how to create an animated gif in .net

Whether or not calling imagemagick is the best choice is kind of hard to awnser without knowing the quality parameters that are important. Some other options would be:

• Rick van den Bosch's code archive.org mirror
• NGif article on codeplex

these have the advantage that you don't have a dependency on a third partly library which might or might not be available on all systems executing your code.

This article at MS Support explains how to save a gif with a custom color table (this does require full trust). A animated gif is just a set of gifs for each image with some additional information in the header. So combining these two articles should get you what you need.

The AnimatedGif package can make animated gifs.

using (var gif = AnimatedGif.AnimatedGif.Create(Path.Combine(outputPath, "output.gif"), 20))
{
    for (var i = 0; i < 10; i++)
    {
        Image img = Image.FromFile(Path.Combine(outputPath, $"{i.ToString().PadLeft(3, '0')}.png"));
        gif.AddFrame(img, delay: -1, quality: GifQuality.Bit8);
    }
}

Quote from fireydude answer: https://stackoverflow.com/a/16598294/8917485

This method is not complete, cause the .gif can't repeat. I found some additional code on other question, make .gif repeat.

.NET - Creating a looping .gif using GifBitmapEncoder http://www.matthewflickinger.com/lab/whatsinagif/bits_and_bytes.asp

The complete code should looks like the code below:

System.Windows.Media.Imaging.GifBitmapEncoder gEnc = new GifBitmapEncoder();
foreach (System.Drawing.Bitmap bmpImage in bitMaps)
{
    var bmp = bmpImage.GetHbitmap();
    var src = System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(
        bmp,
        IntPtr.Zero,
        Int32Rect.Empty,
        BitmapSizeOptions.FromEmptyOptions());
    gEnc.Frames.Add(BitmapFrame.Create(src));
    DeleteObject(bmp); // recommended, handle memory leak
    bmpImage.Dispose(); // recommended, handle memory leak
}

// After adding all frames to gifEncoder (the GifBitmapEncoder)...
using (var ms_ = new MemoryStream())
{
    gEnc.Save(ms_);
    var fileBytes = ms_.ToArray();
    // This is the NETSCAPE2.0 Application Extension.
    var applicationExtension = new byte[] { 33, 255, 11, 78, 69, 84, 83, 67, 65, 80, 69, 50, 46, 48, 3, 1, 0, 0, 0 };
    var newBytes = new List<byte>();
    newBytes.AddRange(fileBytes.Take(13));
    newBytes.AddRange(applicationExtension);
    newBytes.AddRange(fileBytes.Skip(13));
    File.WriteAllBytes("abc.gif", newBytes.ToArray());
}