More on Photoshop Selection
Here are some more random thoughts and tips on the art of selection in Photoshop that I didn't really have space for last week.
Selections are Masks, Masks are Selections
Most people trying to find their way in Photoshop make the mistake of compartmentalizing different tools too much. In the case of selections versus masks, you're much better off thinking of the two as being mostly interchangeable. Selections are masks, and masks are selections. Although the tools used for each are different, the effectively do the same thing. If you create a selection with any tools that work for you, you can then save that selection as a layer mask. If you create a mask somehow, you can use it as a selection.
If you're already familiar with layer masks, this should make at least some sense. With a mask, the mantra is that white reveals and black conceals. In terms of selections, this is the same as saying that the white portion of the mask is inside the selection boundary and the black from the mask is outside. Things can be partially selected just as portions of a mask can lie somewhere between black and white. Gray areas of a mask are effectively partially selected.
What this means is that you can be somewhat lazy when using the actual selection tools, so long as you use your initial selection as the basis of creating an adjustment layer. When you do, that lazy selection will become a layer mask that you can then refine all you want. The whole time, your underlying image will be perfectly safe since an adjustment layer is nondestructive. And if you ever do need to turn that mask back into an actual selection, you can easily do so by right-clicking on the mask in the Layers panel and choosing "Add Mask to Selection". Once you understand this, this whole topic of masks and selections becomes a whole lot simpler. When first learning Photoshop, I can remember stressing out when making selections since they seemed so permanent. As long as I could see the "marching ants" selection outline, I could refine things as much as I wanted to, but once I effectively deselected things, there seemed to be no going back. At least some of you can likely relate to this. But once you get used to the fact that masks and selections are really the same thing in different forms, you can relax.
Channels are Masks Too
Click on the Channels panel of an open document or choose Window >> Channels from the Photoshop menu. If you look at the icons for the red, green and blue channels you may notice they look at least somewhat like layer masks. By that I mean each is a small grayscale image that has a relation to your current image. The reason I bring up this comparison is that sometimes it would be great if you could use a channel as a ready-made mask. Well, you can.
Last week, I discussed how to load a mask as a selection by choosing "Add Mask to Selection" from the mask's right-click context menu in the Layers panel. For those who are really into mouse clicks, you can do the same thing by simply holding down the Control key (Command key on Mac OS X) and then mouse-clicking on the mask icon. If you go to the Channels panel, you may notice that this option doesn't appear on the right-click menu for any of the red, green or blue channels. But don't despair. While Adobe didn't give you the menu option on a channel, they do honor the equivalent Control-click shortcut for it. Simply hold down the Control key and click on a channel to load it as a selection.
Sometimes one of the channels may be close to what you want to select, but not really exactly what you had in mind. While you could mess up the color and levels in your image make the channel a good candidate for creating a mask from, it really doesn't make sense to sacrifice your image just for that.
Instead, Photoshop lets you make a copy of that channel, after which you can do with it as you will without affecting your actual image. To do so, right-click on the channel you wish to copy and choose "Duplicate Channel," then click on "OK." If you now click on your new channel copy all others will be deselected so you can see just it. You can now use Levels, Curves, a filter or the paintbrush, or pretty much anything else to modify its contents. Unfortunately, you can't use an adjustment layer on a channel, but most anything else is fair game. When you get what you want, just click on the RGB channel at the top of the list and the display will revert to the image itself rather than your new channel. You can then Control-click on your channel/mask to load it as the selection and use it as needed.
Between last week and now, this pretty much covers what I wanted to regarding selection. I'll probably cover more in the future, but this covers most of what you should now for optimizing images. You can tell from the above that I don't really use all the tools possible for selections and masks. Specifically, since my use of Photoshop is centered on photography, I rarely use vector masks and associated tools. Also, I don't really get into things such as replacing the sky in an image with a better sunset, or cutting and pasting elements from multiple images to create a composite that never really was in nature. If you were hoping to find out how to do such things here, I hope I gave you enough other helpful tips to make up for it. I just don't do that. I know graphic artists do, but I don't really feel that photographers should. In this age of digital everything, the lines have become somewhat blurred, but for me at least, this is how I see them.