显示像素值已更改的图像openCV

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;

}