How do you use System.Drawing in .NET Core?

I've been doing .NET image processing since the beginning. In fact I wrote about it over 13 years ago on this blog when I talked about Compositing two images into one from the ASP.NET Server Side and in it I used System.Drawing to do the work. For over a decade folks using System.Drawing were just using it as a thin wrapper over GDI (Graphics Device Interface) which were very old Win32 (Windows) unmanaged drawing APIs. We use them because they work fine.

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For a while there was a package called CoreCompat.System.Drawing that was a .NET Core port of a Mono version of System.Drawing.

However, since then Microsoft has released System.Drawing.Common to provide access to GDI+ graphics functionality cross-platform.

There is a lot of existing code - mine included - that makes assumptions that .NET would only ever run on Windows. Using System.Drawing was one of those things. The "Windows Compatibility Pack" is a package meant for developers that need to port existing .NET Framework code to .NET Core. Some of the APIs remain Windows only but others will allow you to take existing code and make it cross-platform with a minimum of trouble.

Here's a super simple app that resizes a PNG to 128x128. However, it's a .NET Core app and it runs in both Windows and Linux (Ubuntu!)

using System;

using System.Drawing;

using System.Drawing.Drawing2D;

using System.Drawing.Imaging;

using System.IO;


namespace imageresize

{

    class Program

    {

        static void Main(string[] args)

        {

            int width = 128;

            int height = 128;

            var file = args[0];

            Console.WriteLine($"Loading {file}");

            using(FileStream pngStream = new FileStream(args[0],FileMode.Open, FileAccess.Read))

            using(var image = new Bitmap(pngStream))

            {

                var resized = new Bitmap(width, height);

                using (var graphics = Graphics.FromImage(resized))

                {

                    graphics.CompositingQuality = CompositingQuality.HighSpeed;

                    graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;

                    graphics.CompositingMode = CompositingMode.SourceCopy;

                    graphics.DrawImage(image, 0, 0, width, height);

                    resized.Save($"resized-{file}", ImageFormat.Png);

                    Console.WriteLine($"Saving resized-{file} thumbnail");

                }       

            }     

        }

    }

}

Here it is running on Ubuntu:

NOTE that on Ubuntu (and other Linuxes) you may need to install some native dependencies as System.Drawing sits on top of native libraries

sudo apt install libc6-dev 

sudo apt install libgdiplus

There's lots of great options for image processing on .NET Core now! It's important to understand that this System.Drawing layer is great for existing System.Drawing code, but you probably shouldn't write NEW image management code with it. Instead, consider one of the great other open source options.

• ImageSharp - A cross-platform library for the processing of image files; written in C#
  • Compared to System.Drawing ImageSharp has been able to develop something much more flexible, easier to code against, and much, much less prone to memory leaks. Gone are system-wide process-locks; ImageSharp images are thread-safe and fully supported in web environments.

Here's how you'd resize something with ImageSharp:

using (Image<Rgba32> image = Image.Load("foo.jpg"))

{

    image.Mutate(x => x

         .Resize(image.Width / 2, image.Height / 2)

         .Grayscale());

    image.Save("bar.jpg"); // Automatic encoder selected based on extension.

}

• Magick.NET -A .NET library on top of ImageMagick
• SkiaSharp - A .NET wrapper on top of Google's cross-platform Skia library

It's awesome that there are so many choices with .NET Core now!

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