conv.fft {dcemri} | R Documentation |
Convolve a
conv.fft(A, B, C, FFTA=NULL)
A |
is a three-dimensional array (“the template”). |
B |
is a three-dimensional array (“the target”). |
C |
is a vector of length three (the center of “the template”). |
FFTA |
is the three-dimensional Fourier transform of A ,
this may save time when looping over multiple “targets”. |
The arrays A and B are transformed into the Fourier domain and multiplied together (equivalent to a convolution in the image domain across all spatial locations simultaneously).
A three-dimensional array, the same dimension as the input arrays, that is the convolution of the “target” to the “template” at all spatial locations.
Brandon Whitcher
Briggs, W.L. and Henson, V.E. (1995) The DFT: An Owner's Manual for the Discrete Fourier Transform, SIAM: Philadelphia.
cube <- array(0, c(20,20,1)) cube[9:12,9:12,1] <- 1 tkernel <- array(0, c(20,20,1)) tkernel[,,1] <- c(.5, 1, .5, rep(0,20-3)) tcenter <- find.center(ifelse(tkernel > 0, TRUE, FALSE)) out <- conv.fft(tkernel, cube, tcenter) out[8:13,8:13,1] ## text output par(mfrow=c(2,2)) ## graphic output image(drop(tkernel), col=tim.colors(), main="Template") image(drop(cube), col=tim.colors(), main="Target") image(drop(out), col=tim.colors(), main="Output")