The document provides an introduction to OpenCV, an open-source computer vision library developed by Intel, which supports multiple programming languages including C++, Python, and Java. It discusses the library's features, such as its modular structure with various image processing and machine learning modules, and compares OpenCV with MATLAB in terms of speed and resource efficiency. The document emphasizes the user interface capabilities for Java and outlines support for users encountering issues with OpenCV installations.

1. Computer Vision
Luigi De Russis
Introduction to
OpenCV

2. 2
OpenC… what?
OpenCV in brief
Introduction to OpenCV
07/11/2013

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. 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
Motivations - OpenCV
Always ask “why?”
Introduction to OpenCV
07/11/2013

6. Why OpenCV?
6
vs.
Introduction to OpenCV
07/11/2013

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. 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. 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
Motivation - Java
When Java meets OpenCV
Introduction to OpenCV
07/11/2013

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. 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. 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. 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. 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. 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. 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
OpenCV meets Java
Getting started with OpenCV and Java
Introduction to OpenCV
07/11/2013

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. 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. 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. 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. 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. 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. 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. 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
Let’s get practical!
Getting started (without going crazy)
Introduction to OpenCV
07/11/2013

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. 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. 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. 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. An e-mail not to be sent!
32
Introduction to OpenCV
07/11/2013

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
Demo Hour
Put everything together
Introduction to OpenCV
07/11/2013

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