We, the image-rs group, are glad to announce the release of a new version of the central image library. This is especially noteworthy since it resolves some long standing interface issues, removes some old deprecated items and marks some new ones, and finally contains a plethora of improvement to the set of image decoders and encoders.

Notable changes

We have updated the compiler requirements to Rust 1.34.2 (from 1.24.1), together with the Debian stable release Buster. This gives us the freedom to choose the Rust edition, many std library improvements and basic const fn¹. We will try to keep versions stable for as long as possible but may bump the required version in a SemVer breaking release. Overall, you should view this as a best effort and not an absolute guarantee.

A general rework of the ImageDecoder trait. All decoders now have their own reader types which allows greater flexibility for the future. These were intended to offer an std::io::Read interface only. If this leads to performance pessimissations it would be possible to introduce dedicated methods for concrete decoders.

Multiple unsafe interfaces have been retired. The (largely) broken generic PixelsMut iterator of GenericImage has been removed after its deprecation some versions ago. Note that the specialized version on ImageBuffer is still available and an even more diverse set of iterators has been added for it, e.g. RowsMut.

A new method save_with_formats on ImageBuffer and DynamicImage is now available to make saving images easier. Encode other GenericImage implementors by cloning their content into an ImageBuffer first. The supported formats are currently only jpeg, png, ico, bmp and tiff but that list will expand in the future.

Colors as now tuple types. This had ergonomic problems in a rather ancient version of Rust. As a style help, remember that you can match tuples and slices exhaustively on the left-hand side of an assignment, like so:

let Rgb([r, g, b]) = image.get_pixel(10, 10);

The overlay and replace operations no longer require both image types to be the same but only their pixels. These changes are complementary to an update to the GenericImage::copy_from method, which previously returned a bool to indicate success. This could silently fail to do anything.

The png library has been updated and now handles interlacing of sub-byte pixel formats correctly.

Future changes

There are already important plans for the next version. The ecosystem is slowly moving towards edition 2018, which is now the default for new projects, and many improvements on quality of life but also semantic clarity are dearly missed once one has gotten used to them. We intend to make use of our bumped compiler version to modernize code and add interoperability where useful. Spotted a missing and useful TryFrom? Give us a PR and we’re happy to discuss.

In an effort to remove even more unsafety from the library there are also some newly depreated methods on top of some previously deprated parts that were removed. These will stay until we have figured out the best solution to replace their current functionality and/or performance.

1. Also TryFrom for integer conversion, improvements for reference matching, nested imports, basic const functions, endianess conversion on integers types, #[repr(transparent)], more in core, impl Trait returns and many many more. ↩