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For more information, please see full course syllabus of Adobe Photoshop CS6
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Alpha Channels & Calculations

  • Alpha Channels are saved selections. They are saved in B&W.
  • Black is the masked (protected) area, and White is the active selected area.
  • To load an Alpha Channel as a selection, COMMAND (Mac) or CONTROL (PC) click the Alpha Channel.
  • Calculations let you use existing selections, and combine them by adding or subtracting to create new Alpha Channels (selections). This is a great time saver.
  • Calculations require using some visualization to determine what will happen and which channels you need to get the result you are looking for. I will be adding some more examples soon to clarify and help you understand Calculations better. They can be a very useful time saver!

Alpha Channels & Calculations

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Lesson Overview 0:06
  • Demonstration 1: Scenery 1:43
    • Alpha Channels: What Are They & How to Use Them
  • Demonstration 2: Car 8:05
    • Working With Alpha Channels
    • Introduction to Calculations
  • Demonstration 3: People 14:54
    • More On Alpha Channels & Calculations
  • Lesson Summary 19:35

Transcription: Alpha Channels & Calculations

Hi everyone, Mike Brown back with you, welcome back to's Adobe Photoshop CS6 course.0000

In the last several lessons we've been talking about the most important technique in Photoshop; making selection.0007

You need to make them flawlessly, you need to make them efficiently, and along the lines of being efficient is how quickly you can make that flawless selection without having to start over and do it again.0013

Alpha channels are a real life saver, what they allow you to do is save any selection as a black and white representation that can always be reloaded as the selection.0029

There's also some other things that it can do; number one, if you have a selection that you use repeatedly, it allows for easy retrieval.0044

Number two, it's a time saver, if you're building up a complicated selection, you can work for a while on the selection and then save it.0053

That partial piece of the selection--go ahead and save it, so that if you continue to work and you blow it and somehow you lose the selection, you don't have to go all the way back to the beginning, you just retrieve the partial selection and lose a little bit of time.0065

And then it's a black and white visual that can be corrected--it's used for correction purposes.0081

And then I'm going to talk to you about a feature called Calculations which is sometimes a little bit visually complex--it's a time saver that allows you to create new selections from existing alpha channels, so let's get started here.0087

Here's a shot that I have, we already have a selection--I'm going to trash it...I'm going to trash both of them and start all over again.0106

This is a fairly easy one, we're going to take our Quick Selection tool, we've done this before, just run it through, and what we have here is a selection that you can see with the Quick Mask.0119

We're going to go to the Select menu--by the way your channels panel is a panel under the Window dropdown menu, there it is as channels.0131

To save a selection go to the Select menu, down at the bottom save your selection, we're going to call it Partial Sky, and we'll click OK, and I'm going to de-select--Command or Control+D--de-select.0141

We've lost the selection, I realize that we can get it back with Command+Z or with History but let's say we've worked on some other things like done a little bit of retouch...let's just go here...I'll do a couple of little just blips around, and now you can't get back your selection because it's far back.0157

You could on the History panel...unless you've gone 40 or so more, but let's just say you can't get it back any other way.0181

You've always got...come on, the channels open up...this is your channel, the saved selection is right there in black and white--white being the transparent, black being the masked area, all you have to do is Command on a Mac, Control on a PC, click the channel--you don't have to click the thumbnail--just the channel.0191

There it is reloaded, click RGB or the shortcut Command or Control+2, and there's your selection back.0216

Now this was the raw selection, so let's make an adjustment on that real quickly...we'll go to the refine edge dialog box, let's set up our Edge Detection tool that we dealt with in the last...what happened, I went to the wrong view...0224

And we're going to very quickly just run this thing down the edge one time and let it cook, in other words we're modifying this selection...and there we have it, done.0245

Click OK, and now we have another selection.0260

We can save this one; Select, Save Selection, we're going to call it...Sky Two...and save that.0264

Now we're going to de-select, we're going to highlight the channel and zoom up to see what it looks like.0277

You can see that with the channel loaded, you can also by the way load the selection by going to Load Selection, and pick the channel--we're going to go to Sky Two and load it.0284

Look at it under the Quick Mask, you really can't see, even if we go to 100% can't see, just barely any imperfections in this particular selection--it's hard to see with the color.0297

But over here, in the black and white, notice for example, it partially selected the land area, so if we were to strip the sky in it would partially show through--that should be all black, just the sky should be white, so we can paint this to correct it.0317

Paint with again, foreground color--in this case it's black, and we just very quickly take our brush and blacken out--we're going to paint at 100% here and I notice that the trees don't go down in there--there's no selections.0337

We've got all that, and you can see, if we go back to RGB this is all greenery, the only show through is right we can paint the greenery and we don't want things to show through in that particular area, we'll just paint it.0352

And get that taken care of--in other words, we're correcting any mistakes on a selection--there's another big piece right there--by simply painting on them and if I make a mistake, just like with selections, keep going...come back, flip the foreground/background and just paint away.0370

And we've collected that, go back to black again, go back through and just clean up this area here that we know is not see-through, and let's just come back very quickly--there's a little bit get the point, right?0389

OK, so...yes, we'll just leave it at that.0404

Alright, you see that--there's another one, I just can't leave it alone.0409

So you can correct an existing alpha channel by painting on it and it really helps you with things that you can't see by using Quick Mask, now this Sky Two is all fixed up and ready to go, so if we either go Load Selection with Sky Two, we'll do it that way this time...0413

Now we have a clean selection for use, go back to RGB and we're there, so that's one of the primary things; black and white visual of the selection--easy to see and correct any mistakes that have been made, so you can correct a selection as an alpha channel.0435

You can also easily retrieve it obviously as long as it is an alpha channel you can come back and forth, if you want to load it several times, and as I pointed out, if you're making a complicated selection, you can continually save the various...iterations if you will as you continue to improve the selection, save the bigger and bigger piece of it and you can throw the other ones away.0455

Very, very simple use of alpha channels.0482

Now, I want to show you another usage of the alpha channels--here's a composite I made and you can see there's a whole lot of channels in here.0485

Now, I needed a channel...let me see if I can find that one...hood logo I need...let's see where it is...oh I know where it is down in here, I have so many of them sometimes it's hard to find them...there it is.0495

This particular selection is--I'm going to load it so you can see it--Command or Control click--wrong selection, there it is, Command or Control click, go back to the RGB mode.0517

This is part of a windshield, and what I needed to do was put a graduation in here, a gradient, so that I can add a little bit of haze that's completely see through here but as it curves around I needed that little bit of haze on it.0530

So what I did, is I made a clean selection of the windshield and I will save that permanently so if I ever make another mistake I can completely reload it, I'm going to duplicate that selection...duplicate channel.0547

Now I have a copy down at the bottom.0568

I'm going to load this selection, and what I need to do, is I need to make a gradient...across that channel starting about in the middle--in other words block this and open it up so I need to go black to white across there.0570

So now we have a new channel by duplicating, and the selection's in place so all I have to do is get the angle more time...and there we have it.0589

There I have now made a gradation across the windshield from a copied channel--there's the actual windshield, there's the modified one as a new channel, so that allows you to modify selections by gradients on a channel as well and now I can apply whatever I want on the actual image--let's load it...0604

And go to the image and now if I wanted to for example put a light blue--let me just choose...same color foreground/background--I'm going to do a gradient in there at 10% and just click and drag, let's see what happens here.0628

Let's go back and right you can see the haze--let me do it at 20%, see a little haze build up?0648

Off and on, I'll do it one more time--now you can see that I'm adding that haze and protecting the other part, so that's one of the other things you can do with channels--you can modify them by duplicating and correcting them and still saving the original so that if you ever screw up, I can always go back to this and start all over, make another copy and go from there.0655

Alright, there's another thing you can do with it.0677

Now, the third thing you can do--let me show you with this example save time by creating new selection from existing selections, so that you don't have to make a complex selection.0680

Originally, when I made this, when I stripped the car in to begin with, I had to make a selection of the car...stripped it in.0694

I also made a selection of the car in its original shadow, here's the original car right there--see the shadow?0703

So I made that one and it was pretty easy to add, I already had this selection, so all I had to do was just make a selection of that black area and come back inside--I mean I could do that--let me show you real quick how we do that.0712

We're going to go back to the regular freehand tool, hold down the Shift key and I'll do this roughly just to give you an idea, and you know you do it in pieces...that's why I say when you're making a complex selection--this is not accurate but I just want to give you the idea.0728

So there we have that piece and add the little black piece, and low and behold, then if I save this, and if it was accurate, I would have had this selection, pretty easy to do.0745

So now I have the car, now I have the car and the shadow, and now I want to make the car plus the shadow plus the pavement--now that one's really easy, all I have to do is load up the car and the shadow, take my straight polygonal tool, and with the plus (I'm adding) click, click, click, click, click, and save that selection and that's what you get.0759

So now I have the car, the car with everything and the car with the shadow, pretty easy to get there.0789

What I really wanted to get to, is I want this complicated selection just of the pavement.0795

I could go in and spend the time of making it but here's a much easier way and the feature is Calculations.0802

You go under the Image menu, down the Calculations and here's the box.0809

We have source one, source two, any blend mode and opacity, and the results, that simple.0816

You're always going to be sourcing in this case when I do it from the same document so the source is always the same, the layer; we don't worry about the layers, we're just using channels, so what we're doing is using Calculations on channels.0826

So what I want to do (let me cancel for a moment) I want to take the overall and I want to take away the car and the shadow because I want to get the pavement, so alpha two is the overall, alpha three is car and the pavement, so if I go to calculation and I go alpha three, doesn't matter which order you do it, you only have to have the two of them.0841

Alpha two--actually we'll do it in the right order--alpha two is everything, alpha three is the car and the shadow, and what I want to do is the difference between the two--I want to take the one out of the other one and you can actually see the result occur right there, click OK, and it created a new channel, right off the bat.0867

I didn't have to make any selection at all, time saver supreme.0889

Let me show you one more, I just did this last night, somebody was interested in getting a composite done...where is the composite?0894

Must be...come on, there it is...go back to RGB.0908

This was the original shot that I was given right here, just a little boy in some playground toy.0914

They wanted me to composite in his sister, which is this shot they sent me--this is not professional work but we've pulled it off anyway.0921

Put that together with him, and I looked at this and I went "well, I can put her outside this tube in the back, but that means that I have to make a selection of all of the open area so that we can do that".0930

And what I have here (let me turn her off) there we have the shot--I made the selection very easily using our refine edge of the open area, so we had that and I saved it as alpha one.0949

Then I made a selection of the girl...and that's all of this--she's pasted into that as a composition, but the entire girl to that point, and I saved that selection, and that selection is that one.0966

And what I wanted to end up with, is a selection of...let's go down one...just the girl behind the tube, so that I could make a blur on her and also make, you see a curves and a hue saturation layer.0984

But how do I do that?1011

Now yes, we could go in and I could make that selection but it's not going to accurately fit with the real selection, so here's where we use Calculations again.1013

We have alpha one, which is the opening.1025

We have alpha two, which is the girl overall, but we want to fit her in here, and how do we do that?1029

We'll go back to Image, Calculations...get your head around this one, you can almost see it right there--it's kind of there.1037

We're going to take alpha one which is the opening...there it is, and we're going to take alpha two which is the girl, and you see if we use difference that didn't work, if we subtract them that didn't work, if we add them it kind of worked, but now what do we do?1050

Now, there's another blend mode--I don't use all of them, I use for Calculations either add, subtract or difference, and in this case I found one that works--the multiply blend mode.1075

When you're putting two things over each other, if one of them is black, doesn't matter what the other one is, it'll go black.1089

If they're both black it'll be black.1097

If they're both white, it will stay white, so if we look--I'm going to cancel for a moment...anything outside of that opening...has black, so anything outside of that opening will definitely disappear.1100

Anything outside of her is black, and that too will disappear--the only place that it'll show is where both this one and this one are white with multiply, so we go back to the Calculations, we go alpha one, alpha two, go to multiply, and look what happened.1122

The only place where they overlapped in the selected area is here behind it, and so by very simply just taking a blend mode of multiply on alpha one, alpha two, we came up with exactly the selection I needed, didn't have to do a thing, and the edging and everything is absolutely perfect.1146

We load it, go back to RGB, and now we can apply anything we want to through the use of Calculations.1167

So, we now have looked at alpha channels, basically saved selections that can be worked on, retrieved or used to help you as you're building a complex selection.1175

And also we've taken a look at Calculations, which allow you to add and create new selections from existing selections slash alpha channels.1187

Another really cool feature in Photoshop CS6.1200