Re: Characterizing semi-Translucent materiel
Re: Characterizing semi-Translucent materiel
- Subject: Re: Characterizing semi-Translucent materiel
- From: Phil Green <email@hidden>
- Date: Mon, 27 Nov 2000 13:19:26 +0000
- Organization: LCP
Roger Breton wrote:
I am debating whether I should make those measurements with
>
having placed some piece of white cardboard underneath the target (therefore
>
artificially boosting their lightness range) or simply leave on the dark
>
black metallic materiel of the Spectroscan the table (and this way more
>
"closely" adhering to the standard measurement methodology)?
The main reason for using black backing is to reduce the effect of
printing on the back of the sheet being measured. This doesn't normally
apply on translucent material, which isn't covered by graphic arts
standards.
Any measurement is only as good as its ability to predict the appearance
of a colour within a given viewing condition. So Jan's suggestion of
using the pack contents as backing is quite reasonable, although you
could have problems in ensuring consistency. The alternatives would be
to prepare some opaque backing materials which have a colour similar to
the products in question, but will not vary in colour over time; or to
use an opaque grey material as Joe suggested. If possible, the grey
backing should be chosen to have a lightness similar to that of the pack
contents.
This should be adequate for profiling purposes, although if you wanted
to use the measurements for other purposes (e.g. compare results between
print sites or between instruments, or quantify the difference between
two samples), there are a number of issues to be aware of, including an
error that arises as a result of the translucency of the material (known
as lateral diffusion error or translucent blurring). Minimising this
error requires a larger aperture than you find on most hand-held
instruments.
It's not obvious whether the measurement geometry for translucent
materials should be 0/diffuse or 0/45; I think I'd probably go for
0/diffuse but I don't see any major problems in using 0/45 in profiling
if that's the geometry of the instruments available.
You could have a further problem in proofing, as the pack contents would
create a surround colour effect. Unless you simulate this on the proof,
your profile could lead to a proof that matches the final product
colorimetrically yet appears different.
--
Phil Green
Colour Imaging Group
School of Printing and Publishing
LCP
Elephant and Castle, London SE1 6SB
Tel: +44 020 7514 6759 Fax: +44 020 7514 6772
http://twinpentium.lcp.linst.ac.uk/digitalcolor/