The question you are asking amounts to who's calibration standard is better, Gretag's or X-Rite's. My answer is Gretag's, and thus no XRGA if I can avoid it. Details: XRGA uses different weighting (for reds, mostly). Thus spectral data can be converted from one standard to another. dE worst case 1.4. The slightest differences in aperture and measuring geometry have more effect than the difference between Gretag and X-Rite. Gretag geometry is generally more accurate, with better conformance to 45/0. In some ways one can view XRGA as an attempt to correct for systematic geometry error.
PS: Please have a look at Tom Lianza's account on the matter http://www.color.org/events/frankfurt/Lianza_ICCFrankfurt2013instrument_compare.pdf
Few things about Mr. Lianza here: http://patents.justia.com/inventor/thomas-a-lianza
I am sorry, but back to "how many angels can stand on the point of a pin?" (c).
Consider for example i1Pro2 device... it has both XRGA and non XRGA modes (at least available through software like BabelColor PatchTool and it does not seem that mr. Pascale invented that on his own - just implemented something that X-Rite itself gives out of the driver, no ?).
That means that the device itself is operating either with GmB calibration standard/geometry or with X-Rite calibration standard/geometry and then whatever is implemented inside is then (can be) translated to XRGA (by driver, I'd assume, shall ask mr. Pascale - which I actually did this morning).
So which "blood" runs in i1Pro2 then ?
I run both XRGA and non XRGA measurments yesterday, averaged for both, and run compare in PatchTool :
PatchTool COMPARE TOOL - COMPARE STATS REPORT
This file combines and compares the data of two files which have the same number of samples.
This report presents statistical data derived from the differences between the color values of these two data sets.
Date: "2015-11-18"
Time: "02:13:30 AM"
Version: "5.0.0 b397"
REFERENCE
- Name: "PatchTool Avg-9 (5 files)"
# The SOURCE data type is < spectrum >.
SAMPLE
- Name: "CC24 (ColorChecker Classic) 2014-11 = i1Pro2(SN#1044184, 2015-11-17, spectral, GMDI, AVG-5).cie (M0)"
# The SAMPLE data type is < spectrum >.
STATS-SETTINGS
Delta parameter: "E*"
Illuminant: "D50"
Observer: "2 deg."
Delta-E* formula: "CIEDE2000"
Absolute values: "NO"
Separate Neg./Pos. stats: "NO"
Negative samples: 0
Positive samples: 24
Number of samples: 24
AVERAGE
All samples: 0.10
Best 90%: 0.09
Worst 10%: 0.19
STANDARD-DEVIATION
All samples: 0.05
Best 90%: 0.04
Worst 10%: 0.01
MAXIMUM-ERROR
10th percentile: ± 0.03
Median (50th perc.): ± 0.10
90th percentile: ± 0.16
95th percentile: ± 0.17
Of all samples: ± 0.20
HISTOGRAM-DATA
Bin-size: 0.0500
Bin center 0.0250 0.0750 0.1250 0.1750
No patches 5 6 9 4
CUMULATIVE RELATIVE FREQUENCY (CRF) DATA
CRF of all-samples:
Max-error 0.0293 0.0311 0.0329 0.0391 0.0470 0.0512 0.0726 0.0750 0.0752 0.0980 0.1027 0.1034 0.1040 0.1265 0.1353 0.1366 0.1396 0.1408 0.1568 0.1722 0.1988
CRF 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100%
"PatchTool Avg-9 (5 files)" in the text above is XRGA mode measurements.
it seems that the difference between XRGA and non XRGA results points ( based on table 3 in
https://www.xrite.com/documents/literature/en/L7-462_XRGA_WhitePaper_en.pdf ) that i1Pro2 is operating more like legacy X-Rite devices and then using i1Pro2 in XRGA mode shall actually bring it closer to GmB legacy devices, which you state is "better"...
!!!
PS: "table 3"
