lightcraft/crates/tiff

lightcraft-tiff (L0)

TIFF / IFD reader and writer. Used by lightcraft-raw (DNG, CR2, NEF, ARW…), lightcraft-meta (Exif) and later the TIFF/DNG exporters.

Features

• Classic TIFF and BigTIFF, little- and big-endian (II/MM). Also accepts the TIFF-like magic numbers of some raw formats (ORF IIRO/IIRS, RW2 IIU) when ParseOptions::accept_raw_magic is set (default).
• Every field type: BYTE, ASCII, SHORT, LONG, RATIONAL, SBYTE, UNDEFINED, SSHORT, SLONG, SRATIONAL, FLOAT, DOUBLE, IFD, LONG8, SLONG8, IFD8.
• IFD chain + SubIFDs (330) + Exif (34665) / GPS (34853) / Interoperability (40965) pointer IFDs, resolved into a tree (Ifd::sub_ifds, exif, gps, interop). Entry::offset records the absolute position of each value (needed for maker notes and embedded blobs).
• parse_ifd_at(data, offset, order, base, bigtiff, opts) parses an IFD whose offsets are relative to an arbitrary base; makernote::parse_makernote knows the header / byte-order / offset-base conventions of Canon, Nikon (types 1 and 3), Sony, Fujifilm, Olympus (old and new), Panasonic and Pentax notes.
• image::ImageInfo — width/height, bits, samples, compression, photometric, planar config, predictor, sample format and the strip or tile chunk list (chunks(), chunk_bytes()); missing byte counts are inferred.
• directory_entries, entry_span, ParseOptions::budget_for and decode_value are the reader's own rules (directory layout and entry limit, which entries it reads, its value budget, value decoding), for callers that must select entries exactly as parse_ifd_at would without decoding the whole directory (lightcraft-raw's Sony SR2Private lookup).
• TiffWriter writes IFD chains with strips or tiles, SubIFDs and pointer IFDs, in either byte order, classic or BigTIFF; writer::rational / srational approximate floats as rationals.

Robustness

The reader never panics on malformed input (proptests feed random and mutated files): offsets are bounds-checked; out-of-range or unknown-type entries are skipped; IFD loops are detected; IFD count, nesting depth and entries per IFD are limited; at most 65,536 directory entry slots (ParseOptions::max_entries_total) are accepted across the main IFD chain and all child IFDs, even when tables overlap at distinct offsets, and an IFD past that bound ends the chain or is skipped like any other bad IFD after the first; a next-IFD pointer is followed only when every declared entry was read, with the counts compared as 64-bit numbers (a BigTIFF declaring 4,294,967,297 entries but holding one can't pass for a whole directory on a 32-bit target); the total bytes of decoded values are capped at 8 × input + 1 MiB so a file cannot make us allocate far more than its own size.

Sources

Public specifications only: TIFF 6.0 (Adobe, 1992), the TIFF 6.0 supplements (IFD type, SubIFDs), the BigTIFF format description (AWare Systems), Adobe DNG Specification 1.7 (tag numbers), CIPA DC-008 Exif 2.32, and the ExifTool tag-name documentation (maker-note header conventions, prose only). No third-party code was consulted.