Hi Gerhard, nice to her from you -- and many thanks for your help :-) Gerhard Fuernkranz wrote:
Am 26.06.2010 00:22, schrieb Klaus Karcher:(I dare say the radiation maximum of the lamp is still above the relevant wavelengths at the end of the reading, but I have no idea which compensation mechanism might affect the result).Hello Klaus, the IR output of the tungsten lamp is certainly rather high, but I'm not sure whether there is possibly an IR filter in the play? Do you know?
I don't know. Maybe a filter to attenuate unwanted diffraction orders? The raw readings seem to fall off at both ends considerably as far as I can see.
And the sensor sensitivity might be already down in this region, too.
I don't know which kind of sensor it is, but I guess the IR sensitivity should be sufficient (AFAIK silicon sensors are very sensitive to near-infrared normally).
In order to assess whether the instrument can still deliver reasonable values in this region, one rather needs to take a look at the raw values obtained from the sensor.
That's what I am struggling with at the moment. I played quite a while with raw readings extracted from "chartread -D5 -H" (calibration, 60sec pause, approx. 10sec measurement on white tile = 18090 white tile readings). But I still wonder how to interpret the raw data correctly.
I thought I got the trick in i1pro_meas_to_abssens(): if (rval >= maxpve) rval -= 0x00010000; /* Convert to -ve */but I still get many overflows. (I use the maxpve value returned from i1pro_getmisc(): 0xfa00)
Maybe what I found so far is just my misinterpretation of the raw data, but I'm stuck and don't know how to do better, so take my endeavors with a pinch of salt:
There seems to be a second (dark) calibration at the beginning of each strip, maybe with different integration times (Graeme mentioned something like this when we met in Munich, but I can't remember the details).
This is a plot that shows the raw data of some bands of the stip reading (no overflow issues in this case):
When I compare the dark current values obtained from the initial calibration with the (assumed) dark readings at the beginning of the strip (213...233), band 3 catches my eye as it seems to be an extreme outlier (a "hot pixel"?) -- see
<http://digitalproof.info/argyll/eye-one_IR_calibration/offsets.pdf> (btw.: the bands get read out from red to blue)A closer look reveals even more strange dark current results at the red end (bands 1...4), whereas the max value in band 4 might be simply an overflow issue (i.e. aninterpretation error).
In the initial dark calibration everything seems to be ok: <http://digitalproof.info/argyll/eye-one_IR_calibration/boxplot_initial_dark_cal.pdf> ... but in the strip dark calibration, bands 1...4 get out of line: <http://digitalproof.info/argyll/eye-one_IR_calibration/boxplot_strip_dark_cal.pdf> see also <http://digitalproof.info/argyll/eye-one_IR_calibration/summary_offset.txt> and here -- just for completeness - the chartread -D5 output: <http://digitalproof.info/argyll/eye-one_IR_calibration/chartread-D5_on_whiteref.txt>- my failed attempt to interpret the raw data correctly (10 bands out of 127, strip calibration removed):
<http://digitalproof.info/argyll/eye-one_IR_calibration/10_bands.pdf> - and the protocol of my evaluation in R: <http://digitalproof.info/argyll/eye-one_IR_calibration/R_record.txt> Klaus