Posted by
Herbie-4 on
Jan 27, 2015; 8:25pm
URL: http://imagej.273.s1.nabble.com/Measuring-Dominant-Wavelength-tp5011335p5011336.html
Marcel,
for wavelengths you would need an additional dimension lambda, i.e. a
spectrometer at every pixel.
At best RGB-images give you three values of this lambda-dimension.
Furthermore, you can't be sure how these values are generated. They
depend on the properties of the three color filters of the camera that
usually spectrally overlap. Finally, most digital color cameras don't
use three sensors (RGB) but a Bayer color-mask which necessitates that
the RGB values at every pixel are at least partially computed from the
surrounding pixels.
That said, there is little to no chance that you get the desired
spectral information.
HTH
Herbie
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On 27.01.15 20:35, Marcel Tschudin 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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