Bala - 4 months ago 27

C++ Question

`int main(){`

Mat cmp, Ref, Diff;

cmp = imread("image1.tif", CV_LOAD_IMAGE_UNCHANGED);

Ref = imread("image2.tif", CV_LOAD_IMAGE_UNCHANGED);

ShiftChk(cmp, Ref);

absdiff(cmp, Ref, Diff);

imshow("difference image", Diff);

waitKey(0);

double min, max;

minMaxLoc(Diff, &min, &max);

Point min_loc, max_loc;

minMaxLoc(Diff, &min, &max, &min_loc, &max_loc);

Size sz = Diff.size();

cout << "max val : " << max << endl;//5

cout << "max val: " << max_loc << endl; //[26,38]

vector<vector<double>>test;

for (int i = 0; i < Diff.cols; i++) {

for (int j = 0; j < Diff.rows; j++) {

Point difference = Diff.at<uchar>(26, 38) - Diff.at<uchar>(j, i);

double dist = sqrt(difference.x*difference.x + difference.y*difference.y);

test.push_back(dist);

}

}

}

I am trying to find the Euclidean distance between a single point in an image to all other pixels. The distance values are to be stored in vector test but its showing some error in it. And also I don't know whether the logic I have used is correct to give the right answer(Euclidean distance). Can anyone help me out. Thanks in advance

Error message is:

`error C2664:`

'void std::vector<std::vector<double,std::allocator<_Ty>>,std::allocator<std::vector<_Ty,std::allocator<_Ty>>>>::push_back(const std::vector<_Ty,std::allocator<_Ty>> &)' :

cannot convert argument 1 from 'double' to 'std::vector<double,std::allocator<_Ty>> &&'

Answer

There are two major issues:

You're appending the values to the

`test`

vector wrong. You need either to create an intermediate vector and`push_back`

it to`test`

(as shown in @0X0nosugar answer), or better initialize your vectors with correct dimensions and put the value at the right place.`vector<vector<double>> test(Diff.rows, vector<double>(Diff.cols)); for (int i = 0; i < Diff.rows; i++) { for (int j = 0; j < Diff.cols; j++) { test[i][j] = ... } }`

As shown in the snippet above, it's better (and faster) to scan by rows, becuase OpenCV stores images row-wise.

You are not computing the distance between two points. You are in fact taking the difference of the values at two given points and creating a

`Point`

object out of this (which makes no sense). Also you can avoid to compute explicitly the euclidean distance. You can use`cv::norm`

:`test[i][j] = norm(Point(38, 26) - Point(j, i)); // Pay attention to i,j order!`

Putting all together:

```
Point ref(38, 26);
vector<vector<double>> test(Diff.rows, vector<double>(Diff.cols));
for (int i = 0; i < Diff.rows; i++) {
for (int j = 0; j < Diff.cols; j++) {
test[i][j] = norm(ref - Point(j,i));
}
}
```