Book Image

Learn OpenCV 4 By Building Projects - Second Edition

By : David Millán Escrivá, Vinícius G. Mendonça, Prateek Joshi
Book Image

Learn OpenCV 4 By Building Projects - Second Edition

By: David Millán Escrivá, Vinícius G. Mendonça, Prateek Joshi

Overview of this book

OpenCV is one of the best open source libraries available, and can help you focus on constructing complete projects on image processing, motion detection, and image segmentation. Whether you’re completely new to computer vision, or have a basic understanding of its concepts, Learn OpenCV 4 by Building Projects – Second edition will be your guide to understanding OpenCV concepts and algorithms through real-world examples and projects. You’ll begin with the installation of OpenCV and the basics of image processing. Then, you’ll cover user interfaces and get deeper into image processing. As you progress through the book, you'll learn complex computer vision algorithms and explore machine learning and face detection. The book then guides you in creating optical flow video analysis and background subtraction in complex scenes. In the concluding chapters, you'll also learn about text segmentation and recognition and understand the basics of the new and improved deep learning module. By the end of this book, you'll be familiar with the basics of Open CV, such as matrix operations, filters, and histograms, and you'll have mastered commonly used computer vision techniques to build OpenCV projects from scratch.
Table of Contents (14 chapters)

Graphic user interface with Qt

The Qt user interface gives us more control and options to work with our images.

The interface is divided into the following three main areas:

  • Toolbar
  • Image area
  • Status bar

We can see these three areas in the following picture. At the top of the image is the toolbar, the image is the main area, and the status bar can be seen at the bottom of the image:

The toolbar has the following buttons from left to right:

  • Four buttons for panning
  • Zoom x1
  • Zoom x30, show labels
  • Zoom in
  • Zoom out
  • Save current image
  • Show properties

These options can be seen clearly in the following image:

The image area shows an image and a contextual menu when we push the right mouse button over the image. This area can show an overlay message at the top of the area using the displayOverlay function. This function accepts three parameters: the window name, the text that we...