Full text: Commissions I and II (Part 3)

G. Brock said that since the objective is a linear plot, MTF cannot be derived for densities. However, we should 
consider, if we need the MTF at all for image evaluation, we might rely solely on edge sharpness. At Itek it 
was noted that the human eye is very good at classifying degrees of sharpness, the human operator can 
distinguish between two edge images which are very hard to differentiate by a microdensitometer: however, 
for system analysıs MTF is superior. 
A. Sorem noted that Kodak also had found observers very sensitive to small differences in edge sharpness. 
G. Brock commented on the statement in E. Welander’s Paper that resolving power is applied only at one 
frequency. When the resolving power of a three-bar target is measured, the response is measured for a spectrum 
of frequencies. Resolving power measurement is a good representation of system performance out to the 
frequency limit. (see SPIE January-February 1972) 
The Commission President offered the authors of presented papers an opportunity to review the highlights of 
their papers. 
Z.D. Kalensky summarized a presented paper ‘Definition in the Three Image Layers of Aerial Colour Film” 
by Carman and Kalensky, providing quantitative data on the variations in MTF, granularity and resolution 
in the three layers. He emphasized the desirability of knowing the performance data for all three layers of 
colour film, not just the neutral ones. 
R. Welch pointed out that in actual aerial photography, haze would affect the relative results. He mentioned 
that tests had been made using SO 121 in a mapping camera from the air, and had showed lower MTF, yet 
higher resolution, than for similar tests with a black and white film. 
Z. Kalensky commented that MTF alone does not provide a complete measure of image definition, and for that 
reason granularity and resolution had been included in their test. 
J. Haddarainen summarized his presented paper, “The Resolving Power and the MTF of Terrestrial and Aerial 
Cameras in Working Conditions”. For both types of test, bar (square wave) targets were used. The target array 
for aerial cameras provided 5 to 50 cycles/mm at a scale of 1:4000. Photographs were measured on a Joyce 
MK III microdensitometer to provide *(MTF)"' values near the theoretical MTF. Results were given for three 
types of terrestrial cameras and three types of aerial cameras. 
J.C. Trinden summarized his presented paper, “Relationship Between Pointing Precision, Spread Functions 
and Modulation Transfer Function”. The relationship between pointing accuracy and image quality was 
studied to find the ideal target size. A Gaussian point spread function was assumed as an approximation to 
usual point spread function. Means for computing optimum target size were established. Pointing precision of 
2 to 376 of the point spread function € was found for medium to high contrast targets. 
The meeting was adjourned. 
Wednesday July 26 1972, 15:45 
After opening the meeting, the Commission President discussed the Resolution on OTF from the XI Congress, 
and the subsequent division of the subject into MTF and OTF. He then turned the meeting over to Mrs. Norton. 
She introduced R.E. Hopkins, who presented his Invited Paper, Lens Testing or Image Evaluation". 
Mrs. Norton asked R. Hopkins about combining monochromatic light to give white light information. How 
is it certain that the measurements are referred to the same origin? 
R. Hopkins replied that it was a problem of good metrology. The scanner is accurate to a micron, as long as 
it is not moved to another image point. 
Mrs. Norton listed some questions she wanted the panel to consider. How do we define what we are seeking 
in an OTF standard?. How should we proceed now? What should our point of view be - that of the 
photogrammetric user? 
G. Brock said he had written more against the OTF than most people, but now his views had changed, and 
he would advocate it. He agreed with many of R. Hopkins' points, particularly his emphasis of the metrological 
problem, but he felt that a more simple-minded approach was possible. He pointed out that all of the problems 
mentioned by R. Hopkins also occur in resolving power measurements, but may not be as apparent because 
of lower sensitivity of the test. 
 
	        
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