OpenCV Workshop

OpenCV C++ Workshop
Lentin Joseph
Founder of Qbotics Labs
www.qboticslabs.com

About OpenCV
●
Open Source Computer Vision library
●
Real-time Computer vision library
●
Started by Intel Russia, launched in 1999
●
2000 : First alpha release
●
2006: First stable release
●
2009: Second major release
http://www.qboticslabs.com

About OpenCV
●
2012 : opencv -> opencv.org
●
Current version : OpenCV 3.0 beta
●
Opensource BSD license
●
Cross platform
●
Now supporting by Willow Garage and Itseez

About OpenCV
●
Written in C++ and C
●
Full Interfaces for Python, Java, Matlab/
Octave
●
Wrappers in C#, Perl, Ruby
●
OS Support : Windows, Linux, Android, Maemo,
FreeBSD, IOS, OS X, BlackBerry 10

Applications of OpenCV
●
Gesture recognition
●
Human-computer interaction(HCI)
●
Mobile robotics
●
Segmentation and recognition
●
Motion tracking
●
Augmented reality
●
Machine learning

Installing OpenCV
●
Installing from source code
●
Installing from Ubuntu packages

Installing OpenCV from Ubuntu
packages
$ sudo apt-get update
$ sudo apt-get install
libopencv-dev

Installing OpenCV from source
code
●
Install prerequisites packages
● [compiler] sudo apt-get install build-essential
● [required] sudo apt-get install cmake git
libgtk2.0-dev pkg-config libavcodec-dev
libavformat-dev libswscale-dev
● [optional] sudo apt-get install python-dev python-
numpy libtbb2 libtbb-dev libjpeg-dev libpng-dev
libtiff-dev libjasper-dev libdc1394-22-dev

code
● cd ~/opencv
● git clone https://github.com/Itseez/opencv.git
● mkdir release
● cd release
● cmake -D CMAKE_BUILD_TYPE=RELEASE -D
CMAKE_INSTALL_PREFIX=/usr/local -D WITH_TBB=ON -D
BUILD_NEW_PYTHON_SUPPORT=ON -D WITH_V4L=ON -D
INSTALL_C_EXAMPLES=ON -D INSTALL_PYTHON_EXAMPLES=ON -D
BUILD_EXAMPLES=ON -D WITH_QT=ON -D WITH_OPENGL=ON ..
● make

code
● cd ~/opencv
● git clone https://github.com/Itseez/opencv.git
● mkdir release
● sudo apt-get install cmake-qt-gui
●

code

Check OpenCV is installed !!!
● $ pkg-config opencv –cflags
$ pkg-config opencv --libs

Setting OpenCV in Eclipse
●
Install OpenJDK from Ubuntu Software

Check Ubuntu Version !!!
●
System settings -> Details -> Overview

Download Eclipse
●
http://www.eclipse.org/downloads/

Extract and Install Eclipse
● cd /opt/ && sudo tar -zxvf
~/Downloads/eclipse-*.tar.gz
●
Without using command
● $ gksudo nautilus

Adding Shortcut for Eclipse
● $ gksudo gedit /usr/share/applications/eclipse.desktop
●
Paste the following to this file
[Desktop Entry]
Name=Eclipse 4
Type=Application
Exec=/opt/eclipse/eclipse
Terminal=false
Icon=/opt/eclipse/icon.xpm
Comment=Integrated Development Environment
NoDisplay=false
Categories=Development;IDE;
Name[en]=Eclipse

●
Setting Include path
– Properties -> C/C++ Build->Settings->Cross G++
Compiler->Includes
– $ pkg-config opencv --cflags

●
Setting Lib path and libraries
– Properties -> C/C++ Build->Settings->Cross G++
Compiler->Libraries
– $ pkg-config opencv --libs

Running test code !!!
●
Reading an Image
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
using namespace cv;
using namespace std;
int main( int argc, char** argv )
{
if( argc != 2)
{
cout <<" Usage: display_image ImageToLoadAndDisplay" << endl;
return -1;
}
Mat image;
image = imread(argv[1], CV_LOAD_IMAGE_COLOR); // Read the file
if(! image.data ) // Check for invalid input
{
cout << "Could not open or find the image" << std::endl ;
return -1;
}
namedWindow( "Display window", WINDOW_AUTOSIZE );// Create a window for display.
imshow( "Display window", image ); // Show our image inside it.
waitKey(0); // Wait for a keystroke in the window
return 0;
}

Running test code !!!
●
Setting command line argument
– Project -> Run as-> Run Configurations

Compile code without Eclipse
●
Save code as .cpp using an text editor
●
Compile using following command
● $ g++ <input_file.cpp> `pkg-config
opencv –cflags –libs` -o
<output_name>
● $ ./output_name

OpenCV Modules
●
OpenCV has modular structure
●
OpenCV contain several shared/static libraries
● Core : Contain basic image data structure such as
Mat
● Imgproc : image processing module contain linear
and non linear filter, color space conversion,
histogram etc
● Video : Motion estimation, background substraction,
object tracking algorithms etc

OpenCV Modules
● Calib3d : mainly for camera calibration
● Features2d : contain feature detectors,
descriptors and descriptor matchers
● Objdetect: contain object detection algorithms
● Highgui: contain UI functionality to handle video
and image
● Gpu : GPU-accelerated algorithms

About OpenCV API's
● All OpenCV classes are placed in cv
namespace

Reading an Image
OpenCV Header Files Used
● #include <opencv2/highgui/highgui.hpp>
OpenCV API's used
● imread(file_name,flags)
● imshow(“window_title”,image_variable)
● namedWindow(“window_title”,flags)
● WaitKey(0)
● Refer
http://docs.opencv.org/modules/refman.html

Reading a Video
OpenCV API's used
● VideoCapture cap(argv[1])
● waitKey(30)

Reading from Camera
OpenCV API's used
● VideoCapture cap(argv[1])
● waitKey(30)

Reading Pixel from Image and
Mouse Interaction
OpenCV API's used
● image.at<uchar>(y,x);
● image.at<Vec3b>(y,x)[0];
● setMouseCallback("Display window",
mouse_callback, NULL);

Working with Mat type
OpenCV API's used
● Mat red(480,640,CV_8UC3,Scalar(0,0,255));
● imwrite("red.jpg",red);

Adjusting brightness and contrast
OpenCV API's used
● new_image.at<Vec3b>(y,x)[c] =
saturate_cast<uchar>( alpha*( image.at<Vec3b>(y
,x)[c] ) + beta );
● Alpha = contrast
● Beta = Brightness
● saturate_cast ensure value is valid or not

Image Smoothing demo
● #include "opencv2/imgproc/imgproc.hpp"
● #include "opencv2/highgui/highgui.hpp"
OpenCV API's used
● Blur
● GaussianBlur
● MedianBlur
● bilateralFilter

Segmentation: Thresholding
OpenCV API's used
● cvtColor( src, src_gray, CV_RGB2GRAY );
● threshold( src_gray, dst, threshold_value,
max_BINARY_value,threshold_type );
● createTrackbar( trackbar_value,
window_name,&threshold_value,
max_value, Threshold_Demo );

Edge Detection
OpenCV API's used
● Canny( detected_edges, detected_edges,
lowThreshold, lowThreshold*ratio,
kernel_size );

Laplace & Sobel
OpenCV API's used
● Sobel( src_gray, grad_x, ddepth, 1, 0, 3,
scale, delta, BORDER_DEFAULT );
● Laplacian( src_gray, dst, ddepth, kernel_size,
scale, delta, BORDER_DEFAULT );

Hough Transform(Circle & Line)
OpenCV API's used
● HoughCircles( src_gray, circles,
CV_HOUGH_GRADIENT, 1, src_gray.rows/8,
cannyThreshold, accumulatorThreshold, 0, 0 );
● HoughLines( edges, s_lines, 1, CV_PI/180,
min_threshold + s_trackbar, 0, 0 );

Contour Detection
OpenCV API's used
● findContours( canny_output, contours,
hierarchy, CV_RETR_TREE,
CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );

Histogram
OpenCV API's used
● calcHist( &bgr_planes[0], 1, 0, Mat(), b_hist,
1, &histSize, &histRange, uniform,
accumulate );

Harris_Corner_Detection
OpenCV API's used
● cornerHarris( src_gray, dst, blockSize,
apertureSize, k, BORDER_DEFAULT );

Motion Detection, LK,FB,BS
● #include "opencv2/video/tracking.hpp"
OpenCV API's used
● calcOpticalFlowPyrLK(prevGray, gray, points[0],
points[1], status, err, winSize,
● calcOpticalFlowFarneback(prevgray, gray, flow,
0.5, 3, 15, 3, 5, 1.2, 0);
● cvCalcMotionGradient( mhi, mask, orient,
MAX_TIME_DELTA, MIN_TIME_DELTA, 3 );

Face Detection
● #include "opencv2/objdetect/objdetect.hpp"
OpenCV API's used
● cascade.detectMultiScale( smallImg, faces2,
1.1, 2, 0 |CV_HAAR_SCALE_IMAGE, Size(30,
30) );

Conclusion
●
Discussed basics of Computer Vision
●
Discussed about OpenCV
●
Discussed OpenCV programming using C++
●
Discussed basic level examples to advanced
level

Thanks !!!
Lentin Joseph
Founder of QboticsLabs
http://www.lentinjoseph.com

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