Luminosity masks are layer mask. Apart from being a luminance based mask, it shares all other characteristics, advantages and disadvantages of a layer mask.
Even though luminosity masks are highly selective and targeted, sometimes the selection itself may not be sufficiently opaqued for adjustments to show through. Let me explain.
Going back to the basics of layer mask, we know white reveals and black conceals. When you've applied an adjustment through a luminosity mask and the effect isn't strong enough, that's because the selection doesn't have enough white (not white enough!) to fully reveal the adjustment.
This is why you need to know how to customize luminosity masks to suit your needs. Make it reveal or conceal the selections more.
In this tutorial, you're going to learn several techniques to customize luminosity masks. This helps to refine the selection which will subsequently affect the aesthetic of your images.
Refine Luminosity Masks
Luminosity masks use luminance of the pixels to make selections.
The selection may not always be restricted to the area you want because other parts of the image may also have similar luminance. These unwanted areas end up getting included into the selection.
An easy way to fix this is to group the layer and apply a layer mask to the group to mask out the area you don't want adjustments.
In other times, you get the perfect luminosity mask that has just the selection you need but the strength of the mask isn't strong enough (not 100% or near 100% white). Because of that, your adjustment isn't being revealed enough.
If you look at the example image above, I want to brighten up the clouds in the background to make it pop.
The only luminosity mask that isolates the clouds perfectly is Brights 3 but the selection isn't white enough. This means any adjustments I apply wouldn't be revealed enough to have a good effect.
Once I've refined the Brights 3 luminosity mask, the adjustment shines through beautifully. You can see the before and the after image below.
Increase The Contrast of The Mask
One of the ways to refine luminosity mask is to apply a Levels or a Curves adjustment directly onto it.
An increase in contrast makes the brights brighter and the darks darker. You can utilize this principle to refine luminosity masks.
In this image below, I want to increase the contrast in the sky without affecting the building, particularly the shadows.
Comparing Brights 1 and the Brights 2 luminosity masks, Brights 2 isolates the sky better (because the building is almost excluded) but the luminance of the mask in the sky isn't great.
So here's how you can refine the mask to optimize for the sky:
- Go to the Channels panel and click on Brights 2.
- From the top menu, choose Image > Adjustments > Levels / Curves (or use keyboard shortcut cmd + L (Levels) or M (Curves).
- Apply contrast to make the sky brighter and the building darker on the luminosity mask.
- Now cmd / ctrl + click to select the now refined luminosity mask and apply your adjustment.
The above before and after is to compare how the image looks with a Brights 1 luminosity mask (before) and a refined Brights 2 luminosity mask (after). You can see the contrast and the shadows of the building is not affected in the "after" image.
Increase The Contrast of The Image
If you don't like the idea of messing with the tonal value of a luminosity mask, you can increase the contrast in the image itself to separate the highlights and the shadows more before creating luminosity masks.
Now, check out Brights 2 luminosity mask from the first method and the Brights 2 luminosity mask from this method.
As you can see, both masks look almost identical. If you look closely, the Brights 2 mask in this method has more darks in the building. This means the building is going to get even less affected after tonal adjustments of the sky.
Filling In A Mask With White
Another way to customize luminosity masks is to increase the luminance of the selection. The principle is the same as the above two methods - to increase the contrast of the mask, especially within the selection.
Back to our example image. I'm going to use the Brights 2 luminosity mask again. This time, we create luminosity masks without applying Levels/Curves adjustment to the image or the mask itself. Select the Brights 2 mask from the Channels panel and apply it to a Levels adjustment.
Here's what you do next:
- Hold down opt (Mac) or alt (Win) + click on the layer mask loaded with Brights 2 luminosity mask for mask view.
- Make sure the selection for Brights 2 luminosity mask is active. If you accidentally deselected the selection, hold down cmd (Mac) or ctrl (Win) + left click on the layer mask itself. This will bring back the marching ants. Hide it with cmd or ctrl + H.
- To increase the luminance of the selection, you need to fill the selection with more white. Use the keyboard shortcut Shift + Backspace to bring out the fill panel. Choose White in Contents and press ok. You will see the luminance of the selection has increased (becomes whiter).
- Switch back to the normal view of your image to see how the effect looks.
- Repeat Step 3 until you are satisfied with the result.
Images below compare the original Brights 2 mask (before) without any refinement and the Bright 2 masks filled with more white (after).
Painting A Mask With White
Similar to filling in a mask, the idea is to fill the selection with more white. The main difference with painting a mask is you paint in more white manually.
I find this technique to have more control because I get to decide where in the selection I want to have more luminance (revealing more adjustments underneath). These are the areas I want to paint more white in.
Let's go back to our Brights 2 luminosity mask. Similar to filling in a mask, you select the luminosity mask from the Channels panel and apply it to an Adjustment layer.
In the Layers panel:
- Opt / alt + click on the layer mask to view mask in the image area.
- Make sure the selection is still active. If not, reactivate the selection by cmd / ctrl + click on the layer mask. You should see marching ants again.
- Select the Brush tool and change the color to white. Keep hardness to 0% and start with an opacity of 50%.
- Paint white into areas you want more luminance (i.e. adjustment effect to be stronger).
- You can increase the opacity of the brush to add more adjustment in a single pass.
Use Refine Mask In Photoshop For Further Fine Tuning
This is Photoshop's built-in tool to refine layer mask. You can use this to refine luminosity masks or as a tool to further refine the mask after using one of the methods above. I don't usually start with this because it doesn't give you much control like the others.
With Refine Mask, I often use Contrast and Shift Edge to isolate my selection even more.
- Load your luminosity mask onto the layer mask of an adjustment layer.
- Opt / Alt + click on the mask to go into mask view.
- Open Refine Mask by either from the menu on top, Select > Refine Mask or click on Refine Mask in the layer mask's properties panel.
- Use Contrast and Shift Edge to refine luminosity mask.
- Click OK when you're done.
You don't have to use all the techniques explained in this tutorial to customize luminosity masks.
What I would suggest is to learn all and pick one or two methods you prefer for your workflow. Keep others in mind as you might need it in challenging cases.