Hi Rich,
may I try to answer your question in somewhat more detail?
Should the slide give neutral/white-balanced values for the black to white areas or is a bluish cast expected on this slide when calibrated correctly?
To know the proper appearance of the grey patches one has to look into the reference file coming with the target. Relevant to your question are the a- and b-values for patches labelled GS0 (white) to GS23 (black). These a- and b-values specify the colours of the light source used to expose the target slide. What you aim at with the whole calibration process is, that on your calibrated monitor the patches appear with these colours as close as possible. The original colours of the light source are modified by the colour response of the Fuji film and the colour response of the scanner. Both of these have to be calibrated out via the ICC profile created from the IT8-target to achieve this goal.
For most targets I know the GS patches are of neutral grey, i.e. their a- and b-values are close to 0 (this is not mandatory but helpful. Ignore the L-values, they specify the luminance.). If the human eye should not be able to discern any colour cast in these grey patches the quantity dE calculated as dE = srqt(a^2+b^2) should be less than ~1.
An easy way to calculate the dE values is to load the reference data into EXCEL and do the calculation there. Here are the data for one of my Fuji targets:
Code: Select all
SAMPLE_ID L a b dE
GS0 90.99 0.16 1.60 1.61
GS1 80.88 0.02 0.67 0.67
GS2 77.18 0.03 1.31 1.31
GS3 73.18 0.23 0.73 0.77
GS4 69.27 -0.63 0.55 0.84
GS5 65.26 -0.59 -0.05 0.59
GS6 61.06 -0.04 0.38 0.38
GS7 57.18 -0.42 0.49 0.65
GS8 52.97 -0.07 0.00 0.07
GS9 48.91 0.04 -0.19 0.19
GS10 45.06 -0.55 -0.10 0.56
GS11 41.01 -0.60 -0.01 0.60
GS12 36.98 -0.39 0.09 0.40
GS13 33.02 -0.51 -0.35 0.62
GS14 28.99 -0.26 -0.12 0.29
GS15 24.78 -0.28 -0.15 0.32
GS16 20.96 -0.34 -0.03 0.34
GS17 17.27 -0.66 0.44 0.79
GS18 13.20 -0.53 0.95 1.09
GS19 9.36 -0.43 -0.30 0.52
GS20 5.53 -0.46 0.31 0.55
GS21 3.49 -0.33 -0.17 0.37
GS22 1.84 0.05 -0.07 0.09
GS23 0.85 0.18 -0.14 0.23
Therefore the grey patches for this target should appear on my calibrated monitor as really neutral grey -- and they do. The target slide, of course, if viewed on a light table, will look different and the greys have a colour cast introduced by the colour sensitivity of the film. For one of my other Fuji targets the a-values in the reference file are in the range -1 to -3, b-values scatter around 0. Thus I would expect a very, very slight greenish cast in the grey values.
You should measure the a- and b-values for your calibrated scan of the target. As there seems to be an issue with the the Lab-values displayed by the densitometer in SilverFast8, I would use SilverFast6 HDR or RawTherapee to measure the patches and check, if their dE value is indeed as specified by your reference table, on average.
Hermann-Josef