等比例缩放图片（C#）

1. private Bitmap ZoomImage(Bitmap bitmap, int destHeight, int destWidth)
2. {
3. try
4. {
5. System.Drawing.Image sourImage = bitmap;
6. int width = 0, height = 0;
7. //按比例缩放
8. int sourWidth = sourImage.Width;
9. int sourHeight = sourImage.Height;
10. if (sourHeight > destHeight || sourWidth > destWidth)
11. {
12. if ((sourWidth * destHeight) > (sourHeight * destWidth))
13. {
14. width = destWidth;
15. height = (destWidth * sourHeight) / sourWidth;
16. }
17. else
18. {
19. height = destHeight;
20. width = (sourWidth * destHeight) / sourHeight;
21. }
22. }
23. else
24. {
25. width = sourWidth;
26. height = sourHeight;
27. }
28. Bitmap destBitmap = new Bitmap(destWidth, destHeight);
29. Graphics g = Graphics.FromImage(destBitmap);
30. g.Clear(Color.Transparent);
31. //设置画布的描绘质量
32. g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
33. g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
34. g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
35. g.DrawImage(sourImage, new Rectangle((destWidth - width) / 2, (destHeight - height) / 2, width, height), 0, 0, sourImage.Width, sourImage.Height, GraphicsUnit.Pixel);
36. g.Dispose();
37. //设置压缩质量
38. System.Drawing.Imaging.EncoderParameters encoderParams = new System.Drawing.Imaging.EncoderParameters();
39. long[] quality = new long[1];
40. quality[0] = 100;
41. System.Drawing.Imaging.EncoderParameter encoderParam = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
42. encoderParams.Param[0] = encoderParam;
43. sourImage.Dispose();
44. return destBitmap;
45. }
46. catch
47. {
48. return bitmap;
49. }
50. }