In this work an imaging method used for studying metallic system oxidation is presented. This implementation monitors changes in the molecular absorption of visible light with a redox probe, a ruthenium polypyridine complex. As the transmission microscopy method avoids irradiation of the sample with high intensity light in comparison to fluorescence techniques, images can be acquired using an inexpensive commercial digital camera, making this an excellent low-cost tool for oxidation mapping. Molar fractions of reduced and oxidized species of the probe are calculated using different channels of an RGB camera, green and red, respectively, allowing a ratiometric measurement for redox potential determination with a high temporal and spatial resolution.