The top photo editing computer programs provide professional photographers and amateur snapshooters alike with powerful tools for improving their images. Starting with a digital camera or using a scanner with a conventional film-based camera, you can correct and enhance your images and create impressive artistic effects without exposing yourself to smelly darkroom chemicals.

But even the top programs, including Adobe Photoshop (http://www.adobe.com) and its slimmed down, less expensive sibling Photoshop Elements, can’t do it all. A few years after Photoshop was introduced in 1990, an aftermarket emerged for plug-ins that provide imaging tools that can be used with any photo editing program that accepts Photoshop-style plug-ins, including Corel’s popular Paint Shop Pro (http://www.corel.com).

Two of the most visible companies making such plug-ins are Alien Skin Software and onOne Software. Both companies provide tools that Photoshop doesn’t along with similar tools that have a slightly different approach or produce slightly different results.

Alien Skin (http://www.alienskin.com) is an appropriate name for a company whose “Eye Candy” packages let you impart strange and sometimes wondrous special effects.

Eye Candy 5 includes three packages: Impact, Nature, and Textures. Eye Candy 5: Impact lets you alter a photo to simulate the look of chrome, brushed metal, glass, bevels, shadows, and reflections. Eye Candy 5: Nature creates such natural effects as fire, smoke, rust, snow, and ice. Eye Candy 5: Textures produces such texture effects as lizard skin, fur, brick, stone, and wood. These three packages can be purchased separately or bundled together in Eye Candy 5: Bundle.

Another useful package from Alien Skin is Image Doctor. As its name implies, it’s an image fixer rather than a special effects creator. You can use it to remove blemishes from a photo, repair over-compressed JPEGs, or replace unwanted details and larger objects. It allows you to correct an entire image or select part of an image for enhancement. A before/after toggle lets you decide whether your doctoring actually improves things before finalizing it.

onOne Software (http://www.ononesoftware.com) has its own set of plug-ins. PhotoFrame Pro provides thousands of different frames and mattes you can surround a photo with—realistic-looking ones that simulate an actual picture frame as well as the fanciful and the strange. Genuine Fractals lets you enlarge photos without losing as much detail as Photoshop’s own enlargement tool. This is particularly useful if you’re starting out with a low-resolution image, a small part of a larger image, or a poster-size final output.

The company has also teamed with Nik Software (http://www.niksoftware.com), yet another plug-in company, to offer a bundled package consisting of onOne’s Genuine Fractals and Nik Sharpener Pro. The latter is for sharpening an image, whether it has been enlarged or not, and can be used after using Genuine Fractals.

onOne has its own bundled package as well; it’s called Photoshop Plug-In Suite. It consists of Genuine Fractals and PhotoFrame Pro as well as two additional tools, Mask Pro and Intellihance Pro. Mask Pro has enhanced features for masking out parts of a photo while working on other parts. Intellihance Pro lets you interactively adjust color, contrast, and sharpening and compare up to 25 combinations at once.

For enlarging and sharpening photos, the company has another package, pxl SmartScale. It’s better for scaling images that have very well-defined edges, such as architecture and scanned-in line art. Genuine Fractals, on the other hand, is better with continuous-tone images such as landscapes, fine art, nature, and portraits.

Though they can be very useful, some of these plug-ins (both the bundles and the individual packages) can be pricey. Fortunately, plug-in sets from both Alien Skin and onOne can be downloaded for free for a 30-day trial.

If you want to try out other free photo plug-ins, FreePhotoshop.com (http://www.freephotoshop.com) is an interesting site. The person behind it, who prefers to remain anonymous, has put a lot of effort into it, though some parts of the site are becoming dated.

You can download freeware plug-ins that offer additional brushes, shapes, gradients, textures, frames, patterns, and other tools at the site or through links provided at the site. FreePhotoshop.com also offers reviews of commercial plug-ins from companies such as Alien Skin and onOne.

The Plugin Site (http://www.thepluginsite.com) is also useful, specifically about Photoshop-style plug-ins. It’s an offering from Harald and Miriam Heim of Nuremberg, Germany. (Harald Heim is a plug-in developer.)

The site is in English and includes, among many offerings, a useful “Plugin Essentials” backgrounder with lots of information about programs with which you can use plug-ins, incompatibilities, and other details.