6 THE PHOTOGRAPHIC IMAGE, BROCK 
  
  
  
TABLE 1. Factors in image formation and use. 
Factor Principal characteristics 
Scene Size/distribution of light, shade and colour. 
Atmosphere Turbulence, haze. 
Window | Light-scatter and absorption, optical flatness. 
Aircraft Steadiness, speed, vibration. 
Camera enclosure Temperature control, air pressure. 
Mounting Vibration-absorption, steadiness. 
Filter | Spectral transmittance, optical flatness, absorption, scatter. 
Lens | Aperture, uniformity of illuminance, definition, absorption, 
| scatter. 
Shutter | Time, efficiency, mechanical shock. 
Focal plane | Flatness, (scatter and absorption where register glass 
| used). 
I.M.C. | Accuracy. (Not normally used for photogrammetry.) 
Film (emulsion) | Speed, contrast, spectral sensitivity, definition, exposure. 
Film (base) | Flatness, halation. 
Processing | Contrast, speed, definition. 
Printing equipment Contact or other factors affecting definition. 
Printing material Contrast, definition. 
Viewing technique | Definition, scatter. 
Interpreter Skill and health. 
  
  
  
common terms expressing directly their influence on the whole process. The ideas of 
frequency response may contribute to this end. These ideas are now well known to phy- 
sicists specializing in opties and electronics, but are possibly new to the majority of 
people using cameras for photogrammetry. The subject has sufficient topical interest to 
justify a major place in the review. It can be given a highly mathematical treatment by 
those suitably qualified, but the simple introductory account given here may be accept- 
able. 
The writer is not at present aware of any other themes of outstanding importance 
or of any outstanding technical advances during the past four years, other than those 
noticed in Section 5. 
2.  Frequency-response and image quality. 
2.1. General considerations. 
For the present purpose, object-image relations in a monochromatic system can be 
thought of with the aid of a few basic concepts, luminance (or “tone”), size, and bound- 
ary (edge). Luminance carries little or no information until it appears in areas of dif- 
ferent size, and the information is limited unless the areas can be bounded by definite 
edges. Neither luminance nor boundary is obviously the more important in a photograph, 
where the two are inseparably linked; removal of either destroys that close resemblance 
to the object which is the essence of photographic reproduction. In more general imagery, 
boundary alone can convey a wealth of meaning, as when symbolised by the lines of a 
pen and ink sketch *), (Fig.1). Boundary is of course, no more than a rapid change of 
*) A paper by Dr. R. E. Hopkinson, W. R. Stevens and J. M. Waldron stimulated this 
idea. 
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