122 DISCUSSION ON PRESENTED PAPERS 
that in a limited class room situation he can look 
at more stereogram examples and it is also 
possible to give every student a look at the same 
time so that everyone is seeing and discussing 
the same item at a given moment. It is also 
possible to grid these to make sure that we are 
looking at the same part of the picture. 
These stereograms or negatives are placed 
in the repository. I have just a few of them here 
illustrative of what we are doing and also to 
answer any question that some of you may have 
as to the quality of this sort of production. Have 
I answered the question fully enough? 
CHAIRMAN: Because of the time we are going 
to have to restrict our questions and answers to 
monosyllables, but I have one more question. 
Have you a catalogue of your stereogram 
library? 
Mr Orson: Not yet, but it is in preparation. 
It is due to work load, it was not ready for this 
meeting. Is there another question? 
Mr LaMsoir: Yes. | would like to ask 
whether you are subsidised in any way by the 
University or whether you are self-supporting. 
Mr OrsoN: I have to answer this both ways. 
Yes and No. We are self-supporting in that all 
of our cash outlays must be met by income. 
However the University Photographic Labora- 
tory was in existence by the time we began to 
use it. Their light is paid and operating ex- 
penses are paid by the University and so to this 
extent we are subsidised. We do not, however, 
pay the rent of our stations, we do not have to 
pay utility bills but we have to pay our help to 
process pictures; we have to purchase the 
chemicals actually to process the pictures with 
and to purchase paper. These are our expenses 
and it is on this basis that the repository is 
maintained. We have just covered those — shall 
I call them — direct operating costs as opposed 
to fixed costs of maintaining a photographic 
laboratory. 
QUESTION: What about aircraft maintenance? 
Mr Orsow: The aircraft maintenance was 
going on anyhow. The University has a standard 
price for the aircraft. We have to operate with 
an old (SMJ or A 6) at $29.00 an hour, which 
includes the photographer, the pilot, cost and 
maintenance but does not include the pho- 
tographic camera or film. 
CHAIRMAN: There is nothing to prevent us at 
the end of the Session going beyond the time 
that has been assigned so that some of you who 
may not have had an opportunity to ask your 
questions now will have a chance then perhaps. 
CHAIRMAN: Now, the last. Are there any 
more questions of Dr Jackson concerning his 
paper, "The Factors Affecting Photographic 
Interpretability". 
Dr ZEIDNER: I'd like to ask Dr Jackson: 
Have you related image quality to interpretative 
performance? 
Dr JACKSON: No, this has not been done 
either by ourselves or by any other investigators 
I know of, on a numerical basis. As you know, 
the factors which control the interpreter's 
ability to recognize detail are a function of the 
contrast — I use this word loosely for a moment 
— and the contrast gradient. That is, the rate of 
change of contrast often called the acuteness or 
edge sharpness. These are very difficult things 
to express numerically and this co-relation, 
called an interpreter's ability to recognise but 
one item, that was left out of my paper *) (it's in 
the printed version but not in the delivered 
version) has to do with the use of squares and 
circles as an index to recognition. At the thresh- 
old, the ability to recognize the distinction be- 
tween a square and a circle is a fair index to an 
interpreter's ability to recognize detail. Some 
work has been done on this and it looks like a 
useful concept. 
Mr Orson: I feel condemned in this case to 
answer the question. Here I would state only 
from my own personal feelings where my back- 
ground is that of trying to identity species oi 
hardwood trees and tell one oak from another 
oak. In this situation minor differences in tone 
and sometimes local forms are the key to the 
interpretation. We occasionally get this in the 
shadow but not often. More often we get it 
from actually seeing the detail. In some cases 
the branch may not be any larger than my 
thumb. We would like to have that resolved if 
we could. 
In some cases, some interpreters claim that 
they have seen that and I should add one other 
thing. We were working on one Occasion On à 
scale of 1/5500 and we were able to detect the 
light streaks of a power transmission line, the 
actual cables in the air. That is not the shadow 
*) Dr Jackson's paper is in Part 4, Comm T. 
  
  
but th 
power 
volt © 
would 
Mr 
Qu 
scribe« 
Mr 
can de 
none ij 
sectior 
is in t 
diamet 
CH! 
that th 
tion is 
someth 
Dr 
detects 
identifi 
to diffe 
was ab 
charact 
capabil 
it has : 
effect « 
reflecte 
or thin; 
that the 
than it 
in a nc 
that me 
other o; 
that is 1 
little pie 
might n 
acter of 
the ima, 
continui 
fill in th 
be seen. 
I wo 
tograph 
the Me 
can see 
could nc 
CHAI 
Jackson’ 
another