Photoshop 101: Understanding Layers and Masks

Acquiring Adobe Photoshop is the first step towards serious image-editing potential.  This program, renowned world-wide for its power and versatility, is both incredibly useful and complex.  Upon first glance, its interface is intimidating and overwhelming.  When editing in Photoshop, there is a oft-heard buzzword known as "non-destructive editing."  What this phrase essentially means is that when editing images, any changes that you make are simple to "turn off," there is no permanent change to the original image. 

 In Photoshop, this is accomplished by using layers and masks.  These terms you have probably heard before, but to have a complete understanding of them and their use is the first step to becoming a Photoshop power-user.  By the time you finish this article, you will begin to have that understanding.

When you bring an image file into Photoshop after importing it from your camera, it is completely unedited.  This becomes your "background."  The background refers to that very image, without any changes of any sort.  As an intelligent Photoshop user, you never want to make any changes directly to that background.  This is where layers come in.  A "layer" in Photoshop is an adjustment or component of an image that affects the background, changing the original image, but sits "above" the background.  A layer can be best understood visually, by using the Layers palette in Photoshop.  In this image, you can see the "Background" in the layers palette, and a new blank layer above it.  This new layer can be turned off and on using the "eyeball" to the left of the layer.  When the eyeball is clicked off, any change that layer imparts on the image beneath it is hidden, but not erased.  

Basic Photoshop - Image 1.jpg
The original image, showing the background layer, and a new blank layer above it.

To reiterate, after an image is opened in Photoshop, it becomes the background.  As you make adjustments, layers are added above the background to impart those adjustments without directly editing the background itself.  This type of workflow is the non-destructive editing mentioned at the start of this article.  

You can have as many layers as you want on an image.  The most influential variety is known as an adjustment layer.  Adjustment layers consist of brightness, contrast, color, etc changes to an image.  Using these special layers, you can make any change you want, and always be able to switch it off with a click, or remove it permanently by dragging it to the trash icon on the bottom right of the layers palette.  To create a new adjustment layer, go to Layers in the toolbar on the top of the screen, then New Adjustment Layer.  Alternatively, click on the half black/half white circle icon on the bottom of the layers palette.  This will give you the option to create any kind of adjustment layer desired.  

Now that you can make non-destructive image adjustments, the next step is localization.  With layers, not only can you make overall changes, but also highly specific ones.  Using masks, you can direct an adjustment layer to only affect certain areas of the image.  An adjustment layer is created automatically with a mask attached.  It is the white box to the left of the layer's title.  

The status of a mask is referred to as "active" or "inactive."  The area of a mask that is inactive does not affect the image in any way.  This area will be black.  The active area of a mask will be white or any shade of gray, the closer to black the less active the adjustment.  This concept allows selective adjustments to be made, by "covering up" the mask with black where you do not want your adjustment to show through.  The simplest way to do this is with a black or white paintbrush.  With the brush tool, you can "paint" directly on the mask.  Painting a shade of gray will make the mask partially active, so that only some of the adjustment shows through.  By holding the "alt" key and clicking on the mask, the image itself will switch over to "mask view" and you can see the mask that you have created in full, as shown in this image.  

Basic Photoshop - Image 2.jpg
"Mask view" in Photoshop, the result of holding the "alt" key and clicking on a mask.

Here is an example of these concepts in action.  In this portrait, the grass on the right side of the frame needs to be darker.  After opening the image, you can see the untouched background.  Next, a levels adjustment layer is added.  By using the middle slider, the image overall is now darkened.  In this situation, it is important to remember that you want to focus only on the area that you want to adjust, and not be concerned about the image overall.  Once the levels are adjusted ideally for the grass, the mask is inverted, using the apple-I (control-I on a PC).  This makes the fully active (white) mask into a fully inactive (black) mask.  The levels adjustment is no longer affecting the image.  Now take the brush tool, set it to white, and paint over the area of the image (in this case the grass) to selectively darken it down.   

Using the opacity of the brush, found on the top-center of the screen in the tool options bar, you can precisely control how much of the adjustment you would like to have.  A lower opacity is equivalent to painting with a dark gray, so that only some of the adjustment shows through.  Now alt-click on the mask and see the result.  Sometimes a mask can be a work of art in itself.  

Basic Photoshop - Image 3.jpg
The image, with an adjustment layer, after a white paint brush is used on the grass areas to bring out the adjustment, in this case, to make the grass darker.

With the power behind layers and masks, you can make highly precise selective adjustments, overall adjustments, or anything else you can dream up without ever directly changing the background image.  At any time during the editing process, it is easy to delete or hide adjustments to bring back the original image, assuring that any change made is not permanent.  It is important to note that when saving a file that has layers in Photoshop, you must save it in the PSD, or Photoshop Document, format.  This will allow you to open the file again with all of the layers intact.  When the file is ready for uploading to the web or sharing, simply "save-as" the file as a jpeg.  

jf.gifJoshua Lehrer | Website
Josh is a recent graduate of the Advertising Photography program at the Rochester Institute of Technology.  His career started in the NJ/NYC area where he worked as a freelance photographer, writer, and consultant.  He also worked as marketing coordinator for a large photography retailer.  He currently resides in South Florida, where he continues to be heavily involved in the photography industry.