IT8 calibration. what am I doing wrong?

[Gregory C]

I probably don't understand this so please help me.

I did a scanner response check as described on Ian's site and found that gamma 2.2 was the best setting to get a mid GS11 of 100-110 on my Microtek ScanMaker 5700.

I then placed the IT8 chart into the scanner and prescanned. GS11 was approximately correct but GS0 and GS23 were off. GS0 was only 225-230 while GS23 was around 30.

I clicked the Calibrate button in SF Ai Studio 6.4.2r9 and ran the calibration. After calibration, SF automatically implemented the new ColorSync profile and re-prescanned the chart.

After prescan and with the new profile in place, GS0 still measured around 225-230 and GS23 was still around 30. Why isn't GS0 whiter and why isn't GS23 darker?

What have I done wrong?

regards,
Gregory

[LSI_Noack]

Dear Gregory

GS0 and GS23 are not meant to represent either "pure white" or "pure black". What's important is that the values come near to what had been measured in the lab, cf. the target's reference file's values.

Best regards
Sonny Noack
- Manager Technical Support, LaserSoft Imaging AG -

[Gregory C]

I have two targets with different R###### numbers. I checked the files online and they have slightly different GS Lab numbers. how does SF Ai Studio know which reference file to use?

R041119
GS11
45.52 0.69 -2.34
GS23
5.78 -0.15 -1.05

R040209
GS11
45.66 -1.12 -0.15
GS23
6.16 0.18 -1.41

the Lab readings for the preview of the chart:
GS11
44-45 0-2 -4 to -6
GS23
11-12 -5 to -13 -6 to +7
note how the readings vary as I drag the mouse through the grey bars. the colours are not evenly scanned. is that a limitation of my scanner or the preview process?

should I only compare the Lab values to a completed scan at 100dpi?

[LSI_Noack]

Dear Gregory

SilverFast reads the barcode underneath the greyscale. It will even download the correct reference file from our web server if not already present on your computer and creating the directories necessary itself.

Yes and yes. Please note also that CCDs have the inherent problem (especially with darkish areas) of producing random colour noise.
However, SilverFast reads a random number of points in the colour / greyscale patch and can thus cancel the odd pixel value out.

Best regards
Sonny Noack
- Manager Technical Support, LaserSoft Imaging AG -

[Gregory C]

I think a lot of the noise in the scan is caused by the glossy reflective surface of the target.

in Ian's review of inCamera, he noted that the software had an option to ignore the shiny squares of the GretagMacbeth ColorChecker DC target, thereby producing more accurate results.

I truly believe that the target would be more effective if it was a matte card rather than gloss.

regards,
Gregory

[LSI_Noack]

Dear Gregory

perhaps, yes. But keep in mind the matte appears that way e.g. to our eyes because light gets deflected. This might cause problems for scanners that need light not "to go astray".
However, I can also image and have experienced troubles with matte reflective material.
Well, it depends...

Best regards
Sonny Noack
- Manager Technical Support, LaserSoft Imaging AG -