This is ONLY interfaces/enums/data objects - NO IMPLEMENTATION. It is used by https://github.com/matgr1/FreeImage-dotnet-core which provides a bitmap implementation and various image codecs based on FreeImage (http://freeimage.sourceforge.net/)
nuget package: https://www.nuget.org/packages/System.Drawing-dotnet-core/
Install-Package System.Drawing-dotnet-core
MIT