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Selecting image luminosity

From: Photoshop CS4: Selections in Depth

Video: Selecting image luminosity

With just one click, you can make a selection based on the tonal value or the luminosity of pixels in an image. This opens up all kinds of creative possibilities. In this movie, I'll show you how quick and easy it is to make an image luminosity selection and I'll give you one example of something creative you can do with that selection which is to create a split toned image. To make a selection based on the luminosity of the tonal values in the image, I'm going to go to the Channels panel. There in the Channels panel, you can see the Red, Green and Blue color channels that make up the color image as well as a Composite RGB Channel.

Selecting image luminosity

With just one click, you can make a selection based on the tonal value or the luminosity of pixels in an image. This opens up all kinds of creative possibilities. In this movie, I'll show you how quick and easy it is to make an image luminosity selection and I'll give you one example of something creative you can do with that selection which is to create a split toned image. To make a selection based on the luminosity of the tonal values in the image, I'm going to go to the Channels panel. There in the Channels panel, you can see the Red, Green and Blue color channels that make up the color image as well as a Composite RGB Channel.

The way to load image luminosity as a selection is to hold down the Command key on the Mac or the Ctrl key on the PC. And click on the thumbnail on that RGB Channel. This creates a selection with the brightest areas fully selected and the less bright areas partially selected according to their brightness. It's hard to visualize that in this marching ants view of the selection. I am going to show you this selection as a grayscale mask in an Alpha channel, which as you know from other movies in this course is just another way to represent a selection.

To create an Alpha channel from this selection, I'll go to the bottom of the Channels panel and I click this icon which saves the selection as a channel. Then I'm going to deselect by pressing Command +D on the Mac or Ctrl+D on the PC, and I'm going to click on that Alpha Channel to display it here in the document window. It looks almost like a black and white photograph. Doesn't it? What it really is, is a representation of the selection with the fully selected pixels in white, the fully non- selected pixels in black, and the partially selected pixels in all of the shades of gray and between.

Now that you have had a chance to see this visual representation of an image luminosity selection, I'm going to delete this Alpha channel because it's really not necessary for the rest of the exercise. So I'll click on it in the Channels panel and drag it to the Trashcan. So what can you do with the selection based on image luminosity? There are lots of things. Once you've got the highlight areas selected, you might brighten them to increase contrast. You might invert your selections so that you have the shadow areas selected, and darken those. What I'm going to do is tone the highlight areas in gold and then tone the shadow areas in a dark purple blue to create what's known as a split toned image.

Simulating the kind of split toning that you can do with a lot more time and some chemicals in the traditional dark room. The first step in making a split toned image is to convert a color image to black and white. To do that, I'm going to click on the Layers panel. There is a single layer in the file which I do have selected and so I'm going to convert that to black and white by going up to the Image menu, choosing Adjustments and choosing Black & White. I'm going to accept all of the black and white settings and just click OK.

Now I'm going to go back to the Channels panel because I want you to see that this is still a Red, Green, Blue color mode image. I had basically just taken the color out and I'm left with the same tonal values that were underlying the image when you saw it in color a few moments ago. Because these tonal values are the same, I can load them again as a selection by going to the RGB Composite Channel, and again holding down the Command key on a Mac or the Ctrl key on a PC and clicking on the thumbnail on the RGB Channel.

So now I have the highlight selected in the image and I would like to tone them a gold color. I'll go back to the Layers panel and then I'm going to go to the bottom of the Layers panel and click this icon, the Black & White circle to create a new fill layer. This menu lists all of the adjustment layers and at the top, it lists three flavors of fill layer. I'm going to choose Solid Color. That opens the Color Picker where you can choose a color for tinting the highlights. I'm going to use this gold color and I'll click OK.

Now all of the highlights in the image are tinted gold. And there is a mask that automatically comes with every fill layer that is protecting the non-selected areas, the dark areas here from that gold tint. Displaying the gold tint on the brightest areas and partially displaying the gold tint on the gray areas in between. Next, I would like to add a tint to the shadows in this image. I'm going to bring back my selection of the highlights by going to the Select menu and choosing Reselect.

And then I'm going to invert that selection so the shadow areas are selected rather than the highlights. So I'll go to the Select menu and I'll go to Inverse. Now with the shadow areas selected, I'm going to add another fill layer by going to the bottom of the Layers panel, clicking that Black & White circle icon and choosing Solid Color again. In the Color Picker that opens, I'll use the slider in the middle to move to the blue purple range, somewhere around there and I want a very dark purple, something like that. I'll click OK.

And now I have another color fill layer with its own layer mask based on the inverted image luminosity selection and the purple color is tinting all of the dark areas of the image, the lighter areas are protected from this tint. I think this tint is actually a little bit too strong, so I'm going to reduce the opacity of the purple color fill layer by making sure I have that layer selected in the Layers panel and then going to the Opacity slider at the top of the Layers panel, moving my mouse over the Opacity label and dragging to the left and maybe I'll put this at about 50%.

So I have managed to use that image luminosity selection that was so quick and easy to make by clicking on the thumbnail on the RGB Channel. As the basis for double tinting this image, tinting the highlights gold and the shadows dark blue. This is just one of the creative possibilities that you have when you make a selection based on image luminosity. As you can see, making a selection like this is a really powerful feature but it's one that's sometimes overlooked, and I urge you to keep it in mind as you are working on your own images.

Show transcript

This video is part of

Image for Photoshop CS4: Selections in Depth
Photoshop CS4: Selections in Depth

46 video lessons · 18055 viewers

Jan Kabili
Author

 
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  1. 2m 26s
    1. Welcome
      1m 19s
    2. Using the exercise files
      1m 7s
  2. 21m 1s
    1. Why select?
      7m 13s
    2. What is a selection?
      4m 22s
    3. Deselecting and reselecting
      1m 59s
    4. Hiding a selection boundary
      2m 41s
    5. Using the Select All command
      4m 46s
  3. 38m 56s
    1. Using the Rectangular Marquee tool
      8m 25s
    2. Using the Elliptical Marquee tool
      6m 26s
    3. Drawing freehand selections with the Lasso tool
      5m 26s
    4. Selecting straight edges with the Polygonal Lasso tool
      4m 58s
    5. Selecting with the Pen tool and paths
      8m 17s
    6. Making selections from shapes
      5m 24s
  4. 37m 1s
    1. Using the Quick Selection tool
      5m 44s
    2. Using the Magic Wand tool
      6m 39s
    3. Working with the Color Range feature
      8m 0s
    4. Selecting edges with the Magnetic Lasso tool
      7m 48s
    5. Selecting layer transparency
      2m 37s
    6. Selecting image luminosity
      6m 13s
  5. 33m 0s
    1. Moving selections
      2m 55s
    2. Transforming selections
      3m 13s
    3. Using contextual commands for transformation
      3m 13s
    4. Inverting selections
      3m 50s
    5. Anti-aliasing selections
      6m 52s
    6. Feathering selections
      6m 49s
    7. Fine-tuning selections in Refine Edge
      6m 8s
  6. 24m 27s
    1. Saving selections
      6m 0s
    2. Loading and modifying saved selections
      4m 57s
    3. Saving selections to other images
      4m 55s
    4. Creating layer masks from selections
      6m 36s
    5. Loading selections from layer masks
      1m 59s
  7. 15m 41s
    1. Adding, subtracting, and intersecting selections
      5m 26s
    2. Combining selections to build a graphic
      5m 8s
    3. Expanding selections with Grow and Similar
      5m 7s
  8. 22m 1s
    1. Cleaning up selections in Quick Mask
      6m 37s
    2. Creating selections from scratch in Quick Mask
      2m 44s
    3. Changing Quick Mask options
      2m 37s
    4. Varying edge softness in Quick Mask
      2m 28s
    5. Filtering selections in Quick Mask
      2m 5s
    6. Making Step and Repeat selections in Quick Mask
      5m 30s
  9. 35m 53s
    1. Making selections from color channels
      4m 55s
    2. Working with the Background Eraser tool
      10m 44s
    3. Pasting into selections
      5m 28s
    4. Installing the legacy Extract filter
      5m 19s
    5. Using the Extract filter
      9m 27s
  10. 52s
    1. Goodbye
      52s

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