Support DynamicImage in canny and remove imperative .to_luma8() in docs and README

README.md

@@ -9,8 +9,8 @@ many computer vision applications.
 
 ```rust
 let source_image = image::open("testdata/line-simple.png")
-    .expect("failed to read image")
-    .to_luma();
+    .expect("failed to read image");
+
 let detection = edge_detection::canny(
     source_image,
     1.2,  // sigma

src/edge.rs

@@ -1,4 +1,4 @@
-use image::{self, GenericImageView};
+use image::{self, GenericImageView,DynamicImage, GrayImage};
 use rayon::prelude::*;
 use std::f32::consts::*;
 use std::*;
@@ -193,13 +193,14 @@ impl Edge {
 /// * If either `strong_threshold` or `weak_threshold` are outisde the range of 0 to 1 inclusive.
 /// * If `strong_threshold` is less than `weak_threshold`.
 /// * If `image` contains no pixels (either it's width or height is 0).
-pub fn canny<T: Into<image::GrayImage>>(
+pub fn canny<T: Into<DynamicImage>>(
     image: T,
     sigma: f32,
     strong_threshold: f32,
     weak_threshold: f32,
 ) -> Detection {
-    let gs_image = image.into();
+    let dyn_img: DynamicImage = image.into();
+    let gs_image: GrayImage    = dyn_img.into_luma8();
     assert!(gs_image.width() > 0);
     assert!(gs_image.height() > 0);
     let edges = detect_edges(&gs_image, sigma);

src/lib.rs

@@ -8,8 +8,8 @@
 //!
 //! ```
 //! let source_image = image::open("testdata/line-simple.png")
-//!     .expect("failed to read image")
-//!     .to_luma8();
+//!     .expect("failed to read image");
+//! 
 //! let detection = edge_detection::canny(
 //!     source_image,
 //!     1.2,  // sigma