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diff --git a/doc/i1proDriver.html b/doc/i1proDriver.html new file mode 100644 index 0000000..0894f59 --- /dev/null +++ b/doc/i1proDriver.html @@ -0,0 +1,157 @@ +<!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) The OMD internally calculated L*a*b* value<br> +B) The L*a*b* value calculated by Argyll from the OMD +spectral values.<br> +C) The L*a*b* value calculated from the Argyll measured +spectral values.<br> +D) 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> + The result was an average Delta E (CIE76) of 0.006, +with a maximum of 0.012.<br> +<br> + 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> + The result was an average Delta E (CIE76) of 0.028, +with a maximum of 0.051.<br> +<br> + This shows that the OMD and Argyll driver are in +close agreement in spectral measurement.<br> + 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> + 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> + 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> + The result was an average Delta E (CIE76) of 0.158, +with a maximum of 0.353.<br> +<br> + Because the ColorChecker samples have relatively +smooth reflectance spectra, it can be expected that<br> + the normal and Hi-Res mode results should be fairly +similar. And indeed, this is the case. The biggest<br> + differences are for patches +with the largest spectral transitions in them, which is to be expected +as the<br> + Hi-Res measurement more +closely follows the spectral shape, while the differences for +spectrally flat<br> + patches is neglegable, since both can follow the +spectral shape well.<br> +<br> +Example Yellow-Green Patch, Hi-Res & 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> |