c#でBITMAP画像マスク

Bitmap canvas = new Bitmap(inputFile);
Graphics graph = Graphics.FromImage(canvas);
Bitmap mask= new Bitmap(maskFile);
mask.MakeTransparent(Color.White); // Transparent Color
graph.DrawImage(mask, 0, 0, mask.Width, mask.Height);
Bitmap canvas = new Bitmap(inputFile);
Graphics graph = Graphics.FromImage(canvas);
Bitmap mask= new Bitmap(maskFile);
mask.MakeTransparent(Color.White); // Transparent Color
graph.DrawImage(mask, 0, 0, mask.Width, mask.Height);