Like its higher-end Dimage X siblings, the X31 is less than an inch thick with a squarish body that slips nicely into most pockets. Even though it's mainly plastic instead of the brushed metal of the more expensive X cameras, its two AA batteries make it a bit heavier than they are--but it's still quite lightweight at 6 ounces.
The battery compartment and the coverless SD/MMC card slot are located on the side, so you can easily switch cards and batteries when the camera is mounted on a tripod. Because the lens is positioned in the upper-left corner, you have to grip its body carefully, lest you take a picture of your fingers. With such a small device, it's no surprise that there's no optical viewfinder and that the LCD measures only 1.5 inches. The screen gains up to give you a usable if noisy preview in low light but is washed out in bright sunlight. One handy design touch is a little convex mirror on the front for composing arm's-length shots of yourself (and a friend, presumably).
The Dimage X31 has very few external controls: a little switch for selecting photo or video-clip capture, menu and playback buttons, and a small, difficult-to-use joystick. You change settings by navigating a graphical LCD menu with the joystick. Once you learn the icons, selecting submenus works quite well. You can also program the joystick to directly access a setting such as exposure compensation or white balance, and its up and down arrows control the not-entirely-smooth 3X optical zoom.
In addition to core snapshot functions, the Dimage X31 provides a nice selection of creative effects. Not only can you shoot in black and white or sepia, but there are posterization and soft-focus options. If you want to get really fancy, you can add a frame or a border effect to an image. And in playback mode, you can copy and resize an image so that it's ready to be e-mailed.
The Dimage X31 excels at start-up time; it took us less than 2 seconds to power up and snap. At about 3.6 seconds--or 6 seconds with flash--shot-to-shot time is slightly below average for this camera's class, although the continuous-shooting mode clicked off four images at a rate of about 1.3 frames per second at the highest resolution. The autofocus didn't always have an easy time locking on subjects in typical indoor lighting, prolonging the otherwise quick shutter lag of about 0.4 second.
Our test images were generally pleasing, with nicely saturated colors. Exposures, with the exception of some overexposed macro shots, were relatively accurate with a tendency to meter for highlights. Although the photos weren't the most crisp we've seen and there was some noticeable noise in wide expanses of sky, we think that snapshot prints will look just fine.