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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."
Now we have got a great blend between the adjusted sky, the exposed sky and the exposed landscape right here. And by the way I should say I am working in a catchup document called The better sky mask.psd that you can open from the 17_16bitHDR folder and just to give you a sense of what kind of difference we have made, using this layer. Here is what the scene looks like without that Levels adjustment layer and this is what the scene looks like with that Levels adjustment layer. So it's just affecting the top most portion of the sky but it's doing a great job of making the sky nice and dramatic. Now at this point here, I want to go ahead and convert the document from the 32 bit per channel mode down to the 16 bit per channel mode so that I can apply other modifications for example, I want to bring up the saturation of my scene but I don't want to apply a pass of the Hue/Saturation command, I want something that affords to me a little more control.
So I want to switch to the Lab mode but the Lab mode the L-A-B mode is not available to me when I am working with 32 bits per channel. In fact, only RGB and Grayscale are available to me, nothing more so I need to down sample to 16 bit. Also if I hope to share this image with a client or something like that or even family members in my case, I need to get out of 32 bit per channel mode. So I am going to do that by doing the following, I am going to go up to the image menu, I am going to choose mode and I am going to choose 16 bits per channel. Now Photoshop is going to ask me if I want to merge or not. Now frequently when you are switching between modes you can say don't merge the layers together because we have a two layer image. But when you are going for a 32 bit to 16 bit you have got to merge unless you want this effect to totally fall apart on you. It doesn't go look anything like this in 16 bit per channel mode because we can't draw highlights from another room, right, we can't draw a completely lost highlights like we can in 32 bit per channel, we can't do that in a 16 bit per channel.
So the Levels command is going to have a completely different effect. So we have got to merge first. Even clicking on the merge button will force the change in this scene. Photoshop has done what we asked, went ahead and merged the two layers together which is a good thing and now it's just kind of monkeyed with the exposure settings, that's basically what's happened here. Now there are different methods for down sampling an image from 32 bit to 16 bit. And you can play around with them, you can play around with highlight compression, for example, and there is no options associated with highlight compression by the way. You can also try equalize histogram which is a bad idea; it's just going to try to distribute the histogram equally so basically all the points in histogram were of the same height which almost never works.
But it is an option if you want to try it out. You have got this option called Local adaptation and when you choose Local adaptation here, you get sort of this shadow highlight effect going. So you will see halos appearing around the various edges inside of the image unless you take this radius value way up. And that's when your halo start to go away but then when you take the radius value way up, you are going to start blowing highlights and filing in shadow details to a larger extent. The idea though of course, this looks terrible at this point. The idea is that you have now access to a toning curve.
So you can click this double-down pointing arrow head button here in order to reveal the curve and then you can play with the curve in order to darken the scene if you need to or lighten the scene in other points and you have a lot of control but you are still dealing with the effects of the radius and threshold values here which I quite don't appreciate actually. I don't find these options to be very useful so what I tend to do is I switch over to Exposure and Gamma and I must say this area of the dialog box is a little controversial, it's not like I am speaking for everyone out there. There are people who appreciate these controls and think that they end up producing nice effects. I just don't happen to be one of them. I am going to go ahead and switch over to Exposure and Gamma which produce more uniform effects, you are not getting those strange halos around your edges, the way you are with Exposure and Gamma but also you don't have access to your tone curve anymore. Notice that the toning curve is no longer functional, even though it's still visible on screen, you just can't access it.
So we might as well close it so that we don't have to look at something that's not working for us, which is a little bit frustrating and then you just go ahead and expose the scene you just go ahead and modify the Exposure control the Exposure slider here and you modify the Gamma slider as well if you want to. Very small adjustments make huge differences; I am here to warn you. So I am going to go ahead and raise the Exposure value for my part, what seems to look pretty good is an Exposure value of 1.16 and you can arrow that value up and down if you like and that tends to actually be a pretty good way to work.
Once again though, you are eyeballing things. You are just trying to see okay, am I keeping this area white or am I sending it down to gray a little bit or what am I doing? And then I would go ahead and take well, I guess, 1.14 works for me, I don't know, I am just playing around, I have to admit. And I am going to take the Gamma value up just a little bit as well but I don't want to take it too high, let's see what it looks like if it's just flat, 1.0. It looks pretty good actually, all right, so I will go ahead and click OK in order to accept that modification. What's really important is that your highlights and shadows are where you want them because once you switch to 16 bit; you are locking down your highlights and shadows now. You are going into that big room full of chairs but you can no longer move through the walls, you could no longer retrieve clipped highlights or shadows at this point.
But what you can do assuming that you like to look at the scene, you could tweak it a little bit like I could bring up the Levels dialog box and I could go ahead and tweak the histogram, this is a more meaningful histogram, more sort of trustworthy at this point and so I can say, okay, I want to you know bring the shadow point in line with the beginning of the histogram and then I am going to go ahead and raise the Gamma value just a little bit to compensate for example and I could take it even higher if I want to, but I know what the scene to get sort of drab either. Or I am going to cancel out because what I really want to do is I want to make my Levels modification in the Lab mode so I am going to go to the Image menu, I am going to choose Mode and I am going to choose Lab color. Now I am going into somewhat unfamiliar territory at this point, when I am showing you Lab, we have seen Lab before; we set the outset of this entire series. And you may recall that it's luminosity channel mixed with a tint channel in the form of an a channel and the temperature channel in the form of the b channel but I haven't shown you this technique before for the Lynda.com Online Training Library, I am hoping to create a Lab series because Lab is an extremely powerful mode where color correction are concerned. I am going to go ahead and press Ctrl+L now. At this point having switched over to Lab and I am going to darken the lightness channel just slightly to just bring the shadows over a little bit and I could bring down the Gamma or up the Gamma, I might being the Gamma up a couple of clicks there.
So 6 and 1.03, I am going to leave of course the highlights along here. We already have some blown highlights here and now I am going to switch over to the a channel, here is the little technique that I want to share with you. You can darken the black point and lighten the white point in the a and b channels in order to expand the saturation of an image. So check this out, this is a great way to elevate saturation. It might be the best way to elevate saturation inside of all Photoshop. I am going to click inside the black point value right there and I am going to press Shift+Up Arrow a several times in a row like four times in row let's say and then I will tab to the white point there and I will press Shift+Down Arrow four times in a row because I want to compensate equally on both sides and notice that that increases the saturation of the a colors which are the tint colors so they are green and magenta. So I have increased the saturation of the greens and the magenta colors inside the scene.
So this fully edge down here has become more saturated and check it out this is before and this after. So you can see that's become more saturated. The red inside of the rocks is sort of the magenta inside of the rocks has become more saturated as well. All right, so that throws the scene out of balance so we need to go over to the b channel and do the exact same thing. Let's take this first value upto 40, Tab, Tab, take the second value down to 215 and we end up getting this more elevated saturation in general. Now if feel like the scene has gone a little bit too blue which I do because this color right there, it should be more of a neutral color, it was a little bit blue but not this blue. So let's try taking 215 down a little more. So I press Shift+Down Arrow to take the white point value that is down from 215 to 205 and that fixes the scene pretty nicely there as you can see if that's still not enough, you can want to warm it up further, you could take it down another click but I think then we are going too far.
So I will raise it, let's try 200, 202, something along those lines, looks pretty darn good where this scene is concerned and then I will go ahead and click OK in order to accept that modification. Now this is a heck of a great looking scene in my opinion especially given let's go back to the Bridge for a moment, especially given that this is what I had to choose from, right. So this is let's go ahead and scroll down to ake Powell here, this is Lake Powell-1, this is Lake Powell-2 and this is Lake Powell-3, they are all looking terrible, right? But when I merge them HDR and modify them especially inside of the Lab mode in 16 bit, at the very end here, then I end up getting this effect which is much better looking, I think just a pretty darn sweet image.
And not the kind of thing I could have exposed for on the fly when I was shooting the photograph. Now it's possible that a more talented photographer could have actually captured this scene but I couldn't have, I will tell you that much and I wonder if anybody else could have either, I just think this is one of those scenes that defies capturing this beautifully but thanks to Merge to HDR we were able to pull to off. Okay, so one last thing that I am going to do. I am going to go ahead and rotate the scene of course because it's an angle. So let's go ahead and grab our Ruler tool right there, from the Eyedropper tool fly-out menu and I am going to drag along what I presume to be the horizon which would be this line right here and actually if we go with the chalk line which is where the lake level used to be at some point in time then I think this will give us a pretty accurate reading of the angle that this scene should be at and then of course we will go up to the Image menu, choose Rotate Canvas, choose Arbitrary or you could smash your fist down on the keyboard and press the R key depending on if you loaded deke keys way, way back when and it's telling me that it's going to rotate it at angle of 0.59 degrees counter clockwise, I say, oky-doky don't really care just do it and it goes ahead and applies the rotation, then I will grab my Crop tool, I suppose and I will go ahead and drag around the scene to try to crop it and this looks pretty good to me. And I will go ahead and press the Enter key of the Return key on the Mac in order to crop that scene and there it is people.
A beautifully rendered scene here in the Lab mode, if you want to, you can switch back to RGB in order to apply further edits you could also down sample to 8 bits per channel, if you want to. But I am just going to leave it the way it is because I think it looks gorgeous. I am going to fill the screen with the image Tab away the palettes and zoom on in and here it is the final version of the image exposed; just properly every piece of it, the sky is exposed beautifully, look at that sky, the ground is exposed beautifully, the lake is exposed beautifully. We have three motion trails in a water that doesn't bother me. That's the only even slight mistake however. Thanks to the wonders of 16 bit and 32 bit editing, high dynamic range here inside Photoshop CS3.
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