Measurement of filamentous cyanobacteria by image analysis

A method of image analysis is described for measuring total filament lengths of cyanobacteria collected on membrane filters from samples of natural populations or cultures. Images of autofluorescent filaments viewed by epifluorescence microscopy were transferred to a computer screen by using a high resolution television camera and an image integrator to enhance sensitivity. The digitised images, saved as 0.4 Mbyte bitmap computer files, were analysed with an image analysis program. An evaluation is made of procedures for determining the total length of filaments from the detected area or perimeter of their skeletonised images. Methods are described for correcting errors arising from the orientation, crossing and overlapping of filaments.