How do I loop through Matrix data how it appears? - c++

Question

Situation
I have a matrix which is 300 columns and 1 row. When I cout << it, I get:
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
...which is of the form I expect/want.
Problem
However, when I loop through it, I want to get each single value each iteration. However, instead I get a slightly different order (sometimes it is quite similar, though).
Code
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/core/core.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/imgcodecs/imgcodecs.hpp"
using namespace std;
using namespace cv;
int main(){
Mat test(1,300,CV_8UC1, 255);
cout << test;
Mat frame, grayFrame,threshFrame,smaller;
VideoCapture cap(0);
while(true){
cap.read(frame);
cvtColor(frame, grayFrame, cv::COLOR_RGB2GRAY);
threshold(grayFrame, threshFrame, 160, 255, THRESH_BINARY);
smaller = threshFrame(Rect(0,0,300,1));
cout << smaller;
for(int x=0;x<smaller.cols;x++){
int color = smaller.at<Vec3b>(x,1)[0];
cout << color;
}
break;
}
}
... And the weird output that does not follow the exact same order of 0s and 255s as the original Matrix:
00000000000000000000000000000000000000000000000000000000000000000000000000000000000002552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552552550000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
The matrix has many 0s at first, and few 255s, where as the loop output has many 255s, and not so much beginning 0s.
Essentially, I want to loop through the matrix first shown, and for each iteration, get each value. So 0,0,255,255... etc.

Answer 1

You're reading garbage.
The at function needs (row, col), and not (x, y). Remember that row = y, and col = x.
If your matrix is just a single row, the row index must be 0, not 1.
Your matrix is a single channel of unsigned char, so you need to use at<uchar>
In practice, use:
uchar color = smaller.at<uchar>(0, x);
cout << int(color);
or using indices:
uchar color = smaller.at<uchar>(x);