利用.NET 提供的类，如Drawing.Bitmap ，Drawing.Bitmap 等，很容易就可以实现对图片的简单处理。包括打水印，放大缩小，等操作。

public partial class WebForm4 : System.Web.UI.Page
{
// 原始图片路径
private string path;
private System.Drawing.Bitmap bitmap;
private System.Drawing.Graphics graphics;
string Message = "<script>alert(\"{0}\");</script>";
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
this.txtPicPath.Text = Server.MapPath("/upload/tech/20091011/20091011143606_941e1aaaba585b952b62c14a3a175a61.jpg");
}
path = this.txtPicPath.Text.Trim();
if (!System.IO.File.Exists(path))
{
MessageShow("指定的源文件不存在！");
return;
}
}
// 打水印Logo
protected void btnLogo_Click(object sender, EventArgs e)
{
string log = txtLog.Text.Trim();
if (log.Length < 1)
{
MessageShow("请输入水印字符！");
return;
}

bitmap = new Bitmap(path);
graphics = Graphics.FromImage(bitmap);
graphics.DrawString(log, new Font("宋体", 16), System.Drawing.Brushes.GreenYellow, new PointF(bitmap.Width / 2 - (log.Length) * 5, bitmap.Height / 2));
try
{
bitmap.Save(Server.MapPath("/upload/tech/20091011/20091011143606_e2ef524fbf3d9fe611d5a8e90fefdc9c.jpg"), System.Drawing.Imaging.ImageFormat.Jpeg);
MessageShow("已经生成水印图片，路径为" + @Server.MapPath("/upload/tech/20091011/20091011143607_07e1cd7dca89a1678042477183b7ac3f.jpg").Replace("\\", "\\\\"));

}
catch (Exception ex)
{
MessageShow("生成图片错误！" + ex.Message);
throw;
}
graphics.Dispose();
bitmap.Dispose();
}
private void MessageShow(string msg)
{
Page.ClientScript.RegisterStartupScript(Page.GetType(), "Message", string.Format(Message, msg));

}
//放大X*X倍
protected void btnBig_Click(object sender, EventArgs e)
{
int i = int.Parse(txtBig.Text.Trim());
System.Drawing.Image img = System.Drawing.Image.FromFile(path);
bitmap = new Bitmap(img.Width * i, img.Height * i);
graphics = Graphics.FromImage(bitmap);
graphics.DrawImage(img, 0, 0, img.Width * i, img.Height * i);
try
{
bitmap.Save(Server.MapPath("/upload/tech/20091011/20091011143607_e07413354875be01a996dc560274708e.jpg"), System.Drawing.Imaging.ImageFormat.Jpeg);
MessageShow("已经生成图片，路径为" + @Server.MapPath("/upload/tech/20091011/20091011143607_e07413354875be01a996dc560274708e.jpg").Replace("\\", "\\\\"));

}
catch (Exception ex)
{
MessageShow("生成图片错误！" + ex.Message);
throw;
}
graphics.Dispose();
bitmap.Dispose();
}

//缩小为原始图像的1/(X*X)
protected void btnSmall_Click(object sender, EventArgs e)
{
float i = float.Parse(txtBig.Text.Trim());
System.Drawing.Image img = System.Drawing.Image.FromFile(path);
int w = Convert.ToInt32(img.Width / i);
int h = Convert.ToInt32(img.Height / i);

// 防止过度变形
if (w < 1) w = 10;
if (h < 1) h = 0;
bitmap = new Bitmap(w, h);
graphics = Graphics.FromImage(bitmap);
graphics.DrawImage(img, 0, 0, w, h);
try
{
bitmap.Save(Server.MapPath("/upload/tech/20091011/20091011143608_bd686fd640be98efaae0091fa301e613.jpg"), System.Drawing.Imaging.ImageFormat.Jpeg);
MessageShow("已经生成图片，路径为" + @Server.MapPath("/upload/tech/20091011/20091011143608_bd686fd640be98efaae0091fa301e613.jpg").Replace("\\", "\\\\"));

}
catch (Exception ex)
{
MessageShow("生成图片错误！" + ex.Message);
throw;
}
graphics.Dispose();
bitmap.Dispose();
}
//倾斜（ 右转90度）
protected void btnIncline_Click(object sender, EventArgs e)
{
System.Drawing.Image img = System.Drawing.Image.FromFile(path);
// 图像旋转，可以利用RotateFlipType的枚举值，在编程的时候，IDE会自动显示每一个枚举的意思
img.RotateFlip(RotateFlipType.Rotate90FlipXY);
bitmap = new Bitmap(img);
graphics = Graphics.FromImage(bitmap);
graphics.DrawImage(img, new Point(0, 0));
try
{
bitmap.Save(Server.MapPath("/upload/tech/20091011/20091011143609_74bba22728b6185eec06286af6bec36d.jpg"), System.Drawing.Imaging.ImageFormat.Jpeg);
MessageShow("已经生成图片，路径为" + @Server.MapPath("/upload/tech/20091011/20091011143609_74bba22728b6185eec06286af6bec36d.jpg").Replace("\\", "\\\\"));

}
catch (Exception ex)
{
MessageShow("生成图片错误！" + ex.Message);
throw;
}
graphics.Dispose();
bitmap.Dispose();
}

// 图像压扁
protected void btnStave_Click(object sender, EventArgs e)
{
System.Drawing.Image img = System.Drawing.Image.FromFile(path);
// 宽度不变
int w = img.Width;
// 高度为原始高度的1/2
int h = img.Height / 2;

// 防止过度变形
if (w < 1) w = 10;
if (h < 1) h = 0;
bitmap = new Bitmap(w, h);
graphics = Graphics.FromImage(bitmap);
graphics.DrawImage(img, 0, 0, w, h);
try
{
bitmap.Save(Server.MapPath("/upload/tech/20091011/20091011143613_85fc37b18c57097425b52fc7afbb6969.jpg"), System.Drawing.Imaging.ImageFormat.Jpeg);
MessageShow("已经生成图片，路径为" + @Server.MapPath("/upload/tech/20091011/20091011143613_85fc37b18c57097425b52fc7afbb6969.jpg").Replace("\\", "\\\\"));

}
catch (Exception ex)
{
MessageShow("生成图片错误！" + ex.Message);
throw;
}
graphics.Dispose();
bitmap.Dispose();
}
//图像拉宽
protected void btnElongate_Click(object sender, EventArgs e)
{
System.Drawing.Image img = System.Drawing.Image.FromFile(path);
// 放大宽度
int w = img.Width / 2;
// 高度不变
int h = img.Height;

// 防止过度变形
if (w < 1) w = 10;
if (h < 1) h = 0;
bitmap = new Bitmap(w, h);
graphics = Graphics.FromImage(bitmap);
graphics.DrawImage(img, 0, 0, w, h);
try
{
bitmap.Save(Server.MapPath("/upload/tech/20091011/20091011143613_3416a75f4cea9109507cacd8e2f2aefc.jpg"), System.Drawing.Imaging.ImageFormat.Jpeg);
MessageShow("已经生成图片，路径为" + @Server.MapPath("/upload/tech/20091011/20091011143613_3416a75f4cea9109507cacd8e2f2aefc.jpg").Replace("\\", "\\\\"));

}
catch (Exception ex)
{
MessageShow("生成图片错误！" + ex.Message);
throw;
}
graphics.Dispose();
bitmap.Dispose();
}
}

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