From c07d0c2d2f6f7b0eb6e92cc6204bf05037957e82 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?J=C3=B6rg=20Frings-F=C3=BCrst?= Date: Mon, 1 Sep 2014 15:43:52 +0200 Subject: Imported Upstream version 1.6.3 --- doc/i1proHiRes.html | 177 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 177 insertions(+) create mode 100644 doc/i1proHiRes.html (limited to 'doc/i1proHiRes.html') diff --git a/doc/i1proHiRes.html b/doc/i1proHiRes.html new file mode 100644 index 0000000..d6d8078 --- /dev/null +++ b/doc/i1proHiRes.html @@ -0,0 +1,177 @@ + + + + The i1pro Hi Res. Mode + + + + +

Does the + i1pro High Resolution mode improve accuracy ?
+

+ A question that has been asked is : "You've extended the Eye-One Pro with a high resolution + spectral mode, giving readings at 3.3nm spacing rather than the + default 10nm. Does this mode improve accuracy ?"
+
+ This is a quite reasonable question. The following attempts to + answer it.
+

Why would a higher + resolution spectral mode improve accuracy ?
+

+ A spectrometer computes CIE tri-stimulus values by measuring + spectral values and then weighing those values by the observer + curves before summing the weigted values. The accuracy depends on + the correct weighting being applied at each wavelength. If the color + is composed of very narrow spectra peaks, as is sometimes the case + for certain light sources and many display devices, then the exact + positioning of one of the peaks on the observer curves may be + influencial in the final color value, and too coarse a quanization + of the spectral readings may lead to tri-stimulus errors. So in + theory increasing the spectral reading resolution to 3.3 nm should + lead to improved color accuracy with narrow spectra color sources.
+

Why may this not work in + practice ?

+

The instrument spectral resolving power is set by a number of + factors, and a critical one is the entrance slit width. By + measuring a very narrow band source such a as a laser, using the + default 10nm resolution indicates a FWHM (Full + + + + + width at half maximum) of about 25nm. Doing a measurement at + 3.3nm resolution reveals that the optical limit seems to be about + 15nm, so there is some hope of improvement from that perspective.

+

Another factor is that the calibration data for the instrument is + only given at 10nm intervals. So to produce calibrated readings at + 3.3nm intervals, it is necessary to up-sample the calibration data + with sufficient accuracy. If the calibration data is sufficiently + smooth (indicating that the underlying device characteristics are + also smooth), or any slight inaccuracy will get calibrated out + (which is typically the case for reflective measurements) then + this may not be a limitation either. In the case of the i1pro2, + which seems to have a diffraction grating/light sensor with a less + smooth spectral efficiency curve than the Rev A - D models, the + task of up-sampling the emissive calibration data with sufficient + accuracy is a more difficult.
+

+

The verification experiment
+

+ To give some indication of whether ArgyllCMS's high resolution + spectral mode is capable of improving color measurement accuracy, or + at least to indicate that it doesn't noticeably worsen it, the + following fairly simple, real world experiment was performed:
+
+ A measurement target consisting of white + primary + secondary + colors (White, Red, Green, Blue, Cyan, Magenta, Yellow) repeated 10 + times was used. This target was displayed on a conventional LCD + screen with a CCFL backlight (MacBook display), and measured using + using ArgyllCMS V1.6.0 dispread:
+
+ 1) Using a JETI + + + + + specbos 1211 reference Tele-Spectro-Radiometer.
+
+ 2) Using an i1pro2 in standard 10nm mode.
+
+ 3) Using an i1pro2 in ArgyllCMS 3.3nm mode.
+
+ The resulting readings were then analyzed using colverify.
+
+ The results were analyzed two ways, first in absolute value error + terms, and secondly in brightness (Y) normalized terms, the latter + corresponding to the typical way such readings are used for display + calibration and profiling.
+
+ A second, similar experiment was run on a CRT type display.
+

Results:

+


+ LCD display:
+

+

Absolute errors of i1pro2 10nm mode to specbos 1211:
+

+   Total errors (CIEDE2000):     peak = + 3.070420, avg = 2.204137
+
+ Absolute errors of i1pro2 3.3nm mode to specbos 1211:
+
+   Total errors (CIEDE2000):     peak = + 2.108411, avg = 1.568577
+
+
+ White Y normalised errors of i1pro2 10nm mode to specbos 1211:
+
+   Total errors (CIEDE2000):     peak = + 2.419800, avg = 0.747926
+
+ White Y normalised errors of i1pro2 3.3nm mode to specbos 1211:
+
+   Total errors (CIEDE2000):     peak = + 1.595033, avg = 0.578270
+
+
+ So in this particular situation, hi-res mode improves accuracy by + somewhere between 0.2 and 0.6 DeltaE 2K.
+
+
+ Example of white spectrum for the three measurements (red: 10nm + i1pro2, green: 3.3nm i1pro2, black: specbos):
+ specbos 1211 (Black), i1pro2 10nm (Red), i1pro2 3.3nm + (Green)
+
+


+ CRT display:
+

+

Absolute errors of i1pro2 10nm mode to specbos 1211:
+

+   Total errors (CIEDE2000):     peak = + 1.516886, avg = 0.965740
+
+ Absolute errors of i1pro2 3.3nm mode to specbos 1211:
+
+   Total errors (CIEDE2000):     peak = + 1.751776, avg = 0.887878
+
+
+ White Y normalised errors of i1pro2 10nm mode to specbos 1211:
+
+   Total errors (CIEDE2000):     peak = + 1.509129, avg = 0.654752
+
+ White Y normalised errors of i1pro2 3.3nm mode to specbos 1211:
+
+   Total errors (CIEDE2000):     peak = + 1.284044, avg = 0.622501
+
+

Conclusions:

+ The results for the conditions of this particular experiment + indicate that ArgyllCMS High Resolution mode can very slightly + improve colorimetric measurement accuracy of display devices. + Accuracy may conceivably be improved a little more than indicated by + this experiment for i1pro rev A-D instruments which have a smoother + diffraction grating/light sensor characteristic, or it is also + conceivable that an unfortunate combination of display spectra and + the i1pro2 may result in reduced accuracy. The High Resolution mode + is primarily useful for showing more spectral detail, and should + probably not be used for colorimetric measurement when the highest + possible robustness and reliability is desired. The potential for + improved accuracy may be of benefit in other situations though.
+

Raw Data:

+ The raw measurement data is available in this .ti3 archive.
+
+
+
+
+
+
+ + -- cgit v1.2.3