ortho_diff(
  img,
  pred,
  roi,
  xyz = NULL,
  cols = c("#56B4E9", "#D55E00", "#009E73"),
  levels = c("False Negative", "False Positive", "True Positive"),
  addlegend = TRUE,
  center = TRUE,
  leg.cex = 1.5,
  ...
)

multi_overlay_diff(
  x,
  pred,
  roi,
  z = NULL,
  cols = c("#56B4E9", "#D55E00", "#009E73"),
  ...
)

set.seed(5)
dims = rep(10, 3)
arr = array(rpois(prod(dims), lambda = 2), dim = dims)
nim = oro.nifti::nifti(arr)
roi = nim > 2
pred = nim > 1.5
ortho_diff(nim, pred, roi)
set.seed(5)
dims = rep(10, 3)
arr = array(rnorm(prod(dims)), dim = dims)
nim = oro.nifti::nifti(arr)
mask = nim > 2
pred = nim > 1.5
multi_overlay_diff(nim, roi = mask, pred = pred)



 if (requireNamespace("brainR", quietly = TRUE)) {
   visits = 1:3
   y = paste0("Visit_", visits, ".nii.gz")
   y = system.file(y, package = "brainR")
   y = lapply(y, readnii)

   y = lapply(y, function(r){
     pixdim(r) = c(0, rep(1, 3), rep(0, 4))
     dropImageDimension(r)
   })

   x = system.file("MNI152_T1_1mm_brain.nii.gz", 
                 package = "brainR")
   x = readnii(x)
   mask = x > 0
   alpha = function(col, alpha = 1) {
       cols = t(col2rgb(col, alpha = FALSE)/255)
       rgb(cols, alpha = alpha)
   }
   roi = y[[2]]
   pred = y
   multi_overlay_diff(x, roi = roi, pred = pred)
   multi_overlay_diff(x, roi = roi, pred = pred, 
         mask = mask, 
         main = paste0("\n", "Visit ", visits),
         text = LETTERS[visits],
         text.x = 0.9,
         text.y = 0.1,
         text.cex = 3)
 }