I always used the term colorimeter for display calibration devices. I mean they meter (measure) color: the term was so intuitively describing this fact that I never questioned its correctness.
Now it was pointed out to me that the device I own (a ColorMunki Photo), is actually a spectrophotometer. What's the difference between a colorimeter and a spectrophotometer?
I found this article from datacolor that tries to explain the differences.
It basically says that all of the following is wrong (in general):
- a spectrophotometer is reflective device (reads patches on paper), and a colorimeter is an emissive device (reads displays)
- spectrophotometers are expensive devices, and colorimeters are cheap ones
- spectros are more accurate than colorimeters
The real difference is supposedly "the method they use for reading color":
A spectrophotometer breaks light up into a spectrum, using a color grating or similar system. Then an array of sensors reads each section of the spectrum, producing spectral data. This is ideal if you are analyzing the spectral emissions of a lightbulb, a star, or some other light source, which is why spectrophotometers are often used as scientific devices.
A colorimeter uses edge band filters, or some similar system, to separate light out into color components, and then fits those to matching curves based on the human eye, to produce color values in one or another three-value color space (XYZ, xyY, Lab, etc) based on what the human eye would see. This is ideal for matching the human visual response
Ok, hang on there. Color is determined by the frequency of the light. The spectrum is (very basically speaking) a list of all the available frequencies and their intensities (comparable to how a histogram is a list of intensities of a photo, to keep this in the photography realm). Thus color and the spectrum are closely related.
From what I understand, they both do the same thing: pick certain parts of the spectrum and analyse them. Sure they do, because they both measure "color". The spectro does so by diffraction (think dark side of the moon cover: similar result, different cause) and analysis of the result and the colori by band filters, which essentially means it looks at a limited range of colors while doing its thing. (a band pass filter is similar to only looking at the "highlights" part of the histogram, to reuse that analogy).
The article doesn't really explain things well (to me, at least). One device is described by how it obtains the spectrum of light (diffraction) and the other by how it analyses it (band pass filter). That's an apples and oranges comparison, like "Apples grow on trees and oranges are sour" - different properties have different values. That's not very helpful to distinguish them, they might as well be the same for both.
What's the exact difference between the two devices?
I agree with the closing statement of the article:
So you should feel free to choose the device you use for profiling based on its own merits, rather than worrying about which device type it may be.
However, I'm left with the question as to how to refer to those devices in general. As the article suggests, some are neither of the two types but inverse spectrocolorimeter. What term specifies the common functionality to to "measure color" without going into detail about the used technology?