The- reconstruction of a daylight energy c\irve from filr.i exposures 

 is shown In Figure 10. 



These tv;o examples illustrate a method v.'hereby a color 

 film can be calibrated and used as an abridged spectral measuring 

 device. It must be emphasized that this procedure m.ust be used 

 with caution. Each problera must be analyzed and specific calibrations 

 derived for that problem. The four main requirem.ents v;hich miust 

 be met for the application of this procedure are listed belovj: 



1. The population of spectral curves must be specifiable. 

 Only curves dravrn from this population can be measured. 



2. Three characteristic vectors must describe the 

 population of curves v;lth sufficient accuracy. 



3. The population of curves contains no metamers, in 

 terms of the film spectral sensitivities . 



k. A transformation betv/een the vector space and the 



film exposure, space can be found. 



If more than three vectors are required to describe the population, 



a color film cannot be used. A panchromatic black-and-white film. 



exposed through several narrov; band filters could be used for 



more complicated system.s. 



51-12 



