Hello all! I have a question regarding calibration standards. You mention that the X-rite colorChecker passport is convenient as it has a range of grey levels, and it certainly looks both brilliant and affordable. However, looking at the website and user manuals I can’t seem to find any information on the reflectance values of the range of grey standards that are included at the bottom of the classic card. Would you advise calibrating the standards with a spectroradiometer and master standards or are you aware of some other (cheaper) method of obtaining this data? Many thanks!
Yes the x-rite is a fairly decent grey standard for visible-only photography. It’s important to note that it is not as perfectly diffuse or quite as “grey” as a sintered PTFE (e.g. spectraon) standard. But for most purposes in the human-visible range it will be fine.
I took reflectance recordings of my x-rite passport and these are included in the toolbox itself (in imagej/plugins/Cone Mapping/Charts/XRite Passport 400-700.csv).
From these I calculated the grey reflectance values as the average reflectance from 420-680nm (the main region of sensitivity for a digital camera). The values were:
Feel free to use these values, though of course there is a chance your chart isn’t the same as mine.
Alternatively you could measure them yourself against a master 99% standard, though it’s surprisingly tricky to measure these things accurately.