The rapid increase during the post-war era in university- 
level course offerings dealing with one aspect or another 
of photo interpretation and photogrammetry; 
(b) Associated with the above item, the rapid increase in the 
number and quality of textbooks dealing with aerial photo- 
graphic interpretation and photogrammetry; 
(c) The rapid increase in the number, quality and types of 
equipment for use in photo interpretation and photogrammetric 
activities; and 
(d) The growing stature of photo interpretation in various 
professional societies. 
2. Efforts Aimed at the Systematic Training of Photo Interpreters 
in the Post-War Era 
It was roughly a quarter century ago that one of the first attempts 
was made to list the most significant components that govern the 
quality (and hence the interpretability) of photographic images 
and to categorize the various measures that might be taken to 
rectify image deficiencies. As set forth at the time (Colwell, 1952) 
there reportedly were three such components, viz., the tone or 
color contrast between a photographic image and its background; 
the sharpness of the image as measured by the abruptness with 
which this tone or color change occurred on the photograph at the 
"edge" of the image in question; and (applicable only in the event 
that the feature in question had differences in elevation with 
respect to its background), the amount of stereo-parallax exhibited 
by the image. Stereo parallax is defined as the shift in the 
apparent position of the image with respect to its background 
caused by a shift in the point of observation (as when the camera 
station shifted from the point from which the left member of a 
stereo pair of photos was taken to the point from which the right 
member of that pair was taken). 
  
  
  
It was recognized that the factors which govern any one of these 
image quality characteristics are, for the most part, different 
than those which govern either of the other two. Thus, it was 
pointed out that there were four primary factors governing the 
tone or color contrast (spectral reflectivity of the feature and 
its background; spectral sensitivity of the film; spectral trans- 
missivity of the filter; and spectral scattering by atmospheric 
haze particles). Similarly there reportedly were four primary 
but quite different factors governing image sharpness (aberrations 
of the lens system; focus of the lens system; image notions at 
the instant of exposure; and characteristics of the photographic 
materials). Finally, there were considered to be three primary 
factors governing stereoscopic parallax (altitude of photography; 
length of the stereo base as governed by the distance between 
overlapping exposures; and difference in elevation between the 
feature and its surroundings). 
Even to this day, the rather simplistic treatment of image quality 
that has just been given would seem to have merit in each of two 
respects: 
a) It is highly meaningful to speak of three separate measures 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   
  
  
  
  
   
   
   
  
  
  
  
   
  
  
  
    
  
  
      
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