wim/image-tiff
1
0 Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Merge pull request #386 from aarshivv/palette-cielab-transparency-lzw

Browse Source 
support palette expansion, CIE L*a*b*, transparency mask, and lzw end…
This commit is contained in:
Aurelia Molzer authored and GitHub committed 2026-07-24 06:14:30 +00:00
2 parents f3f9ff1244 d0c9198016
commit 31919c7bfc
3 files changed
+213 -32
Download Patch File Download Diff File Expand all files Collapse all files

No files matched your search

src/decoder/image.rs
+52 -28
View File
@@ -597,20 +597,25 @@ impl Image {
),
)),
},
// Unsupported due to inherently heterogeneous sample types. This is represented as:
// ```
// struct TiffLab /* Interpretation 8* {
// pub L: u8, // SampleFormat::Uint
// pub a: i8, // SampleFormat::Int
// pub b: i8, // SampleFormat::Int
// }
// ```
PhotometricInterpretation::CIELab => Err(TiffError::UnsupportedError(
// CIE L*a*b* (TIFF6 Section 23, pp 110-115) encodes a/b as signed int8
// (-128..=127) while ICC L*a*b* (photometric=9) uses unsigned samples with
// a +128 bias. For 8-bit we re-bias a/b in post-processing (see
// `cielab_to_icclab`) so callers see the same encoding as ICCLab.
//
// Only 8-bit is accepted here. 16-bit CIELab is a valid format that libtiff
// does decode (`putcontig8bitCIELab16`, selected by `initCIELabConversion`
// in tif_getimage.c line 2216 @ 04884181e8903915038be553bfab404302d98ea0),
// but it uses L=uint16 with a/b=int16 — a mixed layout that `SampleFormat`,
// which applies uniformly to every sample, cannot express. Left as follow-up.
PhotometricInterpretation::CIELab => match self.photometric_samples {
3 if matches!(self.bits_per_sample, 8) => 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) =>
@@ -666,14 +671,16 @@ impl Image {
),
)),
PhotometricInterpretation::RGBPalette => Ok(ColorType::Palette(self.bits_per_sample)),
PhotometricInterpretation::TransparencyMask | PhotometricInterpretation::Unknown(_) => {
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],
),
))
}
)),
}
}
@@ -1046,6 +1053,7 @@ impl Image {
| ColorType::YCbCr(n)
| ColorType::Gray(n)
| ColorType::Palette(n)
| ColorType::Lab(n)
| ColorType::Multiband {
bit_depth: n,
num_samples: _,
@@ -1057,6 +1065,7 @@ impl Image {
| ColorType::YCbCr(n)
| ColorType::Gray(n)
| ColorType::Palette(n)
| ColorType::Lab(n)
| ColorType::Multiband {
bit_depth: n,
num_samples: _,
@@ -1214,9 +1223,12 @@ impl Image {
// the row is exact).
super::mask_samples_to_bit_depth(out_row, tiff_bps, out_bps, self.sample_format);
if photometric_interpretation == PhotometricInterpretation::WhiteIsZero {
super::invert_colors(out_row, color_type, 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.
@@ -1244,9 +1256,12 @@ impl Image {
self.sample_format,
);
if photometric_interpretation == PhotometricInterpretation::WhiteIsZero {
super::invert_colors(tile, color_type, 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.
@@ -1272,9 +1287,12 @@ impl Image {
}
// No masking here: the floating point predictor requires
// IEEEFP samples, which are never depth-promoted.
if photometric_interpretation == PhotometricInterpretation::WhiteIsZero {
super::invert_colors(row, color_type, self.sample_format)?;
}
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.
@@ -1311,9 +1329,12 @@ impl Image {
self.sample_format,
);
if photometric_interpretation == PhotometricInterpretation::WhiteIsZero {
super::invert_colors(row, color_type, 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
@@ -1363,9 +1384,12 @@ impl Image {
self.sample_format,
);
if photometric_interpretation == PhotometricInterpretation::WhiteIsZero {
super::invert_colors(row, color_type, self.sample_format)?;
}
super::post_process_row(
row,
photometric_interpretation,
color_type,
self.sample_format,
)?;
}
}
src/decoder/mod.rs
+36 -2
View File
@@ -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,
ValueBuffer,
ByteOrder, IfdPointer, PhotometricInterpretation, PlanarConfiguration, Predictor, SampleFormat,
Tag, TiffVariant, Type, ValueBuffer,
};
use crate::{
ColorType, Directory, TiffError, TiffFormatError, TiffResult, TiffUnsupportedError, UsageError,
@@ -711,6 +711,40 @@ 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 int8 where 0 is neutral.
/// ICCLab (photometric=9) stores them as uint8 where 128 is neutral.
/// Adding 128 (wrapping) converts between the two representations.
/// See libtiff's `TIFFCIELabToXYZ` for reference (tif_color.c line 45
/// @ 04884181e8903915038be553bfab404302d98ea0).
fn cielab_to_icclab(buf: &mut [u8]) {
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),
_ => {}
}
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();
tests/decode_images.rs
+125 -2
View File
@@ -1,11 +1,11 @@
extern crate tiff;
use tiff::decoder::{ifd, Decoder, DecodingSampleBuffer};
use tiff::tags::{ByteOrder, Type};
use tiff::tags::{ByteOrder, PhotometricInterpretation, 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/";
@@ -1059,3 +1059,126 @@ 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);
}
// ---- TransparencyMask ----
/// Build a minimal uncompressed TIFF in memory with the given photometric interpretation.
/// Returns a 2x2 image with the provided pixel data as a single strip.
fn build_raw_tiff(
photometric: PhotometricInterpretation,
bits_per_sample: u16,
samples_per_pixel: u16,
pixel_data: &[u8],
) -> Vec<u8> {
let width: u16 = 2;
let height: u16 = 2;
let num_tags: u16 = 8;
let ifd_offset: u32 = 8;
let ifd_size = 2 + (num_tags as u32) * 12 + 4;
let strip_offset = 8 + ifd_size;
let mut buf = Vec::new();
buf.extend_from_slice(b"II");
buf.extend_from_slice(&42u16.to_le_bytes());
buf.extend_from_slice(&ifd_offset.to_le_bytes());
buf.extend_from_slice(&num_tags.to_le_bytes());
// IFD entries (must be ascending tag order). Tag IDs stay raw for the
// ascending-order property; the field type uses the `Type` enum.
for &(tag, typ, value) in &[
(256u16, 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
] {
buf.extend_from_slice(&tag.to_le_bytes());
buf.extend_from_slice(&typ.to_u16().to_le_bytes());
buf.extend_from_slice(&1u32.to_le_bytes());
buf.extend_from_slice(&value.to_le_bytes());
}
buf.extend_from_slice(&0u32.to_le_bytes()); // 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(
PhotometricInterpretation::TransparencyMask,
8,
1,
&[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(PhotometricInterpretation::CIELab, 8, 3, &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"),
}
}