Merge pull request #27433 from amd:fast_bilateral_simd

imgproc: Bilateral filter performance improvement #27433

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [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
- [ ] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/imgproc/src/bilateral_filter.dispatch.cpp

@@ -13,6 +13,7 @@
 // Copyright (C) 2000-2008, 2018, Intel Corporation, all rights reserved.
 // Copyright (C) 2009, Willow Garage Inc., all rights reserved.
 // Copyright (C) 2014-2015, Itseez Inc., all rights reserved.
+// Copyright (C) 2025, Advanced Micro Devices, all rights reserved.
 // Third party copyrights are property of their respective owners.
 //
 // Redistribution and use in source and binary forms, with or without modification,
@@ -174,8 +175,8 @@ bilateralFilter_8u( const Mat& src, Mat& dst, int d,
         return;
     }
 
-    double gauss_color_coeff = -0.5/(sigma_color*sigma_color);
-    double gauss_space_coeff = -0.5/(sigma_space*sigma_space);
+    float gauss_color_coeff = (float)(-0.5/(sigma_color*sigma_color));
+    float gauss_space_coeff = (float)(-0.5/(sigma_space*sigma_space));
 
     if( d <= 0 )
         radius = cvRound(sigma_space*1.5);
@@ -195,15 +196,31 @@ bilateralFilter_8u( const Mat& src, Mat& dst, int d,
     int* space_ofs = &_space_ofs[0];
 
     // initialize color-related bilateral filter coefficients
+    i = 0;
+#if (CV_SIMD || CV_SIMD_SCALABLE)
+    int nlanes = VTraits<v_float32>::vlanes();
+    v_float32 v_gauss_color_coeff = vx_setall_f32(gauss_color_coeff);
+    float counter[16] = {0.0, 1., 2., 3., 4., 5., 6., 7.,
+                    8., 9., 10., 11., 12., 13., 14., 15.};
+    v_float32 v_i = vx_load(counter);
+    v_float32 v_inc = vx_setall_f32(float(nlanes));
 
-    for( i = 0; i < 256*cn; i++ )
+    for( ; i < (256*cn) - nlanes; i += nlanes )
+    {
+        v_float32 v_color_weight = v_mul(v_mul(v_i,v_i), v_gauss_color_coeff);
+        v_store(color_weight + i, v_exp(v_color_weight));
+        v_i = v_add(v_i, v_inc);
+    }
+#endif
+    for(; i < 256*cn; i++ )
+    {
         color_weight[i] = (float)std::exp(i*i*gauss_color_coeff);
+    }
 
     // initialize space-related bilateral filter coefficients
     for( i = -radius, maxk = 0; i <= radius; i++ )
     {
         j = -radius;
-
         for( ; j <= radius; j++ )
         {
             double r = std::sqrt((double)i*i + (double)j*j);