Creating selections in Photoshop can be a painstaking process, oftentimes with mixed results. I learned about luminosity masking by way of exposure blending for landscapes, but its applications are varied.
Luminosity masks, or better yet, luminosity channels, are selections of tonal values in an image that allow you to execute seamless edits as they are perfectly feathered. There are actions you can pay for online to create these masks but the process of doing so yourself is pretty straightforward, so why not invest your cash elsewhere.
Creating Selections for Light Values
Creating selections for the most luminous values in your image is the starting point. To do so, go to your Channels tab and Cmd+Click, or Ctrl+Click for a PC, on the RGB channel. This will create a set of marching ants that represents only the highlights in your image. Next, click the box with a circle inside a rectangle to save this as a new channel. Name the channel “highlights.”
Using our new highlights channel we can now create additional subsets of channels that select only the brighter and brightest parts of an image. Load the highlights channel as a selection by Cmd+Clicking, or Ctrl+click, the thumbnail. Then intersect the mask by Shift+Opt+Cmd+Click, or Shift+Ctrl+Alt+Click, on the highlights thumbnail one more time. Save this selection as “highlights 2.” You now have a channel that contains the next brightest values in the image. Repeat this process as many times as needed by clicking on each consecutive channel, intersecting the mask, and saving it as a new channel. “Highlights 3” is often sufficient but it really depends on what you intend to use the selection for.
It should be noted that this process lends itself well to being saved as a Photoshop action which will eliminate the need to repeat these steps each time. Once complete, your channels palette will look like this:
Creating Selections for Dark Values
Next we can create channels for our darkest values in the image. Start by Cmd+click, or Ctrl+click on a PC, the highlights thumbnail to load the selection. Then invert the selection by holding Shift+Cmd+I, or Shift+Ctrl+I. Finally, save this inversion as a new channel and name it “shadows.”
Now we can again create consecutive subsets of darker values by loading the shadows channel as a selection and performing the same steps as above. Load the most recent channel and then intersect the mask by Shift+Opt+Cmd+Click, or Shift+Ctrl+Alt+Click on the most recent thumbnail. Once complete, your channels tab should look similar to this:
Creating Selections for Midtone Values
Probably the most useful aspect of this technique is the ability to create a selection for just the midtones in your image.
First, hit Cmd+A, or Ctrl+A, to select your entire image. Next, subtract your highlights channel by Opt+Cmd+Click, or Opt+Ctrl+click, on the highlights thumbnail. Then do the same for the shadows channel. Photoshop will signal a warning about the selection edge not being visible because no pixels greater than 50% are selected which is OK. Save this as a new selection and name it “midtones.”
Using the Luminosity Masks
Now that we have our targeted masks, we can have some fun. Here are three simple suggestions for putting them to work.
Selectively Dodge and Burn
Since we can effectively target just the highlights or shadows, we can enhance those areas as well while keeping the edit unnoticeable. For this portrait I wanted to enhance her facial features by dodging and burning certain areas of her face. To do so I loaded the highlights channel as a selection by Cmd+clicking, Ctrl+clicking, on the thumbnail. With the selection loaded, I created a curves adjustment layer and moved the midpoint up just a touch. Then I did the same with a shadows selection except the midpoint was moved down to darken the shadows. Finally, I moved both layers to a group where I applied a black mask and then painted in the adjustments with a white brush just to her face. The edit now appears much cleaner than if I had freehanded as the masks used to create it are perfectly feathered.
With the midtones channel, we can boost saturation and add color in a controlled and subtle manner. Load the midtones channel as a selection by Cmd+clicking, or Ctrl+clicking, on the thumbnail. Create a new Hue/Saturation layer. Move the saturation slider to taste or adjust the individual colors in your image using the dropdown menu and hue slider. In this shot below, I wanted to boost the fall colors so I adjusted saturation and changed the hue of the greens and red.
Increase Dynamic Range
Luminosity masks are perfect for landscapes where you have extreme highlight and shadow information. This shot of the sunrise consists of four images to retain the sun’s outline and the wavy foreground with each being about a half stop darker than the last. I loaded all four images into Photoshop and stacked them darkest to lightest. With just the first two layers visible, I added a black layer mask to the second. Then I loaded my highlights channel as a selection and with a white brush set to around 20% opacity and 0% hardness, I painted the areas around the sun to bring back its detail. Then I did the same to each consecutive layer above but used highlights 2, and finally 3. This was the result:
The uses for luminosity masks are limitless and only require a little imagination. By saving these steps as actions you can create them quickly and use them to selectively edit your images with precision. As always, constructive feedback and suggestions are appreciated.