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Channel Based Selections
Sometimes, you need to make a selection or a mask out of something that is very complicated like a tree, leaves, something with a lot of detail. Using the quick selection tool, really wouldn't work in this case because, you know, you're not gonna get all that detail and it just becomes very difficult. As you just saw, from that question, selections can be used, or channels can be used as selections. So, I can go into the channels panel and I have all these channels to work with. And actually, I'll delete that one because that one's a finished file. So I have all these channels: red, green and blue. All RGB images are made from red, green and blue. So, when you want to make a selection of something if you really can't use any of the tools because the image is too complicated, go into the channels and see how all the channels look. And I'm looking for the channel that has more contrast between what I'm trying to select, in this case, the tree and the grass, and the background that I want...
to remove, in this case, the sky. So there's a lot of contrast here. So I can use that to make my selection. I can click on this layer, on the channel, drag it over into the new channel icon to duplicate it. So now I have a blue channel copy. You never want to work on the original channels because then you'll adjust the lighting of the image, and it won't look very good, so always duplicate the channel. So now that I have the channel duplicated, I can go into Image, Adjustment Levels, and I can make darker pixels darker, the brighter pixels brighter, press OK. So, as you know, with layer mask, white reveals, black conceals. This is not exactly what we want. We want tree to be white and the sky to be black. So, we can invert that channel by pressing Control + I; Command + I on the Mac. Control + I, Command + I, just remember the I for invert. Control +, Command + I. Now, we have the tree selected and most of the grass. Sometimes, you may have to go into the channel and use the Dodge tool, to brighten up some areas like the grass here, I need to make it brighter. And in other areas, like in some of the detail here, in between the leaves, I have to make those darker, so I'm going to select the Burn tool, and just make those darker, so that they do become 100% invisible. In some cases, you may need to paint with the brush tool. So like the grass here, I'm painting with the brush tool with white, to make everything white, or you can even fill. I can select the rectangular Marquee tool, make a selection, select this part of the tree. I can even use the Lasso tool. I'm holding Shift and I'm just adding to the selection, like so. Then I can fill with white. I've already shown you the keyboard shortcut to fill with white, I'll just show you how to do it now with the Fill menu, if you go into Edit, Fill, you get this window, and you can select from all these things, including white. So, go with white. Press OK, and there it is. Now, I can hold Control, Command on the Mac, and click on the Layer Thumbnail and it makes a selection around the trees but not the sky. So that's a channel based selection. I'm making a selection based off a channel. I'm gonna go into the Layers panel, click. Usually when you go into the Layers panel, and you have the, and you don't have RGB selected, it's gonna look weird. So if that happens to you, don't worry, just come back into the channels panel and make sure that RGB, the little icon is on it and this one's disabled, anyway. Layers panel, tree, and I can just click on the layer mask. And there you go, that is, I was able to remove the sky, Keep a lot of that detail just by using one of the channels. So, always look for the channels, the one that has more contrast between the things that you want to keep and remove. Use that channel and then adjust the luminance value of that channel, using levels or any other adjustment and then using the Dodge tool, to make things brighter the Burn tool, to make things darker.
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Gary Price
Probably mistitled as "for beginners" Moves very quickly, sometimes without clearly describing actions taken. This is fast paced and often assumes that the listener is very familiar with photoshop. Good tips if you are already familiar...
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Adobe Photoshop