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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."
In this exercise, we are going to explore the power of Luminance masks. And all luminance masks are is found Luminance information inside the image. At their most basic you are just taking one of the color channels, either red, green or blue and re-purposing it as a mask, that's it. And yet even though Luminance masks are insanely easy to create, they can be very, very powerful. I am looking at an image from photographer Sharon Dominick of istockphoto.com. The name of the image is Close-up.jpg and it's find inside the 12 Specialty folder. I just love this image because the model has a straight on look, the lighting is great. The only tiny issue that I have, is we have got a little color modeling going on inside of the skin, a little surface action and let's say that we wanted to smooth that away using a layer of digital make up essentially.
That we are going to apply using the Gaussian Blur filter set to the Overlay mode. Pretty common technique inside of Photoshop, not only smooths away surface details but also enhances the contrast of the image and the color inside the image as well. So here is what I am going to do. I am going to start things off because I want to apply a filter and because I want to be able to blend that filtered effect, I am going to go ahead and apply the filter, I am going to apply Gaussian Blur as a Smart Filter here inside Photoshop CS3. So working inside the Layers palette, I'll go to the Layers palette menu and choose Convert to Smart Object, or press Ctrl+, or Command+, on the Mac, if you loaded my Deke Keys shortcuts.
Also another way we could work here if we wanted to, the more traditional way if indeed there is such a thing as tradition where smart filters are concerned. You can go up to the Filter menu and choose this command Convert for Smart Filters which will do exactly the same thing, it will convert that layer into a smart object. So it's now an independent layer as well, and I am going to go ahead and name this new layer makeup because that's the purpose it's going to serve. Then I am going up to the Filter menu, I am going to choose Blur and I am going to choose the Gaussian Blur filter, or if you loaded my Deke Keys shortcuts you can press Shift+F7 and I am going to take the Radius value pretty high actually, I am going to take it up to a whopping 20 pixels and then press the Tab key in order to preview that effect, and you can see that it not only pretty well obliterates any surface details but it also gets rid of rather important details, facial details such as eyes, nostrils, lips and so on.
That's okay because we are -- as I say we are going to be applying the Overlay Blend mode which will bring the image back. So I am going to click OK in order to accept that modification. Now, let's apply the Blend mode by double-clicking on this little Slider icon to the right of the word Gaussian Blur and that will bring up the Blending Options and I am going to change the Mode to Overlay. Now if that's too much, you could switch the Blend mode to Soft Light instead. Hard Light is not really going to prove to be too much different than Overlay because I was telling you that Overlay and Hard Light are kind of opposites of each other. If you were to set image A that's on top of image B, if you were to take image A and set it to Overlay, it is the same as turning the layers around putting image B on top of image A and setting it to Hard Light.
And in our case, the only difference that we are going to see is that the highlights are a little muted in the Hard Light mode where they are nice and shinny in the Overlay mode. So I suggest we go with the Overlay mode for this effect, a 100% Opacity is fine, go ahead and click OK in order to accept that modification. So this is what the image looks like without the Gaussian Blur effect set to the Overlay mode, this is what it looks like with Gaussian Blur set to Overlay mode. So definitely a more vibrant, smoother image all the way around.
Now the thing is though, the effect pretty well takes over the entire image. You can see I am going to go ahead and turn the effect off again. Notice her hair, she actually has hair in the original image whereas when I turned the Smart Filter on, the hair goes away. We are just basically darkening the hair well into the shadows. So I would like to go ahead and just apply the Gaussian Blur effect inside of the lightest details, inside of the highlights of the image and we are going to do that using a Luminance mask. So I want you to turn the Smart Filters off for a moment, go ahead and click the eyeball in front of Smart Filters in order to deactivate them. Then I want you to switch to the Channels palette, and the idea here is we want to see the channels that are associated with the original version of the image.
Now I could just go ahead and load the luminance data that's associated with the entire RGB composite image. And I would do that by Ctrl+Clicking or Command+Clicking on that RGB thumbnail and you can see that loads the lightest colors as a selection, deselects the darkest color; just as if the image were a mask. Or I could checkout one of the individual channels instead, and that's what I am going to do. I am going to Ctrl+D or Command+D in order to deselect the image, click on Red to check it out that's where we are going to have the most contrast because this is a portrait shot, so any human being has a lot of red in him or her in our case.
Here is the Green channel a little darker, more detail and more of that surface modeling that we are trying to get rid off notice that and then here is the Blue channel which has the most surfacing modeling involved. It's also got some pretty crisp transitions, some sort of jagged edges going on around some of the shadow details like her pupils, and her lips, and so on. So my favorite channel is the Red channel because it's also the smoothest channel, notice that. So we are just going to load the Red channel as a selection outline and we can do that in any number of ways. You can Ctrl+Click or Command+Click on that channel if you want to, or you can press the keyboard shortcut because it's the first channel, you can press Ctrl+Alt+1 or Command+Option+1 on the Mac. And that's what I'll go ahead and do just for laughs.
Now, let's go back to the Layers palette, I want you to turn on the Smart Filters again. Now I could click inside Smart Filters mask. Notice that we have an empty mask going, but hat I want to do is I want to fill the area outside of the selection outline with black. So I would go up to the Select menu and choose Inverse and then fill it with black or here is a kind of different and potentially easier way to go. I want to show you how you can manufacture a mask for your Smart Filters if you want to. I am going to go ahead and take this mask and I am going to throw it away. So click on the mask thumbnail right there, the empty mask thumbnail and Alt+Click or Option+Click on your Trash can icon in order to delete that mask.
Now, you just have the Smart Filters without the mask. This is also great if you are trying to save room inside your Layers palette and you don't want those big galumphing filter masks all over the place. Now I am going to reintroduce the filter mask and I am going to do that by right-clicking on the word Smart Filters and choosing Add Filter Mask and that will go ahead and convert the selection outline into a filter mask as you see right there. So different ways to work. I am going to go ahead and zoom out, so that we can take in the image, this is the way she looks without that mask. This is how she looks with the mask, invoking those two views by Shift+ Clicking on the mask to turn it off and back on and you can see that now we can see more of the information inside of her hair and we are relegating the effect to just the highlights inside of the image, which in this case turns out to the be the flesh tones, a really great use and a very simple use for Luminance masks inside Photoshop.
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