Luminosity Masks For Advanced Photoshop Users

Ever noticed how there are always multiple ways to do the same thing inside of Photoshop? Every time you download photoshop for mac free there is a whole new swag of tools, many of which do the same job as the old tools. Combine this with the fact that Adobe is reluctant to remove old tools (for obvious reasons) and pretty soon you have a massive program with multiple ways of completing the same task. What does all this mean? Don’t get me wrong I’m not complaining, this is great for advanced users because it gives them a set of different tools all with different nuances. However, this confounds many Photoshop newbies because they get confused by all the different tools and techniques. If there are 6 tools for doing the same job which one should you use? Knowing which one to use only really comes with experience. However, there is one old technique that I use all the time, Luminosity masks.

Luminosity masking is a method for selecting pixels based on their light level. This has become my ‘go-to’ tool for making selections and converting them to masks because 1) it is quick 2) it is easy and 3) it is a subtle method for making masks. Before we dive in I would like to state that this is a fairly advanced guide and that if you haven’t heard of this technique before then I would advise you to check out the beginner’s guide to Luminosity masks and then to return to this one. Further, I would also like to state that this technique is not my original idea but rather one I have learned from Tony Kuyper’s fantastic tutorial. I have however modified Tony’s technique to suit my own style of image editing and this is what I would like to share with you.

Luminosity masks stay within the conventions of layer masks in that using white reveals the top layer and masks the bottom layer and black does the. I used to create masks and then use different selection methods to reveal the underlying layers, for example, brushes, the pen tool, color selections, and so on. While these methods work great and can be highly accurate they often take a very long time. Luminosity masks work in the same way however they are a way of getting Photoshop to do most of the heavy lifting for you. An added bonus is that they are very fast to use. Luminosity masks have now become the ‘go-to’ starting point for me when creating a mask.

Free stuff

I have created some Photoshop actions for luminosity masks, surface masks, and edge masks. Feel free to download them and play with them, if you’re like me you will soon discover their value and incorporate them into your workflow. However, I strongly recommend reading this post and watching the instructional video so that you better understand how luminosity masks work, and then downloading the actions.

How to make luminosity masks

In essence, a luminosity mask is a way of selecting only a certain value of pixels based on their luminance level. It ignores color and instead evaluates the Image in greyscale. The best part is Photoshop does it all for you. To get started simply press (ctrl + alt + 2) or (ctrl + alt + [tilde] ~) for older versions of Photoshop. Doing this tells Photoshop to analyze the current layer in greyscale and to only select the pixels with a brightness value of 50% or brighter. By doing this you have created a selection of the brightest pixels and excluded the darker ones. Note how in the example below the marching ants are only selecting the brightest parts of the image and leaving out the rest.

basic selection based on luminosity levels

What to do with a selection that is based on the luminosity

Now that you have your selection you can do whatever you want with it. By clicking on an adjustment layer you can load it into a mask. Or by pressing (ctrl + J) Photoshop will create a new layer based on the selection. I recommend saving the selection as an Alpha Channel so that you can reuse them later (see the image below). By doing this you can reload them later when needed by ctrl-clicking on the Alpha channel. Be warned though if you save them as an Alpha Channel they will dramatically increase the file size of your document, so I recommend deleting them after you edit an image in order to save space.

how to save a selection as a channel

How to modify the mask

Darker pixels:

Now that you have a basic luminosity mask you can do much more to it. If you invert the selection (Ctrl + [the letter] I), the selection will include the pixels that are 50% or darker.

Controlling the mask:

After creating a basic mask if you click on the mask and then run the levels command (ctrl + L) you can control the areas that the masking effect.

Intersecting the mask on itself:

Once you have created a basic masked and saved it as an Alpha channel you can intersect the mask in order to select the next brightest pixels. For instance, if you have a selection with the brightest pixels, you can then run the mask again on that mask and select the next brightest pixels to the exclusion of the darker pixels. To do this save the basic mask and then click on the mask while holding down (ctrl + shift + alt). I know it’s a long shortcut. Now you can save that selection as another mask. You can run this command again and again to create more ‘exclusive’ masks and this will give you finer control over the selection.

Subtracting masks:

After loading a mask you can subtract another mask by clicking on it while holding (ctrl + alt). This is a common method for deselecting the brightest and also the darkest part of an image in order to control the mid-tones. Be aware though that if you deselect the brightest and the darkest channels and then convert to a mask you may get a warning saying no pixels were selected – ignore it and carry on. Photoshop doesn’t think you have selected any pixels but you actually have, don’t worry. See the image below.

photoshop warning

Other practical applications for luminosity masks

Surface mask:

I often use a basic luminosity mask in tandem with a noise reduction layer. For instance, if you apply noise reduction on a layer and then run the basic mask (ctrl + alt + 2), and then go to filter>stylize>find edges, Photoshop will only select the edges based on the luminosity of the image (see image below). Now your noise reduction layer will only affect the surface areas of the image, where there is low detail. This is an effective method for preventing noise reduction from blurring the detailed areas of an image. I recommend blurring the mask with the Gaussian filter set to about 4 pixels in order to create a smoother transition.

surface mask inside of photoshop

Edge mask:

The opposite of a surface mask is an edge mask, this is useful for sharpening a photo. Start by creating a new layer and sharpen the image (for tips on sharpening see this blog post). After sharpening create a basic luminosity mask and run the filter>stylize>find edges, just the same as the surface mask. This will tell Photoshop to find the edges, however, if you look at the mask you will notice that Photoshop has selected the surface area and masked off the edges. Simply press (ctrl [the letter] I) and this will invert the mask. Now when you sharpen the image it will only affect the edges rather than the whole image. I recommend using the Gaussian blur filter at around1-3 pixels on this mask as well so that it blends more seamlessly.

edge mask inside of photoshop

A complete list of shortcuts

Basic mask =

(ctrl + alt + 2) or (ctrl + alt + [tilde] ~) for older computers

Inverting the mask =

(ctrl [the letter] I)

Selecting a saved alpha channel mask = click on the channel while holding ctrl

Intersecting a mask =

click on the channel while holding (ctrl + alt + shift)

Subtracting a mask =

click on the channel while holding (ctrl + alt)

Surface mask =

create a mask and then run the filter>stylize>find edges

Edge mask =

create a mask the same as a surface mask and invert (ctrl + [the letter] I)

Conclusion

I realize that this has been a very technical guide. Don’t worry if it doesn’t make sense yet. I recommend starting off with the basic masks and then learning the more advanced masks as you get used to working with luminosity masks and channels. I have prepared an instructional video to go along with this guide; you may find it easier to follow along with me while I demonstrate after reading the guide. (see down below).

I strongly recommend creating your own masks and channels in order to gain an understanding of how the process works. However, after learning about the masks you may find it useful to save them as an action this will save you a lot of time in the long run. One thing is for sure, although the luminosity masking technique is one of those older tools, it certainly is very useful. I use it on almost every image that I work on. But I seldom hear or read anything about it, that is why I have called it Photoshop’s best-kept secret.

Max
Written by Max