Digital BW, The Print

Hi Ernst,

Thanks for your suggestions.

> It could be different on the Eye One but my SpectroCam is 
> quite sensitive to the distance to the target and the angle. 
> The automatic  measuring setup with an old HP plotter had the 
> spectrometer slightly higher at first and the results were 
> darker readings. A slightly different angle of the head on the 
> patch showed similar changes. I had already made another strip 
> guide that allows longer strips to be measured manually and 
> that works good. The head doesn't touch the strip but is at 
> the right height and a thin PET foil protects the rest of the 
> target when the spectrometer is running over it.

I checked this and it does not seem to explain what happens. The eye-
one is well constructed to keep the angle fixed. Also distance seems 
to be wel controlled, both with and without guide. Furhtermore, if I 
artificially increase the distance a bit, the meaused l* LOWERS (i.e. 
less light light reflected, which is logical to me) instead of 
increasing (what is what I find if the measurement seems not to be 
OK).  

> I'm an advocate for multiple targets and multiple measurements 
> + averaging. The SpectroCam does that already on its way over 
> the patches, between 7-15 readings per patch. But I use more 
> targets where possible, the targets printed in another 
> direction etc.

Given my recent experience, I'll will make this common practice as 
well. However, my current results seem to be obscured by systematic 
artifacts. No stochastic process will eliminate this.
> 
> An interesting fact about the HP Z3100 and Z2100 is that the 
> integrated calibration and profiling measures per patch and 
> the dark patches get a longer time for the measurement. 
> Something that is difficult to achieve with strip reading or 
> one should increase the size of the dark patches.

That's interesting indeed, confirming that black readings are more 
prone to errors. 

> Any change in the surface of matte black should give different 
> readings.

I come to that conclusion as well. It's not illogical. My explanation 
is that any contamination or damage increases the scattering at the 
surface and, by that, increases the reflectivity of the surface. Is 
that what you mean as well? But I'm surprised by the size of the 
effect.

Joost