CONCLUSIONS 
1, 
c 
Modern aerial photography can produce better images containing much more 
information than was possible in a former period. This has been achieved 
through continuous and succesful efforts in optical and photographic research 
and manufacture and through the application of more suitable methods in 
aerial survey. It is not justified to destroy this quality by using unsuitable 
image-processing methods. Contact copying is still one of the real causes 
of degradation of image detail, particularly in the highlight and in the 
shadow areas. 
Details are lost when the full density range of aerial negatives is copied onto 
the paper density range; this fact is generally known. It is not generally 
known, however, that losses occur also when copying a modern-quality 
negative onto diapositive emulsions of any contrast grade. These losses are 
appreciable, being even more than 50% R in the shadow areas. 
Dodging and masking methods can, basically, provide the means to locate 
all negative details well within the 90% R sharpness range of the positive 
emulsion. To this end, they shall fulfil the following requirements: 
1. The aerial negative's density range (possibly 2.0 D or 2.5 D in medium 
and large scale photographs) shall be compressed to apparent density 
range = 0,6 D if positive transparencies must be produced. 
2. The negative density range shall be compressed to 0.3 apparent D range 
if paper prints must be produced. 
3. In this combination, contrasty positive emulsions shall be used. Paper 
prints are then practically equivalent to transparencies as far as minute 
detail reproduction is concerned (not, of course, as far as tone repro- 
duction range is concerned). 
4. The density compression shall take place in all areas carrying highlight 
or shadow details of interest, including the boundary areas between different 
terrain or vegetation types; in other words; the mask unsharpness of the 
scanning spot shall be very small. 
Existing dodging printers do no fulfil these requirements and are, conse- 
quently, not yet of full value to photogrammetry as far as economy of micro 
detail is concerned. 
Conservation of fine detail in the above-mentioned way can be obtained only 
at the cost of appreciable tone reproduction distortion of macro contrast 
between terrain areas. This fact is basic to "dodging". 
In cases where the photo scale is determined by the recognizability of small 
details - e.g. for height measurements in tree shadows, for differentiation 
in bright road and concrete surfaces, for recognition of forest texture, 
etcetera - a los of micro detail is equivalent to a loss of survey economy. 
The necessity of adapting the photo scale to the visibility of micro detail 
can account for a factor V 2 (approx. ) in photo scale and consequently a 
factor 2 (approx,.) in number of photographs. 
      
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   
    
   
   
   
    
   
   
   
   
   
   
   
   
   
   
   
  
  
  
  
  
  
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