Posted by
Chuck Harrison-2 on
URL: http://imagej.273.s1.nabble.com/Measuring-Dominant-Wavelength-tp5011335p5011339.html
My thoughts:
1. As Herbie writes, this task is impossible without further constraints.
The camera doesn't give you enough information.
2. I think the best you could hope for would be to do a characterization of
a single camera in this specific task. This would require a series of
sunset measurements using an independent instrument (spectroradiometer)
which DOES measure what you want, and simultaneous photographs. Then you
could develop an empirical correlation.
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.
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.
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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