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#' Remove Whitespace from Images
#'
#' @description
#' This is a wrapper function around `convert -trim` to automatically remove any
#' whitespace from locally saved images. Note that 'ImageMagick' must be
#' installed on your local system, see Source.
#'
#' @param path File path leading to image files as `character`, defaults to the
#' current working directory.
#' @param pattern A regular expression as `character` accepted by
#' [list.files()], defaults to `c(".png$", ".tiff$")`.
#'
#' @return
#' A `character` vector containing the names of the processed images.
#'
#' @author
#' Florian Detsch
#'
#' @seealso
#' [system()]
#'
#' @source
#' Ooms J (2018) The **magick** package: Advanced Image-Processing in R.
#' Available online: <https://cran.r-project.org/package=magick/vignettes/intro.html>.
#'
#' @examples
#' \dontrun{
#' ## trim image of bart simpson
#' download.file("http://pngimg.com/uploads/simpsons/simpsons_PNG93.png?i=1"
#' , destfile = (ofl <- file.path(tempdir(), "bart.png", fsep = "\\"))
#' , mode = "wb")
#'
#' par(mfrow = c(1, 2))
#'
#' img = brick(ofl)
#' plotRGB(img)
#'
#' jnk = trimImages(tempdir(), "bart.png")
#' trm = brick(jnk)
#' plotRGB(trm)
#'
#' dev.off()
#' }
#'
#' @export
trimImages <- function(path = ".", pattern = c(".png$", ".tiff$")) {
## list files matching specified pattern
lst_fls <- lapply(pattern, function(i) {
list.files(path = path, pattern = i, full.names = TRUE)
})
chr_fls <- unlist(lst_fls)
if (length(chr_fls) == 0)
stop("No files found in ", path, " matching specified pattern.")
## trim images
for (i in chr_fls) {
ch_sysstring <- paste("magick", i, "-trim", i)
system(ch_sysstring)
}
## return list of processed files
return(chr_fls)
}
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