[argyllcms] Re: Using an i1 to measure FWA content?

Martin Weberg wrote:
>
>> 1) There is something different about the instrument calibration for UV vs. 
>> no UV filter. Measuring the calibration tile may
>>   reveal whether this is the case.
>>     
>
> The readings are different. See attached.
>   

Martin, I assume, after switching between UV-filtered and non-filtered,
you always calibrate the instrument against the calibration tile again,
before taking some readings, do you?

Well, if we'd assume that the filtered light does not contain any energy
below 400nm or 420nm, then basically we would have to discard the
readings for these wavelengths completely, as they would be the result
of a zero by zero division (no light multiplied by the reflectance of
the sample (+ noise), divided by no light multiplied by the reflectance
of the reference tile (+ noise)). I could also imagine that the
instrument possibly applies some kind of regularization in order to
avoid completely unfeasible readings (dominated by noise only) at the UV
wavelengths.

Regards,
Gerhard

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