Gray Scale

using System.Drawing.Imaging;

public Image GrayScaleImage(Graphics graph, Image img, int left, int top)
        {
                     
            ColorMatrix colorMix = new ColorMatrix();           
            colorMix.Matrix00 = 1 / 3f;
            colorMix.Matrix01 = 1 / 3f;
            colorMix.Matrix02 = 1 / 3f;
            colorMix.Matrix10 = 1 / 3f;
            colorMix.Matrix11 = 1 / 3f;
            colorMix.Matrix12 = 1 / 3f;
            colorMix.Matrix20 = 1 / 3f;
            colorMix.Matrix21 = 1 / 3f;
            colorMix.Matrix22 = 1 / 3f;

            ImageAttributes imgAttrib = new ImageAttributes();
            imgAttrib.SetColorMatrix(colorMix);

            graph.DrawImage(img, new Rectangle(left, top, img.Width,
                 img.Height), 0, 0, img.Width, img.Height,
                 GraphicsUnit.Pixel, imgAttrib);
            Bitmap bmp = new Bitmap(img);
            return bmp;

        }