Figure 3. Fitness testing between a standard normalization method (I/I₀) and the combined triple-reference normalization technique using FFT digital bandpass filtration of smartphone images.

Adjacent channels within a nine channel array were imaged and compared with a focal center (FC) channel on which the image white balance and focus were locked. The normalized relative intensities and the standard error between testing methods were compared for (a) directional angles of point source lighting (45° increments between 0°–360°), for (b) increasing imaging height (9.2 cm–20.3 cm), for (c) different imaging backgrounds (black and white), and for (d) different qualities of lighting (natural direct and shaded sunlight, indoor fluorescent light, and smartphone flash light) (n = 8).