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Creating an alpha channel

From: Photoshop CS4 One-on-One: Mastery

Video: Creating an alpha channel

In this exercise I'm going to show you how to create an alpha channel that will serve as the basis for a mask here inside of Photoshop. I'm going to switch over to the Channels palette and I would like you to do the same. Now this image is utterly wonderful for masking purposes because it's got some interesting things going on. First of all, it's a low light snapshot because the camera was set to just auto-functions all around, auto- metering. We have got a high ISO of 800 which means that we have just ton of noise going on the background and it's kind of wormy noise because of Camera Raw's automatic sharpening. So I ran this to Raw, it really didn't pay much attention to the image inside of Raw, I just brought it over, did a little bit of development.

Creating an alpha channel

In this exercise I'm going to show you how to create an alpha channel that will serve as the basis for a mask here inside of Photoshop. I'm going to switch over to the Channels palette and I would like you to do the same. Now this image is utterly wonderful for masking purposes because it's got some interesting things going on. First of all, it's a low light snapshot because the camera was set to just auto-functions all around, auto- metering. We have got a high ISO of 800 which means that we have just ton of noise going on the background and it's kind of wormy noise because of Camera Raw's automatic sharpening. So I ran this to Raw, it really didn't pay much attention to the image inside of Raw, I just brought it over, did a little bit of development.

But I did allow the noise to get sharpened a little bit and as a result, we have some sort of warm like texture going on in the background, which is definitely one of the things that Camera Raw tends to do if you don't watch it. Anyways, that's okay. We can work with it. We also have a lot of stray hair which is great because this is the kind of thing that Photoshop just excels at selecting masking is terrific where hair is concerned. So if you have light hair against the dark background, as we do, or dark hair against the light background, even if it's only occurring in a single channel inside of the image, then you are in great shape. That means you can select that hair.

So a lot of people are scared of hair, rightly so, I mean it looks like will be extremely complicated to select all of this junk, and of course, if we are relying on any of the selection tools, we'd never get anywhere with it. We are not going to trace around these hairs with the Magnetic Lasso tool, for example. And we are really not going to do it with the Color Range command either because it tends to exaggerate the hair details and kind of clump them up. What you want to do instead is create a journeyman alpha channel here inside of the Channels palette. But you need to choose the right channel in the first place from which to build your alpha channel.

So here we are in the Channels palette, you can see that I have got RGB composite image, which comprises the Red, Green and Blue channels. So RGB is not a channel in and of itself, it's the composite blend of the channels that follow it. And then we have two extra channels; these alpha channels right here called Partial Mask and Final Mask and if you were paying attention in the previous exercise, you may notice that we have more channels than we used to have and that's because I just went ahead and added one behind the scenes between exercises there. The reason being when I was actually creating my web graphic, I didn't worry about the lower section of Russell here, I just worried about the portion of his head and his hand that were going to be above the marquee but I figured as long as we are here in masking, as long as we are doing a project, we might as well do it for real. So I went ahead and masked all of the flesh and the hair away from the background. I didn't worry about the shirt; the shirt would be a completely different beast in terms of masking. It would be possible but because it's dark on dark, it would be a little more complicated.

So that's the high irony of masking folks. It's that something like hair; these filigree details as long as you have good contrast definition there, no problem. It's when you start running out the contrast then you start having problems inside of Photoshop. So fabric details are typically more difficult to select than hair. If you want to learn all about the stuff, please checkout My Channels and Masks series here on the Lynda.com Online Training Library. What we need to do is to find the channel that is going to enable us to take the image and use the image to select itself and that is what masking is all about. You are trying to trick Photoshop into seeing what you are seeing; you can't just click on Russell and select him.

However, you can use Photoshop's way of seeing the image to your advantage in order to use the image just I say to select itself. So why don't we go about doing that? Well we want to find a channel inside the image that already gets us a large portion of the way there. So we are going for this. This is what we want. We want Russell totally white to indicate that he is selected against the pitch black background to indicate that he is totally deselected with some nice sort of anti-aliased edges around Russell and these edges are what really sell the effect, it's not about the interior, it's not about the area that's not selected, it's all about these edges right there. So you want some grayness in the edges.

So let's go ahead and zoom out again. Which channel resembles this the most? Well let's go back to the RGB image for starters and notice that we have got these keyboard shortcuts. So you can either click on a channel to see the channel to select it or you can use a keyboard shortcut and these keyboard shortcuts have changed since Photoshop CS3. So it's CTRL+2 or Command+2 on Mac to see the Composite image. It's Ctrl+3 or Command+3 on the Mac to see the first channel, which is in this case is the Red channel. It's Ctrl+4 or Command+4 on a Mac for the Green channel and then Ctrl+5 or Command+5 on the Mac for the Blue channel and they are all listed right there so you can't help but remember them.

Notice that he looks very high contrast in the Red channel. He does have quite as much contrast in the Green channel. So he is very white in the Red channel against a fairly dark background. The background is fairly similar in the Green channel but he is darkening up and then by time we get to the Blue channel, the background is darkening a little bit but Russell is darkening like crazy in the Blue channel. This isn't Russell, not resonating well in the Blue channel, this is all of us and especially under low light like this we are just noise like crazy creep up in the Blue channel. When things start going wrong inside of an image, it's the Blue channel that suffers first and suffers foremost and then the other channels start trailing behind it. You are going to look in the Green channel but you are going to look best in the Red channel. Why? We are all different luminance levels essentially of orange, which is mostly red with a little bit of green. Not much blue at all.

All right, so that's my long winded way of saying you want to blend the Red channel and the Green channel together, the Red channel and Blue channel together, using this command under the Image menu called Calculations, by spending an entire chapter on Calculations in my Channels and Mask series. And that command is useful when no channel is really doing what you wanted to do; when you have to blend a couple of channels to get to a good base. Anyway, we have already got good channel so we have got red, he is dark in the background, he is light in the foreground, he already looks a lot like the Final mask as you can see. So once you do the first step here, once you have identified the channel that's going to work for you, you grab that channel.

Don't just start editing it because the image relies on that Red channel. For example, I'll just select an area in the Red channel and press the Backspace key to get rid of it. Well that kind of damages the RBG image. So you can't touch that Red channel. You cannot, if you are trying to make some color modifications but you don't want to mask directly. So Ctrl+Z, Command+Z on the Mac, let's go ahead and press Ctrl+D or Command+D on the Mac to deselect the image. Instead what you do is you grab that Red channel and you duplicate it by dragging it on to the page icon down at the bottom of the Channels palette and releasing. Now you have got a copy of the channel, now you can do anything you want with it. This is now an alpha channel that's ready for your editing and I'm going just go ahead and rename it my mask or something along those lines. By double-clicking on its name and entering a new name just as you do with layers and we are now good to go.

By good to go, I mean we are going to begin to build our mask, we are going to increase the contrast to the mask and I'm going to show you how to save an alpha channel along with an image in the next exercise.

Show transcript

This video is part of

Image for Photoshop CS4 One-on-One: Mastery
Photoshop CS4 One-on-One: Mastery

147 video lessons · 27722 viewers

Deke McClelland
Author

 
Expand all | Collapse all
  1. 21m 17s
    1. Welcome
      1m 21s
    2. Installing the DekeKeys keyboard shortcuts
      5m 38s
    3. Resetting the Function keys on a Mac
      3m 51s
    4. Installing the CS4 color settings
      4m 34s
    5. Setting up the CS4 color settings
      5m 53s
  2. 2h 31m
    1. Introduction to masking
      51s
    2. Introducing color range
      4m 22s
    3. Adding base colors and adjusting fuzziness
      4m 46s
    4. Localized color clusters
      6m 12s
    5. The Quick Mask mode
      7m 33s
    6. Viewing a quick mask by itself
      6m 40s
    7. Testing the quality of edges
      3m 55s
    8. Introducing the Masks palette
      7m 45s
    9. Editing a layer mask
      6m 18s
    10. Choking a mask with Gaussian Blur and Levels
      6m 44s
    11. Choking a mask with Mask Edge
      7m 43s
    12. Adding a Gradient Overlay shadow
      4m 23s
    13. Using live Density and Feather
      6m 12s
    14. Journeyman masking
      5m 44s
    15. Creating an alpha channel
      7m 6s
    16. Increasing contrast
      7m 15s
    17. Overlay painting
      8m 28s
    18. Cleaning up whites and blacks
      5m 48s
    19. Soft light painting
      5m 47s
    20. Selecting in style
      6m 55s
    21. Employing masks as selections
      5m 2s
    22. Scaling and compositing layers
      6m 30s
    23. Compositing glass
      5m 10s
    24. Selecting glass highlights
      8m 41s
    25. Working with found masks
      5m 46s
  3. 1h 34m
    1. Introduction to vector-based shapes
      1m 10s
    2. Vector-based type outlines
      7m 23s
    3. The benefits of vectors
      6m 27s
    4. Upsampling vs. nondestructive scaling
      7m 35s
    5. Vectors and effects
      8m 7s
    6. Fill Opacity and clipped layers
      4m 24s
    7. Basic shape creation
      3m 15s
    8. Drawing interacting shapes
      6m 21s
    9. Power-duplicating paths
      3m 12s
    10. Combining pixels and vector masks
      5m 19s
    11. Line tool and layer attributes
      7m 5s
    12. Copying and pasting path outlines
      3m 28s
    13. Drawing custom shapes
      3m 59s
    14. Drawing with the Pen tool
      7m 48s
    15. Creating cusp points
      7m 28s
    16. Defining a custom shape
      3m 34s
    17. Assigning a vector mask to an image
      2m 38s
    18. Adding a vector object to a composition
      5m 40s
  4. 1h 23m
    1. Introduction to Vanishing Point
      1m 11s
    2. Creating and saving the first plane
      8m 9s
    3. Creating perpendicular planes
      5m 16s
    4. Healing in perspective
      8m 47s
    5. Cloning and scaling in perspective
      8m 33s
    6. Patching an irregularly shaped area
      6m 59s
    7. Healing between planes
      3m 34s
    8. Importing an image into a 3D scene
      5m 45s
    9. Adding perspective type
      5m 37s
    10. Removing and matching perspective
      5m 36s
    11. Applying a reflection in perspective
      5m 1s
    12. Creating a perspective gradient
      6m 11s
    13. Converting a gradient to a mask
      2m 58s
    14. Swinging planes to custom angles
      4m 32s
    15. Wrapping art around multiple surfaces
      5m 49s
  5. 1h 15m
    1. Introduction to Smart Objects
      58s
    2. Placing a Smart Object
      5m 7s
    3. Saving a PDF-compatible AI file
      4m 27s
    4. Performing nondestructive transformations
      6m 7s
    5. Editing a Smart Object in Illustrator
      6m 50s
    6. Converting an image to a Smart Object
      6m 50s
    7. Cloning Smart Objects
      5m 24s
    8. Creating a multilayer Smart Object
      5m 51s
    9. Updating multiple instances at once
      2m 54s
    10. Creating a Camera Raw Smart Object
      4m 17s
    11. Editing a Camera Raw Smart Object
      3m 25s
    12. Assembling a layered ACR composition
      5m 54s
    13. Using an ACR Smart Object to effect
      3m 41s
    14. Blending multiple ACR portraits
      6m 56s
    15. Live type that inverts everything behind it
      6m 32s
  6. 1h 48m
    1. Introducing nondestructive Smart Filters
      46s
    2. Applying a Smart Filter
      4m 22s
    3. Adjusting filter and blend settings
      4m 25s
    4. Heaping on the Smart Filters
      5m 19s
    5. Smart Filter stacking order
      7m 23s
    6. Resolution and Smart Filter radius
      6m 12s
    7. Masking Smart Filters
      4m 41s
    8. Employing nested Smart Objects
      5m 5s
    9. Dragging and dropping Smart Filters
      6m 31s
    10. Using the Shadows/Highlights filter
      5m 53s
    11. Regaining access to the pixels
      7m 8s
    12. Parametric wonderland
      5m 52s
    13. Working with the Filter Gallery
      6m 28s
    14. Freeform filter jam
      5m 51s
    15. Swapping filters from the Filter Gallery
      3m 45s
    16. Mixing all varieties of parametric effects
      7m 30s
    17. Addressing a few Smart Filter bugs
      3m 11s
    18. Applying a Smart Filter to live type
      5m 30s
    19. Choking letters with Maximum
      3m 7s
    20. Duplicating a Smart Filter
      2m 38s
    21. Enhancing a filter with a layer effect
      6m 30s
  7. 1h 6m
    1. Introduction to Auto-Align, Auto-Blend, and Photomerge
      1m 2s
    2. Merging two shots into one
      3m 49s
    3. Applying Auto-Align layers
      3m 44s
    4. Masking images into a common scene
      1m 38s
    5. Auto-Align plus Auto-Blend
      8m 11s
    6. Assigning weighted Opacity values
      4m 7s
    7. Employing a Difference mask
      7m 17s
    8. Masking smarter, not harder
      3m 53s
    9. Capturing multiple depths of field
      3m 37s
    10. Auto-blending real focus
      8m 31s
    11. Creating a panorama with Photomerge
      7m 27s
    12. Correcting a seamless panorama
      4m 52s
    13. An altogether nondestructive Lab correction
      7m 59s
  8. 1h 44m
    1. Introduction to new CS4 technologies
      1m 1s
    2. Applying Content-Aware Scale
      7m 18s
    3. What works and what doesn't with Content-Aware Scale
      4m 19s
    4. Protecting areas with masks
      7m 31s
    5. Applying incremental edits
      7m 6s
    6. Protecting skin tones
      7m 12s
    7. Scaling around a model with TLC
      9m 0s
    8. Adjusting the scale threshold
      5m 22s
    9. When Content-Aware Scale fails
      4m 2s
    10. Creating a lens distortion effect
      8m 39s
    11. Layer masking the family
      11m 44s
    12. Installing the Pixel Bender
      3m 42s
    13. Introducing Pixel Bender kernels
      6m 50s
    14. Pixel Bender kernel roundup
      7m 24s
    15. Tube View and Ripple Blocks
      3m 58s
    16. Making a seamless pattern with Kaleidoscope
      6m 13s
    17. Introducing the Pixel Bender Toolkit
      3m 24s
  9. 1h 20m
    1. Introduction to actions
      42s
    2. Creating an action
      5m 45s
    3. Recording operations
      5m 12s
    4. Reviewing and editing an action
      4m 45s
    5. Playing an action (the Button Mode)
      4m 50s
    6. Saving and loading actions
      5m 0s
    7. Copying and modifying an action
      4m 8s
    8. Permitting the user to change settings
      5m 50s
    9. The Best Chrome Effect Ever II
      3m 41s
    10. Recording a fail-safe action
      7m 33s
    11. Rounding corners with a mask
      4m 33s
    12. Cleaning up layers
      3m 51s
    13. Automating layer effects
      7m 1s
    14. Applying chrome with Gradient Map
      6m 24s
    15. Action anomalies
      4m 11s
    16. Rendering effects to layers
      5m 1s
    17. Testing that it works
      2m 0s
  10. 1m 14s
    1. See ya
      1m 14s

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