AVS Special Member
Join Date: May 2008
Location: San Francisco - East Bay area
Mentioned: 1 Post(s)
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Quoted: 21 Post(s)
There is a difference between characterizing/profiling versus creating a correction matrix. In characterization/profiling, you measure one thing... a shade of gray or white and you measure the same thing with the reference meter and that ONE measurement (for red, green, and blue) is applied to the meter being characterized for ALL luminance values of red, green, and blue.
To fully correct a questionable meter against a reference meter, you would measure multiple values of red, green, and blue with both meters and create a correction matrix that "fixes" the meter being calibrated so it measures the same as the reference meter at any luminance level.
With characterization/profiling, you assume that one measurement is enough to make the meter-in-question accurate, or reasonably accurate at all luminance levels even though you measure just one (or maybe some small number of reference levels). Correction is potentially more accurate, but it's also more time consuming... potentially quite time consuming if there are a lot of measurement points involved.
Calibration is the ultimate "fix" for a questionable meter... here the meter is completely measured against standards (often by a factory technician) and in the case of colirimeters, the filters are replaced (if necessary) and the entire meter is restored to factory specifications. Many inexpensive meters don't have calibration offered for them as calibration would cost as much as making a new meter. The meter I use costs $800 to re-calibrate and frankly, each time I have it done, I wonder if I should just buy a new lower-cost meter... especially now that meters like the C5 and the newest i1 have become available. I could probably buy one of these meters every year and sell it for half-price as a used meter and be calibrating for less than I spend just to re-calibrate the high-end meter I use. On the other hand, the meter I use can't be fooled by the light source (CRT phosphors, plasma phosphors, CCFL, LED, OLED, laser, projection lamps, and anything likely to ever come along that doesn't exist now). It's difficult, perhaps impossible, to design a low-cost filter-based meter (colorimeter) that can do that. They typically need some kind of correction factor for different display types.
"Movies is magic..." Van Dyke Parks
THX Certified Professional Video Calibration
ISF -- HAA --
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