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Extracting luminance information

From: Photoshop CS5 One-on-One: Advanced

Video: Extracting luminance information

In this exercise, we're going to see yet another way to use this Grayscale command right there to extract a black and white image from a full color photograph, but this time as opposed to extracting that black and white image from an RGB photograph, we're going to take advantage of an alternate color model known as Lab. Now, I've gone ahead and saved our progress so far. First, there is this image called Grayscale composite.jpg, which is the grayscale fusion of all three of those color channels into one.

Extracting luminance information

In this exercise, we're going to see yet another way to use this Grayscale command right there to extract a black and white image from a full color photograph, but this time as opposed to extracting that black and white image from an RGB photograph, we're going to take advantage of an alternate color model known as Lab. Now, I've gone ahead and saved our progress so far. First, there is this image called Grayscale composite.jpg, which is the grayscale fusion of all three of those color channels into one.

The next image is called Blue to gray.jpg, and that's that Blue Channel from the RGB image, we just went ahead and abandoned the Red and Green Channels in order to get this effect here. And then we also have our original Agrarian gothic.jpg file. And what I'm going to do here is switch to the original color image and then go up to Arrange icon and click on Consolidate All, or if you loaded dekeKeys, you've got a keyboard shortcut, Ctrl+Shift+A, Command+Shift+A on the Mac. Let's go ahead and scroll this image over that so that we can see more of it at a time, and notice that we do have an RGB image, with independent Red, Green, and Blue Channels.

And the reason I mention this is because, this is an extremely popular color model for very good reasons. First of all, it's a color model that's employed by your digital camera, it's the color model that's employed by your scanner, it's used by your computer monitor and your TV set and your overhead projector and everything that either captures or projects color. So basically the one big exception is a printer, and whenever you're putting ink on a page, then you're using CMYK or some other mix of inks or pigments, something along those lines.

But then in addition to RGB and CMYK, we have yet another color model. This one is device independent, that is to say, it's not subject to the interpretation of a digital camera or a scanner or a computer screen or a printer or any of that stuff, and it's designed to emulate the way that we perceive colors, but it's going to seem awfully foreign at first. So I want you to watch the Channels panel right here, we've got an RGB composite that contains a Red version of the image, a Green version, and a Blue version, and in any point in time, you can actually mix these together.

If I click on Red and then also eyeball Green right there, I'll see a combination of the Red and Green Channels working as one here inside the Image window. So we've got everything but the Blue information. So we've got our Greens, we've got our Reds, we've got our Yellows, which are a combination of Green and Red working together, to get the full color image, we add Blue, and that will become useful information in just a moment. I'm going to go up here to the Image menu, choose mode, and choose Lab Color, and that's going to convert our RGB image into a Lab image.

Some folks call it LAB; totally up to you how you decide to work, but A and B don't stand for anything. L stands for Lightness, which is the luminance information inside the image. So notice we still have three channels of information working together. This is the luminance information or Lightness, if you prefer, and then A and B are arbitrary letter designations for both the tint information inside the image; I know it doesn't look like anything so far, just be patient for a moment.

This is tint information inside the image and this here B is the temperature information. So temperature is more of an important topic than tint, so let's take a look at B and Lightness together. As soon as I turn on this Lightness Channel by clicking on its eyeball, things begin to make a little more sense. So instead of seeing this nebulous gray information inside the B Channel, we now see that nebulous gray represented as color, and we can see that we've got our yellows, all the way through our blues.

So think of that big color wheel that we saw way back in the Fundamentals portion of the series and imagine a slice going right through it from yellow to blue, which are complementary colors, as you may recall. This is what the B Channel is able to convey, is basically that slice of information, so we can see the warm information inside the image, which is going to be the skin tones, and we can see the cool information, the blues, which are showing up in basically the synthetic materials. So the earring in the Goth girl here and we've got the jacket in the figure in the background.

Let's now go ahead and turn off B for a moment and turn on A. Now, A is a perpendicular slice through that same color wheel, and this time this tint information is representing essentially the pinks. We don't have a real color, people say it's the greens to the magentas, but that's not strictly speaking true. It's more of the pinks inside of the image, all the way through the turquoise colors. So just think of a perpendicular slice of complementary colors, and then together when you add them both up, if you go ahead and click on B again, then you get that full color image.

Now, you can also choose to look at just the color independently of the Lightness if you want to, it's not going to make a lot of sense, but then we're seeing all of the colors inside the image independently of the luminance levels. And the reason everything looks this murky gray is because gray is the default luminance level where A and B are concerned when they're mixing together. So all we're missing here is the whites and the blacks to go along with it and then we end up having a recognizable image like this. All right! So where does this factor into creating a grayscale image? Well, what you can do is you can click on Lightness, and this is the way a lot of folks advocate that you create grayscale images, I don't necessarily advocate it, it's just yet another way to work.

Some folks say this is the purest way there is, because this is the real luminance data, man. I say, just another option. Anyway, click on Lightness to make it active. You might want to go ahead and turn off the other two channels as well, so that you can see what it is you're getting. And then you go up to the Image menu, choose mode, and you choose Grayscale, and once again Photoshop is going to say, do you want to discard the other channels? Do you want to get rid of A and B? And your answer is OK. After all of this, if you get sufficiently familiar with things, you can say don't show again. I'm not going to do that though, I'll just click OK.

Now, there is that Grayscale version of the image, and now let's go ahead and view all of these images together by clicking on the 3 Up range icon, and our images have been rearranged, because Photoshop's very fond of doing that, but let's go ahead and tab away all of the panels in the toolbox and the Options bar and everything else, and let's see if I can go ahead and get these images arranged into alignment. I'm Spacebar dragging this left-hand image here and then I'm adding the Shift key once I get that guy aligned, so that I'm moving everybody together.

So what we're seeing here, in the middle we're seeing the Grayscale composite, that's a fusion of the Red, Green, and Blue Channels. Over here on the right-hand side, we're seeing the Blue Channel by itself; we could have just as easily chosen the Green Channel or the Red Channel by itself as well. And then over here on the far left side, we have that luminance information that was extracted from the Lab image, and it ends up being the lightest of the bunch. It wouldn't necessarily if we were comparing it to the Red Channel. So you never know how it's going to shake out. But these are three very easy ways to capture a Grayscale image inside of Photoshop.

But then there is the option of mixing your own custom black and white image using one of two commands, either the Channel Mixer or the Black and White command, and we'll see how those functions work, beginning in the next exercise.

Show transcript

This video is part of

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

247 video lessons · 32910 viewers

Deke McClelland
Author

 
Expand all | Collapse all
  1. 40m 2s
    1. Welcome
      2m 1s
    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 6s
  2. 1h 5m
    1. What you can do with Photoshop
      1m 46s
    2. The mission-critical eyes
      2m 44s
    3. Copy Merged and Paste in Place
      6m 52s
    4. Sharpening details to match
      4m 34s
    5. Masking eyes
      9m 22s
    6. Working with clipping-mask layers
      9m 5s
    7. Shading with layer effects
      8m 10s
    8. Color and highlight effects
      4m 2s
    9. Refining layer masks
      5m 43s
    10. Fabricating the highlights in the pupils
      7m 33s
    11. Using a merged copy to sharpen
      5m 34s
  3. 2h 14m
    1. Highlights, shadows, and midtones
      1m 16s
    2. Introducing the Auto commands
      7m 23s
    3. Adjusting Cache Level settings
      6m 8s
    4. Reading a channel-by-channel histogram
      6m 21s
    5. How the Auto commands work
      5m 22s
    6. Auto Tone, Auto Contrast, and Auto Color
      7m 7s
    7. Blending the Auto results
      4m 4s
    8. Introducing the Levels command
      6m 15s
    9. Using Levels as an adjustment layer
      3m 12s
    10. Applying custom Levels adjustments
      6m 8s
    11. Understanding the gamma value
      7m 39s
    12. The futility of Output Levels
      2m 56s
    13. Selections and adjustment layers
      5m 48s
    14. Opening up the shadows
      3m 40s
    15. Previewing clipped pixels
      4m 51s
    16. The black, white, and gray eyedroppers
      5m 7s
    17. Gray card tips and tricks
      6m 5s
    18. Making channel-by-channel adjustments
      7m 29s
    19. Introducing the Curves command
      7m 44s
    20. Curves dialog box tricks
      7m 16s
    21. Curves adjustment layer tricks
      5m 45s
    22. Correcting an image with Curves
      5m 32s
    23. Filling in the highlights
      5m 42s
    24. Neutralizing casts and smoothing transitions
      5m 37s
  4. 1h 46m
    1. The art of enhancing edges
      1m 26s
    2. How sharpening works
      6m 2s
    3. The single-shot sharpeners
      6m 7s
    4. Introducing Unsharp Mask
      6m 19s
    5. Radius and Threshold
      6m 24s
    6. Sharpening colors vs. luminosity
      5m 56s
    7. Gauging the ideal settings
      8m 59s
    8. Unsharp Mask vs. Smart Sharpen
      7m 1s
    9. Using the Remove settings
      9m 30s
    10. The More Accurate checkbox
      6m 8s
    11. Saving your Smart Filter settings
      5m 31s
    12. The Advanced sharpening settings
      7m 52s
    13. Accounting for camera shake
      6m 18s
    14. Sharpening with the Emboss filter
      6m 43s
    15. Sharpening with High Pass
      9m 23s
    16. The new and improved Sharpen tool
      6m 22s
  5. 1h 34m
    1. Edge's evil twin: noise
      1m 12s
    2. Color vs. luminance noise
      7m 21s
    3. Reducing color noise
      7m 45s
    4. Reducing luminance noise
      4m 59s
    5. Relegating an effect to the shadows
      6m 27s
    6. Switching between layer and mask
      6m 59s
    7. The Dust & Scratches filter
      4m 56s
    8. Adjusting shadow saturation
      5m 52s
    9. Combining High Pass with Lens Blur
      6m 57s
    10. Masking a layer of Lens Blur
      7m 34s
    11. Painting away High Pass sharpening
      8m 22s
    12. Building up a noise pattern
      6m 40s
    13. Converting noise to texture
      4m 24s
    14. Bleeding colors into paper
      6m 16s
    15. Matching different noise levels
      8m 31s
  6. 1h 32m
    1. We are the stuff of light
      1m 24s
    2. Applying automatic lens correction
      5m 53s
    3. Introducing Shadows/Highlights
      3m 44s
    4. Shadows/Highlights in depth
      7m 59s
    5. Creating a "bounce" with Gaussian Blur
      4m 43s
    6. Sharpening on top of blur
      7m 3s
    7. Sharpening the merged composition
      6m 16s
    8. Grouping and masking layers
      5m 40s
    9. Adjusting the density of a mask
      7m 14s
    10. Creating a Shadows/Highlights shortcut
      5m 47s
    11. Restoring detail with Shadows/Highlights
      6m 23s
    12. Changing the Shadows/Highlights defaults
      6m 21s
    13. Smoothing skin details with Gaussian Blur
      3m 56s
    14. Smoothing with High Pass
      5m 44s
    15. Lowering contrast with Gaussian Blur
      7m 4s
    16. Inverting a sharpening effect
      7m 5s
  7. 2h 32m
    1. Color becomes monochrome
      1m 31s
    2. Converting an image to grayscale
      6m 49s
    3. Extracting luminance information
      7m 37s
    4. Introducing the Channel Mixer
      10m 23s
    5. Aggressive channel mixing
      9m 42s
    6. Proofing CMYK colors
      7m 49s
    7. Color settings and intent
      7m 6s
    8. Practical Channel Mixer variations
      4m 30s
    9. Saving variations as layer comps
      7m 57s
    10. The default grayscale recipe
      8m 55s
    11. Creating a custom black-and-white mix
      6m 59s
    12. Shadows/Highlights in black and white
      4m 58s
    13. Introducing the Black & White command
      5m 55s
    14. Adjusting Black & White settings
      9m 39s
    15. Mixing a Black & White portrait
      6m 32s
    16. Black & White vs. Channel Mixer
      9m 21s
    17. Adding tint and color
      8m 0s
    18. Introducing the Gradient Map
      7m 10s
    19. Loading custom gradients
      4m 32s
    20. Editing gradient color stops
      9m 58s
    21. Colorizing with blend modes and Opacity
      7m 13s
  8. 2h 10m
    1. Two great commands working great together
      1m 18s
    2. Introducing the Color Range command
      5m 13s
    3. Setting key colors and Fuzziness
      5m 38s
    4. Predefined vs. sampled colors
      3m 57s
    5. The Localized Color Clusters option
      5m 41s
    6. Defining a selection with care
      4m 44s
    7. Introducing the Quick Mask mode
      5m 20s
    8. Testing edges with the Magic Wand
      5m 14s
    9. Hand-brushing a selection
      5m 39s
    10. Saving and loading an alpha channel
      4m 35s
    11. Converting a selection to a layer mask
      2m 46s
    12. Switching between an image and a layer mask
      6m 58s
    13. Protecting elements with a layer mask
      8m 5s
    14. Duplicating and editing a layer mask
      7m 34s
    15. Introducing the Refine Edge command
      4m 46s
    16. Accessing the various Refine Edge options
      5m 35s
    17. Refine Edge's preview options
      6m 21s
    18. The Adjust Edge values
      4m 11s
    19. Edge Detection and Smart Radius
      6m 5s
    20. Using the Refine Radius tool
      8m 8s
    21. Using the Decontaminate Colors option
      7m 30s
    22. Old-school masking adjustments
      7m 7s
    23. Four micro mask adjustments
      8m 33s
  9. 3h 13m
    1. Photoshop's vector exceptions
      1m 11s
    2. Making text in Photoshop
      6m 18s
    3. Creating and editing a text layer
      6m 56s
    4. Font and type style
      7m 35s
    5. Type size and color
      7m 52s
    6. Combining layer effects and type
      10m 57s
    7. Drawing a custom shape layer
      8m 34s
    8. Side bearing, kerning, and tracking
      10m 36s
    9. Point text vs. area text
      8m 26s
    10. Selecting and formatting a paragraph
      5m 19s
    11. Copying and pasting unformatted text
      7m 45s
    12. Creating text inside a custom path
      6m 26s
    13. Creating text along a path
      8m 13s
    14. Adjusting baseline shift
      6m 16s
    15. Drawing a fading arrowhead
      7m 29s
    16. Fading a shadow with a layer
      5m 32s
    17. Logo creation and Fill Opacity
      7m 44s
    18. Stretching a background element
      6m 9s
    19. Drawing with shape outlines
      6m 18s
    20. Combining vector-based shapes
      6m 42s
    21. Masking vector-based shape layers
      6m 7s
    22. Correcting spacing problems
      7m 44s
    23. Drawing the ultimate specular sparkle
      8m 45s
    24. Preparing text for commercial output
      5m 9s
    25. Saving a high-resolution PDF file
      7m 11s
    26. Inspecting the final PDF document
      7m 8s
    27. Saving large poster art
      9m 32s
  10. 2h 36m
    1. What filters ought to be
      1m 25s
    2. Layer effects vs. filters
      6m 14s
    3. Carving with an Inner Shadow effect
      7m 45s
    4. Selling an effect with Drop Shadow
      7m 17s
    5. Creating blurry shadow type
      5m 30s
    6. Saving custom default settings
      6m 22s
    7. Creating a custom contour
      7m 3s
    8. Introducing Bevel and Emboss
      7m 35s
    9. Adjusting Angle and Altitude
      7m 8s
    10. Exploiting global light
      8m 11s
    11. Gloss and edge contour
      5m 8s
    12. Applying and creating layer styles
      6m 45s
    13. Loading, saving, and merging styles
      6m 17s
    14. Creating a textured bevel effect
      6m 56s
    15. Using shadows as highlights
      7m 39s
    16. Combining filters and effects
      6m 58s
    17. Working with random effects
      6m 55s
    18. Smoothing with Gaussian Blur and Levels
      6m 13s
    19. Masking blacks from whites
      4m 37s
    20. Applying liquid styles
      4m 36s
    21. Simulating liquid reflections
      8m 12s
    22. Finessing and cropping a liquid effect
      7m 25s
    23. Initiating a displacement map
      6m 17s
    24. Applying a displacement map
      7m 37s
  11. 1h 12m
    1. Two words: Free Transform
      34s
    2. Scale, rotate, and constrain
      6m 30s
    3. Using the transformation origin
      7m 42s
    4. Applying a slant (aka skew)
      3m 37s
    5. The four-point "perspective" distortion
      7m 51s
    6. Two ways to make gradient text
      5m 59s
    7. Building complexity from a simple shape
      4m 42s
    8. Duplicating a series of transformations
      6m 3s
    9. Rasterizing a layer with its effects
      6m 41s
    10. Applying a custom warp
      7m 24s
    11. Blending and softening a warped layer
      4m 39s
    12. Creating spherical highlights
      6m 30s
    13. Using a center-source inner glow
      3m 51s
  12. 2h 42m
    1. Distorting reality
      1m 33s
    2. Extracting a foreground element
      6m 45s
    3. Introducing the Puppet Warp command
      7m 20s
    4. Setting and manipulating pins
      7m 48s
    5. Rotating pins and switching warp modes
      6m 41s
    6. Expanding and contracting the mesh
      6m 11s
    7. Changing the Density setting
      8m 0s
    8. Adjusting the pin depth
      5m 18s
    9. Winding an image into a pretzel
      6m 2s
    10. Applying Puppet Warp to type
      6m 30s
    11. Warping single characters
      6m 25s
    12. Editing puppet-warped text
      8m 24s
    13. Extending an image with Free Transform
      8m 46s
    14. Extracting from a white background
      10m 5s
    15. Tracing a shape with Puppet Warp
      9m 1s
    16. Introducing the Liquify command
      5m 4s
    17. Warp, Twirl, Pucker, and Bloat
      8m 53s
    18. Saving and loading a mesh
      5m 59s
    19. Push, Mirror, and Turbulence
      11m 49s
    20. Lifting and slimming details
      8m 22s
    21. Warping fabric, arms, and legs
      7m 1s
    22. Masking and finessing the results
      10m 8s
  13. 3h 3m
    1. Welcome to the digital darkroom
      1m 44s
    2. Introducing Camera Raw
      7m 40s
    3. Adjusting white balance
      7m 0s
    4. Selecting and synchronizing images
      6m 9s
    5. Making automatic adjustments and saving changes
      7m 19s
    6. Creating and managing snapshots
      8m 23s
    7. Adjusting the Exposure value
      6m 24s
    8. Working with clipping warnings
      5m 5s
    9. Adjusting Brightness and Contrast
      7m 35s
    10. Vibrance, Saturation, and Clarity
      9m 25s
    11. Recovery and Fill Light
      6m 57s
    12. Using the Graduated Filter tool
      7m 2s
    13. Painting edits with the Adjustment Brush
      9m 44s
    14. Straighten, crop, and geometric distortions
      7m 49s
    15. Applying manual lens corrections
      7m 19s
    16. Vignette and chromatic aberrations
      6m 21s
    17. Introducing the Tone Curves
      6m 9s
    18. Parametric curves and targeted adjustments
      6m 26s
    19. Correcting a low-noise photograph
      7m 35s
    20. Sharpening and high-noise photos
      8m 25s
    21. Selective Hue/Saturation adjustments
      5m 34s
    22. Selective Luminance adjustments
      5m 39s
    23. Adding grain and vignetting effects
      5m 23s
    24. Mixing a subjective black-and-white image
      7m 53s
    25. Colorizing with the Split Toning options
      4m 29s
    26. Opening a raw image as a Smart Object
      5m 39s
    27. Camera Raw wrap-up
      8m 38s
  14. 55s
    1. Until next time
      55s

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