myselfesteem - 6 months ago 47

C++ Question

I am extremely new to computer vision and the opencv library.

I've done some googling around to try to find how to make a new image from a vector of Point2fs and haven't found any examples that work. I've seen

`Mat`

I'm working from this example and any help would be appreciated.

Code: I pass in occludedSquare.

`resize(occludedSquare, occludedSquare, Size(0, 0), 0.5, 0.5);`

Mat occludedSquare8u;

cvtColor(occludedSquare, occludedSquare8u, CV_BGR2GRAY);

//convert to a binary image. pixel values greater than 200 turn to white. otherwize black

Mat thresh;

threshold(occludedSquare8u, thresh, 170.0, 255.0, THRESH_BINARY);

GaussianBlur(thresh, thresh, Size(7, 7), 2.0, 2.0);

//Do edge detection

Mat edges;

Canny(thresh, edges, 45.0, 160.0, 3);

//Do straight line detection

vector<Vec2f> lines;

HoughLines( edges, lines, 1.5, CV_PI/180, 50, 0, 0 );

//imshow("thresholded", edges);

cout << "Detected " << lines.size() << " lines." << endl;

// compute the intersection from the lines detected...

vector<Point2f> intersections;

for( size_t i = 0; i < lines.size(); i++ )

{

for(size_t j = 0; j < lines.size(); j++)

{

Vec2f line1 = lines[i];

Vec2f line2 = lines[j];

if(acceptLinePair(line1, line2, CV_PI / 32))

{

Point2f intersection = computeIntersect(line1, line2);

intersections.push_back(intersection);

}

}

}

if(intersections.size() > 0)

{

vector<Point2f>::iterator i;

for(i = intersections.begin(); i != intersections.end(); ++i)

{

cout << "Intersection is " << i->x << ", " << i->y << endl;

circle(occludedSquare8u, *i, 1, Scalar(0, 255, 0), 3);

}

}

//Make new matrix bounded by the intersections

...

imshow("localized", localized);

Answer

Should be as simple as

```
std::vector<cv::Point2f> points;
cv::Mat image(points);
//or
cv::Mat image = cv::Mat(points)
```

The probably confusion is that a cv::Mat is an image `width*height*number`

of channels but it also a mathematical matrix , `rows*columns*other dimension`

.

If you make a Mat from a vector of 'n' 2D points it will create a 2 column by 'n' rows matrix. You are passing this to a function which expects an image.

If you just have a scattered set of 2D points and want to display them as an image you need to make an empty cv::Mat of large enough size (whatever your maximum x,y point is) and then draw the dots using the drawing functions http://docs.opencv.org/doc/tutorials/core/basic_geometric_drawing/basic_geometric_drawing.html

If you just want to set the pixel values at those point coordinates search SO for opencv setting pixel values, there are lots of answers