Opencv C++ Tutorial Sliding Window

Sliding Window, search objects single scale

Opencv C++ tutorial about the object detection with sliding window. Sliding window is easy to implement in single scale and also not to much harder  to implement in multi scale for example detection inside the bigger mat. I would like to visualize all the step during the code and described by natural c++ way. As a // comments. Enjoy the coding.. 

First tutorial about mat resizeing is Mat Resize
Second tutorial mat roi Roi

Opencv instalation for the tutorial

You can simple prepare the project inside the Visual Studio 2015 by Nuget Packages. This approach is easy for beginers and better than standard installation with all the environmental variables problems. Just follow the installation steps inside here

I am using Visual Studio 2015,  How to use Opencv 3.0.0 with Visual Studio can be found here install opencv visual studio 2015.

  Sliding window for detection opencv code

#include <Windows.h>

#include "opencv2\highgui.hpp"
#include "opencv2\imgproc.hpp"

#include "opencv2/video/background_segm.hpp"
#include "opencv2/video/tracking.hpp"

using namespace cv;
using namespace std;

int main(int argc, const char** argv)
{
//
//  Load the image from file
//
Mat LoadedImage;
// Just loaded image Lenna.png from project dir to LoadedImage Mat
LoadedImage = imread("Lenna.png", IMREAD_COLOR);
//I would like to visualize Mat step by step to see the result immediately.

// Show what is in the Mat after load
namedWindow("Step 1 image loaded", WINDOW_AUTOSIZE);
imshow("Step 1 image loaded", LoadedImage);
waitKey(1000);
        

// Same the result from LoadedImage to Step1.JPG
imwrite("Step1.JPG", LoadedImage);



// Parameters of your slideing window

int windows_n_rows = 60;
int windows_n_cols = 60;
         // Step of each window
        int StepSlide = 30;

// Just copy of Loaded image
// Note that Mat img = LoadedImage; This syntax only put reference on LoadedImage
// Whot does it mean ? if you change img, LoadeImage is changed 2. 
// IF you want to make a copy, and do not change the source image- Use clone();
Mat DrawResultGrid= LoadedImage.clone();

                // Cycle row step
for (int row = 0; row <= LoadedImage.rows - windows_n_rows; row += StepSlide)
{
     // Cycle col step
for (int col = 0; col <= LoadedImage.cols - windows_n_cols; col += StepSlide)
{
// There could be feature evaluator  over Windows

// resulting window
Rect windows(col, row, windows_n_rows, windows_n_cols);

Mat DrawResultHere = LoadedImage.clone();

// Draw only rectangle
rectangle(DrawResultHere, windows, Scalar(255), 1, 8, 0);
// Draw grid
rectangle(DrawResultGrid, windows, Scalar(255), 1, 8, 0);

// Show  rectangle
namedWindow("Step 2 draw Rectangle", WINDOW_AUTOSIZE);
imshow("Step 2 draw Rectangle", DrawResultHere);
waitKey(100);
imwrite("Step2.JPG", DrawResultHere);

                         

// Show grid
namedWindow("Step 3 Show Grid", WINDOW_AUTOSIZE);
imshow("Step 3 Show Grid", DrawResultGrid);
waitKey(100);
imwrite("Step3.JPG", DrawResultGrid);

                      

// Select windows roi
Mat Roi = LoadedImage(windows);

//Show ROI
namedWindow("Step 4 Draw selected Roi", WINDOW_AUTOSIZE);
imshow("Step 4 Draw selected Roi", Roi);
waitKey(100);
imwrite("Step4.JPG", Roi);

}
}

}