图片的按比例缩小.

1. public static byte[] ResizeImageFile(byte[] imageFile, int targetSizeW, int targetSizeH)
2.     {
3.         System.Drawing.Image original = System.Drawing.Image.FromStream(new MemoryStream(imageFile));
4.         int targetH, targetW;
5.         targetW = targetSizeW;
6.         targetH = (int)(original.Height * ((float)targetSizeW / (float)original.Width));
7.         if (targetH > targetSizeH)
8.         {
9.             targetH = targetSizeH;
10.             targetW = (int)(original.Width * ((float)targetSizeH / (float)original.Height));
11.         }
13.         if (targetSizeW < (int)original.Width || targetSizeH < (int)original.Height)
14.         {
15.             System.Drawing.Image imgPhoto = System.Drawing.Image.FromStream(new MemoryStream(imageFile));
16.             // Create a new blank canvas.  The resized image will be drawn on this canvas.
17.             Bitmap bmPhoto = new Bitmap(targetW, targetH, PixelFormat.Format24bppRgb);
18.             bmPhoto.SetResolution(72, 72);
19.             Graphics grPhoto = Graphics.FromImage(bmPhoto);
20.             grPhoto.SmoothingMode = SmoothingMode.AntiAlias;
21.             grPhoto.InterpolationMode = InterpolationMode.HighQualityBicubic;
22.             grPhoto.PixelOffsetMode = PixelOffsetMode.HighQuality;
23.             grPhoto.DrawImage(imgPhoto, new Rectangle(0, 0, targetW, targetH), 0, 0, original.Width, original.Height, GraphicsUnit.Pixel);
24.             // Save out to memory and then to a file.  We dispose of all objects to make sure the files don't stay locked.
25.             MemoryStream mm = new MemoryStream();
26.             bmPhoto.Save(mm, System.Drawing.Imaging.ImageFormat.Jpeg);
27.             original.Dispose();
28.             imgPhoto.Dispose();
29.             bmPhoto.Dispose();
30.             grPhoto.Dispose();
31.             return mm.GetBuffer();
32.         }
33.         else
34.         {
35.             return imageFile;
36.         }
37.     }