OpenCV cvtColor modifies original image too - c++

Question

I have a function that takes an image, converts it to HSV, and sets V to 100. However, it appears to modify the original image too.
Mat hsvfilter(const Mat& img) {
Mat result;
cvtColor(img, result, CV_BGR2HSV);
for (int j = 0; j < img.rows; j++)
for (int i = 0; i < img.cols; i++)
result.at<Vec3d>(i, j)[2] = 100;
return result;
}
Here's how I call it:
Mat original = imread( "pic.png" );
Mat converted = hsvfilter(original);
namedWindow( "original", CV_WINDOW_AUTOSIZE );
imshow( "original", original );
namedWindow( "converted", CV_WINDOW_AUTOSIZE );
imshow( "converted", converted );
waitKey(0);
Both the original image and the converted images end up having strange black vertical bars. I believe my code has some issues with pointers or memory, but I can't quite figure out where. Any help would be appreciated.
EDIT: HERE'S THE FIXED CODE
Mat hsvfilter(const Mat& img) {
Mat result;
cvtColor(img, result, CV_BGR2HSV);
for (int j = 0; j < result.rows; j++) {
for (int i = 0; i < result.cols; i++) {
result.at<cv::Vec3b>(j, i)[2] = 100;
}
}
return result;
}

Answer 1

Your hsvFilter function should looks like this:
Mat hsvfilter(const Mat& img) {
Mat result;
cvtColor(img, result, CV_BGR2HSV);
for (int j = 0; j < result.rows; j++) //you are modyfying "result" object, not img
for (int i = 0; i < result.cols; i++) //same as above
result.at<Vec3d>(j, i)[2] = 100; //OpenCV uses (y,x) indexing
return result;
}
In this situation ther is no difference in using img.cols, img.rows / result.cols, result.rows, because size of both arrays (images) is the same, but generally don't forget about it :) The second comment doesn't need any more explanation.
Generally you code looks fine, in my opinion it should work. Did you try testing it without calling hsvFilter function (just display the original image)?
If you want to keep created windows for some time, use this code instead of waitKey(0);:
while(waitKey(100) != 'q')
{
//all imshow calls
}
Now, when you want to exit, just press 'q' (you need to have one of your app windows active).