An Idiot’s Guide To Making Sense of Luminosity Masks

(Updated September 2018)

Luminosity masks are highly selective, customizable selection tool in Photoshop to help you apply targeted local adjustment that blends naturally in your image.

To be able to use luminosity masks, you need:

In this tutorial, you'll start off by learning how luminosity masks work. Then, visualize the masks in gradient map and lastly, see how it is applied as a layer mask. The intention of this article it to help you make better sense of luminosity masks.

I use Adobe Photoshop, don't worry if you use other software. The steps might be different but the principles are the same.

Luminance, marching ants, brights, darks and midtones masks are among the words you hear with luminosity masks.

Now, I want you to forget about these just for a minute.

All I want you to know for the time being is that it is a selection tool and a layer mask (more of the latter later). It works exactly the same as other selection tools such as the Magic Wand tool or the Quick Selection tool that you might be more familiar with.

That wasn't too complicated, was it?

Now, let's take it a step further...

The difference between luminosity masks and other conventional selection tools is that it creates selection based on the brightness value of the pixels. This means you don't need to physically draw the selection with your mouse cursor.

Don't worry if that didn't make sense. Let's try a different way of explaining things.

Ordinarily, to create a selection, you'll have to pick a selection tool from the menu. These allow you to draw a selection with a circle, square, free-hand, etc. The selection is created based on where you click with your mouse cursor.

With luminosity masks, you don't have to draw the selection manually. The "action" analyzes the brightness of every pixels in the image and automatically creates a set of what is known as brights, midtones and darks luminosity masks. All you have to do now is to choose from a selection of masks you have created and use that as a selection.

Understand better now? Let's take a closer look at brightness and pixels!

Brightness, lightness or luminance, it all means the same thing. The level of brightness is defined by the amount of black or white added to a color.

Pixels, on the other hand, are the building blocks of a rasterized image (JPEG, TIFF, Raw image, etc. are all rasterized image).

To visualize pixels yourself, open an image in Photoshop. Select the Zoom tool and zoom in to the maximum until you see multiple square boxes.

Each square is a single pixel!

It's actually very simple, right?

Now that you're clear about luminance and pixels, the rest is fairly straight forward!

Luminosity masks create selections based on the brightness of the pixels. There are three types of masks:

Brights, darks and midtones luminosity masks.

Using these masks, you can target select parts of the image with a single or a combination of luminosity masks. 

For example, if you want to reduce the brightness of the sky without affecting other parts of your image, use a brights mask targeting the sky (because the sky is bright in the image) and apply a tonal adjustment layer to it.

I found the black and white gradient map intuitive when it comes to demonstrating how luminosity masks work.

It will helps you to visualize what we've talked about so far - luminance of the pixels and creating selections based on that.

I encourage you to experiment with luminosity masks on the gradient map. Add, subtract and intersect the masks to see how it changes. Below are the keyboard shortcuts you need.

When you click on a luminosity mask, marching ants will appear around the selection.

The area within the marching ants (the selected areas) will appear white on the layer mask. This means parts of the image covered by the mask will be revealed.

Conversely, the area outside the selection is unselected. This means it will appear black on the layer mask and parts of the image covered by it will be concealed.

The lines formed by the marching ants are not the border of the selection but the midpoint of the feathering transition. So, don't be fooled by the marching ants thinking that's the area being selected - the actual selection is always beyond where the lines are!

Go to the Channels Panel to find the three groups of masks: brights, darks and midtones. Go through the masks in each group and the area the masks reveal and conceal.

Let's start with the brights mask. Brights 1 has almost half of the gradient map selected (the area in white). It feathers into the black (which conceals) in a smooth transition.

As you move from Brights 1 to Brights 6, you'll notice the area being revealed becomes less and the area being concealed becomes more. If you pay closer attention, you'll also notice that Bright 6 has the whitest of the whites. This means the selection is on the brightest area of the image.

To summarize, Brights masks select the bright areas of the image with Brights 1 selecting all the brights and Brights 6 selecting only the brightest. Brights 2-5 fall into the transition between Brights 1 and 6.

Now look at the darks masks. It's basically the reverse of the brights masks.

Similar to the brights masks but in reverse. Darks masks select the dark areas of the image. As you move through each mask, the area being selected becomes more restrictive.

When you move from Darks 1 to Darks 6, you'll notice the area being revealed (white) becomes less and the area being concealed (black) becomes more. You'll also notice that Darks 6 has the whitest of the whites. Because it's a dark masks, this means the selection is on the darkest area of the image.

So, to summarize, Darks masks select the dark areas of the image with Darks 1 selecting all the darks and Brights 6 selecting only the darkest. Brights 2-5 fall into the transition between Darks 1 and 6.

 I hope that makes sense!

The midtones masks are a bit different. As the name implies - midtones. It's in the middle of the gradient map.

But here's what's interesting.

As opposed to the brights and the darks masks, the area being revealed becomes more as you move from Midtones 1 to Midtones 6.

Midtones masks can be challenging to understand. The best way I found is to visualize using the gradient map!

Scroll up to the collection of brights, darks and midtones masks above. In the first row, you'll see Brights 1, Darks 1 and Midtones 1. Midtones 1 is essentially the area that isn't covered by white in both Brights 1 and Darks 1!

As you move from Midtones 1 to Midtones 6, the area being selected becomes wider. All of these correspond to the areas not being selected by the respective brights and darks masks.

To summarize, the area being selected by Midtones masks increases from Midtones 1 to Midtones 6.

The easiest way I found to understand luminosity masks so far is to experiment with it and visualize the result with the gradient map.

To begin with, select Brights 1 mask and see the area it selects. Note how half of the gradient map is selected. Work your way to Brights 6 mask and you should see the selection gets narrower until only the brightest of the brights are selected.

Do the same for the darks and the midtones masks. It will give you an instant visualization on the selection of each mask.

So, essentially, luminosity masks is a layer mask.

Don't get confused with the terminology, both mean the same thing!