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.net中上传图片时，怎样将宽度大于640px的自动生成宽为640px的等比例图片。哪位能帮写一下代码

用System. Drawing. Graphics可以生成缩略图，下面是大概的代码。（没调试过）

use System.Drawing;

string imagePath = 'img/1.jpg'; //原图路径
string thumPath = 'img/1_s.jpg'; //缩略图保存路径
int thumWidth = img.Width / 2; //缩略图宽度

int thumHeight = img.Height * thumWidth / img.Width;
Image img = Image.FromFile(Server.MapPath(imagePath));
Image bitmap = new Bitmap(thumWidth, thumHeight);
Graphics graphic = Graphics.FromImage(bitmap);
graphic.DrawImage(img, new Rectangle(0, 0, thumWidth, thumHeight), new Rectangle(0, 0, img.Width, img.Height), GraphicsUnit.Pixel);
bitmap.Save(Server.MapPath(thumPath));
graphic.Dispose();
bitmap.Dispose();
img.Dispose();