C#等比例缩放图片

1. 等比例缩放图片（C#）

2. private Bitmap ZoomImage(Bitmap bitmap, int destHeight, int destWidth)
3. {
4. try
5. {
6. System.Drawing.Image sourImage = bitmap;
7. int width = 0, height = 0;
8. //按比例缩放
9. int sourWidth = sourImage.Width;
10. int sourHeight = sourImage.Height;
11. if (sourHeight > destHeight || sourWidth > destWidth)
12. {
13. if ((sourWidth * destHeight) > (sourHeight * destWidth))
14. {
15. width = destWidth;
16. height = (destWidth * sourHeight) / sourWidth;
17. }
18. else
19. {
20. height = destHeight;
21. width = (sourWidth * destHeight) / sourHeight;
22. }
23. }
24. else
25. {
26. width = sourWidth;
27. height = sourHeight;
28. }
29. Bitmap destBitmap = new Bitmap(destWidth, destHeight);
30. Graphics g = Graphics.FromImage(destBitmap);
31. g.Clear(Color.Transparent);
32. //设置画布的描绘质量
33. g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
34. g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
35. g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
36. g.DrawImage(sourImage, new Rectangle((destWidth - width) / 2, (destHeight - height) / 2, width, height), 0, 0, sourImage.Width, sourImage.Height, GraphicsUnit.Pixel);
37. g.Dispose();
38. //设置压缩质量
39. System.Drawing.Imaging.EncoderParameters encoderParams = new System.Drawing.Imaging.EncoderParameters();
40. long[] quality = new long[1];
41. quality[0] = 100;
42. System.Drawing.Imaging.EncoderParameter encoderParam = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
43. encoderParams.Param[0] = encoderParam;
44. sourImage.Dispose();
45. return destBitmap;
46. }
47. catch
48. {
49. return bitmap;
50. }
51. }