代數運算，就是對兩幅圖像的點之間進行加、減、乘、除的運算。四種運算相應的公式為：

代數運算中比較常用的是圖像相加和相減。圖像相加常用來求平均值去除addtive噪聲或者實現二次曝光（double-exposure）。圖像相減用于減去背景或周期噪聲，污染等。

圖像相加

OpenCV中提供了相加的函數 [cpp]?view plaincopy

1. void?cvAcc(???
2. ???????????const?CvArr*?image,//輸入圖像??
3. ???????????CvArr*?sum,??//累積圖像???
4. ???????????const?CvArr*?mask=NULL//可選的運算??
5. ?);??

我們還需要用到一個線性變換轉換函數來對相加的結果求平均 [cpp]?view plaincopy

1. void?cvConvertScale(???
2. ????????const?CvArr*?src,?//輸入數組??
3. ????????CvArr*?dst,//輸出數組??
4. ????????double?scale=1,//比例??
5. ????????double?shift=0?//縮放比例，可選??
6. );??
7. #define?cvCvtScale?cvConvertScale??
8. #define?cvScale??cvConvertScale??
9. #define?cvConvert(?src,?dst?)??cvConvertScale(?(src),?(dst),?1,?0?)??

實踐：平均值去噪

我們用NASA的一段幸運團的視頻做實驗，截取視頻的某幾個連續幀求平均值： [cpp]?view plaincopy

1. int?main()??
2. {??
3. ????CvCapture*?capture=cvCaptureFromFile("media.avi");??
4. ????IplImage*?frame=??NULL;??
5. ????IplImage?*?imgsum?=NULL;??
6. ??????
7. ????int?start=301;??
8. ????int?end=304;??
9. ????cvSetCaptureProperty(capture,?CV_CAP_PROP_POS_FRAMES,?start);??
10. ??????
11. ????int?count?=?start;??
12. ????while(?cvGrabFrame(capture)?&&?count?<=?end?)??
13. ????{??
14. ????????frame?=?cvRetrieveFrame(capture);//?獲取當前幀??
15. ????????if(imgsum==NULL){??
16. ????????????imgsum=cvCreateImage(cvGetSize(frame),IPL_DEPTH_32F,3);??
17. ????????????cvZero(imgsum);??
18. ????????}??
19. ????????cvAcc(frame,imgsum);??
20. ??
21. ????????char?testname[100];??
22. ????????sprintf(testname,"%s%d%s","image",count,".jpg");??
23. ????????cvShowImage(testname,frame);??
24. ????????cvSaveImage(testname,frame);??
25. ??????????
26. ????????count++;??
27. ????}??
28. ????IplImage?*?imgavg?=?cvCreateImage(cvGetSize(frame),IPL_DEPTH_8U,3);??
29. ????cvConvertScale(imgsum,imgavg,1.0/4.0);??
30. ??????
31. ????cvShowImage("imageavg",imgavg);??
32. ????cvSaveImage("imageavg_4.jpg",imgavg);??
33. ??????
34. ????cvWaitKey(0);??
35. ????cvReleaseCapture(&capture);??
36. ????return?0;??
37. }??

以下從左到右分別是連續兩幀、四幀、八幀、十六幀求均值的結果： ? ?
? ?

實踐：圖像二次曝光

曝光和去噪是一樣的，也是對幾幅圖像求平均 [cpp]?view plaincopy

1. //通過求平均二次曝光??
2. int?main()??
3. {??
4. ????IplImage*?image1=??cvLoadImage("psu3.jpg");??
5. ????IplImage*?image2=??cvLoadImage("psu4.jpg");??
6. ??????
7. ????IplImage?*?imgsum?=cvCreateImage(cvGetSize(image1),IPL_DEPTH_32F,3);??
8. ????cvZero(imgsum);??
9. ????cvAcc(image1,imgsum);??
10. ????cvAcc(image2,imgsum);??
11. ??
12. ????IplImage?*?imgavg?=?cvCreateImage(cvGetSize(image1),IPL_DEPTH_8U,3);??
13. ????cvConvertScale(imgsum,imgavg,1.0/2.0);??
14. ??
15. ????cvShowImage("imageavg",imgavg);??
16. ????cvSaveImage("avg.jpg",imgavg);??
17. ??
18. ????cvWaitKey(0);??
19. ????cvReleaseImage(&image1);??
20. ????cvReleaseImage(&image2);??
21. ????cvReleaseImage(&imgsum);??
22. ????cvReleaseImage(&imgavg);??
23. ????return?0;??
24. }??

下圖是對同學街舞截圖的“二次曝光”效果：

圖像相減

OpenCV中用cvAbsDiff函數計算兩數組的差的絕對值 [cpp]?view plaincopy

1. void?cvAbsDiff(???
2. ????????const?CvArr*?src1,//第一個輸入數組??
3. ????????const?CvArr*?src2,//第二個輸入數組??
4. ????????CvArr*?dst//輸出數組??
5. );??

實踐：減去背景

減去背景是通過兩幅圖像代數相減，可以判斷出前景區域和運動區域，這是最簡單（很多時候也是效果很好的）運動檢測方法。 [cpp]?view plaincopy

1. //減去背景??
2. int?main()??
3. {??
4. ????IplImage*?pFrame?=?NULL;???
5. ????IplImage*?pFrImg?=?NULL;??
6. ????IplImage*?pBkImg?=?NULL;??
7. ??
8. ????CvMat*?pFrameMat?=?NULL;??
9. ????CvMat*?pFrMat?=?NULL;??
10. ????CvMat*?pBkMat?=?NULL;??
11. ??
12. ????CvCapture*?pCapture?=?NULL;??
13. ??
14. ????int?nFrmNum?=?0;??
15. ??
16. ????//創建窗口??
17. ????cvNamedWindow("video",?1);??
18. ????cvNamedWindow("background",1);??
19. ????cvNamedWindow("foreground",1);??
20. ??
21. ????pCapture?=?cvCaptureFromFile("media.avi");??
22. ????while(pFrame?=?cvQueryFrame(?pCapture?))??
23. ????{??
24. ????????nFrmNum++;??
25. ??
26. ????????//如果是第一幀，需要申請內存，并初始化??
27. ????????if(nFrmNum?==?1)??
28. ????????{??
29. ????????????pBkImg?=?cvCreateImage(cvSize(pFrame->width,?pFrame->height),??IPL_DEPTH_8U,1);??
30. ????????????pFrImg?=?cvCreateImage(cvSize(pFrame->width,?pFrame->height),??IPL_DEPTH_8U,1);??
31. ??
32. ????????????pBkMat?=?cvCreateMat(pFrame->height,?pFrame->width,?CV_32FC1);??
33. ????????????pFrMat?=?cvCreateMat(pFrame->height,?pFrame->width,?CV_32FC1);??
34. ????????????pFrameMat?=?cvCreateMat(pFrame->height,?pFrame->width,?CV_32FC1);??
35. ??
36. ????????????//轉化成單通道圖像再處理??
37. ????????????cvCvtColor(pFrame,?pBkImg,?CV_BGR2GRAY);??
38. ????????????cvCvtColor(pFrame,?pFrImg,?CV_BGR2GRAY);??
39. ??
40. ????????????cvConvert(pFrImg,?pFrameMat);??
41. ????????????cvConvert(pFrImg,?pFrMat);??
42. ????????????cvConvert(pFrImg,?pBkMat);??
43. ????????}??
44. ????????else??
45. ????????{??
46. ????????????cvCvtColor(pFrame,?pFrImg,?CV_BGR2GRAY);??
47. ????????????cvConvert(pFrImg,?pFrameMat);??
48. ????????????//當前幀跟背景圖相減??
49. ????????????cvAbsDiff(pFrameMat,?pBkMat,?pFrMat);??
50. ????????????//二值化前景圖??
51. ????????????cvThreshold(pFrMat,?pFrImg,?60,?255.0,?CV_THRESH_BINARY);??
52. ????????????//更新背景??
53. ????????????cvRunningAvg(pFrameMat,?pBkMat,?0.003,?0);??
54. ????????????//將背景轉化為圖像格式，用以顯示??
55. ????????????cvConvert(pBkMat,?pBkImg);??
56. ??
57. ????????????cvShowImage("video",?pFrame);??
58. ????????????cvShowImage("background",?pBkImg);??
59. ????????????cvShowImage("foreground",?pFrImg);??
60. ??
61. ????????????if(?cvWaitKey(2)?>=?0?)??
62. ????????????????break;??
63. ????????}??
64. ????}??
65. ????cvDestroyWindow("video");??
66. ????cvDestroyWindow("background");??
67. ????cvDestroyWindow("foreground");??
68. ????cvReleaseImage(&pFrImg);??
69. ????cvReleaseImage(&pBkImg);??
70. ????cvReleaseMat(&pFrameMat);??
71. ????cvReleaseMat(&pFrMat);??
72. ????cvReleaseMat(&pBkMat);??
73. ????cvReleaseCapture(&pCapture);??
74. ????return?0;??
75. }??

效果圖：

轉載請注明出處：http://blog.csdn.net/xiaowei_cqu/article/details/7610665
實驗代碼及視頻下載：http://download.csdn.net/detail/xiaowei_cqu/4335573

轉載于:https://www.cnblogs.com/alan666/p/8312343.html

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