Lightroom Classic’s masking tools use a combination of AI subject recognition and regular brush and gradient tools to offer huge scope for local adjustments and enhancements. But you can get even more control by using masks in combination – in other words, with ‘sub-masks’.
There are many situations where this can be useful, but our sample image shows a very common one – where you want to darken a sky progressively towards the horizon but without darkening any buildings or other objects that jut up into the sky.
In our example, a linear gradient produces the right gradual darkening but would also darken the building. A sky mask would darken the whole sky, right down to the horizon without any natural gradation in tone.
But by ‘intersecting’ a sky mask and a linear gradient, we can get a gradual tonal gradation that affects only the sky. Our cheat sheet shows the location of the key Lightroom Classic masking controls.
Masking mode
To create and edit masks in Lightroom Classic you need to swap to the masking mode. This panel will give you a list of mask types to choose from. When you choose one, it appears in the Masks panel which opens out to the left of the tools sidebar.
Main mask
The Masks panel will show the area affected by your mask as a tiny thumbnail. Each new mask you add to your photo will appear as a new thumbnail. Any or all of these masks can include sub-masks.
Sub-masks
Every mask will have at least one sub-mask. If you’ve just used a single masking tool it will still appear here. Sub-masks become important if you want to combine or edit the masks that Lightroom has created.
Sky mask
To demonstrate this powerful ‘intersect’ command we’ve started off with a sky mask and used the adjustment tools in the right sidebar to darken it. This produced a very ‘flat’ adjustment that didn’t look natural. This is a common issue with sky masks if they are used on their own.
Sky masks identify sky areas very well but don’t offer any natural gradation towards the horizon.
Linear mask 'intersected'
The ideal way to darken a sky progressively is with a linear mask, but these are indiscriminate in that they darken everything at the top of the frame whether it’s actually part of the sky or not.
This is where an ‘intersected’ sky mask and linear mask can achieve what’s needed – a progressive darkening of the sky with other objects in the foreground left untouched. The linear mask achieves the gradual tonal adjustment, while the sky mask restricts it to the sky alone.
Gradient sub-masks remain editable, e.g. you can move them around even if they’ve been ‘intersected’, added or subtracted from the mask.
Add/Subtract buttons
The Masks panel can look pretty busy, especially if you have all your masks expanded to show sub-masks too – so how do the Add/Subtract buttons fit in? In fact, they apply to the main mask you’ve selected. When you use them, they add new sub-masks. They do not apply to sub-masks.
Adjustment tools
Keep in mind that Lightroom’s local adjustment tools apply to the main mask. Any sub-masks you create simply change the area covered by the mask. These sub-masks do not have their own adjustments. If you need to create a new set of adjustments for a different part of the image then you will need a new mask.
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