REQUIRES `imagemagick` installed. ONLY TESTED ON MY LAPTOP. BUYER BEWARE! Export four individual image files from one source image file. (Source is one big file from entire flatbed scanner or four Polaroids. Each individual Polaroid gets exported to its own file.)

crop_export_subimages.rb

source_files = ARGV[0]

# optional file type args
# passed in like: ruby crop.rb path/to/files source_extension export_extension
#                 ruby crop.rb path/to/files heic png
source_extension_arg = ARGV[1]
export_extension_arg = ARGV[2]

# both extensions default to heic if not passed in
SOURCE_EXTENSION = source_extension_arg.nil? ? "heic" : source_extension_arg
EXPORT_EXTENSION = export_extension_arg.nil? ? "heic" : export_extension_arg

RECTANGLES = {
  a: "4641x5643+455+611",  # top_left
  b: "4641x5643+5125+600", # top_right
  c: "4641x5643+455+6232", # bottom_left
  d: "4641x5643+5125+6210" # bottom_right
}

# go to directory passed into script as a CLI arg
Dir.chdir(source_files) do
  # find only files that have the right file extension
  # TODO: hardcoded to .png above (for now?), is this YAGNI?
  Dir.glob("*.#{SOURCE_EXTENSION}").each do |current_file|
    # STEP: delete already exported files
    # already exported files’ names are formatted: 1a.png (NUMBER + LETTER + .png)
    if current_file =~ /\d+[a-z].#{SOURCE_EXTENSION}/
      export_current_file = current_file

      # delete already exported files so magick doesn’t need to confirm overwrite [y/N]
      # TODO: what is the magick arg to confirm overwrite
      File.delete export_current_file

      # then move onto next file, aka don't delete source files
      next
    end

    # STEP: crop and export from source files
    # source files’ names are formatted: 1.png (NUMBER + .SOURCE_EXTENSION)
    if current_file =~ /\d+.#{SOURCE_EXTENSION}/
      # get the source filename’s number to use in export’s filename with letter
      number, _extension = current_file.split(".")

      # go through each exportable image area
      RECTANGLES.each do |letter, whxy_args|
        # export files’ names are formatted: 1a.png (NUMBER + LETTER + .EXPORT_EXTENSION)
        export_filename = "#{number}#{letter}.#{EXPORT_EXTENSION}"

        command = <<~IMAGEMAGICK_COMMAND
          magick #{current_file} -crop #{whxy_args}  #{export_filename}
        IMAGEMAGICK_COMMAND

        system command
      end
    end
  end
end