为图片添加水印，功能很常用，生成缩略图，也是c#或asp.net编程中经常遇到的。

以下代码，实现为图片添加水印，及生成缩略图等。

代码：

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

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

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

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

   #region 给图片加水印
   /// 
   /// 添加水印(分图片水印与文字水印两种)
   /// 
   /// 原图片绝对地址
   /// 新图片放置的绝对地址
   /// 要添加的水印的类型
   /// 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
   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.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);
     }
    }  
   }

   /// 
   ///   加水印文字
   /// 
   /// imge 对象
   /// 水印文字内容
   /// 水印位置
   /// 被加水印图片的宽
   /// 被加水印图片的高
   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);
   }

   /// 
   ///   加水印图片
   /// 
   /// imge 对象
   /// Image对象（以此图片为水印）
   /// 水印位置
   /// 被加水印图片的宽
   /// 被加水印图片的高
   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(_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();
   }

   /// 
   ///   加水印图片
   /// 
   /// imge 对象
   /// 水印图片的地址
   /// 水印位置
   /// 被加水印图片的宽
   /// 被加水印图片的高
   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

   #region 生成缩略图
   /// 
   /// 保存图片
   /// 
   /// Image 对象
   /// 保存路径
   /// 指定格式的编解码参数
   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();
   }

   /// 
   /// 获取图像编码解码器的所有相关信息
   /// 
   /// 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
   /// 返回图像编码解码器的所有相关信息
   private ImageCodecInfo GetCodecInfo(string mimeType)
   {
    ImageCodecInfo[] CodecInfo = ImageCodecInfo.GetImageEncoders();
    foreach(ImageCodecInfo ici in CodecInfo)
    {
     if(ici.MimeType == mimeType)
      return ici;
    }
    return null;
   }

   /// 
   /// 生成缩略图
   /// 
   /// 原图片路径(相对路径)
   /// 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)
   /// 缩略图的宽度（高度与按源图片比例自动生成）
   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
}
}

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