lightcraft/crates/tiff/README.md

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.
• 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; 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.