This code sample shows you how to do basic image manipulation to an image and display the result using the QLabel widget. The code loads The_Chapter_House.jpg from the assets/ directory and provides two buttons to perform some basic manipulation.

The same program written in Python is available in the python/ directory.

To compile and run the code, you need to have Qt 5 installed on your computer. The code is successfully tested on the following environment:

• Mac OS X Mavericks
• Qt 5.3.0
• OpenCV 3.0.0
• Python 3.4.1

Open ImageApp.pro and modify the variables to match with your system. For example, you might need to modify the paths for the includes and libraries especially if you're on Windows.

INCLUDEPATH += /usr/local/include
LIBS += -L/usr/local/lib -lopencv_core -lopencv_highgui -lopencv_imgproc -lopencv_imgcodecs

Change your working directory and compile the code by typing:

qmake
make

If everything is ok, it will produce an executable: ImageApp (Linux), ImageApp.exe (Windows), or ImageApp.app (Mac). Run the executable and you will see the GUI like the screenshot above.

In ImageApp.cpp, the code using relative path to locate the input image:

img = cv::imread("../assets/The_Chapter_House.jpg");

If the program cannot display the image and shows the "Cannot load the input image!" warning, try to use absolute path instead. For example:

img = cv::imread("/full/path/to/The_Chapter_House.jpg");