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You're probably already aware that the color information in our photos comes from individual channels. A typical image has a red, green, and blue channel, each of which indicate the intensity of red, green, or blue light that is reflected in each pixel. In other words, those channels define the actual color for each pixel in our images. But we can also use that information to create a selection. Let me show you how. We'll start off by going to the channels panel, if your Channels panel is invisible, you can choose it from the Window menu.
And then we're gong to click on each of the individual channels for this image. First, I'll click on the thumbnail for the red channel, so that I can take a look at that channel, and see if it might be a good candidate as a starting point for my selection. In this case, that's certainly not the case. I want to create a selection of this poppy including the stem. And you can see that on the red channel, parts of the poppy are very bright relative to the background and parts of the poppy, especially the stem, are very dark relative to the background. And that means we're not going to be easily isolate the poppy from the background using the red channel.
Next we'll take a look at the green channel, so I'll click on that thumbnail. And you can see that we have a better looking image. We have night contrast overall, but still not good contrast to separate the poppy from the background. When we take a look at the blue channel, however, we see a very good starting point. The poppy overall is very dark, and the background is very light. And that makes sense, of course, because the blue channel reflects the amount of blue light. The sky contains lots of blue, the poppy contains no blue or very little blue. And in fact, it contains the opposite of blue, lots of yellow. So the blue channel, in this case, is the best starting point. And actually you'll find that in many cases the blue channel is the best starting point for this technique, especially when a sky is involved. But for portraits, the red channel might work out better, and in some cases the green channel will work best.
You'll want to take a look at all three channels though to decide which one will give you the best starting point. Of course, the blue channel provides a great starting point, but not a final result. So, we're going to need to apply some adjustments here in order to enhance the contrast that already exists. Of course, I don't want to modify my blue channel directly, because that would affect the color in my image. And so instead, I'm going to drag the thumbnail For that blue channel, down to the blank sheet of paper icon, that create new channel button, at the bottom of the channels panel. And that will produce a blue copy layer.
Now, I can apply changes directly to this blue copy because it is an alpha channel. It's an extra channel you might say. Not one of the red, green, or blue channels that define the color in my image. Image. So to adjust that channel, I'll go to the Image menu and choose Adjustments followed by Levels, and then I'll drag the black point inward to darken the poppy, and the white point inward in order to brighten the sky, and ultimately I want to try and bring them all the way right next to each other, so that I end up with a really good selection here.
Well it's not a selection yet but it will be shortly but I want to have that silhouette effect. I want the poppy to be entirely completely black and the sky to be entirely completely white. And with this level's adjustment that appears to be the case so I will go ahead and click okay. In order to apply that change, but now I notice there's a little bit of a problem. Up toward the top right, you'll see that the entire sky did not go white, and I have some black areas up there. Now, you might assume that I would want to modify that levels adjustment in order to get those areas white, but in this case, that simply wasn't going to work.
If I applied a different adjustment, sure, I might get those areas to be white, but I would also cause some problems for the poppy. The form, here, would no longer match the exact edges of the poppy. So instead, I'll use a slight variation, here. I'll just choose the Brush tool from the toolbox. And then I'll press the letter D on the keyboard to make sure my colors are set to the default values. Which, in the case of a channel is white for the foreground and black for the background. I can then move my mouse out over the image and adjust the brush size as needed, using the Left Square Bracket key to reduce the brush size.
And the right square bracket key to increase the brush size. I'll also make sure that the blend mode on the options bar is set to normal and that I'm working at a 100. Percent opacity for my Brush tool. And then, with white as my foreground color, I can press X as needed to switch foreground and background colors. I'll simply click and paint over those areas in order to effectively erase those black spots in the sky, replacing them with white. (SOUND) And of course I could also paint with black in the poppy if I needed to tune any areas, but at this point I think I'm in good shape. I have a black poppy set against a white sky and that is a great basis for selection.
So at the bottom of the channels panel, all I need to do is click on the load channel as selection button. That dash circle icon. And that will create a selection where all white areas of this alpha channel are selected, and all black areas are deselected. And any shades of gray would be partially selected. So at this point I have my selection created. I can click on my color tile, the RGB tile, to get back to my full image. And as needed, I could also invert the selection. In this case, I do want the opposite selection because I actually wanted the poppy to be selected. So I'll go to the Select menu and choose Inverse, and now I have the opposite selection, although I'm also noticing that there are still a couple of problems up at the top left.
So I missed a couple of those specks on that blue copy channel, but that's okay. I can still modify the result. Even though I didn't use a selection tool to create my selection. I can use additional selection tools to modify that selection. So, for example, in this case, I can choose the Lasso tool from the toolbox, and then hold the Alt key on Windows or the Option on Macintosh in order to access the Subtract From Selection option. And then I can just draw a lazy loop around that area where I have a couple of pixels that were still selected. And that will remove those pixels from the selection.
So I can utilize one of the channels as the basis of a great selection but then fine tune my results as needed in order to get the best selection possible.
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