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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."
So we have seen several ways to mask a complicated foreground image set against the busy background. We have seen how to use a Pen tool, of course, along with the Free Form and Magnetic Pen tool variations. We have seen Arbitrary Maps, that you apply using the Pencil tool inside of the Curves dialog box. We have also seen how you can use History to blend between different Arbitrary Map variations. In the next few exercises I am going to show you worst case scenario masking. This is like when you can't get anything else to work, you bring out the High Pass Filter and the thing about the High Pass Filter is it is brain dead. It's very easy to apply, it's very easy to get a sense of how it works, but it also is the most laborious technique of them all.
It requires you to basically convert the image into this widely complicated coloring book and then you are in charge of deciding which lines are important and which lines are not important in coloring white inside the parrot or I am sorry the macaw, in this case, and painting black inside the background. It gets kind of Zen, really you will see, it does take the most time also and it is just kind of the most tedious. So get ready for that, something to look forward to. So here I am working inside of an image called Completed arb mask.tif and it's found inside the 16_tough_stuff folder. You can see that we have got basically everything we have created so far. We have got that original arb map Alpha channel that we created a few exercises ago now. Then we have got the completed really good mask that we created over the course of last few exercises using a bunch of different Arbitrary Maps along with the History Brush and so on. We have got that path that I built using the Pen tool around the bill outline. So it's all there. I will just try to show you that everything that we have done so far is here, just FYI, doesn't really matter, because we are going to start over from scratch.
This time we are going to grab the Green channel and the reason we are going to work with the Green channel is because it provides the highest degree of contrast overall and it has the lowest amount of noise and posterization going on. So I am going to go ahead and grab Green and I am going to drag it to the little Page icon in order to make a duplicate of it. You may recall that the Green channel is our when in doubt channel. If you are not really sure which channel to grab, go ahead and dupe the Green channel and it's very often by the way the best channel for High Pass Masking. So let's go ahead and rename as High Pass and then we are going to grab the High Pass Filter. Now you may recall we saw the High Pass Filter back in Chapter 12 when we were looking at using High Pass as a sharpening tool. Now we are going to use it as a coloring book tool as you will see.
So go up to the Filter menu, choose Other and choose High Pass or you can press my keyboard shortcut if you loaded my Deke Keys shortcuts way back when, and that's Shift+F10. What it does, you may recall that it's basically sending all non-edges to gray and the edges are hanging on for dear life, essentially, and they are trying to remain high-contrast if they can. Now, where masking is concerned, higher radius values are going to give you less precise, more generalized results. So they are going to result in less complicated, but less accurate coloring books, meaning that you are going to fly through it more quickly, but you are also not going to get very good results.
If you go low with the radius value, like I have gone as low and this is criminally insane by the way to go this low, but I have gone as low as 3 for a radius value, which gives you a super duper accurate coloring book, really, really accurate and you will spend the rest of your life working on it. It turns the masking process into about, not really that long, but about a conservatively a 20-30 minute process and that's if you really get it and you really move through it quickly. It could be more like an hour or two hours, frankly. I suggest that we go from 10 to 20, that we work in the 10-20 range with High Pass. I am, in fact, going to enter a radius of 10, I invite you to do that along with me and click OK.
Now it doesn't look like a coloring book at all so far. So we need to turn these very vague gray outlines that we have crafted thus far into serious black and white outlines and we are going to do that using our old friend the Levels command. So press Ctrl+L, Command+L on the Mac and you want to basically squish this histogram like so, just really tighten it on the central part of this histogram. What I recommend, in this case, is a 120 for the black point value and a 135, which is 255 white minus a 120. So we are going a 120 in on both sides here, 135 for the white point value and then click OK. We have created ourselves something that looks like a macaw that has been photocopied about 20 times, that is, we have got 20 iterations of photocopy going.
In other words, it looks pretty bad. But, as a coloring book it looks great. Now the problem with it is that sometimes, let's go ahead and zoom in down here, sometimes Photoshop has done us this service of tracing black on the inside of said animal and white on the outside. So we need some uniformity here. What I am suggesting we are going to do, because we ultimately want the bird to be white and the background to be black, I am suggesting we shift the whites inside and the blacks outside. So get the Lasso tool by pressing the L key, of course, and then I am going to go ahead and select around this region. Can you see what I am doing? It's hard to sort of track this since I have got a Lasso tool in this black and white area that I am tracing this outline around this black and white image, but it goes around like this here, you can see. So I am coming in right about there.
I'm cleaving in on this portion of the animal's chin, is it? And on this area where its buck teeth would come out if it had them. So we have this area selected and then I am going to press Ctrl+I or Command+I on the Mac to invert it. Now all of a sudden I am not terribly concerned about the Anti-alias edges. Well for one thing I have Anti-alias turned off with my Lasso tool, so that's probably the best way to work actually. But it doesn't really matter for this technique, you could have the Anti-alias on or off, it's going to fair pretty much the same, not matter what.
Now let's go ahead and grab this tuft, this unknown anatomical region on this animal, and let's go ahead and select it and press Ctrl+I or Command+I on the Mac to move the black edges out and the white edges in. Then let's go ahead and grab this area and again you have got to make some choices, sometimes actually that was a bad choice on my part. Sometimes you are not exactly sure where you want to trace the threshold between the inverted area and the non inverted area, but just do your best, just make whatever choices, because you are going to have to go back and fuss with it a little anyway.
I have gone ahead and selected this region, press Ctrl+I, Command+I on the Mac in order to invert that and it's questionable what I have done here. I am not sure that I have made exactly the right choice, but the choice stands and now there is just this little guy right here that needs to be inverted to and again am I making the right choice? I don't know, let's just make a decision and go with it. Press Ctrl+I, Command+I on the Mac in order to invert that. We have some iffy details going on there. But now the great news is, I can go in and start coloring in the interior of the macaw and I can color the background as well. I can color the interior white and I can color the background black and that's what we are going to do in the very next exercise.
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