This is a short python program for turning a picture taken on an iPhone with the iSpex spectrograph addon into a spectral plot.
Take a jpg image using an iPhone with the iSpex device. The script is currently hard-coded to use the 2448x3264 resolution of the iPhone 4S camera. This means the pictures must be taken in vertical mode, or rotated afterwards.
Run python iSpex_spectrum.py image.jpg to produce the spectral plot.
The code requires NumPy, Matplotlib and the Python Imaging Library PIL (or its more recent fork, Pillow).
The wavelength calibration is based on photos taken of a fluorescent lamp. It seems rather unstable, different photos taken of the same lamp produce spectra with shifts up to tens of nanometres. If you have a better calibration source, you can try to measure better calibration coefficients (make a pull request if you do!).
The spectrum is computed simply by integrating pixel values in the image. Since the iSpex produces a spectrum of colours on the iPhone camera sensor, the spectra produced by this code are affected by the spectral sensitivity of the iPhone camera. There is no correction for Bayer filtering etc. either.
This code is written only to demonstrate simple principles of spectrometry and does not produce results precise or accurate enough for scientific or any other work. If you need a true spectrum, buy a proper spectrometer.