A basic knowledge of C++ would be helpful in understanding this book. The examples are built using the following technologies: OpenCV 4.0; CMake 3.3.x or newer; Tesseract; Leptonica (a dependency of Tesseract); Qt (optional); and OpenGL (optional).

Detailed installation instructions are provided in the relevant chapters.

You can download the example code files for this book from your account at www.packt.com. If you purchased this book elsewhere, you can visit www.packt.com/support and register to have the files emailed directly to you.

You can download the code files by following these steps:

1. Log in or register at www.packt.com.
2. Select the SUPPORT tab.
3. Click on Code Downloads & Errata.
4. Enter the name of the book in the Search box and follow the onscreen instructions.

Once the file is downloaded, please make sure that you unzip or extract the folder using the latest version of:

• WinRAR/7-Zip for Windows
• Zipeg/iZip/UnRarX for Mac
• 7-Zip/PeaZip for Linux

The code bundle for the book is also hosted on GitHub at https://github.com/PacktPublishing/Learn-OpenCV-4-By-Building-Projects-Second-Edition. In case there's an update to the code, it will be updated on the existing GitHub repository.

We also have other code bundles from our rich catalog of books and videos available at https://github.com/PacktPublishing/. Check them out!

We also provide a PDF file that has color images of the screenshots/diagrams used in this book. You can download it here: https://www.packtpub.com/sites/default/files/downloads/9781789341225_ColorImages.pdf.

Visit the following link to check out videos of the code being run:
http://bit.ly/2Sfrxgu

There are a number of text conventions used throughout this book.

CodeInText: Indicates code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles. Here is an example: "Also, installing this package is optional. OpenCV will work just fine if you don't install opencv_contrib."

A block of code is set as follows:

// Load image to process 
  Mat img= imread(img_file, 0); 
  if(img.data==NULL){ 
    cout << "Error loading image "<< img_file << endl; 
    return 0; 
  } 

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

for(auto i=1; i<num_objects; i++){ 
    cout << "Object "<< i << " with pos: " << centroids.at<Point2d>(i) << " with area " << stats.at<int>(i, CC_STAT_AREA) << endl; 

Any command-line input or output is written as follows:

C:> setx -m OPENCV_DIR D:OpenCVBuildx64vc14

Bold: Indicates a new term, an important word, or words that you see on screen. For example, words in menus or dialog boxes appear in the text like this. Here is an example: "Select System info from the Administration panel."