These samples are normal bits in the encoded (e.g. compressed) stream of
each tile or row of the image. However, when considering the photometric
interpretation of an image these samples should be discarded. They are
only relevant for multiband.
For the most part we previously rejected these images due to a mismatch
between sample count and the color as indicated by the interpretation.
Only, for alpha we never really verified if the extra channel is indeed
alpha or something unrelated. We don't have a perfect solution as
GeoTiff motivates us having a MultiBand pseudo-color output
configuration that has no related photometric interpretation and borrows
the usual gray tone instead. We can only really distinguish this from a
gray-alpha image through looking at the values of the ExtraSamples
vector. Then again we do not yet support GrayAlpha anyways.
As a simplification for the discarding process we only support full-byte
extra samples and require all samples to be the same bit-depth, not only
those which we return. This is blessed by Tiff's recommendations for
baseline decoding as well as libtiff.
It was left in but marked as deprecated as part of #132 to avoid breaking API changes.
However, #130 is going to mark a 0.7.0 release, so we can remove it altogether for simplicity.
- Switch to streaming decompression via `flate2`. Aside from performance improvements and lower RAM consumption, this fixes a bug where `max_uncompressed_length` was precalculated for a single tile but then used as a hard limit on the whole data, failing to decompress any tiled images.
- Deprecate `InflateError` - this was used for wrapping `miniz_oxide` raw status, but `flate2` already reports them as `io::Error` instead. This makes errors from both Lzw and Deflate modes more consistent - they're all now just `io::Error`.
- Add support for new `Deflate` tag in addition to `OldDeflate` - format-wise it's same Zlib, and on practice decodes successfully with the same underlying code.
- Slightly simplify partial reads from the `Reader` by using the `std::io::copy` helper instead of doing it manually.
Fixes#131.
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.
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.
A. Molzer