C#彩色图片变黑白

public static Bitmap MakeGrayscale(Bitmap original)
{
    //create a blank bitmap the same size as original
    Bitmap newBitmap = new Bitmap(original.Width, original.Height);

    //get a graphics object from the new image
    Graphics g = Graphics.FromImage(newBitmap);

    //create the grayscale ColorMatrix
    System.Drawing.Imaging.ColorMatrix colorMatrix = new System.Drawing.Imaging.ColorMatrix(
       new float[][] 
      {
         new float[] {.3f, .3f, .3f, 0, 0},
         new float[] {.59f, .59f, .59f, 0, 0},
         new float[] {.11f, .11f, .11f, 0, 0},
         new float[] {0, 0, 0, 1, 0},
         new float[] {0, 0, 0, 0, 1}
      });

    //create some image attributes
    System.Drawing.Imaging.ImageAttributes attributes = new System.Drawing.Imaging.ImageAttributes();

    //set the color matrix attribute
    attributes.SetColorMatrix(colorMatrix);

    //draw the original image on the new image
    //using the grayscale color matrix
    g.DrawImage(original, new Rectangle(0, 0, original.Width, original.Height), 0, 0, original.Width, original.Height, GraphicsUnit.Pixel, attributes);

    //dispose the Graphics object
    g.Dispose();
    return newBitmap;
}