Images can be input directly through a video camera, as either negatives or positive transparencies. Digitization of video input with a framegrabber allows real-time display of digitized images, with video images digitized at the rate of 30 frames per second. Graphics-overlay positioning grids are used for precise positioning of photographs. An interactive classification routine allows the user to adjust a threshold intensity value that distinguishes foliage from canopy openings, producing a classified image. The user can toggle instantaneously between a continuous tone display of the canopy photograph and a threshold display of the classified image.
Results can be automatically output to data files for archiving and further analysis.
Typically, each photograph can be analyzed in two to five minutes, including all steps of film positioning, digitization, selection of a threshold, calculation, and output of results. Access to intermediate calculations of the distribution of canopy openings as a function of zenith and azimuth angles allows users to design their own detailed analyses of canopy geometry. In addition, the image analysis system must include a video display monitor, video camera fitted with a macro lens, backlighting source, film holder, and copy stand. Appendix B gives further details concerning hardware. Costs are approximate.