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Displaying multiple images

asked 2016-01-08 04:35:09 -0500

updated 2016-01-08 15:54:31 -0500

Hi All,

i tried to update an outdated sample code on opencv/wiki

The changes I have made up to now are as follows.

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

using namespace cv;
using namespace std;

int showManyImages( const String winName, const vector<Mat> images );

int main( int argc, char** argv )
{
    vector<Mat> images;

    for ( int i = 0; i < 15; i++ )
    {
        Mat image( 240,320,CV_8UC3, Scalar( (rand()&255), (rand()&255), (rand()&255) ));
        circle( image, Point( image.cols / 2, image.rows / 2 ), image.cols / 3, Scalar( (rand()&255), (rand()&255), (rand()&255) ) );
        images.push_back( image );
        showManyImages("showManyImages test", images);
        waitKey();
    }
    return 0;
}

int showManyImages( const String winName, const vector<Mat> images )
{
    int nImg = images.size() > 12 ? 12 : (int)images.size();

    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;

    // TODO: code-block #1 - should be replaced with more robust code 
    // start of code-block #1
    if (nImg <= 0) 
    {
        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;
    }
    // end of code-block #1
    Mat dispayImage = 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 = images[i].cols;
        y = images[i].rows;

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

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

        Mat imageROI = dispayImage( Rect( m, n, (int)( x / scale ), (int)( y / scale )));
        resize( images[i], imageROI, Size((int)( x / scale ), (int)( y / scale )));
    }

    imshow( winName, dispayImage );
    return 0;
}

i think the part marked as code-block #1 should be replaced with more robust code.

any suggestion and contribution is welcome

EDIT

I found a simple way to replace the block #1

int w = images.size() == 2 ? 2 : cvCeil( sqrt( images.size() ));
int h = cvRound( sqrt( images.size() ));
int size = images.size() <= 2 ? 300 : 300 / w * 2;

github link

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Comments

2

Using switch case will be more beautiful

thdrksdfthmn gravatar imagethdrksdfthmn ( 2016-01-08 06:45:20 -0500 )edit
1

Why not make w, h and size parameters input variables and let the user decide. I find it quite useless whenever I see stuff like that being auto calculated using some weird rule or using predefined values. Give the user more freedom by generalizing the sample.

StevenPuttemans gravatar imageStevenPuttemans ( 2016-01-11 08:51:11 -0500 )edit
1

yes. your suggestions were on my todo list :)

sturkmen gravatar imagesturkmen ( 2016-01-11 09:05:02 -0500 )edit
1

oh, sorry i misunderstood your comment. i did not think it before.

sturkmen gravatar imagesturkmen ( 2016-01-11 09:12:22 -0500 )edit

Haha great :D

StevenPuttemans gravatar imageStevenPuttemans ( 2016-01-11 09:15:11 -0500 )edit

I thought before like

int showManyImages( const String winName, const vector<Mat> images, Size displayImageSize, int border_width = 0 );

it could be like below taking your idea ( if parameter is 0 will be calculated internally)

int showManyImages( const String winName, const vector<Mat> images, Size displayImageSize, int border_width = 0, int row_count = 0 );
sturkmen gravatar imagesturkmen ( 2016-01-11 09:30:13 -0500 )edit

1 answer

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4

answered 2016-01-11 07:47:46 -0500

Kellerspeicher gravatar image
  • ceil( sqrt(2) ) == 2 so there is no need for ? :.
  • sqrt() is an expensive function and not needed twice.
  • be careful with operator order better use brackets or unambiguous order

Your should (not tested) get the same with:

int w = cvCeil( sqrt( ( double )( images.size() ) ) );
int h = cvCeil( ( double )( images.size() ) / w );
int size = images.size() <= 2 ? 300 : 2 * 300 / w;

But you will not get the same result as your original code e.g. images.size() == 7 results in w == 3 not w == 4. Having such a limited number of cases (12) the fastest and most flexible method are lookup tables:

static const int wl[] = { 0,1,2,2,2,3,3,3,3,3,4,4,4 };
static conat int hl[] = { 0,1,1,2,2,2,2,3,3,3,3,3,3 };
static const int sl[] = { 0,300,300,200,150 };
int w = wl[n];
int h = hl[n];
int size = sl[w];

But take care of being consistent. Lookup tables do also offer many ways to create faults.

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Comments

thank you for your answer. it is not necessary to be dependant on older code. i know still must do some corrections when i have time

sturkmen gravatar imagesturkmen ( 2016-01-11 08:01:55 -0500 )edit
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Asked: 2016-01-08 04:35:09 -0500

Seen: 497 times

Last updated: Jan 11 '16