Two Simple Techniques for Creating Luminosity Masks in Affinity Photo

by Jul 8, 2022Photo Editing Tutorials

Robin Whalley Landscape Photographer

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Two Simple Techniques for Creating Luminosity Masks in Affinity Photo

If you come from a Photoshop background and have tried creating luminosity masks in Affinity Photo you may have been disappointed. Photoshop has lots of tools and plugins to help you create Luminosity Masks whilst these don’t exist in Affinity Photo.

In the past, I’ve produced tutorials and videos trying to help with this problem. Whilst they work, they aren’t always easy to follow, and they aren’t very flexible. So, I’ve put on my thinking cap and may have a solution.

In this tutorial I’ll share two easy ways you can use to create high quality Luminosity Masks in Affinity Photo. The second method is by far the more powerful and flexible but is still relatively simple. All you need to know for that is how to use the Curves Adjustment layer, which is the same in Photoshop and Affinity Photo.

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Method 1 – Creating Base Lights Luminosity Masks

Our first step is to produce base Lights Luminosity Masks which we can use to target the light tones in an image.

In Affinity Photo, open the image that you want to work with and add a new Black and White Adjustment Layer. You can do this by clicking the Adjustment Layer icon at the bottom of the Layers Studio Panel and then selecting Black and White from the list of layers.

Adding a new black and white adjustment layer in the layers studio panel

You will then see the black and white controls dialog displayed. This is used to control how light or dark a colour appears when converted. For creating luminosity masks, you don’t need to do anything with this and can close the dialog.

The black and white image you now see is our first basic Luminosity mask for selecting the light tones in the image. Some people call this the Lights 1 mask.

Saving the Lights Luminosity Mask

You now need to save a copy of this mask so that you can use it in the future. You can do this in the Affinity Photo Channels Studio Panel.

After selecting the Channels Studio Panel, you will see the composite red, green, and blue channels at the top. Click the red channel to select it. You could use one of the other channels instead, but they are all the same because this is black and white image.

Selecting the Composite Red Channel in the Channels studio panel

Right click the red channel with your mouse to display a popup menu. In the menu select the option to “Load to Pixel Selection”. This will create a selection based on how light or dark the pixels of the image are.

Having loaded the selection, you will see the marching ants on the image, indicating an active selection. You will also see the “Pixel Selection” in the Channels Studio Panel now has a small thumbnail representing the selection.

Next, right click with your mouse on the “Pixel Selection” in the Channels Studio Panel. Then in the menu select “Create Spare Channel”. You should now see a spare channel created at the bottom of the Channels panel.

It’s a good idea to rename the new spare channel by right clicking with your mouse and selecting the rename option in the menu. You can call this new spare channel “Lights”.

Creating a Darks Luminosity Mask

Having saved our Lights luminosity mask the selection we used should still be active. We can now use this to create a base Darks luminosity masks. This luminosity masks is used to target adjustments onto the dark tones in the image.

Start by inverting the active selection. You can do this in the Affinity Photo Select menu where you will find the “Invert Pixel Selection” option. When you click this, you will see the marching ants on the image change as they are inverted. You should also see that the thumbnail of the “Pixel Selection” in the Channels Studio panel becomes inverted.

Now we need to save the Pixel Selection to a new spare channel as we did before. You should do this by right clicking the “Pixel Selection” in the Channels Studio panel with your mouse. Then in the popup menu selection the option “Create Spare Channel”.

Rename the new channel by right clicking it at the bottom of the Channels panel. Call this spare channel Darks.

Now you can clear the active selection in the Affinity Photo. Do this in the Select menu by clicking the “Deselect” option.

When you click on either the Lights or Darks spare channels in the Channels panel you are able to view those channels. Here is an example.

Lights and darks luminosity masks in Affinity Photo

For many applications of luminosity masking like dodging and burning and even exposure blending, these two basic masks are sufficient.

It’s also possible to use the two masks to create a basic Midtones mask selecting the image midtones. You can do this by subtracting one mask from the other in the popup menu by right clicking the channel. There is though an easier way to produce midtone mask and one that gives much greater control. Let’s look at that next.

Method 2 – Adding a Lights Curves Adjustment Layer

Let’s go back to the Layers Studio Panel and add a new Curves Adjustment Layer.

As before, click the new Adjustment Layer icon to the bottom of the Layers panel. Then in the popup menu select the “Curves” option.

You should now see the new Curves layer in the Layers panel and the open Curves dialog.

Adding the new Curves Adjustment Layer

It’s a good idea to rename this Curves layer to be “Lights” because we will use it to produce our Lights luminosity masks.

Earlier we said that the Black and White image is a base Lights luminosity mask. This is also what you see before you adjust the Curves layer. But if we apply an S-shape curve we can modify our luminosity mask.

Here’s an example of the curve and it’s effect on the image.

Applying an s-shape curve to create the Lights mask

If we convert this black and white image to a mask it will still target the lighter tones in the image but less of the darker areas than the basic lights mask. Best of all, we can continue to refine this curve until it targets the areas of the image that we want.

As before, you can load the image to a selection using the composite red channel in the Channels panel. You can then save the selection as a spare channel or use it to edit the image.

Now let’s look at how to create a similar Darks curve to target dark areas of the image.

Step 3 – Adding a Darks Curves Adjustment Layer

Back in the Layers Studio Panel you should hide the Lights Curve layer added above before continuing.

Now add a new Curves layer to the image and call this Darks.

In the Curves dialog, click the bottom left corner of the curve line and drag it to the top. Then click the top right end of the curve line and drag it to the bottom. This creates an inverted curve line running from top left to bottom right.

Creating the Darks curve luminoisty mask

The effect on the image is produce a negative which is the same as Darks luminosity mask we saved earlier. We can then adjust the shape of the curve to target the areas of the image that we want.

Darks luminosity mask in affinity photo

We can continue with this approach by adding a third Curve to produce a Midtones luminosity mask that target the midtones of the image. But rather than continuing with the written instructions, it’s best to see the process in action.

Creating Affinity Photo Luminosity Masks Video

Watch the following video which explains the entire process for creating Affinity Photo luminosity masks. As well as demonstrating the Curves technique for lights, darks and midtone luminosity masks, the video shows applying them to an image.

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This tutorial has explained two ways that you can create luminosity masks in Affinity Photo. The first is the most basic which only produces two luminosity masks; one targets the light tones in an image and the other the darks. The second method is much more powerful and can even be used interactively to target image tones precisely.

I hope that you’ve found this tutorial helpful. Now expand your Affinity Photo skills further with my  “Affinity Photo How To” book.

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You’ll find more high quality, free tutorials on my Affinity Photo Tutorials page.

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