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Add a comment about TIFF/EP vs libtiff

This commit is contained in:
Přemysl Eric Janouch 2021-12-12 00:21:04 +01:00
parent 121c63e35e
commit 2147dba8c4
Signed by: p
GPG Key ID: A0420B94F92B9493
1 changed files with 20 additions and 0 deletions
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fastiv-io.c
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@ -1492,6 +1492,26 @@ open_libtiff(const gchar *data, gsize len, const gchar *path, GError **error)
if (!tiff)
goto fail;
// In Nikon NEF files, IFD0 is a tiny uncompressed thumbnail with SubIFDs--
// two of them JPEGs, the remaining one is raw. libtiff cannot read either
// of those better versions.
//
// TODO(p): If NewSubfileType is ReducedImage, and it has SubIFDs compressed
// as old JPEG (6), decode JPEGInterchangeFormat/JPEGInterchangeFormatLength
// with libjpeg-turbo and insert them as the starting pages.
//
// This is not possible with libtiff directly, because TIFFSetSubDirectory()
// requires an ImageLength tag that's missing, and TIFFReadCustomDirectory()
// takes a privately defined struct that cannot be omitted.
uint32_t subtype = 0;
uint16_t subifd_count = 0;
const uint64_t *subifd_offsets = NULL;
if (TIFFGetField(tiff, TIFFTAG_SUBFILETYPE, &subtype) &&
(subtype & FILETYPE_REDUCEDIMAGE) &&
TIFFGetField(tiff, TIFFTAG_SUBIFD, &subifd_count, &subifd_offsets) &&
subifd_count > 0 && subifd_offsets) {
}
do {
// We inform about unsupported directories, but do not fail on them.
GError *err = NULL;