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image v0.23.0 Release Notes

Release Date: 2020-02-07 // about 4 years ago

  • 🚀 This major release intends to improve the interface with regards to handling of color format data and errors for both decoding and encoding. This necessitated many breaking changes anyways so it was used to improve the compliance to the interface guidelines such as outstanding renaming.

    It is not yet perfect with regards to color spaces but it was designed mainly as an improvement over the current interface with regards to in-memory color formats, first. We'll get to color spaces in a later major version.

    • Heavily reworked ColorType:
      • This type is now used for denoting formats for which we support operations on buffers in these memory representations. Particularly, all channels in pixel types are assumed to be an integer number of bytes (In terms of the Rust type system, these are Sized and one can crate slices of channel values).
      • An ExtendedColorType is used to express more generic color formats for which the library has limited support but can be converted/scaled/mapped into a ColorType buffer. This operation might be fallible but, for example, includes sources with 1/2/4-bit components.
      • Both types are non-exhaustive to add more formats in a minor release.
      • A work-in-progress (#1085) will further separate the color model from the specific channel instantiation, e.g. both 8-bit RGB and 16-bit BGR are instantiations of RGB color model.
    • Heavily rework ImageError:
      • The top-level enum type now serves to differentiate cause with multiple opaque representations for the actual error. These are no longer simple Strings but contains useful types. Third-party decoders that have no variant in ImageFormat have also been considered.
      • Support for Error::source that can be downcast to an error from a matching version of the underlying decoders. Note that the version is not part of the stable interface guarantees, this should not be relied upon for correctness and only be used as an optimization.
      • Added image format indications to errors.
      • The error values produced by decoder will be upgraded incrementally. See something that still produces plain old String messages? Feel free to send a PR.
    • Reworked the ImageDecoder trait:
      • read_image takes an output buffer argument instead of allocating all memory on its own.
      • The return type of dimensions now aligns with GenericImage sizes.
      • The colortype method was renamed to color_type for conformity.
    • The enums ColorType, DynamicImage, imageops::FilterType, ImageFormat no longer re-export all of their variants in the top-level of the crate. This removes the growing pollution in the documentation and usage. You can still insert the equivalent statement on your own: use image::ImageFormat::{self, *};
    • The result of encode operations is now uniformly an ImageResult<()>.
    • ✂ Removed public converters from some tiff, png, gif, jpeg types, mainly such as error conversion. This allows upgrading the dependency across major versions without a major release in image itself.
    • On that note, the public interface of gif encoder no longer takes a gif::Frame but rather deals with image::Frame only. If you require to specify the disposal method, transparency, etc. then you may want to wait with upgrading but (see next change).
    • 👍 The gif encoder now errors on invalid dimensions or unsupported color formats. It would previously silently reinterpret bytes as RGB/RGBA.
    • The capitalization of ImageFormat and other enum variants has been adjusted to adhere to the API guidelines. These variants are now spelled Gif, Png, etc. The same change has been made to the name of types such as HDRDecoder.
    • The Progress type has finally received public accessor method. Strange that no one reported them missing.
    • Introduced PixelDensity and PixelDensityUnit to store DPI information in formats that support encoding this form of meta data (e.g. in jpeg).