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Selecting by luminosity

From: Photoshop CC Selections and Layer Masking Workshop

Video: Selecting by luminosity

In some cases you may realize that the area you want to select can be defined based on brightness values. For example, with this photo I have relatively extreme example, of course. But I might want to select the sky, the brightest areas, in order to apply an adjustment there. Or I might want to select the dark areas, the foreground, in order to apply an adjustment that affects only the dark areas. This can be useful, for example, to open up shadow detail, or perhaps to create a silhouette effect of the darker areas of a photo. Let's take a look at a technique we can use to create a selection based on luminosity values or brightness values. I'll start off by creating a copy of my background image layer, because I'm going to apply a very destructive adjustment.

Selecting by luminosity

In some cases you may realize that the area you want to select can be defined based on brightness values. For example, with this photo I have relatively extreme example, of course. But I might want to select the sky, the brightest areas, in order to apply an adjustment there. Or I might want to select the dark areas, the foreground, in order to apply an adjustment that affects only the dark areas. This can be useful, for example, to open up shadow detail, or perhaps to create a silhouette effect of the darker areas of a photo. Let's take a look at a technique we can use to create a selection based on luminosity values or brightness values. I'll start off by creating a copy of my background image layer, because I'm going to apply a very destructive adjustment.

And I certainly don't want to harm my original pixels, so I'll drag the thumbnail from my background image layer down to the Create New Layer button. The blank sheet of paper icon at the bottom of the Layers panel. That will create my background copy, and in order to make it easy to see the effect of what I'm doing here, I'm going to change the opacity for this Background Copy layer down to about 50%. The reason for this will become evident in just a moment. Next, I'm going to adjust this image based on luminance values, so I'll go to the Image menu. And then choose Adjustments, followed by Threshold.

And the Threshold adjustment is an interesting one. It will convert my image to black and white. And I don't mean black and white like a typical black and white photograph. I mean literally only black and white. Only those two tonal values. But the key here is that I can determine where that shift between black and white occurs. So I'll choose that Threshold command and then move the dialog out of the way so I can see the image. And now I can drag upward to increase the threshold value, so that only the very brightest areas of the image are white and the rest are black. Or I can reduce the value so that only the very darkest areas of the image are black and the rest of the image is white.

And because I reduced the Opacity for my background copy layer to 50%, I'm able to see the underlying image peeking through and I can use that to determine when I've established a good value for Threshold. In this case, of course, because I'm using an image with some exaggerated tonal issues, it's relatively easy to see when I've established a good value. I want it to be a high enough value that all of the building becomes dark, but not so high that parts of the sky become dark. And in this case, the range right in between will work well.

Once I've established that value for Threshold, I can click OK in order to finalize the effect. And then I'll bring the Opacity back up to 100%, so that I can see that black and white image. That literally black or white image. And this, essentially, is my selection. I haven't made a selection just yet, but I can do so with just one click on the Channels panel. I'll switch to the Channels panel and then down at the bottom I will click on the first button. The Load Selection from Channel button, and I don't even have to choose a particular channel because all three channels are exactly the same.

White in the sky, black in the building. And so when I click, I get a selection of the white areas, in this case the sky. Of course if I actually wanted the opposite, for the buildings to be selected, I can choose Select and then Inverse from the menu. Once I have that selection I can go back to the Layers panel and turn off the Visibility of my background copy layer or even throw it away altogether just by dragging it down to the Trashcan button at the bottom of the Layers panel. But, as you can see with that simple technique, I've been able to create a selection based on specific brightness values within my photo.

Show transcript

This video is part of

Image for Photoshop CC Selections and Layer Masking Workshop
Photoshop CC Selections and Layer Masking Workshop

51 video lessons · 10349 viewers

Tim Grey
Author

 
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  1. 1m 27s
    1. Welcome
      1m 27s
  2. 46m 26s
    1. Selections, alpha channels, and layer masks, oh my!
      5m 48s
    2. Anti-aliasing and selections
      6m 6s
    3. The case for not feathering selections
      6m 50s
    4. Adding, subtracting, and intersecting
      7m 31s
    5. Inverting a selection
      3m 4s
    6. Mixing and matching selection tools
      2m 32s
    7. Using Deselect and Reselect
      3m 47s
    8. Temporarily hiding a selection
      2m 7s
    9. Saving and loading selections
      6m 14s
    10. Using the cursor for selections
      2m 27s
  3. 51m 42s
    1. The Rectangular Marquee tool
      8m 24s
    2. The Elliptical Marquee tool
      6m 2s
    3. The Lasso tool
      4m 55s
    4. The Polygonal Lasso tool
      6m 27s
    5. The Magnetic Lasso tool
      10m 9s
    6. The Quick Selection tool
      5m 33s
    7. The Magic Wand tool
      10m 12s
  4. 38m 38s
    1. Selecting the border of an existing selection
      1m 50s
    2. The Color Range command
      7m 19s
    3. Focusing a Color Range selection
      2m 55s
    4. Selecting faces with Color Range
      2m 31s
    5. The Pen tool
      5m 40s
    6. Selecting by luminosity
      3m 39s
    7. Selecting from a channel
      6m 13s
    8. Transforming a selection
      4m 4s
    9. Quick Mask mode
      4m 27s
  5. 50m 46s
    1. Combining layers into a single document
      1m 49s
    2. Layering images manually
      1m 55s
    3. Assembling a panorama automatically
      3m 1s
    4. Advanced blending
      4m 0s
    5. Painting to hide and reveal
      3m 24s
    6. Creating a selection-based composite
      2m 43s
    7. Select, then paint
      3m 28s
    8. Advanced mask cleanup
      6m 18s
    9. Creating an edge-fade effect
      2m 23s
    10. Using a filter to add an artistic edge
      3m 6s
    11. Using a brush effect to add an artistic edge
      5m 30s
    12. Transforming a masked object
      1m 51s
    13. Unlinking image and mask
      2m 53s
    14. Matching composite images
      2m 17s
    15. Adding layer effects with masks
      2m 21s
    16. Reviewing layer masks
      3m 47s
  6. 28m 58s
    1. Painting in an adjustment
      3m 20s
    2. Shades of gray
      3m 14s
    3. Using the Gradient tool
      4m 4s
    4. Adjusting a selected area
      1m 42s
    5. Creating a vignette effect with masking
      2m 13s
    6. Using a layer group
      3m 34s
    7. Working with multiple masks
      4m 5s
    8. Refining an adjustment mask
      6m 46s

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