Use image_data() to consistently get 4 channel bitmap array, fixes #20

DESCRIPTION

@@ -15,7 +15,7 @@ Imports:
     tibble,
     Rcpp,
     RcppParallel,
-    magick,
+    magick (>= 1.6),
     purrr,
     magrittr,
     dplyr,

R/histogram.R

@@ -34,11 +34,12 @@
 #'
 #' @importFrom tibble as_tibble
 #' @importFrom dplyr mutate
+#' @importFrom magick image_data
 #' @importFrom magrittr %>%
 #'
 #' @export
 image_histogram_data <- function(im){
-  bitmap <- im[[1]]
+  bitmap <- image_data(im, 'rgba')
   as_tibble(magick_image_histogram(bitmap))
 }
 

R/pixelize.R

@@ -1,6 +1,6 @@
 as_bitmap <- function(img){
   if( inherits(img, "magick-image")){
-    img <- img[[1]]
+    img <- image_data(img, 'rgba')
   }
   img
 }