C++ OpenCV downsized videoCapture frame stretched and cropped - c++

Question

I am trying to get a calibration program for captured thermal video converted from python to C++, and the first step in the process is binning the pixels in the image down from 480x640 to 240x320, so pixel bins of 2x2. The returned image after binning (using the same logic from the correctly functioning python version) the image being returned is the left half of the image stretched across the width of the image, rather than giving the whole image only at the smaller resolution.
#include <opencv2/opencv.hpp>
#include <opencv2/core/core.hpp>
#include <opencv2/videoio/videoio.hpp>
#include <opencv2/video.hpp>
#include <opencv2/imgcodecs.hpp>
#include <iostream>
using namespace std;
using namespace cv;
Mat binImg(Mat);
int asInt(uint8_t);
uint8_t as8bit(int);
Mat rotate(Mat, double);
int main(int argc, char *argv[]){
VideoCapture cap(argv[1]);
int frameCount = cap.get(cv::CAP_PROP_FRAME_COUNT);
int frameWidth = cap.get(cv::CAP_PROP_FRAME_WIDTH);
int frameHeight = cap.get(cv::CAP_PROP_FRAME_HEIGHT);
Mat buf [frameCount]; //create new array of Mat for the calibrated video
int fc = 0;
VideoWriter video("cppThermalTest.avi",CV_FOURCC('X','V','I','D'), 15, Size(240, 320), false); //create empty video #15fps, 320x240, isColor=false
while (fc < frameCount){
Mat frame(640, 480, CV_8UC1, Scalar(70));
cap >> frame;
Mat temp = binImg(frame);//bin the frame
imshow("test", temp);
imwrite("test.jpg", temp);
waitKey(0);
video.write(temp); //write the binned frame to the video
cout << fc << endl;
fc++;
}
cap.release();
video.release();
return 0;
}
Mat binImg(Mat frame){
int frameWidth = frame.cols / 2; //480 / 2
int frameHeight = frame.rows / 2; //640 / 2
cout << frameHeight << " " << frameWidth << endl;
Mat binFrame(frameHeight, frameWidth, CV_8UC1);
for(int i=0; i<binFrame.rows; i++){
for(int j=0; j<binFrame.cols; j++){
int ul = asInt(frame.at<uint8_t>((2*i),(2*j)));
int bl = asInt(frame.at<uint8_t>(((2*i)+1),(2*j)));
int ur = asInt(frame.at<uint8_t>((2*i), ((2*j)+1)));
int br = asInt(frame.at<uint8_t>(((2*i)+1),((2*j)+1)));
int avg = (ul + ur + bl + br) / 4;
binFrame.at<uint8_t>(i,j) = as8bit(avg); //set the matrix element to the new value
}
}
return binFrame;
}
int asInt(uint8_t val){
//convert unsigned 8 bit int to int
int temp = val;
return temp;
}
uint8_t as8bit(int val){
//convert int to unsigned 8 bit int
uint8_t temp = val;
return temp;
}
Mat rotate(Mat src, double angle){ //rotate function returning mat object with parametres imagefile and angle
Mat dst; //Mat object for output image file
Point2f pt(src.cols/2., src.rows/2.); //point from where to rotate
Mat r = getRotationMatrix2D(pt, angle, 1.0); //Mat object for storing after rotation
warpAffine(src, dst, r, Size(src.cols, src.rows)); ///applie an affine transforation to image.
return dst; //returning Mat object for output image file
}

Answer 1

After playing around with things for a while, I found that when doing "at" calls, specifying 0 as a third parameter (e.g. binFrame.at<uint8_t>(i,j, 0) = as8bit(avg);) fixes the issue.