Journal of Microbiological Methods 6 (1987) 199 .-210 199 Elsevier JMM 00200 A microcomputer-based image analysis system and applications to chlorophyll fluorescence studies Joan Torrie, Colin I. Mayfield and William E. Inniss Department of Biology, University of Waterloo, Waterloo, Ontario N2L 3G1 (Canada) (Received 2 August 1986) (Revised version received 5 December 1986) (Accepted 12 December 1986) Summary An IBM-PC based software system to quantify images of biological systems is presented. To illustrate the potential of the imaging system described, UV light-induced chlorophyll fluorescence of Chlorella vulgaris cells was monitored using a video camera interfaced to a microscope. The photoinhibitor, DCMU (30 p.M) inhibited the UV-induced fluorescence decay in heterotrophically grown cells but not in autotrophically grown cells. Algal cells were also incubated in various concentrations of ascorbic acid (500, 250, 100, 50, 10 and 0 mM) prior to UV light exposure. In the presence of 500, 250 and 100 mM ascorbic acid, the decay of chlorophyll fluorescence was significantly delayed in both heterotrophically and autotrophically grown cells. Heterotrophically grown cells were more sensitive to ascorbic acid than autotrophically grown cells since 10 mM ascorbic acid delayed fluorescence decay in heterotrophic cultures. Key words: Microcomputer; Image analysis; Chlorophyll; Fluorescence; IBM-PC Introduction Recently several researchers have explored the potential of computer-assisted image analysis (CIA) to provide the technology needed to produce standardized, re- producible image analysis. Each image received from a camera or scanner via an analog/digital convertor is subdivided into a number of areas (called 'picture elements' or pixels). The average light intensity of each pixel is assigned a relative digital value, referred to as a brightness or grey level. For example, absolute black areas within an image would have a grey level value of zero. The grey level of each pixel is usually stored in a matrix to preserve the co-ordinates of the pixel within the image. The technology and algorithms used to generate and process images by computer have been extensively reviewed [1-2]. Correspondence address: Colin 1. Mayfield, Department of Biology, University of Waterloo, Waterloo, Ontario N2L 3GI, Canada. 0167-7012/87/$3.50 ~:; 1987 Elsevier Science Publishers BN. (Biomedical Division)