You are not using the settings but even if you used it it would not work. Your call to SetDefine does nothing. You will need to call the Charcoal method instead:
And you could also give Sketch (that method is pretty slow though).
string FilePath = "../path/1.jpg"; using (MagickImage image = new MagickImage(FilePath)) { image.Resize(100,0); image.Charcoal(5, 1); image.Write(FilePath); }