optional hd image mode

src/main.rs

@@ -1,6 +1,9 @@
 use std::fmt;
 use std::collections::HashMap;
 
+const IMAGE_DIMENSION_SD: usize = 8;
+const IMAGE_DIMENSION_HD: usize = 16;
+
 #[derive(Eq, PartialEq)]
 struct Colour {
     red:   u8,
@@ -145,11 +148,16 @@ fn image_from_string(string: String) -> Image {
 }
 
 fn image_to_string(image: Image) -> String {
-    let mut string = String::new();
+    image_to_string_opts(image, true)
+}
 
-    for line in image.pixels.chunks(8) {
+fn image_to_string_opts(image: Image, hd: bool) -> String {
+    let mut string = String::new();
+    let chunk_size = if hd {IMAGE_DIMENSION_HD} else {IMAGE_DIMENSION_SD};
+
+    for line in image.pixels.chunks(chunk_size) {
         for pixel in line {
-            string.push(if *pixel {'1'} else {'0'});
+            string.push(*pixel as char);
         }
         string.push('\n');
     }