R/translate.R

In UBC-MDS/AutoTransformR: A robust image transformation generator

require(OpenImageR)

translate <- function(image_path, num_images, max_translation){
  #' Returns an array of images of length num_images randomly translated a random number of pixels up to max_rotation
  #'
  #'Translate takes the path to and image and generates randomly translated images, the desired number
  #'of times. Each translated image will not be translated more than the maximum distance provided.
  #'The translation can be in any direction.
  #'
  #' @param image_path string: The file path of the image to be translated.
  #' @param num_images integer: The number of translated images to be returned.
  #' @param max_translation integer: The maximum distance in pixels that the image can be translated.
  #'
  #' @return array: pixel values of the translated images
  #' @export
  #'
  #' @examples
  #' \dontrun{
  #' translate("../tests/testthat/img/milad.jpg", 5, 10)
  #' translate("../tests/testthat/img/milad.jpg", 10, 20)
  #' translate("../tests/testthat/img/milad.jpg", 15, 50)
  #' translate("../tests/testthat/img/milad.jpg", 20, 100)
  #' }



  # check for correct function inputs
  if(!is.character(image_path)){
    stop("Error: image_path is not a string")
  }
  if(is.character(max_translation)){
    stop("Error: max_translation must be an integer")
  }
  if(is.character(num_images)){
    stop("Error: num_images must be an integer")
  }
  if(num_images < 1){
    stop("Error: num_images must be 1 or greater")
  }

  read_image <- function(file_path){
    tryCatch(
      OpenImageR::readImage(file_path),

      # Catch error from readImage
      error=function(e){
        stop("Incorrect directory/image not found")
      }
    )
  }

  # read in image as array/matrix
  original <- read_image(image_path)

  if(max_translation >= dim(original)[1] | max_translation >= dim(original)[2]){
    stop("Error: max_translation must be less than the width and height of the image")
  }

  translations_x <- sample(-max_translation:max_translation, num_images, replace = TRUE)
  translations_y <- sample(-max_translation:max_translation, num_images, replace = TRUE)

  translated_images <- c(original)

  for(i in 1:(num_images)) { #offset for original being included at the start
    translated_images <- c(translated_images, translation(original, shift_rows = translations_x[i], shift_cols = translations_y[i]))
  }

  translated_images <- array(translated_images, dim = c(dim(original), num_images+1))

  return(translated_images)
}