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December 28, 2010 02:42
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Adding automatic thresholding to cvCanny in OpenCV
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| //M*/ | |
| #include "precomp.hpp" | |
| CV_IMPL void cvCanny( const void* srcarr, void* dstarr, | |
| double low_thresh, double high_thresh, | |
| int aperture_size ) | |
| { | |
| cv::Ptr<CvMat> dx, dy; | |
| cv::AutoBuffer<char> buffer; | |
| std::vector<uchar*> stack; | |
| uchar **stack_top = 0, **stack_bottom = 0; | |
| double percent = low_thresh; | |
| CvMat srcstub, *src = cvGetMat( srcarr, &srcstub ); | |
| CvMat dststub, *dst = cvGetMat( dstarr, &dststub ); | |
| CvSize size; | |
| int flags = aperture_size; | |
| int low, high; | |
| uchar* map; | |
| ptrdiff_t mapstep; | |
| int maxsize; | |
| int i, j; | |
| CvMat mag_row; | |
| if( CV_MAT_TYPE( src->type ) != CV_8UC1 || | |
| CV_MAT_TYPE( dst->type ) != CV_8UC1 ) | |
| CV_Error( CV_StsUnsupportedFormat, "" ); | |
| if( !CV_ARE_SIZES_EQ( src, dst )) | |
| CV_Error( CV_StsUnmatchedSizes, "" ); | |
| if( low_thresh > high_thresh ) | |
| { | |
| double t; | |
| CV_SWAP( low_thresh, high_thresh, t ); | |
| } | |
| aperture_size &= INT_MAX; | |
| if( (aperture_size & 1) == 0 || aperture_size < 3 || aperture_size > 7 ) | |
| CV_Error( CV_StsBadFlag, "" ); | |
| size = cvGetMatSize( src ); | |
| // convolve with sobel operator to get derivative approximations | |
| dx = cvCreateMat( size.height, size.width, CV_16SC1 ); | |
| dy = cvCreateMat( size.height, size.width, CV_16SC1 ); | |
| cvSobel( src, dx, 1, 0, aperture_size ); | |
| cvSobel( src, dy, 0, 1, aperture_size ); | |
| if( flags & CV_CANNY_L2_GRADIENT ) | |
| { | |
| Cv32suf ul, uh; | |
| ul.f = (float)low_thresh; | |
| uh.f = (float)high_thresh; | |
| low = ul.i; | |
| high = uh.i; | |
| } | |
| else | |
| { | |
| low = cvFloor( low_thresh ); | |
| high = cvFloor( high_thresh ); | |
| } | |
| // buffer structure will be: top half for 2d mag array, | |
| // bottom half for map of edges (either 0, 1, or 2...see below) | |
| buffer.allocate( (size.width+2)*(size.height+2) + (size.width + 2)*(size.height+2)*sizeof(int) ); | |
| // mag is a pointer to the magnitude array | |
| int *mag = (int*)(char*)buffer; | |
| // map is a pointer to the edges array | |
| map = (uchar*)(mag + (size.width+2)*(size.height+2)); | |
| mapstep = size.width + 2; | |
| maxsize = MAX( 1 << 10, size.width*size.height/10 ); | |
| stack.resize( maxsize ); | |
| stack_top = stack_bottom = &stack[0]; | |
| memset( mag, 0, (size.width + 2) * (size.height + 2) * sizeof(int) ); | |
| memset( map, 1, mapstep ); | |
| memset( map + mapstep*(size.height + 1), 1, mapstep ); | |
| /* sector numbers | |
| (Top-Left Origin) | |
| 1 2 3 | |
| * * * | |
| * * * | |
| 0*******0 | |
| * * * | |
| * * * | |
| 3 2 1 | |
| */ | |
| #define CANNY_PUSH(d) *(d) = (uchar)2, *stack_top++ = (d) | |
| #define CANNY_POP(d) (d) = *--stack_top | |
| mag_row = cvMat( 1, size.width, CV_32F ); | |
| // we actually want to start from (1,1), because there's a 1-cell border | |
| // around the whole image for padding. | |
| mag = mag + size.width + 2 + 1; | |
| // calculate magnitude and angle of gradient, perform non-maxima supression. | |
| // fill the map with one of the following values: | |
| // 0 - the pixel might belong to an edge | |
| // 1 - the pixel can not belong to an edge | |
| // 2 - the pixel does belong to an edge | |
| for( i = 0; i <= size.height; i++ ) | |
| { | |
| // here we move one column over, b/c the first column is padding. | |
| int *_mag = mag + (size.width + 2) * i; | |
| float* _magf = (float*)_mag; | |
| const short* _dx = (short*)(dx->data.ptr + dx->step*i); | |
| const short* _dy = (short*)(dy->data.ptr + dy->step*i); | |
| int x, y; | |
| if( i < size.height ) { | |
| _mag[-1] = _mag[size.width] = 0; | |
| if( !(flags & CV_CANNY_L2_GRADIENT) ) { | |
| for( j = 0; j < size.width; j++ ) { | |
| _mag[j] = abs(_dx[j]) + abs(_dy[j]); | |
| } | |
| } | |
| else { | |
| for( j = 0; j < size.width; j++ ) { | |
| x = _dx[j]; y = _dy[j]; | |
| _magf[j] = (float)std::sqrt((double)x*x + (double)y*y); | |
| } | |
| } | |
| } | |
| else | |
| memset( _mag-1, 0, (size.width + 2)*sizeof(int) ); | |
| } | |
| // Choose better thresholds | |
| int max = 0; | |
| for (i = 0; i < size.height; i++) { | |
| int *_mag = mag + (size.width + 2) * i; | |
| for( j = 0; j < size.width; j++ ) { | |
| if (_mag[j] > max) { | |
| max = _mag[j]; | |
| } | |
| } | |
| } | |
| // step 2: Get the histogram of the data. | |
| #define NUM_BINS 64 | |
| // might want to make this max - min / NUM_BINS after you have normalized. | |
| int bin_size = max / NUM_BINS; | |
| if (bin_size < 1) bin_size = 1; | |
| int bins[NUM_BINS] = { 0 }; | |
| for (i = 0; i < size.height; i++) { | |
| int *_mag = mag + (size.width + 2) * i; | |
| for( j = 0; j < size.width; j++ ) { | |
| bins[_mag[j] / bin_size]++; | |
| } | |
| } | |
| // step 3: get the high threshold | |
| double percent_of_pixels_not_edges = 0.8; | |
| double threshold_ratio = 0.4; | |
| int total = 0; | |
| high = 0; | |
| // size.height should be here too, but right now we're going row-by-row | |
| while (total < size.height * size.width * percent_of_pixels_not_edges) { | |
| total+= bins[high]; | |
| high++; | |
| } | |
| high *= bin_size; | |
| low = threshold_ratio * high; | |
| cout << "high: " << high << endl; | |
| cout << "low: " << low << endl; | |
| int adit = 10; | |
| // non-maxima suppression | |
| for( i = 1; i <= size.height; i++ ) | |
| { | |
| int *_mag = mag + (size.width + 2) * i; | |
| if( (stack_top - stack_bottom) + size.width > maxsize ) | |
| { | |
| int sz = (int)(stack_top - stack_bottom); | |
| maxsize = MAX( maxsize * 3/2, maxsize + 8 ); | |
| stack.resize(maxsize); | |
| stack_bottom = &stack[0]; | |
| stack_top = stack_bottom + sz; | |
| } | |
| const short* _dx = (short*)(dx->data.ptr + dx->step*(i-1)); | |
| const short* _dy = (short*)(dy->data.ptr + dy->step*(i-1)); | |
| int prev_flag = 0; | |
| int x, y; | |
| uchar* _map; | |
| ptrdiff_t magstep1, magstep2; | |
| _map = map + mapstep*i + 1; | |
| _map[-1] = _map[size.width] = 1; | |
| if (i % 3 == 1) { | |
| magstep1 = size.width + 2; | |
| magstep2 = -(size.width + 2); | |
| } else if (i % 3 == 2) { | |
| magstep1 = -2 * (size.width + 2); | |
| magstep2 = -(size.width + 2); | |
| } else { | |
| magstep1 = size.width + 2; | |
| magstep2 = 2 * (size.width + 2); | |
| } | |
| for( j = 0; j < size.width; j++ ) | |
| { | |
| #define CANNY_SHIFT 15 | |
| // i.e. tan(pi/8) * (1 << CANNY_SHIFT etc...) | |
| #define TG22 (int)(0.4142135623730950488016887242097*(1<<CANNY_SHIFT) + 0.5) | |
| x = _dx[j]; | |
| y = _dy[j]; | |
| int s = x ^ y; | |
| int m = _mag[j]; | |
| x = abs(x); | |
| y = abs(y); | |
| if( m > low ) | |
| { | |
| int tg22x = x * TG22; | |
| int tg67x = tg22x + ((x + x) << CANNY_SHIFT); | |
| y <<= CANNY_SHIFT; | |
| if( y < tg22x ) | |
| { | |
| if( m > _mag[j-1] && m >= _mag[j+1] ) | |
| { | |
| if( m > high && !prev_flag && _map[j-mapstep] != 2 ) | |
| { | |
| CANNY_PUSH( _map + j ); | |
| prev_flag = 1; | |
| } | |
| else { | |
| _map[j] = (uchar)0; | |
| } | |
| continue; | |
| } | |
| } | |
| else if( y > tg67x ) | |
| { | |
| if( m > _mag[j-magstep2] && m >= _mag[j+magstep1] ) | |
| { | |
| if( m > high && !prev_flag && _map[j-mapstep] != 2 ) | |
| { | |
| CANNY_PUSH( _map + j ); | |
| prev_flag = 1; | |
| } | |
| else { | |
| _map[j] = (uchar)0; | |
| } | |
| continue; | |
| } | |
| } | |
| else | |
| { | |
| s = s < 0 ? -1 : 1; | |
| if( m > _mag[j+magstep2-s] && m > _mag[j+magstep1+s] ) | |
| { | |
| if( m > high && !prev_flag && _map[j-mapstep] != 2 ) | |
| { | |
| CANNY_PUSH( _map + j ); | |
| prev_flag = 1; | |
| } | |
| else { | |
| _map[j] = (uchar)0; | |
| } | |
| continue; | |
| } | |
| } | |
| } | |
| prev_flag = 0; | |
| _map[j] = (uchar)1; | |
| } | |
| } | |
| // now track the edges (hysteresis thresholding) | |
| while( stack_top > stack_bottom ) | |
| { | |
| uchar* m; | |
| if( (stack_top - stack_bottom) + 8 > maxsize ) | |
| { | |
| int sz = (int)(stack_top - stack_bottom); | |
| maxsize = MAX( maxsize * 3/2, maxsize + 8 ); | |
| stack.resize(maxsize); | |
| stack_bottom = &stack[0]; | |
| stack_top = stack_bottom + sz; | |
| } | |
| CANNY_POP(m); | |
| if( !m[-1] ) | |
| CANNY_PUSH( m - 1 ); | |
| if( !m[1] ) | |
| CANNY_PUSH( m + 1 ); | |
| if( !m[-mapstep-1] ) | |
| CANNY_PUSH( m - mapstep - 1 ); | |
| if( !m[-mapstep] ) | |
| CANNY_PUSH( m - mapstep ); | |
| if( !m[-mapstep+1] ) | |
| CANNY_PUSH( m - mapstep + 1 ); | |
| if( !m[mapstep-1] ) | |
| CANNY_PUSH( m + mapstep - 1 ); | |
| if( !m[mapstep] ) | |
| CANNY_PUSH( m + mapstep ); | |
| if( !m[mapstep+1] ) | |
| CANNY_PUSH( m + mapstep + 1 ); | |
| } | |
| // the final pass, form the final image | |
| for( i = 0; i < size.height; i++ ) | |
| { | |
| const uchar* _map = map + mapstep*(i+1) + 1; | |
| uchar* _dst = dst->data.ptr + dst->step*i; | |
| for( j = 0; j < size.width; j++ ) | |
| _dst[j] = (uchar)-(_map[j] >> 1); | |
| } | |
| adit = 20; | |
| } | |
| void cv::Canny( const Mat& image, Mat& edges, | |
| double threshold1, double threshold2, | |
| int apertureSize, bool L2gradient ) | |
| { | |
| Mat src = image; | |
| edges.create(src.size(), CV_8U); | |
| CvMat _src = src, _dst = edges; | |
| cvCanny( &_src, &_dst, threshold1, threshold2, | |
| apertureSize + (L2gradient ? CV_CANNY_L2_GRADIENT : 0)); | |
| } | |
| /* End of file. */ | |
Author
csharma2,
You need to download openCV and compile it. Before compiling, replace canny.cpp with this file. Then check out the openCV examples to learn how to detect edges: http://opencv.willowgarage.com/wiki/Welcome/Introduction
Silly question but with the OpenCV 2.1.0, I cant seem to find the canny.cpp file anywhere in any folders! is there a particular folder it is should be located in (or do i need to download a different version of openCV)
Author
Hmm, things could've changed...this fix is pretty old. Sadly the only version I know that definitely works is this one: https://github.com/egonSchiele/OpenCV
could you provide a newer implement with opencv 2.4.5?
i got some problems in compiling with ios
thanks in advance
I don't suppose anyone has implemented this as a free function that doesn't need to be compiled into OpenCV?
Is this the original canny detector?
Is this the original canny detector?
I think this is socall auto-canny
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how do I implement this autodetection file (canny.cpp) and make it detect the edges automatically?
Thanks