Qt下opencv第一个程序

新建项目，在.pro文件下添加库和头文件：

INCLUDEPATH += /home/wlw/Desktop/opencv-2.4.13.4/out/include

LIBS += -L/home/wlw/Desktop/opencv-2.4.13.4/out/lib -lopencv_calib3d \
-lopencv_features2d  -lopencv_highgui  -lopencv_ml  -lopencv_ocl \
-lopencv_superres    -lopencv_contrib     -lopencv_flann \
-lopencv_imgproc     -lopencv_nonfree     -lopencv_photo   \
-lopencv_video       -lopencv_core        -lopencv_gpu   \
-lopencv_legacy      -lopencv_objdetect   -lopencv_stitching  \
-lopencv_videostab

main.cpp：

#include <stdio.h>
#include <opencv2/opencv.hpp>
#include <QDebug>

using namespace cv;

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
    w.show();

    Mat image;
    image = imread("./a.jpeg", 2 );//目录按照自己的目录
    if ( !image.data )
    {
        printf("No image data \n");
        return -1;
    }
    qDebug() << image.rows << " " << image.cols;
    namedWindow("Display Image", CV_WINDOW_AUTOSIZE );
    imshow("Display Image", image);
    waitKey(0);
    return 0;


    return a.exec();
}

image = imread("./a.jpeg", 2 );
这里imread的第二个参数解释：0： 灰度图；1：彩色图；2：如果图像深度是16位或者32位就返回对应深度的图，否则返回灰度图； 

opencv3中是这样的：