Conversion to/from XRGA
After purchasing Gretag-Macbeth, X-Rite harmonized the subtly
different calibration standards the two companies were using for
their reflective measurement instruments, in order to minimize
changes with the introduction of new instruments. The result was the
standard, introduced in September 2010.
Current X-Rite instruments are natively calibrated to XRGA, while
older instruments from X-Rite are calibrated to XRDI, and
Gretag-Macbeth instruments to GMDI standards. To smooth the
interchange of old and new instruments, a spectral conversion
is possible between these different standards. While such a
conversion is not perfect, it reduces the discontinuities between
old instrument families and current X-Rite instruments.
By default, Argyll will use the native calibration of Gretag-Macbeth
and X-Rite instruments. These are summarized here:
You can override this and force reflective data to be a particular
calibration standard in two ways:
Using the -A command line option in spotread and chartread:
The N argument sets
the calibration to Native.
The A argument sets
the calibration to XRGA.
The X argument sets
the calibration to XRDI.
The G argument sets
the calibration to GMDI.
Or by setting an environment variable:
(Note that command line options will override this.)
If the ARGYLL_XRGA environment variable is set to:
XRGA, then all Getag-MacBeth/X-Rite
reflective measurements will be converted to XRGA.
XRDI, then all Getag-MacBeth/X-Rite
reflective measurements will be converted to XRDI.
GMDI, then all Getag-MacBeth/X-Rite
reflective measurements will be converted to GMDI.
If not set (or set to some other string), then the native
calibration will be used. Note that the values must be upper case.
All of the above except the DTP51 can have a conversion
(The DTP51 returns only colorimetric data, while the conversion
requires spectral data.)
You can also convert from one standard to the other using spec2cie.