Since it is known that libtiff produces other sample format variants we
do not support, represent these as variants. This also allows returning
the sample formats in errors so that composition of formats and known
and unknown formats are clearly reported.
The byte count for strips is the compressed length. The compressed
length may be larger than the uncompressed length, especially with poor
compression choices (multi-byte samples with packbits) or small images.
Convert most unchecked size/index `as` casts to checked casts with
`TryFrom`, included another top-level error variant.
This has several motivations:
- Making the library as robust as possible, including to platform
differences.
- Unchecked casts are susceptible to breakage during refactorings.
- Preparing for BigTIFF support, which will require the introduction of
generics and associated types for some parts of the de/encoders.
Unchecked primitive casts cannot be bound, while TryFrom can, and
overflowing conversions become more likely.
- Remaining u16 casts may be prone in failure in existing practice and
not just in theory during future changes.
Tag representations are not decoder- or encoder-specific, so should live
in their own module accessible to both for reuse. The decoder::ifd
module remains since this module is mainly dedicated to decoding the
IFD.
Resolve several TODOs where tag values were cast from u32 without checks
by providing generic methods that error when the value fails casting to
the desired type. In addition to being more correct, this simplifies and
shortens decoding logic.
Remove `find_tag_u32` and `find_tag_u32_vec` as they are now redundant
and a GitHub code search found no usages outside copies of
`image-tiff`.
Make the behavior of RGB and RGBA like Gray in returning ColorTypes for
all homogeneous bit depths, even if those depths are not 8, 16, 32 or
64. Note that this does not change which color types can actually be
decoded.
Note that this adds the LONG8 data type from BigTIFF because of bounds
requiring TiffValue. However, this datatype should not actually be
written to tags.
This makes it cheaper to introduce new features that might require
amending the list of variants by allowing us to introduce previously
uncovered causes or more specialized representations.
It encapsulates the implementation detail of holding a miniz_oxide
status within. The derived traits are not too extensive for other
possible representations as well.
Avoids leaking the dependency on `miniz_oxide` into the public interface
by making a constructor taking a status argument crate internal. It
would otherwise not be possible to replace the deflate decoder without
breaking that interface.
The discriminant of some enum types can be retrieved with the `as`
operator and in C style enums it is also possible to set a specific
discriminant. However, that may silently change—breaking the value
written to the file. It is better to use that technique mostly for ffi
purposes.
Spencer Nelson