Introduction to OpenCV (with Java)

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A brief introduction to OpenCV 2.x (with Java) for the Computer Vision course at Politecnico di Torino (academic year 2013/2014).

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Introduction to OpenCV (with Java)

  1. 1. Computer Vision Luigi De Russis Introduction to OpenCV
  2. 2. 2 OpenC… what? OpenCV in brief Introduction to OpenCV 07/11/2013
  3. 3. What is OpenCV? 3  Open source Computer Vision library BSD License  http://opencv.org     Originally developed by Intel Has more than 2500 optimized algorithms Supports a lot of different languages C, C++, Python, Java  but is written natively in C++   Cross platform  also available for Android and iOS Introduction to OpenCV 07/11/2013
  4. 4. What it is used for? 4          Human-Computer Interaction (HCI) Object Identification Object Recognition Face Recognition Gesture Recognition Motion Tracking Image Processing Mobile Robotics … and so on Introduction to OpenCV 07/11/2013
  5. 5. 5 Motivations - OpenCV Always ask “why?” Introduction to OpenCV 07/11/2013
  6. 6. Why OpenCV? 6 vs. Introduction to OpenCV 07/11/2013
  7. 7. OpenCV: pros 7  Specificity  OpenCV was made for image processing  Matlab is quite generic  Speed  30+ frames processed per seconds in real time image processing with OpenCV  around 4-5 frames processed per seconds in real time image processing with Matlab  Efficient  Matlab Introduction to OpenCV needs more system resources than OpenCV 07/11/2013
  8. 8. OpenCV: cons 8  Easy of use  Matlab  won hands down! Integrated Development Environment (IDE)  you can use Eclipse, Netbeans, Visual Studio, Qt, XCode, … even a simple text editor for OpenCV  Matlab has is own IDE  Memory management Introduction to OpenCV 07/11/2013
  9. 9. OpenCV: pros (final) 9   Price (!) OpenCV Wrappers  SimpleCV,  Emgu CV, ruby-opencv… More similar to industry-level frameworks Introduction to OpenCV 07/11/2013
  10. 10. 10 Motivation - Java When Java meets OpenCV Introduction to OpenCV 07/11/2013
  11. 11. Some facts… 11  The OpenCV APIs have few capabilities for user interfaces  i.e. you can open a window with an image inside. Do you want a button? You cannot have it!  to have a “decent” user interface you need to install “something else” (e.g., Qt for C++)…  … and then compile OpenCV for adding Qt support  C++ learning curve is quite… steep  source: experiences from teaching this course in the last years Introduction to OpenCV 07/11/2013
  12. 12. Some (other) facts… 12  OpenCV C++ APIs exists since OpenCV 1.0  It is possible, but not recommended, to “mix” different OpenCV version  Typically, it is a good way to get into trouble!  It is possible to use OpenCV C APIs together with C++ APIs  Typically Introduction to OpenCV it is a good way to get into trouble! 07/11/2013
  13. 13. Some (other) facts… 13  OpenCV C++ API exists since OpenCV 1.0  It is possible, but not recommended, to “mix” different OpenCV version  Typically, it is a good way to get into trouble! Yeah, some students did it!  It is possible to use OpenCV C APIs together with C++ APIs  Typically Introduction to OpenCV it is a good way to get into trouble! 07/11/2013
  14. 14. A better world is possible? 14  OpenCV provides also the Java APIs nothing to compile (on Windows)  they works on Android, also   Java 7 has a first-grade user interface not Swing, but JavaFX  http://www.oracle.com/technetwork/java/javafx    Almost everybody here should have some (basic) experience with Java Performance between the C++ APIs and the Java APIs are comparable Introduction to OpenCV 07/11/2013
  15. 15. A better world is possible? 15  The OpenCV Java APIs are almost identical to the C++ version knowledge can be transferred!  examples:  to store an image in memory both use the Mat object  to write an image on disk both use the imwrite method   Something change a bit  examples:  CV_RGB2GRAY (C++) becomes COLOR_RGB2GRAY (Java)  Point, Point2d, Point2f (C++) becomes 3 overloaded constructor of Point (Java) Introduction to OpenCV 07/11/2013
  16. 16. A better world is possible? 16  Question:  is OpenCV with Java/JavaFX the “best” solution for every application? Introduction to OpenCV 07/11/2013
  17. 17. A better world is possible? 17  Question:  is OpenCV with Java/JavaFX the “best” solution for every application?  Response:  No, obviously  Do you need a GUI? Go with JavaFX!  Do you have memory constraint? Go with C/C++! …  Please, no extremism! Introduction to OpenCV 07/11/2013
  18. 18. 18 OpenCV meets Java Getting started with OpenCV and Java Introduction to OpenCV 07/11/2013
  19. 19. Modules 19 OpenCV has a modular structure: the package includes several shared or static libraries  core   imgproc   basic structures and algorithms image processing algorithms (such as image filtering, geometrical image transformations, histograms, etc.) video  video analysis (such as motion estimation and object tracking) Introduction to OpenCV 07/11/2013
  20. 20. Modules 20  highgui   calib3d   camera calibration and 3D reconstruction features2d   basic operation to read/write/encode images; in C, C++ and Python it provides also basic UI capabilities 2D features framework (feature detectors, descriptors, and descriptor matchers) objdetect  detection of objects and other items (e.g., faces, eyes, mugs, people, …) Introduction to OpenCV 07/11/2013
  21. 21. Modules 21  ml  machine learning classes used for statistical classification, regression and clustering of data  gpu  GPU-accelerated  photo  computational  algorithms photography ccl  OpenCL-accelerated Introduction to OpenCV algorithms 07/11/2013
  22. 22. Data Structures 22    We speak about Java API All the OpenCV classes and methods are placed into the org.opencv.* packages Mat  the primary image structure in OpenCV 2.x  overcomes the “old” IplImage/CvMat problems (OpenCV 1.x/C API)  automatic memory management (more or less in C++)  two data parts: matrix header (contains information about the matrix)  a pointer to the matrix containing the pixel values  Introduction to OpenCV 07/11/2013
  23. 23. Data Structures 23  Point  2D point  defined by x, y coordinates    Point first = new Point(2, 3); Size  2D size structure  specify the size (width and height) of an image or rectangle Rect  2D rectangle object Introduction to OpenCV 07/11/2013
  24. 24. Basic Image I/O 24  Highgui.imread  loads an image from file and return the corresponding Mat object Mat Highgui.imread(String filename, int flags)  Highui.imwrite  save an image on disk bool Highgui.imwrite(String filename, Mat img, MatOfInt params) Introduction to OpenCV 07/11/2013
  25. 25. Basic Drawing Operations 25     Core.circle  draws a simple or filled circle with a given center and radius on a given image Core.line  draws a line between two point in the given image Core.ellipse  draws an ellipse outline, a filled ellipse, an elliptic arc, a filled ellipse sector, … Core.rectangle  draws a rectangle outline or a filled rectangle  note that negative thickness will fill the rectangle Introduction to OpenCV 07/11/2013
  26. 26. Color Spaces 26  Imgproc.cvtColor   converts an input image from one color space to another examples:     cvtColor(src, dest, Imgproc.COLOR_RGB2GRAY); cvtColor(src, dest, Imgproc.COLOR_HSV2BGR); cvtColor(src, dest, Imgproc.COLOR_RGB2BGR); Important! Images in OpenCV uses BGR instead of RGB Introduction to OpenCV 07/11/2013
  27. 27. 27 Let’s get practical! Getting started (without going crazy) Introduction to OpenCV 07/11/2013
  28. 28. How can we use OpenCV? 28  LABINF:  already installed under Windows  version 2.4.6  Eclipse (Kepler) is the IDE  At home:  you can use whatever IDE you like  but we give full support only for Eclipse  Installation:  see the PDF document in the teaching portal Introduction to OpenCV 07/11/2013
  29. 29. What if I got problems? 29  Small problems  drop me a line   luigi.derussis@polito.it Normal problems Problems with JavaFX and a gray scale image Awesome student to me Hi, […] I’m using “cvtColor(image, gray, COLOR_BGR2GRAY);” but it give this exception: […] Can you help me? come to office hours  every Wednesday, 9:00 - 11:00  LAB6, second floor of DAUIN  please send an e-mail beforehand   Regards, … Enormous problems pray?  no, seriously, we can schedule an extra “lesson”  Introduction to OpenCV 07/11/2013
  30. 30. What if I got problems? 30 OpenCV installation  Small problems  drop me a line   luigi.derussis@polito.it Normal problems Not-So-Awesome student to me Hi, […] I followed the guide for installing OpenCV on my Mac but I have an error after step 3. Can we meet on next Wednesday to solve the problem? Thanks! Regards, … come to office hours  every Wednesday, 9:00 - 11:00  LAB6, second floor of DAUIN  please send an e-mail beforehand   Enormous problems pray?  no, seriously, we can schedule an extra “lesson”  Introduction to OpenCV 07/11/2013
  31. 31. What if I got problems? 31  Small problems  drop me a line   luigi.derussis@polito.it Normal problems come to office hours  every Wednesday, 9:00 - 11:00  LAB6, second floor of DAUIN  please send an e-mail beforehand  Help with OpenCV Good student to me Hi, […] I see the solution of Exercise 2.1 but I don’t understand the following expressions: main(); System.out.println(); @Override. Can you explain to me what they are?  Enormous problems Regards, … pray?  no, seriously, we can schedule an extra “lesson”  Introduction to OpenCV 07/11/2013
  32. 32. An e-mail not to be sent! 32 Introduction to OpenCV 07/11/2013
  33. 33. Useful Resources… 33  OpenCV Wiki   OpenCV Official Documentation   http://answers.opencv.org/questions/ OpenCV Javadocs   http://docs.opencv.org/ User Q&A forum   http://code.opencv.org/projects/opencv/wiki http://docs.opencv.org/java/ JavaFX Documentation  http://www.oracle.com/technetwork/java/javafx/document ation Introduction to OpenCV 07/11/2013
  34. 34. 34 Demo Hour Put everything together Introduction to OpenCV 07/11/2013
  35. 35. License 35   This work is licensed under the Creative Commons “AttributionNonCommercial-ShareAlike Unported (CC BY-NC-SA 3,0)” License. You are free:    Under the following conditions:     to Share - to copy, distribute and transmit the work to Remix - to adapt the work Attribution - You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work). Noncommercial - You may not use this work for commercial purposes. Share Alike - If you alter, transform, or build upon this work, you may distribute the resulting work only under the same or similar license to this one. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/3.0/ Introduction to OpenCV 07/11/2013

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