Luminosity masks provide a convenient way to select specific tones in an image, based on pixel luminance, which can then be altered as the user sees fit. They can conveniently help overcome shortcomings in the tonal values that were captured by the camera and to correct tones that shifted during image manipulation. Luminosity masks also encourage a very individual approach to interpreting light. They make the captured light incredibly flexible and thereby provide unique opportunities to use Photoshop to explore a personal vision through photography.
While luminosity masks are created in Photoshop, they aren't available from the drop-down menus and can't be created with tools in Photoshop's Tools palette. This tutorial will describe the masks, how to make them using Photoshop, and the basic way to use them. The two primary masks, "Lights" and "Darks", are relatively easy to create. From there, however, it becomes more complex as the various selections are intersected and subtracted. All the steps will be explained in the tutorial. While it’s important to understand the basics of how to create luminosity masks and the tones they select, mask creation can be a bit cumbersome. So, to efficiently use the masks in a Photoshop workflow, it’s usually best to create a set of Photoshop actions to do all the key strokes. Actions greatly simplify the process of generating the masks; a couple of clicks and you're done. There are free actions and a free panel for making all the masks on the Panels & Videos; however, I would urge you to take the time to gain an understanding of the process by which the masks are created and to actually practice making a few. It will be useful when reading the other tutorials on this website and will allow you to develop a very personal approach to employing the masks, which, in the end, will make your images more distinctive.
Several of the other tutorials on this website are an extension of the concept of tone-based adjustments that the luminosity masks make possible. While this first tutorial will provide the basic concepts, there is a wide range of possibilities beyond what it can cover. The other tutorials will look at additional ways that the masks can be used as well as exploring other techniques for tonal adjustments. Please visit them when you have time. The "tutorials" link in the header of each page will take you to the tutorial table of contents.
Before going too far, I should mention a few things. First is that I work on a Windows-based computer running Photoshop CS when this tutorial was written (2006). The instructions and illustrations in this tutorial are presented with those parameters in mind. Some facility with Photoshop will be assumed. While the details of the processes are explained, I won't attempt to provide definitions of every Photoshop term or how to perform common steps. If you've worked (or played) with Photoshop, you're probably familiar enough with the program to do the necessary steps. Additionally, I use Photoshop shortcut keys in several situations. These are a combination of the SHIFT, CTRL, and/or ALT keys being held down at the same time and, while continuing to hold them down, hitting a letter, number, or symbol on the key board. The ones I list will be the defaults that came programmed into Photoshop at the time this tutorial was written. Mac users will know that "CTRL" on a PC is the same as "command" on a Mac and that "ALT" on a PC is the same as "option" on a Mac. There are usually drop-down menu commands that correspond to the shortcut keys, and these could also be used, though I won't always list them.
To move through the tutorial, there's a table like the one below that links to the various short sections. If you're ready to start, click the entry that says NEXT—The Basic Mask—"Lights" to take your first steps into the wonderful world of luminosity masks.