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How the Add blend mode works

From: Photoshop CS3 Channels & Masks: Advanced Techniques

Video: How the Add blend mode works

Now thus far we've spent remarkably little time looking at the Calculations Command just a couple of exercises. That changes starting now. We are going to begin to immerse ourselves in that command. And things we are going to start to get little bit technical. Now, that's not to say this is going to be over your head. Hopefully it won't be. Hopefully you'll be able to keep up with me. But I am going to fire off some technicalities that you right now beginning in this exercise and continuing into the next one, because I want you to have a clear understanding of the two blend modes which are really super useful blend modes that are unique to the Apply Image in Calculations dialog boxes.

How the Add blend mode works

Now thus far we've spent remarkably little time looking at the Calculations Command just a couple of exercises. That changes starting now. We are going to begin to immerse ourselves in that command. And things we are going to start to get little bit technical. Now, that's not to say this is going to be over your head. Hopefully it won't be. Hopefully you'll be able to keep up with me. But I am going to fire off some technicalities that you right now beginning in this exercise and continuing into the next one, because I want you to have a clear understanding of the two blend modes which are really super useful blend modes that are unique to the Apply Image in Calculations dialog boxes.

And those are the Add and Subtract Modes. And the thing about those modes are, if I were to switch to a layer here inside of this image, you can see that they do not appear anywhere inside the Layers palette. And the reason that they don't appear inside the Layers palette, at least one of the reasons, there are a couple of reasons actually, but one of the reasons that they don't appear inside the Layers palette is because they have additional numerical controls that the Layers palette really can't accommodate. All right, so here is what I want you to do. I want you to go ahead and open this image that's called Add and subtract.psd.

It's found inside of the 14 Calculations folder. And it's going to walk us through how the Add and Subtract blend modes work in just so that you are clear here. These modes appear just inside the Apply Image dialog box if I went over to the Image menu and chose Apply Image. You would see that if were to change the blend mode from Multiply to Add for example or Subtract, in addition to applying this blend mode I would also get two new values, Scale and Offset. And I am going to explain how those values work. So I just want you to see these blend modes do occur inside the Apply Image dialog box. I have said in the past in the previous chapter, I am not all that keen on the Apply Image command, I don't use it all that frequently, because 99% of what it can do you can accomplish more easily using layers, especially adjustment layers.

Anyway, I am going to cancel out of here. But I am a big fan of the Calculations Command. So we are going to be focusing on the Calculations Command here on Add and Subtract inside the Calculations dialog box. And again, just so that we have a frame of reference I am going to go to the Image menu, choose Calculations, and you can see of course the last blend mode that we applied inside of this chapter was Color Dodge. But right there, there is Add, and there is Subtract, and if I choose either of these modes then I get the Offset and Scale values right here. Both modes provide access to these values, none of the other modes do. I am going to cancel out of there.

Now let's focus on the diagram here. I am going to go ahead and hide the Layers palette and I am going to bring up my Layer Comps palette which you can get to of course by choosing the Layer Comps command from the Window menu. And notice right now I am seeing Source #1. Now just again as a refresher, just as a reminder, you may recall inside of the Calculations dialog box, we've got Source #1 at the top here, and Source # 2 at the bottom, and I was telling you, you want to think of it as if Source #2 is sitting on top of Source #1.

So they are actually kind of listed in the wrong order here. Source #2 is on top and Source #1 is on the bottom. So I'll go and cancel out. And by Source #1 and Source #2 I just mean channels inside the image. These could be color bearing channels, they could be Alpha channels. In our case we are going to think in terms of Alpha Channels, and very simple Alpha Channels as well. So this is Source #1, it's something that I am calling the Shadow. It's basically an ellipse that I drew with the Elliptical Marquee tool. I filled it with white against the black background, and then I applied the Gaussian Blur Command with a Radius of 24 pixels.

The next source, the Source #2 item right here if I click in front of Source #2, is the Sun. And the only difference it's still Gaussian Blur with a Radius of 24 pixels. I still drew it with the Ellipse tool. The big difference is that it's a circle instead of an ellipse. And these two guys partially overlap each other. So you can see them back and forth here. Here is Source #1, and here is Source #2. So Source #2 is bigger, it's more circular and it's offset slightly to the right. Here is the way that they overlap. If we advance to the Overlapped Layer Comp you can see the two Alpha Channels as if we are viewing them at the same time in that Quick Mask mode, so that we can see them in color and blue represents the Shadow channels, and Red represents the Sun channel. So wherever we are seeing this purple/violet color here, that's black inside of both channels.

Where we are seeing blue that means that the Shadow channel is black and the Sun channel is white. Where we are seeing Red, that means the Shadow channel is white and the Sun channel is black, and where we are seeing white, both channels are white. Does that make sense? We are seeing the two channels overlap each other. Now, let's focus on how Add works inside of this exercise, and then in the next exercise we'll focus on Subtract. I am going to go ahead and apply the Add Mode. This is what things would look like if I apply the Add blend mode using the Calculations command. And here is that you want to think about it. We are taking Source #2, and we are adding Source #1 to it. So I was telling you Source #1 is sitting on top of Source #2.

so that means we start at the back of the stack here, Source #1, then we add Source #2 to it obviously if we were to flip that equation around it wouldn't matter really where adding is concerned. But once we come to Subtract the order does matter. So best to think of it this way right upfront. And we are really adding Luminance levels, so we are brightening the resulting pixels fairly significantly here. Then we divide by the Scale value and we add the Offset value and we get the result. Now, that's the part that I think sort of twists a lot of people that we are going through Scale and Offset, oh, my goodness! How in the world can we keep track of all these stuff? We'll, all right. Let's say that we've got a pixel that has a Luminance level of 100 inside of the Source #2 channel, which would be the Sun channel. And another pixels of that same location that has a Luminance level of 50 inside of the Shadow channel. Well, then you add them together and you would get a Luminance level of 150 which is slightly brighter than medium gray. Then you would divide that by the Scale value.

The Scale value can be anything between one and two. Obviously, if you divide by one you don't make any change. If you divide by two you are going to take that value down, it can be anything between one and two by the way, it can be decimal values. And the idea is that you can easily add Luminance levels to the point that they get way too bright. Like if you have White plus White, 255 plus 255 that ends up being a Brightness value of more than 500 which is of course off the scale, and use the Scale value to bring it back down to earth essentially. And then you can add the Offset value. The Offset value can be anything between -255 and +255. So you can Subtract or Add using this Offset value. So in our case right here what we are seeing on-screen is Sun plus Shadow, the Sun channel plus the Shadow channel divided by 1.0 which is the Default Scale value plus 0, which is the default Offset value, and you get this effect right here. So bear in mind this was Source #1, this is Source #2, this is what it looks like when you add the two together.

Next, I tried applying that same blend mode, but this time I took the Scale value up to 2.0, and you can see the difference here. This is without the Scale value or the Scale value is set to 1; the default value. And this is a Scale value of 2.0. Things look pretty similar between those two results except that the second result; the scaled result is much softer. So by scaling the effect, by raising the Scale value to it's maximum in this case the 2.O, we are softening the effect, something to bear in mind.

You can also of course offset the effect if you prefer. So I change the Scale value in this case with the Add Offset -128 right here Layer Comp. I change the Scale value back to 1.0, so we are not applying any scale. And I went ahead and changed Offset to -128. So we are subtracting 128, bear in mind that 128 is about a medium gray. So we are subtracting 128 from the picture. And as a result we end up making the highlight effect smaller. So this is what it looked like without any Offset applied. This is what the effect looks like with the Offset applied. But notice that it's also sharp that we have a Sharp effect as a result, because we didn't add any Scale into the picture. Does that make sense? I assure you that if it's like just completely overwhelming you at this point that by time we are done with this chapter you'll have a working knowledge of how to use the Add Mode, because we will be experimenting with it.

But I did want to give a sense of what's going on under the hood. In the next exercise I am going to show you Subtract; I want you to be there for it. I want you to stick with me here if you can. And then following that we will actually put those blend modes into play.

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This video is part of

Image for Photoshop CS3 Channels & Masks: Advanced Techniques
Photoshop CS3 Channels & Masks: Advanced Techniques

190 video lessons · 26326 viewers

Deke McClelland
Author

 
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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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