If you want to specify it like that you need to use the SetDefine method in Magick.NET:
using (MagickImage image = images.Flatten()) { image.ColorSpace = ColorSpace.RGB; image.Resize(0.5); // implicit cast to Percentage image.ColorSpace = ColorSpace.sRGB; image.SetDefine(MagickFormat.Png, "compression-strategy", "0"); image.SetDefine(MagickFormat.Png, "compression-filter", "0"); image.Write("image.png"); }