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Discussion
la densité moyenne 0.3 que pour la densité moyenne 2. Le Prof. Jackson en conclut que lorsqu’on
doit utiliser un dispositif compensateur aussi puissant que ceux qu’il a mentionnés, la densité
maximum des clichés doit être limitée à 0.5 et le gamma doit être réduit en conséquence.
Mr. F. L. Corten: I would like to ask Prof. Jackson two questions. The first
is: where this work will be published? The second question is: I draw the con
clusion from what you have said that you advise to develop aerial negatives to
a maximum density of not more than 0.5. The question arises, that can be done
only by developing to a lower gamma. Is that the point which you make, so
that developing to a lower gamma is more useful when you apply the new
technique than developing to a gamma, let’s say 1.2—1.3 as we did up till today?
Prof. K. B. Jackson: In case of publication, this is not yet determined. The
work was originally started under the Ontario Research Council that has now
ceased to exist so we must find another publisher but I hope that this will not be
too difficult.
The second question is: We find that enough density to perceive details gives
you the highest resolution and more density spoils the resolution, progressively
from a very low level. We need contrast in our final positives but we can ampli
fy very low contrast obtained by our method of low gamma and longer ex
posure, by the new methods of printing with high contrast positive material.
As long as we get a signal, as long as we get any contrast, we can amplify it and
we find that low density gives high resolution.
Mr. G. C. Brock: I would only like to make clear, what kind of developer
Prof. Jackson used. I am very surprised that he gets maximum resolution at a
density as low as 0.3 unless that maximum density refers to an exceedingly low
gamma something less than 0.5 perhaps. In all our experience we have found that
you get maximum resolution somewhere about the point where the slope of the
curve* reaches its maximum. If you are getting a maximum resolution at a
density of 0.3, that means that the gamma must be very low indeed, and I
would dare to suggest that we must have more proof before taking over that
into aerial photography. Especially in view of the great loss of speed that must
be encountered when developing at such a low gamma.
Prof. K. B. Jackson: I can only say that the results indicated in the graph
are the values we obtained by the methods described. It is true that we Were
developing to a very low gamma in order to hold down the maximum density
to a low value, because we find that the resolution is much better at a very low
density and we can only use it because we can amplify the contrast which is
necessary for good perception. There are the two qualities, contrast and sharp
ness, and if we can get more sharpness by low density and then increase the
contrast by other printing methods without going through the roof then we
save the situation. But they are very low gammas and very low densities for
maximum lines for millimetre.
Mr. F. L. Corten: I would like to ask Mr. Jackson two more questions:
1. Whether you did compare the ultimate results with this, let us call it, new
technique with the old technique of say gamma 0.2 or 0.3 and normal printing.
So the first question is what is the difference between your optimum results and
the optimum results which we get until now in the normal technique.
2. The second question or remark is, that we must be very careful before we
apply this scanning printing in aerial survey at all. I mean not for mapping and
for plotting but for interpretation. Interpretation means that for instance for
forestry, for soil survey, that you apply a certain density of a certain area to a
certain property of that area. And you compare those areas with each other with
certain keys. If we use the scanning spot principle in our positive technique, we
make the experience, in the same way as for the masking technique, that the
positive then cannot be used any more for, let us say, soil survey interpretation.
