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test code for the function contrast_measure

#include "opencv2/imgproc.hpp"
#include "opencv2/highgui.hpp"
#include "iostream"

using namespace cv;

double contrast_measure( const Mat&img )
{
    Mat dx, dy;
    Sobel( img, dx, CV_32F, 1, 0, 3 );
    Sobel( img, dy, CV_32F, 0, 1, 3 );
    magnitude( dx, dy, dx );
    return sum(dx)[0];
}

int main( int argc, char** argv )
{
    char* filename = argc >= 2 ? argv[1] : (char*)"lena.jpg";
    Mat src = imread( filename );

    if(src.data)
    {
        std::cout << "original image : " << contrast_measure( src ) / 1e3 << std::endl;

        for( int i =3; i < 80; i+=2 )
        {
            Mat blurred;
            GaussianBlur( src, blurred, Size(i,i), 0);
            imshow(  "blurred image", blurred );
            waitKey(200);
            std::cout << "blurred image  : " << contrast_measure( blurred ) / 1e3 << std::endl;
        }
    }
    return 0;
}

resuts :

original image : 11776.9
blurred image  : 8875.25
blurred image  : 7615.93
blurred image  : 6441.79
blurred image  : 5861.6
blurred image  : 5255.5
blurred image  : 4961.99
blurred image  : 4524.56
blurred image  : 4291.87
blurred image  : 4021.77
blurred image  : 3822.97
blurred image  : 3622.91
blurred image  : 3521.31
blurred image  : 3320.35
blurred image  : 3181.87
blurred image  : 3105.9
blurred image  : 2952.72
blurred image  : 2878.29
blurred image  : 2751.65
blurred image  : 2689.6
blurred image  : 2670.44
blurred image  : 2539.05
.
.

test code for the function contrast_measurecalcBlurriness which is an undocumented OpenCV function

#include "opencv2/imgproc.hpp"
#include "opencv2/highgui.hpp"
#include "iostream"

using namespace cv;

double contrast_measure( const Mat&img )
{
    Mat dx, dy;
    Sobel( img, dx, CV_32F, 1, 0, 3 );
    Sobel( img, dy, CV_32F, 0, 1, 3 );
    magnitude( dx, dy, dx );
    return sum(dx)[0];
}

int main( int argc, char** argv )
{
    char* filename = argc >= 2 ? argv[1] : (char*)"lena.jpg";
    Mat src = imread( filename );

    if(src.data)
    {
        std::cout << "original image : " << contrast_measure( src ) / 1e3 << std::endl;

        for( int i =3; i < 80; i+=2 )
        {
            Mat blurred;
            GaussianBlur( src, blurred, Size(i,i), 0);
            imshow(  "blurred image", blurred );
            waitKey(200);
            std::cout << "blurred image  : " << contrast_measure( blurred ) / 1e3 << std::endl;
        }
    }
    return 0;
}

resuts : ( the lesser value means more sharpness )

original image : 11776.9
blurred image  : 8875.25
blurred image  : 7615.93
blurred image  : 6441.79
blurred image  : 5861.6
blurred image  : 5255.5
blurred image  : 4961.99
blurred image  : 4524.56
blurred image  : 4291.87
blurred image  : 4021.77
blurred image  : 3822.97
blurred image  : 3622.91
blurred image  : 3521.31
blurred image  : 3320.35
blurred image  : 3181.87
blurred image  : 3105.9
blurred image  : 2952.72
blurred image  : 2878.29
blurred image  : 2751.65
blurred image  : 2689.6
blurred image  : 2670.44
blurred image  : 2539.05
4.97583e-005
blurred image  : 7.70266e-005
blurred image  : 9.97529e-005
blurred image  : 0.000134977
blurred image  : 0.000161698
blurred image  : 0.00020089
blurred image  : 0.000226519
blurred image  : 0.000275304
blurred image  : 0.00030933
blurred image  : 0.000356515
blurred image  : 0.000399192
blurred image  : 0.000450388
blurred image  : 0.000483238
blurred image  : 0.00054965
blurred image  : 0.000603829
blurred image  : 0.000645158
blurred image  : 0.00071919
blurred image  : 0.000767566
blurred image  : 0.000847372
blurred image  : 0.000895128
blurred image  : 0.000917833
blurred image  : 0.00102065
blurred image  : 0.00113219
.
.

test code for the function calcBlurriness which is an undocumented OpenCV function

#include "opencv2/imgproc.hpp"
#include "opencv2/highgui.hpp"
#include "iostream"

using namespace cv;

double contrast_measure( float calcBlurriness( const Mat&img Mat &src )
{
    Mat dx, dy;
Gx, Gy;
    Sobel( img, dx, src, Gx, CV_32F, 1, 0, 3 0 );
    Sobel( img, dy, src, Gy, CV_32F, 0, 1, 3 );
    magnitude( dx, dy, dx );
1 );
    double normGx = norm( Gx );
    double normGy = norm( Gy );
    double sumSq = normGx * normGx + normGy * normGy;
    return sum(dx)[0];
static_cast<float>( 1. / ( sumSq / src.size().area() + 1e-6 ));
}

int main( int argc, char** argv )
{
    char* filename = argc >= 2 ? argv[1] : (char*)"lena.jpg";
    Mat src = imread( filename );

    if(src.data)
    {
        std::cout << "original image : " << contrast_measure( calcBlurriness( src ) / 1e3 << std::endl;

        for( int i =3; i < 80; i+=2 )
        {
            Mat blurred;
            GaussianBlur( src, blurred, Size(i,i), 0);
            imshow(  "blurred image", blurred );
            waitKey(200);
            std::cout << "blurred image  : " << contrast_measure( calcBlurriness( blurred ) / 1e3 << std::endl;
        }
    }
    return 0;
}

resuts : ( the lesser value means more sharpness )

original image : 4.97583e-005
blurred image  : 7.70266e-005
blurred image  : 9.97529e-005
blurred image  : 0.000134977
blurred image  : 0.000161698
blurred image  : 0.00020089
blurred image  : 0.000226519
blurred image  : 0.000275304
blurred image  : 0.00030933
blurred image  : 0.000356515
blurred image  : 0.000399192
blurred image  : 0.000450388
blurred image  : 0.000483238
blurred image  : 0.00054965
blurred image  : 0.000603829
blurred image  : 0.000645158
blurred image  : 0.00071919
blurred image  : 0.000767566
blurred image  : 0.000847372
blurred image  : 0.000895128
blurred image  : 0.000917833
blurred image  : 0.00102065
blurred image  : 0.00113219
.
.