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Add, Subtract, Offset, and Scale

From: Photoshop CS5 One-on-One: Mastery

Video: Add, Subtract, Offset, and Scale

In this exercise, I'm going to explain how the Add and Subtract Blend modes work, since they're so useful where masking is concerned. And how you can modify their behavior using the Offset and Scale values. I'm still working away inside Hair in flight.tif. I've gone ahead and chosen the Calculations command, set the first channel to Blue, the second channel to Red, and Inverted both of them, and then set the Blend mode to Add. The Add blend mode does what it says it does. It adds the luminance levels of one channel to the luminance levels of the other. And as you might imagine, that means the luminance levels get quite a bit brighter.

Add, Subtract, Offset, and Scale

In this exercise, I'm going to explain how the Add and Subtract Blend modes work, since they're so useful where masking is concerned. And how you can modify their behavior using the Offset and Scale values. I'm still working away inside Hair in flight.tif. I've gone ahead and chosen the Calculations command, set the first channel to Blue, the second channel to Red, and Inverted both of them, and then set the Blend mode to Add. The Add blend mode does what it says it does. It adds the luminance levels of one channel to the luminance levels of the other. And as you might imagine, that means the luminance levels get quite a bit brighter.

Now because we've inverted both the channels at this point, they're quite bright where the hair is concerned, for example. So the hair is gone from very dark to very bright now. And when you add the hair, this bright hair from one channel to the bright hair from the other channel, it goes beyond white. It's clipping like crazy. So the only colors that aren't clipping inside of this image are the ones that were bright before we inverted the channels and are now quite dark indeed. Well this is pretty typical behavior for the Add mode. It goes ahead and blows highlights across the board, which is why you can drop things down using the Offset value or the Scale value.

Now Offset just goes ahead and subtracts luminance levels from the result of the operation whereas the Scale value allows you to divide away the results. And we'll see what that looks like in a moment, but first I'm just going to say, you know what, let's go ahead and subtract, so I'll enter a negative value, -150 luminance levels and see what we come up with, and as a result, notice the hair remains white. That's how far beyond 255 it was. Remember that 0 is black and 255 is white, so it must have been out there in the stratosphere in a 400s or 500s or what have you.

By entering -150 though, we go ahead and sync the background. And then at this point you might want to tweak the value. Now, of course, you wouldn't just know that -150 was a good place to start, you would experiment and see what you come up with, but if I press Shift+Down Arrow I'm going to incrementally darken the image. And at some point I'll start to see a bunch of details show up in the hair which happens for me at about -200. The problem with this so far is that we don't have a lot of darkness to work with in the background. The hair is bright, it's great, but we're running out of darkness at the ends of the hairs.

And so that's going to create troubles for us. And I've got a workaround, don't worry about it, but for now let's get a sense of how the Scale value works. You can divide a number by anything from 1 to 2. So you don't have a lot of range here and what's funny is if I enter 4 or something like that and press the Tab key it's going to get mad at me and say nope, the only numbers are between 1.000 and 2.000 and the closest value is inserted which is 2. So you have a high degree of accuracy where this value is concerned, but you don't have much range.

Now what ends up happening when you scale the results of your modification is that you're going to darken things. So if I'm dividing all the luminance levels by 2, that's going to darken the heck out of them. So I'll go ahead and brighten things up again, let's take the Offset value to -100 to go brighter. And you'll notice that you have a lot less contrast as a result of that scale value. Now you only want to use the scale value when you want to reduce the contrast and that's typically if you want to smooth out the results. If you're getting super sharp transitions inside of your new alpha channel, then dividing the results by something between 1 and 2 can prove helpful.

However, if that's not the problem, if you're in need of more contrast not less, then you want to leave that value set to 1. Anyway, the closest I'm going to come to something halfway decent right now is something like Add with -200 or I could go ahead and try out the Subtract mode instead and see what I come up with. Now, Subtract is going to do exactly what it says it's going to do,e it's going to subtract the luminance levels of one channel from those of another channel. And you still have the option of adding an Offset and a Scale value. Now, of course, that's going to end up with something very dark for us because if we're subtracting one inverted channel from the other inverted channel, why then we're going to get a lot of zeros as a result, and zero is black.

So not surprisingly we're getting a very dark result. And then you could then add luminance levels using that Offset value or if you wanted to further darken things and smooth out the transitions, you could increase the Scale value. We're not going to do that, but notice that we're getting a terrible result. You might think well subtract, what a horrible mode. It's not delivering what we need. Well that's because we're subtracting two very similar images from each other. We need to exploit the differences once again. So we need to turn off one of these Invert checkboxes. So I'll start by turning off the Invert checkbox associated with Red and we end up getting dark hair against a fairly bright background.

Interesting, but not what I'm looking for. So I'll turn Invert back on and now I'll turn Invert off for Blue and I end up coming up with something that's much more in keeping with what I want, and then I could adjust this Offset value. So if the result of the Blend mode is too dark, I could raise that Offset value like so. And if it's getting to be too light, then I could go ahead and back off the Offset value. And in my case, for this image, I might take that Offset value down to 50 or something along those lines, but really I got to tell you, this just isn't doing it for me.

I don't have nearly enough contrast in this background over here and I'm running out of contrast over on the left -hand side. So what do I do? Well, tell you what, I'm just going to go ahead and accept this new base alpha channel for now. Subtract, Offset of 50, notice that, I'll click OK. And I'll go ahead and name this guy subtract and offset 50 just so I remember how I created it. And then I'm going to go back to the drawing board because you know what I need to do, I need to do something I've never really tried this before, and it's working out brilliantly, I have to tell you.

I'm going to increase the contrast of the image before I even start creating the mask. And I'll show you how to do that in the next exercise.

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This video is part of

Image for Photoshop CS5 One-on-One: Mastery
Photoshop CS5 One-on-One: Mastery

192 video lessons · 44095 viewers

Deke McClelland
Author

 
Expand all | Collapse all
  1. 40m 45s
    1. Welcome
      2m 45s
    2. Making Photoshop your default image editor
      7m 43s
    3. Installing the dekeKeys keyboard shortcuts
      8m 10s
    4. Remapping OS shortcuts
      7m 37s
    5. Installing the Best Workflow color settings
      4m 31s
    6. The color settings explained
      6m 54s
    7. Loading the CS5 color settings in Bridge
      3m 5s
  2. 1h 11m
    1. Your creative range continues to expand
      1m 46s
    2. The Avatar project so far
      2m 38s
    3. Painting on a photograph
      7m 50s
    4. Adding texture and depth
      6m 14s
    5. Simulating chalky white paint
      7m 23s
    6. Masking and placing an image
      7m 20s
    7. Upsampling and Lens Blur
      5m 9s
    8. Blending blurry elements
      3m 48s
    9. Making a Smart Object
      6m 46s
    10. Placing an image as a Smart Object
      3m 22s
    11. Blending away a background
      5m 56s
    12. Applying Smart Filters
      4m 34s
    13. Creating a glow with Lens Flare
      3m 45s
    14. Blending and masking a glow
      5m 3s
  3. 1h 26m
    1. Using the image to select itself
      1m 53s
    2. Introducing masking
      6m 32s
    3. Making an alpha channel
      6m 54s
    4. Using the Calculations command
      6m 48s
    5. Add, Subtract, Offset, and Scale
      5m 54s
    6. Prepping an image with the Dodge tool
      6m 55s
    7. Fixing mistakes before they get too big
      6m 32s
    8. Painting in the Overlay mode
      5m 51s
    9. Exaggerating and selecting flesh tones
      7m 39s
    10. Smudge, Median, and the Blur tool
      6m 59s
    11. Masking low-contrast details
      6m 7s
    12. Creating a flesh-and-clothing mask
      5m 45s
    13. Masking and compositing the foreground
      5m 27s
    14. Finessing the final composition
      7m 39s
  4. 2h 24m
    1. Connecting the dots
      1m 40s
    2. The Pen tool and the Paths panel
      6m 32s
    3. Drawing a straight-sided outline
      6m 25s
    4. Editing a path outline
      6m 36s
    5. Adding and editing smooth points
      5m 35s
    6. Creating vector masks with the shape tools
      4m 59s
    7. Building a complex outline from shapes
      4m 26s
    8. Subtracting and transforming shapes
      6m 45s
    9. Cloning, flipping, and combining shapes
      8m 58s
    10. Roughing in non-symmetrical paths
      7m 41s
    11. Finessing a complex outline
      9m 15s
    12. Masking a layer effect
      8m 26s
    13. Isolating an image element
      6m 8s
    14. Smooth points and control handles
      9m 3s
    15. Stretching curved segments
      7m 49s
    16. Using the Rubber Band option
      9m 33s
    17. Drawing smooth points with the Pen tool
      6m 59s
    18. Shading an isolated object
      3m 45s
    19. Drawing cusp points
      7m 14s
    20. Setting points in the pasteboard
      9m 57s
    21. Using the Convert Point tool
      6m 42s
  5. 2h 57m
    1. Everything you need to know about blending
      1m 45s
    2. Photoshop CS5's blend modes
      7m 21s
    3. Cycling between blend modes
      6m 15s
    4. Darken and Lighten and their derivatives
      6m 3s
    5. The blend mode shortcuts
      8m 6s
    6. The Multiply and Burn modes
      4m 28s
    7. The Screen and Dodge modes
      6m 0s
    8. How opposite blend modes work
      8m 24s
    9. Why Multiply darkens and Divide lightens
      5m 23s
    10. Cleaning up a client's bad art
      5m 3s
    11. Dropping out a white background
      5m 56s
    12. Blending inside blend modes
      8m 3s
    13. Overlay, Soft Light, and Hard Light
      6m 26s
    14. Vivid, Linear, and Pin Light (and Hard Mix)
      6m 35s
    15. Difference, Exclusion, Subtract, and Divide
      7m 34s
    16. Great uses for the Difference mode
      6m 18s
    17. Promising uses for the Divide mode
      9m 6s
    18. Hue, Saturation, Color, and Luminosity
      7m 0s
    19. Blending an inverted layer
      3m 32s
    20. The "Fill Opacity Eight"
      7m 25s
    21. Making bad blend modes good
      5m 16s
    22. Making a knockout layer
      6m 53s
    23. Blending in the CMYK mode
      8m 3s
    24. Overprinting black text
      8m 29s
    25. Using the Luminance slider
      5m 24s
    26. Parametric luminance masking
      6m 21s
    27. Adjusting the behavior of luminance effects
      10m 8s
  6. 2h 2m
    1. Smart Objects = protective containers
      1m 35s
    2. Placing an Illustrator graphic
      6m 30s
    3. Vector copy and paste options
      6m 56s
    4. Applying Puppet Warp to vectors
      8m 9s
    5. "Gluing" vector art for Puppet Warp
      5m 50s
    6. Warping art onto the surface of an image
      8m 7s
    7. Blending a Smart Object
      4m 30s
    8. Blurring and blending a Smart Object
      6m 8s
    9. Making changes in Illustrator
      5m 57s
    10. Creating "true clones"
      7m 18s
    11. Double-flipping text
      4m 44s
    12. Applying effects to multiple layers
      3m 24s
    13. Updating true clones in one operation
      7m 36s
    14. Editing JPEGs as Camera Raw objects
      5m 49s
    15. Creating a double-exposure effect
      7m 15s
    16. Masking and shading transitions
      7m 47s
    17. Applying and repeating Camera Raw edits
      6m 9s
    18. Copying vs. cloning a Smart Object
      5m 18s
    19. Flipping a Smart Object and its mask
      3m 42s
    20. Adjusting multiple Camera Raw clones
      3m 53s
    21. Text that inverts everything behind it
      5m 34s
  7. 1h 59m
    1. This time, "smart" means dynamic
      1m 37s
    2. Introducing Smart Filters
      6m 28s
    3. Traditional High Pass sharpening
      5m 17s
    4. Smart High Pass in the Lab mode
      7m 57s
    5. Sharpening a high-frequency image
      7m 46s
    6. Retroactively reducing noise
      7m 31s
    7. Which filters are Smart Filters?
      6m 20s
    8. Shadows/Highlights as a Smart Filter
      4m 37s
    9. Nesting one Smart Object inside another
      7m 11s
    10. Drawing a mask from a nested Smart Object
      8m 7s
    11. Better Shadows/Highlights inside Lab
      9m 16s
    12. Tempering saturation values in Lab
      7m 0s
    13. Filtering live, editable text
      9m 2s
    14. Enhancing filters with layer effects
      4m 33s
    15. Applying a filter multiple times
      5m 0s
    16. Creating a synthetic star field
      7m 7s
    17. Making a stucco or drywall pattern
      6m 28s
    18. Land, sea, and clouds
      8m 30s
  8. 2h 50m
    1. Photoshop's advanced painting tools
      2m 3s
    2. Canvas texture and brush libraries
      6m 40s
    3. Painting with a predefined custom brush
      9m 21s
    4. Dissecting a custom brush
      11m 9s
    5. Designing and using a custom brush
      4m 54s
    6. Saving and loading brush presets
      5m 27s
    7. The ten styles of bristle brushes
      9m 47s
    8. Size, Spacing, and Angle
      7m 2s
    9. Using the Bristle Brush preview
      7m 53s
    10. Bristles, Length, Thickness, and Stiffness
      6m 53s
    11. Stylus tilt and mouse behavior
      5m 25s
    12. Stroking a path outline with a brush
      4m 0s
    13. Troubleshooting a stylus
      5m 49s
    14. Introducing the Mixer Brush
      7m 22s
    15. The Load, Mix, and Wet values
      5m 1s
    16. Cleaning and loading a brush
      6m 26s
    17. Shading a piece of graphic art
      6m 34s
    18. Shading with color
      7m 53s
    19. Mixing a photographic portrait
      6m 11s
    20. Tracing the fine details in an image
      5m 52s
    21. Crosshatching and brush size
      5m 53s
    22. Covering up and augmenting details
      7m 36s
    23. Painting in hair and fabric
      5m 54s
    24. Painting and scaling very fine hairs
      8m 7s
    25. Adding texture with the Emboss filter
      8m 31s
    26. Exploiting a "happy accident"
      2m 46s
  9. 1h 40m
    1. Artificial intelligence that works
      1m 22s
    2. The Auto-Align Layers command
      7m 25s
    3. The Auto-Blend Layers command
      3m 54s
    4. Masking auto-aligned layers
      4m 50s
    5. The Geometric Distortion setting
      6m 44s
    6. The Seamless Tones and Colors checkbox
      4m 8s
    7. Creating the best possible layer mask
      9m 18s
    8. Auto-blending depths of field
      5m 54s
    9. Finessing masks, accepting imperfections
      6m 29s
    10. Shooting and downsampling panorama images
      5m 54s
    11. Introducing the Photomerge command
      6m 40s
    12. Evaluating the Layout settings
      6m 47s
    13. Loading, aligning, and blending with Photomerge
      5m 36s
    14. Tracing and extracting seams
      7m 18s
    15. Adding a masked element into a panorama
      5m 55s
    16. Simplifying and correcting a panorama
      5m 58s
    17. Smart Filters and nondestructive cropping
      6m 43s
  10. 1h 18m
    1. The most mysterious of mysterious topics
      2m 29s
    2. Introducing HDR Toning
      6m 43s
    3. Reigning in clipped highlights
      5m 54s
    4. The Local Adaptation options
      9m 5s
    5. Nondestructive editing with HDR Toning
      8m 22s
    6. Using the HDR Toning Curve
      7m 2s
    7. HDR Toning vs. Shadows/Highlights
      6m 0s
    8. Merging multiple exposures
      7m 14s
    9. A first look at HDR Pro
      6m 24s
    10. Removing ghosts, correcting backlighting
      7m 11s
    11. Generating and editing an HDR comp
      7m 0s
    12. HDR rendered to completion
      5m 19s
  11. 1h 27m
    1. Processing hundreds of files in no time
      1m 43s
    2. Creating an action set
      6m 37s
    3. Making an action
      7m 7s
    4. Stop, Delete, and Record
      7m 12s
    5. Add, Undo, and Rerecord
      6m 40s
    6. Playing and testing an action
      6m 31s
    7. Playing and editing a specific operation
      6m 39s
    8. Permitting the user to change settings
      4m 58s
    9. Explaining an action with a custom stop
      5m 0s
    10. Batch-processing multiple images
      7m 22s
    11. Adding a Save As operation
      6m 34s
    12. Creating an action to save web graphics
      7m 59s
    13. Batching two actions into one
      7m 15s
    14. Saving and loading actions
      5m 30s
  12. 1m 19s
    1. See ya
      1m 19s

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