Show the detected face images in a window

Question

How can I show all the images in a window? My face detection will come out with different size of detected face images. Should I save all the detected images then read using imread(), then display it using showmanyimage()? But this step will eat my storage. I need another solution please.

Answer 1

take a look at the code below

#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include "opencv2/objdetect.hpp"

using namespace cv;
using namespace std;

int showManyImages( const String& _winName, const vector<Mat>& _imgs );

int main( int argc, char** argv )
{
    string cascadeName = "haarcascade_frontalface_alt.xml";

    Mat img = imread(argv[1]);
    if( img.empty() )
    {
        printf( "Could not read input image file\n");
        return -1;
    }

    CascadeClassifier cascade;

    if( !cascade.load( cascadeName ) )
    {
        printf("ERROR: Could not load classifier cascade\n");
        return -1;
    }

    vector<Mat> imgs;
    vector<Rect> faces;
    cascade.detectMultiScale( img, faces, 1.3, 2, 0|CASCADE_SCALE_IMAGE, Size(30, 30) );

        for ( size_t i = 0; i < faces.size(); i++ )
        {
             if(i < 12)
             imgs.push_back(img(faces[i]));
        }

    showManyImages("Images", imgs);
    waitKey();
    return 0;
}

int showManyImages( const String& _winName, const vector<Mat>& _imgs )
{
    int nImg = (int)_imgs.size();

    Mat dispImg;

    int size;
    int x, y;

    // w - Maximum number of images in a row
    // h - Maximum number of images in a column
    int w, h;
    // scale - How much we have to resize the image
    float scale;
    int max;

    if (nImg <= 0)
    {
        printf("Number of arguments too small....\n");
        return -1;
    }
    else if (nImg > 12)
    {
        printf("Number of arguments too large....\n");
        return 1;
    }

    else if (nImg == 1)
    {
        w = h = 1;
        size = 300;
    }
    else if (nImg == 2)
    {
        w = 2;
        h = 1;
        size = 300;
    }
    else if (nImg == 3 || nImg == 4)
    {
        w = 2;
        h = 2;
        size = 300;
    }
    else if (nImg == 5 || nImg == 6)
    {
        w = 3;
        h = 2;
        size = 200;
    }
    else if (nImg == 7 || nImg == 8)
    {
        w = 4;
        h = 2;
        size = 200;
    }
    else
    {
        w = 4;
        h = 3;
        size = 150;
    }

    dispImg = Mat::zeros(Size(100 + size*w, 60 + size*h), CV_8UC3);

    for (int i= 0, m=20, n=20; i<nImg; i++, m+=(20+size))
    {
        x = _imgs[i].cols;
        y = _imgs[i].rows;

        max = (x > y)? x: y;
        scale = (float) ( (float) max / size );

        if (i%w==0 && m!=20)
        {
            m = 20;
            n += 20+size;
        }

        Mat imgROI = dispImg(Rect(m, n, (int)(x/scale), (int)(y/scale)));
        resize(_imgs[i], imgROI, Size((int)(x/scale), (int)(y/scale)));
    }

    imshow(_winName, dispImg);
    return 0;
}

input image : output image :