Color Meters 101: How We Measure
Color meters take on many forms, but they all fall into two categories: tri-stimulus colorimeters and spectroradiometers (also known as spectrophotometers).
The less-expensive option is the tri-stim, and that's the type of meter included with the Spyder4Elite. It employs sensors that read light through colored filters. The sensors themselves are simple photodiodes that read only the luminance (brightness) of the light falling on them, and return a particular voltage. The colored filters separate the light into the color primaries so that a spectral analysis can be performed by the meter’s firmware. A value for each color is then returned to the software, which gives you the final numbers in any one of several formats.
Tri-stimulus meters like this are a great value and work very quickly. A measurement typically takes only a second or two versus 20-30 seconds for a spectroradiometer in low light. In fact, many professionals profile their tri-stim device to a spectro in order to shorten the calibration process. Tri-stim meters are also small and light, making them easy to set up and use for those quick touch-up calibrations favored by photo and graphics pros.
The disadvantage is accuracy and repeatability. If you take a series of readings from a single test pattern, you’ll quickly find a slight variance in the results. Most meters take and average multiple readings to mitigate this, but ultimately, a spectroradiometer is a more precise and accurate instrument for measuring your display.
Another downside is, as luminance meters, they are not the best choice for measuring color. Color accuracy in a tri-stim is determined by the quality of the filters used, and this can vary. The filters also change over time requiring the instrument itself to be recalibrated every so often. Their best use is for measuring luminance and grayscale, also known as white balance. Since this is the only adjustment available on the vast majority of computer monitors, it isn't perceived as a major shortcoming for average users, especially considering that correcting the white balance on any display will consequently have the additional benefit of improving its color accuracy.
At Tom’s Hardware, we use the X-Rite i1 Pro spectrophotometer, which, at over $1000, is still the least-expensive device of its type. For around the price of a new Honda Civic, you can get spectroradiometers from Minolta, Photo Research, and a few other companies. These are super-precise instruments that come in large chassis about the size of an old camcorder. The i1 Pro we use is much more compact and very easy to use with any direct-view or projection display.
The spectro measures the actual wavelength of incoming light to determine its spectral properties. No colored filters are used. The difference in price between the i1 Pro and its pricier brethren is related to the resolution of the instrument’s sensors. The i1 measures down to 10 nanometers, while the other meters are in the three-to-four range.
Now that you have an understanding of the hardware needed to calibrate your monitor, let’s see what it is we’re actually measuring when we calibrate.