Posted by
GDC on
URL: http://imagej.273.s1.nabble.com/Measuring-Dominant-Wavelength-tp5011335p5011342.html
Probably the best you can do without a spectrometer would be to convert
the color space of your image to a cylindrical one such as HSV and use
the H (Hue) value to get an approximation of the dominant color (not
wavelength). Alternatively, you might get better results with a simple
diffraction grating spectrometer in front of the camera ala the public
lab spectrometer.
Greg
On 1/27/2015 2:35 PM, 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
>
> --
> ImageJ mailing list:
http://imagej.nih.gov/ij/list.html--
ImageJ mailing list:
http://imagej.nih.gov/ij/list.html