OpenCV - OpenCV DevZone

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h1. How to Display more than one image in a single window:

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There is no inbuilt support to display more than one image in OpenCV. Here is a function illustrating how to display more than one image in a single window using Intel OpenCV. The method used is to set the ROIs of a Single Big image and then resizing and copying the input images on to the Single Big Image.

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<pre><code class="cpp">

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#include <cv.h>

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#include <highgui.h>

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#include <stdio.h>

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#include <stdarg.h>

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/*Function///////////////////////////////////////////////////////////////

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Name:       cvShowManyImages

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Purpose:    This is a function illustrating how to display more than one

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               image in a single window using Intel OpenCV

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Parameters: char *title: Title of the window to be displayed

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            int nArgs:   Number of images to be displayed

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            ...:         IplImage*, which contains the images

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Language:   C++

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The method used is to set the ROIs of a Single Big image and then resizing

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and copying the input images on to the Single Big Image.

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This function does not stretch the image...

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It resizes the image without modifying the width/height ratio..

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This function can be called like this:

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cvShowManyImages("Images", 2, img1, img2);

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or

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cvShowManyImages("Images", 5, img2, img2, img3, img4, img5);

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This function can display upto 12 images in a single window.

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It does not check whether the arguments are of type IplImage* or not.

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The maximum window size is 700 by 660 pixels.

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Does not display anything if the number of arguments is less than

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    one or greater than 12.

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If you pass a pointer that is not IplImage*, Error will occur.

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Take care of the number of arguments you pass, and the type of arguments,

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which should be of type IplImage* ONLY.

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Idea was from [[BettySanchi]] of OpenCV Yahoo! Groups.

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If you have trouble compiling and/or executing

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this code, I would like to hear about it.

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You could try posting on the OpenCV Yahoo! Groups

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[url]http://groups.yahoo.com/group/OpenCV/messages/ [/url]

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Parameswaran,

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Chennai, India.

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cegparamesh[at]gmail[dot]com

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...

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///////////////////////////////////////////////////////////////////////*/

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void cvShowManyImages(char* title, int nArgs, ...) {

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    // img - Used for getting the arguments

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    IplImage *img;

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    // [[DispImage]] - the image in which input images are to be copied

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    IplImage *DispImage;

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    int size;

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    int i;

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    int m, n;

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    int x, y;

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    // w - Maximum number of images in a row

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    // h - Maximum number of images in a column

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    int w, h;

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    // scale - How much we have to resize the image

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    float scale;

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    int max;

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    // If the number of arguments is lesser than 0 or greater than 12

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    // return without displaying

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    if(nArgs <= 0) {

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        printf("Number of arguments too small....\n");

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        return;

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    else if(nArgs > 12) {

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        printf("Number of arguments too large....\n");

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        return;

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    // Determine the size of the image,

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    // and the number of rows/cols

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    // from number of arguments

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    else if (nArgs == 1) {

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        w = h = 1;

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        size = 300;

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    else if (nArgs == 2) {

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        w = 2; h = 1;

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        size = 300;

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    else if (nArgs == 3 || nArgs == 4) {

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        w = 2; h = 2;

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        size = 300;

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    else if (nArgs == 5 || nArgs == 6) {

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        w = 3; h = 2;

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        size = 200;

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    else if (nArgs == 7 || nArgs == 8) {

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        w = 4; h = 2;

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        size = 200;

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    else {

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        w = 4; h = 3;

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        size = 150;

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    // Create a new 3 channel image

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    [[DispImage]] = cvCreateImage( cvSize(100 + size*w, 60 + size*h), 8, 3 );

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    // Used to get the arguments passed

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    va_list args;

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    va_start(args, nArgs);

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    // Loop for nArgs number of arguments

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    for (i = 0, m = 20, n = 20; i < nArgs; i++, m += (20 + size)) {

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        // Get the Pointer to the IplImage

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        img = va_arg(args, IplImage*);

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        // Check whether it is NULL or not

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        // If it is NULL, release the image, and return

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        if(img == 0) {

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            printf("Invalid arguments");

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            cvReleaseImage(&DispImage);

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            return;

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        // Find the width and height of the image

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        x = img->width;

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        y = img->height;

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        // Find whether height or width is greater in order to resize the image

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        max = (x > y)? x: y;

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        // Find the scaling factor to resize the image

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        scale = (float) ( (float) max / size );

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        // Used to Align the images

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        if( i % w == 0 && m!= 20) {

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            m = 20;

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            n+= 20 + size;

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        // Set the image ROI to display the current image

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        cvSetImageROI(DispImage, cvRect(m, n, (int)( x/scale ), (int)( y/scale )));

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        // Resize the input image and copy the it to the Single Big Image

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        cvResize(img, DispImage);

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        // Reset the ROI in order to display the next image

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        cvResetImageROI(DispImage);

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    // Create a new window, and show the Single Big Image

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    cvNamedWindow( title, 1 );

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    cvShowImage( title, DispImage);

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    cvWaitKey();

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    cvDestroyWindow(title);

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    // End the number of arguments

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    va_end(args);

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    // Release the Image Memory

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    cvReleaseImage(&DispImage);

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</code></pre>

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You can use this function as in this sample program:

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<pre><code class="cpp">int main() {

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    IplImage *img1 = cvLoadImage("Image01.jpg");

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    IplImage *img2 = cvLoadImage("Image02.jpg");

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    IplImage *img3 = cvLoadImage("Image03.jpg");

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    IplImage *img4 = cvLoadImage("Image04.jpg");

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    IplImage *img5 = cvLoadImage("Image05.jpg");

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    IplImage *img6 = cvLoadImage("Image06.jpg");

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    cvShowManyImages("Image", 6, img1, img2, img3, img4, img5, img6);

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    return 0;

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</code></pre>

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The method used is to set the ROIs of a Single Big image and then resizing and copying the input images on to the Single Big Image.

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This function does not stretch the image... It resizes the image without modifying the width/height ratio..

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This function can be called like this:

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<pre><code class="cpp">    cvShowManyImages("Image", 2, img1, img2);</code></pre>

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or

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<pre><code class="cpp">    cvShowManyImages("Image", 6, img1, img2, img3, img4, img5, img6);</code></pre>

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upto 12 images.

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This function can display upto 12 images in a single window. It does not check whether the arguments are of type IplImage* or not. The maximum window size is 700 by 660 pixels. Does not display anything if the number of arguments is less than one or greater than 12.

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If you pass a pointer that is not IplImage*, Error will occur. Take care of the number of arguments you pass, and the type of arguments, which should be of type IplImage* ONLY.

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Idea was from BettySanchi of OpenCV Yahoo! Groups.

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If you have trouble compiling and/or executing this code, I would like to hear about it.

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Here is a sample ScreenShot:

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!DisplayManyImages.jpg!

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Regards :) Paramesh.

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