ITC, in an effort to give the subjective judgement some objective basis as much as possible for 
the time being, considers and judges image quality in a sequence of four stages in the cascade of 
tone reproduction: 
3.4.1 OBJECT QUALITY 
....degree of brightness contrasts in object details, and the degree of sharpness - i.e. abrupt 
edges between brightness differences - ín the object. 
NOTE: in some cases it is not possible to assess the object quality, at the quality assessment 
phase. Example: tracks in sand desert either covered after a sand storm, or subject to "chasse 
sable" (fr) during exposure, or being refreshed again by a recent truck travel. 
3.4.2 ATMOSPHERIC QUALITY 
....degree of optical transparancy of the atmosphere which is adversely affected by absorption and 
diffuse scattering of the light rays through the aerosol due to: 
- water vapour (relative and absolute humidity) 
- humidity haze (minute water droplets suspended in the aerosol) 
- haze fog and cloud (suspension of larger water droplets and ize crystals) 
- dust (minute solíd matter suspended in aerosol) 
- gand haze and sand dust (sand crystals suspended in air and blown by wind) 
- smoke (particles of carbon residual from fire) 
— etcetera. 
NOTE: in many cases it is not possible to assess the atmospheric quality at the quality assessment 
stage. A non-rigid but still indicative estimate can be derived from density measurements at 
different areas of the negative. The density fall-off from centre to edge (corner) is caused by 
a) illumination distribution of the lens-filter combination, being enhanced by the negative's 
gradient factor and mostly having a constant value throughout any project - taking into account the 
variations in emulsion/processing conditions; these, in turn, could be monitored if sensitometric 
wedges would be available at the negatives, and 
b) light-and-shadow illumination distribution, including no-shadow-area, and c) haze light 
distribution in the aerosol - into various azimuth directions with respect to solar angle. 
3.4.3 PHOTOGRAPHIC QUALITY 
....the quality of photographic tone reproduction which is controlled by photographic factors such 
as — illumination distribution by the lens 
- emulsion type 
— development and processing 
and which can be impaired by physical damages such as 
- scratching 
— dust spots 
— abrasions 
— etcetera 
NOTE: the photogrphic quality is measurable by means of density measurements at the negative: D $ 
Dax etc. (See "Specifications for Aerial Photography). fog 
NOTE: Sensitometric data can be measured only when sensitometric wedges are imprinted on the 
negative. 
3.4.1 IMAGE QUALITY 
The combined effect of the above mentioned influences will result in a certain image 
quality 
«ess. being the degree to which the final image is conform to the original object. 
NOTE 1: In any reproduction technique - and certainly also in aerial photography - each step in the 
chain of events will cause a deterioration of the signal-to-noise ratio, and - after each step — the 
interpretability of the aerial photograph is degraded. 
NOTE 2: as is apparent from quality stages (3.4.1), (3.4.2) and (3.4.3), the image quality (3.4.4) 
can be physically measured and assessed only partly - i.e. for the part of photographic quality - 
and can be estimated only for the part of object quality and of atmospheric quality. 
4. CONCLUSION 
Quality Assessment of aerial photography can be carried out in an objetive way on 
- navigational quality, 
- metric quality, and on 
- administrative quality 
On image quality, however, only subjective judgements can be made. 
In this respect, the weakes element is the impossibility - until now - to measure the 
attenuating effect of haze. 
5. REFERENCE 
CORTEN, F.L.J.H. & LORENZ, R.W. "Specifications for Vertical Aerial Photography - for black-and-white 
photography - for line mapping and orthophoto mapping". (Draft 
proposal for updating the RICS Specifications). I.T.C., P.O. Box 6, 
7500 AA Enschede, Netherlands, April, 1982. 
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