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The elusive alpha channel remains one of the most misunderstood yet powerful tools in Photoshop. Alpha channels are collections of luminance data that control the transparency of an image, and they inform just about every aspect of Photoshop. As he builds transitional blended layers, fashions a depth map, makes edge adjustments, and takes on extreme channel mixing, Omni Award-winning expert Deke McClelland teaches Photoshop users that where there's a will, there's a way. Photoshop CS3 Channels and Masks: Advanced Techniques covers mapping texture on an image, turning flesh into stone, using vector masks, working with all different channels, creating a rustic edge effect, and much more. Exercise files accompany the tutorials.
Download Deke's customized keyboard layouts for Channels and Masks from the Exercise Files tab."
One of the most common ways that people use layer mask inside of Photoshop is to limit the effects of adjustment layers. In case you don't know what those are, adjustment layers are independent layers of color adjustment, such as Levels and Curves, Hue/Saturation, and so on, that you can mix, and match, and modify, and mask, of course. Consider this image right here, it's called Complimentary colors.psd. It's found inside the 11 layer mask folder, and you can see that this is a photographic image that's modified by two adjustment layers, both Levels adjustment layers, both of which have layer mask associated with them. So let's check out what's going on here. I want you to Alt+Click or Option+Click on the eyeball in front of the Background layer, then you will see the original image, part of the iStockphoto.com image library. This image happens to come to us from photograph Alex Nikada, and I got into my head that I wanted a richer, bluer, more saturated deeper background, so that we had more contrast between the background, and the orange tones of her skin, and her hair and so on. So I went ahead and built this adjustment layer right here, and you can see that it just effects the background. Thanks to this layer mask. I will go ahead and Alt+Click or Option+Click on the layer mask.
The fact that I have made the model black inside of the layer mask rules out the adjustment layer inside of this model, and limits the adjustment layer just to the white areas in the sky. All right, so I am going to Alt or Option click on the layer mask once again. Next I decided that I wanted her teeth to be whiter. Not to say, she has pretty white teeth, but in this photograph they appear kind of pinkish, kind of gummy almost. These highlights across here clavicle, and her chest, and her nose, and her eyebrows and so forth, they appear a little pinkish as well. So I wanted to draw all of those highlights out using this teeth layer right here. So go ahead and turn that on, and you can see that the teeth indeed do brighten up, so do the other highlights along with. And we have a more high contrast image I think, more of a coming image as well. The subtle modification overall, but a good one, and sometimes these kinds of subtle modifications take a fair amount of work where layer masking is concerned. So I suggest we get started.
We are going to build this first adjustment layer inside of this exercise, we are going to finish this layer mask inside of this next exercise, and then we will build the final adjustment layer in the exercise after that. So go ahead and select the sky and teeth layers by clicking on one, and shift clicking on the other. Then I want you to Alt+Click or Option+Click on this Thrash can icon, in order to delete both of those layers. All right, so we are going to create an adjustment layer just right off the bat here, but first I want to make sure that you and I are in the same page. I suggest that you make the following modification in an earlier chapter, but I just need to confirm it right now.
So go up to the Layers palette menu, click, and then choose this option right there palette Options, and I want you to make sure that Use Default Masks on Adjustments is turned off. Make sure that check box is turned off. It's turned on by default. But it's better if it's turned off, because that way you can make your own layer mask. So instead of automatically creating a layer mask with every single adjustment layer, you get to be in control, which is a better way to work. All right, so turn off that check box, click OK. Next I want you to press and hold the Alt key, or the Option key on the Mac. Keep that key down as you click and hold on this Black & White icon, and then choose the Levels command, and by virtue of the fact that you have the Alt or Option key down, you can release it now. You bring up the New Layer dialog box, just a better way to work. Just a good habit to get into. That way you can name your layer as you make it. So I am going to go ahead and call this the sky layer, and then I am going to click OK in order to bring up the Levels dialog box.
Now we are going to make a very significant modification with this layer, and we are going to apply our changes on a channel-by-channel basis. So I want you press Ctrl+1, or Command +1 on the Mac to switch to the Red Channel, you can also choose the Red Channel from this list. Then I want you to change the black point Input Levels value here to 45, and I want you to change the Output Levels white point, this value right here, down in lower right corner of the dialog box to 100. So we are robbing the image of a lot of red. We are sucking a lot of Red out of the image, making the Red Channel much, much darker, and as a result we are boosting the appearance of the Blue Channel, because that's the complimentary color. All right, next press Ctrl+2 or Command+2 to switch to the Green channel, and I want you to change that black point to 60, so we are making the Green channel darker as well. Change the white point for the Output levels to 170.
So 60 up here, 170 down here. Then press Ctrl+3 or Command+3 for the Blue Channel, and I want you to change the black point to 80, and that's it. We are not going to change any of the other values inside the Blue Channel. So we have really made all the channels darker. When it's done though, because we have robbed the image of more Red and Green, than we have Blue, we have really upped the saturation of the blues inside the background here, as well as robbed all kind of colors from the foreground. But we are going to mask out that foreground, aren't we? So anyway, go ahead and click OK in order to accept this modification. Now we are going to want to build our layer mask from a channels inside the Channels palette. The Channels palette is always working from the composite image. Our composite image, thanks to this adjustment layers, pretty messed up here. So let's go ahead and turn the adjustment layer off for a moment, so that we can see our Pristine original. Go ahead and click on the Background layer to select it. Then click on the Channels tab to switch over to the Channels palette, and let's see what we have to work with.
Here is the Red channel. Fair amount of contrast going on there. Here is the Green channel, more contrast. That's better, here is the Blue channel most contrast, that's best. So let's go ahead and start things off form the blue channel. I want you to load that Blue channel as a selection by Ctrl clicking on it or Command clicking on the Mac. Now return to the RGB composite, then switch over to the Layers palette, click on the sky layer, turn it on, and then convert the selection to a layer mask, by clicking on the layer mask icon down here at the bottom of the Layers palette. And there we have it.
We have now masked the contents of the adjustment layer. It looks better than it did before. It's not nearly so dark, this is before, and this is after. However, we still need to finish this mask. Notice what its looks like here. If was to Alt+Click or Option+Click on this layer mask thumbnail inside the Layers palette, you would see that she is dark, but she is not black. We need to make her completely black inside of the layer mask, and we need to make her Background completely white, and we will be doing just that inside the next exercise.
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