Photoshops Best Kept Secret Luminosity Masks

Luminosity masks are one of the best-kept secrets of Photoshop cs6 mac, and once you learn how to use them your images will benefit tremendously and they will speed your workflow up exponentially. This is a very simple guide on luminosity masks which is intended to introduce you to the technique, explain what it is, what sort of images it is useful on, and how to get started. You don’t have to know anything about Luminosity masks prior to reading this. In fact, if you are already familiar with the technique I would advise you to check out the more advanced blog post entitled: luminosity masks for the Advanced users.

As we learn more and more about how to use Adobe Photoshop (the learning never stops) we stumble across many techniques, some of which are useful to us and some of which are not. Luminosity masking definitely fits into the former category for me. I only learned how to use them 6 months ago but I have to say they have become an integral part of my photo editing workflow. Simply put luminosity masking techniques have saved me countless hours of brushing, masking, and selecting pixels inside of Photoshop. I use them on about 90% of the images I retouch. And after learning how to make them and understanding how they work I recommend saving them as an action so that they speed up your workflow too.

The problem

Have you ever wanted to create an adjustment layer that only affects the part of the underlying layers but not all of them? Of course, you have because you use a non-destructive workflow right? No, but seriously adjustment layers are an essential part of a good workflow, and if you use them you will inevitably be masking them off certain parts of the image. In the above image, I wanted to brighten the shadow areas without brightening the whole image. Normally this would involve the use of a selection method like a lasso tool, path, magic wand, or brush (and many more). These tools still have their place and are still extremely useful; however, there are some images where you can get away with a quicker and more efficient method of selecting, luminosity masks.

So what is a luminosity mask and how to make one?

A luminosity mask is a method for selecting and masking pixels of a certain level of luminosity. Simple right? In other words, it is a way of only picking the pixels that are bright and not picking the pixels that are dark. Don’t be put off by the fancy name, you don’t have to understand the mathematics of luminosity masks in order to benefit from them; you just have to know how to get Photoshop to do the heavy lifting for you. The most basic mask is the one where Photoshop only selects the pixels that are 50% or brighter. Open an image in Photoshop and hold down ctrl, alt, and press the number 2 (note on some previous versions of Photoshop the shortcut was ctrl, alt, tilde [the key to the left of the number 1, it looks like this `]. This shortcut will tell Photoshop to analyze the combined RGB channels and to only select the pixels that have a value of 50% brightness or higher. So clever isn’t it. After pressing this shortcut you will see the image get covered by thousands of ‘marching ants’ like in the image below. Don’t panic, you now have your selection so what are you going to do with it.

How to apply the mask to an adjustment layer

The easiest way to apply this mask is to select an adjustment layer. If you have your workspace set to photography then the adjustment layers panel should be open. If you’re unsure it looks like this:

If however this panel isn’t showing then go to the window and select adjustment. Now click on one of the adjustment layers. Personally, I do most of my work with curves layers so I’ll select it. Notice when you select one of the adjustment layers while the ants are marching it will automatically load that selection into the mask for you. The ants will disappear but the mask will inherit the selection. If you look closely at the mask (next to the adjustment layer) it will look like a B&W version of the image, like the one below.

This mask works like all others in that the black parts of the mask are not affected but the white parts of the mask are. The various tones of grey are affected to varying degrees. In this example, I only wanted to brighten the shadow areas and not the bright parts so I’ll need to invert the mask. To do this click on the mask, hold down ctrl and press the letter I. Your mask should now look reversed or negative and you can now make adjustments to the shadow areas without affecting the brighter parts of the image.

Conclusion

This technique is invaluable. Once you get the hang of the basics you can combine this technique with various others in order to make Photoshop a more powerful tool for you. Some of the more advanced techniques that I’ll cover in my next blog post involve intersecting the mask in on itself to create a more targeted mask, how to create a surface mask using the filters and how to save the masks as an action. Persevere with this technique until you master it, if you have any questions feel free to contact me and if you prefer to learn by instructional video then feel free to check out the video below for a more hands-on approach to learning luminosity masks.