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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."
All right, I have gone ahead and saved up both modified versions of Max here. Both of ones that I modified in the 8-bit/Channel space and the one that I modified in the 16-bit/Channel space, I went ahead and converted the 16-bit image back to the 8-bit/Channel space, so both images are saved as JPEG files; one of them is called Max8-bit edit.jpg and the other is called Max16-bit edit.jpg. They are both found inside of a sub folder called Color_Corrected_Max inside of the 17_16bit_HDR folder.
All right, I am just going to keep them open on screen here. We are going to open yet another version of this very same image and we are going to do so by switching over to the Bridge. So I am going to go ahead and click on the Bridge button, here in the Options bar in order to switch over to the Adobe Bridge. Here is the 17_16bit_HDR folder that I have been telling you about and here is this image that I want you to open, it's called The original raw photo.dng and this is the original raw digital camera file that I have converted to the DNG file format but it has got all of that high bit-depth data that was captured by the digital camera and this happens to be a 10-bit/Channel image.
But it's more than 8-bits/Channel, it's about a 1000 different luminance levels that are available inside of this image on a channel by channel basis. So let's go ahead and open it on up by double- clicking on it's thumbnail and that will open the image inside of Camera Raw, in my case it's opening it inside Camera Raw 4.2 which is the most recent version of Camera Raw that's available as I am filling this. And I don't want you to make any color modifications, we will see that in the next exercise. Right now all I want you to do is I want you to click on this link down here, and notice this link that says Adobe RGB (1998): 8-bit and the size of the file and so on. Go ahead and click on it.
This dialog box, that comes up as a result, allows you to determine how the file opens up inside of Photoshop, what's going to be the color space, leave that set to Adobe RGB (1998) for now. What's going to be the bit-depth, let's go ahead and open it as a 16-bit/Channel image. So instead of going from 10-bits/Channel and down sampling it to 8-bits/Channel, we will just keep it at 10-bits/Channel inside of the 16-bit/Channel space. So in other words, we are just making more chairs for these 1000 luminance levels/Channel that will be available to us. And the size should read 8.0 MP for this particular image. We don't want any of the reduced image sizes which have minuses next to them or the larger images sizes that have pluses next to them because that would require either downsampling or upsampling, we are interested in doing neither, so just go ahead and click on this middle guy that doesn't have plus or a minus next to it.
Resolution by the way, does not matter, completely meaningless for our purposes here and I want you to leave this check box off. So go ahead and click OK in order to open a flat version of the file inside of Photoshop in the 16-bit/Channel space and now go ahead and click on Open Image, in order to open the image on up. And it might take a few moment for the image to appear inside the Photoshop, but ultimately you will see it up here on screen and I am going to go ahead and make it little bigger here, I am going to make the window bigger that is to say and zoom in on Max so he is visible at the same size as the other images, which I guess is the 25% zoom ratio.
And let's apply those exact same color modifications again, so assuming that you were with me in the previous exercise, you would press Ctrl+Alt+U or Command+Option+U on the Mac in order to bring up the Hue/Saturation dialog box with an enhanced saturation of plus 30 and then click OK. And then you would press Ctrl+Alt+M or Command+Option+M on the Mac, in order to bring up the Curves dialog box with those same Curves modifications that we applied before. On a channel by channel basis you can see, we do have some channel by channel differences going on. Then click OK in order to enhance that image.
All right, now let's take a look at that Histogram, why don't we. If I press Ctrl+L or Command+L on the Mac, notice it's completely smooth, none of those little fillers popping off the top that we saw before. So a very, very smooth histogram all the way around and we could further modify the histogram here if we wanted to and I am going to do that just so that you can see that the histogram will still remain smooth, even if I take this white point down to 225 at this point inside of the Levels dialog box, to further brighten Max right here.
And let's go ahead and make some sort of Gamma adjustment too. Let's take the Gamma value down a little bit, I am going to take it down to let's say 0.88 in order to diminish the brightness just a little bit, to account for the fact that I increase the highlights, I am going to go ahead and darken the mid tones in other words and then I will go ahead and click OK in order to accept that modification and now if I revisit the Levels dialog box, Ctrl+L or Command+L on the Mac, we are starting to get some of feeler up at the top just little guys that are starting to shake apart up there but the majority of the histogram is in great shape of course. So let's cancel out of there.
Then let's say I am going to hand this image off to a client. I don't know why a client would want a picture of my kid but still I am going to go up to the Image menu, choose Mode and choose 8-Bits/Channel in order to downsample the image. Now let's press Ctrl+L or Command+L on the Mac, perfectly smooth histogram, oh my goodness! So great. And compare this by the way just so that we can see how these guys compare of course, here is the original 8-bit edit of the file that we applied in the previous exercise, terrible of course. It's just a horrible histogram, click Cancel, means that we probably have some banding and posterization in there.
Here is the 16-bit/Channel edit, where we started with an 8-bit/Channel image and then applied the 16-bit/Channel modification it looks better, but working in 16-bit the whole way, so basically going from 10-bit to 16-bit/Channel and then to 8-bit produces this histogram right here; the smoothest histogram of them all. All right, pretty nice stuff now it gets even better than that though. It gets even better if we just go ahead and apply our modifications directly inside of Camera Raw and that's what we are going to do in the next exercise.
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