Introduction to OpenCV 3.0 (with Java)

Computer Vision

OpenCV

Luigi De Russis

Politecnico di TorinoDipartimento di Automatica e Informatica (DAUIN)

Torino - Italy

[email protected]

This work is licensed under the Creative Commons (CC BY-SA)

License. To view a copy of this license, visit

http://creativecommons.org/licenses/by-sa/3.0/

mailto:[email protected]

What is OpenCV?

Computer Vision library Open Source (BSD License)

http://opencv.org

Originally developed by Intel

With more than 2500 optimized algorithms

Supports a lot of different languages C, C++, Python, and Java

but is written natively in C++

Cross platform also available for Android and iOS

10/14/2015 Introduction to OpenCV 2

http://opencv.org/

What is used for?

Human-Computer Interaction (HCI)

Object Identification

Object Recognition

Face Recognition

Gesture Recognition

Motion Tracking

Image Processing

Mobile Robotics

… and so on


Why OpenCV?

We looked for a software/library:

that covers most of Computer Vision techniques

widely used or de-facto standard

free/open, possibly

in a language known by most students

in which a UI can be created

able to handle real-time image processing


Alternatives?


vs.

OpenCV: pros

Specificity OpenCV was made for computer vision/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

Efficiency Matlab needs more system resources than OpenCV


OpenCV: cons

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


OpenCV: pros (final)

Price (!)

OpenCV Wrappers

SimpleCV, Emgu CV, ruby-opencv…

More similar to industry-level frameworks


OpenCV in C++: why not?

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 with Qt support

C++ learning curve is quite… steep

source: experiences from teaching this course in the first years


OpenCV in C++: why not?

OpenCV C++ APIs exist since OpenCV 1.0

but they dramatically changed starting from

OpenCV 2.0

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 it is a good way to get into trouble!


OpenCV in Java: why?

OpenCV provides also Java APIs nothing to compile (on Windows)

they works on Android, too

Java 7/8 has a first-grade user interface not Swing, but JavaFX

https://docs.oracle.com/javase/8/javase-clienttechnologies.htm

Almost everybody here should have some (basic) experience with Java

Performances between the C++ APIs and the Java APIs are comparable



OpenCV in Java: why?

The OpenCV Java APIs are really similar 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 changes a bit examples:

CV_RGB2GRAY (C++) becomes COLOR_RGB2GRAY (Java)

Point, Point2d, Point2f (C++) becomes 3 overloaded constructor of Point (Java)


OPENCV IN JAVA

Getting started…


Main Modules


core

basic structures and algorithms

imgproc

image processing algorithms (such as image filtering,

geometrical image transformations, histograms, etc.)

videoio

media I/O

OpenCV has a modular structure:

the package includes several shared or static libraries

New

Main Modules


video video analysis (such as motion estimation and object

tracking)

imgcodecs image file reading and writing

calib3d camera calibration and 3D reconstruction

features2d 2D features framework (feature detectors, descriptors, and

descriptor matchers)

objdetect detection of objects and other items (e.g., faces, eyes,

mugs, people, …)

New

Main Modules


highgui

provides basic UI capabilities (in C, C++, and Python)

ml

machine learning classes used for statistical

classification, regression and clustering of data

photo

computational photography

cuda*

various modules with CUDA-optimized algorithms

New

Not available in Java

Data Structures


We speak about Java APIs

All the OpenCV classes and methods are placed into the org.opencv.* packages

Mat

the primary image structure in OpenCV 2.x/3.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

Duplicate Mat objects…

Mat first = Mat.eye(3, 3, CvType.CV_8U1C);


1 0 0

0 1 0

0 0 1

Header

first



Mat second = first;


1 0 0

0 1 0

0 0 1

Header

first

Header

second



Mat second = first;

first.put(0, 0, 2, 2, 2);


Header

first

Header

second

2 2 2

0 1 0

0 0 1



Mat second = new Mat();

second = first.clone(); // first.copyTo(second);

first.put(0, 0, 2, 2, 2);


2 2 2

0 1 0

0 0 1

Header

first

Header

second1 0 0

0 1 0

0 0 1

Data Structures


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

Basic Drawing Operations


Imgproc.circle()

draws a simple or filled circle with a given center and radius

on a given image

Imgproc.line()

draws a line between two point in the given image

Imgproc.ellipse()

draws an ellipse outline, a filled ellipse, an elliptic arc, a filled

ellipse sector, …

Imgproc.rectangle()

draws a rectangle outline or a filled rectangle

note that negative thickness will fill the rectangle

Basic Image I/O


Imgcodecs.imread()

loads an image from file and return the corresponding Mat objectMat Imgcodecs.imread(String filename,

int flags)

Imgcodecs.imwrite()

save an image on diskbool Imgcodecs.imwrite(String filename,

Mat img, MatOfInt params)

Color Spaces


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

Getting started (without going crazy)

LET’S GET PRACTICAL!

10/14/2015 26 Introduction to OpenCV

How can we use OpenCV?


LABINF: already installed under Windows

Java 7 and OpenCV version 3.0

Eclipse (Luna) is the IDE

At home: we recommend Eclipse Mars/Luna, Java 8 and

OpenCV 3.0

feel free to use any Java IDE you like

Installation: see the PDF document in the teaching portal

What if I got problems?


Small problems

drop me a line

[email protected]

Normal problems

come to office hours

please send an e-mail beforehand

Enormous problems

pray?

no, seriously, we can schedule an extra “lesson”

Awesome student to me

Hi,

[…] I’m using “cvtColor(image, gray, COLOR_BGR2GRAY);” but it give this exception: […]

Can you help me?

Regards,

…

Problems with JavaFX and a gray scale image

mailto:[email protected]



Small problems

drop me a line

[email protected]

Normal problems



Enormous problems

pray?


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,

…

OpenCV installation



Small problems

drop me a line

[email protected]

Normal problems



Enormous problems

pray?


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?

Regards,

…

Help with OpenCV

An e-mail not to be sent!


Useful Resources…


OpenCV Wiki https://github.com/Itseez/opencv/wiki

OpenCV Official Documentation http://docs.opencv.org/3.0.0/index.html

User Q&A forum http://answers.opencv.org/questions/

OpenCV Javadocs http://docs.opencv.org/java/3.0.0/

JavaFX Documentation https://docs.oracle.com/javase/8/javase-clienttechnologies.htm

Daniel Lélis Baggio, OpenCV 3.0 Computer Vision with Java, PACKT Publishing, 2015, ISBN 978-1-78328-397-2

https://github.com/Itseez/opencv/wiki

http://docs.opencv.org/3.0.0/index.html

http://answers.opencv.org/questions/

http://docs.opencv.org/java/3.0.0/


Put everything together

DEMO HOUR

10/14/2015 33 Introduction to OpenCV

License


This work is licensed under the Creative Commons “Attribution-NonCommercial-ShareAlike Unported (CC BY-NC-SA 3,0)” License.

You are free: to Share - to copy, distribute and transmit the work

to Remix - to adapt the work

Under the following conditions: 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.

Introduction to OpenCV 3.0 (with Java)

Technology

Transcript of Introduction to OpenCV 3.0 (with Java)