In general it is not possible to make accurate colorimetric and spectral measurements in conventional photographic images for two main reasons. First because variation in illumination spectra cannot be discounted, and second because the number of degrees of freedom in reflectance spectra is potentially much greater than the three provided by camera RGB signals. Consequently, colorimetry requires either spectrometers or multi- and hyper-spectral imaging, which are costly and inconvenient. ColourWorker uses automatic calibration and statistical modelling to improve the accuracy of color measurement in photographic images. This app implements ColourWorker technology on iOS. It allows users to select application areas, to take a photograph with a calibration standard, and returns estimated an average L*a*b* colorimetric value and for pixels in a defined region of the image along with a plot of the reflectance spectrum.
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