750 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1952 



obscure the correlation effects, it is useful to make additional measure- 

 ments which enable us to subtract them out completely. This leaves us 

 with a 'pure' autocorrelation A(As/d_), which is then normalized so as 

 to have a peak value of unity. It is given by 



A{As/0) 



T^{-'ill)-T.{fll)T.{-f/e) 



(3) 



T2(0) - Tim 



where T2 ( —pr— /^ ) is the transmission through the two cascaded slides 



As 

 shifted by equal and opposite amounts — at an angle 6 with the hori- 

 zontal, and 2'i ( — /^ ) is the transmission of a single slide with displace- 

 As 

 ment — at the same angle 6. 



SCENE C SCENE D 



Fig. 4 — Test pictures whose statistics are included in this article. 



