如何从彩色矩形构建 cv::Mat

Question

My goal is to create yield maps using OpenCV. These yield maps need to be built with coloured rectangles to indicate yield. An example of a Mat built by rectangles here .

So is it possible to create a cv::Mat with coloured rectangles? The amount of rectangles isn't constant, thus changes with every use.

To make the question clear: if I have 4 boxes (2x2 grid) I want to automatically make a Mat which is as big as the 4 boxes. If I have 16 boxes (4x4 grid) I want to make a Mat which is as big as the 16 boxes.

I couldn't find a way to make it work, so I hope somebody here knows if it is possible.

If somebody can help me that would be great, if it is not possible alternatives are also welcome! Thanks

Some info:

• OpenCV version:4.5.3
• OS: Ubuntu 20.04
• Language: C++

Answer 1

You can create rectangle with OpenCV function.

Basic Geometric Drawing OpenCV

int x = 0;
int y = 0;
int width = 10;
int height = 20;
// our rectangle...
cv::Rect rect(x, y, width, height);
// and its top left corner...
cv::Point pt1(x, y);
// and its bottom right corner.
cv::Point pt2(x + width, y + height);
// These two calls...
cv::rectangle(img, pt1, pt2, cv::Scalar(0, 255, 0));
// essentially do the same thing
cv::rectangle(img, rect, cv::Scalar(0, 255, 0))

ref

Answer 2

OpenCV has cv::hconcat and cv::vconcat . Use them like numpy's hstack/vstack.

make sure your parts have the same type (and number of channels).

The documentation has a code example.

cv::Mat matArray[] = { cv::Mat(4, 1, CV_8UC1, cv::Scalar(1)),
                       cv::Mat(4, 1, CV_8UC1, cv::Scalar(2)),
                       cv::Mat(4, 1, CV_8UC1, cv::Scalar(3)),};
cv::Mat out;
cv::hconcat( matArray, 3, out );
//out:
//[1, 2, 3;
// 1, 2, 3;
// 1, 2, 3;
// 1, 2, 3]