Though digital cameras are constantly improving Dynamic Range, they still struggle when dealing with scenes portraying extreme contrasts in tonal values. Scenarios where the sky is bright and the foreground is dark is a typical example.
Capturing these scenes in a single frame is often impossible. That’s why many photographers rely on photo editors such as Adobe Photoshop for merging multiple exposures.
In other words, they capture one image that’s exposed for the landscape and one that’s exposed for the sky and blend them together in order to get an image that’s correctly exposed.
There are a number of ways to merge images but not all are as accurate as you might like. Using Luminosity Masks in Photoshop is one of the more popular approaches; it’s slightly more advanced but the results can be flawless.
What are Luminosity Masks?
However, if it’s a new subject to you, let me give you a brief introduction before looking at the step-by-step workflow of using them to blend multiple images:
- Luminosity Masks are advanced types of selections that are based on the brightness of a pixel. This makes them extremely precise in targeting only pixels of a given luminosity.
- There are 3 main types of Luminosity Masks: Darks, Midtones
andBrights. However, all of these can be refined to only include the brightest brights or darkest darks.
- The Luminosity Mask itself doesn’t affect the image but you can apply adjustments through them. That means we’re able to, for example, darken only the brightest parts of the image
Recommended Reading: Understanding Layers & Masks in Photoshop
Why Use Luminosity Masks to blend images?
There are many techniques used to blend multiple images in Photoshop. The easiest is to use a black brush on a white layer mask and paint on the areas where you want to reveal the layer below.
It’s easy but also extremely inaccurate. You’re likely to accidentally brush over areas you don’t want to
Using Luminosity Masks is similar but instead of freely painting on a white layer mask, we do it through a selection that targets a specific part of the image. That lets us accurately avoid areas we don’t want to change
There are other types of selections you can use as well but Luminosity Masks are the most accurate when it comes to the brightness of pixels, which is what we want to use when working with image blending to fix dynamic range issues.
When do you need to blend images?
Take a look at the image below:
What is wrong with that image?
The landscape is properly exposed and has many details but the sky is completely white and contains no information. It’s clipping the histogram.
You might think it’s easy to fix this using Lightroom or another RAW editor but when elements are as blown out as they are in this image, they’re impossible to recover. Here’s what happens when I lower the exposure, decrease the highlights and increase the shadows to bring back some light in the foreground:
As you can see, it looks horrible.
To overcome this obstacle, you need to take a second exposure that is darker than the first. You might need to take more than two images, depending on how great the dynamic range is. I recommend bracketing in intervals of 1 stop in the shutter speed.
For this particular image I needed a total of four images in order to properly expose for both the brightest highlights and darkest shadows. This is the fourth, and darkest, shot:
Blending more than two images using Luminosity Masks is slightly more advanced and I recommend you take a look at our eBook if you’d like to learn more about that.
Step-by-Step: How to blend images using Luminosity Masks in Photoshop
Let’s use a more common example where there are only a few parts of the sky that are overexposed and need to be replaced with a darker exposure. Here are the two exposures we’re going to work with:
The first exposure will be our ‘base exposure’. This shot is well-exposed for all the landscape (and even parts of the sky) but you can clearly notice that it’s been clipped in some of the highlights. In those areas, we’ll use the second exposure.
Let’s get started.
Step 1-2: Open the images as layers in Photoshop & align them
Start by opening the two images as layers in Photoshop. You can do this by opening them individually and dragging one file over to the other or, in Lightroom, select both images, right-click and choose Edit In -> Open As Layers in Photoshop… from the dropdown menu.
It’s up to you whether you choose to have the dark or bright exposure on the top. I prefer to have the bright exposure on top and paint the dark exposure back into the clipped areas. It’s this workflow I’ll be using throughout the article. If you prefer having the dark exposure on top, you simply need to do the opposite of what’s explained below (i.e. use a black Layer Mask with a white brush)
We need to align the layers in order to avoid ‘ghosting’ or other unwanted artifacts. This is done by selecting both layers and going to Edit -> Auto-Align Layers… Select the Auto option and click OK.
It’s essential that you follow this step. There might have been some movement between the exposures, even if the camera was mounted on a tripod.
Step 3-4: Create a Layer Mask and a Luminosity Mask
The next step is to create a white Layer Mask on the top layer. Do this by selecting the layer and clicking the Add Layer Mask icon below the Layers Panel.
Make sure to familiarize yourself with what a Layer Mask is if you haven’t used one before. Simply put, a white layer mask keeps all of the layer visible but painting on it with a black brush reveals the layer beneath.
Now that we’ve created the Layer Mask, it’s time to create the Luminosity Mask. I use the Raya Pro plug-in to easily preview and select them. You can also manually create all the Brights Luminosity Masks and select the one that best fits. For this image, I’m going to use Brights 3.
Recommended Reading: How to Create Luminosity Masks in Photoshop
The monochrome image above represents the Brights 3 Luminosity Mask. Only the white areas will be affected by any adjustment I apply. You can see that the white areas match perfectly with the overexposed parts of the image.
Step 5: Brush through the Luminosity Mask
The fifth and final step is to use a black brush and paint on the white Layer Mask through an active Luminosity Mask.
Activate the Luminosity Mask by Cmd/Ctrl clicking on the dedicated Luminosity Mask layer in the Channels Panel or click on Select in RayaPro’s InstaMask panel.
The Luminosity Mask is active when marching ants are visible around the bright areas of the image:
Now it’s time to paint the correctly exposed sky back into the base exposure. Make sure that the selection is active (you can hide the marching ants by clicking Cmd/Ctrl + H), select a large white brush at 0% hardness, and reduce the opacity to roughly 50%.
Use long brush strokes on the overexposed area to start revealing the darker exposure. You can always adjust the opacity to increase or decrease the visibility of the new brush strokes. If you’ve revealed too much of the darker exposure, you can use a black brush to remove it again.
This is what the Layer Mask looked like after using a Luminosity Mask to introduce the darker exposure:
The darker exposure has only been introduced into the black areas of the mask shown above. The darker shade of grey an area of the mask is, the more of the dark exposure has been used.
Comparing the before and after
That’s it! It only took 5 steps to blend the two images using Luminosity Masks in Photoshop. Not too difficult, right?
Remember the two files we started with? Here’s what the image looks like after the blending:
Quite an improvement for only a few minutes work! The file is now ready to be processed further according to your liking.
Note that you might need to crop/scale the image slightly due to aligning the two layers in the first step to get rid of black or transparent borders around the image.
Learn more about Luminosity Masks
Luminosity Masks were one of the techniques that took my post-processing to the next level. Even though they aren’t required for every single image, I typically use at least one whenever an image goes into Photoshop. Either to work on contrast, color, sharpening, blending, or something else.
I’ve written several free articles about Luminosity Masks as well as a comprehensive eBook teaching you everything you need to know about using them as a landscape photographer. Be sure to take a look if you’re ready to skyrocket your post-processing skills too!