Note: the command-line examples use ImageMagick 7 which consolidates all functionality into a single magick command. Each example can be run and modified interactively in the browser using a WebAssembly build of ImageMagick. The rest of this post will give an overview of the ImageMagick command-line interface, driven by examples of GIF generation from the test suite. You can find the GIF test suite on GitHub 1. Using this we can programmatically and systematically generate a suite of GIFs that exhibit all different kinds of GIF features: perfect for testing a decoder. It turns out that we can use ImageMagick’s command-line interface to conjure animated GIFs out of thin air. I needed a better way.Įnter ImageMagick, an extremely powerful open-source platform for creating, converting, manipulating, inspecting, and visualising over 200 image file formats. It wasn’t long before a few edge cases and bugs cropped up as people discovered GIFs with as-yet unimplemented features, and as I fixed one, another would break. Initially this involved me browsing r/gifs and the occasional Google Doodle, however it’s quite difficult to find contemporary GIFs that exhibit some of the more obscure GIF functionality. In my endeavours to build a GIF decoder for SerenityOS I soon realised the need for a suite of test GIFs to have reference targets to aim for in my implementation.
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