0.22 release series received a few bug fixes and feature releases,
the next major version was being worked on in the background, and comes with
improvements to error handling, and the buffer and loading interfaces. A more
detailed view on the changes is in the following paragraphs.
We’ve redesigned the error representation from the ground up
based on lessons learned from the old error type, which had slowly but steadily
grown over time into an unsightly amalgamation of ideas. The new design still
present an enum at the top-level, but each variant is similar to
std::io::Error which allows attaching decoder specific Error sources and
presents more detailed information.
New decoder interface
ImageDecoder allows reading images into pre-allocated buffers instead of
insisting on returning a
Vec<u8>. The color type indicated by the decoder
informs the consumer how the output bytes have to be interpreted. This has the
secondary effect of allowing reading of images directly into buffers of other
samples types, such as a
[u16]. Note that this required no additional
image’s part as the
bytemuck crate encapsulates the casts. We
chose the crate due to its stability promise and focus on a small, and easily reviewed
core of operations.
Updates to the crates behind
image have ensure that no more dependencies on
outdated versions of the proc-macro
syn crate are present and to minimize
some dependencies overall. It was not possible to easily do this previously as
the crate publicly exposed a few types of the underlying decoder crates. This
meant that they couldn’t be upgraded beyond the SemVer compatible versions
without a SemVer bump of
image. Due to the friction involved in propagating
such updates through the ecosystem, the goal was to minimize the number of
breaking changes in the future. We’ve now ensured that dependencies which we
want to evolve independently are properly hidden.
Towards better color space handling
Let’s be frank, color spaces are far from a solved problem in
image and it is
often necessary to reach for the lower-level decoder libraries such as
directly. However, this release should bring us a step closer. We’ve greatly
ColorType enum and split parts into one type that represents
color layout in
ImageBuffer type and one for original layouts from the
decoder. Critically, we’ve also made both non-exhaustive so that new variants
may be added without a major release.
Call for participation
Do You have an idea for color space handling in decoders? Or can provide educational resources on the topic specifically to Rust programmers? This will be the main project for the next major version and we’d like to hear from You and collaborate on the issue to find an amicable solution.
Also, as alluded to above, there is some remaining work behind-the-scenes for propagating the error improvements across image formats. You can help by claiming and fixing a format in tracking issue #1134.