Selene

Selene is a C++17 image representation, processing, and I/O library, focusing on ease of use and a clean, modern, type-safe API.

• Overview: Brief summary of the current feature set.
• Rationale: Why implement a new library for image representation, processing, and I/O?

Building & usage:

• Building the library: How to build from source.
• Dependencies: Description of optional dependencies.
• Installation: Installation using package managers (vcpkg/Conan).
• Usage: Using the built and/or installed library as a dependency in other projects.

Documentation & status:

• Documentation: API documentation & examples.
• Status: Supported compilers & status/roadmap of the library.
• Known issues: Known issues and possible workarounds.
• Contribution guidelines: How to contribute to the library.

Summary

• Strongly typed image and multi-channel pixel representations, and functions for image data access.
• Easy-to-use APIs to read and write images in JPEG, PNG, and TIFF formats (leveraging libjpeg, libpng, and libtiff).
• Basic image processing algorithms such as color conversions, pixel-wise operations, convolutions, rotation, etc.
• Lightweight and easy to build using CMake on Linux, MacOS, Windows.

Example

A first impression of the API:

// Decode JPEG image data from disk
DynImage img_data = read_image(FileReader("example.jpg"));
assert(img_data.nr_channels() == 3 && img_data.nr_bytes_per_channel() == 1);

// Convert to strongly typed RGB image
Image<PixelRGB_8u> img_rgb = to_image<PixelRGB_8u>(std::move(img_data));
assert(img_rgb.width() > 400_px && img_rgb.height() > 350_px);

// Create non-owning view on part of the image
MutableImageView<PixelRGB_8u> img_part = view(img_rgb, {100_idx, 100_idx, 300_px, 250_px});

// Darken this part
for_each_pixel(img_part, [](auto& px){ px /= 4; });

// Flip this part horizontally
flip_horizontally_in_place(img_part);

// Apply a convolution to this part (1-D Gaussian kernel in x-direction, sigma=5.0, range: 3 std. deviations)
Kernel<double> kernel = gaussian_kernel(5.0, 3.0);
const auto img_part_copy = convolution_x<BorderAccessMode::Unchecked>(img_part, kernel);

// And copy the result back to the original image (i.e. to the view).
clone(img_part_copy, img_part);

// Convert whole image to RGBA, adding semi-transparent alpha channel
const Image<PixelRGBA_8u> img_rgba =
  convert_image<PixelFormat::RGBA>(img_rgb, std::uint8_t{192});

// Encode in-memory to PNG
std::vector<std::uint8_t> encoded_png_data;
write_image(to_dyn_image_view(img_rgba), ImageFormat::PNG,
          VectorWriter(encoded_png_data));

// Write encoded binary data to disk (or do something else with it...)
write_data_contents("example_out.png", encoded_png_data);

Package managed

Building from source "at head" using CMake is the recommended way to use Selene (see Building the library). But the library is also available as a

• Conan package on Bintray
• vcpkg port

Selene's own dependencies can be installed using

• Conan
• vcpkg

besides OS level package managers or from source.

Feedback encouraged

Please send me a message if you're using Selene. I would love to know what you think of it, and what your use cases are! Contributions are also very encouraged; see here for more information.