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+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
+<html>
+<head>
+ <title>The i1pro Driver</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;">How can I
+have confidence in the i1pro Driver ?<br>
+</h2>
+A question that has been asked is : "<span style="font-weight: bold;">You've
+written your own driver for the Eye-One Pro. How can I have confidence
+that the measurements are accurate, and will match those made with the
+original manufacturers driver </span>?"<br>
+<br>
+This is a quite reasonable question. The following attempts to answer
+it.<br>
+<h4 style="text-decoration: underline;">Why does Argyll use it's own
+i1pro driver ?</h4>
+Primarily because the Original Manufacturers Driver (OMD) isn't
+available for all the platforms that ArgyllCMS supports (Linux in
+particular). A side benefit is that it's possible to tweak many of the
+driver parameters for slightly better results and more flexibility. It
+has also helped in understanding the characteristics and limitations of
+such instruments.<br>
+<h4 style="text-decoration: underline;">Does it match the OMD ?</h4>
+In principle the behaviour should be very similar. While the Argyll
+driver has been written from scratch, it does use exactly the same
+calibration values from<br>
+inside the instrument, and attempts to use the calibration values and
+process the raw instrument readings in an equivalent manner to that of
+the OMD.<br>
+<br>
+But the proof of the pudding is in the measuring, so to actually verify
+this, the following experiment was conducted:<br>
+<br>
+The Argyll version used was V1.2.0<br>
+<br>
+The Macbeth 24 patch ColorChecker was used as a sample target. For each
+patch (and the calibration tile), the following steps were performed:<br>
+<br>
+1) Place the instrument on the calibration tile.<br>
+<br>
+2) Use Argyll spotread to calibrate the Argyll driver.<br>
+<br>
+3) Change drivers to the OMD.<br>
+<br>
+4) Use the OMD to calibrate the instrument.<br>
+<br>
+5) Move the instrument to the patch on the ColorChecker.<br>
+<br>
+6) Read the color using the OMD.<br>
+<br>
+7) Change the back to the Argyll driver.<br>
+<br>
+8) Using the calibration made in step 2), read the color using Argyll.<br>
+<br>
+Each calibration or reading was performed 15 seconds from the previous
+one, to put the instrument lamp in a repeatable state.<br>
+The instrument was kept in exactly the same position for calibration
+and patch measurement with the two drivers.<br>
+(The whole idea is to reduce all other sources of error, other than the
+driver itself.)<br>
+<br>
+This measurement was repeated just once for each patch + the
+calibration tile. This was done in one run, and the readings were not
+specially selected.<br>
+<h4 style="text-decoration: underline;">Results:</h4>
+The following D50 L*a*b* values were recorded for each measurement:<br>
+<br>
+A) &nbsp;&nbsp; The OMD internally calculated L*a*b* value<br>
+B) &nbsp;&nbsp; The L*a*b* value calculated by Argyll from the OMD
+spectral values.<br>
+C) &nbsp;&nbsp; The L*a*b* value calculated from the Argyll measured
+spectral values.<br>
+D) &nbsp;&nbsp; The L*a*b* value calculated from the Argyll
+Hi-Resolution mode measured spectral values.<br>
+<br>
+<span style="text-decoration: underline;">A is compare to B, to check
+that the spectral to standard observer calculations are equivalent.</span><br>
+<br>
+&nbsp;&nbsp;&nbsp; The result was an average Delta E (CIE76) of 0.006,
+with a maximum of 0.012.<br>
+<br>
+&nbsp;&nbsp;&nbsp; This shows that there is very close agreement in the
+way spectral values are converted to XYZ and L*a*b*.<br>
+<br>
+<span style="text-decoration: underline;">B is compared to C to check
+that the Argyll driver behaves the same as the OMD.</span><br>
+<br>
+&nbsp;&nbsp;&nbsp; The result was an average Delta E (CIE76) of 0.028,
+with a maximum of 0.051.<br>
+<br>
+&nbsp;&nbsp;&nbsp; This shows that the OMD and Argyll driver are in
+close agreement in spectral measurement.<br>
+&nbsp;&nbsp;&nbsp; This error is an order of magnitude smaller than
+uniformity induced errors typical in the media being measured.<br>
+<br>
+<span style="text-decoration: underline;">A is compared to C to check
+that the Argyll driver and spectral to XYZ differences don't compound.</span><br>
+<br>
+&nbsp;&nbsp;&nbsp; The result was an <span style="font-weight: bold;">average</span>
+Delta E (CIE76) of <span style="font-weight: bold;">0.026</span>, with
+a <span style="font-weight: bold;">maximum</span> of <span
+ style="font-weight: bold;">0.048</span>.<br>
+<br>
+&nbsp;&nbsp;&nbsp; Rather than compounding, any spectral to XYZ
+differences tend to cancel
+out slightly. This is the <span style="font-weight: bold;">bottom line</span>
+experimental difference between
+the two drivers. The actual underlying difference may in fact be less
+than this, but it would be necessary to do multiple test runs to
+filter out experimental error.<br>
+<br>
+<span style="text-decoration: underline;">C is compare to D to check
+that the Argyll Hi-Resolution mode is behaving reasonably.</span><br>
+<br>
+&nbsp;&nbsp;&nbsp; The result was an average Delta E (CIE76) of 0.158,
+with a maximum of 0.353.<br>
+<br>
+&nbsp;&nbsp;&nbsp; Because the ColorChecker samples have relatively
+smooth reflectance spectra, it can be expected that<br>
+&nbsp;&nbsp;&nbsp; the normal and Hi-Res mode results should be fairly
+similar. And indeed, this is the case. The biggest<br>
+&nbsp;&nbsp;&nbsp; differences are for patches
+with the largest spectral transitions in them, which is to be expected
+as the<br>
+&nbsp;&nbsp;&nbsp; Hi-Res measurement more
+closely follows the spectral shape, while the differences for
+spectrally flat<br>
+&nbsp;&nbsp;&nbsp; patches is neglegable, since both can follow the
+spectral shape well.<br>
+<br>
+Example Yellow-Green Patch, Hi-Res &amp; Normal spectrum:<br>
+<img style="width: 709px; height: 259px;"
+ alt="Yellow-Green patch, Hi-Res vs. Normal" src="YellowGreen.jpg"><br>
+<br>
+<h4 style="text-decoration: underline;">Conclusions:</h4>
+The experimental average difference of <span style="font-weight: bold;">0.026</span>
+Delta E76 shown above provides evidence that despite using a completely
+different instrument driver to that supplied with the instrument, the
+ArgyllCMS Eye-One pro measurement values have comparable accuracy, and
+can be relied upon to match measurements made using the original
+manufactures driver.<br>
+<h4 style="text-decoration: underline;">Raw Data:</h4>
+The raw data is available in this <a href="i1proDriver.xls">spread
+sheet</a>.<br>
+<br>
+<br>
+<br>
+<br>
+<br>
+<br>
+</body>
+</html>