fix: preserve aspect ratio in thumbnail

AzHicham · Jul 18, 2024 · ea0faa8 · ea0faa8
1 parent e46776c
commit ea0faa8
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Showing 3 changed files with 100 additions and 13 deletions.
diff --git a/src/utils.rs b/src/utils.rs
@@ -3,9 +3,42 @@ use {
     crate::{errors::OpenSlideError, Result, Size},
     fast_image_resize as fr,
     image::{RgbImage, RgbaImage},
-    std::{iter::zip, num::NonZeroU32},
+    std::{cmp, iter::zip, num::NonZeroU32},
 };
 
+#[cfg(feature = "image")]
+pub fn preserve_aspect_ratio(size: &Size, dimension: &Size) -> Size {
+    // Code adapted from https://pillow.readthedocs.io/en/latest/_modules/PIL/Image.html#Image.thumbnail
+    fn round_aspect<F: FnMut(f32) -> f32>(number: f32, mut key: F) -> u32 {
+        cmp::max(
+            cmp::min_by_key(number.floor() as u32, number.ceil() as u32, |n| {
+                key(*n as f32).round() as u32
+            }),
+            1,
+        )
+    }
+    let w = size.w as f32;
+    let h = size.h as f32;
+    let aspect: f32 = dimension.w as f32 / dimension.h as f32;
+    if { w / h } >= aspect {
+        Size {
+            w: round_aspect(h * aspect, |n| (aspect - n / h).abs()),
+            h: h as u32,
+        }
+    } else {
+        Size {
+            w: w as u32,
+            h: round_aspect(w / aspect, |n| {
+                if n == 0. {
+                    0.
+                } else {
+                    (aspect - w / n).abs()
+                }
+            }),
+        }
+    }
+}
+
 #[cfg(feature = "image")]
 pub(crate) fn resize_rgb_image(image: RgbImage, new_size: &Size) -> Result<RgbImage> {
     let src_image = fr::Image::from_vec_u8(
@@ -81,3 +114,45 @@ pub fn _bgra_to_rgb(image: &RgbaImage) -> RgbImage {
     }
     rgb_image
 }
+
+#[cfg(test)]
+#[cfg(feature = "image")]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_preserve_aspect_ratio() {
+        assert_eq!(
+            preserve_aspect_ratio(&Size { w: 100, h: 100 }, &Size { w: 50, h: 50 }),
+            Size { w: 100, h: 100 }
+        );
+        assert_eq!(
+            preserve_aspect_ratio(&Size { w: 100, h: 100 }, &Size { w: 25, h: 50 }),
+            Size { w: 50, h: 100 }
+        );
+        assert_eq!(
+            // Edge case
+            preserve_aspect_ratio(&Size { w: 1, h: 1 }, &Size { w: 25, h: 50 }),
+            Size { w: 1, h: 1 }
+        );
+        assert_eq!(
+            // Edge case
+            preserve_aspect_ratio(&Size { w: 100, h: 200 }, &Size { w: 1, h: 1 }),
+            Size { w: 100, h: 100 }
+        );
+        assert_eq!(
+            // Edge case
+            preserve_aspect_ratio(&Size { w: 0, h: 5 }, &Size { w: 1, h: 10}),
+            Size { w: 0, h: 1 }
+        );
+        assert_eq!(
+            // Not round ratio
+            preserve_aspect_ratio(&Size { w: 33, h: 100 }, &Size { w: 12, h: 13 }),
+            Size { w: 33, h: 35 }
+        );
+        assert_eq!(
+            // Not round ratio
+            preserve_aspect_ratio(&Size { w: 33, h: 15 }, &Size { w: 12, h: 13 }),
+            Size { w: 13, h: 15 }
+        );
+    }
+}
diff --git a/src/wrapper.rs b/src/wrapper.rs
@@ -4,7 +4,10 @@ use std::path::Path;
 #[cfg(feature = "image")]
 use {
     crate::{
-        utils::{_bgra_to_rgb, _bgra_to_rgba_inplace, resize_rgb_image, resize_rgba_image},
+        utils::{
+            _bgra_to_rgb, _bgra_to_rgba_inplace, preserve_aspect_ratio, resize_rgb_image,
+            resize_rgba_image,
+        },
         Address,
     },
     image::{RgbImage, RgbaImage},
@@ -281,9 +284,9 @@ impl OpenSlide {
             level,
             address: Address { x: 0, y: 0 },
         };
-
         let image = self.read_image_rgba(&region)?;
-        let image = resize_rgba_image(image, size)?;
+        let size = preserve_aspect_ratio(&size, &dimension_level0);
+        let image = resize_rgba_image(image, &size)?;
 
         Ok(image)
     }
@@ -310,7 +313,8 @@ impl OpenSlide {
         };
 
         let image = self.read_image_rgb(&region)?;
-        let image = resize_rgb_image(image, size)?;
+        let size = preserve_aspect_ratio(&size, &dimension_level0);
+        let image = resize_rgb_image(image, &size)?;
 
         Ok(image)
     }

diff --git a/tests/openslide.rs b/tests/openslide.rs
@@ -242,27 +242,35 @@ fn test_slide_read_image_rgba(#[case] filename: &Path) {
 }
 
 #[rstest]
-#[case(boxes_tiff())]
+#[case((boxes_tiff(), &Size { w: 96, h: 80 }))]
 #[cfg(feature = "image")]
-fn test_thumbnail_rgba(#[case] filename: &Path) {
+fn test_thumbnail_rgba(#[case] filename_and_size: (&Path, &Size)) {
+    let (filename, expected_size) = filename_and_size;
     let slide = OpenSlide::new(filename).unwrap();
 
     let size = Size { w: 100, h: 80 };
     let thumbnail = slide.thumbnail_rgba(&size).unwrap();
-    assert_eq!(thumbnail.dimensions(), (size.w, size.h));
-    assert_eq!(thumbnail.len(), (size.h * size.w * 4) as usize);
+    assert_eq!(thumbnail.dimensions(), (expected_size.w, expected_size.h));
+    assert_eq!(
+        thumbnail.len(),
+        (expected_size.h * expected_size.w * 4) as usize
+    );
 }
 
 #[rstest]
-#[case(boxes_tiff())]
+#[case((boxes_tiff(), &Size { w: 96, h: 80 }))]
 #[cfg(feature = "image")]
-fn test_thumbnail_rgb(#[case] filename: &Path) {
+fn test_thumbnail_rgb(#[case] filename_and_size: (&Path, &Size)) {
+    let (filename, expected_size) = filename_and_size;
     let slide = OpenSlide::new(filename).unwrap();
 
     let size = Size { w: 100, h: 80 };
     let thumbnail = slide.thumbnail_rgb(&size).unwrap();
-    assert_eq!(thumbnail.dimensions(), (size.w, size.h));
-    assert_eq!(thumbnail.len(), (size.h * size.w * 3) as usize);
+    assert_eq!(thumbnail.dimensions(), (expected_size.w, expected_size.h));
+    assert_eq!(
+        thumbnail.len(),
+        (expected_size.h * expected_size.w * 3) as usize
+    );
 }
 
 #[rstest]