在opencv中获取纸币的边界框

Question

我想裁剪纸币的边界框。我有以下代码为图像中的轮廓绘制边界框。使用绘制的矩形，我想裁剪最大的矩形。有人能指出我该怎么做吗？

我的代码如下。

#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
#include <stdlib.h>

using namespace cv;
using namespace std;

Mat src; Mat src_gray;
int thresh = 100;
int max_thresh = 255;
RNG rng(12345);

/// Function header
void thresh_callback(int, void* );

/**
 * @function main
 */
int main( int, char** argv )
{
  /// Load source image and convert it to gray
  src = imread( "image_of_the_currency_note.jpg", 1 );

  /// Convert image to gray and blur it
  cvtColor( src, src_gray, COLOR_BGR2GRAY );
  blur( src_gray, src_gray, Size(3,3) );

  /// Create Window
  const char* source_window = "Source";
  namedWindow( source_window, WINDOW_AUTOSIZE );
  imshow( source_window, src );

  createTrackbar( " Threshold:", "Source", &thresh, max_thresh, thresh_callback );
  thresh_callback( 0, 0 );

  waitKey(0);
  return(0);
}

/**
 * @function thresh_callback
 */
void thresh_callback(int, void* )
{
  Mat threshold_output;
  vector<vector<Point> > contours;
  vector<Vec4i> hierarchy;

  /// Detect edges using Threshold
  threshold( src_gray, threshold_output, thresh, 255, THRESH_BINARY );
  /// Find contours
  findContours( threshold_output, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0) );

  /// Approximate contours to polygons + get bounding rects
  vector<vector<Point> > contours_poly( contours.size() );
  vector<Rect> boundRect( contours.size() );
  //vector<Point2f>center( contours.size() );
  //vector<float>radius( contours.size() );

  for( size_t i = 0; i < contours.size(); i++ )
     { approxPolyDP( Mat(contours[i]), contours_poly[i], 3, true );
       boundRect[i] = boundingRect( Mat(contours_poly[i]) );
     }


  /// Draw polygonal contour + bonding rects
  Mat drawing = Mat::zeros( threshold_output.size(), CV_8UC3 );
  for( size_t i = 0; i< contours.size(); i++ )
     {
       Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
       drawContours( drawing, contours_poly, (int)i, color, 1, 8, vector<Vec4i>(), 0, Point() );
       rectangle( drawing, boundRect[i].tl(), boundRect[i].br(), color, 2, 8, 0 );
     }

  /// Show in a window
  namedWindow( "Contours", WINDOW_AUTOSIZE );
  imshow( "Contours", drawing );
}

图片附在此处。 “image_of_the_currency_note”是原始图像，“bounding_box_drawn_for_the_contours_in_the_currency_note”显示为原始图像绘制的边界框。我想将图像中最大的边界框设置为 opencv Mat 对象。

http://oi57.tinypic.com/wjcade.jpg - image_of_the_currency_note

http://oi57.tinypic.com/2cqzbsh.jpg - bounding_box_drawn_for_the_contours_in_the_currency_note

如果有人能告诉我如何做到这一点，那将是一个很大的帮助。

谢谢。

Answer 1

只需检查boundRect[i].width > threshold && boundRect[i].height > threshold。阈值可以是图像大小的三分之一。因此，如果 boundRect[i] 通过条件，则保留它，否则丢弃它。这样就可以得到最大的矩形了。

另一种方法

您的每个轮廓由矩形的四个点（例如 A、B、C、D）组成。您只需提取轮廓每个点的 x 和 y 坐标值。

提取每个点的x和y值后，只需要设置一个条件，如果（两个后续点之间的距离>某个值）则保留该轮廓，否则丢弃它。

例如：只检查是否 (B.x - A.x > 100) then if true..保持轮廓。

Answer 2

我在 opencv 中找到了 contourArea() 函数，并决定使用它来获取最大轮廓并绘制最大轮廓的边界框。

  int largest_area=0;
  int largest_contour_index=0;
  Rect bounding_rect;

  for( size_t i = 0; i < contours.size(); i++ ) { 
      double a=contourArea( contours[i],false);  //  Find the area of contour
      if(a>largest_area){
        largest_area=a;
        largest_contour_index=i;                //Store the index of largest contour
        bounding_rect=boundingRect(contours[i]); // Find the bounding rectangle for biggest contour
      }

  }

  Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
  //drawContours( src, contours,largest_contour_index, color, CV_FILLED, 8, hierarchy ); // Draw the largest contour using previously stored index.
  rectangle(src, bounding_rect,  Scalar(0,255,0),1, 8,0);