Photoshop Top 40
Illustration by John Hersey

25. Selection calculations


Photoshop Top 40

with Deke McClelland

Video: 25. Selection calculations

(Music playing) Deke's Photoshop? Deke's Photoshop? Top 40! Most of Photoshop's top features are expressed as tools or commands, but some are more conceptual. Meaning that they have almost no interface associated with them. Seriously, it goes from your mind to your hands, to the mouse, to the keyboard of Photoshop. Selection Calculations are the best example. Want to make a new selection, just drag. Add to an existing selection, press the Shift key and drag. Subtract from an existing selection, oh, for Pete's sake here. Let me show you.

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Watch the Online Video Course Photoshop Top 40
7h 13m Intermediate Dec 21, 2009

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There's nothing people love more than lists, and Photoshop Top 40 offers a great one, highlighting the best features in Photoshop. Deke McClelland counts down to #1 with a new video each week, detailing one great feature after another in this popular digital imaging application. The videos cover tools, commands, and concepts, emphasizing what's really important in Photoshop.

This is an ongoing course that will be updated monthly.

For the newest updates please go to our blog entry for Deke's Photoshop Top 40.

Topics include:
  • Assembling multiple pieces of artwork with layer comps
  • Creating a black-and-white image from a color photograph
  • Merging multiple channels to create an alpha channel with calculations
  • Selecting images with the Pen tool
  • Masking images using the Brush tool
Design Photography
Deke McClelland

25. Selection calculations

(Music playing) Deke's Photoshop? Deke's Photoshop? Top 40! Most of Photoshop's top features are expressed as tools or commands, but some are more conceptual. Meaning that they have almost no interface associated with them. Seriously, it goes from your mind to your hands, to the mouse, to the keyboard of Photoshop. Selection Calculations are the best example. Want to make a new selection, just drag. Add to an existing selection, press the Shift key and drag. Subtract from an existing selection, oh, for Pete's sake here. Let me show you.

Feature #25 is Selection Calculations, and this is a whole mess of stuff that's working underneath the radar inside of Photoshop, all kinds of little keyboard tricks that you can exploit here inside the program. Very important stuff as well. And it now only spills over from the Selection tool, so you can basically take selection outlines that you're creating using your Marquee tools or your Lasso tool, so your Magic Wand or one of those guys, and you can mix them and match them.

You can add them together, you can subtract them, you can find the intersection. This all happens using keyboard tricks, but it also spills over into selections that you can lift from the Layers palette, the Channels palette or the Paths palette. And it's a ton of stuff, coming at you. I'm just going to be throwing keyboard shortcut after keyboard shortcut, but here's the thing. It works in a kind of rhythm. So we're going to establish that rhythm upfront. We've got Shift, Alt and Shift and Alt together. If you're working on a Mac, that Shift, Option and Shift and Option together.

So we establish that rhythm upfront, I'll repeat myself when we get more into things here, and then we're going to repeat that rhythm over and over again for the Layers palette, the Channels palette and the Paths palette, you'll see what I mean. I am working inside this crazy composition that I've created using a variety of different pieces of stock art from bargain image vendor Fotolia. And let's start off with one of my favorite selection tools, which is this guy right here, the Elliptical Marquee tool. I love this tool, because it could not be easier to use.

And because lots of stuff that you're going to encounter in your everyday average continuous tone photographic images, a lot of stuff is circular or elliptical for that matter, oval. And by that I mean things like all kinds of organic shapes. Leaves and faces really, honestly you can select faces using the Elliptical Marquee tool, if you work hard enough at it. If you take advantage of all your Selection Calculations, you can select eyes. That's a perfect use for the Elliptical Marquee tool. Anyway, let's say I want to draw a new selection outline.

I would just begin dragging with the tool like so, and now I have a selection outline. It could not be simpler. Now if I drag outside that selection outline, then I will create a new selection like so. If I drag inside the selection outline, I'll move the selection outline to a different location. That's because selection outlines are independent objects inside of Photoshop. They operate independently of the image itself. Now let's say that you want to add to this selection outline, then you would press the Shift key, and notice that your cursor gets a little Plus next to it as long as the Shift key is down.

Now I'll tell you, notice these options up here in the Options Bar, so if I release the Shift key, I'll switch back to this guy, which is New selection. I can also click on Add to selection or Subtract from selection or Intersect with selection. But I'll tell you something about those icons, therefore, fools, who don't know how to use Photoshop properly. You don't want to have to be going up there and clicking on an icon every time you want to perform a selection modification. You want to take advantage of Shift for Add to selection, Alt or Option for Subtract from selection, and Shift and Alt together or in a Mac, Shift and Option together for intersection. All right! So let me show you what I mean here.

I'll press the Shift key, which allows you notice. It switches right over to that icon there. It allows you to add selections together, so I'll drag with the Shift key down and notice now that I've create the two blobs that are working together. So two different elliptical selections joined as one, united together. And by the way, I'll go ahead and undo that modification by pressing Ctrl+Z, Cmd +Z on the Mac. The great thing about all of these Selection Calculations is they are all undoable, so anything that you can do to a selection outline can be undone.

Selection outlines are full-fledged members of the Photoshop society, which is a really great thing. Before Photoshop, it didn't used to work this way. Photoshop is the one that introduced this kind of precision to Selection Outlines, which is really awesome. While I'm pressing the Shift key and dragging, and this is true whether I'm dragging or Shift+dragging or anything else, I can press the Spacebar in order to move that selection outline to a different location. So I have the Spacebar down, then as soon as I release the Spacebar, I'm back to scaling the Selection Outline once again.

Then I'll release to go ahead and add those two together. So that's a Shift+Drag by the way when you're adding. If you want to delete one selection outline from another, I'll go ahead and press Ctrl+Z, Cmd +Z on the Mac to reinstate my original ellipse. If you want to subtract one selection from another. For example, let's say I want to create a crescent moon, then I would press the Alt key or the Option key on the Mac, and then I would drag like so. I can use that Spacebar trick once again, to get my selections aligned with each other, and then I'd release and now notice, because I've the Alt key down or the Option key on a Mac.

I went ahead and subtracted that new selection from the old one. And note, up here in the Options Bar, as soon as I press and hold the Alt key, or the Option key in a Mac, you can see that second icon become selected. All right! So we'll go ahead and undo that one as well. Now I was telling you that whole thing about selecting an eye, right. Eyes are so great, you can select eyes like crazy using the Elliptical Marquee tool and eye is ultimately a loss in shape, right. It has sort of a circular top to it, and then a circular bottom, but the inside and the outside edge of the eye meet at corners. So check this out.

This is how you find the intersection of two selection outlines. I'll press Shift and Alt or Shift and Option at the same time. Notice that goes ahead and selects the final icon up here in the Options Bar. And then I'll go ahead and drag, and I can use that Spacebar technique once again to get those selections aligned with each other. Once I like what I'm seeing, and imagine I'm selecting an eye, not just a bunch of sort of rays of sunlight coming off a smiley face in space. Imagine we're working in something more normal here for a moment. As soon as I release my mouse button, then I can release the keys, then notice that I found the intersection of those two selection outlines, and I've a selected a loss in shape which could work for an eye.

Your eyes will vary of course. So that's the basics that you've got, drag to create a new selection outline. You've got Shift+Drag in order to add. You've got Alt+Drag or Option+Drag in order to subtract and you've got Shift+Alt or Shift+Option+Drag to find the intersection. Now here's where it really get super interesting. That old school stuff goes way, way, way back. They changed it little bit over the years and, in Photoshop 4 they changed it. But ultimately we have had that kind of control forever and ever. All right! But here's where things get interesting.

You can do the same thing with selections that you load from layers, channels or paths. So if you want to load a selection outline, let's say I want to go ahead and select a smiley face right there. And he is independent of all the other layers inside the image. If I turn off the Background layer, you can see that everything behind the smiley face is a checkerboard, which indicates that it's transparent. So he set against the transparent background, so he is independent in other words. And I could load his selection outline. That is I can select him, by pressing the Ctrl key or the Cmd key on the Mac.

The other modifier key that we haven't employed so far, Ctrl or Cmd on the Mac and click on that thumbnail, very important when you're working inside the Layers palette, click on the thumbnail not on the layer. So click on the thumbnail and that will load that selection. Once again that's a Ctrl+Click on the PC or Cmd +Click on the Mac. All right! Let's go ahead and put that background back in the place. Now let's say I want to add the rays to that selection. Then I would press -- from here on out, it's just the same stuff I already showed you except just throwing the Ctrl key or the Command key as well.

So if you press Ctrl and Shift or Cmd and Shift on the Mac, and click on those rays, you add the rays. Now the reason that we're seeing the marching end at point is because there is a gradient going on here. And the marching ends are only able to express so much of a selection outline. But the whole darn thing is selected. And I could -- just to really indicate how selected things are. Let's go ahead and grab the big guy. He is this big dude in the foreground here. He is holding his hands up going, yeah, smiley, man. All right! Then press Ctrl and Shift or Cmd and Shift on the Mac, and click again, and you'll add him to the mix as well. All right! Now let's say let's go ahead and just restore the smiley selection.

I'll Ctrl+Click or Cmd+Click on smiley. Without any of the other keys, just load smiley independently. Let's say I want to subtract the rays. Then I would press Ctrl and Alt. And see there is a little Minus sign next to the hand cursor there. Ctrl and Alt, on the Mac this is Cmd and Option and Click. And you subtract those rays from the smiley. All right! You can also find intersections incidentally. So let's say we want to find the intersection. What would be more interesting I think is to work with a crowd here. So let's go ahead and Ctrl+Click on arms 3.

That would be a Cmd+Click on arms 3 on the Mac to load all of those arms there. And let's say I want to find the intersection of the big dude. So now if I wanted to subtract him, I would Ctrl+Alt+Click or Cmd +Option+Click on the big guy thumbnail. That subtracts him from the other selection. That's interesting. All right! Then I could color all these other guys white by -- let's say, assuming that the arms 3 layers active, let's say. By pressing Ctrl+Backspace or Cmd+Delete on the Mac in order to fill that area with white. We saw that back when we looked at the Fill Calculations, in a previous Top 40 episode, can't remember which number that was, 37 I believe actually, now that I think of it.

All right! I'll go ahead and press Ctrl+Z, Cmd +Z on the Mac. So that would be a subtract. I already showed you that. If you want to find the intersection, let's go ahead and Ctrl+Click or Cmd +Click on arms 3 again. To find the intersection with big guy, you pressed all your modifier keys. So Ctrl+Shift+Alt or Cmd+Shift+Option and click on that thumbnail, we're just finding that intersection right there. And then I could go to big guy, and press Ctrl+Backspace or Cmd+Delete to fill that area with white. So the intersecting areas become white. I don't want that, but that's an option.

Ctrl+Alt+Z, Ctrl+Alt+Z, Cmd+Option+Z, Cmd+Option+Z on a Mac to undo that. Now just to cut to the chase, same stuff are channels and paths. So if you got yourself an alpha channel, you could load it up by pressing the Ctrl key or the Cmd key on the Mac and clicking on that thumbnail. It's a little more versatile where channels are concerned. You can click anywhere on that channel. Ctrl+Click or Cmd+Click anywhere in order to load it up. You could also add by pressing Ctrl and Shift+Clicking. That's Cmd and Shift on the Mac. You can subtract by pressing Ctrl and Alt -- I'm not going to do all this because we've already seen it. Ctrl and Alt.

That's Cmd and Option on the Mac, and then find the intersection by pressing all the modifier keys, Ctrl+Shift+Alt or Cmd+Shift+Option on the Mac. Am I going fast enough for you? Paths, it's exactly the same way. If I Ctrl+Click or Cmd+Click on this path right there, I loaded selection outline. If I Ctrl+Shift+Click or Cmd+Shift+Click on a path, then I go ahead and add that selection outline. You also have the option of Ctrl+Alt+ Clicking or Cmd+Option+Clicking to subtract. And then Ctrl+Shift+Alt+Clicking or Cmd+Shift+Option+Clicking in order to find the intersection and that works across everything.

So I can add a selection that I've created using the Marquee tool. I could add it to these existing selections that I created from path outlines, by Shift+Dragging using that Elliptical Marquee tool. So in other words, you can add, subtract, and find the intersection of selection outlines that you create using the tools as well as selections that you lift from layers, channels and or paths. So they all work together like some miraculous gathering. Like the one I've created right here, and that my friends is feature #25, Selection Calculations, the amazing world of Selection Calculations here inside Photoshop.

Find answers to the most frequently asked questions about Photoshop Top 40 .

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Q: Is there a way to batch convert an entire folder of photos from the RBG color mode to the CMYK color mode without having to open and convert each individual image?
A: In the Actions panel in Photoshop, create an action that converts an image from RGB to CMYK. Then link to that action from File > Automate > Batch inside Photoshop.
Next, in the Bridge, select a folder of images. Choose Tools > Photoshop > Batch. Select the action inside the ensuing dialog box.
Or, in Photoshop, select File > Automate > Batch, and select the action and the folder inside the dialog box.
See also: Photoshop CS2 Actions & Automation, Chapter 2 “Action Essentials.”
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