ximgproc: add hole filling for run-length encoded images

modules/ximgproc/include/opencv2/ximgproc/run_length_morphology.hpp

@@ -113,6 +113,19 @@ CV_EXPORTS void createRLEImage(const std::vector<cv::Point3i>& runs, OutputArray
 CV_EXPORTS void morphologyEx(InputArray rlSrc, OutputArray rlDest, int op, InputArray rlKernel,
     bool bBoundaryOnForErosion = true, Point anchor = Point(0,0));
 
+/**
+* @brief   Fills holes in a run-length encoded binary image
+*
+* The function fills holes in the input binary image. A hole is defined as a background region surrounded
+* by connected foreground pixels.
+*
+* @param   rlSrc           input run-length encoded binary image
+* @param   rlDest          output run-length encoded image with holes filled
+* @param   connectivity    connectivity for hole filling, either 4 or 8 (default: 8)
+*
+*/
+CV_EXPORTS void fillHoles(InputArray rlSrc, OutputArray rlDest, int connectivity = 8);
+
 //! @}
 
 }

modules/ximgproc/src/run_length_morphology.cpp

@@ -36,6 +36,7 @@
 #include "precomp.hpp"
 #include <math.h>
 #include <vector>
+#include <stack>
 #include <iostream>
 
 
@@ -807,6 +808,150 @@ CV_EXPORTS void morphologyEx(InputArray rlSrc, OutputArray rlDest, int op, Input
     }
 }
 
+static void getNeighborLookup(std::vector<int>& lutNeighbor, int connectivity, const rlVec& runs, const std::vector<int>& pIdxChord1, const std::vector<int>& pIdxNextRow, int emptyValue)
+{
+    CV_Assert(connectivity == 8 || connectivity == 4);
+    CV_Assert(lutNeighbor.size() != 0 && lutNeighbor.size() == 4u * runs.size());
+    CV_Assert(runs.back().r - runs[0].r + 1 == (int)pIdxChord1.size() && pIdxChord1.size() == pIdxNextRow.size());
+    const int connectionOffset = (connectivity == 4) ? 1 : 0;
+    int nRows = (int)pIdxChord1.size();
+    for (int i = 0; i < nRows - 1; ++i)
+    {
+        int firstRowStart = pIdxChord1[i];
+        int secondRowStart = pIdxChord1[i + 1];
+        int firstRowEnd = pIdxNextRow[i] - 1;
+        int secondRowEnd = pIdxNextRow[i + 1] - 1;
+        if (firstRowStart != emptyValue && secondRowStart != emptyValue)
+        {
+            while (firstRowStart <= firstRowEnd && secondRowStart <= secondRowEnd)
+            {
+                const rlType& first = runs[firstRowStart];
+                const rlType& second = runs[secondRowStart];
+                // Compare runs between two consecutive rows sequentially
+                if ((first.ce + connectionOffset < second.cb))
+                {
+                    firstRowStart++;
+                }
+                else if ((first.cb > second.ce + connectionOffset))
+                {
+                    secondRowStart++;
+                }
+                else
+                {
+                    // Each run stores indices of its 4-connected neighbors in lutNeighbor:
+                    // [0] = Top-leftmost neighbor
+                    // [1] = Top-rightmost neighbor
+                    // [2] = Bottom-leftmost neighbor
+                    // [3] = Bottom-rightmost neighbor
+                    lutNeighbor[firstRowStart * 4 + 3] = secondRowStart;
+                    lutNeighbor[secondRowStart * 4 + 1] = firstRowStart;
+                    if (lutNeighbor[firstRowStart * 4 + 2] == emptyValue)
+                    {
+                        lutNeighbor[firstRowStart * 4 + 2] = secondRowStart;
+                    }
+                    if (lutNeighbor[secondRowStart * 4] == emptyValue)
+                    {
+                        lutNeighbor[secondRowStart * 4] = firstRowStart;
+                    }
+                    if ((first.ce == second.ce))
+                    {
+                        firstRowStart++;
+                        secondRowStart++;
+                    }
+                    else if ((first.ce > second.ce))
+                    {
+                        secondRowStart++;
+                    }
+                    else
+                    {
+                        firstRowStart++;
+                    }
+                }
+            }
+        }
+    }
+}
+
+// @author Yu Changming, [email protected], https://github.com/yuchangminghit
+CV_EXPORTS void fillHoles(InputArray rlSrc, OutputArray rlDest, int connectivity)
+{
+    CV_Assert(connectivity == 8 || connectivity == 4);
+    rlVec runsSource, runsDestination;
+    Size sizeSource;
+    convertInputArrayToRuns(rlSrc, runsSource, sizeSource);
+    if ((int)runsSource.size() <= 3)
+    {
+        convertToOutputArray(runsSource, sizeSource, rlDest);
+        return;
+    }
+    rlVec borderRect, backgroundRuns;
+    cv::Rect boundingRect = getBoundingRectangle(runsSource);
+    if (boundingRect.width < 3 || boundingRect.height < 3)
+    {
+        convertToOutputArray(runsSource, sizeSource, rlDest);
+        return;
+    }
+    createUprightRectangle(cv::Rect(boundingRect.x - 1, boundingRect.y - 1, boundingRect.width + 2, boundingRect.height + 2), borderRect);
+    subtract_rle(borderRect, runsSource, backgroundRuns);
+    int nMinRow = backgroundRuns[0].r;
+    int nMaxRow = backgroundRuns.back().r;
+    int nRows = nMaxRow - nMinRow + 1;
+    const int EMPTY = -1;
+    std::vector<int> pIdxChord1(nRows, EMPTY);
+    std::vector<int> pIdxNextRow(nRows, EMPTY);
+    pIdxChord1[0] = 0;
+    pIdxNextRow[nRows - 1] = (int)backgroundRuns.size();
+    for (int i = 1; i < (int)backgroundRuns.size(); i++) {
+        if (backgroundRuns[i].r != backgroundRuns[i - 1].r) {
+            pIdxChord1[backgroundRuns[i].r - nMinRow] = i;
+            pIdxNextRow[backgroundRuns[i - 1].r - nMinRow] = i;
+        }
+    }
+    std::vector<int> neighborLUT(4u * backgroundRuns.size(), EMPTY);
+    getNeighborLookup(neighborLUT, connectivity, backgroundRuns, pIdxChord1, pIdxNextRow, EMPTY);
+    // Stack stores run indices to be processed
+    std::stack<int> indexStack;
+    indexStack.push(0);
+    // Flags for each run:
+    //   0: Run is adjacent to the outer background (not part of a hole)
+    //   255: Run is isolated from the outer background (part of a hole region)
+    std::vector<uchar> selectedFlags(backgroundRuns.size(), (uchar)255);
+    const int SELECTED = 0;
+    selectedFlags[0] = SELECTED;
+    const int neighborOffsets[] = { 0, 2 };
+    while (!indexStack.empty())
+    {
+        int currentIdx = indexStack.top();
+        indexStack.pop();
+        for (int i = 0; i < 2; i++)
+        {
+            if (neighborLUT[4 * currentIdx + neighborOffsets[i]] != EMPTY)
+            {
+                int startIdx = neighborLUT[4 * currentIdx + neighborOffsets[i]];
+                int endIdx = neighborLUT[4 * currentIdx + neighborOffsets[i] + 1];
+                for (int nbrIdx = startIdx; nbrIdx <= endIdx; ++nbrIdx)
+                {
+                    if (selectedFlags[nbrIdx] != SELECTED)
+                    {
+                        selectedFlags[nbrIdx] = SELECTED;
+                        indexStack.push(nbrIdx);
+                    }
+                }
+            }
+        }
+    }
+    rlVec holesBackground;
+    for (int i = 0; i < (int)selectedFlags.size(); i++)
+    {
+        if (selectedFlags[i] == SELECTED)
+        {
+            holesBackground.push_back(backgroundRuns[i]);
+        }
+    }
+    invertRegion(holesBackground, runsDestination);
+    convertToOutputArray(runsDestination, sizeSource, rlDest);
+}
+
 }
 } //end of cv::ximgproc
 } //end of cv

modules/ximgproc/test/test_run_length_morphology.cpp

@@ -245,5 +245,31 @@ TEST_P(RL_Paint, same_result)
 
 INSTANTIATE_TEST_CASE_P(TypicalSET, RL_Paint, Values(CV_8U, CV_16U, CV_16S, CV_32F, CV_64F));
 
+static void getRuns(std::vector<cv::Point3i>& runs, const cv::Mat& rleImage)
+{
+    runs.clear();
+    cv::Point3i* ptr = (cv::Point3i*)rleImage.ptr(0);
+    for (int i = 1; i < rleImage.rows; i++)
+    {
+        runs.push_back(ptr[i]);
+    }
+}
+
+TEST(RL_FILL_HOLES, accuracyFillHoles)
+{
+    std::vector<Point3i> runsSrc = { Point3i(1,4,0),Point3i(0,0,1),Point3i(2,2,1), Point3i(4,4,1), Point3i(1,4,2), Point3i(2,2,3), Point3i(4,4,3), Point3i(3,3,4) };
+    std::vector<Point3i> runsDest8 = { Point3i(1,4,0),Point3i(0,4,1),Point3i(1,4,2), Point3i(2,4,3), Point3i(3,3,4) };
+    std::vector<Point3i> runsDest4 = { Point3i(1,4,0),Point3i(0,0,1),Point3i(2,4,1), Point3i(1,4,2), Point3i(2,2,3), Point3i(4,4,3), Point3i(3,3,4) };
+    Mat rleSrc, rleDest8, rleDest4;
+    rl::createRLEImage(runsSrc, rleSrc);
+    rl::fillHoles(rleSrc, rleDest8, 8);
+    rl::fillHoles(rleSrc, rleDest4, 4);
+    std::vector<cv::Point3i> runsDest8Get, runsDest4Get;
+    getRuns(runsDest8Get, rleDest8);
+    getRuns(runsDest4Get, rleDest4);
+    EXPECT_EQ(runsDest8Get, runsDest8);
+    EXPECT_EQ(runsDest4Get, runsDest4);
+}
+
 }
 }