cv::RotatedRect 中的非零像素数 [英] Number of non-zero pixels in a cv::RotatedRect

问题描述

正如标题所说，我正在尝试在 cv::Mat 的某个区域(即 RotatedRect 内)中查找非零像素的数量.

as the title says i'm trying to find the number of non-zero pixels in a certain area of a cv::Mat, namely within a RotatedRect.

对于常规 Rect，可以简单地在 ROI 上使用 countNonZeroPixels.然而，ROI 只能是常规(非旋转)矩形.

For a regular Rect one could simply use countNonZeroPixels on a ROI. However ROIs can only be regular (non rotated) rectangles.

另一个想法是绘制旋转的矩形并将其用作蒙版.然而 openCV 既不支持绘制旋转的矩形也不支持 countNonZeroPixels 接受掩码.

Another idea was to draw the rotated rectangle and use that as a mask. However openCV neither supports the drawing of rotated rectangles nor does countNonZeroPixels accept a mask.

有没有人可以优雅地解决这个问题?

Does anyone have a solution for how to elegantly solve this ?

谢谢！

推荐答案

好的，这是我的第一次尝试.

Ok, so here's my first take at it.

这个想法是将图像反向旋转到矩形的旋转，然后在拉直的矩形上应用 roi.

The idea is to rotate the image reverse to the rectangle's rotation and than apply a roi on the straightened rectangle.

• 如果旋转的矩形不完全在图像内，这将中断

• 您可能可以通过在旋转之前应用另一个 roi 来加快速度，以避免旋转整个图像...

• This will break if the rotated rectangle is not completely within the image

• You can probably speed this up by applying another roi before rotation to avoid having to rotate the whole image...

#include <highgui.h>
#include <cv.h>


// From http://stackoverflow.com/questions/2289690/opencv-how-to-rotate-iplimage
cv::Mat rotateImage(const cv::Mat& source, cv::Point2f center, double angle)
{
  cv::Mat rot_mat = cv::getRotationMatrix2D(center, angle, 1.0);
  cv::Mat dst;
  cv::warpAffine(source, dst, rot_mat, source.size());
  return dst;
}

int main()
{
  cv::namedWindow("test1");

  // Our rotated rect
  int x = 300;
  int y = 350;
  int w = 200;
  int h = 50;
  float angle = 47;
  cv::RotatedRect rect = cv::RotatedRect(cv::Point2f(x,y), cv::Size2f(w,h), angle);

  // An empty image
  cv::Mat img = cv::Mat(cv::Size(640, 480), CV_8UC3);

  // Draw rotated rect as an ellipse to get some visual feedback
  cv::ellipse(img, rect, cv::Scalar(255,0,0), -1);

  // Rotate the image by rect.angle * -1
  cv::Mat rotimg = rotateImage(img, rect.center, -1 * rect.angle);

  // Set roi to the now unrotated rectangle
  cv::Rect roi;
  roi.x = rect.center.x - (rect.size.width / 2);
  roi.y = rect.center.y - (rect.size.height / 2);
  roi.width = rect.size.width;
  roi.height = rect.size.height;

  cv::imshow("test1", rotimg(roi));
  cv::waitKey(0);
}

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