A simple extraction method for preparing an organic certifiable stevia extract with high sweetness and optionally with antioxidant properties is provided. Tissue is irradiated with low intensity monochrome radiation in the wave length band of 630 to 645 nm and the fluorescent image is recorded within the band of 650 to 730 nm. One PTS value is sampled and recorded at one time. Each subunit generates two output bits indicative of the two trellis branches exiting the trellis state represented by that particular subunit. The digitizer may include an analog-to-digital converter to convert the analog signals to digital signals, as well as a multiplexer to read the analog signals from multiple channels, a signal conditioner to modify the analog signals from the multiplexer, and an amplifier to amplify the analog signals from the signal conditioner.