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chore: drop palette and LZW, add tests for CIELab and TransparencyMask

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aarshivv committed 2026-04-11 20:48:40 +05:30
1 parent dfd0191403
commit 30e04f3381
4 files changed
+137 -118
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src/decoder/image.rs
+13 -4
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@@ -591,10 +591,17 @@ impl Image {
),
)),
},
// CIE L*a*b* uses signed a/b channels whereas ICC L*a*b* uses unsigned
// with a +128 bias. For 8-bit, the byte-level data is the same size — we
// re-bias a/b from signed to unsigned during expand_chunk so that callers
// can treat CIELab identically to ICCLab (both return Lab(8)).
// CIE L*a*b* (TIFF6 Section 23, pp 110-115) encodes a/b as signed int8
// (-128..127) while ICC L*a*b* uses unsigned with +128 bias. For 8-bit we
// re-bias a/b during expand_chunk so callers see the same encoding as ICCLab.
//
// libtiff takes the same approach — accepts only 8-bit CIELab and converts
// without checking SampleFormat:
// https://libtiff.gitlab.io/libtiff/functions/TIFFcolor.html
// https://gitlab.com/libtiff/libtiff/-/blob/master/libtiff/tif_getimage.c
//
// 16-bit CIELab would need L=uint16 + a/b=int16, which SampleFormat can't
// express (it applies uniformly). libtiff doesn't support it either.
PhotometricInterpretation::CIELab => match self.photometric_samples {
3 if matches!(self.bits_per_sample, 8) => Ok(ColorType::Lab(self.bits_per_sample)),
_ => Err(TiffError::UnsupportedError(
@@ -1033,6 +1040,7 @@ impl Image {
| ColorType::YCbCr(n)
| ColorType::Gray(n)
| ColorType::Palette(n)
| ColorType::Lab(n)
| ColorType::Multiband {
bit_depth: n,
num_samples: _,
@@ -1044,6 +1052,7 @@ impl Image {
| ColorType::YCbCr(n)
| ColorType::Gray(n)
| ColorType::Palette(n)
| ColorType::Lab(n)
| ColorType::Multiband {
bit_depth: n,
num_samples: _,
src/decoder/mod.rs
+8 -107
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@@ -3,8 +3,8 @@ use std::io::{self, Read, Seek};
use std::num::NonZeroUsize;
use crate::tags::{
ByteOrder, IfdPointer, PhotometricInterpretation, PlanarConfiguration, Predictor, SampleFormat,
Tag, TiffVariant, Type, ValueBuffer,
ByteOrder, IfdPointer, PlanarConfiguration, Predictor, SampleFormat, Tag, TiffVariant, Type,
ValueBuffer,
};
use crate::{
ColorType, Directory, TiffError, TiffFormatError, TiffResult, TiffUnsupportedError, UsageError,
@@ -659,97 +659,20 @@ fn invert_colors(
Ok(())
}
/// Convert CIE L*a*b* (photometric=8) byte encoding to ICC L*a*b* (photometric=9).
/// Re-bias CIE L*a*b* a/b channels from signed to unsigned encoding.
///
/// CIELab stores a/b as signed int8 (-128..127). ICCLab stores them as uint8 with
/// a +128 bias (0..255, where 128 = neutral). The L channel is identical in both.
/// This re-biases a/b so that downstream code can treat CIELab the same as ICCLab.
/// 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:
/// https://gitlab.com/libtiff/libtiff/-/blob/master/libtiff/tif_color.c
fn cielab_to_icclab(buf: &mut [u8]) {
for pixel in buf.chunks_exact_mut(3) {
// L stays as-is; a and b get +128 (wrapping handles the two's complement)
pixel[1] = pixel[1].wrapping_add(128);
pixel[2] = pixel[2].wrapping_add(128);
}
}
/// Expand palette indices in `buf` to RGB using the color map.
///
/// `buf` contains packed palette indices at `bits_per_sample` depth. The color map
/// has layout `[R0..Rn, G0..Gn, B0..Bn]` with 16-bit entries. Each index is looked
/// up and replaced with an 8-bit RGB triplet (high byte of the 16-bit color map value).
///
/// Returns a new `Vec<u8>` with 3 bytes (R,G,B) per pixel. Sub-byte indices (1, 2, 4-bit)
/// are unpacked from the row-aligned packed representation.
fn expand_palette(
buf: &[u8],
color_map: &[u16],
width: u32,
height: u32,
bits_per_sample: u8,
) -> Vec<u8> {
let num_colors = 1usize << bits_per_sample;
let pixels = (width as usize) * (height as usize);
let mut rgb = Vec::with_capacity(pixels * 3);
if bits_per_sample == 8 {
for &idx in buf.iter().take(pixels) {
let i = idx as usize;
if i < num_colors {
rgb.push((color_map[i] >> 8) as u8);
rgb.push((color_map[num_colors + i] >> 8) as u8);
rgb.push((color_map[2 * num_colors + i] >> 8) as u8);
} else {
rgb.extend_from_slice(&[0, 0, 0]);
}
}
} else if bits_per_sample == 16 {
for chunk in buf.chunks(2).take(pixels) {
if chunk.len() < 2 {
break;
}
let i = u16::from_ne_bytes([chunk[0], chunk[1]]) as usize;
if i < num_colors {
rgb.push((color_map[i] >> 8) as u8);
rgb.push((color_map[num_colors + i] >> 8) as u8);
rgb.push((color_map[2 * num_colors + i] >> 8) as u8);
} else {
rgb.extend_from_slice(&[0, 0, 0]);
}
}
} else {
// Sub-byte (1, 2, 4-bit): rows are byte-aligned with padding bits at end
let samples_per_byte = 8 / bits_per_sample as usize;
let bytes_per_row = ((width as usize) * bits_per_sample as usize).div_ceil(8);
for row in 0..height as usize {
let row_start = row * bytes_per_row;
let row_end = (row_start + bytes_per_row).min(buf.len());
let mut col = 0u32;
for &byte in &buf[row_start..row_end] {
for bit_idx in (0..samples_per_byte).rev() {
if col >= width {
break;
}
let shift = bit_idx as u8 * bits_per_sample;
let mask = ((1u16 << bits_per_sample) - 1) as u8;
let i = ((byte >> shift) & mask) as usize;
if i < num_colors {
rgb.push((color_map[i] >> 8) as u8);
rgb.push((color_map[num_colors + i] >> 8) as u8);
rgb.push((color_map[2 * num_colors + i] >> 8) as u8);
} else {
rgb.extend_from_slice(&[0, 0, 0]);
}
col += 1;
}
}
}
}
rgb
}
/// 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();
@@ -1476,28 +1399,6 @@ impl<R: Read + Seek> Decoder<R> {
self.image.as_ref().and_then(|img| img.color_map.as_deref())
}
/// Expand a palette-indexed image buffer to 8-bit RGB.
///
/// Takes the raw decoded buffer (palette indices at `bits_per_sample` depth) and
/// returns a new buffer with 3 bytes per pixel (R, G, B), using the image's color map.
/// Sub-byte indices (1, 2, 4-bit) are unpacked from the row-aligned representation.
///
/// Returns `None` if the current image is not a palette image or has no color map.
pub fn expand_palette_to_rgb(&self, indices: &[u8]) -> Option<Vec<u8>> {
let image = self.image.as_ref()?;
let color_map = image.color_map.as_ref()?;
if image.photometric_interpretation != PhotometricInterpretation::RGBPalette {
return None;
}
Some(expand_palette(
indices,
color_map,
image.width,
image.height,
image.bits_per_sample,
))
}
/// Read a tag-entry map from a known offset.
///
/// A TIFF [`Directory`], aka. image file directory aka. IFD, refers to a map from
src/decoder/stream.rs
-6
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@@ -170,12 +170,6 @@ impl<R: Read> Read for LZWReader<R> {
}
}
Ok(weezl::LzwStatus::NoProgress) => {
// Some encoders omit the LZW end-of-information code. If we
// already produced output this call, treat it as a clean EOF
// rather than an error — the decoded data up to this point is valid.
if result.consumed_out > 0 {
return Ok(result.consumed_out);
}
return Err(io::Error::new(
io::ErrorKind::UnexpectedEof,
"no lzw end code found",
tests/decode_images.rs
+116 -1
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@@ -5,7 +5,7 @@ use tiff::tags::{ByteOrder, 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/";
@@ -1057,3 +1057,118 @@ 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: u16,
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)
for &(tag, typ, value) in &[
(256u16, 3u16, width as u32), // ImageWidth
(257, 3, height as u32), // ImageLength
(258, 3, bits_per_sample as u32), // BitsPerSample
(259, 3, 1), // Compression = None
(262, 3, photometric as u32), // PhotometricInterpretation
(273, 4, strip_offset), // StripOffsets
(277, 3, samples_per_pixel as u32), // SamplesPerPixel
(279, 4, pixel_data.len() as u32), // StripByteCounts
] {
buf.extend_from_slice(&tag.to_le_bytes());
buf.extend_from_slice(&typ.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(4, 8, 1, &[0, 255, 128, 64]);
let mut decoder = Decoder::new(Cursor::new(&data)).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(8, 8, 3, &pixels);
let mut decoder = Decoder::new(Cursor::new(&data)).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"),
}
}