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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."
I am devoting the remaining exercises inside of this chapter to the final kind of specialty mask that I want to share with you and this is possibly the most useful specialty mask of them all. I have to say I am partial to all of the specialty mask that I have shown you. I love Luminance masks and Corrective masks and Color masks and Density mask and Depth mask, they are all great. But as I say, this might be the best of them all. It's the Edge mask and it's great for sharpening any kind of photograph, but it's especially great for sharpening archival photographs by which I mean photographs from the pre-digital age especially those that are 50 years or older. This is a great case in point. What we have got here is a 90-year-old print that I went ahead and scanned in, my estimate it was 90-years-old and this actually comes from my own image library.
This woman right here is my maternal grandmother in case you are interested. Of course we are not interested in that, what we are really interested is engaging the quality of this photograph and if we zoom in here, we can see that in addition to the good detail by which I mean the detail that's actually representative of the original subjects of the photograph, we also have a lot of bad detail in the form of noise and dust and various particles, film grain and the general effects of weathering and age.
Now I have to say given that this image is about 90-year-old, it's holding up pretty nicely, you look around this photograph if you were to inspect it, you are not going to find any rips, you are not going to find any tears, you are not going to find any sort of surface scaring, we just have general uniform weathering and this is something that Photoshop is setup to compensate for automatically. It's just that Photoshop's automatic compensation is no good. Let me show you what I am talking about here, let's say what we want to do is we want to sharpen the detail in the photograph, so we want to make this image really pop, when we go ahead and print it out in a publication what have you.
Then what Photoshop suggest you do, what Adobe suggest you do is apply the Unsharp Mask command which is an oldie but goody sharpening function inside of Photoshop. It's been with us since Photoshop 1.0 and Unsharp Mask provides an automated method for ruling out film grain and other sort of surface artifacts. So I am going to go up to the Filter menu and I am going to choose the Sharpen command and then I am going to choose Unsharp Mask. Of course if I loaded my Deke keys as I did, I could go ahead and press Shift+F5 if I wanted to. Once I arrive at the Unsharp Mask dialog box, I am going to go ahead and enter a few settings here, I will go ahead and take the Amount value up to 200% and then I will take the Radius value up to 3 pixels let's say in order to create some nice firm 3 pixel edges.
You can see one of the effects of applying a 3 pixel edge is that we give this kid here; we give him kind of a milk mustache because we are lightening the light side of the edges and we are darkening the dark side of the edges. So above the lip he gets a milk mustache below the lip he gets a darker lip essentially. Now the problem is in addition to firming up these good edges inside of the photograph, we also exaggerate the bad edges. So we have got this sort of infection going on inside of all these people's faces and that's obviously a bad thing which is why there is this Threshold value right here that's available to us and the idea behind the threshold value and before I go any further here, I just want you to note these values. Notice that the Amount value is set to 200%, the Radius value is set to 3 pixels. I will come back to why this is important, just sort of vaguely important in a moment.
Now the Threshold option here is designed to rule out bad edges and so let's say I go ahead and take this value up to 25 levels and notice that I am doing this by scrubbing on the word Threshold. It's another way to change values inside of Photoshop to scrub directly on the option name. So I will go ahead and take this value up to 25 levels and notice that a lot of these edges are going away, a lot of these bad edges are disappearing here and the idea is that where two neighboring pixels are 25 or more luminance levels different from each other, bear in mind we are working from 0 being black and 255 being white, so if 2 neighboring pixels are 25 luminance levels are more different from each other then they are considered to be an edge and they get sharpened. If they are 24 or less luminance levels different from each other, they are not sharpened, they are just skipped over here.
The good news is that we sharpen fewer edges inside the image, the bad news is it's an on off proposition. So either two neighboring pixels get sharpened or they don't get sharpened and therefore those edges that do get sharpen stand out that much more predominantly. So I will go ahead and take now in order to compensate, I will take the Amount value up to 350% we still have the nice, white milk mustache going here which is good, because we want to highlight that edge and we still have the very dark inner side of the upper lip that is to say. But we also have all these very fierce now sort of non-edges that are showing up inside of this kid's face for example and if I zoom out a little bit so that we can take in more of that photograph, you can see that it looks like some sort of horrible post industrial age acne.
Everybody has just got these horrible pockmarks all over their face including this poor child right there, she needs to be obviously rushed to some sort of emergency room as soon as possible and these people lived in like the Middle of Nowhere Arkansas. So I think it would have taken a while for this poor child to get some sort of remedy. Luckily, it's all Photoshop's fault. She is really not infected here and we can take care of this problem using an Edge mask. So I just want to give you a sense of why an Edge mask is so very, very useful. Again, note our values, we have got an amount of 350% this time, Radius 3 pixels, just as before and Threshold of 25 levels.
All right, I am going to go ahead and Cancel out of the Unsharp Mask dialog box and I am going to bring up the Layers palette for just a moment so that you can see that I have actually created two additional layers that are different versions of this image. So I went ahead and jumped the Background layer and then applied different Unsharp Mask USM settings to each. So this is USM 20030 just like we saw in the first portion of this exercise and then on top we have USM 35325 just as we saw a moment ago. And by this I mean USM Unsharp Mask 350%, 3 Radius and 25 Threshold.
I have these layers set here so that we can compare and contrast and what I mean by that is we are going to go ahead and create an Edge mask starting in the next exercise, we will create an edge mask and we will use that edge mask in order to sharpen the image and then we will compare that good sharpening to the bad sharpening that we are able to create automatically using the Unsharp Mask command. So that's it, this is why we so desperately need an edge mask inside of Photoshop. Starting in the next exercise, I will show you how you go about creating one.
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