Smartphone modulated colorimetric reader with color subtraction

Color analysis has been essential for the interpretation of optical readouts, e.g. colorimetry, fluorescence, spectroscopy, and scanometry. However, existing colorimetric readers can hardly eliminate the color interference of colored solutions, e.g., interpreting pH test strips to assess the pH value of red wine. This paper introduces a smartphone modulated colorimetric reader that is compatible with most smartphone models and a novel color subtraction algorithm that eliminates color interferences due to colored solutions. Experiments were conducted to validate the effectiveness of the developed reader and algorithm on evaluating pH test strips produced from transparent and colored solutions using multiple smartphone models. Applicability of the developed reader was demonstrated through its interpretation of pH test strips measuring pH values of colored and non-transparent food samples including red wine and milk.