RE: How to profile metallic paper
RE: How to profile metallic paper
- Subject: RE: How to profile metallic paper
- From: "Robert Rock" <email@hidden>
- Date: Thu, 4 Nov 2010 08:59:39 -0400
- Organization: P. Chan & Edward, Inc.
Perhaps this is a useless work-around suggestion, but here goes, and please
don't laugh at my non technical approach.
Due to the highly reflective nature of the substrate, it seems the biggest
obstacle here is inaccurate measurement of the charts using virtually any
instrument. I had a similar issue when trying to create profiles for various
laminations (matte and gloss) as the appearance of a color would change
based on how the chart is tilted towards or away from the light source. But
that was nowhere near as extreme as this example and I was eventually able
to make acceptable profiles. So for this case, how about taking a very
accurate digital photograph (flat lighting and using a custom profile for
your camera) and then printing the chart, again using custom profiles for
your printer. This would, it seems, at least get you in the ballpark. After
all, when we make a camera profile, all we're doing is photographing a
ColorChecker color chart. After profiling the camera, why not then
photograph and print your test charts, as accurately as possible, and make a
profile from there? Again, not a sophisticated solution, but maybe closer
than no profile at all. It seems we are better able to control the light
reflections in a photograph than under the lens of an i1Pro, DTP20, or other
instrument.
Again, please don't laugh. But tell me what's wrong with my logic. I want to
learn.
Thanks,
Bob Rock
-----Original Message-----
From: colorsync-users-bounces+rock=email@hidden
[mailto:colorsync-users-bounces+rock=email@hidden] On Behalf
Of Klaus Karcher
Sent: Thursday, November 04, 2010 6:09 AM
To: Howard Ehrenfeld
Cc: colorsync-users
Subject: Re: How to profile metallic paper
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&Itemi
d=86>
Klaus Karcher
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