Thursday, June 6, 2013

Wednesday Q & A: Does LR4 Have Alpha Channel Masks?

The easy answer to today question?  No.  The harder answer would be yes.  The first thing that needs to be discussed would be what is an Alpha Channel, and the second would be how are they used.  I did a post a while back about a similar topic.  It was about Alpha Channels in Adobe Photoshop Elements.  The answer is very close to the answer to today’s question.  Full blown Adobe Photoshop CS XX (whatever) definitely has Alpha Channel.  The big difference between PS CS and PSE and I’d think LR5B is that you have access to Alpha Channels in PS CS.  If you have the default Layers Panel open, take a look at the tabs.  It goes Layers/Channels/Paths.  A Channels Panel is available to you.  The first thing you see (if you’re working is an RGB mode) is four “Layers”.  RGB/Red/Green/Blue.  RGB is the composite of the other three.  The Red Channel is a B&W (there’s also an option to see it in color) representation of everything that contains even a little bit of red in the RGB image.  If you click on only the Red Layer you’d see a B&W image.  Full Blacks, full Whites and shades of gray.  Same thing happens when you click of the Green and Blue Layers in the Channel Panel.  As you click through, the B&W representations will change.  If you think of it as a painter would view his/her paints, you see which colors and what amounts the painter would have to mix her/his colors in to get the desired end color.  If you were to put a big old X (make one leg Black and one leg White) across the Red Channel (any Channel you choose) and then look at the RGB Layer you’d see a rainbow of colors.  What’s going on?  You’ve changed to amount of Black and the amount of White in the Alpha Channel.  To find out what happens in PSE and LR, hit the “Read More”.

Photoshop Elements (PSE) definitely uses Alpha Channels.  Make a Selection (any selection) and you’ve created an Alpha Channel.  Click on the Layer Mask icon in the Layers Panel and you’ll see the Alpha Channel being shown as a Layer Mask.  ALT CLICK on the Layer Mask and you can work directly on the Layer Mask/Alpha Channel.  Go to Select/Save Selection and you’ve just saved the Alpha Channel.  What PSE doesn’t have is a Panel called “Channels”.  You can’t break the RGB Channel down into it’s components.  You can create and Save Alpha Channels.  You can recall (saved) Alpha Channels.  You can modify them.  You just can’t “see” them.

In LR it gets a little trickier.  You can take the Adjustment Brush and click the check box that says “Show Selected Mask Overlay”.  Two words are keys in those four words.  Mask and Overlay.  If you create a Mask, you create an Alpha Channel.  The gottcha in Lightroom is that the Alpha Channel is totally hidden.  The same thing goes if you use the Spot Removal Tool or LR5Beta’s Radial Tool.  If you make any global adjustments (adjustments that have an effect on the entire image, you don’t need an Alpha Channel.  If you make any adjustments that effect only a portion of the image you’ve made an Alpha Channel .

Can you go back to a specific Alpha Channel in LR?  Sure, everything is non-destructive in LR.  You can go to the History Panel and go back to whatever you’d like to modify or eliminate.  If you need to adjust something done with the Adjustment Brush or Radial Tool, LR makes it even easier.  To make the change you dropped a pin on the area you want to modify.  If you go back to either Tool (after the fact) you’ll see all the pins you’ve placed.  You can go to any Pin in any order and make your changes.

So, as far as Alpha Channels go, Adobe addresses them differently in each application (PS CS, PSE & LR).  You can make modifications in all three.  You just have to understand what an Alpha Channel is and what you have to do to work with them.

BTW:  Today’s image is just filler.