opencv tutorial 1 chap no.1 and 2

6/1/2015 OpenCVTutorial1

http://dasl.mem.drexel.edu/~noahKuntz/openCVTut1.html 1/5

OpenCVTutorial1Chapters1and2Author:NoahKuntz(2008)Contact:nk752@drexel.edu

Keywords:OpenCV,computervision,imagemanipulaton,gaussianblur,avi

MyVisionTutorialsIndex

Thistutorialassumesthereader:(1)HasabasicknowledgeofVisualC++(2)Hassomefamiliaritywithcomputervisionconcepts

Therestofthetutorialispresentedasfollows:

Step1:InstallingOpenCVStep2:DisplayingImagesandVideoStep3:SimpleTransformationsFinalWords

ImportantNote!

Moreinformationonthetopicsofthesetutorialscanbefoundinthisbook:LearningOpenCV:ComputerVisionwiththeOpenCVLibrary

Step1:InstallingOpenCV

InstallMSVC++onwindowsandGCCorGLIBConLinux.

DownloadOpenCVfromsourceforge

Useopencvwinoropencvlindependingonyourplatformofchoice.

OptionallyyoumaypurchaseIntelIntegratedPerformancePrimitives(IPP)whichoptimizestheperformanceofOpenCV.IntelIPP

OptionallyupdateOpenCVusingthe"ConcurrentVersionsSystem,"withsoftwarelikeTortoiseCVS.

NowyoumustcreateaC++projectandlinkthecorrectfiles.Theseheadersshouldbelinked:

#include"C:\ProgramFiles\OpenCV\cv\include\cv.h"#include"C:\ProgramFiles\OpenCV\ml\include\ml.h"#include"C:\ProgramFiles\OpenCV\cxcore\include\cxcore.h"#include"C:\ProgramFiles\OpenCV\cxcore\include\cxtypes.h"#include"C:\ProgramFiles\OpenCV\otherlibs\highgui\highgui.h"

Linktocv.lib,ml.lib,cxcore.lib,andhighgui.libMakesuretochangetheenvironmentvariabletoPATH=C:\ProgramFiles\OpenCV\bin

Step2:DisplayingImagesandVideo

6/1/2015 OpenCVTutorial1

http://dasl.mem.drexel.edu/~noahKuntz/openCVTut1.html 2/5

AnimagedisplayedwithOpenCV

ThefirstthingwecandowithOpenCVissimplyaccessanimage.Thiscodewilldisplayatheimage"MGC.jpg"inawindow.cvLoadImageloadstheimageintoanIplImage*variable.cvNamedWindowcreatesawindowandcvShowImagepaintstheimageonthewindow.ThencvWaitKey(0)waitsforanykeytobepressedatwhichpointthememoryisreleasedandthewindowisclearedwithcvReleaseImageandcvDestroyWindow.

int_tmain(intargc,_TCHAR*argv[]){ IplImage*img=cvLoadImage("MGC.jpg"); cvNamedWindow("Example1",CV_WINDOW_AUTOSIZE); cvShowImage("Example1",img); cvWaitKey(0); cvReleaseImage(&img); cvDestroyWindow("Example1"); return0;}

Thenextstepistodisplayavideo.NowwehavetocreateaCvCapture*objectwithcvCreateFileCapture.WeloopthroughtheimagesusingcvQueryFrametogeteachframeandcvWaitKey(33)towait33msbetweeneachframe.TheniftheuserpressesEsctheloopbreaksandthecaptureisreleasedandthewindowclosed.Itshouldbenotedthatinordertocapturefromacamerainsteadofavideofile,allthatisneededistoreplacecvCreateFileCapturewithcvCreateCameraCapture(0)whichwillpickthefirstavailablecamerainterface.Hereisthecodeforplayingavideo:

int_tmain(intargc,_TCHAR*argv[]){ cvNamedWindow("Example2",CV_WINDOW_AUTOSIZE); CvCapture*capture=cvCreateFileCapture("MGC_RC_ATV.avi"); IplImage*frame; while(1){ frame=cvQueryFrame(capture); if(!frame)break; cvShowImage("Example2",frame); charc=cvWaitKey(33); if(c==27)break; } cvReleaseCapture(&capture); cvDestroyWindow("Example2"); return0;}

Step3:SimpleTransformations

6/1/2015 OpenCVTutorial1

http://dasl.mem.drexel.edu/~noahKuntz/openCVTut1.html 3/5

Gaussianblurtransformation

Nextwewouldliketobeabletodosomeactualprocessingonanimage.Onesimpletransformationisagaussianblur.Firstweloadanimageasbefore,andmaketwowindows.Anewfunctioninthisexampleiscreatinganemptyimagetoholdtheoutput,withcvCreateImage(cvGetSize(img),IPL_DEPTH_8U,3)whichissayingmakeanewimagethesamesizeas"img",with3channelsof8bitseach.ThenthegaussianblurisaccomplishedwithcvSmooth(img,out,CV_GAUSSIAN,11,11)whichputstheresultin"out"andusesawindowof11x11fortheblur.Hereisthecode:

int_tmain(intargc,_TCHAR*argv[]){ IplImage*img=cvLoadImage("MGC.jpg"); cvNamedWindow("Example3in"); cvNamedWindow("Example3out");

//Showtheoriginalimage cvShowImage("Example3in",img);

//Createanimagefortheoutput IplImage*out=cvCreateImage(cvGetSize(img),IPL_DEPTH_8U,3);

//PerformaGaussianblur cvSmooth(img,out,CV_GAUSSIAN,11,11);

//Showtheprocessedimage cvShowImage("Example3out",out);

cvWaitKey(0); cvReleaseImage(&img); cvReleaseImage(&out); cvDestroyWindow("Example3in"); cvDestroyWindow("Example3out"); return0;}

6/1/2015 OpenCVTutorial1

http://dasl.mem.drexel.edu/~noahKuntz/openCVTut1.html 4/5

DownsampleandCannytransformation

Hereisanexampleofmoretransformations,doingapyramidaldownsampleofanimage,andperformingCannyedgedetection.Thereareafewnewthingsinthisexample.Byaddinganinputof0tocvLoadImagetheimageisforcedtobegrayscale.ThisisrequiredforCannyedgedetection.Alsoweusepropertiesoftheimageloaded,forexample"img>width."Using">"youcanseeallthepropertiesfortheimagethatareavailable.AndthentheimageisprocessedusingcvPyrDown(img,out)forthedownsample,andthencvCanny(out,out,10,100,3)fortheedgedetection.Forthecannyfunctionthesyntaxis"input,""output,""lowerthreshold,""upperthreshold,"and"aperature."

int_tmain(intargc,_TCHAR*argv[]){ IplImage*img=cvLoadImage("MGC.jpg",0); cvNamedWindow("Example4in"); cvNamedWindow("Example4out");

//Showtheoriginalimage cvShowImage("Example4in",img);

//Makesureimageisdivisibleby2 assert(img>width%2==0&&img>height%2==0);

//Createanimagefortheoutput IplImage*out=cvCreateImage(cvSize(img>width/2,img>height/2),img>depth,img>nChannels);

//Reducetheimageby2 cvPyrDown(img,out); //Performcannyedgedetection cvCanny(out,out,10,100,3);

//Showtheprocessedimage cvShowImage("Example4out",out);

cvWaitKey(0); cvReleaseImage(&img); cvReleaseImage(&out); cvDestroyWindow("Example4in"); cvDestroyWindow("Example4out");

return0;}

FinalWords

Thistutorial'sobjectivewastoshowhowtodobasicimageloadingandprocessinginOpenCV.Latertutorialsinthisserieswillexpandonthefunctionalityshownhere.

Clickheretoemailme.ClickheretoreturntomyTutorialspage.

hitcounter

6/1/2015 OpenCVTutorial1

http://dasl.mem.drexel.edu/~noahKuntz/openCVTut1.html 5/5

htmlhitcountercode