Re: Colorsync-users Digest, Vol 2, Issue 356 emissive Target
Re: Colorsync-users Digest, Vol 2, Issue 356 emissive Target
- Subject: Re: Colorsync-users Digest, Vol 2, Issue 356 emissive Target
- From: "Stefan Steib" <email@hidden>
- Date: Thu, 15 Sep 2005 18:07:45 +0200
Hi Rik
Thanks for this very interesting reply, but there are still some questions
that come to my mind:
Date: Wed, 14 Sep 2005 16:20:53 EDT
From: email@hidden
Subject: Re: Issue 350 emissive target
<If the spectral sensitivities and linearity characteristics of the camera
<are known, then this is the fundamental information required to construct
an
<optimum camera profile. The best way to get this data is with a
monochromator.
<The LED target is essentially an abridged (variable wavelength variable
<bandpass) monochromator.
If I read you right, it would be possible to just use 3 monochromatic
sources of light with a known
wavelenght of red,green blue to readout all the spectral response
informations of this (for example Bayerpattern) chip.
The mixture of colors as well as the simulation of "greys" would need
specific modifications of the emissive sources
which may in result not improve the readout of specific values, but in the
opposite diminish the exactness of the measurements ?
Because as we have discussed here recently even high end measurement devices
that would be needed to determine the exactness
of the mixtures will have a certain degree of misreading. Adding up these
errors (system noise!) will most likely result in a loss of profile quality
?
<<Without a spectral
response curve(can be done once in the factory),
metameric information and overall whitepoint calibration of the actual
scene
you will get nowhere>>
I<t would be great if this information was made available, but its generally
<not. So the emissive target provides an opportunity to create an optimal
<camera/lens specific profile for the photographer's particular setup.
But wouldn´t this target be extremely expensive and also hard to handle ?
All the fileds values have to be determined spectrally in a Lab environment.
Any flare or reflections on the surface
of the target will completely destroy the reliability of this approach.
What happens if the environments brightness exceeds the brightness of the
targets emitted lumen?
So it probably could only be used in the dark....?
As the Luminance of the target will be produced by LEDs (?) with electric
power sources ,
how stable is the LED spectral output if voltage goes down ?
<<why the spectral response has to be measured inside
<the camera. I´m pretty shure that the technical (spectral response) specs
<are well known to the chip manufacturer>>
<Each camera is somewhat different. And because of the optical properties of
<a camera chamber (flare, f number, etc), measuring the detector is just not
<enough. Most camera manufacturers, if they have in-camera measurements at
all,
<are loathe to share this information as they consider it to be highly
<proprietary.
As you mention Lens Flare, would this not add wavelenght specific faults
according to the
lens specifics, instead of specifiying single color measurements of the chip
?
I mean there will be totally different values for 12 Lens Zooms or Macro
triplets-
further should a Zoom be measured with the shortest or the longest focal
lenght ?........
<<any other
<system with interchangeable lenses is going to have different values for
<every other lens mounted>>
<Right, but a well determined profile and processing flow can be
surprisingly
<robust. These errors can be rather small in the overall scheme of things.
In
<any case, the emissive target (and presumably smart profiling software)
<could allow the photog to profile each camera/lens combination if he feels
the
<need.
Now what about chip heating, aging, environment temperature and software
changes?
What does the influence of ASA settings/speed as well as exposure times mean
?
Does this mean a photographer should continuously recalibrate with the
emissive target ?
I say, we have been develloping reflective Color Targets since 1995
(YxyMaster), the biggest Problem of all is handling.
Many Users simply don´t get it right. And I would say I´d consider the
hnadling of a reflective target to be easier as an emissive one.
As long as this is not solved, a target means nothing but additional trouble
producing
intense handling needs with very limited use for outputting real
Photographs.
As I see it, this is mostly a scientific Lab solution, normal photograhic
users will have BIG difficulties to achieve any usefulness of this.
Greetings from Munich
Stefan
Stefan Steib
Gabelsbergerstr.48d
D-80333 München
tel.: +49 89 520 59 305
fax: +49 89 520 55 778
www.digitalfoto-trainer.de
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