【opencv+C++】在图像中找四边形
【opencv+C++】在图像中找四边形
- 1562
- /*
- 这个程序的基本思想是:对输入的图像进行滤波去掉噪音,然后进行canny边缘检测,之后进行膨胀,然后寻找轮廓,对轮廓进行多边形的逼近,检测多边形的点数是否是4而且各个角的的余弦是否是小于某个值,程序中认为是0.3,然后就判断该多边形是四边形,之后根据这四个点画出该图像。
- ps:我对程序中余弦定理的使用 感觉公式用错了
- */
- #include "stdafx.h"
- #include "cv.h"
- #include "highgui.h"
- #include <stdio.h>
- #include <math.h>
- #include <string.h>
- int thresh = 50;
- IplImage* img = 0;
- IplImage* img0 = 0;
- CvMemStorage* storage = 0;
- CvPoint pt[4];
- const char* wndname = "Square Detection Demo";
- // helper function:
- // finds a cosine of angle between vectors
- // from pt0->pt1 and from pt0->pt2
- double angle( CvPoint* pt1, CvPoint* pt2, CvPoint* pt0 )
- {
- double dx1 = pt1->x - pt0->x;
- double dy1 = pt1->y - pt0->y;
- double dx2 = pt2->x - pt0->x;
- double dy2 = pt2->y - pt0->y;
- //1e-10就是“aeb”的形式,表示a乘以10的b次方。
- //其中b必须是整数,a可以是小数。
- //?余弦定理CosB=(a^2+c^2-b^2)/2ac??所以这里的计算似乎有问题
- return (dx1*dx2 + dy1*dy2)/sqrt((dx1*dx1 + dy1*dy1)*(dx2*dx2 + dy2*dy2) + 1e-10);
- }
- // returns sequence of squares detected on the image.
- // the sequence is stored in the specified memory storage
- CvSeq* findSquares4( IplImage* img, CvMemStorage* storage )
- {
- CvSeq* contours;
- int i, c, l, N = 11;
- CvSize sz = cvSize( img->width & -2, img->height & -2 );
- IplImage* timg = cvCloneImage( img ); // make a copy of input image
- IplImage* gray = cvCreateImage( sz, 8, 1 );
- IplImage* pyr = cvCreateImage( cvSize(sz.width/2, sz.height/2), 8, 3 );
- IplImage* tgray;
- CvSeq* result;
- double s, t;
- // create empty sequence that will contain points -
- // 4 points per square (the square's vertices)
- CvSeq* squares = cvCreateSeq( 0, sizeof(CvSeq), sizeof(CvPoint), storage );
- // select the maximum ROI in the image
- // with the width and height divisible by 2
- cvSetImageROI( timg, cvRect( 0, 0, sz.width, sz.height ));
- // down-scale and upscale the image to filter out the noise
- //使用gaussian金字塔分解对输入图像向下采样,首先对它输入的图像用指定滤波器
- //进行卷积,然后通过拒绝偶数的行与列来下采样
- cvPyrDown( timg, pyr, 7 );
- //函数 cvPyrUp 使用Gaussian 金字塔分解对输入图像向上采样。首先通过在图像中插入 0 偶数行和偶数列,然后对得到的图像用指定的滤波器进行高斯卷积,其中滤波器乘以4做插值。所以输出图像是输入图像的 4 倍大小。
- cvPyrUp( pyr, timg, 7 );
- tgray = cvCreateImage( sz, 8, 1 );
- // find squares in every color plane of the image
- for( c = 0; c < 3; c++ )
- {
- // extract the c-th color plane
- //函数 cvSetImageCOI 基于给定的值设置感兴趣的通道。值 0 意味着所有的通道都被选定, 1 意味着第一个通道被选定等等。
- cvSetImageCOI( timg, c+1 );
- cvCopy( timg, tgray, 0 );
- // try several threshold levels
- for( l = 0; l < N; l++ )
- {
- // hack: use Canny instead of zero threshold level.
- // Canny helps to catch squares with gradient shading
- if( l == 0 )
- {
- // apply Canny. Take the upper threshold from slider
- // and set the lower to 0 (which forces edges merging)
- cvCanny( tgray, gray,60, 180, 3 );
- // dilate canny output to remove potential
- // holes between edge segments
- //使用任意结构元素膨胀图像
- cvDilate( gray, gray, 0, 1 );
- }
- else
- {
- // apply threshold if l!=0:
- // tgray(x,y) = gray(x,y) < (l+1)*255/N ? 255 : 0
- //cvThreshold( tgray, gray, (l+1)*255/N, 255, CV_THRESH_BINARY );
- cvThreshold( tgray, gray, 50, 255, CV_THRESH_BINARY );
- }
- // find contours and store them all as a list
- cvFindContours( gray, storage, &contours, sizeof(CvContour),
- CV_RETR_LIST, CV_CHAIN_APPROX_SIMPLE, cvPoint(0,0) );
- // test each contour
- while( contours )
- {
- // approximate contour with accuracy proportional
- // to the contour perimeter
- //用指定精度逼近多边形曲线
- result = cvApproxPoly( contours, sizeof(CvContour), storage,
- CV_POLY_APPROX_DP, cvContourPerimeter(contours)*0.02, 0 );
- // square contours should have 4 vertices after approximation
- // relatively large area (to filter out noisy contours)
- // and be convex.
- // Note: absolute value of an area is used because
- // area may be positive or negative - in accordance with the
- // contour orientation
- //cvContourArea 计算整个轮廓或部分轮廓的面积
- //cvCheckContourConvexity测试轮廓的凸性
- if( result->total == 4 &&
- fabs(cvContourArea(result,CV_WHOLE_SEQ)) > 1000 &&
- cvCheckContourConvexity(result) )
- {
- s = 0;
- for( i = 0; i < 5; i++ )
- {
- // find minimum angle between joint
- // edges (maximum of cosine)
- if( i >= 2 )
- {
- t = fabs(angle(
- (CvPoint*)cvGetSeqElem( result, i ),
- (CvPoint*)cvGetSeqElem( result, i-2 ),
- (CvPoint*)cvGetSeqElem( result, i-1 )));
- s = s > t ? s : t;
- }
- }
- // if cosines of all angles are small
- // (all angles are ~90 degree) then write quandrange
- // vertices to resultant sequence
- if( s < 0.3 )
- for( i = 0; i < 4; i++ )
- cvSeqPush( squares,
- (CvPoint*)cvGetSeqElem( result, i ));
- }
- // take the next contour
- contours = contours->h_next;
- }
- }
- }
- // release all the temporary images
- cvReleaseImage( &gray );
- cvReleaseImage( &pyr );
- cvReleaseImage( &tgray );
- cvReleaseImage( &timg );
- return squares;
- }
- // the function draws all the squares in the image
- void drawSquares( IplImage* img, CvSeq* squares )
- {
- CvSeqReader reader;
- IplImage* cpy = cvCloneImage( img );
- int i;
- // initialize reader of the sequence
- cvStartReadSeq( squares, &reader, 0 );
- // read 4 sequence elements at a time (all vertices of a square)
- for( i = 0; i < squares->total; i += 4 )
- {
- CvPoint* rect = pt;
- int count = 4;
- // read 4 vertices
- memcpy( pt, reader.ptr, squares->elem_size );
- CV_NEXT_SEQ_ELEM( squares->elem_size, reader );
- memcpy( pt + 1, reader.ptr, squares->elem_size );
- CV_NEXT_SEQ_ELEM( squares->elem_size, reader );
- memcpy( pt + 2, reader.ptr, squares->elem_size );
- CV_NEXT_SEQ_ELEM( squares->elem_size, reader );
- memcpy( pt + 3, reader.ptr, squares->elem_size );
- CV_NEXT_SEQ_ELEM( squares->elem_size, reader );
- // draw the square as a closed polyline
- cvPolyLine( cpy, &rect, &count, 1, 1, CV_RGB(0,255,0), 3, CV_AA, 0 );
- }
- // show the resultant image
- cvShowImage( wndname, cpy );
- cvReleaseImage( &cpy );
- }
- void on_trackbar( int a )
- {
- if( img )
- drawSquares( img, findSquares4( img, storage ) );
- }
- char* names[] = { "E:\\1.jpg", "E:\\2.jpg", "E:\\3.jpg",
- "E:\\4.jpg", "E:\\5.jpg", 0 };
- int main(int argc, char** argv)
- {
- int i, c;
- // create memory storage that will contain all the dynamic data
- storage = cvCreateMemStorage(0);
- for( i = 0; names[i] != 0; i++ )
- {
- // load i-th image
- img0 = cvLoadImage( names[i], 1 );
- if( !img0 )
- {
- printf("Couldn't load %s\n", names[i] );
- continue;
- }
- img = cvCloneImage( img0 );
- // create window and a trackbar (slider) with parent "image" and set callback
- // (the slider regulates upper threshold, passed to Canny edge detector)
- cvNamedWindow( wndname,0 );
- cvCreateTrackbar( "canny thresh", wndname, &thresh, 1000, on_trackbar );
- // force the image processing
- on_trackbar(0);
- // wait for key.
- // Also the function cvWaitKey takes care of event processing
- c = cvWaitKey(0);
- // release both images
- cvReleaseImage( &img );
- cvReleaseImage( &img0 );
- // clear memory storage - reset free space position
- cvClearMemStorage( storage );
- if( c == 27 )
- break;
- }
- cvDestroyWindow( wndname );
- return 0;
- }
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