diff --git a/src/decoder/image.rs b/src/decoder/image.rs
index 113a66c..849550b 100644
--- a/src/decoder/image.rs
+++ b/src/decoder/image.rs
@@ -29,15 +29,6 @@ pub(crate) struct TileAttributes {
     pub tile_length: usize,
 }
 
-pub(crate) struct PlaneLayout {
-    /// The underlying readout layout.
-    pub readout: ReadoutLayout,
-    /// Buffer offset from one plane of output to the next.
-    pub plane_offsets: Vec<usize>,
-    /// Total number of bytes for all planes in given order.
-    pub total_bytes: usize,
-}
-
 impl TileAttributes {
     pub fn tiles_across(&self) -> usize {
         self.image_width.div_ceil(self.tile_width)
@@ -132,6 +123,16 @@ pub(crate) struct ReadoutLayout {
     pub chunks_per_plane: u32,
 }
 
+/// A `ReadoutLayout` with pre-calculated plane information.
+pub(crate) struct PlaneLayout {
+    /// The underlying readout layout.
+    pub readout: ReadoutLayout,
+    /// Buffer offset from one plane of output to the next.
+    pub plane_offsets: Vec<usize>,
+    /// Total number of bytes for all planes in given order.
+    pub total_bytes: usize,
+}
+
 impl Image {
     pub fn from_reader<R: Read + Seek>(
         decoder: &mut ValueReader<R>,
diff --git a/src/decoder/mod.rs b/src/decoder/mod.rs
index e303e01..3fa2d4a 100644
--- a/src/decoder/mod.rs
+++ b/src/decoder/mod.rs
@@ -1009,9 +1009,6 @@ impl<R: Read + Seek> Decoder<R> {
         Ok(())
     }
 
-    // FIXME: it's unusual for this method to take a `usize` dimension parameter since those would
-    // typically come from the image data. The preferred consistent representation should be `u32`
-    // and that would avoid some unusual casts `usize -> u64` with a `u64::from` instead.
     // FIXME: when planes are not homogenous (i.e. subsampled or differing depths) then the
     // `readout_for_size` or `to_plane_layout` needs a parameter to determine the planes being
     // read instead of assuming a constant repeated size for them.
@@ -1020,12 +1017,6 @@ impl<R: Read + Seek> Decoder<R> {
         read: &image::ReadoutLayout,
         planes: core::ops::Range<u16>,
     ) -> TiffResult<DecodingExtent> {
-        let bits_per_sample = read.color.bit_depth();
-
-        // If samples take up more than one byte, we expand it to a full number (integer or float)
-        // and the number of samples in that integer type just counts the number in the underlying
-        // image itself. Otherwise, a row is represented as the byte slice of bitfields without
-        // expansion. The output did that computation for us.
         let buffer = read.to_plane_layout()?;
 
         // The layout is for all planes. So restrict ourselves to the planes that were requested.
@@ -1044,6 +1035,7 @@ impl<R: Read + Seek> Decoder<R> {
         };
 
         let buffer_bytes = end - offset;
+        let bits_per_sample = read.color.bit_depth();
 
         Ok(match self.image().sample_format {
             SampleFormat::Uint => match bits_per_sample {