ball bat are moving so fast that they’re blurred.  The shot was made at 1/500th of a second at F 5.6.  That shutter speed was enough to freeze the catcher completely and all but the hands of the batter.  We have two elements with sharp focus and two with blurred focus.  I’ll treat the two sharply focused pieces differently than the two unsharp  pieces. 

That starts with how the Selections are made.  The Quick Selection Tool (W) makes short work of the static elements.  The Elliptical Marquee Tool (M) does a better job on the ball.  It can be Feathered to produce a soft Selection.  The Polygonal Lasso Tool (L) is a better solution for the bat and basically for the same reason as the ball.  It can be feathered to give an illusion of speed. 

By isolating the elements, finer control can be applied to each.  Working directly on the Alpha Channel you would be able to see the effect being used.  Working on a Selection provides a little less visualization.  You can get some of that back by switching the Selection to Quick Mask mode. 

My recommendation would be to play with Save Selection and Load Selection.  Make a Selection, save the Selection, Deselect your Selection and go on to other things.  When you need that particular piece of your image go to Load Selection.  Put it back up and do what needs to be done.  You can think of it as saving something to a permanent “clipboard”.  If you were using a word processing application and you needed to insert the word “Connecticut” in several places in the document, as long as you don’t make any mistakes, you could keep hitting CRTL V whenever you needed the word.  The Save Selection and Load Selection is kind of like that.  Use it when you need it.


Clipping Path said...

This article was quite interesting. I am going to read more on your blog. I do agree with everything you are saying.