OpenCV, Qt, imread, namedWindow, imshow does not work - image

Question

In the .pro file:
QT += core
QT -= gui
TARGET = latihan_2
CONFIG += console
CONFIG -= app_bundle
TEMPLATE = app
SOURCES += main.cpp
INCLUDEPATH += E:\OpenCV\OpenCV\opencv\build\include
LIBS += E:\OpenCV\OpenCV\opencv\build\x86\mingw\lib\libopencv_core246.dll.a
LIBS += E:\OpenCV\OpenCV\opencv\build\x86\mingw\lib\libopencv_highgui246.dll.a
LIBS += E:\OpenCV\OpenCV\opencv\build\x86\mingw\lib\libopencv_imgproc246.dll.a
LIBS += E:\OpenCV\OpenCV\opencv\build\x86\mingw\lib\libopencv_features2d246.dll.a
LIBS += E:\OpenCV\OpenCV\opencv\build\x86\mingw\lib\libopencv_calib3d246.dll.a
In main.cpp:
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
using namespace cv;
int main(){
//read image
Mat image = imread("img.jpg", 1);
//create image window named "My image"
namedWindow("My Image", CV_WINDOW_AUTOSIZE);
//show the image on window
imshow("My image", image);
//wait key for 5000ms
waitKey(5000);
return 1;
}
When I hit run, there is no error, but it only shows a black window named qtcreator_process_stub.exe.
Why the "My image" window doesn't come out and shows the img.jpg?
I use Qt creator 2.8.1, based on Qt 5.1.1, and openCV-2.4.6.0.

Answer 1

You could also display a cv::Mat on a Qt window. I demonstrate how to do that on cvImage. The code below is adapted from cvImage::_open():
std::string filename = ...
cv::Mat mat = cv::imread(filename);
// Since OpenCV uses BGR order, we need to convert it to RGB
// NOTE: OpenCV 2.x uses CV_BGR2RGB, OpenCV 3.x uses cv::COLOR_BGR2RGB
cv::cvtColor(mat, mat, cv::COLOR_BGR2RGB)
// image is created according to Mat dimensions
QImage image(mat.size().width, mat.size().height, QImage::Format_RGB888);
// Copy cv::Mat to QImage
memcpy(image.scanLine(0), mat.data, static_cast<size_t>(image.width() * image.height() * mat.channels()));
// Display the QImage in a QLabel
QLabel label;
label.setPixmap(QPixmap::fromImage(image));
label.show();

Answer 2

First guess is that the image is in the wrong path, so first test should be to specify the full path to the image.
Also check the return value of your program (make sure the it doesn't return some crash error code - be consistent and return 0 for success and other values for fail).
And a little bit of coding that tells you where the code fails doesn't hurt, so check image.data or you can also use image.empty():
if(! image.data )
{
std::cout << "No image to display";
//can be any other method to display the error: qDebug, a messagebox...
//you can also
return 1;
}
else
{
//use the image
//if nothing goes wrong:
//return 0;
}

Answer 3

Check Projects->Run Settings ->Run in Terminal checkbox. If it is disabled, enable it.

Answer 4

I faced same problem and I solved it by fixing path environment variable. In my path environment variable I added some opencv folders wrongly, then I deleted them and add only bin folder for opencv DLLs and then the problem was solved.