- fix tiled image reading

src/decoder/image.rs

@@ -36,6 +36,9 @@ impl TileAttributes {
     pub fn tiles_down(&self) -> usize {
         self.image_height.div_ceil(self.tile_length)
     }
+    pub fn tiles_per_plane(&self) -> usize {
+        self.tiles_across() * self.tiles_down()
+    }
     fn padding_right(&self) -> usize {
         (self.tile_width - self.image_width % self.tile_width) % self.tile_width
     }
@@ -1016,7 +1019,15 @@ impl Image {
             }
             ChunkType::Tile => {
                 let tile_attrs = self.tile_attributes.as_ref().unwrap();
-                let (padding_right, padding_down) = tile_attrs.get_padding(chunk_index as usize);
+                // The chunk index counts the tiles of all planes, but the tile grid repeats per
+                // plane, so only the position within the plane decides the padding.
+                let tiles_per_plane = tile_attrs.tiles_per_plane();
+                let tile = if tiles_per_plane == 0 {
+                    0
+                } else {
+                    chunk_index as usize % tiles_per_plane
+                };
+                let (padding_right, padding_down) = tile_attrs.get_padding(tile);
 
                 let tile_width = tile_attrs.tile_width - padding_right;
                 let tile_length = tile_attrs.tile_length - padding_down;

tests/decode_images.rs

@@ -506,6 +506,47 @@ fn test_tiled_extra_samples_border_u8() {
     assert_eq!(data, expected);
 }
 
+#[test]
+fn test_tiled_planar_border_u16() {
+    // A planar (separate) tiled image whose dimensions are not multiples of the tile size.
+    // The tile grid repeats for every plane, but the chunk (tile) index counts all planes, so
+    // the border padding of the second plane used to be looked up with the wrong tile index.
+    // The bottom-right tile of plane 1 then claimed a full tile height, and the decoder ran
+    // past the end of the output buffer.
+    //
+    // Note that `read_image` only decodes the first plane, so this has to go through
+    // `read_image_to_buffer` to reach the tiles that were mis-sized.
+    let path = PathBuf::from(TEST_IMAGE_DIR).join("tiled-planar-2c-16b.tif");
+    let img_file = File::open(path).expect("Cannot find test image!");
+    let mut decoder = Decoder::open(img_file).expect("Cannot create decoder");
+    decoder.next_image().expect("Cannot read image IFD");
+    assert_eq!(decoder.dimensions().unwrap(), (30, 20));
+    assert_eq!(
+        decoder.colortype().unwrap(),
+        ColorType::Multiband {
+            bit_depth: 16,
+            num_samples: 2
+        }
+    );
+
+    let mut buffer = DecodingSampleBuffer::U16(Vec::new());
+    decoder.read_image_to_buffer(&mut buffer).unwrap();
+    let DecodingSampleBuffer::U16(data) = buffer else {
+        panic!("Wrong bit depth")
+    };
+    assert_eq!(data.len(), 2 * 20 * 30);
+
+    let mut expected = Vec::with_capacity(2 * 20 * 30);
+    for plane in 0..2u16 {
+        for y in 0..20u16 {
+            for x in 0..30u16 {
+                expected.push(1000 * plane + 10 * y + x);
+            }
+        }
+    }
+    assert_eq!(data, expected);
+}
+
 #[test]
 fn test_inner_access() {
     let path = PathBuf::from(TEST_IMAGE_DIR).join("tiled-rect-rgb-u8.tif");