Showing image with changed pixel values openCV - c++

Question

I'm new to openCV and C++. I would like to change the pixel values of an image I loaded and display that new image in another window to compare the results (just visually). However, when I run the code, I get two original images. This means that either my for loop isn't doing what's it suppose to do (which i doubt since it makes sense to me) or the pixel value is lost and is not being saved to show the new image. I read a previous post that said I should include this statement after working with each pixel to set in to the altered image. The statement is: img.at(Point(x,y)) = color.
Could somebody please tell me what I'm doing wrong?
Thank you
cv::Mat img = cv::imread("12.jpg", CV_LOAD_IMAGE_COLOR);
// start of pixel navigation
Mat navigateImage(Mat) {
for(int x = 0; x > img.rows; x++)
{
for(int y = 0; y > img.cols; y++){
Vec3b color = img.at<Vec3b>(Point(x,y));
if ( color[0] > 10 && color [1] > 10 && color[2]> 10 )
{
color[0] = 0 ;
color[1] = 0;
color[2] = 0;
img.at<Vec3b>(Point(x,y)) = color;
}
else
{
color.val[0] = 255 ;
color.val[1] = 255;
color.val[2] = 255;
img.at<Vec3b>(Point(x,y)) = color;
}
}
}
return img;
}
// end of pixel navigation
int main( int argc, char** argv )
{
if(! img.data){
cout << "could not open or find the image" << endl;
return -1;}
Mat newImage = navigateImage(img);
cv::imshow( " Original", img);
cv::imshow( " Altered ", newImage);
cv::waitKey(0);
return 0;
}

Answer 1

(1). Firstly,
for(int x = 0; x > img.rows; x++)
and
for(int y = 0; y > img.cols; y++)
should be
for(int x = 0; x < img.cols; x++)
and
for(int y = 0; y < img.rows; y++)
respectively.
Since, you never enter the loop because of this mistake, both images are same.
(2). Secondly,
Mat navigateImage(Mat)
should be
Mat navigateImage(Mat img)
(3). Thirdly, put
cv::Mat img = cv::imread("12.jpg", CV_LOAD_IMAGE_COLOR);
in main function.
(4). Lastly,
replace,
Mat newImage = navigateImage();
by
Mat newImage = navigateImage(img.clone());
else, both images will be same.
CORRECTED CODE -
#include <iostream>
#include <opencv2/opencv.hpp>
using namespace cv;
using namespace std;
// start of pixel navigation
Mat navigateImage(Mat img) {
for(int x = 0; x < img.cols; x++)
{
for(int y = 0; y < img.rows; y++){
Vec3b color = img.at<Vec3b>(Point(x,y));
if ( color[0] > 10 && color [1] > 10 && color[2]> 10 )
{
color[0] = 0 ;
color[1] = 0;
color[2] = 0;
img.at<Vec3b>(Point(x,y)) = color;
}
else
{
color.val[0] = 255 ;
color.val[1] = 255;
color.val[2] = 255;
img.at<Vec3b>(Point(x,y)) = color;
}
}
}
return img;
}
// end of pixel navigation
int main( int argc, char** argv )
{
Mat img = cv::imread("12.png", CV_LOAD_IMAGE_COLOR);
if(! img.data){
cout << "could not open or find the image" << endl;
return -1;
}
Mat newImage = navigateImage(img.clone());
cv::imshow( " Original", img);
cv::imshow( " Altered ", newImage);
cv::waitKey(0);
return 0;
}