Merge pull request #24621 from chacha21:remap_relative

First proposal of cv::remap with relative displacement field (#24603) #24621

Implements #24603

Currently, `remap()` is applied as `dst(x, y) <- src(mapX(x, y), mapY(x, y))` It means that the maps must be filled with absolute coordinates.

However, if one wants to remap something according to a displacement field ("warp"), the operation should be `dst(x, y) <- src(x+displacementX(x, y), y+displacementY(x, y))`

It is trivial to build a mapping from a displacement field, but it is an undesirable overhead for CPU and memory.

This PR implements the feature as an experimental option, through the optional flag WARP_RELATIVE_MAP than can be ORed to the interpolation mode.

Since the xy maps might be const, there is no attempt to add the coordinate offset to those maps, and everything is postponed on-the-fly to the very last coordinate computation before fetching `src`. Interestingly, this let `cv::convertMaps()` unchanged since the fractional part of interpolation does not care of the integer coordinate offset.

### 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
- [X] 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/perf/perf_warp.cpp

@@ -9,14 +9,15 @@ enum{HALF_SIZE=0, UPSIDE_DOWN, REFLECTION_X, REFLECTION_BOTH};
 
 CV_ENUM(BorderMode, BORDER_CONSTANT, BORDER_REPLICATE)
 CV_ENUM(InterType, INTER_NEAREST, INTER_LINEAR)
+CV_ENUM(InterTypeExtended, INTER_NEAREST, INTER_LINEAR, WARP_RELATIVE_MAP)
 CV_ENUM(RemapMode, HALF_SIZE, UPSIDE_DOWN, REFLECTION_X, REFLECTION_BOTH)
 
 typedef TestBaseWithParam< tuple<Size, InterType, BorderMode> > TestWarpAffine;
 typedef TestBaseWithParam< tuple<Size, InterType, BorderMode> > TestWarpPerspective;
 typedef TestBaseWithParam< tuple<Size, InterType, BorderMode, MatType> > TestWarpPerspectiveNear_t;
-typedef TestBaseWithParam< tuple<MatType, Size, InterType, BorderMode, RemapMode> > TestRemap;
+typedef TestBaseWithParam< tuple<MatType, Size, InterTypeExtended, BorderMode, RemapMode> > TestRemap;
 
-void update_map(const Mat& src, Mat& map_x, Mat& map_y, const int remapMode );
+void update_map(const Mat& src, Mat& map_x, Mat& map_y, const int remapMode, bool relative = false );
 
 PERF_TEST_P( TestWarpAffine, WarpAffine,
              Combine(
@@ -204,7 +205,7 @@ PERF_TEST_P( TestRemap, remap,
              Combine(
                  Values( CV_8UC1, CV_8UC3, CV_8UC4, CV_32FC1 ),
                  Values( szVGA, sz1080p ),
-                 InterType::all(),
+                 InterTypeExtended::all(),
                  BorderMode::all(),
                  RemapMode::all()
                  )
@@ -224,7 +225,7 @@ PERF_TEST_P( TestRemap, remap,
 
     declare.in(source, WARMUP_RNG);
 
-    update_map(source, map_x, map_y, remapMode);
+    update_map(source, map_x, map_y, remapMode, ((interpolationType & WARP_RELATIVE_MAP) != 0));
 
     TEST_CYCLE()
     {
@@ -234,7 +235,7 @@ PERF_TEST_P( TestRemap, remap,
     SANITY_CHECK_NOTHING();
 }
 
-void update_map(const Mat& src, Mat& map_x, Mat& map_y, const int remapMode )
+void update_map(const Mat& src, Mat& map_x, Mat& map_y, const int remapMode, bool relative )
 {
     for( int j = 0; j < src.rows; j++ )
     {
@@ -267,6 +268,12 @@ void update_map(const Mat& src, Mat& map_x, Mat& map_y, const int remapMode )
                 map_y.at<float>(j,i) = static_cast<float>(src.rows - j) ;
                 break;
             } // end of switch
+
+            if( relative )
+            {
+                map_x.at<float>(j,i) -= static_cast<float>(i);
+                map_y.at<float>(j,i) -= static_cast<float>(j);
+            }
         }
     }
 }