Check if resizing to the same size

src/imageops/sample.rs

@@ -7,7 +7,7 @@ use std::f32;
 
 use num_traits::{NumCast, ToPrimitive, Zero};
 
-use crate::image::GenericImageView;
+use crate::image::{GenericImage, GenericImageView};
 use crate::traits::{Enlargeable, Pixel, Primitive};
 use crate::utils::clamp;
 use crate::{ImageBuffer, Rgba32FImage};
@@ -750,16 +750,24 @@ where
 /// Resize the supplied image to the specified dimensions.
 /// ```nwidth``` and ```nheight``` are the new dimensions.
 /// ```filter``` is the sampling filter to use.
-pub fn resize<I: GenericImageView>(
+pub fn resize<I, P, S>(
     image: &I,
     nwidth: u32,
     nheight: u32,
     filter: FilterType,
-) -> ImageBuffer<I::Pixel, Vec<<I::Pixel as Pixel>::Subpixel>>
+) -> ImageBuffer<P, Vec<S>>
 where
-    I::Pixel: 'static,
-    <I::Pixel as Pixel>::Subpixel: 'static,
+    I: GenericImageView<Pixel = P>,
+    P: Pixel<Subpixel = S> + 'static,
+    S: Primitive + 'static,
 {
+    // check if the new dimensions are the same as the old. if they are, make a copy instead of resampling
+    if (nwidth, nheight) == image.dimensions() {
+        let mut tmp = ImageBuffer::new(image.width(), image.height());
+        tmp.copy_from(image, 0, 0).unwrap();
+        return tmp;
+    }
+
     let mut method = match filter {
         FilterType::Nearest => Filter {
             kernel: Box::new(box_kernel),
@@ -860,7 +868,7 @@ where
 #[cfg(test)]
 mod tests {
     use super::{resize, FilterType};
-    use crate::{ImageBuffer, RgbImage};
+    use crate::{GenericImageView, ImageBuffer, RgbImage};
     #[cfg(feature = "benchmarks")]
     use test;
 
@@ -875,6 +883,29 @@ mod tests {
         b.bytes = 800 * 800 * 3 + 200 * 200 * 3;
     }
 
+    #[test]
+    #[cfg(feature = "png")]
+    fn test_resize_same_size() {
+        use std::path::Path;
+        let img = crate::open(&Path::new("./examples/fractal.png")).unwrap();
+        let resize = img.resize(img.width(), img.height(), FilterType::Triangle);
+        assert!(img.pixels().eq(resize.pixels()))
+    }
+
+    #[bench]
+    #[cfg(all(feature = "benchmarks", feature = "tiff"))]
+    fn bench_resize_same_size(b: &mut test::Bencher) {
+        let path = concat!(
+            env!("CARGO_MANIFEST_DIR"),
+            "/tests/images/tiff/testsuite/mandrill.tiff"
+        );
+        let image = crate::open(path).unwrap();
+        b.iter(|| {
+            test::black_box(image.resize(image.width(), image.height(), FilterType::CatmullRom));
+        });
+        b.bytes = (image.width() * image.height() * 3) as u64;
+    }
+
     #[test]
     fn test_issue_186() {
         let img: RgbImage = ImageBuffer::new(100, 100);