Re: How to profile metallic paper
Re: How to profile metallic paper
- Subject: Re: How to profile metallic paper
- From: Klaus Karcher <email@hidden>
- Date: Thu, 04 Nov 2010 11:08:37 +0100
Howard Ehrenfeld wrote:
I am experimenting with Red River Silver Metallic paper. It has a shiny
silver metallic surface and I am unsure of how to create a profile for this
paper. I am using either Profilemaker or MonacoProfiler with a DTP70 or
iOne for measuring the patches. The silver patches where it is usually
white keep causing errors when I attempt to read them. Does anyone have an
idea of how to create a profile with this paper?
As soon as it comes to metallic surfaces, it's getting extremely
challenging to get meaningful measurement results.
Prepress instruments like i1, DTP70, ... use 45°/0° measurement geometry
(sample illuminated at 45° and measured at 0° relative to the surface
normal). This geometry often correlates well with what we see in a
viewing booth or in real world conditions: we typically try to avoid
specular reflections in the filed of view in this cases. But gloss,
unevenness, surface structure and angle-dependent effects (e.g. caused
by metallic samples or interference pigments) affect the correlation
between measurement and visual impression.
Instruments for quality inspection, e.g. in the paper or paints and
coatings industry often use measurement devices with diffuse
illumination (integrating sphere), e.g. d/8° SCI: diffuse illumination,
measurement at 8°, specular component included. No matter in which
direction the gloss of the sample is reflected it always stays into the
sphere and will be measured. Because of this one gets nearly the same
results no matter if the surface is glossy, matt or structured.
Another variant of the d/8° geometry is the measurement with specular
component excluded: d/8° SCE. In this case a small hole (gloss trap) in
the sphere "catches" the highlight spot of shiny, flat samples.
Many d/8° instruments have a gloss trap which can be switched on or off.
When you measure a perfect mirror with a 45°/0° instrument, the result
will be black. When you measure it with d/8° SCI the result will be
white and with d/8° SCE it will be "some" gray. And what you see in the
real world when you look into a mirror purely depends on the viewing
conditions.
At first glance, d/8° SCE seems to be a good compromise for metallic
surfaces, but in practice the measurement often does not correlate well
with the visual assessment. Moreover the results are not robust against
uneven or structured samples.
Measurement results of metallic samples are often to dark when with
45°/0°, too light with d/8° SCI and too inaccurate with d/8° SCE.
Alternatives are multi-angle measurements (gonio measurements) and
models to combine several measurement geometries (e.g. combination of
45°/0° and d/8° SCI based on gloss measurements).
See also
<http://www.binder-muc.de/index.php?option=com_content&task=view&id=44&Itemid=86>
Klaus Karcher
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