Adobe's new Photoshop CS4 packs a ton of fresh features and an updated interface, which alone make it a worthy upgrade for existing users.

But the big news is that Photoshop now comes in both 32- and 64-bit Windows Vista versions. The 64-bit edition will allow PCs with lots of RAM to work on very large images with less hard-disk swapping (ideally, no swapping at all), thus speeding up operations. With the shrinking amount of RAM available to modern PCs (due to a 4GB limit on 32-bit Windows versions and those operating systems' increasing hunger for RAM), that's a significant update.

I tested betas of both the 32- and 64-bit versions of Photoshop CS4 by installing them on a workstation with dual Intel Xeon CPUs, running Windows Vista 64-bit and 8GB of RAM. Photoshop requires that you manually allocate a specific amount of RAM to it, rather than its acquiring the RAM on the fly. I was able to set the 64-bit version to take up 6879MB of RAM, and to set the 32-bit version to consume 3185MB of RAM. The amounts will vary depending on your system, especially your graphics card.

In the 64-bit version, I was able to create and work with an image of 45,000 pixels by 45,000 pixels, for a total of a little over 2000 megapixels and a 5.6GB file size. Obviously, most people don't need that sort of capability, but many professional photographers shoot with large- or medium-format cameras with digital backs that can capture nearly 40 megapixels or even higher, and they often create much larger compositions. Adobe says that Photoshop keeps its editing history in RAM for as long as possible, too, so even if you're working with smaller images but making lots of edits to them, allocating more RAM will help you in that situation as well. For people who do work on very large images, it's probably more cost-effective to buy more RAM for your PC than to buy large RAID systems, and Photoshop will probably perform better.

Running the 64-bit version will provide little performance benefit other than the ability to address more RAM. And even a system with lots of RAM won't be able to avoid reading and writing data to your hard disk--a process that still proves time-consuming. I got to watch a dialog box for a coffee-break-length period when I asked Photoshop to apply a simple monochrome gradient to my 5.6GB file.

Fun-House Mirror, Fixed

Of course, the added under-the-hood elements aren't the only updates in Photoshop CS4. The most gee-whiz update is the new context-sensitive scaling, which allows you to resize pictures while retaining foreground objects' scale. Usually when you rescale an image, all elements in the image resize proportionally--and in the process, some elements warp or squash when they shouldn't. In the example I've provided (see the images in the gallery above), resizing with the traditional method would have made the people in the foreground unrealistically skinny; with context-aware scaling, the vinyl character in the back shrank, but the people remained the same size. The feature doesn't always work perfectly--I found that expanding the canvas size caused tiling of the background elements--but it's still an awesome tool to have.

A new adjustments palette (see the image in the gallery above) contains many often-used photo enhancements that you'd usually have to dig into a menu for. But its role is far more important than just offering convenience: Effects initiated through this palette apply as adjustment layers, so any edits you make are nondestructive to the original image. If you adjust levels, for example, a levels layer appears in your layers palette; instead of toggling a preview of your work in the levels dialog box, you can turn the layer on and off. If you decide you don't like the effect, you can simply trash it, and your base image is unaffected.

A new depth-of-field tool lets you combine multiples of the same image but in varying focus depths; the software attempts to make everything in the shot in focus. It works very well, but you do have to set up your shots this way, most likely by using a tripod and a timed release.

And what would a refreshed Adobe app be without some sort of new online component? Photoshop provides access to Kuler, a component that other Creative Suite applications can draw on, too. Kuler (see the gallery above) appears as a palette with many choices of "color themes"--that is, color sets that are supposed to go together. They're hosted online, and you can create your own themes and upload them to Adobe's online repository. Users can rate them (on the Web only, not from within Photoshop), and you can sort the themes in the palette based on their popularity, newness, or randomness. It doesn't seem like much at this point--just an indication of things to come--and I keep wondering whether it will cause designs to all look alike, once everyone joins the herd and uses the same themes.

Owners of systems using OpenGL graphics cards will enjoy additional performance enhancements. After enabling a preference setting, you can zoom with infinite smoothness (rather than in steps) by holding down a key: If you hold down the H key while zooming, it zips to 100 percent so you can locate where in an image you want to work--at which point the view zips back in to the previous magnification. Furthermore, you can hold down a key to resize brushes on the fly, and adjust their hardness. I found that latter function particularly time-saving when performing such operations as cloning and healing. OpenGL rendering also eliminates jagginess in the display of images at odd magnification percentages. For example, if you look at an electrical line at 27 percent on a system without OpenGL rendering, the line will appear jagged; view it at 25 percent or 50 percent, and the line will look straight. With Photoshop CS4, the line will look straight no matter what the magnification is, as long as your system has an OpenGL-compatible graphics card.

Photoshop CS4 Extended--a $999 version found in the Design Premium, Web Premium, Production Premium, and Master Collection versions of Creative Suite--has, among other things, enhanced 3D editing capabilities. You can apply 2D images (for example, a logo) to a 3D object, with excellent results. It won't make Photoshop an artist's primary 3D application, but it will be useful for some people to have on hand.

More Bits, More Better

I expect that most Photoshop CS4 owners will continue to run it in its 32-bit form, but over time more people will transition to the 64-bit version, especially as RAM limitations become more imposing. I wish that Adobe would offer 64-bit versions of its other applications--for example, Premiere Pro--but I give it credit for starting with Photoshop. Even without the new operating system compatibility, the latest version has many new features that make it a substantial, worthy upgrade.