OpenCV: output image is blue - c++

Question

so i'm making this project where i'm making the reflection of an image on OpenCV (without using the flip function), and the only problem (i think) to finish it, is that the image that is suppose to come out reflected, is coming out as all blue.
The code i have (i took out the usual part, the problem should be around here):
Mat imageReflectionFinal = Mat::zeros(Size(220,220),CV_8UC3);
for(unsigned int r=0; r<221; r++)
for(unsigned int c=0; c<221; c++) {
Vec3b intensity = image.at<Vec3b>(r,c);
imageReflectionFinal.at<Vec3b>(r,c) = (uchar)(c, -r + (220)/2);
}
///displays images
imshow( "Original Image", image );
imshow("Reflected Image", imageReflectionFinal);
waitKey(0);
return 0;
}

Answer 1

There are some problems with your code. As pointed out, your iteration variables go beyond the actual image dimensions. Do not use hardcoded bounds, you can use inputImage.cols and inputImage.rows instead to obtain the image dimensions.
There’s the variable (a BGR Vec3b) that is set but not used - Vec3b intensity = image.at<Vec3b>(r,c);
Most importantly, it is not clear what you are trying to achieve. The line (uchar)(c, -r + (220)/2); does not give out much info. Also, which direction are you flipping the original image around? X or Y axis?
Here’s a possible solution to flip your image in the X direction:
//get input image:
cv::Mat testMat = cv::imread( "lena.png" );
//Get the input image size:
int matCols = testMat.cols;
int matRows = testMat.rows;
//prepare the output image:
cv::Mat imageReflectionFinal = cv::Mat::zeros( testMat.size(), testMat.type() );
//the image will be flipped around the x axis, so the "target"
//row will start at the last row of the input image:
int targetRow = matRows-1;
//loop thru the original image, getting the current pixel value:
for( int r = 0; r < matRows; r++ ){
for( int c = 0; c < matCols; c++ ) {
//get the source pixel:
cv::Vec3b sourcePixel = testMat.at<cv::Vec3b>( r , c );
//source and target columns are the same:
int targetCol = c;
//set the target pixel
imageReflectionFinal.at<cv::Vec3b>( targetRow , targetCol ) = sourcePixel;
}
//for every iterated source row, decrease the number of
//target rows, as we are flipping the pixels in the x dimension:
targetRow--;
}
Result: