Re: Spectrophotometer measurements
Re: Spectrophotometer measurements
- Subject: Re: Spectrophotometer measurements
- From: Joachim Euler <email@hidden>
- Date: Mon, 08 Jul 2002 12:44:06 +0000
>
> How critical is it to place a piece of blank media underneath the chart
>
> when taking measurements on, say a Gretag MacBeth SpectroScan? For remote
>
> profiling purposes this would require you have on hand every kind of paper,
>
> unless your client is nice enough to include an extra sheet.
>
>
>
> Is this necessary? How would it affect the accuracy of the measurements?
>
>
It depends very much on the paper stock in question. With a realy
>
opaque paper, it shouldn't be necessary. With more translucent
>
papers, it ranges from desirable to essential. In the most extreme
>
case I've encountered so far, the difference amounted to 9 units in
>
L* between measuring on the black table of the Spectroscan and
>
measuring on a stack of paper white. (Measuring over an opaque white
>
paper overestimated the L* of white by 2 units, so it's probably a
>
slightly better fallback position than measuring over black.
...if it just were the change of L* coordinates. Another problem with black
backing which is more important IMO is a hue shift which may occur
especially in yellow tones (and can be seen in every profile created from
e.g. the FOGRA data set for LWC paper).
Bruce is right qith his pragmatic approach ("Can you see the registration
marks of the table?").
If you don't have another sheet of the very same paper at hand IMO any white
paper will do. At least you'll be better off than without any backing.
Jo Euler
--
Public P3 - Pre Print Professionals GmbH Joachim Euler
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