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Photoshop CS3 Channels & Masks: Advanced Techniques
Illustration by John Hersey

Adding a knockout mask


From:

Photoshop CS3 Channels & Masks: Advanced Techniques

with Deke McClelland

Video: Adding a knockout mask

In the previous exercise we added a sky to my Stonehenge photograph. We converted the sky to a Smart Object, and we scaled it to about 150%, so it better fits its new environment. We went ahead and masked the sky, so that it appears to be behind the rocks, and we blurred the sky using a Smart Filter application of Gaussian Blur. In this exercise we are going to take care of some of the aberrant edges inside of the sky mask. I am working inside of an image called Stone meets sky.psd, it's found inside the 11 layer masks folder, and I am going to zoom in on this right side of the image here, and you can see one of the problems, even though the mask is in pretty good shape, we have got a very sharp edge above the tree line here, which doesn't make any sense whatsoever, because the trees are entirely out of focus so this should be a very, very soft edge. And you can see that the hard edge goes all the way across the photograph.
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  1. 2h 13m
    1. The Odyssey Continues
      2m 39s
    2. Mapping one image onto another
      7m 12s
    3. Making a custom contrast mode
      7m 10s
    4. Luminance blending
      8m 40s
    5. Forcing the visibility of underlying layers
      4m 4s
    6. Adjusting the appearance of clipped layers
      4m 34s
    7. Selecting a Blend If channel
      6m 12s
    8. Enhancing highlights by hiding them
      5m 9s
    9. Smart Object first, layer mask second
      7m 22s
    10. The Fill Opacity Eight
      4m 30s
    11. Blending Smart Filters
      7m 24s
    12. Cleaning up edges
      7m 39s
    13. More fun with luminance blending
      6m 22s
    14. A first peek at the Calculations command
      12m 11s
    15. Masking a softly focused model
      11m 46s
    16. Moving layers and masks between images
      7m 35s
    17. Matching colors
      9m 13s
    18. Building transitional blended layers
      6m 33s
    19. Restoring normal colors
      6m 50s
  2. 2h 33m
    1. Layer masks, clipping masks, and knockouts
      1m 20s
    2. Rotating and stretching
      7m 54s
    3. A jet of motion blur
      9m 18s
    4. Keyboard tricks
      5m 4s
    5. Merging sky and landscape
      6m 3s
    6. Masking an adjustment layer
      6m 37s
    7. Creating two windows into an image
      7m 42s
    8. Whitening teeth and adding other highlights
      3m 46s
    9. Mapping a texture onto an image
      4m 1s
    10. Isolating a texture with a layer mask
      6m 44s
    11. Welcome to the glass composition
      3m 18s
    12. Balancing shadows and highlights
      5m 51s
    13. Masking the glass
      7m 24s
    14. Masking the text
      9m 23s
    15. Adding and blending the goldfish
      8m 45s
    16. Assembling the perfect group photo
      5m 12s
    17. Aligning photographs automatically
      5m 26s
    18. Masking in each person's best shot
      5m 18s
    19. Masking densely packed people
      6m 17s
    20. Crafting the perfect final poster
      5m 16s
    21. From the improbable to the impossible
      1m 56s
    22. The fantastical "world of clones" effect
      10m 0s
    23. Upsampling and blurring a background
      8m 39s
    24. Adding a knockout mask
      8m 3s
    25. Choking edges with Gaussian Blur and Levels
      3m 46s
  3. 2h 27m
    1. The corrective power of masking
      1m 6s
    2. The amazing luminance mask
      7m 22s
    3. Brightening and neutralizing the eyes
      8m 22s
    4. Adjusting a nondestructive composition
      5m 52s
    5. Creating a corrective mask
      6m 4s
    6. Averaging away irregular flesh tones
      3m 52s
    7. Modifying specific colors
      7m 46s
    8. Initiating the color mask
      6m 0s
    9. Refining the color mask
      6m 40s
    10. Adjusting the edges around fabric
      7m 56s
    11. Perfecting hair
      9m 35s
    12. Sharpening with a High Pass layer
      10m 12s
    13. The also-amazing density mask
      4m 48s
    14. Adjusting the knockout depth
      8m 48s
    15. Fashioning a depth map
      6m 12s
    16. Invoking a depth mask from Lens Blur
      6m 38s
    17. The perfect depth-of-field effect
      6m 25s
    18. Sharpening an archival photograph
      7m 7s
    19. Creating an edge mask
      8m 29s
    20. Making a High Pass sandwich
      7m 46s
    21. Applying the edge mask
      6m 2s
    22. Customizing your sharpening effect
      4m 6s
  4. 2h 3m
    1. Channel Mixer, I am your father!
      1m 39s
    2. Three ways to gray
      7m 49s
    3. Meet the Channel Mixer
      8m 26s
    4. Mixing a custom black-and-white image
      7m 10s
    5. Creating a professional-level sepia tone
      5m 36s
    6. Employing the Black & White command
      8m 1s
    7. Extreme channel mixing
      4m 50s
    8. The infrared photography effect
      6m 43s
    9. Taking shadows to the brink of black
      3m 56s
    10. Elevating highlights, leeching saturation
      5m 58s
    11. Deepening a black-and-white sky
      5m 49s
    12. Infusing luminance levels with color
      5m 44s
    13. Creating an opposing colorization scheme
      4m 58s
    14. Bolstering contrast with the Green channel
      5m 37s
    15. A tiny improvement to a terrific technique
      7m 39s
    16. The simple (but wrong) approach to red-eye correction
      6m 39s
    17. Channel-mixing red pupils
      9m 18s
    18. The expert approach to red-eye correction
      5m 20s
    19. Fixing problem coronas (pupil edges)
      8m 9s
    20. Making pupils match
      4m 8s
  5. 2h 33m
    1. Chops are dead; long live maskops
      1m 37s
    2. The Calculations command
      8m 16s
    3. Blue Screen blending
      7m 40s
    4. Refining the Blue Screen mask
      5m 53s
    5. Brushing away color fringing
      7m 24s
    6. Locking the transparency of a layer
      6m 22s
    7. Nondestructive layer painting
      7m 36s
    8. How the Add blend mode works
      8m 40s
    9. How the Subtract blend mode works
      6m 43s
    10. Focus, noise, and other masking challenges
      5m 33s
    11. The Add mode in action
      7m 51s
    12. The Subtract mode in action
      8m 25s
    13. Comparing two channels with Difference
      5m 24s
    14. Enhancing the contrast with Curves
      9m 11s
    15. Gathering details with Apply Image
      9m 43s
    16. Dodge highlights, burn shadows
      6m 6s
    17. Dodge and Burn in action
      8m 24s
    18. Painting in the scalp
      10m 1s
    19. Painting away the face and chin
      4m 53s
    20. Compositing complementary images
      4m 13s
    21. Multiply, Minimum, Blur, and Apply Image
      6m 40s
    22. Crafting the final composition
      7m 7s
  6. 1h 57m
    1. Mark of the Pen tool
      1m 35s
    2. The big paths project overview
      6m 51s
    3. How to make a path
      8m 25s
    4. Corner points and freeform polygons
      8m 6s
    5. Editing paths with the arrow tools
      5m 2s
    6. Adding and deleting endpoints
      5m 15s
    7. Adding and deleting interior points
      6m 6s
    8. Converting a path to a selection
      3m 35s
    9. Converting a path to a mask
      6m 38s
    10. Smooth points and control handles
      8m 57s
    11. Making cusp points
      6m 0s
    12. Combining paths in a vector mask
      7m 55s
    13. Turning a path into a shape layer
      8m 57s
    14. Combining paths to make a layer mask
      7m 52s
    15. Mixing layer and vector masks
      10m 14s
    16. Editing character outlines as paths
      8m 39s
    17. Using the Convert Point tool
      7m 8s
  7. 3h 17m
    1. Where there's a will, there's a way
      1m 18s
    2. Masking natural cast shadows
      4m 10s
    3. Applying the cast show
      4m 2s
    4. Creating a difference mask
      3m 7s
    5. Applying an arbitrary map
      3m 50s
    6. Making the flesh mask
      7m 17s
    7. Roughing in an object mask
      6m 49s
    8. Drawing missing details with the Lasso tool
      4m 7s
    9. Combining flesh and object masks
      3m 53s
    10. Amplifying the cast shadow
      4m 10s
    11. Selectively choking edges
      3m 58s
    12. Power duplication in Photoshop
      7m 9s
    13. Masking blond hair
      5m 48s
    14. Using Levels to mask iterations
      3m 14s
    15. Drawing an iteration boundary
      4m 55s
    16. Merging the best of two Levels iterations
      4m 4s
    17. More fun with Dodge and Burn
      6m 14s
    18. Fixing edges with the Pen and Stamp tools
      7m 29s
    19. Pulling from another file with Apply Image
      4m 52s
    20. Blending clipped layers independently
      5m 43s
    21. Building the flame mask
      9m 22s
    22. Amplifying the flame
      3m 53s
    23. Masking an image against a busy background
      5m 15s
    24. The Freeform and Magnetic Pen tools
      6m 52s
    25. Masking with arbitrary maps
      9m 32s
    26. A more deliberate approach to arb maps
      10m 51s
    27. Combining arb maps with paths
      9m 28s
    28. Masking with the help of the History brush
      11m 38s
    29. Creating a High Pass mask
      7m 25s
    30. Coloring in the outlines
      8m 31s
    31. Mastering Calculations
      7m 29s
    32. Subtracting and merging the beak
      11m 6s
  8. 1h 33m
    1. The meaning of bit depth (and why you care)
      2m 50s
    2. Scanning line art in 8-bit and 16-bit
      5m 9s
    3. Measuring the 16-bit difference
      8m 9s
    4. Correcting 8-bit images in the 16-bit space
      9m 31s
    5. Opening a raw image directly in 16-bit
      6m 13s
    6. Editing in Camera Raw, opening in 16-bit
      8m 22s
    7. 16-Bit/channel vs. 32-bit/channel (HDR)
      8m 18s
    8. Working with auto-bracketed photographs
      5m 6s
    9. Using the Merge to HDR command
      6m 0s
    10. Adjusting the HDR preview
      6m 0s
    11. Building a 32-bit sky mask
      6m 29s
    12. Properly exposing land and sky
      4m 25s
    13. Modifying a layer mask in 32-bit
      4m 56s
    14. Converting to and correcting in 16-bit Lab
      12m 7s
  9. 2h 8m
    1. Photoshop flirts with the third dimension
      1m 13s
    2. The displacement map
      8m 24s
    3. Making custom waves
      7m 14s
    4. Creating a Gaussian distribution
      4m 32s
    5. Using a two-channel displacement map
      6m 28s
    6. Creating a rustic edge effect
      8m 21s
    7. Distorting and shading with a DMap
      6m 34s
    8. Moonlight reflecting off water
      8m 48s
    9. Mapping the reflection onto the water
      7m 7s
    10. Dipping the moon into the water
      6m 18s
    11. Turning flesh into stone
      7m 55s
    12. Wrapping the stone around the face
      7m 27s
    13. Softening a displacement map
      8m 5s
    14. Making a repeating watermark pattern
      9m 22s
    15. 3D embossing with Lighting Effects
      10m 48s
    16. The amazing credit card type effect
      6m 56s
    17. Lightening the credit card letters
      6m 16s
    18. Wrapping the background around the text
      6m 27s
  10. 1m 43s
    1. Goodbye
      1m 43s

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Photoshop CS3 Channels & Masks: Advanced Techniques
20h 48m Advanced Nov 21, 2007

Viewers: in countries Watching now:

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."

Topics include:
  • Distorting and shading with a DMap
  • Understanding bits and channels
  • Creating paths with the Pen tool
  • Using blend modes and the Dodge and Burn feature
  • Understanding channel mixing
  • Using layer masks, clipping masks, and knockouts
  • Applying Smart Filters
Subjects:
Design Photography Masking + Compositing
Software:
Photoshop
Author:
Deke McClelland

Adding a knockout mask

In the previous exercise we added a sky to my Stonehenge photograph. We converted the sky to a Smart Object, and we scaled it to about 150%, so it better fits its new environment. We went ahead and masked the sky, so that it appears to be behind the rocks, and we blurred the sky using a Smart Filter application of Gaussian Blur. In this exercise we are going to take care of some of the aberrant edges inside of the sky mask. I am working inside of an image called Stone meets sky.psd, it's found inside the 11 layer masks folder, and I am going to zoom in on this right side of the image here, and you can see one of the problems, even though the mask is in pretty good shape, we have got a very sharp edge above the tree line here, which doesn't make any sense whatsoever, because the trees are entirely out of focus so this should be a very, very soft edge. And you can see that the hard edge goes all the way across the photograph.

Notice that, and it looks just weird as heck. So we need to take care of that problem, eventually, we are going to address this issue using something called a Knockout Layer, but first let me show you the more traditional approach. I would go over here to the Sky layer mask and click on it to make it active, then I would probably grab something like the Gradient tool, it's probably the simplest solution. So I will go ahead and click on the Gradient tool to make it active. I still have my radial gradient from the magazine cover exercise selected here, so I am going to right click on this down pointing arrow head and chose reset tool in order to restore the default settings. And my foreground color is black currently, make sure that yours is as well, and then I am going to switch the style of my Gradient to this guy right here, which is Foreground to Transparent. And then I will press the Enter key or the Return key on the Mac in order to accept that modification, and I will drag upwards. So I am actually shift dragging to constraint the angle of my drag to exactly vertical, and then I will release.

And it looks pretty good; it's nice that now the sky is being peeled away from the trees, and we have a soft transition there, but let's say that's not exactly what I want, I want the Gradient to be a little higher. So I would have to press Ctrl+Z or Command+Z on the Mac in order to Undo that gradient, and try again, and then if I think that's too much, I have to undo it again, and try a smaller gradient. Basically the thing is, even though, this is a point I am trying to make, even though, we are basically creating what most folks would term non-destructive modifications, because we haven't harmed a single pixel in the Stonehenge image.

And thanks to the fact that we applied a Smart Filter and a layer mask to a Smart Object, we are not harming a single pixel inside of the sky layer either. However, we are now making permanent modifications to the layer masks. So if I were to Alt+Click or Option+Click on this layer mask thumbnail, you can see that I am indeed editing the layer mask on a pixel basis, meaning that I can't really modify the gradient independently of the rest of the layer mask, the way that I would like to, What I would really like to have happen, is I would really like to have layers inside of my layer masks, so that I could put the Gradient on an independent layer and be able to modify it independently, but that would be a lot of nesting of functions inside of Photoshop. Can you imagine if you had a layer that had its own mask, and the mask has its own layers, and those layers had their own masks, and so on, and so on. We would have a layers palette that was about as wide as the screen with all the indents that would be going on.

So rather than go that route which would be pretty weird, we are going to go another weird route. We are going to apply a knockout layer. And that knockout layer will serve as an independent layer of transparency. So I am going to undo the gradient that I just added there. I am going to Alt+Click or Option+Click on a layer mask thumbnail in order to return to the RGB composite. I am going to press Ctrl+Shift+N or Command+Shift+N to make a new layer, and I am going to call this layer knockout. And you don't have to select anything else, you don't have to change to blend mode, just go ahead and click OK in order to make that new layer. I still have my gradient tool active. Now I could draw a Black to Transparent Gradient, but I am going to work with a different color just to make a point here. I am going to go ahead and expand my color palette for a moment, and I am going to change the saturation and brightness values to 100 a piece like so. So that we have 0, 100, 100 for Red.

It doesn't matter which color you choose, it could be any color you want, it could even be white, just some color needs to be a work there. Then you definitely want to be creating a Foreground to Transparent gradient, very important that it turns transparent, and now I am going to draw a gradient like so. Notice that I still have the shift key down so that I am constraining the angle of my gradient to exactly vertical, and then I will release, and at this point you might question what in the world I am doing? I mean, why am I covering the entire image with this bright blood red gradient, other than of course to destroy the image entirely? The reason is that once we convert this layer to a knockout layer, anywhere where the layer is Opaque will cut a hole, anywhere where the layer is transparent will cut no hole at all, and translucent pixels will basically soften the transition.

All right, so check it out. We have got this knockout layer. Right now it's just called knockout. I am going to double-click on it, either on the layer or on its thumbnail in order to bring up the Blending Options panel of the layers style dialog box. Let's move things over here a little bit. Notice we have got this option that's called knockout. Now by default it's set to None, you have two other options, Shallow or Deep. Shallow is designed to cut to the bottom of a group. If we had a group going, it would cut to the bottom of the group in no further. Deep will cut all the way through to the background layer.

Well, because we have no group at work here inside of the layers palette, meaning one of those little folders that's what a group is, because we don't have one, Shallow and Deep are going to do exactly the same thing. So I am just going to go ahead and choose Shallow. But you will notice exactly the same thing, but right now it means nothing. I am not doing anything to the image whatsoever. And that's because knockout alone doesn't do anything, you need to combine it with a function that's going to make the pixels transparent, and the best way to work is with this fill opacity value. It's not the only way to go, but it's by far the most predictable way to go.

Don't use Opacity, it doesn't work, you need Fill Opacity instead, and I am going to reduce the Fill Opacity value all the way down to 0%, thereby making those red pixels entirely transparent, and forcing them to cut through to the background layer. So once again that's a combination of knockout set to Shallow or Deep, either one would work for our purposes, and Fill Opacity is set to 0%, that's very important, all the way down to 0%. Then click OK, and we now have a knockout layer.

And check it out; let's see what it does here. You can see if I zoom in, that it is cutting down to the contents of the background layer, so this is what things look like without the knockout layer. This is what they look like with the knockout layer. And now, here is what I consider to be the coolest thing, I can press the Ctrl key in order to temporarily get the Move tool, that's the Command key on the Mac, and with Ctrl+Shift+Down, so that I am performing a vertical drag, I can move that gradient up and down. Every once in a while you may see it peel away from the edge, but that's just because for a second it's getting mixed up and performing a horizontal movement. So this would be command+Shift+Dragging on the Mac, and I can move that gradient up and down independently of the layer mask. So it really is an independent masking layer, which is exactly what I want. This is a truly non-destructive modification.

In the next and final exercise of this chapter we are going to take care of the remaining problems with the edges as you can see. See how they are a little far out right there, a little bit of haloing going on, and we are going to take care of those edges. We are going to choke them in, you are going to see a combination of Gaussian Blur and the Levels command, stay tuned.

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