http://imagej.273.s1.nabble.com/Measuring-Dominant-Wavelength-tp5011335p5011379.html
response spectrum of a detector "dominant wavelength". I was not aware that
this expression is already used in colour science. I noticed also that
others tend to misinterpret it as the statistical modal value. I find
wavelength" of the camera's response spectrum. The sun's spectrum outside
the atmosphere is known. With a fairly high probability the result will be
between e.g. 500nm and 700nm. The transmission through the atmosphere can
be estimated using aerosol measurements. But here we start now to estimate
> How many assumptions are you willing to make?
>
> The human eye is no more able to compute the “dominant wavelength” of an
> arbitrary spectrum than a camera is. But, the human eye did not evolve in
> an environment of arbitrary spectra.
>
> If you assume “natural light”, or “black body radiation”, then there is
> some hope. If you want to do this in the face of arbitrary lighting
> conditions - then, no - it simply can’t be done. Either by the human
> visual system or a traditional camera.
>
> How many samples are required (across the spectrum)? Alas, in general the
> answer is: an infinite number. Any claim that you can use fewer is simply
> an assertion about the nature of the lighting.
>
> In fact, even the concept of “Dominant Wavelength” involves considerable
> assumptions. In fact…in those cases where “Dominant Wavelength” makes
> sense… then human eyes and conventional RGB cameras can do the job just
> fine. The difficulty comes when you try to extend this concept into
> domains where it doesn’t apply. “Dominant Wavelength” is a concept that
> really only makes sense in a color system that is 3D - one where “Hue” is a
> possible dimension. It’s really a psychological concept, not a physical
> one [except to the extent that psychology evolved to match a certain flavor
> of physical reality].
>
> Confused, yet? Good!
>
> --
> Kenneth Sloan
>
[hidden email]
>
>
> > On Jan 27, 2015, at 13:35 , Marcel Tschudin <
[hidden email]>
> wrote:
> >
> > Hello everyone,
> >
> > I am new here. I am wondering whether I could use ImageJ (or an other
> program) for measuring in photos the 'Dominant Wavelength' of the colors
> within a selected pixel area. I provide here some further explanations
> because I am not sure whether what I intend to do would actually even be
> possible with photos.
> >
> > I would like to estimate the sun's 'Dominant Wavelength' in photos of
> the setting sun. For a detector like the human eye the 'Dominant
> Wavelength' would result from the sun's spectrum after passing the
> atmosphere and after passing the eye's spectral detector efficiency. It
> would be calculated from the detector's spectrum as Ldom, with the
> radiation intensity, I, at a certain wavelength, L, in increments, dL, over
> the visible spectrum as a ratio of two sums (integrals):
> > Ldom = Sum(I*L*dL) / Sum(I*dL)
> > (Because 'Dominant Wavelength' could be misinterpreted others suggest to
> call this the 'Balanced Wavelength' instead.)
> >
> > Consumer cameras do not record the spectrum, they rather approximate the
> detected spectral content, i.e. the color perceived by the human eye, with
> the RGB information. Would it now be possible to estimate the original
> 'Dominant Wavelength' from the available RGB information in the photo? If
> yes, do you know if ImageJ (or an other program) provides such a feature or
> a similar one?
> >
> > Thanks,
> > Marcel
> >
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