in modules/imgproc/src/canny.cpp [580:961]
void cv::Canny( InputArray _src, OutputArray _dst,
double low_thresh, double high_thresh,
int aperture_size, bool L2gradient )
{
const int type = _src.type(), depth = CV_MAT_DEPTH(type), cn = CV_MAT_CN(type);
const Size size = _src.size();
CV_Assert( depth == CV_8U );
_dst.create(size, CV_8U);
if (!L2gradient && (aperture_size & CV_CANNY_L2_GRADIENT) == CV_CANNY_L2_GRADIENT)
{
// backward compatibility
aperture_size &= ~CV_CANNY_L2_GRADIENT;
L2gradient = true;
}
if ((aperture_size & 1) == 0 || (aperture_size != -1 && (aperture_size < 3 || aperture_size > 7)))
CV_Error(CV_StsBadFlag, "Aperture size should be odd");
if (low_thresh > high_thresh)
std::swap(low_thresh, high_thresh);
CV_OCL_RUN(_dst.isUMat() && (cn == 1 || cn == 3),
ocl_Canny(_src, _dst, (float)low_thresh, (float)high_thresh, aperture_size, L2gradient, cn, size))
Mat src = _src.getMat(), dst = _dst.getMat();
#ifdef HAVE_TEGRA_OPTIMIZATION
if (tegra::useTegra() && tegra::canny(src, dst, low_thresh, high_thresh, aperture_size, L2gradient))
return;
#endif
#ifdef USE_IPP_CANNY
CV_IPP_CHECK()
{
if( aperture_size == 3 && !L2gradient && 1 == cn )
{
if (ippCanny(src, dst, (float)low_thresh, (float)high_thresh))
{
CV_IMPL_ADD(CV_IMPL_IPP);
return;
}
setIppErrorStatus();
}
}
#endif
#ifdef HAVE_TBB
if (L2gradient)
{
low_thresh = std::min(32767.0, low_thresh);
high_thresh = std::min(32767.0, high_thresh);
if (low_thresh > 0) low_thresh *= low_thresh;
if (high_thresh > 0) high_thresh *= high_thresh;
}
int low = cvFloor(low_thresh);
int high = cvFloor(high_thresh);
ptrdiff_t mapstep = src.cols + 2;
AutoBuffer<uchar> buffer((src.cols+2)*(src.rows+2));
uchar* map = (uchar*)buffer;
memset(map, 1, mapstep);
memset(map + mapstep*(src.rows + 1), 1, mapstep);
int threadsNumber = tbb::task_scheduler_init::default_num_threads();
int grainSize = src.rows / threadsNumber;
// Make a fallback for pictures with too few rows.
uchar ksize2 = aperture_size / 2;
int minGrainSize = 1 + ksize2;
int maxGrainSize = src.rows - 2 - 2*ksize2;
if ( !( minGrainSize <= grainSize && grainSize <= maxGrainSize ) )
{
threadsNumber = 1;
grainSize = src.rows;
}
tbb::task_group g;
for (int i = 0; i < threadsNumber; ++i)
{
if (i < threadsNumber - 1)
g.run(tbbCanny(Range(i * grainSize, (i + 1) * grainSize), src, map, low, high, aperture_size, L2gradient));
else
g.run(tbbCanny(Range(i * grainSize, src.rows), src, map, low, high, aperture_size, L2gradient));
}
g.wait();
#define CANNY_PUSH_SERIAL(d) *(d) = uchar(2), borderPeaks.push(d)
// now track the edges (hysteresis thresholding)
uchar* m;
while (borderPeaks.try_pop(m))
{
if (!m[-1]) CANNY_PUSH_SERIAL(m - 1);
if (!m[1]) CANNY_PUSH_SERIAL(m + 1);
if (!m[-mapstep-1]) CANNY_PUSH_SERIAL(m - mapstep - 1);
if (!m[-mapstep]) CANNY_PUSH_SERIAL(m - mapstep);
if (!m[-mapstep+1]) CANNY_PUSH_SERIAL(m - mapstep + 1);
if (!m[mapstep-1]) CANNY_PUSH_SERIAL(m + mapstep - 1);
if (!m[mapstep]) CANNY_PUSH_SERIAL(m + mapstep);
if (!m[mapstep+1]) CANNY_PUSH_SERIAL(m + mapstep + 1);
}
#else
Mat dx(src.rows, src.cols, CV_16SC(cn));
Mat dy(src.rows, src.cols, CV_16SC(cn));
Sobel(src, dx, CV_16S, 1, 0, aperture_size, 1, 0, BORDER_REPLICATE);
Sobel(src, dy, CV_16S, 0, 1, aperture_size, 1, 0, BORDER_REPLICATE);
if (L2gradient)
{
low_thresh = std::min(32767.0, low_thresh);
high_thresh = std::min(32767.0, high_thresh);
if (low_thresh > 0) low_thresh *= low_thresh;
if (high_thresh > 0) high_thresh *= high_thresh;
}
int low = cvFloor(low_thresh);
int high = cvFloor(high_thresh);
ptrdiff_t mapstep = src.cols + 2;
AutoBuffer<uchar> buffer((src.cols+2)*(src.rows+2) + cn * mapstep * 3 * sizeof(int));
int* mag_buf[3];
mag_buf[0] = (int*)(uchar*)buffer;
mag_buf[1] = mag_buf[0] + mapstep*cn;
mag_buf[2] = mag_buf[1] + mapstep*cn;
memset(mag_buf[0], 0, /* cn* */mapstep*sizeof(int));
uchar* map = (uchar*)(mag_buf[2] + mapstep*cn);
memset(map, 1, mapstep);
memset(map + mapstep*(src.rows + 1), 1, mapstep);
int maxsize = std::max(1 << 10, src.cols * src.rows / 10);
std::vector<uchar*> stack(maxsize);
uchar **stack_top = &stack[0];
uchar **stack_bottom = &stack[0];
/* 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
#if CV_SSE2
bool haveSSE2 = checkHardwareSupport(CV_CPU_SSE2);
#endif
// calculate magnitude and angle of gradient, perform non-maxima suppression.
// 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 (int i = 0; i <= src.rows; i++)
{
int* _norm = mag_buf[(i > 0) + 1] + 1;
if (i < src.rows)
{
short* _dx = dx.ptr<short>(i);
short* _dy = dy.ptr<short>(i);
if (!L2gradient)
{
int j = 0, width = src.cols * cn;
#if CV_SSE2
if (haveSSE2)
{
__m128i v_zero = _mm_setzero_si128();
for ( ; j <= width - 8; j += 8)
{
__m128i v_dx = _mm_loadu_si128((const __m128i *)(_dx + j));
__m128i v_dy = _mm_loadu_si128((const __m128i *)(_dy + j));
v_dx = _mm_max_epi16(v_dx, _mm_sub_epi16(v_zero, v_dx));
v_dy = _mm_max_epi16(v_dy, _mm_sub_epi16(v_zero, v_dy));
__m128i v_norm = _mm_add_epi32(_mm_unpacklo_epi16(v_dx, v_zero), _mm_unpacklo_epi16(v_dy, v_zero));
_mm_storeu_si128((__m128i *)(_norm + j), v_norm);
v_norm = _mm_add_epi32(_mm_unpackhi_epi16(v_dx, v_zero), _mm_unpackhi_epi16(v_dy, v_zero));
_mm_storeu_si128((__m128i *)(_norm + j + 4), v_norm);
}
}
#elif CV_NEON
for ( ; j <= width - 8; j += 8)
{
int16x8_t v_dx = vld1q_s16(_dx + j), v_dy = vld1q_s16(_dy + j);
vst1q_s32(_norm + j, vaddq_s32(vabsq_s32(vmovl_s16(vget_low_s16(v_dx))),
vabsq_s32(vmovl_s16(vget_low_s16(v_dy)))));
vst1q_s32(_norm + j + 4, vaddq_s32(vabsq_s32(vmovl_s16(vget_high_s16(v_dx))),
vabsq_s32(vmovl_s16(vget_high_s16(v_dy)))));
}
#endif
for ( ; j < width; ++j)
_norm[j] = std::abs(int(_dx[j])) + std::abs(int(_dy[j]));
}
else
{
int j = 0, width = src.cols * cn;
#if CV_SSE2
if (haveSSE2)
{
for ( ; j <= width - 8; j += 8)
{
__m128i v_dx = _mm_loadu_si128((const __m128i *)(_dx + j));
__m128i v_dy = _mm_loadu_si128((const __m128i *)(_dy + j));
__m128i v_dx_ml = _mm_mullo_epi16(v_dx, v_dx), v_dx_mh = _mm_mulhi_epi16(v_dx, v_dx);
__m128i v_dy_ml = _mm_mullo_epi16(v_dy, v_dy), v_dy_mh = _mm_mulhi_epi16(v_dy, v_dy);
__m128i v_norm = _mm_add_epi32(_mm_unpacklo_epi16(v_dx_ml, v_dx_mh), _mm_unpacklo_epi16(v_dy_ml, v_dy_mh));
_mm_storeu_si128((__m128i *)(_norm + j), v_norm);
v_norm = _mm_add_epi32(_mm_unpackhi_epi16(v_dx_ml, v_dx_mh), _mm_unpackhi_epi16(v_dy_ml, v_dy_mh));
_mm_storeu_si128((__m128i *)(_norm + j + 4), v_norm);
}
}
#elif CV_NEON
for ( ; j <= width - 8; j += 8)
{
int16x8_t v_dx = vld1q_s16(_dx + j), v_dy = vld1q_s16(_dy + j);
int16x4_t v_dxp = vget_low_s16(v_dx), v_dyp = vget_low_s16(v_dy);
int32x4_t v_dst = vmlal_s16(vmull_s16(v_dxp, v_dxp), v_dyp, v_dyp);
vst1q_s32(_norm + j, v_dst);
v_dxp = vget_high_s16(v_dx), v_dyp = vget_high_s16(v_dy);
v_dst = vmlal_s16(vmull_s16(v_dxp, v_dxp), v_dyp, v_dyp);
vst1q_s32(_norm + j + 4, v_dst);
}
#endif
for ( ; j < width; ++j)
_norm[j] = int(_dx[j])*_dx[j] + int(_dy[j])*_dy[j];
}
if (cn > 1)
{
for(int j = 0, jn = 0; j < src.cols; ++j, jn += cn)
{
int maxIdx = jn;
for(int k = 1; k < cn; ++k)
if(_norm[jn + k] > _norm[maxIdx]) maxIdx = jn + k;
_norm[j] = _norm[maxIdx];
_dx[j] = _dx[maxIdx];
_dy[j] = _dy[maxIdx];
}
}
_norm[-1] = _norm[src.cols] = 0;
}
else
memset(_norm-1, 0, /* cn* */mapstep*sizeof(int));
// at the very beginning we do not have a complete ring
// buffer of 3 magnitude rows for non-maxima suppression
if (i == 0)
continue;
uchar* _map = map + mapstep*i + 1;
_map[-1] = _map[src.cols] = 1;
int* _mag = mag_buf[1] + 1; // take the central row
ptrdiff_t magstep1 = mag_buf[2] - mag_buf[1];
ptrdiff_t magstep2 = mag_buf[0] - mag_buf[1];
const short* _x = dx.ptr<short>(i-1);
const short* _y = dy.ptr<short>(i-1);
if ((stack_top - stack_bottom) + src.cols > maxsize)
{
int sz = (int)(stack_top - stack_bottom);
maxsize = std::max(maxsize * 3/2, sz + src.cols);
stack.resize(maxsize);
stack_bottom = &stack[0];
stack_top = stack_bottom + sz;
}
int prev_flag = 0;
for (int j = 0; j < src.cols; j++)
{
#define CANNY_SHIFT 15
const int TG22 = (int)(0.4142135623730950488016887242097*(1<<CANNY_SHIFT) + 0.5);
int m = _mag[j];
if (m > low)
{
int xs = _x[j];
int ys = _y[j];
int x = std::abs(xs);
int y = std::abs(ys) << CANNY_SHIFT;
int tg22x = x * TG22;
if (y < tg22x)
{
if (m > _mag[j-1] && m >= _mag[j+1]) goto __ocv_canny_push;
}
else
{
int tg67x = tg22x + (x << (CANNY_SHIFT+1));
if (y > tg67x)
{
if (m > _mag[j+magstep2] && m >= _mag[j+magstep1]) goto __ocv_canny_push;
}
else
{
int s = (xs ^ ys) < 0 ? -1 : 1;
if (m > _mag[j+magstep2-s] && m > _mag[j+magstep1+s]) goto __ocv_canny_push;
}
}
}
prev_flag = 0;
_map[j] = uchar(1);
continue;
__ocv_canny_push:
if (!prev_flag && m > high && _map[j-mapstep] != 2)
{
CANNY_PUSH(_map + j);
prev_flag = 1;
}
else
_map[j] = 0;
}
// scroll the ring buffer
_mag = mag_buf[0];
mag_buf[0] = mag_buf[1];
mag_buf[1] = mag_buf[2];
mag_buf[2] = _mag;
}
// 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 = maxsize * 3/2;
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);
}
#endif
// the final pass, form the final image
const uchar* pmap = map + mapstep + 1;
uchar* pdst = dst.ptr();
for (int i = 0; i < src.rows; i++, pmap += mapstep, pdst += dst.step)
{
for (int j = 0; j < src.cols; j++)
pdst[j] = (uchar)-(pmap[j] >> 1);
}
}