Masking different layers based on brightness is an often tricky but vital Photoshop skill to have. There’s a bunch of different ways of doing it from the simple to the advanced. Two of the most common methods are by using Luminosity Masks or with Photoshop’s “Blend If” layer options.
While the two might appear to do similar things on a quick glance, there are some pretty distinct differences between the two. Black Rudis from F64 Academy looks into both methods to show us how they work. Each has advantages over the other depending on what you’re trying to achieve. And both will let you do things that the other simply cannot.
The key difference to note between the two is that luminosity masks are generally static once they’re created. Unless you go in and manually alter them, they just stay as they are. Blend If, on the other hand, is more of a dynamic effect. As you do things to the layer, it automatically effects what is clipped out or left in by the Blend If options.
You can see this difference demonstrated here when a curves adjustment is applied to the underlying layer. The selected area of brightness, highlighted in hot pink, is about the same between the two methods with the default image. But, once the curves adjustment is applied and the layer brightened, we see some pretty drastic changes to the layer using Blend If. The luminosity mask, however, doesn’t change.
Sometimes you want that selection to remain static throughout the changes in your image. At other times, you really need it to update dynamically as you alter the underlying layers. What’s important is to know when each method will work best for the situations you find yourself in.
There are also times when you may need to combine the two methods. I often find myself using luminosity masks and Blend If together in the same layer to help refine a selection.
You can even nest them inside a group and apply a new mask to that without destroying the information contained on the layers within the group. I use this one often when shooting portraits on location.
In the above example, there’s a small bit of wall I want to reduce the highlight from. The luminosity mask shows the brightest areas from the entire scene, including parts I don’t want to affect. Nesting this layer and adjustments inside a group allows me to only have it work its magic on that one specific area of the wall. Not the window, not my subject, or the parts of the wall I want to be bright.
In my regular use, I tend to find myself using luminosity masks far more often than Blend If, but both have their place.
Which method do you find yourself using the most? Or is it a pretty even mix between the two? What other Photoshop selection tools do you use often? Let us know in the comments.
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