使用OpenCV从图像中提取不同尺寸的矩形

使用OpenCV从图像中提取不同尺寸的矩形不正常工作它不会给我们所有字符的补丁，只给我们一个补丁，但是我想要所有字符的补丁

#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 argc, char** argv )
{
  /// Load source image and convert it to gray
  src = imread( "1a.bmp" );
  /// Convert image to gray and blur it
  cvtColor( src, src_gray, CV_BGR2GRAY );
  blur( src_gray, src_gray, Size(3,3) );
  /// Create Window
  char* source_window = "Source";
  namedWindow( source_window, CV_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, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );
  /// Approximate contours to polygons + get bounding rects and circles
  vector<vector<Point> > contours_poly( contours.size() );
  vector<Rect> boundRect( contours.size() );
  vector<Point2f>center( contours.size() );
  vector<float>radius( contours.size() );
  for( int i = 0; i < contours.size(); i++ )
     { approxPolyDP( Mat(contours[i]), contours_poly[i], 3, true );
       boundRect[i] = boundingRect( Mat(contours_poly[i]) );
       minEnclosingCircle( (Mat)contours_poly[i], center[i], radius[i] );
     }

  /// Draw polygonal contour + bonding rects + circles
  Mat drawing = Mat::zeros( threshold_output.size(), CV_8UC3 );
  for( int 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, i, color, 1, 8, vector<Vec4i>(), 0, Point() );
       rectangle( drawing, boundRect[i].tl(), boundRect[i].br(), color, 2, 8, 0 );
      //circle( drawing, center[i], (int)radius[i], color, 2, 8, 0 );
     }
  /// Show in a window
  namedWindow( "Contours", CV_WINDOW_AUTOSIZE );
  imshow( "Contours", drawing );
  for(int i = 0; i < boundRect.size(); i++)
{
     Mat patch = src(boundRect[i]);
     //Do whatever you want with the patch (imshow, imwrite,...)
     imshow("Patch",patch);
}
}