5. Conclusion
This paper proposes a self-referencing colorimeter for the determination of chlorine concentration in water by using a mobile device such as a smart phone and a tablet. Our key idea is to utilize the 2D detection from the digital camera of the mobile device by means of arranging both the reference material and the small transparent bottle in such a way that they both fit in the camera's field of view. In this way, one color image simultaneously contains regions from the reference material and from the small transparent bottle. After that, a specific color ratio called CR from these two image regions are used for specifically converting the water color inside the small transparent bottle into its corresponding chlorine concentration. Experimental demonstration using a smart phone with an Android operating system, a white A4 paper, and the KI–starch solution shows a promising result in determining chlorine concentrations in 0.3–1.0 ppm with