等比例压缩图片

//生成缩略图函数 //顺序参数：源图文件流、缩略图存放地址、模版宽、模版高 //注：缩略图大小控制在模版区域内 public static void MakeSmallImg(System.IO.Stream fromFileStream, string fileSaveUrl, System.Double templateWidth, System.Double templateHeight) { //从文件取得图片对象，并使用流中嵌入的颜色管理信息 System.Drawing.Image myImage = System.Drawing.Image.FromStream(fromFileStream, true); //缩略图宽、高 System.Double newWidth = myImage.Width, newHeight = myImage.Height; //宽大于模版的横图 if (myImage.Width > myImage.Height || myImage.Width == myImage.Height) { if (myImage.Width > templateWidth) { //宽按模版，高按比例缩放 newWidth = templateWidth; newHeight = myImage.Height * (newWidth / myImage.Width); } } //高大于模版的竖图 else { if (myImage.Height > templateHeight) { //高按模版，宽按比例缩放 newHeight = templateHeight; newWidth = myImage.Width * (newHeight / myImage.Height); } } //取得图片大小 System.Drawing.Size mySize = new Size((int)newWidth, (int)newHeight); //新建一个bmp图片 System.Drawing.Image bitmap = new System.Drawing.Bitmap(mySize.Width, mySize.Height); //新建一个画板 System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap); //设置高质量插值法 g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High; //设置高质量,低速度呈现平滑程度 g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality; //清空一下画布 g.Clear(Color.White); //在指定位置画图 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("宋体",10); //System.Drawing.Brush b=new SolidBrush(Color.Black); //G.DrawString("myohmine",f,b,10,10); //G.Dispose(); ///图片水印 //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(); //保存缩略图 bitmap.Save(fileSaveUrl, System.Drawing.Imaging.ImageFormat.Jpeg); g.Dispose(); myImage.Dispose(); bitmap.Dispose(); } private void button2_Click(object sender, EventArgs e) { OpenFileDialog fileDialog = new OpenFileDialog(); fileDialog.Title = "选择图片文件"; // 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, "缩略图.jpg", 150, 150); // file.Close(); } } 详细出处参考：http://www.jb51.net/article/22515.htm