/// <summary>

        /// 方法一  设置图像透明度

        /// </summary>

        /// <param name="srcImage"></param>

        /// <param name="opacity"></param>

        /// <returns></returns>

        public static Image TransparentImage(Image srcImage, float opacity)

        {

            float[][] nArray ={ new float[] {1, 0, 0, 0, 0},

                        new float[] {0, 1, 0, 0, 0},

                        new float[] {0, 0, 1, 0, 0},

                        new float[] {0, 0, 0, opacity, 0},

                        new float[] {0, 0, 0, 0, 1}};

            ColorMatrix matrix = new ColorMatrix(nArray);

            ImageAttributes attributes = new ImageAttributes();

            attributes.SetColorMatrix(matrix, ColorMatrixFlag.Default, ColorAdjustType.Bitmap);

            Bitmap resultImage = new Bitmap(srcImage.Width, srcImage.Height);

            Graphics g = Graphics.FromImage(resultImage);

            g.DrawImage(srcImage, new Rectangle(0, 0, srcImage.Width, srcImage.Height), 0, 0, srcImage.Width, srcImage.Height, GraphicsUnit.Pixel, attributes);

            return resultImage;

        }