ASP.NET產生高品質縮圖通用函數(c#程式碼)

在網站開發時,生成縮圖是一個非常常見和實用的功能.以前在asp裡只能藉助com組件實現,現在在.net裡可以利用框架的強大的類庫輕鬆實現.下面帖出完整的代碼(帶詳細註釋),參考了網上的一些文章及.net sdk相關內容.QQROOM網絡家園的圖片上傳用到了所有的4種生成方式.
/// <summary>
/// 產生縮圖
/// </summary>
/// <param name="originalImagePath">來源圖路徑（物理路徑）</param>
/// <param name="thumbnailPath">縮圖路徑（物理路徑）</param>
/// <param name="width">縮圖寬度</param>
/// <param name="height">縮圖高度</param>
/// <param name="mode">產生縮圖的方式</param>
public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)
{
Image originalImage = Image.FromFile(originalImagePath);

int towidth = width;
int toheight = height;

int x = 0;
int y = 0;
int ow = originalImage.Width;
int oh = originalImage.Height;

switch (mode)
{
case "HW"://指定高寬縮放（可能變形）
break;
case "W"://指定寬，高比例
toheight = originalImage.Height * width/originalImage.Width;
break;
case "H"://指定高，寬按比例
towidth = originalImage.Width * height/originalImage.Height;
break;
case "Cut"://指定高寬裁減（不變形）
if((double)originalImage.Width/(double)originalImage.Height > (double)towidth/(double)toheight)
{
oh = originalImage.Height;
ow = originalImage.Height*towidth/toheight;
y = 0;
x = (originalImage.Width - ow)/2;
}
else
{
ow = originalImage.Width;
oh = originalImage.Width*height/towidth;
x = 0;
y = (originalImage.Height - oh)/2;
}
break;
default :
break;
}

//新建一個bmp圖片
Image bitmap = new System.Drawing.Bitmap(towidth,toheight);

//新建一個畫板
Graphics g = System.Drawing.Graphics.FromImage(bitmap);

//設定高品質插值法
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

//設定高品質,低速度呈現平滑程度
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

//清空畫布並以透明背景色填充
g.Clear(Color.Transparent);

//在指定位置並且按指定大小繪製原始圖片的指定部分
g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight),
new Rectangle(x, y, ow,oh),
GraphicsUnit.Pixel);

try
{
//以jpg格式儲存縮圖
bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
}
catch(System.Exception e)
{
throw e;
}
finally
{
originalImage.Dispose();
bitmap.Dispose();
g.Dispose();
}
}

關鍵方法Graphics.DrawImage見ms-help://MS.NETFrameworkSDKv1.1.CHS/cpref/html/frlrfsystemdrawinggraphicsclassdrawimagetopic11.htm

http://www.cnblogs.com/jialine/archive/2006/09/15/505459. html