Color Film as an Abridged Spe- ctral Radiometer 



Spectral measurements are usee in many research problems . 



Can color film be used to make these measurem.ents? The ansv;er 



is yes for some problems. In many instances the problem is 



not one of identifying one particular sper'.i.j^al curve from an 



infinity of possible ones . More often one is v;orking V7ith a 



fairly well-defined population of possible spectral curves. Tv;o 



exam.ples of such populations are the spectral absorbances of 



algae samples and the spectral distribution variations of natural 



daylight . 



A color film measures the amount of redj green, and blue 



light it sees reflected fr-om an object. These m.easurements , 



the red, green, and blue layer exposui^es of the film, then control 



the amount of cyan, m.agenta, and yellov; dye that are formed in 



the layers. If we measure the spectral density curve of a filmi 



imagp and compa.re this curve "with that of the original object, 



we usually find a poor correlation. Such a comparison is shov.n 



in Figure 1. The absorbanee curve of an algae sample is shovrn 



as a dotted line, the film iniage as a solid line. This is 



• 31-5 



