R/tunnel_filter.R

In UBC-MDS/Rmagine: Image Manipulation Package

# Created on February 28, 2020
# author: Katie Birchard
# Implementation of the tunnel distortion filter in the Rmagine package.
#'
#' Apply tunnel distortion filter to a given image.
#'
#' Returns the given image with the user-specified distortion applied.
#'
#' @param image_path string: the local file path for the image to which the filter will be applied.
#' @param rot double: Rotation degree holding value between -0.5 and 0.5. Default: 0.5.
#' @param return_file_name string: File name for the transformed image to be saved
#' @param dest_folder string: Destiname folder name for storing transformed images
#'
#' @return location of saved image with filter applied.
#' @export
#'
#' @example
#' tunnel_filter("imgs/pic.jpg", rot=0.2)

tunnel_filter <- function(image_path, rot=0.5, return_file_name = "tunnel.jpeg", dest_folder = "transformed_imgs/") {

  # Exception handling
  if(!is.character(image_path)) {
    stop("Image file path must be a string")
  }

  if(!endsWith(image_path, ".jpg") & !endsWith(image_path, ".jpeg") & !endsWith(image_path, ".png")) {
    stop("Image file path should lead to an image")
  }

  if(startsWith(image_path, "https:") | startsWith(image_path, "http:") | startsWith(image_path, "www")) {
    stop("Image file path must be in a local directory")
  }

  if(!is.numeric(rot)) {
    stop("Rotation degree, rot, must be numeric")
  }

  if(rot > 0.5 | rot < -0.5) {
    stop("Rotation degree must be between -0.5 and 0.5")
  }

  if(!is.character(return_file_name)){
    stop("Error: Output file name must be a string")
  }

  if(!endsWith(tolower(return_file_name), "jpg") & !endsWith(tolower(return_file_name), "png") & !endsWith(tolower(return_file_name), "jpeg")){
    stop("Error: Path given must end with .png, .jpg, or .jpeg")
  }

  if(!is.character(dest_folder)){
    stop("Error: Destination folder must be a string")
  }

  # Read in the image file
  image <- imager::load.image(image_path)

  # Obtain width and height
  w <- imager::width(image)
  h <- imager::height(image)

  # Convert image to array and specify output array
  original_array <- as.array(image)
  tunnel_array <- as.array(image)

  # Calculate max radius for normalization
  max_radius = sqrt(w**2 + h**2)/2

  # Loop through colour channels, width, and height
  for (c in 1:3) {
    for (x in 1:w) {
      for (y in 1:h) {

        # Normalize x and y values
        norm_y <- (2*y - h)/h
        norm_x <- (2*x - w)/w

        # Calculate radius and normalize
        r = sqrt(norm_x^2 + norm_y^2)/max_radius
        x2 = norm_x / (1 + (0.5*(r^4) + 0.5*(r^2) + 0.5*r))
        y2 = norm_y/ (1 + (0.5*(r**4) + 0.5*(r**2) + 0.5*r))

        # Creating variables for distortion and rotation
        x3 = ((rot*cos(atan2(x2, y2)) + 1)*w)/2.0
        y3 = ((rot*sin(atan2(x2, y2)) + 1)*h)/2.0

        # Apply distortion and rotation to output array
        tunnel_array[x, y, 1, c] <- original_array[x3, y3, 1, c]
      }
    }
  }
  # Convert array to image
  tunnel_image <- imager::as.cimg(tunnel_array)

  # Save image
  # plot(tunnel_image)
  imager::save.image(tunnel_image, file = paste0(dest_folder, return_file_name))
  #print("The filtered image has been saved to the specified directory")
  return(tunnel_array)
}