c# 添加图片水印，可以指定水印位置+生成缩略图

using System;
using System.IO;
using System.Collections;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;

namespace BLL
{
    /**//// <summary>
    /// 水印的类型
    /// </summary>
    public enum WaterMarkType
    {
        /**//// <summary>
        /// 文字水印
        /// </summary>
        TextMark,
        /**//// <summary>
        /// 图片水印
        /// </summary>
        //ImageMark // 暂时只能添加文字水印
    };

    /**//// <summary>
    /// 水印的位置
    /// </summary>
    public enum WaterMarkPosition
    {
        /**//// <summary>
        /// 左上角
        /// </summary>
        WMP_Left_Top,
        /**//// <summary>
        /// 左下角
        /// </summary>
        WMP_Left_Bottom,
        /**//// <summary>
        /// 右上角
        /// </summary>
        WMP_Right_Top,
        /**//// <summary>
        /// 右下角
        /// </summary>
        WMP_Right_Bottom
    };

    /**//// <summary>
    /// 处理图片的类（包括加水印，生成缩略图）
    /// </summary>
    public class ImageWaterMark
    {
        public ImageWaterMark()
        {
            //
            // TODO: 在此处添加构造函数逻辑
            //
        }

        给图片加水印#region 给图片加水印
        /**//// <summary>
        /// 添加水印(分图片水印与文字水印两种)
        /// </summary>
        /// <param name="oldpath">原图片绝对地址</param>
        /// <param name="newpath">新图片放置的绝对地址</param>
        /// <param name="wmtType">要添加的水印的类型</param>
        /// <param name="sWaterMarkContent">水印内容，若添加文字水印，此即为要添加的文字；
        /// 若要添加图片水印，此为图片的路径</param>
        public void addWaterMark(string oldpath, string newpath, 
            WaterMarkType wmtType, string sWaterMarkContent)
        {
            try
            {
                Image image = Image.FromFile(oldpath);

                Bitmap b = new Bitmap(image.Width, image.Height, 
                    PixelFormat.Format24bppRgb);

                Graphics g = Graphics.FromImage(b);
                g.Clear(Color.White);
                g.SmoothingMode = SmoothingMode.HighQuality;
                g.InterpolationMode = InterpolationMode.High;

                g.DrawImage(image, 0, 0, image.Width, image.Height);

                switch (wmtType)
                {
                    /**//*case WaterMarkType.ImageMark:
                        //图片水印
                        this.addWatermarkImage(g, 
                            Page.Server.MapPath(Watermarkimgpath), 
                            WatermarkPosition,image.Width,image.Height);
                        break;*/
                    case WaterMarkType.TextMark:
                        //文字水印
                        this.addWatermarkText(g, sWaterMarkContent, "WM_BOTTOM_RIGHT", 
                            image.Width, image.Height);
                        break;
                }

                b.Save(newpath);
                b.Dispose();
                image.Dispose();
            }
            catch
            {
                if(File.Exists(oldpath))
                {
                    File.Delete(oldpath);
                }
            }
            finally
            {
                if(File.Exists(oldpath))
                {
                    File.Delete(oldpath);
                }
            }  
        }

        /**//// <summary>
        ///  加水印文字
        /// </summary>
        /// <param name="picture">imge 对象</param>
        /// <param name="_watermarkText">水印文字内容</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>
        private void addWatermarkText(Graphics picture, string _watermarkText, 
            string _watermarkPosition, int _width, int _height)
        {
            // 确定水印文字的字体大小
            int[] sizes = new int[]{32, 30, 28, 26, 24, 22, 20, 18, 16, 14, 12, 10, 8, 6, 4};
            Font crFont = null;
            SizeF crSize = new SizeF();
            for (int i = 0;i < sizes.Length; i++)
            {
                crFont = new Font("Arial Black", sizes[i], FontStyle.Bold);
                crSize = picture.MeasureString(_watermarkText, crFont);

                if((ushort)crSize.Width < (ushort)_width)
                {
                    break;
                }
            }

            // 生成水印图片（将文字写到图片中）
            Bitmap floatBmp = new Bitmap((int)crSize.Width + 3, 
                           (int)crSize.Height + 3, PixelFormat.Format32bppArgb);
            Graphics fg=Graphics.FromImage(floatBmp);
            PointF pt=new PointF(0,0);

            // 画阴影文字
            Brush TransparentBrush0 = new SolidBrush(Color.FromArgb(255, Color.Black));
            Brush TransparentBrush1 = new SolidBrush(Color.FromArgb(255, Color.Black));
            fg.DrawString(_watermarkText,crFont,TransparentBrush0, pt.X, pt.Y + 1); 
            fg.DrawString(_watermarkText,crFont,TransparentBrush0, pt.X + 1, pt.Y); 

            fg.DrawString(_watermarkText,crFont,TransparentBrush1, pt.X + 1, pt.Y + 1); 
            fg.DrawString(_watermarkText,crFont,TransparentBrush1, pt.X, pt.Y + 2); 
            fg.DrawString(_watermarkText,crFont,TransparentBrush1, pt.X + 2, pt.Y); 

            TransparentBrush0.Dispose(); 
            TransparentBrush1.Dispose();

            // 画文字
            fg.SmoothingMode=System.Drawing.Drawing2D.SmoothingMode.HighQuality; 
            fg.DrawString(_watermarkText, 
                crFont, new SolidBrush(Color.White), 
                pt.X, pt.Y, StringFormat.GenericDefault);

            // 保存刚才的操作
            fg.Save(); 
            fg.Dispose();
            // floatBmp.Save("d:\\WebSite\\DIGITALKM\\ttt.jpg");

            // 将水印图片加到原图中
            this.addWatermarkImage(
                picture, 
                new Bitmap(floatBmp), 
                "WM_BOTTOM_RIGHT", 
                _width, 
                _height);
        }

        /**//// <summary>
        ///  加水印图片
        /// </summary>
        /// <param name="picture">imge 对象</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>
        private void addWatermarkImage( Graphics picture,Image iTheImage, 
            string _watermarkPosition,int _width,int _height)
        {
            Image watermark = new Bitmap(iTheImage);
 
            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 "WM_TOP_LEFT":
                    xpos = 10;
                    ypos = 10;
                    break;
                case "WM_TOP_RIGHT":
                    xpos = _width - WatermarkWidth - 10;
                    ypos = 10;
                    break;
                case "WM_BOTTOM_RIGHT":
                    xpos = _width - WatermarkWidth - 10;
                    ypos = _height -WatermarkHeight - 10;
                    break;
                case "WM_BOTTOM_LEFT":
                    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();
        }

        /**//// <summary>
        ///  加水印图片
        /// </summary>
        /// <param name="picture">imge 对象</param>
        /// <param name="WaterMarkPicPath">水印图片的地址</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>
        private void addWatermarkImage( Graphics picture,string WaterMarkPicPath, 
            string _watermarkPosition,int _width,int _height)
        {
            Image watermark = new Bitmap(WaterMarkPicPath);
 
            this.addWatermarkImage(picture, watermark, _watermarkPosition, _width, 
                _height);
        }
        #endregion

        生成缩略图#region 生成缩略图
        /**//// <summary>
        /// 保存图片
        /// </summary>
        /// <param name="image">Image 对象</param>
        /// <param name="savePath">保存路径</param>
        /// <param name="ici">指定格式的编解码参数</param>
        private void SaveImage(Image image, string savePath, ImageCodecInfo ici)
        {
            //设置 原图片 对象的 EncoderParameters 对象
            EncoderParameters parameters = new EncoderParameters(1);
            parameters.Param[0] = new EncoderParameter(
                System.Drawing.Imaging.Encoder.Quality, ((long) 90));
            image.Save(savePath, ici, parameters);
            parameters.Dispose();
        }

        /**//// <summary>
        /// 获取图像编码解码器的所有相关信息
        /// </summary>
        /// <param name="mimeType">包含编码解码器的多用途网际邮件扩充协议 (MIME) 类型的字符串</param>
        /// <returns>返回图像编码解码器的所有相关信息</returns>
        private ImageCodecInfo GetCodecInfo(string mimeType)
        {
            ImageCodecInfo[] CodecInfo = ImageCodecInfo.GetImageEncoders();
            foreach(ImageCodecInfo ici in CodecInfo)
            {
                if(ici.MimeType == mimeType)
                    return ici;
            }
            return null;
        }

        /**//// <summary>
        /// 生成缩略图
        /// </summary>
        /// <param name="sourceImagePath">原图片路径(相对路径)</param>
        /// <param name="thumbnailImagePath">生成的缩略图路径,如果为空则保存为原图片路径(相对路径)</param>
        /// <param name="thumbnailImageWidth">缩略图的宽度（高度与按源图片比例自动生成）</param>
        public void ToThumbnailImages(
            string SourceImagePath,
            string ThumbnailImagePath,
            int ThumbnailImageWidth)
        {
            Hashtable htmimes = new Hashtable();
            htmimes[".jpeg"] = "image/jpeg";
            htmimes[".jpg"] = "image/jpeg";   
            htmimes[".png"] = "image/png";   
            htmimes[".tif"] = "image/tiff";
            htmimes[".tiff"] = "image/tiff";
            htmimes[".bmp"] = "image/bmp";
            htmimes[".gif"] = "image/gif";

            // 取得原图片的后缀
            string sExt = SourceImagePath.Substring(
                SourceImagePath.LastIndexOf(".")).ToLower();

            //从 原图片 创建 Image 对象
            Image image = Image.FromFile(SourceImagePath);  
            int num = ((ThumbnailImageWidth / 4) * 3);
            int width = image.Width;
            int height = image.Height;

            //计算图片的比例
            if ((((double) width) / ((double) height)) >= 1.3333333333333333f)
            {
                num = ((height * ThumbnailImageWidth) / width);
            }
            else
            {
                ThumbnailImageWidth = ((width * num) / height);
            }
            if ((ThumbnailImageWidth < 1) || (num < 1))
            {
                return;
            }

            //用指定的大小和格式初始化 Bitmap 类的新实例
            Bitmap bitmap = new Bitmap(ThumbnailImageWidth, num, 
                PixelFormat.Format32bppArgb);

            //从指定的 Image 对象创建新 Graphics 对象
            Graphics graphics = Graphics.FromImage(bitmap);

            //清除整个绘图面并以透明背景色填充
            graphics.Clear(Color.Transparent);

            graphics.SmoothingMode = SmoothingMode.HighQuality;
            graphics.InterpolationMode = InterpolationMode.High;

            //在指定位置并且按指定大小绘制 原图片 对象
            graphics.DrawImage(image, new Rectangle(0, 0, ThumbnailImageWidth, num));
            image.Dispose(); 
   
            try
            {   
                //将此 原图片 以指定格式并用指定的编解码参数保存到指定文件 
                SaveImage(bitmap, ThumbnailImagePath, 
                    GetCodecInfo((string)htmimes[sExt]));
            }
            catch(System.Exception e)
            {
                throw e;
            }
        }
        #endregion
    }
}