Restore as_flat_samples methods for DynamicImage

Because the return type depends on the buffer's bits per channel, make
the return optional and provide separate methods for 8 and 16 bit
images.

src/dynimage.rs

@@ -22,6 +22,7 @@ use buffer::{
     RgbaImage, Rgba16Image,
 };
 use color::{self, IntoColor};
+use flat::FlatSamples;
 use image;
 use image::{
     GenericImage, GenericImageView, ImageDecoder, ImageError, ImageFormat, ImageOutputFormat, ImageResult,
@@ -392,6 +393,30 @@ impl DynamicImage {
         }
     }
 
+    /// Return a view on the raw sample buffer for 8 bit per channel images.
+    pub fn as_flat_samples_u8(&self) -> Option<FlatSamples<&[u8]>> {
+        match *self {
+            DynamicImage::ImageLuma8(ref p) => Some(p.as_flat_samples()),
+            DynamicImage::ImageLumaA8(ref p) => Some(p.as_flat_samples()),
+            DynamicImage::ImageRgb8(ref p) => Some(p.as_flat_samples()),
+            DynamicImage::ImageRgba8(ref p) => Some(p.as_flat_samples()),
+            DynamicImage::ImageBgr8(ref p) => Some(p.as_flat_samples()),
+            DynamicImage::ImageBgra8(ref p) => Some(p.as_flat_samples()),
+            _ => None,
+        }
+    }
+
+    /// Return a view on the raw sample buffer for 16 bit per channel images.
+    pub fn as_flat_samples_u16(&self) -> Option<FlatSamples<&[u16]>> {
+        match *self {
+            DynamicImage::ImageLuma16(ref p) => Some(p.as_flat_samples()),
+            DynamicImage::ImageLumaA16(ref p) => Some(p.as_flat_samples()),
+            DynamicImage::ImageRgb16(ref p) => Some(p.as_flat_samples()),
+            DynamicImage::ImageRgba16(ref p) => Some(p.as_flat_samples()),
+            _ => None,
+        }
+    }
+
     /// Return this image's pixels as a byte vector.
     pub fn to_bytes(&self) -> Vec<u8> {
         image_to_bytes(self)