libcaesium

Libcaesium is a simple library performing JPEG, PNG, WebP and GIF (experimental) compression/optimization written in Rust, with a C interface.
IMPORTANT: starting from v0.6.0 the library is written in Rust and no longer in C. There's a C interface, but it's not backward compatible with the <0.6.0.

Usage in Rust

Libcaesium exposes one single function, auto-detecting the input file type:

pub fn compress(
    input_path: String,
    output_path: String,
    parameters: CSParameters
) -> Result<(), Box<dyn Error>>

Parameters

• input_path - input file path (full filename)
• output_path - output file path (full filename)
• parameters - options struct, containing compression parameters (see below)

The output folder where the file is compressed must exist.

Compression options

Libcaesium supports a few compression parameters for each file it supports. They are defined into a top level struct containing each supported file parameters, as follows:

pub struct CSParameters {
    pub jpeg: jpeg::Parameters,
    pub png: png::Parameters,
    pub gif: gif::Parameters,
    pub webp: webp::Parameters,
    pub keep_metadata: bool,
    pub optimize: bool,
    pub width: u32,
    pub height: u32,
}

Each file type has its own options, but the last two are generic:

• keep_metadata: will keep metadata information for any supported type. JPEG and PNG supported. Default false.
• optimize: forces optimization, when available. With this option enabled the compression will be lossless. JPEG, PNG and WebP supported. Default false.
• width: Resizes the image to the given width. If this value is 0 and the height value is also 0, no resizing will be done. If this is 0 and height is > 0, the image will be scaled based on height keeping the aspect ratio. Default 0.
• height: Resizes the image to the given height. If this value is 0 and the width value is also 0, no resizing will be done. If this is 0 and width is > 0, the image will be scaled based on width keeping the aspect ratio. Default 0.

jpeg

pub struct Parameters {
    pub quality: u32,
}

• quality: in a range from 1 to 100, the quality of the resulting image. Default 80.

png

pub struct Parameters {
    pub oxipng: oxipng::Options,
    pub level: u32,
    pub force_zopfli: bool
}

• oxipng: oxipng options. Should be left as default unless you want to do something advanced. Refer to oxipng for documentation.
• level: level of optimization, from 1 to 7. Increasing the level will result in a smaller file, at the cost of computation time. If the optimization flag is true, the level is set to 6. Default: 3.
• force_zopfli: if optimization is true and this option is also true, will use zopfli algorithm for compression, resulting in a smaller image but it may take minutes to finish the process. Default false.

gif

GIF support is experimental, has many know issues and does not support optimization. Expect bugs (especially on Windows).

pub struct Parameters {
    pub quality: u32,
}

• quality: in a range from 0 to 100, the quality of the resulting image. If the optimization flag is true, the level is set to 100. Default: 80.

webp

WebP compression is tricky. The format is already well optimized and using the optimize flag will probably result in a bigger image.

pub struct Parameters {
    pub quality: u32,
}

• quality: in a range from 0 to 100, the quality of the resulting image. If the optimization flag is true, this option will be ignored. Default: 60.

Usage in C

Libcaesium exposes one single C function, auto-detecting the input file type:

pub extern fn c_compress(
    input_path: *const c_char,
    output_path: *const c_char,
    params: CCSParameters
) -> bool

Parameters

• input_path - input file path (full filename)
• output_path - output file path (full filename)
• parameters - options struct, containing compression parameters (see below)

Return

true if all goes well, false otherwise.

Compression options

The C options struct is slightly different from the Rust one:

#[repr(C)]
pub struct CCSParameters {
    pub keep_metadata: bool,
    pub jpeg_quality: u32,
    pub png_level: u32,
    pub png_force_zopfli: bool,
    pub gif_quality: u32,
    pub webp_quality: u32,
    pub optimize: bool,
    pub width: u32,
    pub height: u32,
}

The option description is the same as the Rust counterpart.

Download

Binaries not available. Please refer to the compilation section below.

Compilation and Installation

Compilation is available for all supported platforms: Windows, MacOS and Linux.

cargo build --release

Note: if you don't use the --release flag, the PNG optimizations can take a very long time to complete, especially using the zopfli algorithm.

The result will be a dynamic library usable by external applications through its C interface.

Compression vs Optimization

JPEG is a lossy format: that means you will always lose some information after each compression. So, compressing a file with 100 quality for 10 times will result in an always different image, even though you can't really see the difference. Libcaesium also supports optimization, by setting the quality to 0. This performs a lossless process, resulting in the same image, but with a smaller size (10-12% usually).
PNG is lossless, so libcaesium will always perform optimization rather than compression. GIF optimization is possible, but currently not supported. WebP optimization is also possible, but it will probably result in a bigger output file as it's well suited to losslessly convert from PNG or JPEG.s