In C# Winform, add a picture watermark to the picture

        My input parameter is of byte[] (byte array) type, so I will convert byte[] to image type below. If the input parameter of friends is of image type, change the parameter type of the method, and then remove the conversion below.

        /// <summary>
        ///   加水印图片
        /// </summary>
        /// <param name="picture_Input">imge 对象（在此图片上加水印）</param>
        /// <param name="iTheImage">Image对象（以此图片为水印）</param>
        /// <param name="_watermarkPosition">水印位置</param>
        /// <param name="_width">被加水印图片的宽</param>
        /// <param name="_height">被加水印图片的高</param>
        public static byte[] GetMaterMarkImg(byte[] picture_Input, Image iTheImage,
         WatermarkPosition _watermarkPosition, int _width = 0, int _height = 0)
        {
            Image watermark = new Bitmap(iTheImage);

            #region 将byte[]类型的图片数据转为img类型
            MemoryStream ms = new MemoryStream(picture_Input);
            Image image = System.Drawing.Image.FromStream(ms);
            #endregion

            Graphics picture = Graphics.FromImage(image);

            if (_width == 0)
            {
                _width = image.Width;
            }
            if (_height == 0)
            {
                _height = image.Height;
            }

            ImageAttributes imageAttributes = new ImageAttributes();
            ColorMap colorMap = new ColorMap();

            colorMap.OldColor = Color.FromArgb(255, 0, 255, 0);
            colorMap.NewColor = Color.FromArgb(0, 0, 0, 0);
            ColorMap[] remapTable = { colorMap };

            imageAttributes.SetRemapTable(remapTable, ColorAdjustType.Bitmap);

            float[][] colorMatrixElements = {
             new float[] {1.0f, 0.0f, 0.0f, 0.0f, 0.0f},
             new float[] {0.0f, 1.0f, 0.0f, 0.0f, 0.0f},
             new float[] {0.0f, 0.0f, 1.0f, 0.0f, 0.0f},
             new float[] {0.0f, 0.0f, 0.0f, 0.3f, 0.0f},
             new float[] {0.0f, 0.0f, 0.0f, 0.0f, 1.0f}
            };

            ColorMatrix colorMatrix = new ColorMatrix(colorMatrixElements);

            imageAttributes.SetColorMatrix(colorMatrix, ColorMatrixFlag.Default, ColorAdjustType.Bitmap);

            int xpos = 0;
            int ypos = 0;
            int WatermarkWidth = 0;
            int WatermarkHeight = 0;
            double bl = 1d;

            //计算水印图片的比率
            //取背景的1/4宽度来比较
            if ((_width > watermark.Width * 4) && (_height > watermark.Height * 4))
            {
                bl = 1;
            }
            else if ((_width > watermark.Width * 4) && (_height < watermark.Height * 4))
            {
                bl = Convert.ToDouble(_height / 4) / Convert.ToDouble(watermark.Height);

            }
            else if ((_width < watermark.Width * 4) && (_height > watermark.Height * 4))
            {
                bl = Convert.ToDouble(_width / 4) / Convert.ToDouble(watermark.Width);
            }
            else
            {
                if ((_width * watermark.Height) > (_height * watermark.Width))
                {
                    bl = Convert.ToDouble(_height / 4) / Convert.ToDouble(watermark.Height);

                }
                else
                {
                    bl = Convert.ToDouble(_width / 4) / Convert.ToDouble(watermark.Width);

                }

            }

            WatermarkWidth = Convert.ToInt32(watermark.Width * bl);
            WatermarkHeight = Convert.ToInt32(watermark.Height * bl);

            switch (_watermarkPosition)
            {
                case WatermarkPosition.左上:
                    xpos = 10;
                    ypos = 10;
                    break;
                case WatermarkPosition.右上:
                    xpos = _width - WatermarkWidth - 10;
                    ypos = 10;
                    break;
                case WatermarkPosition.中间:
                    xpos = (_width / 2) - (WatermarkWidth / 2);
                    ypos = (_height / 2) - (WatermarkHeight / 2);
                    break;
                case WatermarkPosition.右下:
                    xpos = _width - WatermarkWidth - 10;
                    ypos = _height - WatermarkHeight - 10;
                    break;
                case WatermarkPosition.左下:
                    xpos = 10;
                    ypos = _height - WatermarkHeight - 10;
                    break;
            }
            picture.DrawImage(
             watermark,
             new Rectangle(xpos, ypos, WatermarkWidth, WatermarkHeight),
             0,
             0,
             watermark.Width,
             watermark.Height,
             GraphicsUnit.Pixel,
             imageAttributes);

            watermark.Dispose();
            imageAttributes.Dispose();

            MemoryStream ms_OutPut = new MemoryStream();
            image.Save(ms_OutPut, System.Drawing.Imaging.ImageFormat.Jpeg);
            byte[] buffer = new byte[ms_OutPut.Length];
            ms_OutPut.Seek(0, SeekOrigin.Begin);
            ms_OutPut.Read(buffer, 0, buffer.Length);

            return buffer;
        }

        public enum WatermarkPosition
        {
            无 = 1000,
            左上 = 1001,
            右上 = 1002,
            中间 = 1003,
            右下 = 1004,
            左下 = 1005
        }