A new depth from focus technique for in situ determination of cell concentration in bioreactors

A new depth-from-focus technique is introduced that requires only a single image to determine the distance of simple shaped objects from the focal plane. The technique has been applied to evaluate the concentration of cells in a bioreactor during a fermentation process. Since the low-intensity fluorescent light gathered by a light-amplifying camera results in images of low signal-to-noise ratio, an adaptive smoothing filter is used. A sharpness criterion derived from bandpass decomposition of the image in a Laplacian pyramid is used to define a virtual measuring volume. In this volume, process parameters such as cell concentration, cell size and intensity of cell fluorescence are evaluated. The technique is also suitable for other types of simple objects.