In the previous tutorials (about linear blending and the brightness and contrast adjustments) you might have noted that we needed to give some input to our programs, such as and . We accomplished that by entering this data using the Terminal
Well, it is time to use some fancy GUI tools. OpenCV provides some GUI utilities (highgui.h) for you. An example of this is a Trackbar
In this tutorial we will just modify our two previous programs so that they get the input information from the trackbar.
In this tutorial you will learn how to:
Let’s modify the program made in the tutorial Adding (blending) two images using OpenCV. We will let the user enter the value by using the Trackbar.
#include <opencv2/opencv.hpp>
using namespace cv;
/// Global Variables
const int alpha_slider_max = 100;
int alpha_slider;
double alpha;
double beta;
/// Matrices to store images
Mat src1;
Mat src2;
Mat dst;
/**
* @function on_trackbar
* @brief Callback for trackbar
*/
void on_trackbar( int, void* )
{
alpha = (double) alpha_slider/alpha_slider_max ;
beta = ( 1.0 - alpha );
addWeighted( src1, alpha, src2, beta, 0.0, dst);
imshow( "Linear Blend", dst );
}
int main( int argc, char** argv )
{
/// Read image ( same size, same type )
src1 = imread("../../images/LinuxLogo.jpg");
src2 = imread("../../images/WindowsLogo.jpg");
if( !src1.data ) { printf("Error loading src1 \n"); return -1; }
if( !src2.data ) { printf("Error loading src2 \n"); return -1; }
/// Initialize values
alpha_slider = 0;
/// Create Windows
namedWindow("Linear Blend", 1);
/// Create Trackbars
char TrackbarName[50];
sprintf( TrackbarName, "Alpha x %d", alpha_slider_max );
createTrackbar( TrackbarName, "Linear Blend", &alpha_slider, alpha_slider_max, on_trackbar );
/// Show some stuff
on_trackbar( alpha_slider, 0 );
/// Wait until user press some key
waitKey(0);
return 0;
}
We only analyze the code that is related to Trackbar:
First, we load 02 images, which are going to be blended.
src1 = imread("../../images/LinuxLogo.jpg");
src2 = imread("../../images/WindowsLogo.jpg");
To create a trackbar, first we have to create the window in which it is going to be located. So:
namedWindow("Linear Blend", 1);
Now we can create the Trackbar:
createTrackbar( TrackbarName, "Linear Blend", &alpha_slider, alpha_slider_max, on_trackbar );
Note the following:
Finally, we have to define the callback function on_trackbar
void on_trackbar( int, void* )
{
alpha = (double) alpha_slider/alpha_slider_max ;
beta = ( 1.0 - alpha );
addWeighted( src1, alpha, src2, beta, 0.0, dst);
imshow( "Linear Blend", dst );
}
Note that:
Our program produces the following output:
As a manner of practice, you can also add 02 trackbars for the program made in Changing the contrast and brightness of an image!. One trackbar to set and another for . The output might look like: