Project 1: Hello World (with OpenCV)
This simple project loads and displays an image in OpenCV using a single C++ source code file.
Table of Contents
The Gist
The process of loading and displaying the image is handled by
the main() function. The details regarding each of those actions
are described in the OpenCV source code, but I do not intend to
cover those in this project. Rather, I hope to learn how
to use OpenCV (understanding cv::Mat’s, etc.) and to demonstrate
that my project structure is effective and works on multiple platforms.
While this code is relatively simple, I will highlight the most important part here and remark on four of its parts:
Generating a Filename
string filename = MEDIA_DIRECTORY;
filename += "RedFox.png";
I have defined MEDIA_DIRECTORY in the root CMake script.
It defines the path to the root media folder containing
all images and videos I use in these projects.
Here I intend to load a test image, called “RedFox.png”,
that resides in that MEDIA_DIRECTORY.
Loading an Image
Mat image = imread(filename);
imread is a function defined by the OpenCV library.
It can decode many kinds of images and place them
into a cv::Mat, a matrix that stores all the values
of all the pixels in an image.
Showing an Image
imshow("Test image", image);
imshow is also a function defined by OpenCV.
It creates a new window and renders the cv::Mat
called image onto that window named “Test image”.
I will not use this function frequently. OpenCV is not meant
to be an extensive graphics library, and I have demonstrated that
cv::Mat’s can be rendered in windows with interactive user interfaces
in Project 5.
Waiting for the User to Exit the Window
waitKey(0);
waitKey is a function defined by OpenCV
that tells OpenCV to pause the program until
the user has pressed any key.
I will not use this function frequently because of my personal preference to use my own UI.