Target Audience • Features • Image Formats • Getting Started • FAQ

SAIL is a high-quality cross-platform image decoding library providing rich APIs, from one-liners to complex use cases with custom I/O sources. It supports loading and saving static, animated, and multi-paged images along with metadata and ICC profiles. ⛵

• Image viewers
• Game developers
• Anyone who needs to load or save images in different image formats with a clean and comprehensive API

• Thread-safe C, C++, and Python interfaces
• Versatile APIs: junior, advanced, deep diver, and technical diver
• Input/output: files, memory, custom I/O streams (see custom-io.c)
• Load by file extensions, paths, and magic numbers
• Format-specific tuning options (e.g., PNG filters). See FORMATS
• Metadata support: text comments, EXIF, ICC profiles
• Access to image properties without decoding pixels (probing)
• Access to source image properties (source encoding, etc.)
• Preserve original pixel formats when saving
• Extensible codec architecture demonstrated by Intel [*]

* One day Intel demonstrated the advantages of their IPP technology in speeding up decoding JPEG and JPEG 2000 images with the help of ksquirrel-libs, the predecessor of SAIL.

See the full list here. Work to add more image formats is ongoing.

Time to load and output default pixels (without explicit conversion) was measured. See BENCHMARKS.

• Python: PyPI - pip install sailpy
• Windows: Conan, vcpkg
• macOS: brew, Conan, vcpkg
• Linux: native packages if available, Conan, vcpkg

See BUILDING.

SAIL provides four levels of APIs, depending on your needs. Let's have a quick look at the junior level.

struct sail_image *image;

SAIL_TRY(sail_load_from_file(path, &image));

/*
 * Handle the image pixels here.
 * Use image->width, image->height, image->bytes_per_line,
 * image->pixel_format, and image->pixels for that.
 *
 * In particular, you can convert it to a different pixel format with functions
 * from libsail-manip. With sail_convert_image(), for example.
 */

sail_destroy_image(image);

sail::image image(path);

// Handle the image and its pixels here.
// Use image.width(), image.height(), image.bytes_per_line(),
// image.pixel_format(), and image.pixels() for that.
//
// In particular, you can convert it to a different pixel format with image::convert().

import sailpy

image = sailpy.Image.from_file(path)

# Handle the image and its pixels here.
# Use image.width, image.height, image.bytes_per_line,
# image.pixel_format, and image.to_numpy() for that.
#
# In particular, you can convert it to a different pixel format with image.convert().

# View documentation
# python -m sailpy --readme

# Run image viewer example
# pip install PySide6
# python -m sailpy.examples.12_image_viewer

See also FAQ for more information.

Programming language: C11
Bindings: C++11, Python 3.10+

• FreeImage
• DevIL
• SDL_Image
• stb_image
• Boost.GIL
• gdk-pixbuf
• imlib2
• CImg
• WIC (Windows only)

• Easily extensible with new image format plugins
• Intuitive API with well-defined abstractions: images, palettes, pixels, etc.
• Access to source pixel data (supported by most codecs)
• Access to image properties without decoding pixel data (probing)

Opening a GitHub issue is the preferred method for communication and problem resolution.

See FAQ for more information.

SAIL is written in pure C11 without using any third-party libraries (except for codecs). It also provides bindings to C++ and Python.

SAIL codecs represent the lowest level. This is a set of standalone, dynamically loaded codecs (SO on Linux and DLL on Windows). They implement the actual decoding and encoding capabilities. End users never work with codecs directly; they always use the abstract, high-level APIs in libsail.

Every codec is accompanied by a codec info (description) file, which is a plain text file. It describes the codec's capabilities: supported pixel formats for loading and output, compression types, and more.

By default, SAIL loads codecs on demand. To preload them, use sail_init_with_flags(SAIL_FLAG_PRELOAD_CODECS).

libsail-common holds common data types (images, pixel formats, I/O abstractions etc.) and a small set of functions shared between SAIL codecs and the high-level APIs in libsail.

libsail is a feature-rich, high-level API. It provides comprehensive and lightweight interfaces for decoding and encoding images. End users implementing C applications work with libsail.

libsail-manip is a collection of image manipulation functions, such as pixel format conversion.

libsail-c++ is a C++ binding to libsail. End users implementing C++ applications may choose between libsail and libsail-c++. Using libsail-c++ is recommended for C++ applications due to its simplified interface.

See BUILDING.

SAIL's philosophy is modularization and simplicity.

Image codecs are designed as standalone dynamically loaded files. Future improvements will be implemented as separate libraries, allowing users to choose which components to use (i.e., link against) and which to exclude.

If you like the project, please consider starring the repository.

Dmitry Baryshev

Released under the MIT license.

Copyright (c) 2020-2025 Dmitry Baryshev

The MIT License

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