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Blending the Red and b channels

From: Photoshop CS3 Mastering Lab Color

Video: Blending the Red and b channels

Hey, I see you are back. Very encouraging, I mean saying you are tenacious which is what I love about you and your reward is going to be a special masking technique that's only found inside this series, nowhere else, at least nowhere else inside the lynda.com Online Training Library. What we are going to be doing is we are going to be merging an RGB channel with the Lab channel in order to create the best base Alpha channel that we could possibly get where this particular image is concerned. So the particular image concerned is Blue shirt man.jpg found inside of the 05_selective folder and we and need to create a mask in order to distinguish his shirt from the background because no other methods are left to us.

Blending the Red and b channels

Hey, I see you are back. Very encouraging, I mean saying you are tenacious which is what I love about you and your reward is going to be a special masking technique that's only found inside this series, nowhere else, at least nowhere else inside the lynda.com Online Training Library. What we are going to be doing is we are going to be merging an RGB channel with the Lab channel in order to create the best base Alpha channel that we could possibly get where this particular image is concerned. So the particular image concerned is Blue shirt man.jpg found inside of the 05_selective folder and we and need to create a mask in order to distinguish his shirt from the background because no other methods are left to us.

We are going to be using the Curves command inside the Lab mode in order to effect our color shift and Curves, by itself, doesn't provide any masking control that we saw that even though Hue/Saturation does provide limited masking controls, they are just not going to work for our purposes. All right, so here's what I want you to do. For starters, and those of you who have worked with me in my Photoshop CS3 Channels and Mask series, also part of the lynda.com Online Training Library, know that when you are creating a mask, you start by examining the channels that are available to you. So this is an RGB image and actually we have Red, Green, and Blue channels, so let's check them out.

Here's the Red channel, now there is a high degree of contrast. Bear in mind, while we are making a mask, we want a lot of contrast. What we are really looking for is the opposite of this; we want a white shirt against the black background but we can change that as easily as just by pressing Ctrl+I or Cmd+I in the Mac in order to invert the colors. So we have a white shirt against a dark background that's great. But you can see now that we don't really have as much contrast as we really need and of course, you wouldn't want to change the Red channel. That's going to fairly mess up the composite RGB image. Yeah, let's not do that.

But this is a good starting point. Green, not so good. We have a little bit of contrast between the shirt and the guy's flesh in the background but we are losing it. We have a lot of shared gray values going on. Then Blue is just no good at all for our purposes because that's where his shirt and the background are the best match. And then, of course, he looks quite gruesome in the Blue channel. I have to say it's not just him, we all look our worst in the Blue channel, but older we get too that's the great thing about it; aging really happens in the Blue channel.

In a perfect world, we wouldn't have Blue, then we wouldn't age. That's my theory because look at me. It looks great in the Red channel. Let's go back to RGB. So we want the Red channel to be available to us but we need the Lab mode to be available to us as well in order to perform this little technique here. So let's go ahead and duplicate them and then convert into Lab. Go up to the Image menu, choose the Duplicate command, and let's just go ahead and call this guy Living large in Lab so that we can find him very easily later inside the 05_selective folder and I'll click OK.

We'll go ahead and zoom in, move him over to the right a little bit and of course, convert him into Lab. That's very important. Go to the Image menu, choose Mode and choose Lab Color. Now we have Lightness, a, and b channels. So let's check them out. There's a Lightness channel, a good looking channel but not enough contrast. It looks a lot like a Green channel, in fact. Here's the a channel. If you have thought he looked bad in the Blue channel, check him out in the a channel. You know what, he is not a spring-fall kind of person; the turquoises and the crimsons don't work for him.

I don't know if those are spring-fall colors but whatever colors they are, they are not his colors. Very, very gruesome indeed but if we go to b, hey he is still looking bad but we've got some contrast going on. We've got a little bit of contrast between the shirt and the background and his flesh. Actually, his flesh is going really light. I have a hanker in here, that if we somehow mix the best of the b channel with the best of the Red channel, we are going to get somewhere. So let's try that out, let's test out that theory. Let's go up to Lab once again, go back to the composite image. Then I want you to go to the Image menu and choose the Calculations command.

Now, Calculations allows you to blend two channels, two channels that are already inside of the image in order to create a new Alpha channel, a base Alpha channel that you will eventually develop into a mask. You can not only blend channels inside the same image but you can blend channels inside different images, different open images as long as they contain the same exact number of pixels wide and tall. So go to Calculations and you'll see up here for Source 1, notice right now, it's trying to multiply the two Lightness channels by each other.

So pretend that they are different layers; Source 1 is on top and Source 2 is on bottom, set to Multiply at 100%. Well we want to start with Red because it's our really great channel. So go up to the Source 1 pop-up menu and choose Blue shirt man. If you have Available in these designer colors open as well, you'll also see it because it's also the same physical dimensions. Well, let's go to Blue shirt man here and we want Red and we want the Background layer. These are flat files so background is all you are going to see. Then for Source 2, Living large in Lab that's what we want, we want Background and we want to change it to the b channel.

Right now we are multiplying, which I don't know, it could work if there were no other blend modes on earth, this could service reasonably well. Let's check out a couple of other things. First set it to Normal and this allows you to see the Red channel by itself just so that that we can be reminded of the channels that we have to work with. Setting it to Normal 100% allows us to just see Source 1. If we set things to Normal 0% then we are just going to see Source 2 because we are seeing through Source 1 so this is the b channel right there. All right, so interesting. Let's change Opacity back to 100% and let's try out some other modes.

Like Overlay. Let's go ahead and kind of burn the two channels into each other and that is better than what we saw a moment ago with Multiply. If we wanted a stronger effect, we could go with something like Linear Light but it doesn't work out very well for this image. What we really need is to lighten the effect more than we are seeing here so let's try Screen, the opposite of Multiply. So we are getting a very, very light image and that's interesting but we are losing our darks. Now there's an even lighter mode than Screen called Linear Dodge (Add) and tell you about Add in just a second but if you choose that, it's really going to blow out the colors.

This is actually a good degree of contrast between highlights and shadows but we need to save the shadows to more darken them up and to bring the highlights back into the Normal realm because right now it looks like he has got his face about three inches from the sun. So I want a control that gives me this kind of brightness but it allows me to darken things up and add, notice that Add in parenthesis that's because it's really dRAWing from this guy right there, Add. If you switch to Add, you are going to get exactly the same effect but you are going to get a couple of different options. Offset allows you to brighten or darken the image by a certain amount of luminance level.

So if I start pressing Shift+Down arrow, you are going to notice that we are reducing the brightness of the entire image at this point by 60 luminance Levels. That's still bringing some of the colors back into the visible range because these colors, these whites are so blown out, they are way beyond white. If I kept reducing this value, we could really get those whites down to something more reasonable but if we did that, we would start bringing in too many grays as well. So what I suggest we do is take the Offset value down to -70, let's say.

In that way, we have some decent blacks, we got some good whites, we have a few midtones in between them that we can rub them out pretty easily. But here, I just want you to see this. This is a difference just so you know we've made some progress. This is a difference between just having the Red channel which was as close as we were with the single channel. Notice the difference between that and Add according to our current setting. So we are really getting rid of a lot of those bright colors especially in the background. We are brightening up this section of the color but that's okay. It's worth to hit, and now I'm going to click OK in order to accept that modification.

So this is going to become our base, I'll go ahead and rename this channel right here, base. It's going to be the base for mask. We are going to actually turn that into a mask, we are going to elevate the contrast with the Levels command and then do a little bit of brush work, you'll see it's very quick and easy. We are going to be doing all that in the next exercise.

Show transcript

This video is part of

Image for Photoshop CS3 Mastering Lab Color
Photoshop CS3 Mastering Lab Color

70 video lessons · 10802 viewers

Deke McClelland
Author

 
Expand all | Collapse all
  1. 23m 32s
    1. Your doorway to better color
      2m 18s
    2. Lab and the untreated JPEG image
      6m 15s
    3. Lab and Camera Raw with a JPEG file
      6m 5s
    4. Lab and Camera Raw with a raw photograph
      8m 54s
  2. 1h 6m
    1. Don't fear the Lab mode
      1m 5s
    2. Why color is 3D
      4m 22s
    3. Device-dependant RGB and CMYK
      5m 15s
    4. Device-dependant CIELAB D50
      5m 33s
    5. Color by the numbers (mixing Lab values)
      5m 35s
    6. The Hue/Saturation color wheel
      4m 0s
    7. The slightly skewed Lab color wheel
      9m 56s
    8. Lab's wide world of "imaginary colors"
      6m 41s
    9. Examining RGB and CMYK channels
      6m 37s
    10. The strange (but powerful) Lab channels
      6m 47s
    11. How RGB and CMYK channels blend
      6m 45s
    12. How channels blend in Lab
      3m 54s
  3. 1h 17m
    1. Bad becomes great, great becomes better
      1m 0s
    2. Cheapening a perfectly good image in RGB
      5m 3s
    3. Making a great image even better in Lab
      8m 9s
    4. Saving a Lab image file
      2m 13s
    5. Favoring yellow to balance skin tones
      6m 12s
    6. Dropping out the blues
      5m 34s
    7. Correcting a very bad image in RGB
      7m 20s
    8. Sharpening luminance independently of color
      5m 22s
    9. Correcting a very bad image in Lab
      7m 34s
    10. Sharpening the Lightness channel
      5m 47s
    11. Finessing the Lightness channel with Curves
      8m 27s
    12. Applying Curves to the a and b channels
      7m 52s
    13. Sharpening for effect, blurring away noise
      7m 14s
  4. 57m 23s
    1. The convergence of all things nondestructive
      1m 26s
    2. Correcting saturation and color cast
      8m 5s
    3. Fading the oranges and reds
      4m 32s
    4. The secret power of Brightness/Contrast in Lab
      5m 5s
    5. Smart Objects and sharpening
      3m 33s
    6. Fixing chromatic aberrations in RGB
      8m 51s
    7. Adding clarity with High Pass
      3m 13s
    8. Reducing color noise with Median
      4m 35s
    9. Protecting the sky with a density mask
      5m 48s
    10. Nondestructive cropping with Canvas Size
      6m 23s
    11. Convert to RGB, flatten, and save
      5m 52s
  5. 1h 34m
    1. Images with bigger issues
      1m 6s
    2. Fixing a color cast
      6m 14s
    3. Exaggerating a color cast
      5m 23s
    4. Quantifying and correcting a color cast
      8m 11s
    5. Sharpening an image with the Emboss command
      4m 38s
    6. Introducing a more complicated color cast
      3m 43s
    7. Drawing a custom contrast curve
      7m 21s
    8. Performing a gross color cast compensation
      3m 49s
    9. Fine-tuning a color cast compensation
      5m 52s
    10. Restoring neutral highlights
      6m 8s
    11. Masking away aberrant hues
      5m 16s
    12. Sharpen, save, convert to RGB, and crop
      6m 18s
    13. Applying a Shadows/Highlights Smart Filter
      5m 1s
    14. Tweaking Shadows/Highlights in Lab
      5m 25s
    15. Rendering Shadows/Highlights in Lab
      7m 57s
    16. Correcting color cast and contrast
      6m 16s
    17. Completing a low-frequency portrait with High Pass
      5m 22s
  6. 1h 5m
    1. Changing some colors, leaving others as is
      1m 7s
    2. Rotating hues in RGB with Hue/Saturation
      5m 0s
    3. Modifying colors in Lab with Curves
      5m 47s
    4. Blending colors with Underlying Layer
      6m 8s
    5. Changing colors in wardrobe shots
      6m 1s
    6. Blending the Red and b channels
      8m 5s
    7. Developing a base mask
      8m 8s
    8. Colorizing an isolated area
      7m 33s
    9. Revealing complementary highlights
      3m 18s
    10. Repairing strangely colored shadows
      5m 37s
    11. Tanning and deepening skin tones
      4m 13s
    12. Exposing bright eyes and teeth
      4m 39s
  7. 1m 8s
    1. See ya
      1m 8s

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