Replace chunked scratch-buffer approach with direct indexed writes
into the pre-allocated output. Simpler and faster in practice.
Co-Authored-By: Claude <noreply@anthropic.com>
Replace single-byte pushes with chunk-based processing: pre-allocate
zeroed output, shuffle 4 values at a time into a stack buffer, then
copy_from_slice each byte lane into the output.
Co-Authored-By: Claude <noreply@anthropic.com>
Process the difference step in reverse 16-byte chunks, reading both
curr and prev into local arrays before writing. This makes all 16
subtractions independent, enabling autovectorization (confirmed with
SSE2: movdqu + psubb).
Co-Authored-By: Claude <noreply@anthropic.com>
Replace the two near-identical floating-point predictor encoding
functions with a single fp_predict! macro parameterized on the float
type, using core::mem::size_of to derive the byte size.
Co-Authored-By: Claude <noreply@anthropic.com>
Add support for encoding TIFF images with the floating-point predictor,
which improves compression ratios for floating-point image data.
The floating-point predictor works by:
1. Converting floats to big-endian bytes
2. Shuffling bytes so all first bytes are together, all second bytes, etc.
3. Applying byte-level horizontal differencing across the buffer
This complements the existing decoding support for Predictor 3.
Supported types: Gray32Float, Gray64Float, RGB32Float, RGB64Float,
RGBA32Float, RGBA64Float, CMYK32Float, CMYK64Float.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
This complements the entry API of the encoder with the byte slice based
method. Note we don't provide it for writing raw data, here a
`std::io::Write` would be more appropriate and we should not attempt to
make it `write_all`, nor compress. You'd get all the benefits of the
other API through `[u8]: TiffValue` since that interface is otherwise
type agnostic and `u8` specifically is endian agnostic.
We have not released this yet, let's align these names before it is too
late. The decoder adopted the `_buf` suffix and I find it more
convincing than the more generic `_value` (that also confusingly shares
it with `TiffValue`).
Implement the encoder's `TiffValue` trait for the tags commonly defined
and represented as separate types in our own code. We don't tie the
tag for an entry of these to the value type (yet). This lets us keep the
trait exactly as-is and we avoid unnecessary churn. We can always add a
separate trait on top.
We have a fundamental choice here: We could add more proxy
implementations for `Vec` and `Box` to follow `&'_ T`, for some types
that indirections is clear. Vec and arrays are also both very natural
ways of expressing a repeated value. However, passing an allocated value
to the interface forces us to drop it inside. We might be able to
utilize the allocation for an in-place byteswap in a future increment
but not with the current design.
So, overall, I think that inherently `Drop`-y types should be avoided in
these implementations. Instead, we can use the amazing diagnostic tools
in the compiler to just help the users navigate the type system. We can
still provide the impl for arrays.
For context, see: https://users.rust-lang.org/t/what-type-is-u16/137395
Now they see:
|
38 | .write_tag(tiff::tags::Tag::GeoKeyDirectoryTag, &geokey);
| ^^^^^^ the trait `TiffValue` is not implemented for `&Vec<u16>`
|
= note: the trait is implemented for primitive types (`u8`, `i16`, `f32`, etc.)
= note: the trait is implemented for shared references to values
= note: the trait is implemented for slices, pass them by reference (e.g. `&[u8]`)
= note: the trait is implemented for arrays if it is implemented for a slice
= note: values in a `Vec` or `Box` should be dereferenced, e.g. `&vec[..]`
= help: the following other types implement trait `TiffValue`:
Previously the compiler would both strip the `&` in its first message
(due to our forwarding impl) and not list any way of getting a
reference-to-slice.
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.
A. Molzer