I recently bought a (used) color calibration device: the ColorMunki Photo from X-Rite. Although it looks like an oversized tape measure, it is used to calibrate computer displays (either LCD or projector) and it can calibrate printer/ink/paper combinations. In either case, calibration is done by comparing the output colors against the intended color and by adjusting for the inevitable deviations within the computer. This kind of calibration is used heavily in the photography and graphics industries or by anyone else who needs accurate colors.
De ColorMunki calibrates the colors of an LCD monitor (or projector) by measuring the output colors while it controls the display using special software. It then generates unique correction data (an “ICC profile”) for compensating for display behavior within the graphics hardware in the computer. For an LCD monitor, the measurement device actually is hung facing and touching the LCD screen, while for an LCD projector the devices monitors the screen from a few meters away. In both cases, the device measures the colors of the light coming from the screen (this takes a few minutes and is largely automated).
Display calibration is generally done by serious photographers: if you don’t have a calibrated display, there is little point is worrying about exact colors of photos or prints.
Supplied ICC profiles for displays are seldom good enough because the display colors depend too much on brightness/contrast/color temperature settings. Furthermore displays (probably mainly the backlights) age, recalibration is needed every 1-4 weeks.
Printer calibration is a bit more complex and done by fewer people. This is because a manufacturer will typically supply accurate ICC profiles for a printer for major (often its own) paper types. Because periodic recalibration is less essential, and because profiles for major printer/paper combinations can be found on the Internet, one can often do without. The ink also plays a major role in this, but people who worry about color will typically not want to complicate matters by using 3rd party inks.
Printer calibration again uses special software (supplied with the device) to print test charts with 5 strips of 10 color patches each. The ColorMunki measures by illuminating the patches using a built-in light source (presumably white LEDs) that it can in turn calibrate using a built-in reference target or tile(which is not directly visible). You can a scan a strip of patches at a time by slowly pulling (works better than pushing) the sensor over each strip. The software will tell you whether or not the strip was scanned properly – if not you just repeat that strip.
As first original owner warned, this “pulling” over glossy paper does not go smoothly because the Teflon runners at the base of the device have a lot of friction when used with glossy paper. In fact, you can see some faint scratches on the photo after the scan. These do not impact the scan because the optical sensor is between the two runners. The sticky Teflon problem can be resolved by covering the Teflon with scotch tape or Post-It paper.
Compared to fancier printer calibration devices, this device uses fewer patches (a minimum of 2×50 - although you can add more if you want) and the stripwise scanning is probably unique: the alternative is to manually scan each patch or to use a small robot-like arm to position the sensor in two dimensions.
The device can also calibrate a projector attached to a computer. This is similar to calibrating an LCD monitor except that the device needs to see the screen from a distance (equal to roughly the screen width). As the device will be nearer to the screen than the projector, you should avoid shadows or limit them to the edges of the screen. This is not a big problem because the “eye” of device can be adjusted to point upwards a bit.
Unless you project in te dark (like a movie theatre), the blackest black you can get with a projector is determined largely by the ambient lighting. I doubt whether you would need to recalibrate if the ambient lighting changes: the ColorMunki essentially just measures the obtainable lighting range (per color) and ensures that the intermediate values are sufficiently linear. Arguably the only impact of significant background lighting (providing it doesn’t change during calibration) is to increase measurement noise slightly.
Real world color extraction
The scanner can also scan the color of printwork not coming out of your own printer or even physical objects (paint, cloth, etc). This is probably more useful for designers who need to specify or match product colors, but may come in handy if you want to compare a photo to the object being photographed. If you like, you can consider the device a 1-pixel color calibrated camera. You can sample colors a few millimeters in diameter which the ColorMunki can be placed on (not a car across the street).
As the software has recently (July 2009) been upgraded from version 1.0 to 1.1, I directly installed version 1.1. This provides a bit more technical control if you want that. But also gets rid of an annoying 3-computer activation limit. This 3-computer limit was mentioned as a drawback in many reviews, but was actually never enforced in any way.