Fig. 2. Water samples with different chlorine concentrations under the KI–starch solution.
4. Experimental demonstration
4.1. Setup
Based on available components in our laboratory and by following Fig. 1, our experimental setup is shown in Fig. 3. Our mobile device is a smart phone Samsung Galaxy S GT-I9000 embedded with Android 2.2 operating system, a 2592 × 1944 pixel digital camera, 512 MB of RAM, and a 1 GHz processing unit. The digital camera of this smart mobile phone has a measured 53◦ full field of view. Our cheap uniformly white reference scene is a white A4 paper available in our office. The measured distance z between the smart phone and the white reference paper is 12 cm. The measured environmental illuminant level is 300 lx, which corresponds to an appropriate illumination level recommended in 2006 Ministeria Regulation under the Ministry of Labor of Thailand.
A blue rectangle of 100 × 360 pixels is programmed to show on the display of the smart phone so that the user can conveniently adjust the position and orientation of the smart phone in such a way that the glass bottle is properly fitted in. In addition, there are three regions of interest (ROIs) assigned on the display of the smart phone. The first two ROIs function as reference ROIs. Each of them contains 60 × 60 pixels and is positioned on the side of the blue rectangle. These two reference ROIs are used to collect the image data in red, green, and blue color planes associated with the white reference scene. Another 60 × 60 pixel ROI is specifically assigned