Posted by
Marcel Tschudin on
URL: http://imagej.273.s1.nabble.com/Measuring-Dominant-Wavelength-tp5011335p5011340.html
On Tue, Jan 27, 2015 at 11:44 PM, Chuck Harrison <
[hidden email]> wrote:
> ...
> 3. Do look for a different term; "dominant wavelength" has a precise
> meaning in colorimetry. "Power averaged wavelength" might be a suitable
> term for your computation.
>
The original intention was actually indeed to select the balance point
within the spectrum. I would therefore also favour "Balance Wavelength" as
an alternative.
> 4. Your computed value makes no reference to the human eye response, so I
> hope you are not expecting it to have a consistent relationship to what the
> setting sun looks like when observed by a human being.
>
It looks like I have to provide some further details: The detector, eye or
camera, receives a response spectrum from the setting sun (yes, also
depending on the detector's response). Which wavelength within this
spectrum was responsible for the amount of refraction that this light
package actually did hit the detector and not a place above or below it?
One way of estimating it is by simulation, using an appropriate atmospheric
model. I just was wondering now whether the photos themselves, made with a
normal consumer camera, would allow estimating this wavelength. I learned
so far that this does not appear to exist, and that it would likely not
even be possible.
Regards,
Marcel
>
> Cheers,
> Chuck
>
>
> On Tue, Jan 27, 2015 at 11:35 AM, 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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http://imagej.nih.gov/ij/list.html> >
>
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