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Why Multiply darkens (blend mode math)

From: Photoshop CS3 Channels and Masks: The Essentials

Video: Why Multiply darkens (blend mode math)

talking about every single one of the equations and by the way, some of the blend modes have two equations actually, all of the contrast modes do, but we're not going to go into that, that was just a little FYI in case you're curious. We're going to be talking about why it is, specifically that the Linear Dodge mode, which adds luminance levels brightens the image whereas the Multiply mode, which multiplies luminance levels ends up darkening the image. last I checked, when you add two numbers they get bigger, but when you multiply two numbers, they even get bigger than that. So why doesn't multiply end up brightening colors as well. Well, let's go ahead and switch to this image right here, which is called Mode math.psd and I'm going to go ahead and switch to the full screen mode so that we can see the slide all by itself.

Why Multiply darkens (blend mode math)

talking about every single one of the equations and by the way, some of the blend modes have two equations actually, all of the contrast modes do, but we're not going to go into that, that was just a little FYI in case you're curious. We're going to be talking about why it is, specifically that the Linear Dodge mode, which adds luminance levels brightens the image whereas the Multiply mode, which multiplies luminance levels ends up darkening the image. last I checked, when you add two numbers they get bigger, but when you multiply two numbers, they even get bigger than that. So why doesn't multiply end up brightening colors as well. Well, let's go ahead and switch to this image right here, which is called Mode math.psd and I'm going to go ahead and switch to the full screen mode so that we can see the slide all by itself.

So here it is, 'Why add lightens, but multiply darkens.' When working with values greater than one which is what we're normally used to, right, division usually delivers the smallest results, then subtraction and we're just talking about basic arithmetic here, we're not talking about square roots and logarithmic operations and exponents and bla, bla, bla, just divide, subtract, add and multiply. Division is the smallest, subtraction is next, then addition and then we end up with multiplication as the top doc, so in other words, you multiply two numbers, you're going to get the biggest result. For example, let's say we have a couple of numbers, let's call them 204 and 76. Where did I get those numbers, you'll see, but anyway, 204 and 76. If we were to divide them, 204 divided by 76, we get approximately 3, it's actually 2.9 something, but let's call it three. Subtract, if we were to take 204 and subtract 76 we get 128, so medium gray, oh, so we're talking about luminance levels in this case. Fine, so that would be the equation right there. If we were to add them, 204 plus 76 we get 280, 255 is white, so that would go beyond 280 right and then if we were to multiply, 204 times 76 we get 15,504 which last I checked, is quite a bit higher than 255 and as a result, we would be blowing the heck out of the image so any time we multiply two images by each other, they just turn white, just except for the darkest shadows, the entire image would turn white. So what good would multiply be. It would be the most ridiculous radical operation on earth, but here's the deal, blend modes are standardized and that means that black is zero, White is 1 and 50% gray is 0.5, so everything happens in this tiny realm from zero to one.

In this tiny realm multiplication and subtraction decrease, division and addition increase. So things switch on us. For example our standardize levels are 0.8 and 0.3. So those are the same. If we took luminance level of 204, it becomes 0.8 in this new world of ours and 76 becomes 0.3. Fair enough, so if we were to multiply 0.8 times 0.3 we get 0.24, that's an even smaller number. It's much darker than 0.8, but it's even darker than 0.3. So we end up getting something that's more like 60 or something along those lines in terms of a luminous level. Subtract, we get 0.8 minus 0.3, we get 0.5, so that's bigger, but wouldn't necessarily be that way, it depends what numbers we're working with. Subtract could end up being smaller than multiply, but they're both going to be darker. Add, we get 0.8 plus 0.3, so 1.1, is white, so that means we just blew out that color, just went beyond white, so and of course anything that's lighter than white is going to become white, anything that's darker than black is going to be black, and then divide 0.8 by 0.3 and you get 2.67, which is way the hack white and that's why there really isn't a devide mode. There is a couple of subtract modes actually inside of Photoshop, but there is no straight divide mode instead what you have is more complex blending equations that involv some addition as well as some other operators. So basically what you got is the Multiply blend mode does this operation right here, goes ahead and multiplies it to luminance levels.

The Linear Dodge mode does this, it goes ahead and adds the two luminous levels together. So what's up with something like Screen. Well Screen goes ahead and adds the two colors together just like Linear Dodge and then it subtracts the two colors multiplied by each other. So it's really a combination of Linear Dodge and Multiply working together in order to create an effect that is in opposition to Multiply, just so as you know, you know, if you're curious. All right, in the next exercise we're going to get away from all this math stuff. I hope you enjoyed it, I hope you found it useful and we're going to take a look at the seven contrast modes.

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This video is part of

Image for Photoshop CS3 Channels and Masks: The Essentials
Photoshop CS3 Channels and Masks: The Essentials

140 video lessons · 32811 viewers

Deke McClelland
Author

 
Expand all | Collapse all
  1. 17m 33s
    1. Welcome
      2m 47s
    2. Setting a few key preferences
      3m 42s
    3. Loading the dekeKeys shortcuts
      3m 43s
    4. Loading color settings into Photoshop
      3m 52s
    5. Synchronizing color settings across CS3
      3m 29s
  2. 1h 17m
    1. Channels are everything
      1m 35s
    2. The Channels palette
      6m 30s
    3. Channels in color
      3m 57s
    4. RGB color
      4m 43s
    5. Single-channel grayscale
      5m 56s
    6. Lab color
      8m 56s
    7. CMYK plates
      7m 8s
    8. Introducing multichannel
      4m 40s
    9. RGB to multichannel to CMYK (and back)
      6m 26s
    10. CMYK to multichannel to RGB
      3m 57s
    11. Duotones, tritones, and quadtones
      6m 1s
    12. Editing a quadtone
      3m 49s
    13. Separating a composite quadtone
      6m 13s
    14. 16-bit advantages
      7m 36s
  3. 1h 13m
    1. The non-color-bearing channel
      51s
    2. The alpha channel
      3m 35s
    3. The anatomy of a mask
      5m 19s
    4. Making an alpha channel
      4m 28s
    5. Using the new channel icons
      5m 18s
    6. Saving an image with an alpha channel
      4m 38s
    7. Loading an alpha channel
      4m 6s
    8. Putting a mask into play
      3m 14s
    9. Using additional masks
      3m 12s
    10. Loading a mask from one image into another
      5m 22s
    11. Viewing a mask as a rubylith overlay
      4m 13s
    12. Changing a mask's overlay color
      4m 21s
    13. Modifying a mask
      6m 33s
    14. Combining masks
      4m 12s
    15. Blending image elements
      4m 55s
    16. The lossless translation
      6m 49s
    17. The goodness of masks
      1m 56s
  4. 56m 42s
    1. The selections is key, your understanding is core
      1m 29s
    2. The marquee tools
      5m 12s
    3. The lasso tools
      4m 38s
    4. The automation tools
      3m 59s
    5. Modifying a selection outline
      3m 59s
    6. Moving and cloning selected pixels
      3m 28s
    7. The floating selection
      4m 23s
    8. Promoting a floater to a layer
      3m 29s
    9. Nudging and aligning
      6m 49s
    10. The Anti-alias check box
      3m 59s
    11. How antialiasing works
      5m 6s
    12. Partially selecting pixels
      3m 43s
    13. Blurring a selection with Feather
      6m 28s
  5. 1h 27m
    1. Magic, quick, and magnetic
      1m 44s
    2. The Magic Wand revealed
      5m 46s
    3. Contiguous and Sample All Layers
      4m 24s
    4. Changing the sample size
      5m 40s
    5. Selecting with the Wand
      4m 26s
    6. The Wand's fake antialiasing
      3m 11s
    7. Dragging, dropping, and registering
      4m 41s
    8. Perfecting your composition
      6m 46s
    9. Meet the Quick Selection tool
      6m 0s
    10. Using the Quick Selection tool
      6m 48s
    11. Meet the Magnetic Lasso tool
      6m 30s
    12. Using the Magnetic Lasso tool
      5m 51s
    13. The new Refine Edge command
      6m 49s
    14. The five Refine Edge slider bars
      6m 55s
    15. Testing a refined selection outline
      5m 18s
    16. QS + ML + RE = success
      7m 4s
  6. 56m 59s
    1. I'm trapped! Marching ants on the loose!
      1m 45s
    2. Add, subtract, and intersect
      3m 46s
    3. Single-tool calculations
      6m 59s
    4. Networking selection tools
      8m 57s
    5. The Polygonal Lasso trick
      7m 13s
    6. Finessing your selection outline
      6m 37s
    7. Transforming and warping a selection outline
      5m 21s
    8. Pasting an image inside a selection
      6m 21s
    9. Shading and intersecting
      6m 10s
    10. Combining a selection with a mask
      3m 50s
  7. 1h 20m
    1. The best selection tool is a command
      1m 27s
    2. Meet the Color Range command
      8m 18s
    3. Working in the Color Range dialog box
      4m 50s
    4. Primary colors and luminance ranges
      5m 50s
    5. Sample all visible layers all the time
      2m 53s
    6. Using the Color Range command
      5m 11s
    7. Smoothing away auto-sharpened edges
      6m 5s
    8. Remaking corners with the Magnetic Lasso
      4m 57s
    9. Now for something a bit more complicated
      4m 53s
    10. Meet the Quick Mask mode
      3m 56s
    11. Editing in the Quick Mask mode
      2m 44s
    12. Quick Mask and Quick Selection
      7m 6s
    13. Making fine-tuned adjustments
      7m 48s
    14. Hand-painting refinements
      7m 35s
    15. Pasting an image in back of a selection
      3m 19s
    16. Neutralizing a color cast
      3m 15s
  8. 1h 15m
    1. Extraction erases pixels for good (or ill)
      1m 21s
    2. Meet the Magic Eraser tool
      4m 21s
    3. The Magic Eraser in action
      5m 0s
    4. Using the Background Eraser
      9m 16s
    5. The Background Eraser's shameful secret
      6m 16s
    6. The power of partial extractions
      5m 47s
    7. Why the Extract command erases pixels
      4m 21s
    8. Masking a tiger (or another colorful animal)
      8m 50s
    9. Using the Extract command
      7m 44s
    10. Smoothing edges with Textured Image
      4m 17s
    11. Extracting with an alpha channel
      6m 1s
    12. Shading an extracted image
      6m 47s
    13. Cleaning up the rough edges
      4m 59s
  9. 1h 51m
    1. It's time to select some hair
      1m 12s
    2. Trompe l'oeil with hair
      3m 48s
    3. Choosing a base channel
      7m 3s
    4. Levels or Curves
      8m 1s
    5. Overlay painting pt. 1: The highlights
      8m 2s
    6. Overlay painting pt. 2: The shadows
      3m 57s
    7. Cleaning up with the Lasso
      6m 5s
    8. Re-aliasing a selection outline
      8m 26s
    9. Fixing the rough patches
      9m 44s
    10. Testing your mask
      7m 52s
    11. Creating a detailed silhouette
      4m 38s
    12. Adding an underlighting effect
      7m 14s
    13. Previewing the blended composition
      2m 55s
    14. Blending hair and sky
      7m 11s
    15. Select menu equivalents
      5m 59s
    16. Toasting the edges
      7m 51s
    17. Further toasting with Inner Glow
      8m 12s
    18. Setting the image in a $3000 frame
      3m 26s
  10. 1h 52m
    1. The world of parametric editing
      1m 9s
    2. Bringing in a scanned logo
      8m 53s
    3. The power of Multiply
      6m 27s
    4. Resizing a Smart Object
      7m 25s
    5. Invert and Screen
      7m 39s
    6. Coloring the logo
      8m 29s
    7. The amazing Difference logo
      9m 24s
    8. The 25 standard CS3 blend modes
      6m 53s
    9. Cycling from one blend mode to the next
      5m 26s
    10. Lighten, Darken, and their composite offspring
      7m 37s
    11. Screen, Multiply, Dodge, and Burn
      7m 28s
    12. Why Multiply darkens (blend mode math)
      5m 5s
    13. The seven contrast modes
      8m 34s
    14. The two inversion modes
      7m 26s
    15. Unearthing JPEG details with the Difference blend mode
      4m 53s
    16. The four HSL modes
      5m 21s
    17. Combining the effects of two blend modes
      4m 27s
  11. 1m 38s
    1. Bye for now!
      1m 38s

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