doc typo

Upgrade zstd to 0.14

.gitignore

@@ -1,5 +1,6 @@
-
 /target/
 **/*.rs.bk
 Cargo.lock
 tests/benches/corpus/
+.idea
+.agentbridge

CHANGES.md

@@ -1,5 +1,12 @@
 # Version 0.12.0 (unreleased)
 
+Fixes:
+- Decoding a tiled image whose width is not a multiple of the tile width no
+  longer corrupts the columns below the right border tiles when extra samples
+  are discarded (e.g. RGB with an unspecified extra sample). The horizontal
+  tile padding was written past the end of the output row, spilling into the
+  leftmost columns of the following row.
+
 Additions:
 - Added the `TiffHeader` type. It can be used to create a `Decoder` in a state
   before the first IFD and allows opening files at an arbitrary first IFD

Cargo.toml

@@ -1,8 +1,7 @@
 [package]
-name = "tiff"
+name = "ndbioimage-tiff"
 version = "0.11.3"
 edition = "2021"
-resolver = "2"
 
 # note: when changed, also update test runner in `.github/workflows/rust.yml`
 rust-version = "1.88.0"
@@ -16,6 +15,9 @@ categories = ["multimedia::images", "multimedia::encoding"]
 
 exclude = ["tests/images/*", "tests/fuzz_images/*", "tests/**/*.tif"]
 
+[lib]
+name = "tiff"
+
 [dependencies]
 half = { version = "2.4.1" }
 quick-error = "2.0.1"
@@ -24,7 +26,8 @@ quick-error = "2.0.1"
 fax34 = { package = "fax", version = "0.2.6", optional = true }
 flate2 = { version = "1.0.20", optional = true }
 weezl = { version = "0.2.1", optional = true }
-zstd = { version = "0.13", optional = true }
+zstd = { version = "0.14", optional = true }
+zrip-decode = { version = "0.8.2", features = ["paranoid"], optional = true }
 zune-jpeg = { version = "0.5.1", optional = true }
 image-webp = {version = "0.2.4", optional = true }
 
@@ -45,6 +48,9 @@ jpeg = ["dep:zune-jpeg"]
 lzw = ["dep:weezl"]
 webp = ["dep:image-webp"]
 zstd = ["dep:zstd"]
+# Fully safe Rust but somewhat slower Zstd decoding.
+# When both zstd and zstd-safe-rust are enabled, zstd takes precedence.
+zstd-safe-rust = ["dep:zrip-decode"]
 
 [[bench]]
 name = "lzw"

README.md

@@ -5,6 +5,8 @@
 
 TIFF decoding and encoding library in pure Rust
 
+Forked from https://github.com/image-rs/image-tiff. Changes: read images containing RGBPalette frames, ignoring colormaps.
+
 ## Supported
 
 ### Features

benches/lzw.rs

@@ -9,9 +9,9 @@ use tiff::decoder::Decoder;
 fn read_image(image: &[u8]) {
     let image = std::io::Cursor::new(image);
     let decoder = Decoder::open(black_box(image));
-
     let mut reader = decoder.unwrap();
     while reader.more_images() {
+        reader.next_directory().unwrap();
         reader.read_image().unwrap();
     }
 }

examples/decode.rs

@@ -2,13 +2,15 @@ use tiff::decoder::{BufferLayoutPreference, Decoder, DecodingSampleBuffer, Decod
 
 fn main() -> Result<(), Box<dyn std::error::Error>> {
     let Some(image) = std::env::args_os().nth(1) else {
-        eprintln!("Usage: decode FILE");
+        eprintln!("Usage: decode FILE [--lenient]");
         return Ok(());
     };
 
+    let lenient = std::env::args().nth(2).as_deref() == Some("--lenient");
+
     let file = std::fs::File::open(image)?;
     let io = std::io::BufReader::new(file);
-    let mut reader = Decoder::open(io)?;
+    let mut reader = Decoder::open(io)?.with_lenient(lenient);
 
     let mut data = DecodingSampleBuffer::I8(vec![]);
 

src/decoder/ifd.rs

@@ -363,7 +363,7 @@ impl ::std::fmt::Debug for Entry {
     fn fmt(&self, fmt: &mut ::std::fmt::Formatter) -> Result<(), ::std::fmt::Error> {
         fmt.write_str(&format!(
             "Entry {{ type_: {:?}, count: {:?}, offset: {:?} }}",
-            self.type_, self.count, &self.offset
+            self.type_, self.count, self.offset
         ))
     }
 }
@@ -599,8 +599,10 @@ impl Entry {
                 self.decode_values(self.count, self.type_, reader, |bytes| {
                     v.extend(
                         bytes
-                            .chunks_exact(2)
+                            .as_chunks::<2>()
-                            .map(|ch| Short(u16::from_ne_bytes(ch.try_into().unwrap()))),
+                            .0
+                            .iter()
+                            .map(|&ch| Short(u16::from_ne_bytes(ch))),
                     )
                 })
             }
@@ -609,8 +611,10 @@ impl Entry {
                 self.decode_values(self.count, self.type_, reader, |bytes| {
                     v.extend(
                         bytes
-                            .chunks_exact(2)
+                            .as_chunks::<2>()
-                            .map(|ch| SignedShort(i16::from_ne_bytes(ch.try_into().unwrap()))),
+                            .0
+                            .iter()
+                            .map(|&ch| SignedShort(i16::from_ne_bytes(ch))),
                     )
                 })
             }
@@ -619,8 +623,10 @@ impl Entry {
                 self.decode_values(self.count, self.type_, reader, |bytes| {
                     v.extend(
                         bytes
-                            .chunks_exact(4)
+                            .as_chunks::<4>()
-                            .map(|ch| Unsigned(u32::from_ne_bytes(ch.try_into().unwrap()))),
+                            .0
+                            .iter()
+                            .map(|&ch| Unsigned(u32::from_ne_bytes(ch))),
                     )
                 })
             }
@@ -629,8 +635,10 @@ impl Entry {
                 self.decode_values(self.count, self.type_, reader, |bytes| {
                     v.extend(
                         bytes
-                            .chunks_exact(4)
+                            .as_chunks::<4>()
-                            .map(|ch| Signed(i32::from_ne_bytes(ch.try_into().unwrap()))),
+                            .0
+                            .iter()
+                            .map(|&ch| Signed(i32::from_ne_bytes(ch))),
                     )
                 })
             }
@@ -639,8 +647,10 @@ impl Entry {
                 self.decode_values(self.count, self.type_, reader, |bytes| {
                     v.extend(
                         bytes
-                            .chunks_exact(4)
+                            .as_chunks::<4>()
-                            .map(|ch| Float(f32::from_ne_bytes(ch.try_into().unwrap()))),
+                            .0
+                            .iter()
+                            .map(|&ch| Float(f32::from_ne_bytes(ch))),
                     )
                 })
             }
@@ -649,15 +659,17 @@ impl Entry {
                 self.decode_values(self.count, self.type_, reader, |bytes| {
                     v.extend(
                         bytes
-                            .chunks_exact(8)
+                            .as_chunks::<8>()
-                            .map(|ch| Double(f64::from_ne_bytes(ch.try_into().unwrap()))),
+                            .0
+                            .iter()
+                            .map(|&ch| Double(f64::from_ne_bytes(ch))),
                     )
                 })
             }
             Type::RATIONAL => {
                 v = Self::vec_with_capacity(self.count, self.type_, limits)?;
                 self.decode_values(self.count, self.type_, reader, |bytes| {
-                    v.extend(bytes.chunks_exact(8).map(|ch| {
+                    v.extend(bytes.as_chunks::<8>().0.iter().map(|ch| {
                         Rational(
                             u32::from_ne_bytes(ch[..4].try_into().unwrap()),
                             u32::from_ne_bytes(ch[4..].try_into().unwrap()),
@@ -668,7 +680,7 @@ impl Entry {
             Type::SRATIONAL => {
                 v = Self::vec_with_capacity(self.count, self.type_, limits)?;
                 self.decode_values(self.count, self.type_, reader, |bytes| {
-                    v.extend(bytes.chunks_exact(8).map(|ch| {
+                    v.extend(bytes.as_chunks::<8>().0.iter().map(|ch| {
                         SRational(
                             i32::from_ne_bytes(ch[..4].try_into().unwrap()),
                             i32::from_ne_bytes(ch[4..].try_into().unwrap()),
@@ -681,8 +693,10 @@ impl Entry {
                 self.decode_values(self.count, self.type_, reader, |bytes| {
                     v.extend(
                         bytes
-                            .chunks_exact(8)
+                            .as_chunks::<8>()
-                            .map(|ch| UnsignedBig(u64::from_ne_bytes(ch.try_into().unwrap()))),
+                            .0
+                            .iter()
+                            .map(|&ch| UnsignedBig(u64::from_ne_bytes(ch))),
                     )
                 })
             }
@@ -691,8 +705,10 @@ impl Entry {
                 self.decode_values(self.count, self.type_, reader, |bytes| {
                     v.extend(
                         bytes
-                            .chunks_exact(8)
+                            .as_chunks::<8>()
-                            .map(|ch| SignedBig(i64::from_ne_bytes(ch.try_into().unwrap()))),
+                            .0
+                            .iter()
+                            .map(|&ch| SignedBig(i64::from_ne_bytes(ch))),
                     )
                 })
             }
@@ -701,8 +717,10 @@ impl Entry {
                 self.decode_values(self.count, self.type_, reader, |bytes| {
                     v.extend(
                         bytes
-                            .chunks_exact(4)
+                            .as_chunks::<4>()
-                            .map(|ch| Ifd(u32::from_ne_bytes(ch.try_into().unwrap()))),
+                            .0
+                            .iter()
+                            .map(|&ch| Ifd(u32::from_ne_bytes(ch))),
                     )
                 })
             }
@@ -711,8 +729,10 @@ impl Entry {
                 self.decode_values(self.count, self.type_, reader, |bytes| {
                     v.extend(
                         bytes
-                            .chunks_exact(8)
+                            .as_chunks::<8>()
-                            .map(|ch| IfdBig(u64::from_ne_bytes(ch.try_into().unwrap()))),
+                            .0
+                            .iter()
+                            .map(|&ch| IfdBig(u64::from_ne_bytes(ch))),
                     )
                 })
             }

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
     }
@@ -97,6 +100,7 @@ pub(crate) struct Image {
     /// run on samples directly and thus skip the outer byte order entirely, except potentially
     /// they have interior byte order treatment.
     pub decompression_to_host_endian: bool,
+    pub lenient: bool,
 }
 
 /// Describes how to read a tile-aligned portion of the image.
@@ -158,6 +162,7 @@ impl Image {
     pub fn from_reader<R: Read + Seek>(
         decoder: &mut ValueReader<R>,
         ifd: &Directory,
+        lenient: bool,
     ) -> TiffResult<Image> {
         let mut tag_reader = TagReader { decoder, ifd };
 
@@ -174,7 +179,7 @@ impl Image {
             .map(Value::into_u16)
             .transpose()?
             .and_then(PhotometricInterpretation::from_u16)
-            .ok_or(TiffUnsupportedError::UnknownInterpretation)?;
+            .unwrap_or(PhotometricInterpretation::BlackIsZero);
 
         // Try to parse both the compression method and the number, format, and bits of the included samples.
         // If they are not explicitly specified, those tags are reset to their default values and not carried from previous images.
@@ -465,11 +470,11 @@ impl Image {
                     }
                     Some(map)
                 }
-                None => {
+                // A missing palette is not an error. The pixel values of an indexed image are just
-                    return Err(TiffError::FormatError(
+                // indices into the palette, and the palette itself is only display information, so
-                        TiffFormatError::RequiredTagNotFound(Tag::ColorMap),
+                // the image still decodes. Callers observe the absence as `None` from
-                    ));
+                // `Decoder::color_map`.
-                }
+                None => None,
             }
         } else {
             None
@@ -500,6 +505,7 @@ impl Image {
                 compression_method,
                 CompressionMethod::SgiLog | CompressionMethod::SgiLog24
             ),
+            lenient,
         })
     }
 
@@ -515,10 +521,13 @@ impl Image {
     }
 
     pub(crate) fn colortype(&self) -> TiffResult<ColorType> {
-        let is_alpha_extra_samples = matches!(
+        let is_alpha_extra_samples = match self.extra_samples.as_slice().first() {
-            self.extra_samples.as_slice(),
+            Some(ExtraSamples::AssociatedAlpha) | Some(ExtraSamples::UnassociatedAlpha) => true,
-            [ExtraSamples::AssociatedAlpha, ..] | [ExtraSamples::UnassociatedAlpha, ..]
+            // In lenient mode, keep unspecified alpha interpretation logic compatible with libtiff
-        );
+            // See Issue #341
+            Some(ExtraSamples::Unspecified) if self.lenient && self.samples > 3 => true,
+            _ => false,
+        };
 
         match self.photometric_interpretation {
             PhotometricInterpretation::RGB => match self.photometric_samples {
@@ -591,20 +600,30 @@ impl Image {
                     ),
                 )),
             },
-            // Unsupported due to inherently heterogeneous sample types. This is represented as:
+            // CIE L*a*b* (TIFF6 Section 23, pp 110-115) encodes a/b as signed integers
-            // ```
+            // (int8 at 8-bit, int16 at 16-bit) with 0 neutral, while ICC L*a*b*
-            // struct TiffLab /* Interpretation 8* {
+            // (photometric=9) uses unsigned samples with the neutral at the middle of
-            //     pub L: u8, // SampleFormat::Uint
+            // the range. `SampleFormat` applies uniformly to all samples, so it can't
-            //     pub a: i8, // SampleFormat::Int
+            // describe the L=unsigned + a/b=signed mix; instead we take a/b as signed
-            //     pub b: i8, // SampleFormat::Int
+            // from the photometric interpretation (requiring `SampleFormat::Uint`, like
-            // }
+            // the ICCLab arm) and re-bias them to the unsigned ICCLab encoding in
-            // ```
+            // post-processing (see `cielab_to_icclab`). libtiff does the same, decoding
-            PhotometricInterpretation::CIELab => Err(TiffError::UnsupportedError(
+            // both depths (`putcontig8bitCIELab8` / `putcontig8bitCIELab16`, selected by
-                TiffUnsupportedError::InterpretationWithBits(
+            // `initCIELabConversion` in tif_getimage.c line 2216
-                    PhotometricInterpretation::CIELab,
+            // @ 04884181e8903915038be553bfab404302d98ea0).
-                    vec![self.bits_per_sample; self.samples as usize],
+            PhotometricInterpretation::CIELab => match self.photometric_samples {
-                ),
+                3 if matches!(self.bits_per_sample, 8 | 16)
-            )),
+                    && matches!(self.sample_format, SampleFormat::Uint) =>
+                {
+                    Ok(ColorType::Lab(self.bits_per_sample))
+                }
+                _ => Err(TiffError::UnsupportedError(
+                    TiffUnsupportedError::InterpretationWithBits(
+                        PhotometricInterpretation::CIELab,
+                        vec![self.bits_per_sample; self.samples as usize],
+                    ),
+                )),
+            },
             PhotometricInterpretation::CIELogL => match self.samples {
                 1 if matches!(self.bits_per_sample, 32)
                     && matches!(self.sample_format, SampleFormat::IEEEFP) =>
@@ -660,7 +679,11 @@ impl Image {
                 ),
             )),
             PhotometricInterpretation::RGBPalette => Ok(ColorType::Palette(self.bits_per_sample)),
-            PhotometricInterpretation::TransparencyMask => Err(TiffError::UnsupportedError(
+            // TransparencyMask is a single-channel mask, treat as grayscale.
+            PhotometricInterpretation::TransparencyMask => {
+                Ok(ColorType::Gray(self.bits_per_sample))
+            }
+            PhotometricInterpretation::Unknown(_) => Err(TiffError::UnsupportedError(
                 TiffUnsupportedError::InterpretationWithBits(
                     self.photometric_interpretation,
                     vec![self.bits_per_sample; self.samples as usize],
@@ -712,6 +735,8 @@ impl Image {
             )),
             #[cfg(feature = "zstd")]
             CompressionMethod::ZSTD => Box::new(zstd::Decoder::new(reader)?),
+            #[cfg(all(not(feature = "zstd"), feature = "zstd-safe-rust"))]
+            CompressionMethod::ZSTD => Box::new(zrip_decode::streaming::FrameDecoder::new(reader)),
             CompressionMethod::PackBits => Box::new(PackBitsReader::new(reader, compressed_length)),
             #[cfg(feature = "deflate")]
             CompressionMethod::Deflate | CompressionMethod::OldDeflate => {
@@ -994,7 +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;
@@ -1036,6 +1069,7 @@ impl Image {
             | ColorType::YCbCr(n)
             | ColorType::Gray(n)
             | ColorType::Palette(n)
+            | ColorType::Lab(n)
             | ColorType::Multiband {
                 bit_depth: n,
                 num_samples: _,
@@ -1047,6 +1081,7 @@ impl Image {
             | ColorType::YCbCr(n)
             | ColorType::Gray(n)
             | ColorType::Palette(n)
+            | ColorType::Lab(n)
             | ColorType::Multiband {
                 bit_depth: n,
                 num_samples: _,
@@ -1190,15 +1225,26 @@ impl Image {
                 super::fix_endianness_and_predict(
                     out_row,
                     color_type.bit_depth(),
-                    samples,
+                    data_samples,
                     ByteOrder::native(),
                     predictor,
                     scratch,
                 );
 
-                if photometric_interpretation == PhotometricInterpretation::WhiteIsZero {
+                // An n-bit predictor delta is stored modulo 2^n, but the
-                    super::invert_colors(out_row, color_type, self.sample_format)?;
+                // reconstruction above accumulated it in the promoted u16/u32
-                }
+                // storage width. Reduce back modulo the declared depth so both
+                // the inverted and non-inverted paths see exact, in-range
+                // values (2^n divides the storage modulus, so one mask after
+                // the row is exact).
+                super::mask_samples_to_bit_depth(out_row, tiff_bps, out_bps, self.sample_format);
+
+                super::post_process_row(
+                    out_row,
+                    photometric_interpretation,
+                    color_type,
+                    self.sample_format,
+                )?;
             }
         } else if is_output_chunk_rows && is_all_bits {
             // Here we can read directly into the output buffer itself.
@@ -1216,9 +1262,22 @@ impl Image {
                 );
             }
 
-            if photometric_interpretation == PhotometricInterpretation::WhiteIsZero {
+            // No-op in this branch: promoted layouts (declared depth < storage
-                super::invert_colors(tile, color_type, self.sample_format)?;
+            // width) are handled exclusively by the unpacking branch above.
-            }
+            // Called in every integer branch so they cannot diverge.
+            super::mask_samples_to_bit_depth(
+                tile,
+                layout.tiff_bits_per_sample,
+                layout.output_bits_per_sample,
+                self.sample_format,
+            );
+
+            super::post_process_row(
+                tile,
+                photometric_interpretation,
+                color_type,
+                self.sample_format,
+            )?;
         } else if chunk_row_bytes > data_row_bytes && self.predictor == Predictor::FloatingPoint {
             // The floating point predictor shuffles the padding bytes into the encoded output, so
             // this case is handled specially when needed.
@@ -1242,9 +1301,14 @@ impl Image {
                     }
                     _ => unreachable!(),
                 }
-                if photometric_interpretation == PhotometricInterpretation::WhiteIsZero {
+                // No masking here: the floating point predictor requires
-                    super::invert_colors(row, color_type, self.sample_format)?;
+                // IEEEFP samples, which are never depth-promoted.
-                }
+                super::post_process_row(
+                    row,
+                    photometric_interpretation,
+                    color_type,
+                    self.sample_format,
+                )?;
             }
         } else if is_all_bits {
             // We read row-by-row but each row fits in its output buffer.
@@ -1271,9 +1335,22 @@ impl Image {
                     scratch,
                 );
 
-                if photometric_interpretation == PhotometricInterpretation::WhiteIsZero {
+                // No-op in this branch: promoted layouts only occur in the
-                    super::invert_colors(row, color_type, self.sample_format)?;
+                // unpacking branch. Called so the integer branches cannot
-                }
+                // diverge.
+                super::mask_samples_to_bit_depth(
+                    row,
+                    layout.tiff_bits_per_sample,
+                    layout.output_bits_per_sample,
+                    self.sample_format,
+                );
+
+                super::post_process_row(
+                    row,
+                    photometric_interpretation,
+                    color_type,
+                    self.sample_format,
+                )?;
             }
         } else {
             // The encoded data potentially takes up more space than the output data so we must be
@@ -1300,6 +1377,10 @@ impl Image {
             let photo_range = photometric_bit_end / 8..bits_per_pixel / 8;
             let mut encoded = vec![0u8; chunk_row_bytes];
             for row in buf.chunks_mut(layout.row_stride).take(data_dims.1 as usize) {
+                // Clip to the chunk's data width: border chunks are stored at the full chunk
+                // width, and writing their horizontal padding would spill into the following
+                // output row (and predict/invert would run past the chunk's own columns).
+                let row = &mut row[..data_row_bytes];
                 reader.read_exact(&mut encoded)?;
 
                 Self::compact_photometric_bytes(&mut encoded, row, &photo_range);
@@ -1313,9 +1394,22 @@ impl Image {
                     scratch,
                 );
 
-                if photometric_interpretation == PhotometricInterpretation::WhiteIsZero {
+                // No-op in this branch: promoted layouts only occur in the
-                    super::invert_colors(row, color_type, self.sample_format)?;
+                // unpacking branch. Called so the integer branches cannot
-                }
+                // diverge.
+                super::mask_samples_to_bit_depth(
+                    row,
+                    layout.tiff_bits_per_sample,
+                    layout.output_bits_per_sample,
+                    self.sample_format,
+                );
+
+                super::post_process_row(
+                    row,
+                    photometric_interpretation,
+                    color_type,
+                    self.sample_format,
+                )?;
             }
         }
 

src/decoder/mod.rs

@@ -3,8 +3,8 @@ use std::io::{self, Read, Seek};
 use std::num::NonZeroUsize;
 
 use crate::tags::{
-    ByteOrder, IfdPointer, PlanarConfiguration, Predictor, SampleFormat, Tag, TiffVariant, Type,
+    ByteOrder, IfdPointer, PhotometricInterpretation, PlanarConfiguration, Predictor, SampleFormat,
-    ValueBuffer,
+    Tag, TiffVariant, Type, ValueBuffer,
 };
 use crate::{
     ColorType, Directory, TiffError, TiffFormatError, TiffResult, TiffUnsupportedError, UsageError,
@@ -257,6 +257,8 @@ pub struct Decoder<R> {
     /// Reusable scratch buffer for the floating-point predictor. Stored here so that the
     /// allocation persists across strips/tiles and images, avoiding per-row heap allocation.
     scratch: Vec<u8>,
+    /// Leniency flag that allows libtiff-like TIFF color interpretation behavior
+    lenient: bool,
 }
 
 /// All the information needed to read and interpret byte slices from the underlying file, i.e. to
@@ -292,8 +294,8 @@ fn one_byte_predict<const N: usize>(buf: &mut [u8]) {
     acc.copy_from_slice(&buf[..N]);
 
     // Process N bytes per iteration. Each channel's prefix sum is independent.
-    let mut chunks = buf[N..].chunks_exact_mut(N);
+    let chunks = buf[N..].as_chunks_mut::<N>();
-    for chunk in &mut chunks {
+    for chunk in &mut chunks.0.iter_mut() {
         for c in 0..N {
             acc[c] = chunk[c].wrapping_add(acc[c]);
             chunk[c] = acc[c];
@@ -301,7 +303,7 @@ fn one_byte_predict<const N: usize>(buf: &mut [u8]) {
     }
 
     // Handle trailing bytes (when buf.len() - N is not a multiple of N).
-    for (c, byte) in chunks.into_remainder().iter_mut().enumerate() {
+    for (c, byte) in chunks.1.iter_mut().enumerate() {
         *byte = byte.wrapping_add(acc[c]);
     }
 }
@@ -566,6 +568,56 @@ fn fix_endianness_and_predict(
     }
 }
 
+/// Reduce promoted extended-depth samples (9–15 bits → `u16`, 17–31 bits →
+/// `u32`) modulo their declared bit depth, i.e. mask with `(1 << n) - 1`.
+///
+/// An n-bit horizontal-predicted sample stores its delta in exactly n bits,
+/// i.e. modulo `2^n`, so reconstruction is also defined modulo `2^n`. The
+/// predictor accumulates `prev + delta` in the promoted storage width
+/// (`u16`/`u32`, see `rev_hpredict_nsamp`); since `2^n` divides the storage
+/// modulus, masking once after the predictor yields exactly the mod-`2^n`
+/// value for every sample — including legitimate wrap-arounds (a 9-bit
+/// `511, 0` pair is stored as delta `1`, and `511 + 1 = 512` masks back to
+/// `0`). Masking also bounds any out-of-range sample in malformed input, so
+/// all downstream consumers (`invert_colors`' `max - v` and the non-inverted
+/// output path) see in-range values. For samples already in range it is a
+/// no-op.
+///
+/// This runs in every integer decode branch of `expand_chunk` so the
+/// branches cannot diverge. Outside the unpacking branch it reduces to the
+/// two guards below and touches nothing: promoted layouts (`declared <
+/// storage`) exist only there — standard depths have `declared == storage`,
+/// and sub-byte depths keep byte-granular storage.
+#[inline]
+fn mask_samples_to_bit_depth(
+    buf: &mut [u8],
+    declared_bits: u8,
+    storage_bits: u8,
+    sample_format: SampleFormat,
+) {
+    // Only unsigned samples are promoted with zero-extension; signed
+    // extended depths would need sign extension instead and are not
+    // supported by the unpacking path.
+    if sample_format != SampleFormat::Uint {
+        return;
+    }
+    match storage_bits {
+        16 if declared_bits < 16 => {
+            let mask = (1u16 << declared_bits) - 1;
+            for chunk in buf.as_chunks_mut::<2>().0 {
+                *chunk = (u16::from_ne_bytes(*chunk) & mask).to_ne_bytes();
+            }
+        }
+        32 if declared_bits < 32 => {
+            let mask = (1u32 << declared_bits) - 1;
+            for chunk in buf.as_chunks_mut::<4>().0 {
+                *chunk = (u32::from_ne_bytes(*chunk) & mask).to_ne_bytes();
+            }
+        }
+        _ => {}
+    }
+}
+
 fn invert_colors(
     buf: &mut [u8],
     color_type: ColorType,
@@ -659,6 +711,56 @@ fn invert_colors(
     Ok(())
 }
 
+/// Re-bias CIE L*a*b* a/b channels from signed to unsigned encoding.
+///
+/// CIELab (photometric=8) stores a/b as signed integers where 0 is neutral;
+/// ICCLab (photometric=9) stores them as unsigned with the neutral shifted to
+/// the middle of the range. The two differ by exactly half the sample range, so
+/// the conversion is a wrapping add of 2^(bits-1) — i.e. flipping the sign bit —
+/// applied per a/b sample. `bit_depth` is 8 or 16 (guaranteed by `colortype`);
+/// samples are in native byte order here (post `fix_endianness_and_predict`).
+/// See libtiff's `TIFFCIELabToXYZ` for reference (tif_color.c line 45
+/// @ 04884181e8903915038be553bfab404302d98ea0).
+fn cielab_to_icclab(buf: &mut [u8], bit_depth: u8) {
+    match bit_depth {
+        16 => {
+            for pixel in buf.as_chunks_mut::<6>().0 {
+                // pixel is [L, a, b] as three native-endian u16 samples.
+                let (samples, _) = pixel.as_chunks_mut::<2>();
+                for s in &mut samples[1..=2] {
+                    *s = u16::from_ne_bytes(*s).wrapping_add(0x8000).to_ne_bytes();
+                }
+            }
+        }
+        _ => {
+            for [_, a, b] in buf.as_chunks_mut::<3>().0 {
+                *a = a.wrapping_add(128);
+                *b = b.wrapping_add(128);
+            }
+        }
+    }
+}
+
+/// Apply photometric-interpretation-specific post-processing to a decoded row.
+///
+/// Some interpretations need a fixup once the raw samples are in the output
+/// buffer: `WhiteIsZero` inverts intensities, and `CIELab` re-biases the signed
+/// a/b channels into the unsigned ICCLab encoding. These are mutually exclusive,
+/// so at most one applies to any given row.
+fn post_process_row(
+    buf: &mut [u8],
+    photometric_interpretation: PhotometricInterpretation,
+    color_type: ColorType,
+    sample_format: SampleFormat,
+) -> TiffResult<()> {
+    match photometric_interpretation {
+        PhotometricInterpretation::WhiteIsZero => invert_colors(buf, color_type, sample_format)?,
+        PhotometricInterpretation::CIELab => cielab_to_icclab(buf, color_type.bit_depth()),
+        _ => {}
+    }
+    Ok(())
+}
+
 /// Fix endianness. If `byte_order` matches the host, then conversion is a no-op.
 fn fix_endianness(buf: &mut [u8], byte_order: ByteOrder, bit_depth: u8) {
     let host = ByteOrder::native();
@@ -750,6 +852,7 @@ impl TiffHeader {
             seen_ifds: cycles::IfdCycles::new(),
             image: None,
             scratch: Vec::new(),
+            lenient: false,
         }
     }
 }
@@ -832,6 +935,15 @@ impl<R: Read + Seek> Decoder<R> {
         self
     }
 
+    /// Use a lenient decoder.
+    ///
+    /// Configuring this make the parser respect libtiff's behavior to maintain compatibility with
+    /// some older softwares (e.g. some old Adobe suite products).
+    pub fn with_lenient(mut self, lenient: bool) -> Decoder<R> {
+        self.lenient = lenient;
+        self
+    }
+
     // FIXME: this tuple would be a good candidate for a proxy, like IfdDecoder. That has been
     // requested in some form or another in a number of issues.
     #[expect(clippy::unnecessary_unwrap)] // Lifetimes would overlap due to return.
@@ -846,7 +958,7 @@ impl<R: Read + Seek> Decoder<R> {
             ));
         }
 
-        let image = Image::from_reader(&mut self.value_reader, &self.directory)?;
+        let image = Image::from_reader(&mut self.value_reader, &self.directory, self.lenient)?;
         Ok((
             self.image.insert(image),
             &mut self.value_reader,
@@ -982,6 +1094,7 @@ impl<R: Read + Seek> Decoder<R> {
             current_ifd_pointer: self.current_ifd_pointer,
             image: core::mem::take(&mut self.image),
             scratch: core::mem::take(&mut self.scratch),
+            lenient: self.lenient,
         }
     }
 
@@ -1030,7 +1143,11 @@ impl<R: Read + Seek> Decoder<R> {
     /// error is returned.
     pub fn seek_to_image(&mut self, ifd_index: usize) -> TiffResult<()> {
         let (offset, directory) = self.find_nth_ifd(ifd_index)?;
-        self.image = Some(Image::from_reader(&mut self.value_reader, &directory)?);
+        self.image = Some(Image::from_reader(
+            &mut self.value_reader,
+            &directory,
+            self.lenient,
+        )?);
         self.current_ifd_pointer = Some(offset);
         self.directory = directory;
         Ok(())
@@ -1123,7 +1240,11 @@ impl<R: Read + Seek> Decoder<R> {
     pub fn next_image(&mut self) -> TiffResult<()> {
         let next_ifd = self.directory.next();
         let (offset, directory) = self.read_chained_ifd(self.current_ifd_pointer, next_ifd)?;
-        self.image = Some(Image::from_reader(&mut self.value_reader, &directory)?);
+        self.image = Some(Image::from_reader(
+            &mut self.value_reader,
+            &directory,
+            self.lenient,
+        )?);
         self.current_ifd_pointer = Some(offset);
         self.directory = directory;
         Ok(())
@@ -1167,7 +1288,7 @@ impl<R: Read + Seek> Decoder<R> {
     /// Utility to create a reader like [`Self::read_entry`], from the current IFD.
     ///
     /// Returns an `Ok(None)` if the tag is not found in the current directory. See
-    /// [`Self::read_entry´] of which this is a simple wrapper.
+    /// [`Self::read_entry`] of which this is a simple wrapper.
     pub fn read_tag(&mut self, tag: Tag) -> TiffResult<Option<EntryBytesReader<'_, R>>> {
         match self.current_ifd().find_entry(tag) {
             None => Ok(None),

src/decoder/stream.rs

@@ -141,14 +141,32 @@ pub struct LZWReader<R: Read> {
 impl<R: Read> LZWReader<R> {
     /// Wraps a reader
     pub fn new(reader: R, compressed_length: usize) -> LZWReader<R> {
-        let configuration =
+        let mut buffered = BufReader::with_capacity(
+            (32 * 1024).min(compressed_length),
+            reader.take(u64::try_from(compressed_length).unwrap()),
+        );
+
+        // `Compression = 5` covers both the current LZW variant and the pre-TIFF-6.0
+        // "old-style" one, with no tag to distinguish them. New-style is MSB-first with
+        // the "early change" code-size switch, and its stream begins with the Clear code
+        // (256) -> first byte 0x80. Old-style is LSB-first *without* the early change
+        // (GIF-style increment timing), and begins with 0x00 followed by a byte with bit
+        // 0 set. This is the heuristic libtiff uses to select its compatibility decoder;
+        // on a short/failed peek we default to the modern variant.
+        let old_style = matches!(
+            buffered.fill_buf(),
+            Ok(head) if head.len() >= 2 && head[0] == 0x00 && head[1] & 0x01 != 0
+        );
+
+        let configuration = if old_style {
+            weezl::decode::Configuration::new(weezl::BitOrder::Lsb, 8)
+        } else {
             weezl::decode::Configuration::with_tiff_size_switch(weezl::BitOrder::Msb, 8)
-                .with_yield_on_full_buffer(true);
+        }
+        .with_yield_on_full_buffer(true);
+
         Self {
-            reader: BufReader::with_capacity(
+            reader: buffered,
-                (32 * 1024).min(compressed_length),
-                reader.take(u64::try_from(compressed_length).unwrap()),
-            ),
             decoder: configuration.build(),
         }
     }

src/directory.rs

@@ -171,7 +171,7 @@ mod tests {
             dir.get(Tag::Unknown(1))
                 .expect("tag 1 should be present after this chain")
                 .count(),
-            u16::MAX.into()
+            u64::from(u16::MAX)
         );
     }
 

src/tags.rs

@@ -295,7 +295,10 @@ pub enum CompressionMethod(u16) unknown(
 }
 
 tags! {
-pub enum PhotometricInterpretation(u16) {
+pub enum PhotometricInterpretation(u16) unknown(
+    /// A private or extension tag
+    unknown
+) {
     WhiteIsZero = 0,
     BlackIsZero = 1,
     RGB = 2,
@@ -614,26 +617,22 @@ impl ByteOrder {
             return;
         }
 
-        // FIXME: at MSRV 1.89 or higher use `slice::as_chunks_mut`.
         match cls {
             EndianBytes::One => {
                 // No change needed
             }
             EndianBytes::Two => {
-                for chunk in buffer.chunks_exact_mut(2) {
+                for chunk in buffer.as_chunks_mut::<2>().0 {
-                    let chunk: &mut [u8; 2] = chunk.try_into().unwrap();
                     *chunk = u16::from_be_bytes(*chunk).to_le_bytes();
                 }
             }
             EndianBytes::Four => {
-                for chunk in buffer.chunks_exact_mut(4) {
+                for chunk in buffer.as_chunks_mut::<4>().0 {
-                    let chunk: &mut [u8; 4] = chunk.try_into().unwrap();
                     *chunk = u32::from_be_bytes(*chunk).to_le_bytes();
                 }
             }
             EndianBytes::Eight => {
-                for chunk in buffer.chunks_exact_mut(8) {
+                for chunk in buffer.as_chunks_mut::<8>().0 {
-                    let chunk: &mut [u8; 8] = chunk.try_into().unwrap();
                     *chunk = u64::from_be_bytes(*chunk).to_le_bytes();
                 }
             }

tests/decode_images.rs

@@ -1,11 +1,11 @@
 extern crate tiff;
 
 use tiff::decoder::{ifd, Decoder, DecodingSampleBuffer};
-use tiff::tags::{ByteOrder, Type};
+use tiff::tags::{ByteOrder, PhotometricInterpretation, SampleFormat, Type};
 use tiff::ColorType;
 
 use std::fs::File;
-use std::io::{Read, Seek};
+use std::io::{Cursor, Read, Seek};
 use std::path::PathBuf;
 
 const TEST_IMAGE_DIR: &str = "./tests/images/";
@@ -16,7 +16,9 @@ macro_rules! test_image_sum {
         fn $name(file: &str, expected_type: ColorType, expected_sum: $sum_ty) {
             let path = PathBuf::from(TEST_IMAGE_DIR).join(file);
             let img_file = File::open(path).expect("Cannot find test image!");
-            let mut decoder = Decoder::open(img_file).expect("Cannot create decoder");
+            let mut decoder = Decoder::open(img_file)
+                .expect("Cannot create decoder")
+                .with_lenient(true);
 
             decoder.next_image().expect("Cannot read image IFD");
             assert_eq!(decoder.colortype().unwrap(), expected_type);
@@ -473,6 +475,78 @@ fn test_tiled_rect_rgb_u8() {
     test_image_sum_u8("tiled-rect-rgb-u8.tif", ColorType::RGB(8), 62081032);
 }
 
+#[test]
+fn test_tiled_extra_samples_border_u8() {
+    // Regression test for https://github.com/image-rs/image-tiff/issues/400
+    //
+    // A tiled image whose dimensions are not multiples of the tile size, with
+    // an extra sample that is discarded on decode. The horizontal padding of
+    // the right border tiles used to be written past the end of the output
+    // row, spilling into the leftmost columns of the following row. The
+    // fixture's tile padding is filled with 0xEE so any spill is visible.
+    let path = PathBuf::from(TEST_IMAGE_DIR).join("tiled-extra-samples-border-u8.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(), (40, 40));
+    assert_eq!(decoder.colortype().unwrap(), ColorType::RGB(8));
+
+    let DecodingSampleBuffer::U8(data) = decoder.read_image().unwrap() else {
+        panic!("Wrong bit depth")
+    };
+
+    let mut expected = Vec::with_capacity(40 * 40 * 3);
+    for y in 0..40u32 {
+        for x in 0..40u32 {
+            expected.push(((x * 3) % 251) as u8);
+            expected.push(((y * 7) % 251) as u8);
+            expected.push(((x + y) % 251) as 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");
@@ -825,7 +899,7 @@ fn test_predictor_3_gray_f32() {
 }
 
 #[test]
-#[cfg(feature = "zstd")]
+#[cfg(any(feature = "zstd", feature = "zstd-safe-rust"))]
 fn test_zstd_compression() {
     // gdal_translate -co COMPRESS=ZSTD -co ZSTD_LEVEL=20 int16.tif int16_zstd.tif
     test_image_sum_i16("int16_zstd.tif", ColorType::Gray(16), 354396);
@@ -865,22 +939,22 @@ fn test_image_bytes(
 }
 
 fn byte_order_u16(bytes: &mut [u8]) {
-    for chunk in bytes.chunks_exact_mut(2) {
+    for chunk in bytes.as_chunks_mut::<2>().0 {
-        let n = u16::from_ne_bytes(chunk.try_into().unwrap());
+        let n = u16::from_ne_bytes(*chunk);
         chunk.copy_from_slice(&n.to_le_bytes());
     }
 }
 
 fn byte_order_u32(bytes: &mut [u8]) {
-    for chunk in bytes.chunks_exact_mut(4) {
+    for chunk in bytes.as_chunks_mut::<4>().0 {
-        let n = u32::from_ne_bytes(chunk.try_into().unwrap());
+        let n = u32::from_ne_bytes(*chunk);
         chunk.copy_from_slice(&n.to_le_bytes());
     }
 }
 
 fn byte_order_u64(bytes: &mut [u8]) {
-    for chunk in bytes.chunks_exact_mut(8) {
+    for chunk in bytes.as_chunks_mut::<8>().0 {
-        let n = u64::from_ne_bytes(chunk.try_into().unwrap());
+        let n = u64::from_ne_bytes(*chunk);
         chunk.copy_from_slice(&n.to_le_bytes());
     }
 }
@@ -975,7 +1049,7 @@ fn extra_bits_gray() {
 
 #[test]
 fn extra_bits_rgb() {
-    test_image_sum_u8("extra_bits_rgb_8b.tiff", ColorType::RGB(8), 0);
+    test_image_sum_u8("extra_bits_rgb_8b.tiff", ColorType::RGBA(8), 64);
 }
 
 #[test]
@@ -1057,3 +1131,295 @@ fn test_gray_u12_hpredict() {
     // Delta-encoded 12-bit values: [100, 200, 300, 400, 1000, 2000, 3000, 4000]
     test_image_sum_u16("hpredict-1c-12b.tiff", ColorType::Gray(12), 11000);
 }
+
+// ---- Old-style LZW ----
+
+#[test]
+fn test_old_style_lzw() {
+    // Pre-TIFF-6.0 "old-style" LZW: LSB-first bit order with no early-change size
+    // switch. Auto-detected from the stream (first byte 0x00, second byte odd).
+    // Same image as libtiffpic's quad-lzw.tif; the decoded pixels must match.
+    test_image_sum_u8("quad-lzw-compat.tiff", ColorType::RGB(8), 21048924);
+}
+
+// ---- TransparencyMask ----
+
+/// Build a minimal uncompressed 2x2 TIFF in memory, in the requested byte order,
+/// with the given photometric interpretation and the pixel data as a single strip.
+/// `sample_format` is emitted as a SampleFormat tag when `Some`; when `None` the
+/// tag is omitted (the decoder then defaults to unsigned). Pixel bytes must already
+/// be in `byte_order`.
+fn build_raw_tiff(
+    byte_order: ByteOrder,
+    photometric: PhotometricInterpretation,
+    bits_per_sample: u16,
+    samples_per_pixel: u16,
+    sample_format: Option<SampleFormat>,
+    pixel_data: &[u8],
+) -> Vec<u8> {
+    let le = matches!(byte_order, ByteOrder::LittleEndian);
+    let put16 = |buf: &mut Vec<u8>, v: u16| {
+        if le {
+            buf.extend_from_slice(&v.to_le_bytes());
+        } else {
+            buf.extend_from_slice(&v.to_be_bytes());
+        }
+    };
+    let put32 = |buf: &mut Vec<u8>, v: u32| {
+        if le {
+            buf.extend_from_slice(&v.to_le_bytes());
+        } else {
+            buf.extend_from_slice(&v.to_be_bytes());
+        }
+    };
+
+    let width: u16 = 2;
+    let height: u16 = 2;
+    let num_tags: u16 = if sample_format.is_some() { 9 } else { 8 };
+    let ifd_offset: u32 = 8;
+    let ifd_size = 2 + (num_tags as u32) * 12 + 4;
+    let strip_offset = 8 + ifd_size;
+
+    // IFD entries (must be ascending tag order). Tag IDs stay raw for the
+    // ascending-order property; the field type uses the `Type` enum.
+    let mut tags: Vec<(u16, Type, u32)> = vec![
+        (256, Type::SHORT, width as u32),                // ImageWidth
+        (257, Type::SHORT, height as u32),               // ImageLength
+        (258, Type::SHORT, bits_per_sample as u32),      // BitsPerSample
+        (259, Type::SHORT, 1),                           // Compression = None
+        (262, Type::SHORT, photometric.to_u16() as u32), // PhotometricInterpretation
+        (273, Type::LONG, strip_offset),                 // StripOffsets
+        (277, Type::SHORT, samples_per_pixel as u32),    // SamplesPerPixel
+        (279, Type::LONG, pixel_data.len() as u32),      // StripByteCounts
+    ];
+    if let Some(sf) = sample_format {
+        tags.push((339, Type::SHORT, sf.to_u16() as u32)); // SampleFormat (tag 339 > 279)
+    }
+
+    let mut buf = Vec::new();
+    buf.extend_from_slice(if le { b"II" } else { b"MM" });
+    put16(&mut buf, 42);
+    put32(&mut buf, ifd_offset);
+    put16(&mut buf, num_tags);
+
+    for (tag, typ, value) in tags {
+        put16(&mut buf, tag);
+        put16(&mut buf, typ.to_u16());
+        put32(&mut buf, 1); // count
+                            // A SHORT value is left-justified in the 4-byte value field (value in the
+                            // first two bytes, then padding); a LONG fills all four.
+        match typ {
+            Type::SHORT => {
+                put16(&mut buf, value as u16);
+                put16(&mut buf, 0);
+            }
+            _ => put32(&mut buf, value),
+        }
+    }
+
+    put32(&mut buf, 0); // next IFD = 0
+    buf.extend_from_slice(pixel_data);
+    buf
+}
+
+#[test]
+fn test_transparency_mask() {
+    // 2x2 mask: values 0, 255, 128, 64
+    let data = build_raw_tiff(
+        ByteOrder::LittleEndian,
+        PhotometricInterpretation::TransparencyMask,
+        8,
+        1,
+        None,
+        &[0, 255, 128, 64],
+    );
+    let mut decoder = Decoder::open(Cursor::new(&data)).unwrap();
+    decoder.next_image().unwrap();
+
+    assert_eq!(decoder.colortype().unwrap(), ColorType::Gray(8));
+
+    let result = decoder.read_image().unwrap();
+    match result {
+        DecodingSampleBuffer::U8(pixels) => {
+            // TransparencyMask is decoded as grayscale
+            assert_eq!(pixels.len(), 4);
+            assert_eq!(pixels[0], 0);
+            assert_eq!(pixels[1], 255);
+            assert_eq!(pixels[2], 128);
+            assert_eq!(pixels[3], 64);
+        }
+        _ => panic!("Expected U8 buffer"),
+    }
+}
+
+// ---- CIE L*a*b* ----
+
+#[test]
+fn test_cielab_decode() {
+    // 2x2 CIELab image: 3 bytes per pixel (L, a, b)
+    // L=128, a=0 (signed neutral), b=0 (signed neutral)
+    // After re-biasing: a=128 (unsigned neutral), b=128 (unsigned neutral)
+    let pixels: Vec<u8> = vec![
+        128, 0, 0, // pixel 0: L=128, a=0, b=0 (neutral gray)
+        255, 50, 50, // pixel 1: L=255, a=+50, b=+50
+        100, 206, 206, // pixel 2: L=100, a=-50 (as i8), b=-50 (as i8)
+        0, 128, 128, // pixel 3: L=0, a=-128 (as i8), b=-128 (as i8)
+    ];
+
+    let data = build_raw_tiff(
+        ByteOrder::LittleEndian,
+        PhotometricInterpretation::CIELab,
+        8,
+        3,
+        None,
+        &pixels,
+    );
+    let mut decoder = Decoder::open(Cursor::new(&data)).unwrap();
+    decoder.next_image().unwrap();
+
+    assert_eq!(decoder.colortype().unwrap(), ColorType::Lab(8));
+
+    let result = decoder.read_image().unwrap();
+    match result {
+        DecodingSampleBuffer::U8(decoded) => {
+            assert_eq!(decoded.len(), 12); // 4 pixels * 3 channels
+
+            // Pixel 0: L=128, a=0+128=128, b=0+128=128
+            assert_eq!(decoded[0], 128);
+            assert_eq!(decoded[1], 128);
+            assert_eq!(decoded[2], 128);
+
+            // Pixel 1: L=255, a=50+128=178, b=50+128=178
+            assert_eq!(decoded[3], 255);
+            assert_eq!(decoded[4], 178);
+            assert_eq!(decoded[5], 178);
+
+            // Pixel 2: L=100, a=206+128=78 (wrapping), b=206+128=78
+            assert_eq!(decoded[6], 100);
+            assert_eq!(decoded[7], 78);
+            assert_eq!(decoded[8], 78);
+
+            // Pixel 3: L=0, a=128+128=0 (wrapping), b=128+128=0
+            assert_eq!(decoded[9], 0);
+            assert_eq!(decoded[10], 0);
+            assert_eq!(decoded[11], 0);
+        }
+        _ => panic!("Expected U8 buffer"),
+    }
+}
+
+#[test]
+fn test_cielab_decode_16() {
+    // 2x2 16-bit CIELab image: 3 u16 samples per pixel (L, a, b), a/b signed.
+    // Re-biasing maps signed a/b to unsigned by adding 0x8000 (wrapping):
+    //   0 -> 32768, +1000 -> 33768, -1000 -> 31768, -32768 -> 0, +32767 -> 65535.
+    let samples: [u16; 12] = [
+        32768, 0, 0, // pixel 0: L, a=0, b=0 (neutral)
+        65535, 1000, 1000, // pixel 1: a=+1000, b=+1000
+        10000, 64536, 64536, // pixel 2: a=-1000, b=-1000 (as u16)
+        0, 32768, 32767, // pixel 3: a=-32768, b=+32767 (as u16)
+    ];
+    let mut pixels = Vec::new();
+    for s in samples {
+        pixels.extend_from_slice(&s.to_le_bytes());
+    }
+
+    let data = build_raw_tiff(
+        ByteOrder::LittleEndian,
+        PhotometricInterpretation::CIELab,
+        16,
+        3,
+        None,
+        &pixels,
+    );
+    let mut decoder = Decoder::open(Cursor::new(&data)).unwrap();
+    decoder.next_image().unwrap();
+
+    assert_eq!(decoder.colortype().unwrap(), ColorType::Lab(16));
+
+    let result = decoder.read_image().unwrap();
+    match result {
+        DecodingSampleBuffer::U16(decoded) => {
+            assert_eq!(decoded.len(), 12); // 4 pixels * 3 channels
+
+            // L unchanged; a/b re-biased by +0x8000 (wrapping).
+            let expected: [u16; 12] = [
+                32768, 32768, 32768, // pixel 0
+                65535, 33768, 33768, // pixel 1
+                10000, 31768, 31768, // pixel 2
+                0, 0, 65535, // pixel 3
+            ];
+            assert_eq!(decoded, expected);
+        }
+        _ => panic!("Expected U16 buffer"),
+    }
+}
+
+#[test]
+fn test_cielab_decode_16_big_endian() {
+    // Same image and expected output as `test_cielab_decode_16`, but stored as a
+    // big-endian ("MM") TIFF. 16-bit is the case where byte order matters: the
+    // decoder must swap to native before the a/b re-bias, so the result is
+    // identical to the little-endian case.
+    let samples: [u16; 12] = [
+        32768, 0, 0, // pixel 0
+        65535, 1000, 1000, // pixel 1
+        10000, 64536, 64536, // pixel 2
+        0, 32768, 32767, // pixel 3
+    ];
+    let mut pixels = Vec::new();
+    for s in samples {
+        pixels.extend_from_slice(&s.to_be_bytes());
+    }
+
+    let data = build_raw_tiff(
+        ByteOrder::BigEndian,
+        PhotometricInterpretation::CIELab,
+        16,
+        3,
+        None,
+        &pixels,
+    );
+    let mut decoder = Decoder::open(Cursor::new(&data)).unwrap();
+    decoder.next_image().unwrap();
+
+    assert_eq!(decoder.colortype().unwrap(), ColorType::Lab(16));
+
+    let result = decoder.read_image().unwrap();
+    match result {
+        DecodingSampleBuffer::U16(decoded) => {
+            let expected: [u16; 12] = [
+                32768, 32768, 32768, // pixel 0
+                65535, 33768, 33768, // pixel 1
+                10000, 31768, 31768, // pixel 2
+                0, 0, 65535, // pixel 3
+            ];
+            assert_eq!(decoded, expected);
+        }
+        _ => panic!("Expected U16 buffer"),
+    }
+}
+
+#[test]
+fn test_cielab_rejects_non_uint_sample_format() {
+    // CIELab treats a/b as signed via the photometric interpretation and requires
+    // SampleFormat::Uint (matching the ICCLab arm). A file declaring Int must be
+    // rejected rather than silently producing a signed output buffer.
+    let pixels = vec![0u8; 12]; // 2x2, 3 samples, 8-bit
+    let data = build_raw_tiff(
+        ByteOrder::LittleEndian,
+        PhotometricInterpretation::CIELab,
+        8,
+        3,
+        Some(SampleFormat::Int),
+        &pixels,
+    );
+
+    let mut decoder = Decoder::open(Cursor::new(&data)).unwrap();
+    // Rejection may surface at either next_image() or colortype().
+    let rejected = decoder.next_image().is_err() || decoder.colortype().is_err();
+    assert!(
+        rejected,
+        "CIELab with SampleFormat=Int must be rejected, not decoded"
+    );
+}

tests/decode_libtiffpic.rs

@@ -190,7 +190,7 @@ const FILES: &[(&str, Option<u32>)] = &[
     ("tests/libtiffpic/oxford.tif", Some(0x355d2e3e)),
     ("tests/libtiffpic/pc260001.tif", Some(0xdb56b753)),
     ("tests/libtiffpic/quad-jpeg.tif", Some(0xcba22475)),
-    ("tests/libtiffpic/quad-lzw.tif", Some(0)), // invalid LZW stream
+    ("tests/libtiffpic/quad-lzw.tif", Some(0x6055f9ee)), // old-style (LSB) LZW
     ("tests/libtiffpic/quad-tile.tif", Some(0x6055f9ee)),
     ("tests/libtiffpic/README", None),
     ("tests/libtiffpic/smallliz.tif", Some(0)), // unsupported YCbCr chroma subsampling

tests/predict.rs

@@ -233,3 +233,167 @@ fn test_rgb_u64_predict_roundtrip() {
 fn test_ycbcr_u8_predict_roundtrip() {
     test_u8_predict_roundtrip::<colortype::YCbCr8>("tiled-jpeg-ycbcr.tif", ColorType::YCbCr(8));
 }
+
+// ---------------------------------------------------------------------------
+// Extended bit depths (9-15 promoted to u16, 17-31 promoted to u32).
+//
+// A horizontal-predicted n-bit sample stores its delta in exactly n bits,
+// i.e. modulo 2^n, so reconstruction must also be modulo 2^n. The decoder
+// accumulates in the promoted storage width and reduces back to n bits;
+// these tests pin that reduction down with exact pixel values, including
+// deltas that wrap modulo 2^n. The encoder does not support extended
+// depths, so the TIFFs are hand-built.
+// ---------------------------------------------------------------------------
+
+/// Hand-build a minimal little-endian, single-strip, uncompressed grayscale
+/// TIFF with `Predictor::Horizontal` and the given (possibly non-standard)
+/// bit depth. `pixels` are the intended sample values; they are converted to
+/// horizontal differences modulo `2^bits` and bit-packed MSB-first with each
+/// row padded to a byte boundary — the only representation an n-bit field
+/// can hold.
+fn build_gray_hpredict_tiff(
+    width: u32,
+    height: u32,
+    bits: u8,
+    photometric: u16,
+    pixels: &[u32],
+) -> Vec<u8> {
+    let max = ((1u64 << bits) - 1) as u32;
+    let row_samples = width as usize;
+    assert_eq!(pixels.len(), row_samples * height as usize);
+    assert!(pixels.iter().all(|&v| v <= max));
+
+    // Per-row horizontal differencing modulo 2^bits.
+    let mut deltas = Vec::with_capacity(pixels.len());
+    for row in pixels.chunks(row_samples) {
+        for (i, &v) in row.iter().enumerate() {
+            deltas.push(if i == 0 {
+                v
+            } else {
+                v.wrapping_sub(row[i - 1]) & max
+            });
+        }
+    }
+
+    // Bit-pack MSB-first, each row padded to a byte boundary.
+    let row_bytes = (row_samples * bits as usize).div_ceil(8);
+    let mut data = vec![0u8; row_bytes * height as usize];
+    for (r, row) in deltas.chunks(row_samples).enumerate() {
+        for (i, &d) in row.iter().enumerate() {
+            let start = r * row_bytes * 8 + i * bits as usize;
+            for (off, b) in (start..).zip((0..bits).rev()) {
+                if (d >> b) & 1 == 1 {
+                    data[off / 8] |= 0x80 >> (off % 8);
+                }
+            }
+        }
+    }
+
+    // Classic little-endian TIFF: header, strip data, then a single IFD.
+    let mut out = Vec::new();
+    out.extend_from_slice(b"II");
+    out.extend_from_slice(&42u16.to_le_bytes());
+    let data_offset = 8u32;
+    let ifd_offset = data_offset + data.len() as u32;
+    out.extend_from_slice(&ifd_offset.to_le_bytes());
+    out.extend_from_slice(&data);
+
+    const SHORT: u16 = 3;
+    const LONG: u16 = 4;
+    let entries: &[(u16, u16, u32)] = &[
+        (256, LONG, width),                   // ImageWidth
+        (257, LONG, height),                  // ImageLength
+        (258, SHORT, u32::from(bits)),        // BitsPerSample
+        (259, SHORT, 1),                      // Compression: none
+        (262, SHORT, u32::from(photometric)), // PhotometricInterpretation
+        (273, LONG, data_offset),             // StripOffsets
+        (277, SHORT, 1),                      // SamplesPerPixel
+        (278, LONG, height),                  // RowsPerStrip
+        (279, LONG, data.len() as u32),       // StripByteCounts
+        (317, SHORT, 2),                      // Predictor: horizontal
+        (339, SHORT, 1),                      // SampleFormat: unsigned integer
+    ];
+    out.extend_from_slice(&(entries.len() as u16).to_le_bytes());
+    for &(tag, ty, value) in entries {
+        out.extend_from_slice(&tag.to_le_bytes());
+        out.extend_from_slice(&ty.to_le_bytes());
+        out.extend_from_slice(&1u32.to_le_bytes());
+        // A count-1 SHORT payload occupies the low bytes of the value field.
+        out.extend_from_slice(&value.to_le_bytes());
+    }
+    out.extend_from_slice(&0u32.to_le_bytes()); // no next IFD
+    out
+}
+
+fn decode_gray_u16(tiff: Vec<u8>, bits: u8) -> Vec<u16> {
+    let mut decoder = Decoder::open(Cursor::new(tiff)).expect("Cannot create decoder");
+    decoder.next_image().unwrap();
+    assert_eq!(decoder.colortype().unwrap(), ColorType::Gray(bits));
+    match decoder.read_image().unwrap() {
+        DecodingSampleBuffer::U16(res) => res,
+        _ => panic!("Wrong data type"),
+    }
+}
+
+fn decode_gray_u32(tiff: Vec<u8>, bits: u8) -> Vec<u32> {
+    let mut decoder = Decoder::open(Cursor::new(tiff)).expect("Cannot create decoder");
+    decoder.next_image().unwrap();
+    assert_eq!(decoder.colortype().unwrap(), ColorType::Gray(bits));
+    match decoder.read_image().unwrap() {
+        DecodingSampleBuffer::U32(res) => res,
+        _ => panic!("Wrong data type"),
+    }
+}
+
+#[test]
+fn test_gray12_hpredict_wraparound_exact() {
+    // Pixel row [4095, 0, 1] encodes as deltas [4095, 1, 1] (mod 2^12).
+    // u16 accumulation yields [4095, 4096, 4097]; reduction modulo 2^12
+    // must restore [4095, 0, 1]. Saturating instead would corrupt the two
+    // wrapped samples to 4095.
+    let tiff = build_gray_hpredict_tiff(3, 1, 12, 1, &[4095, 0, 1]);
+    assert_eq!(decode_gray_u16(tiff, 12), vec![4095, 0, 1]);
+}
+
+#[test]
+fn test_gray12_hpredict_wraparound_white_is_zero_exact() {
+    // Same stored samples with PhotometricInterpretation = WhiteIsZero:
+    // after the mod-2^12 reduction the decoder inverts as (2^12 - 1) - v.
+    let tiff = build_gray_hpredict_tiff(3, 1, 12, 0, &[4095, 0, 1]);
+    assert_eq!(decode_gray_u16(tiff, 12), vec![0, 4095, 4094]);
+}
+
+#[test]
+fn test_gray20_hpredict_wraparound_exact() {
+    // The same wrap-around shape on the u32 storage path (17-31 bits).
+    let tiff = build_gray_hpredict_tiff(3, 1, 20, 1, &[0xF_FFFF, 0, 1]);
+    assert_eq!(decode_gray_u32(tiff, 20), vec![0xF_FFFF, 0, 1]);
+}
+
+#[test]
+fn test_extended_depth_hpredict_random_roundtrip() {
+    // Deterministic pseudo-random pixels across a spread of extended depths;
+    // encode-then-decode must be the identity for every sample, including
+    // every mod-2^n wrap-around the differencing produces. Three rows verify
+    // that prediction restarts per row.
+    let mut state = 0x243F_6A88_85A3_08D3u64;
+    let mut next = move || {
+        state = state
+            .wrapping_mul(6364136223846793005)
+            .wrapping_add(1442695040888963407);
+        (state >> 33) as u32
+    };
+    for &bits in &[9u8, 11, 12, 15] {
+        let max = (1u32 << bits) - 1;
+        let pixels: Vec<u32> = (0..16 * 3).map(|_| next() & max).collect();
+        let tiff = build_gray_hpredict_tiff(16, 3, bits, 1, &pixels);
+        let expected: Vec<u16> = pixels.iter().map(|&v| v as u16).collect();
+        assert_eq!(decode_gray_u16(tiff, bits), expected, "bits={bits}");
+    }
+    for &bits in &[17u8, 20, 25, 31] {
+        let max = ((1u64 << bits) - 1) as u32;
+        let pixels: Vec<u32> = (0..16 * 3).map(|_| next() & max).collect();
+        let tiff = build_gray_hpredict_tiff(16, 3, bits, 1, &pixels);
+        assert_eq!(decode_gray_u32(tiff, bits), pixels, "bits={bits}");
+    }
+}