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Merge pull request #28636 from pratham-mcw:imgproc_distance_transform_opt

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imgproc: add SIMD support for distance transform function #28636

- This PR adds OpenCV SIMD intrinsics-based optimizations to the distance transform functions for improved performance.
- The optimized implementation uses vectorized operations to accelerate the forward and backward passes of distance computation.
- In x64 architecture, distance transform function benefit from IPP-based optimized implementations. However, on ARM64 platforms, the execution falls back to scalar implementation, which results in lower performance.
- After introducing these changes, the distance transform functions showed noticeable performance improvements on Windows-ARM64.
<img width="800" height="706" alt="image" src="https://github.com/user-attachments/assets/9786606a-9d92-489d-a5ea-d2e57453ef02" />

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
This commit is contained in:
pratham-mcw
2026-03-16 16:21:03 +05:30
committed by GitHub
parent 2c839967ff
commit 2dd3d1371a
1 changed files with 384 additions and 102 deletions
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modules/imgproc/src/distransform.cpp
+384 -102
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@@ -70,7 +70,7 @@ static void
distanceTransform_3x3( const Mat& _src, Mat& _temp, Mat& _dist, const float* metrics )
{
const int BORDER = 1;
int i, j;
const unsigned int HV_DIST = CV_FLT_TO_FIX( metrics[0], DIST_SHIFT );
const unsigned int DIAG_DIST = CV_FLT_TO_FIX( metrics[1], DIST_SHIFT );
const unsigned int DIST_MAX = UINT_MAX - DIAG_DIST;
@@ -79,65 +79,190 @@ distanceTransform_3x3( const Mat& _src, Mat& _temp, Mat& _dist, const float* met
const uchar* src = _src.ptr();
int* temp = _temp.ptr<int>();
float* dist = _dist.ptr<float>(_dist.rows - 1);
int srcstep = (int)(_src.step/sizeof(src[0]));
int step = (int)(_temp.step/sizeof(temp[0]));
int dststep = (int)(_dist.step/sizeof(dist[0]));
Size size = _src.size();
const int srcstep = (int)_src.step;
const int step = (int)(_temp.step / sizeof(int));
const int dststep = (int)(_dist.step / sizeof(float));
const int width = _src.cols;
const int height = _src.rows;
initTopBottom( _temp, BORDER, DIST_MAX );
// forward pass
unsigned int* tmp = (unsigned int*)(temp + BORDER*step) + BORDER;
const uchar* s = src;
for( i = 0; i < size.height; i++ )
{
for( j = 0; j < BORDER; j++ )
tmp[-j-1] = tmp[size.width + j] = DIST_MAX;
unsigned int* row = (unsigned int*)(temp + BORDER * step) + BORDER;
const uchar* srow = src;
for( j = 0; j < size.width; j++ )
for (int i = 0; i < height; i++)
{
unsigned int* cur = row;
const uchar* s = srow;
const unsigned int* top = (const unsigned int*)(cur - step);
// set horizontal border sentinels
cur[-1] = DIST_MAX;
cur[width] = DIST_MAX;
unsigned int left = cur[-1];
#if defined(CV_SIMD)
const int BLOCK = 8;
int j = 0;
const v_uint32 v_diag = vx_setall<v_uint32>(DIAG_DIST);
const v_uint32 v_hv = vx_setall<v_uint32>(HV_DIST);
for (; j <= width - BLOCK; j += BLOCK)
{
if( !s[j] )
tmp[j] = 0;
else
v_uint32 tl0 = vx_load(top + j - 1);
v_uint32 t0 = vx_load(top + j);
v_uint32 tr0 = vx_load(top + j + 1);
v_uint32 tl1 = vx_load(top + j + 3);
v_uint32 t1 = vx_load(top + j + 4);
v_uint32 tr1 = vx_load(top + j + 5);
tl0 = v_add(tl0, v_diag);
t0 = v_add(t0, v_hv);
tr0 = v_add(tr0, v_diag);
tl1 = v_add(tl1, v_diag);
t1 = v_add(t1, v_hv);
tr1 = v_add(tr1, v_diag);
v_uint32 m0 = v_min(tl0, t0);
m0 = v_min(m0, tr0);
v_uint32 m1 = v_min(tl1, t1);
m1 = v_min(m1, tr1);
v_store(cur + j, m0);
v_store(cur + j + 4, m1);
for (int k = 0; k < BLOCK; k++)
{
unsigned int t0 = tmp[j-step-1] + DIAG_DIST;
unsigned int t = tmp[j-step] + HV_DIST;
if( t0 > t ) t0 = t;
t = tmp[j-step+1] + DIAG_DIST;
if( t0 > t ) t0 = t;
t = tmp[j-1] + HV_DIST;
if( t0 > t ) t0 = t;
tmp[j] = (t0 > DIST_MAX) ? DIST_MAX : t0;
int idx = j + k;
if (!s[idx])
{
cur[idx] = 0;
left = 0;
}
else
{
unsigned int m = cur[idx];
unsigned int lm = left + HV_DIST;
if (lm < m) m = lm;
if (m > DIST_MAX) m = DIST_MAX;
cur[idx] = m;
left = m;
}
}
}
tmp += step;
s += srcstep;
for (; j < width; j++)
{
if (!s[j])
{
cur[j] = 0;
left = 0;
}
else
{
unsigned int t0 = top[j - 1] + DIAG_DIST;
unsigned int t1 = top[j] + HV_DIST;
unsigned int t2 = top[j + 1] + DIAG_DIST;
unsigned int t3 = left + HV_DIST;
unsigned int m = t0 < t1 ? t0 : t1;
m = m < t2 ? m : t2;
m = m < t3 ? m : t3;
cur[j] = m > DIST_MAX ? DIST_MAX : m;
left = cur[j];
}
}
#else
for (int j = 0; j < width; j++)
{
if (!s[j])
{
cur[j] = 0;
left = 0;
}
else
{
unsigned int t0 = top[j - 1] + DIAG_DIST;
unsigned int t1 = top[j] + HV_DIST;
unsigned int t2 = top[j + 1] + DIAG_DIST;
unsigned int t3 = left + HV_DIST;
unsigned int m = t0 < t1 ? t0 : t1;
m = m < t2 ? m : t2;
m = m < t3 ? m : t3;
cur[j] = m > DIST_MAX ? DIST_MAX : m;
left = cur[j];
}
}
#endif
row += step;
srow += srcstep;
}
// backward pass
float* d = (float*)dist;
for( i = size.height - 1; i >= 0; i-- )
float* drow = dist;
unsigned int* cur = row - step;
#if defined(CV_SIMD)
const v_float32 scale_v = vx_setall<v_float32>(scale);
#endif
for (int i = height - 1; i >= 0; i--)
{
tmp -= step;
unsigned int* bottom = cur + step;
for( j = size.width - 1; j >= 0; j-- )
unsigned int right = cur[width];
for (int j = width - 1; j >= 0; j--)
{
unsigned int t0 = tmp[j];
if( t0 > HV_DIST )
unsigned int t0 = cur[j];
if (t0 > HV_DIST)
{
unsigned int t = tmp[j+step+1] + DIAG_DIST;
if( t0 > t ) t0 = t;
t = tmp[j+step] + HV_DIST;
if( t0 > t ) t0 = t;
t = tmp[j+step-1] + DIAG_DIST;
if( t0 > t ) t0 = t;
t = tmp[j+1] + HV_DIST;
if( t0 > t ) t0 = t;
tmp[j] = t0;
unsigned int b1 = bottom[j + 1] + DIAG_DIST;
unsigned int b2 = bottom[j] + HV_DIST;
unsigned int b3 = bottom[j - 1] + DIAG_DIST;
unsigned int r = right + HV_DIST;
unsigned int t = b1 < b2 ? b1 : b2;
t = t < b3 ? t : b3;
t = t < r ? t : r;
if (t < t0)
{
t0 = t;
cur[j] = t0;
}
}
d[j] = (float)(t0 * scale);
right = cur[j];
}
d -= dststep;
#if defined(CV_SIMD)
int j = 0;
const uint32_t* tptr = (const uint32_t*)cur;
float* dptr = drow;
for (; j <= width - 8; j += 8)
{
v_uint32 v0 = vx_load(tptr + j);
v_uint32 v1 = vx_load(tptr + j + 4);
v_float32 f0 = v_mul(v_cvt_f32(v0), scale_v);
v_float32 f1 = v_mul(v_cvt_f32(v1), scale_v);
v_store(dptr + j, f0);
v_store(dptr + j + 4, f1);
}
for (; j < width; j++)
dptr[j] = (float)(tptr[j] * scale);
#else
for (int j = 0; j < width; j++)
drow[j] = (float)(cur[j] * scale);
#endif
cur -= step;
drow -= dststep;
}
}
@@ -146,91 +271,248 @@ static void
distanceTransform_5x5( const Mat& _src, Mat& _temp, Mat& _dist, const float* metrics )
{
const int BORDER = 2;
int i, j;
const unsigned int HV_DIST = CV_FLT_TO_FIX( metrics[0], DIST_SHIFT );
const unsigned int DIAG_DIST = CV_FLT_TO_FIX( metrics[1], DIST_SHIFT );
const unsigned int LONG_DIST = CV_FLT_TO_FIX( metrics[2], DIST_SHIFT );
const unsigned int DIST_MAX = UINT_MAX - LONG_DIST;
const float scale = 1.f/(1 << DIST_SHIFT);
const uchar* src = _src.ptr();
const uchar* src = _src.ptr<uchar>();
int* temp = _temp.ptr<int>();
float* dist = _dist.ptr<float>(_dist.rows - 1);
int srcstep = (int)(_src.step/sizeof(src[0]));
int step = (int)(_temp.step/sizeof(temp[0]));
int dststep = (int)(_dist.step/sizeof(dist[0]));
Size size = _src.size();
initTopBottom( _temp, BORDER, DIST_MAX );
const int srcstep = (int)_src.step;
const int step = (int)(_temp.step / sizeof(int));
const int dststep = (int)(_dist.step / sizeof(float));
const int width = _src.cols;
const int height = _src.rows;
initTopBottom(_temp, BORDER, DIST_MAX);
// forward pass
unsigned int* tmp = (unsigned int*)(temp + BORDER*step) + BORDER;
const uchar* s = src;
for( i = 0; i < size.height; i++ )
{
for( j = 0; j < BORDER; j++ )
tmp[-j-1] = tmp[size.width + j] = DIST_MAX;
unsigned int* row = (unsigned int*)(temp + BORDER * step) + BORDER;
const uchar* srow = src;
for( j = 0; j < size.width; j++ )
for (int i = 0; i < height; i++)
{
unsigned int* cur = row;
const uchar* s = srow;
const unsigned int* top1 = cur - step;
const unsigned int* top2 = cur - step * 2;
cur[-1] = cur[-2] = DIST_MAX;
cur[width] = cur[width + 1] = DIST_MAX;
#if defined(CV_SIMD)
unsigned int left1 = DIST_MAX;
unsigned int left2 = DIST_MAX;
const int BLOCK = 8;
int j = 0;
const v_uint32 v_hv = vx_setall<v_uint32>(HV_DIST);
const v_uint32 v_diag = vx_setall<v_uint32>(DIAG_DIST);
const v_uint32 v_long = vx_setall<v_uint32>(LONG_DIST);
const v_uint32 v_max = vx_setall<v_uint32>(DIST_MAX);
for (; j <= width - BLOCK; j += BLOCK)
{
if( !s[j] )
tmp[j] = 0;
else
v_uint32 t2m1_0 = vx_load(top2 + j - 1);
v_uint32 t2p1_0 = vx_load(top2 + j + 1);
v_uint32 t1m2_0 = vx_load(top1 + j - 2);
v_uint32 t1m1_0 = vx_load(top1 + j - 1);
v_uint32 t1_0 = vx_load(top1 + j);
v_uint32 t1p1_0 = vx_load(top1 + j + 1);
v_uint32 t1p2_0 = vx_load(top1 + j + 2);
t2m1_0 = v_add(t2m1_0, v_long);
t2p1_0 = v_add(t2p1_0, v_long);
t1m2_0 = v_add(t1m2_0, v_long);
t1m1_0 = v_add(t1m1_0, v_diag);
t1_0 = v_add(t1_0, v_hv);
t1p1_0 = v_add(t1p1_0, v_diag);
t1p2_0 = v_add(t1p2_0, v_long);
v_uint32 m0 = v_min(t2m1_0, t2p1_0);
v_uint32 m0_1 = v_min(t1m2_0, t1m1_0);
v_uint32 m0_2 = v_min(t1p1_0, t1p2_0);
m0 = v_min(m0, m0_1);
m0_2 = v_min(m0_2, t1_0);
m0 = v_min(m0, m0_2);
m0 = v_min(m0, v_max);
v_store(cur + j, m0);
v_uint32 t2m1_1 = vx_load(top2 + j + 3);
v_uint32 t2p1_1 = vx_load(top2 + j + 5);
v_uint32 t1m2_1 = vx_load(top1 + j + 2);
v_uint32 t1m1_1 = vx_load(top1 + j + 3);
v_uint32 t1_1 = vx_load(top1 + j + 4);
v_uint32 t1p1_1 = vx_load(top1 + j + 5);
v_uint32 t1p2_1 = vx_load(top1 + j + 6);
t2m1_1 = v_add(t2m1_1, v_long);
t2p1_1 = v_add(t2p1_1, v_long);
t1m2_1 = v_add(t1m2_1, v_long);
t1m1_1 = v_add(t1m1_1, v_diag);
t1_1 = v_add(t1_1, v_hv);
t1p1_1 = v_add(t1p1_1, v_diag);
t1p2_1 = v_add(t1p2_1, v_long);
v_uint32 m1 = v_min(t2m1_1, t2p1_1);
v_uint32 m1_1 = v_min(t1m2_1, t1m1_1);
v_uint32 m1_2 = v_min(t1p1_1, t1p2_1);
m1 = v_min(m1, m1_1);
m1_2 = v_min(m1_2, t1_1);
m1 = v_min(m1, m1_2);
m1 = v_min(m1, v_max);
v_store(cur + j + 4, m1);
for (int k = 0; k < BLOCK; k++)
{
unsigned int t0 = tmp[j-step*2-1] + LONG_DIST;
unsigned int t = tmp[j-step*2+1] + LONG_DIST;
if( t0 > t ) t0 = t;
t = tmp[j-step-2] + LONG_DIST;
if( t0 > t ) t0 = t;
t = tmp[j-step-1] + DIAG_DIST;
if( t0 > t ) t0 = t;
t = tmp[j-step] + HV_DIST;
if( t0 > t ) t0 = t;
t = tmp[j-step+1] + DIAG_DIST;
if( t0 > t ) t0 = t;
t = tmp[j-step+2] + LONG_DIST;
if( t0 > t ) t0 = t;
t = tmp[j-1] + HV_DIST;
if( t0 > t ) t0 = t;
tmp[j] = (t0 > DIST_MAX) ? DIST_MAX : t0;
int idx = j + k;
if (!s[idx])
{
cur[idx] = 0;
left1 = 0;
left2 = 0;
}
else
{
unsigned int m = cur[idx];
unsigned int lm = left1 + HV_DIST;
if (lm < m) m = lm;
if (m > DIST_MAX) m = DIST_MAX;
cur[idx] = m;
left2 = left1;
left1 = m;
}
}
}
tmp += step;
s += srcstep;
for (; j < width; j++)
{
if (!s[j])
{
cur[j] = 0;
left1 = left2 = 0;
}
else
{
unsigned int t0 = top2[j - 1] + LONG_DIST;
unsigned int t = top2[j + 1] + LONG_DIST;
if (t < t0) t0 = t;
t = top1[j - 2] + LONG_DIST; if (t < t0) t0 = t;
t = top1[j - 1] + DIAG_DIST; if (t < t0) t0 = t;
t = top1[j] + HV_DIST; if (t < t0) t0 = t;
t = top1[j + 1] + DIAG_DIST; if (t < t0) t0 = t;
t = top1[j + 2] + LONG_DIST; if (t < t0) t0 = t;
t = left1 + HV_DIST; if (t < t0) t0 = t;
cur[j] = t0 > DIST_MAX ? DIST_MAX : t0;
left2 = left1;
left1 = cur[j];
}
}
#else
unsigned int left = DIST_MAX;
for (int j = 0; j < width; j++)
{
if (!s[j])
{
cur[j] = 0;
left = 0;
}
else
{
unsigned int t0 = top2[j - 1] + LONG_DIST;
unsigned int t = top2[j + 1] + LONG_DIST;
if (t < t0) t0 = t;
t = top1[j - 2] + LONG_DIST;
if (t < t0) t0 = t;
t = top1[j - 1] + DIAG_DIST;
if (t < t0) t0 = t;
t = top1[j] + HV_DIST;
if (t < t0) t0 = t;
t = top1[j + 1] + DIAG_DIST;
if (t < t0) t0 = t;
t = top1[j + 2] + LONG_DIST;
if (t < t0) t0 = t;
t = left + HV_DIST;
if (t < t0) t0 = t;
cur[j] = t0 > DIST_MAX ? DIST_MAX : t0;
left = cur[j];
}
}
#endif
row += step;
srow += srcstep;
}
// backward pass
float* d = (float*)dist;
for( i = size.height - 1; i >= 0; i-- )
{
tmp -= step;
float* drow = dist;
unsigned int* cur = row - step;
for( j = size.width - 1; j >= 0; j-- )
#if defined(CV_SIMD)
const v_float32 scale_v = vx_setall<v_float32>(scale);
#endif
for (int i = height - 1; i >= 0; i--)
{
unsigned int* bot1 = cur + step;
unsigned int* bot2 = cur + step * 2;
unsigned int right = DIST_MAX;
for (int j = width - 1; j >= 0; j--)
{
unsigned int t0 = tmp[j];
unsigned int t0 = cur[j];
if( t0 > HV_DIST )
{
unsigned int t = tmp[j+step*2+1] + LONG_DIST;
if( t0 > t ) t0 = t;
t = tmp[j+step*2-1] + LONG_DIST;
if( t0 > t ) t0 = t;
t = tmp[j+step+2] + LONG_DIST;
if( t0 > t ) t0 = t;
t = tmp[j+step+1] + DIAG_DIST;
if( t0 > t ) t0 = t;
t = tmp[j+step] + HV_DIST;
if( t0 > t ) t0 = t;
t = tmp[j+step-1] + DIAG_DIST;
if( t0 > t ) t0 = t;
t = tmp[j+step-2] + LONG_DIST;
if( t0 > t ) t0 = t;
t = tmp[j+1] + HV_DIST;
if( t0 > t ) t0 = t;
tmp[j] = t0;
unsigned int t = bot2[j + 1] + LONG_DIST;
if (t < t0) t0 = t;
t = bot2[j - 1] + LONG_DIST;
if (t < t0) t0 = t;
t = bot1[j + 2] + LONG_DIST;
if (t < t0) t0 = t;
t = bot1[j + 1] + DIAG_DIST;
if (t < t0) t0 = t;
t = bot1[j] + HV_DIST;
if (t < t0) t0 = t;
t = bot1[j - 1] + DIAG_DIST;
if (t < t0) t0 = t;
t = bot1[j - 2] + LONG_DIST;
if (t < t0) t0 = t;
t = right + HV_DIST;
if (t < t0) t0 = t;
cur[j] = t0;
}
d[j] = (float)(t0 * scale);
right = cur[j];
}
d -= dststep;
#if defined(CV_SIMD)
int j = 0;
const uint32_t* tptr = (const uint32_t*)cur;
float* dptr = drow;
for (; j <= width - 8; j += 8)
{
v_uint32 v0 = vx_load(tptr + j);
v_uint32 v1 = vx_load(tptr + j + 4);
v_float32 f0 = v_mul(v_cvt_f32(v0), scale_v);
v_float32 f1 = v_mul(v_cvt_f32(v1), scale_v);
v_store(dptr + j, f0);
v_store(dptr + j + 4, f1);
}
for (; j < width; j++)
dptr[j] = (float)(tptr[j] * scale);
#else
for (int j = 0; j < width; j++)
drow[j] = (float)(cur[j] * scale);
#endif
cur -= step;
drow -= dststep;
}
}