Re: Outdoor/daylight camera profile
Re: Outdoor/daylight camera profile
- Subject: Re: Outdoor/daylight camera profile
- From: <email@hidden>
- Date: Mon, 22 May 2006 17:28:32 -0400
Michael,
As you are aware, outdoor target profiling with a camera
has a fundamental problem: the light color, its color
temperature, changes with time of day, time of year,
latitude, cloud cover (major effect in no-time), etc.
And we are not talking small changes here, thousands of
kelvin, enough to shift any color! Because of this
situation, I do not believe in using a single profile for
daylight.
A suggestion: when you make a profile, record the color
temperature. By having a few profiles at various
(daylight) color temperatures, you simply select the one
corresponding to the actual conditions. Of course, this
requires an instrument to measure the color temperature,
but you indicated some measurements of it, so this should
not be a problem. I would favor diffuse illumination
measurements, not necessarily with a tent, but 90 degrees
off from direct sun (others may have a different
opinion!).
This is not a miracle cure, but it might work.
A rep for the back said that making my own profile
wouldn't work because of IR and/or UV affects.
IR and UV filters are usually factory installed within
some backs or part of the sensor itself. It is true that
they can have a serious effect if they are not present /
or removed. However, unless these filters are
added/removed between the profile shots and the actual
picture, I do not see what the effect could be (i.e. I
fully agree with you!).
Danny
email@hidden
www.BabelColor.com
On Mon, 22 May 2006 12:30:41 -0700
"Michael Fox Photography News Account"
<email@hidden> wrote:
I'm interested in making a camera profile -- in
particular, a daylight
profile for a digital back -- and I am looking for
pointers.
The existing Outdoor Daylight profile from Phase One
lacks highlight
definition, saturation in light colors and have a hue
shift in the blues
toward cyan. I made a "quickie" profile which did a
much better job. By
"quickie" I mean I stuck the target in the sunlight and
took a shot without
worrying about such things as color reflection from the
tan table it was
sitting on, specular highlights, etc. Even so, when
comparing the
colorchecker numbers in the image using my quickie
profile vs. the
theoretical/average numbers provided by Bruce Lindbloom
and others, I got a
much better match than with the supplied profile. When
applying to various
images, the result was also better, with much better
highlight detail,
better saturation of light colors (like rainbows) and no
hue shift in blue
values.
So, I think I'm on the right track. I've made lots of
printer and scanner
profiles but never a camera profile. So I'm looking for
pointers.
I realize I need to light the target as evenly as
possible, eliminate glare,
and eliminate color reflections from surrounding
objects. I also realize
that if I should shoot the target at mid-day sun, it
will technically not be
correct for any other time of day (different light).
But that's no
different than, say, using daylight film at sunrise or
using the
existing/supplied daylight profile at sunrise. So I
realize it won't be
perfect. But I'd like to get a better result than with
the
existing/supplied profile.
A rep for the back said that making my own profile
wouldn't work because of
IR and/or UV affects. I haven't had the opportunity to
question him about
why he thinks this will be a problem or how they dealt
with it in the
profiles that they produced. But I don't see why that
would be a problem.
I mean, of course they are present in daylight. But
that's what I'm trying
to profile. It seems to me that the camera sees what it
sees and,
regardless of what parts of the spectrum cause the
camera response, the
profile should do its job and characterize the camera's
response.
Should I try to diffuse the sunlight or place the chart
in direct sunlight?
For my quickie experiment, I placed the chart in direct
sunlight. I realize
that direct sun would introduce an undesirable specular
component which may
fool the profiler into thinking the colors are less
saturated than they
really are. A diffuser tent could reduce/eliminate
spectral highlights and
reduce contrast but may also slightly alter the color
temp (mine subtracts
about 200K) but if the image is white balanced, I'm
thinking that it
shouldn't be a problem. Using a tent would also likely
help with evenness
of illumination. So I'm thinking that a diffuser tent
is the way to go.
Comments?
GretagMacbeth has many controls for making the camera
profile. Other than
reading the help-file instructions and experimenting,
does anyone have any
general or specific recommendations for how these
controls might be
optimized for a daylight profile?
Thanks in advance,
Michael
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