Luminosity masks are incredibly powerful image editing tools. It allows you to make targeted and seamless self-feathering selections in your image to apply literally any adjustments. Why is this relevant to you? Good digital image editing is all about applying the right adjustment at the right place. Gone are the days of mass global adjustment. Local adjustment is now the way forward. If you want your images to look professional, you got to use the tools professionals use. In this post, you will get a comprehensive overview of what luminosity masks are, how it works, its application and some pitfalls that you may encounter. Let's dive right in!

The Kickstarter's Guide To Luminosity Masks

1. What Are Luminosity Masks?

First described in Good Light Journal in 2006. Since then, it has been refined and improved, including the creation of 16-bit masks and infinity masks

Essentially, layer masks on steroids.

A selection tool using the luminosity (i.e. brightness) of pixels in an image as the selection method.

The difference compared to other selection tools is that it has "in-built" self-feathering that blends any selection it creates seamlessly back into the image.

Not found in the menu in Photoshop. Can only be created manually or using Photoshop Actions in the Layers Panel.

Multiple applications in post-processing workflow including selective adjustments and blending.

Luminosity = Brightness

Essentially we are talking about the brightness of pixels. A pixel is the building block of an image. Thousands and millions of pixels of different color make up an image. Every pixel has a luminosity value (0-100%). This determines how bright or dark it is. The different level of brightness in each pixel determines if it’s being selected or not. The area of the image selected is based on the type of luminosity masks you choose (more explanation on that later).

Using Brightness To Create Selections

Unlike other selection tools in Photoshop, luminosity masks allow you to create highly targeted selection with seamless feathering. Why is this so important? Let me ask you this: Have you tried creating a selection of the sky but just can't get what you want selected properly? There will always be parts that get left out or unwanted parts included in the selection. Using luminosity masks, you can achieve that desired result more efficiently.



2. How To Use Luminosity Masks?

This might sound like a surprise, but... You can literally use it to apply any kind of adjustment you want. The possibility is only limited by your imagination! In fact, I encourage you to experiment with this technique and try to think outside the box. In fact, this was exactly how I created this image below. Although this technique is more commonly used in landscape photography, you can apply it in any kind of images. I have personally used it in architectural, cityscape and portrait images.

For the purpose of this tutorial, these are the commonest scenarios to apply a luminosity mask: Exposure blending and selective adjustments.

Exposure Blending

As the name implies, it involves merging images of the same frame but taken at different exposure. In photography, the process of merging images can also be called blending. Images are often blended together to create a high dynamic range (HDR) image. You can learn more about HDR in the HDR Photography resource page under Articles in the top menu. "But, aren’t there HDR software to do that already?" You’re absolutely right, there are plenty! But some photographers don’t like the so-called “HDR look” created by HDR software. These images are typically oversaturated and unnatural looking. The main advantage of blending over HDR software is that you can decide where and how much you want to blend the images. With luminosity masks, you have more control and flexibility over this process. The blended image is often thought to be cleaner and more natural, especially among nature photographers.

Targeted Local Adjustments

The image above shows what local adjustment is. With luminosity masks, I applied a Curves adjustment to reduce the highlights in the sky without affecting other parts of the image. The Curve adjustment to the highlights is targeted and localized to the sky only. Global adjustments throughout post-processing is a thing in the past now. Yes, we still do that but sparingly. What makes more sense now is targeted local adjustments. Let's take the above image for example again. To select the sky, you'll have to use a selection tool. This process can be time consuming depending on the complexity of the image and you probably have to refine the selection a few times. Still, the result may not look as natural as you like it to be. It’s frustrating, unproductive and increases unnecessary time spent in post-processing. With luminosity masks, you can get the selection quick, precise and with seamless feathering that allows any adjustments to blend in naturally.

3. What Software Do You need?

Personally, I use Adobe Photoshop. I think it's a very robust and versatile software. To be able use the software, you need pay a low monthly subscription fee (Adobe Creative Cloud) to get both Photoshop and Lightroom under the photography bundle. You check out their free trial here. Again, personally, I think it’s of good value. I know there are many who think otherwise and that's ok. The bottom line is, Photoshop is not the only software you can use luminosity masks. Among other software that support the use of luminosity masks are GIMP (freeware) and Affinity Photo, which has a slightly different way of applying luminosity masks.

4. Where Is It In Photoshop?

Luminosity masks is not a standard tool in Photoshop. By that I mean there isn't a menu or an icon where you can click to access it directly. It's actually tucked away in the "hidden corner" called the channels panel. By default, Photoshop only generates three color based luminosity masks for every image: red, green and blue. As you can see, our choices are going to be very restricted if we were to use the default masks. So, we need to create more variations. We'll go through the steps on creating the masks later on.

The Brights, Darks and Midtones Masks

A set of luminosity masks targets all three main zones of an image: the highlights, the shadows and the midtones. These are often called brights, darks and midtones masks. Similar to a layer mask, white reveals, black conceals and grey partially reveals or conceals depending on the luminosity value.

5. How To Create Luminosity Masks In Photoshop?

Creating a set of luminosity masks manually is extremely time consuming. You will need about 5 minutes to create the masks for every image. The solution? Automation! It’s all about working smart, not hard! Here are a few ways to automate the process of creating the masks.

1 Create the masks manually once, record it and save it as a Photoshop Actions. You can then automate the process the next time you need it.

2 luminosity masks Photoshop Actions here for free. Download thehere for free.

3 Download one of the free Photoshop luminosity masks panel which I’ll explain later.

Just so you know how luminosity masks are created, we'll go through the process step-by-step.

Creating Masks Manually

You’re going to use the channels panel, rather than the layers panel that you normally work in. I use a Mac, so bear in mind that Cmd = Ctrl in a PC and Opt = Alt. Remember to save it as Photoshop Actions so you don’t have to repeat this painful process again.

1 Open your image in Photoshop.

2 Go to the channels panel.

3 Cmd + click on RGB and save the selection as a new channel by clicking the little button at the bottom of the channels panel that looks exactly like the layer mask icon.

4 Now you should see the new channel saved as alpha 1.

5 Without deselecting, hold down shift + cmd + opt and click on alpha 1 to intersect the selection.

6 Again, save it as a new channel by clicking the little button at the bottom. You should now see it saved as alpha 2.

7 Repeat step 5 and 6 until you reach alpha 6.

8 Now rename all alpha 1-6 to brights 1-6. These are your luminosity masks for highlights.

9 Now deselect the selection by holding cmd + D. We’re now going to create the dark masks (which are the inverse of brights masks).

10 Cmd + click on RGB again. Now we need to inverse the selection by shift + cmd + I. Save this as a new channel by clicking the little button at the bottom again.

11 You should see it saved as alpha 1 (this is because you have renamed the previous alpha 1 to brights 1. Don’t worry about the name as you are going to rename it later).

12 Without deselecting, hold down shift + cmd + opt and click on the new alpha 1 to intersect the selection. Save this as a new channel, which should be alpha 2.

13 Repeat step 11 and 12 until you arrive at alpha 6.

14 Now rename the new alpha 1-6 to darks 1-6. These are your luminosity masks for shadows.

15 Cmd + D to deselect everything. Now we need to subtract shadows from the brights to create the midtones masks.

16 Select everything by Cmd + A, then hold down cmd + opt + left click on brights 1 and then darks 1 to subtract both.

17 Save the selection as a new channel by clicking the little button below. It will be saved as alpha 1 (again, don’t worry about the name).

18 Repeat step 16-17 for brights 2 and darks 2, brights 3 and darks 3, etc. until you arrive at alpha 6.

19 Rename all new alpha 1-6 to midtones 1-6. These are your luminosity masks for midtones.

Photoshop Automation Panel

Created by photographers for photographers, these are designed to enhance your experience in using luminosity masks. Besides creating the basic masks, each luminosity masks panel offers different features and tools for post-processing. Below is a list of free luminosity masks panel. Each of them also has a premium version which has more advanced features.

Do you need a panel to use luminosity masks? - Absolutely not! I didn't get one of these until recently. These are meant to make your workflow more efficient. Each panel works works differently and obviously has different layout. My suggestion is to try on the free panel before you take out your credit card! If you like to read reviews of these panels, here's a comprehensive article on that.

6. How To Work With Luminosity Masks?

The principles of luminosity masks are exactly the same as layer masks:

Black = Completely conceals.

Grey = Gives the layer different levels of transparency depending on the amount of grey there is .

White = Completely reveals .

A layer mask only affects the layer it applies to (i.e. the layer below).

3 Important Rules of Luminosity Masking

Let’s say a set of luminosity masks has 18 masks (six brights, six darks and six midtones):

Bright masks – The brightest areas are in white, less bright areas are in different shades of grey and the shadows are in black. The selected area becomes less from brights 1 to brights 6.

Dark masks – The darkest areas are in white, less dark areas are in different shades of grey and the highlights are in black. The selected area becomes less from darks 1 to darks 6.

Midtones masks – All masks are filled with different shades of grey. More midtones are selected in midtones 6 than midtones 1.

Luminosity masks is a way of creating layer masks. The advantage of it over other selection tools is its ability to produce highly targeted and customizable selection with seamless feathering. Once you have the selection you need, you can then apply any adjustments to it - different kinds of tonal, color adjustments, sharpening, etc.



7. How To Apply Luminosity Masks - Case Studies

Now that you've learned the basics of luminosity masks, I feel it's time to dive into some action! We'll go through the two main applications of luminosity masks:

Digital exposure blending

Targeted local adjustment

Digital Exposure Blending

Exposure blending is a post-processing technique to blend images of different exposures together. Its aim is to create a high dynamic range (HDR) image without the need to use an HDR software. The post-processing time is longer than an HDR software but the image is often more tonally balanced and natural. What’s more? Exposure blending stimulates your creativity, gives you total control of your image and forces you to learn how to post-process images yourself instead of relying on presets or filters. To give you an example, I’m going to use the image of the Pantheon taken in Rome.

Shoot Multiple Exposure To Include The Whole Dynamic Range

In the first image, I’ve exposed for the foreground (the buildings), which left the background (the sky) overexposed. This is because the dynamic range of the scene had exceeded what my camera could capture. Exposure bracketing was necessary to ensure the full dynamic range was captured. Even though the shadows between the pillars seem dark, I know from the histogram that there’s no shadows clipping and I could recover the details in post-processing.

In the second image below, I’ve taken it to expose for the background (the sky), which left the foreground (the buildings) underexposed.

The aim here is to blend the foreground in the first image with the background in the second image using luminosity masks.

Create Luminosity Masks For The Base Image

I opened both images in Photoshop. I used the first image as the base image to create a full set of luminosity masks. My aim was to replace the overexposed sky with the sky in the second image. Because the area I wanted to replace was bright, I needed to use a bright mask that targets only the sky. With a single click, I used Photoshop Actions to create all 18 luminosity masks without having cramps in my fingers.

These were the 6 bright masks in the channels panel. I wanted to pick one that has only (or most) of the sky selected (in white). I also wanted to exclude the buildings from my selection, so the buildings should be in black (or darker shades of grey). Looking through the bright masks, I thought Bright 2 or 3 were the most suitable ones. I picked Bright 2 in this case.

There Is No Right or Wrong In Which Mask To Use

Experiment is often the key to success in blending and post-processing in general. I encourage you to experiment with different masks (maybe start with the adjacent ones) to see which gives the best result.

For exposure blending, here's what I did:

1 Place the first image as the first layer and the second image as the second layer.

2 Align the images by going to Edit > Auto-Align Layers. I did this because I shot the bracketed exposures handheld.

3 Create a layer mask for the second image and fill it with black to mask everything. Now you should only see the first image because the second image is now invisible.

4 Cmd + click to select Bright 2 luminosity mask from the channels panel and then click on the layer mask on the second image in the layers panel. You should now see the marching ants, which means selection from the luminosity mask you selected is now active.

5 Now select the brush tool, set the size to large and hardness to 0 (you want a large, soft brush). Make sure the foreground is set to white and start painting the layer mask in the sky to reveal the sky in the second image (top layer).

6 If you find the marching ants annoying (which I often do), cmd + H to hide them. The selection will still be there but you won’t see the marching ants now.

There are certainly other ways to blend images and this is just one way to do it. It's a relatively straightforward example of how to blend images with luminosity masks. There are other advanced blending techniques with luminosity mask. I have provided some useful links at the end of this tutorial if you like to learn more.

Targeted Local Adjustment

Another way of using luminosity masks is to apply adjustments in targeted areas only. To do this, I highly recommend you use a RAW or TIFF file instead of a JPEG because of bit depth. You want the highest number of colors available to avoid posterization. For demonstration, I'm going to use this image below to show you how to apply localized tonal adjustments with luminosity mask. The image was taken near midday so the it looks a bit flat and washout. Let’s bring it to live!

Creating Luminosity Masks

You can probably see a routine here... Everything starts with “create luminosity mask” for the image.

Applying adjustments through a luminosity mask

These are the layers I’ve applied to the image. Let’s go through it together!

1 Layer 0 : I double clicked the background image to convert it to a layer.

2 Layer 1: Curves adjustment layer applied to a Brights 2 to reduce the highlights.

3 Layer 2: Levels adjustment layer applied to Darks 6 to brighten the shadows of the cactus.

4 Layer 3: Curves adjustment layer applied to Brights 3 to reduce the highlights further. I changed the blend mode to multiply.

5 Layer 4: Curves adjustment layer applied to Midtones 2 to bring up the overall contrast with a S-shaped curve. I changed the blend mode to luminosity to preserve the color saturation.

6 Layer 5: Vibrance adjustment layer to boost the overall color.

7 Layer 6 & 7: Dodge and burn with various brights and darks masks targeting only the clouds and the shadows of the cactus.

8 Layer 8 & 9: Overall dodge and burn to create a vignette.

Here’s the before and after.

Subtle Transformation Keeps Your Image Looking Natural

The adjustments are subtle but it does make the image look more contrasty. That’s the advantage of post-processing with luminosity masks. You apply subtle changes to parts of the image but everything adds up to the overall effect. There's one more thing: If you look at the top right-hand corner (the deep blue sky), the tone and color have not changed because it was protected by luminosity mask. This wouldn’t be possible if we’ve applied the adjustments globally. Even with layer masking, the transition wouldn’t be as smooth.

8. Challenges In Luminosity Masking

Luminosity masks are great tool but not a perfect tool. It does have some limitations. In this section, I'm going through some common ones you may encounter in your workflow and show you how to overcome these pitfalls!

Halos

A pain and an unsightly problem. It's caused by a significant difference in the brightness of each bracketed images. The interval between the bracketed exposures is too wide and there isn’t enough tonal information to fill in the gap. This typically happens in high contrast scenes like this. It was in the evening but the sun was still very bright. I spotted an interesting rock formation and used it to frame the sun. I’ve bracketed 3 exposure as below. As you can see, the brightness in the +2EV is greater than the brightness in the 0EV and the -2EV. The result? There is a big gap between the brightest and the darkest image, and there is only 1 image in between for tonal transition.

What could I have done differently? Take bracketed exposures at a closer interval to ease the transition from the darkest to the brightest. In this case, 5 or even 7 bracketed images with 1EV apart (or even smaller) may have helped to reduce or even avoided the halos.

Flattened Shadows

It may seem intuitive to brighten the shadows with a darks mask when you want to see more details in the shadows. It works for highlights so it should work the same for shadows, right? Unfortunately not. Why is that? If you see the luminance mask on the far left below (Darks 2), the whitest part falls on the darkest area of the rock. This means the darkest shadows are all selected. And the problem: If you brighten that up, all the shadows, including the darkest shadow will be brightened. This causes the image to lose overall contrast and becomes flat.

Subtracting Darker Masks From A Dark Mask

You want to brighten the shadows and maintain the contrast at the same time. If you think about it: Contrast is when there is a difference in the darks and the brights. This means preserving the darkest shadows (maybe you can brighten it up a little) while brightening the less (or least) dark shadows. To do that, select a dark mask and subtract the darkest darks to preserve the darkest shadows. (luminosity masks shown below)

Edging

Dark or bright edges sometimes occur when you try to blend images with high contrast together (it’s always high contrast causing problem!). It often appears on the outlines such as tree branch (in this case), rocks or mountains. It’s actually not easy to spot them without zooming into the image. If you can’t see it, why fix it? You're right. But if you happen to print your image large, it will show up and ruin your print. On the other hand, fixing it only takes a few minutes and there’s no reason not to do it.

In this example, you can see the edges of the blue sky painted over the tree branch on the right. On the left, it did the opposite, leaving a white edge between the blue sky and the tree branch. The way to fix it is to reverse select and paint over it. I’ll explain.

Fix Edging With Reverse Selection

To fix the white line on the left, select the magic wand tool in Photoshop. Set the tolerance to 15 (in this case) and make a selection of the tree branch. Now, modify the selection by going to Select > Modify > Contract, and retract the edge of the selection by 1 pixel to exclude the white line from the selection (2 or 3 pixels if you have a thicker white line). Inverse the selection so that the sky and the white line are now selected instead. The next step is easy. Select the brush tool, change the foreground color to the color of the sky by opt/alt + click on the sky and paint it over the white line. For the over-painted area on the right, do the same except select the sky first and inverse the selection after. The inverse selection method can be used in any situations where edging is present.

The Imperfect Mask

There will be times when you find none of the luminosity masks have the selections you need. The mask can either over-select (including areas that you don’t want) or under-select (not including areas that you want). What can we do about it? Here are a few tips to help you refine a mask or create a custom mask for your selection.

1 Add or subtract luminosity masks . You can combine multiple masks together or subtract one from the other. To do that, cmd/ctrl + click on a luminosity mask, then add other masks by holding down shift + cmd/ctrl + click. You can add as many masks as you want. Opt/alt + cmd/ctrl + click to exclude a mask from your selection if needed.

2 Right click on the mask in the layers panel and select refine mask . Change the view mode to black and white and use the adjustments below to refine your mask.

3 Use color range. Go to Select > Color Range. At the bottom of the panel, change the selection preview to greyscale so that you can see the changes directly on your image. You can play with the fuzziness to refine your selection or pick a color from the drop-down menu. To sample a color, use the eyedropper tool on the right and click on the area in the image you want to select. You can add or subtract selection by using the + or – eyedropper tool. This creates a color based mask instead of a tonal based mask. Strictly speaking, this is not a luminosity mask but it helps you to get round the problem.

Ghosting

It’s a head scratcher in exposure blending. In an HDR software, you can use de-ghost to fix the problem. In exposure blending, there are ways to deal with it. So how does ghosting look like?

If ghosting is not obvious and only affecting a small part of the image, you can reduce the opacity of the layer or use the clone stamp tool or healing brush to fix it. But that’s not an option in this case. The solution here is double processing.

Double Processing A Single Raw Image

No, I don’t mean editing the image in both Photoshop and Lightroom. It’s a post-processing technique where you take a single Raw image and make a duplicate copy. You brighten up the shadows in one and darkening the highlights in the other, and you blend both together. In this case, with luminosity masks. I know what you’re thinking: Why can’t you brighten up the shadows and darken the highlights in the Raw image? Remember the greatest strength of luminosity masks is also its weakness. The tonal adjustments will bleed over into the shadows and the highlights. If you do it separately in two images, you don’t have to worry about that because you’re going to blend it. Shadows that are brightened up in the highlights priority image will be recovered by the shadows priority image and vice versa. Now, because only a single image is used, you wouldn’t have a problem with ghosting!

9. Learn More

That's it...I'm glad you made it to the end! I hope I've given you a good overview of luminosity masks and what you can potentially achieve with it. If you like more tutorials related to luminosity masks, you can find them in the “Related Posts” on the sidebar navigation menu. Alternatively, try searching for "luminosity masks Photoshop tutorial". You should be able to find plenty of other resources including YouTube videos. But if you still find it confusing, why not try this instead: An Idiot's Guide To Making Sense of Luminosity Masks.

The Next Step

If all these make complete sense to you and you are excited about the potential of what luminosity masks can add to your creativity in image editing, I do have something for you. Practical Luminosity Masks is a video course created out of passion and the feel for the need to bring all the technical tips and tricks of this technique into a single resource. You can find the course in from the top menu. One thing Practical Luminosity Masks is different from other courses is that it doesn't teach you workflow that relies on a specific luminosity masks panel. In fact, it teaches you the what, why and how of luminosity masks. You'll be equipped with a solid foundational knowledge that you can apply to ANY panels you wish to purchase in the future.

10. Conclusion