Kent Tenney schrieb:
Would it be possible to profile a monitor
using a digital camera to measure the
monitor's output?
Hi Kent,
basically yes, if
a) if the camera permits you to turn off all automatic functions
b) if the camera is able to reproduce measurements with reasonable accuracy
c) you first profile the camera for the spectral power distribution of the monitor phosphors you want to measure.
However, in order to achieve (c) you need a colorimeter - and if you have a colorimeter aynway, there is no need to perform the monitor measurements with the camera.
Here is some background:
The major problem with using a scanner/camera as colorimeter is, that these devices are usually not "colorimetric", i.e. the spectral sensitivities of their sensors are not linear transformation of the CIE color matching functions. This means, a scanner/camera "sees" colors different than the human eye. It may happen that a scanner returns the same RGB values for two colors which look different for the human eye, and a scanner may even return different RGB values for two metamer colors which look equal for the human eye. This phenomenon is also called "scanner metamerism". Basically this implies, that it is actually *impossible* to establish a unique RGB <-> XYZ mapping, which is valid for arbitrary spectral power distributions.
So, how is it possible at all to get scans with reasonable color reproduction? The answer is, it is only possible if we restrict the scans to a specific media type. This usually solves the ambiguity mentioned above, because for a particular media type the set of spectra which can be represented on the medium is very limited, and each CIE color represented on the meduim is usually associated with exactly one spectral power distribution.
However this means, if you use an IT8 target on Kodak paper to profile your scanner, then the profile is only *only* valid for scanning Photos on Kodak paper. If you scan e.g. an inkjet print with the same profile, then you will unfortunately get incorrect colors. The amount of the error will depend on the scanner and the media used.
(I don't have an instrument to measure it, but according to the large, clearly visible difference, I guess that my scanner gives me even differences of up to 10 dE units between photo paper (-> IT8 target) and an inkjet print with canon inks)
And the same applies, if you want to measure the your monitor with a camera. It is only possible to do it accurately, if you characterize the camera for the spectral characteristics of the monitor phosphors.
Regards, Gerhard
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