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OpenCV Computer Vision Application Programming Cookbook Second Edition

OpenCV Computer Vision Application Programming Cookbook Second Edition

By : Robert Laganiere
3.7 (3)
Buy this Book
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OpenCV Computer Vision Application Programming Cookbook Second Edition

OpenCV Computer Vision Application Programming Cookbook Second Edition

3.7 (3)
By: Robert Laganiere
Buy this Book

Overview of this book

OpenCV 3 Computer Vision Application Programming Cookbook is appropriate for novice C++ programmers who want to learn how to use the OpenCV library to build computer vision applications. It is also suitable for professional software developers wishing to be introduced to the concepts of computer vision programming. It can also be used as a companion book in a university-level computer vision courses. It constitutes an excellent reference for graduate students and researchers in image processing and computer vision.
Table of Contents (13 chapters)
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Preface
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Preface
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What this book covers
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What you need for this book
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Who this book is for
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Conventions
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Reader feedback
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Customer support
Free Chapter
1
1. Playing with Images
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1. Playing with Images
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Introduction
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Installing the OpenCV library
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Loading, displaying, and saving images
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Exploring the cv::Mat data structure
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Defining regions of interest
2
2. Manipulating Pixels
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2. Manipulating Pixels
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Introduction
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Accessing pixel values
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Scanning an image with pointers
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Scanning an image with iterators
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Writing efficient image-scanning loops
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Scanning an image with neighbor access
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Performing simple image arithmetic
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Remapping an image
3
3. Processing Color Images with Classes
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3. Processing Color Images with Classes
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Introduction
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Using the Strategy pattern in an algorithm design
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Using a Controller design pattern to communicate with processing modules
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Converting color representations
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Representing colors with hue, saturation, and brightness
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4. Counting the Pixels with Histograms
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4. Counting the Pixels with Histograms
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Introduction
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Computing the image histogram
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Applying look-up tables to modify the image appearance
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Equalizing the image histogram
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Backprojecting a histogram to detect specific image content
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Using the mean shift algorithm to find an object
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Retrieving similar images using the histogram comparison
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Counting pixels with integral images
5
5. Transforming Images with Morphological Operations
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5. Transforming Images with Morphological Operations
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Introduction
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Eroding and dilating images using morphological filters
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Opening and closing images using morphological filters
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Detecting edges and corners using morphological filters
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Segmenting images using watersheds
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Extracting distinctive regions using MSER
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Extracting foreground objects with the GrabCut algorithm
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6. Filtering the Images
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6. Filtering the Images
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Introduction
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Filtering images using low-pass filters
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Filtering images using a median filter
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Applying directional filters to detect edges
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Computing the Laplacian of an image
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7. Extracting Lines, Contours, and Components
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7. Extracting Lines, Contours, and Components
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Introduction
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Detecting image contours with the Canny operator
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Detecting lines in images with the Hough transform
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Fitting a line to a set of points
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Extracting the components' contours
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Computing components' shape descriptors
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8. Detecting Interest Points
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8. Detecting Interest Points
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Introduction
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Detecting corners in an image
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Detecting features quickly
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Detecting scale-invariant features
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Detecting FAST features at multiple scales
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9. Describing and Matching Interest Points
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9. Describing and Matching Interest Points
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Introduction
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Matching local templates
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Describing local intensity patterns
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Describing keypoints with binary features
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10. Estimating Projective Relations in Images
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10. Estimating Projective Relations in Images
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Introduction
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Calibrating a camera
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Computing the fundamental matrix of an image pair
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Matching images using a random sample consensus
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Computing a homography between two images
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11. Processing Video Sequences
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11. Processing Video Sequences
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Introduction
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Reading video sequences
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Processing the video frames
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Writing video sequences
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Tracking feature points in a video
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Extracting the foreground objects in a video
12
Index
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Index

Backprojecting a histogram to detect specific image content

A histogram is an important characteristic of an image's content. If you look at an image area that shows a particular texture or a particular object, then the histogram of this area can be seen as a function that gives the probability that a given pixel belongs to this specific texture or object. In this recipe, you will learn how the concept of histogram backprojection can be advantageously used to detect specific image content.

How to do it...

Suppose you have an image and you wish to detect specific content inside it (for example, in the following image, the clouds in the sky). The first thing to do is to select a region of interest that contains a sample of what you are looking for. This region is the one inside the rectangle drawn on the following test image:

In our program, the region of interest is obtained as follows:

   cv::Mat imageROI;
   imageROI= image(cv::Rect(216,33,24,30)); // Cloud region

You then extract the histogram...

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