Luminosity Masks: An Idiot’s Guide

By YaopeyLuminosity masks, Tutorials

Luminosity masks are highly selective, targeted and customizable (to some extent) selection tool in Photoshop and GIMP. Its best-known feature is self-feathering border making transition seamless.

This technique is often adopted by (but not limited to) landscape photographers in their post-processing workflow.|

Understanding how luminosity masks work can be daunting especially for beginners. Some gave up completely in the early stage of learning because it sounds complicated.

In this tutorial, I will explain how luminosity masks work in the simplest form with the help of the gradient map. The intention of this article it to help those who struggle making sense of luminosity masks.

This article is meant to compliment The Kickstarter’s Guide To Luminosity Masks.



Luminosity Masks In Brief

Luminance, marching ants, brights, darks and midtones masks are among the keywords associated with luminosity masks.

marching ants luminosity masks

Forget about those.

All you need to remember is that it is a selection tool. Like the magic wand or the quick selection tool you’re familiar with.

Simple enough?

Now, let’s take it one step further:

It is a selection tool based on the luminance of the pixels (I’ll explain further below).


The Anatomy of A Luminosity Mask

the anatomy of a luminosity mask

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

The area within the marching ants will be white on the layer mask. This means the part of the image underneath this will be revealed.

Conversely, the area outside the selection is unselected. This means it will be black on the layer mask and the part of the image underneath it will be concealed.

The line formed by the marching ants is not the border of the selection.

In fact, it’s the midpoint of the feathering transition.

Simple and sweet!


Luminance of The Pixels

Allow me to explain before you click on “X” to close this window.

The sentence is not as complex as it sounds if you break it down into small chunks.

Luminance essentially means brightness or lightness. The level of brightness is defined by the amount of black or white added to a color.

luminance or brightness

Pixels, on the other hand, are the building blocks of a rasterized image.

To visualize it yourself, go ahead and open up an image in Photoshop. Select the zoom tool and zoom into the maximum until multiple square boxes appear.

Each of these square is a pixel!


Selection Based On The Brightness of The Pixels

Now that you’re clear about luminance (a.k.a. brightness) and pixels, the rest is simple.

Luminosity masks make a selection according to the brightness of the pixels. There are 3 types of masks:

Brights, darks and midtones masks.

You can use each of these to target select a particular part of the image.

For example, you want to reduce the brightness of the sky without affecting other parts of your image. Use a brights mask targeting the areas you want and apply a Levels or Curves adjustment to it.

That’s all it is to luminosity masks!


Why Gradient Map?

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

It helps you to visualize what we’ve talked about so far, the luminance of the pixels and making selection based on that.

You can also experiment the different types of luminosity masks on the gradient map. Add, subtract and intersect to see the different areas selected by each mask.

Keyboard Shortcuts To Select Luminosity Masks:

Cmd / Ctrl + left click = Select a mask
Cmd / Ctrl + Shift + left click = Add a mask
Cmd / Ctrl + Opt / Alt + left click = Subtract a mask
Cmd / Ctrl + Opt / Alt + Shift + left click = Intersect masks

Remember The Rules of Layer Masks:

Black conceals, white reveals and gray partially conceals/reveals depending if it’s closer to black or white.


Luminosity Masks And The Gradient Map

gradient map

The black and white gradient map is easy to understand.

It starts with pure black on the far left with a gradual transition to the pure white on the far right.

Intuitively, white has the highest luminance and black has none. This makes the middle 50% luminance.

You can create your own gradient map or download this PSD file which contains a gradient map as above and all 18 luminosity masks in the Channels panel. Alternatively, create your own gradient map in Photoshop and generate luminosity masks with the Luminosity Mask Photoshop Action.


The Brights, Darks And Midtones Masks

brights darks midtones gradient luminosity masks

Before you start, go to the Channels panel and check out the brights, darks and midtones masks. Look through 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), creating a smooth transition.

As you move from Brights 1 to Brights 6, you’ll notice that the area being revealed becomes smaller and the area being concealed becomes bigger. In Brights 6 mask, the area in white is significantly smaller compared to the Brights 1 mask.

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

The Brights 1 And The Darks 1 Have The Most Area Selected

So, this is how it works:

Brights 1 and Darks 1 reveal all of the brightest and darkest part of the image respectively. As you move through each mask, the area being revealed becomes more restrictive.

For the brights masks, this means Brights 1 reveals all the pixels that are bright and Brights 6 reveals the brightest of the brights.

This goes the same for the darks masks. Darks 1 reveals all the pixels that are dark and Darks 6 reveals the darkest of the darks.

Makes sense?

The Unique Midtones Masks

The midtones masks are a bit different. As the name implies – midtones. So, it’s in the middle of the gradient map.

But here’s what’s interesting.

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

midtones 1 luminosity mask
Midtones 1 mask

This is because the Midtones 1 mask reveals all the true midtones. If you look at the gradient map again, the true midtones are right in the middle (and not a very wide area).

As you move from Midtones 1 to Midtones 6, the area being revealed becomes more as more “non-true” midtones are also included.


Understand Luminosity Masks Through Visualisation

Nothing is better than working through yourself and seeing the results.

To start off, select the Brights 1 mask to see the area it covers. Note how half of the gradient map is selected. Work your way to Brights 6 mask and you should see the selection gets narrower towards the far right.

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


Adding, Subtracting And Intersecting

You may need to refine the selection made by one of the luminosity masks at times. The most efficient way of doing this is actually with one of the premium luminosity masks panel.

Before you do that, I high recommend you spend some time experimenting with adding, subtracting and intersecting luminosity masks to see the selection you can get.

Doing so will help you understand it more in depth and it will also make more sense when you have a luminosity masks panel.

I’ll give you an example here.

Subtracting Darks Masks

subtracting darks masks
Subtracting Darks 3-6 from Darks 1

In this example, I’ve selected Darks 1 and subtracted Darks 3-6 from it. The result can be seen in the image above where the selection is.

You’re thinking: “what is this?!”

This is a technique used to brighten up shadows without losing its contrast. The details are covered in The Kickstarter’s Guide To Luminosity Masks.


Luminosity masks is not rocket science but it does require a bit of imagination and time to digest.

The easiest way I found is to use the gradient map and just play around with the masks to see its effect.

Once you understood how brights, darks and midtones masks work on the gradient map, move forward by using an image. Every image is different and the use of luminosity masks is really trial and error in most cases.


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