Windows Explorer is both one of the most useful and one of the most constrained parts of Windows. For people who use the Windows feature only occasionally the constraints are a little less obvious, but the more you have to deal with multiple image formats, the more you realize that Windows Explorer can't natively show thumbnail images for any of them.
This is partly the result of Microsoft being pragmatic. The number of image and file formats is rising. They include the plethora of RAW types exported by digital cameras, the various breeds of TIFF, Adobe Photoshop and even the commonplace PDF. It would be futile for Microsoft to try to build thumbnail support for every single one of them directly into Windows.
It's best to leave support for such things to third parties -- whether they're the creators of the image formats in question or providers of tools that allow third-party images to be displayed as thumbnails in Windows Explorer.
The first route seems the most logical one: Who better to support thumbnail images than the creators of the file formats? But a lot of the time, they don't. In the case of Photoshop, Adobe did at one time, but it discontinued that feature.
The second of those two routes, using a third-party add-on to let Explorer display a wider range of image thumbnails, provides support for the greatest number of file formats. Rather than remain at the mercy of a dozen different software vendors, you can stick with a single product and see thumbnails for dozens of image types all at once. That being said, several different vendors have such products, so I set about looking at a few different ones to see how they compared with one another.
Microsoft, amazingly, has its own partial solution to the problem: the Microsoft Camera Codec Pack. This was originally created as an add-on for the Windows Live family of products -- specifically, Windows Live Photo Gallery -- so that they could interact with cameras that produced RAW-format images.
However, each camera manufacturer's RAW image format is slightly different. To that end, the Codec Pack handles RAW formats from most of the major camera makers, including Canon, Nikon, Olympus and Sony.
The drawback to the Codec Pack is that it doesn't deal with anything other than RAW image formats, so it's extremely limited in its scope. If RAW format files are the biggest obstacle for you, the Codec Pack may do the trick, but it's easy to outgrow its usefulness.
Another option, FastPictureViewer Codec Pack, is a commercial product that offers a 15-day trial. Billed as having the broadest compatibility and the best stability of any product in its field, it supports not only RAW files, but also a slew of formats commonly used in gaming and high-end graphics work, such as Maya IFF and Softimage PIC. In addition, the product supports Adobe formats including Photoshop PSD, InDesign INDD and Illustrator AI.
FastPictureViewer Codec Pack works well. It didn't slow down my system in any appreciable way, even when working with multi-megabyte files over a network connection. The pack also works directly with Explorer's internal thumbnail database, so any other programs that talk to the same thumbnail database will be able to use those generated thumbnail images as well. The biggest drawback to the program is that it's $15, although that's a relatively small price to pay.
A third product, and my personal favorite of the bunch, is an open-source (and thus free) project named SageThumbs, which uses the image library from the XnView image viewer to add thumbnail support to Explorer for some 162 image formats.
SageThumbs's biggest plus is that it provides thumbnail support in Explorer for so many image formats, but it also has several other useful capabilities. Supported images can sport a right-click context menu, which allows images to be converted between formats, emailed, used as wallpaper or copied to the clipboard.
SageThumbs can also be set to display an image's own internal thumbnail, if one exists -- .JPG and Photoshop files support this -- instead of a thumbnail generated from the image. This makes it possible to add thumbnail support for some image types without needing a full-blown decoder for the image.
One key difference between SageThumbs and FastPictureViewer is how thumbnails are stored. Rather than use Windows Explorer's own thumbnail cache, SageThumbs keeps its thumbnail images in its own internal database, which can be purged or optimized independently of the Explorer thumbnail cache.
Another handy SageThumbs feature, which boosts performance, is the ability to restrict thumbnail generation to images below a certain file size. This is useful if you constantly explore directories full of Photoshop images that might be well into the hundreds of megabytes and that you don't want indexed because of the load imposed on the system.