代碼如下:

//生成縮略圖函數 
//順序參數：源圖文件流、縮略圖存放地址、模版寬、模版高 
//注：縮略圖大小控制在模版區域內 
public static void MakeSmallImg(System.IO.Stream fromFileStream, string fileSaveUrl, System.Double templateWidth, System.Double templateHeight) 
{ 
//從文件取得圖片對象，并使用流中嵌入的顏色管理信息 
System.Drawing.Image myImage = System.Drawing.Image.FromStream(fromFileStream, true); 
//縮略圖寬、高 
System.Double newWidth = myImage.Width, newHeight = myImage.Height; 
//寬大于模版的橫圖 
if (myImage.Width > myImage.Height || myImage.Width == myImage.Height) 
{ 
if (myImage.Width > templateWidth) 
{ 
//寬按模版，高按比例縮放 
newWidth = templateWidth; 
newHeight = myImage.Height * (newWidth / myImage.Width); 
} 
} 
//高大于模版的豎圖 
else 
{ 
if (myImage.Height > templateHeight) 
{ 
//高按模版，寬按比例縮放 
newHeight = templateHeight; 
newWidth = myImage.Width * (newHeight / myImage.Height); 
} 
} 
//取得圖片大小 
System.Drawing.Size mySize = new Size((int)newWidth, (int)newHeight); 
//新建一個bmp圖片 
System.Drawing.Image bitmap = new System.Drawing.Bitmap(mySize.Width, mySize.Height); 
//新建一個畫板 
System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap); 
//設置高質量插值法 
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High; 
//設置高質量,低速度呈現平滑程度 
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality; 
//清空一下畫布 
g.Clear(Color.White); 
//在指定位置畫圖 
g.DrawImage(myImage, new System.Drawing.Rectangle(0, 0, bitmap.Width, bitmap.Height), 
new System.Drawing.Rectangle(0, 0, myImage.Width, myImage.Height), 
System.Drawing.GraphicsUnit.Pixel); 
///文字水印 
//System.Drawing.Graphics G=System.Drawing.Graphics.FromImage(bitmap); 
//System.Drawing.Font f=new Font("宋體",10); 
//System.Drawing.Brush b=new SolidBrush(Color.Black); 
//G.DrawString("myohmine",f,b,10,10); 
//G.Dispose(); 
///圖片水印 
//System.Drawing.Image copyImage = System.Drawing.Image.FromFile(System.Web.HttpContext.Current.Server.MapPath("pic/1.gif")); 
//Graphics a = Graphics.FromImage(bitmap); 
//a.DrawImage(copyImage, new Rectangle(bitmap.Width-copyImage.Width,bitmap.Height-copyImage.Height,copyImage.Width, copyImage.Height),0,0, copyImage.Width, copyImage.Height, GraphicsUnit.Pixel); 
//copyImage.Dispose(); 
//a.Dispose(); 
//copyImage.Dispose(); 
//保存縮略圖 
bitmap.Save(fileSaveUrl, System.Drawing.Imaging.ImageFormat.Jpeg); 
g.Dispose(); 
myImage.Dispose(); 
bitmap.Dispose(); 
}

復制代碼代碼如下:

private void button2_Click(object sender, EventArgs e) 
{ 
OpenFileDialog fileDialog = new OpenFileDialog(); 
fileDialog.Title = "選擇圖片文件"; 
// fileDialog.Filter = "excel files (*.xls)|*.xls"; 
fileDialog.FilterIndex = 1; 
if (fileDialog.ShowDialog() == System.Windows.Forms.DialogResult.OK) 
{ 

System.IO.FileStream file =System.IO.File.Open(fileDialog.FileName,System.IO.FileMode.Open); 
System.IO.Stream strea = file; 
file.Close(); 
MakeSmallImg(strea, "縮略圖.jpg", 150, 150); 
// file.Close(); 

} 
}