As a tech writer and Macworld editor, screenshots—snapshots of a computer’s onscreen display—are immensely useful. But they’re also important for educators, marketing folks, business people, and even those in IT and tech support. Any time showing something that appears on the screen would be illustrative or assistive, a screenshot comes in handy. But for the most part, screenshot software—including Mac OS X’s built-in feature—has been limited to capturing either the entire screen; a specific portion of the screen; or a single, individual element such as a window, a menu, or an icon. Which means that to get a decent screenshot, you usually have to spend some time organizing windows and clearing out things you don’t want in the image.

An amazing new utility, Wuonm’s Layers, changes all that. As with many other screenshot utilities, Layers takes a snapshot of your computer’s screen at the press of a keyboard shortcut (by default, shift+option+S). But Layers’ resulting image is jaw-droppingly different. Instead of a standard TIFF, JPEG, or PNG file, Layers’ screenshots are Adobe Photoshop files…with every item on your screen contained in a different layer.

Let me repeat that: every item on your screen—every window, every palette, every menu, every menu-bar icon, every folder or file on the Desktop, and even the Dock and the Desktop background for each of your connected displays—is a separate, editable layer in the resulting Photoshop image file. Even if you can’t actually see an item, be it an icon on the Desktop or a window or palette hidden behind other things, Layers captures it and gives it its own layer.

For those who’ve never used Photoshop or layers, allow me a quick aside to explain. Imagine if a physical photo of a landscape was actually a stack of immeasurably thin transparency sheets, each containing a single item in that landscape—a tree, a rock, a bird, and so on. If you decided you didn’t like a particular tree stump, you could simply remove its sheet and it would disappear from your photo. If a rock was in the wrong place, you could move it by sliding its sheet. If a bird’s colors weren’t as bright as you’d prefer, you could add a bit of color to that transparency to make the bird stand out more. This is—oversimplifying greatly—how Photoshop’s layers work: you can work with each layer’s contents separately from all the rest.

What this means is that if you normally process your screenshots in Photoshop anyway, using Layers means you no longer have to meticulously set up your screen beforehand. Instead, you just capture the screen whenever the urge hits you; later, you can move objects around and modify them, change window layering, and delete items to your heart’s content.

I could go on and on about how extraordinary this approach to screenshots is, but Layers also has a good number of other useful features. On the simple side, if all you want is a traditional shot of the frontmost window, shift+option+F will give you just that (in PNG format, with window shadows). Alternatively, if you want to do some tweaking beforehand, pressing shift+option+I brings up Layers’ Inspector window, which offers nearly as much pre-capture flexibility as its layered image files provide afterwards. (Each of Layers’ commands—full screenshot, window shot, and Inspector—are also available via a menu-bar menu.)

The bottom section of the Inspector window provides a list of every onscreen element Layers can capture. By default, none are selected, meaning Layers will capture everything. But if you click on an item to select it—or command+click to select multiple items—you can choose to have Layers capture only those items. In other words, without having to move a single window, you can omit particular windows, icons, or even menu-bar icons from your screenshots. The List Mode button in the toolbar toggles the display between a flat list and a hierarchical listing; the latter is similar to the Finder’s list view, with items grouped by type: applications, the Desktop, menus, and so on. The preview area, just above the list, shows you what the resulting screenshot will look like.

(Unfortunately, the Select All command, found in almost every Mac program that allows you to select items, is missing in action. This means that if you want to exclude just a few items from your screenshot, you can’t highlight everything and then manually de-select those few; instead, you have to painstakingly command+click on every item you want to include.)

At the top of the Inspector are buttons to hide or show the Desktop and to choose which displays to include if you have more than one. There are also buttons—Tight Fit, Shadow, Framing, and Opaque, for tweaking the resulting image. You can get more details about these settings, including comparative examples, at Layers’ FAQ page; tight fit, for example, will crop the resulting screenshot so it’s just large enough to contain the selected items.

Finally, almost hidden at the bottom of the Inspector window is a tiny pop-up menu that offers two useful alternatives to saving your screenshot as a Photoshop file: Composite Image, which saves in PNG format, useful—and smaller—if you don’t need to work with individual elements or if you’re passing the image on to someone who may not have Photoshop; and Bunch Of Images, which saves each selected item as a separate PNG image file, with these images grouped together in a common folder. The latter option works well with one exception: I found that if I didn’t select any items in the list, which should have resulted in all items being captured, I instead got a seemingly random subset—a very small subset at that. However, if I actively selected items, the feature worked as advertised.

As an example of the Inspector feature in action, the left-hand side of the image below is a standard capture of my Mac's screen—actually made up of two displays—with approximately 20 programs running. The right-hand side is the same two-display setup captured just seconds later with Layers. I used the Inspector to include only the left-hand display, and then selected only the Desktop, the menu bar, and a single program window. (I resized the two images to fit here, so they’re not scaled equally.) Taking the same shot using OS X’s built-in functionality, or even Snapz Pro X, would have required a good deal of moving of windows and switching around of programs, even with the help of a utility such as Backdrop.

Given that Layers is only at version 1.0.3, I’m impressed by how mature it feels. But it does have a few rough edges. In addition to the Select-All omission I mentioned above, whenever you refresh the Inspector, it loses any selections you’ve made and expands any folders you’ve collapsed, which can be frustrating. Layers' layered screenshots can take a few seconds, and the program doesn’t let you take timed screenshots, which are useful in situations when you can’t use the program’s keyboard shortcuts, menu-bar menu, or Inspector to initiate a capture. Oddly, your mouse cursor is hidden in screenshots, and the program occasionally has trouble with certain non-standard windows; for example, you can’t use the Inspector with palettes that automatically hide when their program isn’t frontmost. Finally, the current version of Layers doesn’t include a Help system or clear documentation.

Layers is obviously a specialty tool that isn’t for everyone. But for those who’ll find it useful—and you know who you are—it’s one of the most innovative and useful bits of software I’ve seen in a while.

(Layers’ official price is $20, but Wuonm has been offering the program for $15 as an introductory promotion. Note that in demo mode, Layers degrades the quality of its screenshots; once you purchase the program, your screenshots will be full-quality.)

Update: 2/6/09, 1:49pm: Added note about cursor capture.