n4BiasFieldCorrection.Rd
Perform N4 bias field correction on the given image
input antsImage
input mask, if one is not passed one will be made
At each iteration, a new intensity mapping is calculated and applied but there is nothing which constrains the new intensity range to be within certain values. The result is that the range can "drift" from the original at each iteration. This option rescales to the [min,max] range of the original image intensities within the user-specified mask. A mask is required to perform rescaling. Default is FALSE in ANTsR/ANTsPy but TRUE in ANTs.
Shrink factor for multi-resolution correction, typically integer less than 4.
List of: iters
, vector of maximum number of
iterations for each shrinkage factor, and tol
, the convergence tolerance.
Default tolerance is 1e-7 in ANTsR/ANTsPy but 0.0 in ANTs.
Parameter controlling number of control points in spline. Either single value, indicating how many control points, or vector with one entry per dimension of image, indicating the spacing in each direction. Default in ANTsR/ANTsPy is 200 mm per mesh element in each dimension. The ANTs default is a mesh size of 1 per dimension.
bool, return the field instead of the corrected image.
enables verbose output.
antsImage of weight mask
bias corrected image or bias field
dims <- c(50, 50)
img <- makeImage(imagesize = dims, rnorm(prod(dims)))
n4img <- n4BiasFieldCorrection(img)
n4img <- n4BiasFieldCorrection(img, mask = img > 0)
testthat::expect_error(n4BiasFieldCorrection(img, weightMask = "somepath"))
testthat::expect_error(n4BiasFieldCorrection(img, splineParam = rep(200, 3)))
n4img <- n4BiasFieldCorrection(img, splineParam = c(200, 20))
rm(img)
gc()
#> used (Mb) gc trigger (Mb) limit (Mb) max used (Mb)
#> Ncells 4186442 223.6 7574517 404.6 NA 5814732 310.6
#> Vcells 12340301 94.2 22785357 173.9 102400 22785327 173.9
rm(n4img)
gc()
#> used (Mb) gc trigger (Mb) limit (Mb) max used (Mb)
#> Ncells 4186054 223.6 7574517 404.6 NA 5814732 310.6
#> Vcells 12339686 94.2 22785357 173.9 102400 22785327 173.9
fname <- getANTsRData("r16")
in_img <- antsImageRead(fname)
n4 <- n4BiasFieldCorrection(in_img)
rm(n4)
gc()
#> used (Mb) gc trigger (Mb) limit (Mb) max used (Mb)
#> Ncells 4186111 223.6 7574517 404.6 NA 5814732 310.6
#> Vcells 12339777 94.2 22785357 173.9 102400 22785327 173.9
mask <- in_img > 0
mask2 <- antsImageClone(mask, out_pixeltype = "float")
# fails
mask
#> antsImage
#> Pixel Type : unsigned char
#> Components Per Pixel: 1
#> Dimensions : 256x256
#> Voxel Spacing : 1x1
#> Origin : 0 0
#> Direction : 1 0 0 1
#>
sum(mask)
#> [1] 19278
if (FALSE) { # \dontrun{
n4 <- n4BiasFieldCorrection(in_img, mask = mask, verbose = TRUE)
# fails
n4 <- n4BiasFieldCorrection(in_img, mask = mask2)
} # }