Upload
aditya-chaudhary
View
217
Download
0
Embed Size (px)
Citation preview
7/27/2019 Proof of Convolution Theorem
1/2
TheConvolutionTheorem
TheConvolutionTheoremstates:
! ! ! ! ! ! ! ! !"#! ! ! ! ! ! !(!)Proof:
PartI:ProofoftheShiftTheoremorshift-invariance:
Firstweprovetheshiftproperty,thatis,thattheFourierTransform(F),asa
system,isshift-invariant:
Thatis,ifthen
Thatmeansthataddingashift(x-a)doesntchangethespectrum,F(u),itjust
addsalinearphase,whichamountstomultiplicationby!!!!!"#.MultiplyingF(u)
by!!!!!"#fordifferentatranslatesorshiftsf(x)bya.
Letx=x-aanddx=dx
Then! ! !
!=
! ! !!= ! !! !!!!![! !
!!! ]
!"
!
!!
Now!!!!!! !!!!
= !!!!!!" !!!!!!"! !!"!!!!!!!" !"!!"#$%%:
So! ! ! ! = !!!!!!"!(!)whichistheShiftTheorem
Therefore,theFourierTransform,asaSystem,isshift-invariant.
Significance:Shiftingortranslatingaspatialfunctionadistancex=aaddsalinear
phase=uatotheoriginalphase.Conversely,alinearphasefilterproducesatranslationoftheimage.Themagnitudespectrumremainsunchanged.
Ff(x) F(u) Ff(x-a) !
!!!!"#
F(u)
7/27/2019 Proof of Convolution Theorem
2/2