A method for determining calibration parameters for a spectrometer, wherein the spectrometer comprises a Fabry-Perot interferometer having an adjustable mirror gap (d), and an image sensor, the image sensor comprises a plurality of first pixels and a plurality of second pixels, the pixels (P1, P2) are arranged to detect light transmitted through the Fabry-Perot interferometer, the first pixels have a first sensitivity function (η R (λ)), the second pixels have a second different sensitivity function (η G (λ)), the Fabry-Perot interferometer has a first transmission peak (PEAK1) and a second transmission peak (PEAK2), the first pixels are arranged to detect light at the spectral position (λ 0) of the first transmission peak (PEAK1) and the second pixels are arranged to detect light at the spectral position (λ 1) of the second transmission peak (PEAK2), the spectrometer is arranged to determine intensity values (X n, X n+1) from detector signal values (S R, S G) by using a second group of calibration parameters, the method comprising: - providing first calibration light, which has a reference spectral peak (MPEAK) at an adjustable spectral position (λ M), - obtaining first detector signal values (S R, S G) from the image sensor by coupling the first calibration light into the spectrometer when the reference spectral peak (MPEAK) is substantially at a first spectral position (λ 0), - obtaining second detector signal values (S R, S G) from the image sensor by coupling the first calibration light into the spectrometer when the reference spectral peak (MPEAK) is substantially at a second spectral position (λ 1), - determining a first group of calibration parameters from the first detector signal values (S R, S G) and from the second detector signal values (S R, S G), - providing second calibration light, wherein the spectral width (Δλ FWHM,20) of a spectral band of the second calibration light is broader than the spectral width (Δλ FWHM,M) of the reference spectral peak (MPEAK), - obtaining third detector signal values (S R, S G) from the image sensor by coupling the second calibration light into the spectrometer, - determining elements of a second matrix such that the second matrix is an inverse ( Q -1) of a first matrix formed from the first group of calibration parameters, and - determining the second group of calibration parameters from the third detector signal values (S R, S G) and from the elements of the second matrix. - providing first calibration light, which has a reference spectral peak (MPEAK) at an adjustable spectral position (λ M), - obtaining first detector signal values (S R, S G) from the image sensor by coupling the first calibration light into the spectrometer when the reference spectral peak (MPEAK) is substantially at a first spectral position (λ 0), - obtaining second detector signal values (S R, S G) from the image sensor by coupling the first calibration light into the spectrometer when the reference spectral peak (MPEAK) is substantially at a second spectral position (λ 1), - determining a first group of calibration parameters from the first detector signal values (S R, S G) and from the second detector signal values (S R, S G), - providing second calibration light, wherein the spectral width (Δλ FWHM,20) of a spectral band of the second calibration light is broader than the spectral width (Δλ FWHM,M) of the reference spectral peak (MPEAK), - obtaining third detector signal values (S R, S G) from the image sensor by coupling the second calibration light into the spectrometer, - determining elements of a second matrix such that the second matrix is an inverse ( Q -1) of a first matrix formed from the first group of calibration parameters, and - determining the second group of calibration parameters from the third detector signal values (S R, S G) and from the elements of the second matrix.