Fix underflows and panics around Gaussian blur for empty images

src/imageops/filter_1d.rs

@@ -47,11 +47,22 @@ struct KernelShape {
     height: usize,
 }
 
+/// Size of a non-empty image. Width and height are guaranteed to be non-zero.
 #[derive(Debug, Clone, Copy)]
 pub(crate) struct FilterImageSize {
     pub(crate) width: usize,
     pub(crate) height: usize,
 }
+impl FilterImageSize {
+    pub(crate) fn new(dimensions: (u32, u32)) -> Option<Self> {
+        let width = dimensions.0 as usize;
+        let height = dimensions.1 as usize;
+        if width == 0 || height == 0 {
+            return None;
+        }
+        Some(Self { width, height })
+    }
+}
 
 /// Pads an image row with *clamp* strategy
 ///

src/imageops/sample.rs

@@ -1306,9 +1306,11 @@ pub(crate) fn gaussian_blur_dyn_image(
         parameters.y_axis_sigma,
     );
 
-    let filter_image_size = FilterImageSize {
-        width: image.width() as usize,
-        height: image.height() as usize,
+    let Some(filter_image_size) = FilterImageSize::new(image.dimensions()) else {
+        // If the image is empty, return an empty image of the same dimensions and color space.
+        let mut target = DynamicImage::new(image.width(), image.height(), image.color());
+        let _ = target.set_color_space(image.color_space());
+        return target;
     };
 
     let mut target = match image {
@@ -1514,9 +1516,9 @@ fn gaussian_blur_indirect_impl<I: GenericImageView, const CN: usize>(
         parameters.y_axis_sigma,
     );
 
-    let filter_image_size = FilterImageSize {
-        width: image.width() as usize,
-        height: image.height() as usize,
+    let Some(filter_image_size) = FilterImageSize::new(image.dimensions()) else {
+        // if the input image is empty, just return an empty image
+        return image.buffer_like();
     };
 
     match CN {
@@ -1626,7 +1628,7 @@ where
 #[cfg(test)]
 mod tests {
     use super::{resize, sample_bilinear, sample_nearest, FilterType};
-    use crate::{GenericImageView, ImageBuffer, RgbImage};
+    use crate::{DynamicImage, GenericImageView, ImageBuffer, RgbImage};
     #[cfg(feature = "benchmarks")]
     use test;
 
@@ -1898,4 +1900,25 @@ mod tests {
         let huge_u16 = ImageBuffer::from_pixel(1024, 1024, crate::Luma([65535_u16]));
         super::thumbnail(&huge_u16, 1, 1);
     }
+
+    #[test]
+    fn sample_empty_image() {
+        // blurring an empty image should not panic
+        _ = DynamicImage::new(0, 0, crate::ColorType::Rgb8).blur(1.0);
+        _ = DynamicImage::new(10, 0, crate::ColorType::Rgb8).blur(1.0);
+        _ = DynamicImage::new(0, 10, crate::ColorType::Rgb8).blur(1.0);
+
+        _ = crate::imageops::blur(
+            &ImageBuffer::from_pixel(0, 0, crate::Rgb([255_u8, 255_u8, 255_u8])),
+            1.0,
+        );
+        _ = crate::imageops::blur(
+            &ImageBuffer::from_pixel(10, 0, crate::Rgb([255_u8, 255_u8, 255_u8])),
+            1.0,
+        );
+        _ = crate::imageops::blur(
+            &ImageBuffer::from_pixel(0, 10, crate::Rgb([255_u8, 255_u8, 255_u8])),
+            1.0,
+        );
+    }
 }

src/images/generic_image.rs

@@ -65,6 +65,17 @@ pub trait GenericImageView {
     {
         let (width, height) = self.dimensions();
 
+        if width == 0 || height == 0 {
+            // Return an empty iterator for empty images
+            return Pixels {
+                image: self,
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 0,
+            };
+        }
+
         Pixels {
             image: self,
             x: 0,