Read the ColorMap tag (320) for RGBPalette images and return raw
palette indices as the decoded data with ColorType::Palette(n).
Changes:
- Read and validate ColorMap tag during IFD parsing (3 * 2^bps entries)
- Return ColorType::Palette from colortype() for RGBPalette images
- Accept Palette in expand_chunk validation (standard + sub-byte depths)
- Expose color_map() method on Decoder for palette lookup
- Add tests for 1-bit, 4-bit, 8-bit palette images with checksums
- Add test verifying ColorMap accessibility and structure
The decoder returns raw palette indices; consumers apply the lookup
using the color map returned by Decoder::color_map().
This prepares allowing to iterate over a TIFF file with invalid images
while `Image` maintains invariants. For instance we precalculate the
amount of buffer space and verify that the count of strips makes sense
in the constructor—so we do not have to redo that for every other entry
point.
Replace chunked scratch-buffer approach with direct indexed writes
into the pre-allocated output. Simpler and faster in practice.
Co-Authored-By: Claude <noreply@anthropic.com>
Replace single-byte pushes with chunk-based processing: pre-allocate
zeroed output, shuffle 4 values at a time into a stack buffer, then
copy_from_slice each byte lane into the output.
Co-Authored-By: Claude <noreply@anthropic.com>
Process the difference step in reverse 16-byte chunks, reading both
curr and prev into local arrays before writing. This makes all 16
subtractions independent, enabling autovectorization (confirmed with
SSE2: movdqu + psubb).
Co-Authored-By: Claude <noreply@anthropic.com>
Replace the two near-identical floating-point predictor encoding
functions with a single fp_predict! macro parameterized on the float
type, using core::mem::size_of to derive the byte size.
Co-Authored-By: Claude <noreply@anthropic.com>
Add support for encoding TIFF images with the floating-point predictor,
which improves compression ratios for floating-point image data.
The floating-point predictor works by:
1. Converting floats to big-endian bytes
2. Shuffling bytes so all first bytes are together, all second bytes, etc.
3. Applying byte-level horizontal differencing across the buffer
This complements the existing decoding support for Predictor 3.
Supported types: Gray32Float, Gray64Float, RGB32Float, RGB64Float,
RGBA32Float, RGBA64Float, CMYK32Float, CMYK64Float.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Do we even want to error early here? This isn't exactly fatal to reading
the image it is a only nuisance. It becomes crucial only when we are at
the point of reading all the tiles themselves.
Lilith River