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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 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> + <head> + <title>The i1pro Hi Res. Mode</title> + <meta http-equiv="content-type" content="text/html; + charset=ISO-8859-1"> + <meta content="Graeme Gill" name="author"> + </head> + <body> + <h2 style="text-decoration: underline; font-weight: bold;">Does the + i1pro High Resolution mode improve accuracy ?<br> + </h2> + A question that has been asked is : "<span style="font-weight: + bold;">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 ?</span>"<br> + <br> + This is a quite reasonable question. The following attempts to + answer it.<br> + <h4 style="text-decoration: underline;">Why would a higher + resolution spectral mode improve accuracy ?<br> + </h4> + 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. <br> + <h4 style="text-decoration: underline;">Why may this not work in + practice ?</h4> + <p>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 (<a + href="http://en.wikipedia.org/wiki/Full_width_at_half_maximum">Full + + + + + width at half maximum</a>) 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.</p> + <p>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.<br> + </p> + <h4 style="text-decoration: underline;">The verification experiment<br> + </h4> + 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:<br> + <br> + 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 <a href="dispread.html">dispread</a>:<br> + <br> + 1) Using a <a +href="http://www.jeti.com/cms/index.php/instruments-55/radiometer/specbos-1211">JETI + + + + + specbos 1211</a> reference Tele-Spectro-Radiometer.<br> + <br> + 2) Using an i1pro2 in standard 10nm mode.<br> + <br> + 3) Using an i1pro2 in ArgyllCMS 3.3nm mode.<br> + <br> + The resulting readings were then analyzed using <a + href="colverify.html">colverify</a>.<br> + <br> + 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. <br> + <br> + A second, similar experiment was run on a CRT type display.<br> + <h4 style="text-decoration: underline;">Results:</h4> + <p><br> + LCD display:<br> + </p> + <p>Absolute errors of i1pro2 10nm mode to specbos 1211:<br> + </p> + Total errors (CIEDE2000): peak = + 3.070420, avg = 2.204137<br> + <br> + Absolute errors of i1pro2 3.3nm mode to specbos 1211:<br> + <br> + Total errors (CIEDE2000): peak = + 2.108411, avg = 1.568577<br> + <br> + <br> + White Y normalised errors of i1pro2 10nm mode to specbos 1211:<br> + <br> + Total errors (CIEDE2000): peak = + 2.419800, avg = 0.747926<br> + <br> + White Y normalised errors of i1pro2 3.3nm mode to specbos 1211:<br> + <br> + Total errors (CIEDE2000): peak = + 1.595033, avg = 0.578270<br> + <br> + <br> + So in this particular situation, hi-res mode improves accuracy by + somewhere between 0.2 and 0.6 DeltaE 2K.<br> + <br> + <br> + Example of white spectrum for the three measurements (red: 10nm + i1pro2, green: 3.3nm i1pro2, black: specbos):<br> + <img alt="specbos 1211 (Black), i1pro2 10nm (Red), i1pro2 3.3nm + (Green)" src="i1proHiRes.jpg" height="335" width="667"><br> + <br> + <p><br> + CRT display:<br> + </p> + <p>Absolute errors of i1pro2 10nm mode to specbos 1211:<br> + </p> + Total errors (CIEDE2000): peak = + 1.516886, avg = 0.965740<br> + <br> + Absolute errors of i1pro2 3.3nm mode to specbos 1211:<br> + <br> + Total errors (CIEDE2000): peak = + 1.751776, avg = 0.887878<br> + <br> + <br> + White Y normalised errors of i1pro2 10nm mode to specbos 1211:<br> + <br> + Total errors (CIEDE2000): peak = + 1.509129, avg = 0.654752<br> + <br> + White Y normalised errors of i1pro2 3.3nm mode to specbos 1211:<br> + <br> + Total errors (CIEDE2000): peak = + 1.284044, avg = 0.622501<br> + <br> + <h4 style="text-decoration: underline;">Conclusions:</h4> + 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. <br> + <h4 style="text-decoration: underline;">Raw Data:</h4> + The raw measurement data is available in this <a + href="i1proHiRes.zip">.ti3 archive</a>.<br> + <br> + <br> + <br> + <br> + <br> + <br> + </body> +</html> |