photographic method that need the greatest im- 

 provement, serious thought should be given 

 toward improving the present techniques. 



One way to increase the efficiency of this 

 operation is to read the film with an automatic 

 film reader. The measurements are automatic- 

 ally punched on IBM cards and the caluclations 

 then can be accomplished automatically by IBM 

 machines. The automatic film reader is a de- 

 vice that projects a large picture of the negative 

 upon a ground glass plate in front of the oper- 

 ator. Manually operated dials on a board in 

 front of the operator move the cross hairs used 

 in taking the measurements, operate a device 

 that punches the information on IBM cards, 

 focuses the film, and does many other opera- 

 tions . Automatic film readers are commercially 

 available . 



There may be other means of reading the 

 film, however, and work toward designing such 

 a device is desirable. In any event, IBM cards 

 and machines still can be incorporated to help 

 save time when there are enough measurements 

 involved to make the use of them practical. Un- 

 til such time, tables can be made to help reduce 

 lengthy calculations. 



Accuracy 



The photographic measuring device is 

 considered accurate within approximately -1-0.05 

 centimeters when ideal subjects are being 

 measured. 



Experience with the device indicates that 

 the accuracy can be increased by improving the 

 photographic measuring device and by devising 

 a better method of reading the film . 



Better definition of the points of measure- 

 ment can be obtained by (1) changing the color 

 of the background to one that contrasts more 

 with the subject being photographed, (2) elimin- 

 ating areas of glare by designing a more suitable 

 reflector, thus, increasing the detail in those 

 areas, and (3) having lighter grid lines mach- 

 ined accurately upon the base . 



The fact that ideal subjects can be meas- 

 ured accurately does not necessarily mean that 



fish can be measured just as accurately. Two 

 factors inherent in a fish make this problem 

 difficult. (1) The dimensions of a fish will 

 change by the way the fish is laid down and (2) 

 the body of a fish shrinks as the period of time 

 after death increases. Whether these two factors 

 should be investigated extensively depends on the 

 required accuracy of the fish's dimensions. 



It should be noted that the required ac- 

 curacy of the dimensions of a fish does not 

 necessarily eliminate the need for a greater 

 accuracy in the device, since the error in the 

 fish's body and the error in the device are sep- 

 arate and can therefore be additive . The total 

 possible error can be decreased by decreasing 

 the error in the fish or by decreasing the error 

 in the device. 



Other Uses 



This paper has described how the longi- 

 tudinal distance between two points on a three- 

 dimensional object is determined by using two 

 cameras. Other types of measurements might 

 also be useful in separating the various races 

 of salmon. For example, from formula 4 (see 

 "Theory"), it is apparent that we can determine 

 the thickness of the fish at point P (fig. 3) on the 

 fish. Point to point and depth measurements 

 could be determined if suitable formulae for 

 these were developed. 



Our experience has indicated that it also 

 may be possible to count the scales on a fish on 

 a photograph. 



GENERAL EVALUATION 



The many inherent advantages in photo- 

 graphy lend great potential to any photographic 

 method that can be used to determine accurately 

 the dimensions of a fish. From our research to 

 date, it is concluded that in this photographic 

 method (1) the theory as set forth in this paper 

 is sound, (2) the device can be made fully port- 

 able by designing the base so that it can be 

 disassembled, and by reducing the weight of 

 certain parts of the device, (3) the efficiency of 

 this photographic method can be improved by the 

 design of a better method of reading the film and 

 by incorporating IBM cards and machines or 



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