From b41cda2b93cfeca7752a5585e5ff6a49819ebc4c Mon Sep 17 00:00:00 2001
From: Trishanth Mellimi <trishanthmellimi@gmail.com>
Date: Fri, 24 Jul 2026 23:48:00 +0530
Subject: [PATCH] imgproc: accept CV_Bool masks in distanceTransform

cv::Mat_<bool>::depth() returns CV_Bool in 5.0 where it returned CV_8U in
4.x, so distanceTransform started rejecting boolean masks. CV_Bool is a
1-byte type whose values are only zero-tested here, so accept it wherever
a CV_8UC1 mask was previously accepted, matching the 4.x behaviour and the
4->5 migration guide.

Relaxes the type checks on all four reachable paths: the public wrapper,
distanceTransform_L1_8U, trueDistTrans (DIST_MASK_PRECISE) and
distanceATS_L1_8u (CV_8U output).

Closes #29596
---
 modules/imgproc/src/distransform.cpp          | 12 +++--
 .../imgproc/test/test_distancetransform.cpp   | 45 +++++++++++++++++++
 2 files changed, 53 insertions(+), 4 deletions(-)

diff --git a/modules/imgproc/src/distransform.cpp b/modules/imgproc/src/distransform.cpp
index e4a2b4eeac..f85581e34f 100644
--- a/modules/imgproc/src/distransform.cpp
+++ b/modules/imgproc/src/distransform.cpp
@@ -830,7 +830,7 @@ trueDistTrans( const Mat& src, Mat& dst )
 
     CV_Assert( src.size() == dst.size() );
 
-    CV_Assert( src.type() == CV_8UC1 && dst.type() == CV_32FC1 );
+    CV_Assert( (src.type() == CV_8UC1 || src.type() == CV_BoolC1) && dst.type() == CV_32FC1 );
     int i, m = src.rows, n = src.cols;
 
     cv::AutoBuffer<uchar> _buf(std::max(m*2*sizeof(int) + (m*3+1)*sizeof(int), n*2*sizeof(float)));
@@ -886,7 +886,7 @@ distanceATS_L1_8u( const Mat& src, Mat& dst )
     int srcstep = (int)src.step;
     int dststep = (int)dst.step;
 
-    CV_Assert( src.type() == CV_8UC1 && dst.type() == CV_8UC1 );
+    CV_Assert( (src.type() == CV_8UC1 || src.type() == CV_BoolC1) && dst.type() == CV_8UC1 );
     CV_Assert( src.size() == dst.size() );
 
     ////////////////////// forward scan ////////////////////////
@@ -957,7 +957,9 @@ static void distanceTransform_L1_8U(InputArray _src, OutputArray _dst)
 
     Mat src = _src.getMat();
 
-    CV_Assert( src.type() == CV_8UC1);
+    // CV_Bool is a 1-byte mask type (added in 5.0) and is only ever zero-tested
+    // here, so accept it wherever a CV_8UC1 mask was accepted. See #29596.
+    CV_Assert( src.type() == CV_8UC1 || src.type() == CV_BoolC1);
 
     _dst.create( src.size(), CV_8UC1);
     Mat dst = _dst.getMat();
@@ -978,7 +980,9 @@ void cv::distanceTransform( InputArray _src, OutputArray _dst, OutputArray _labe
     Mat src = _src.getMat(), labels;
     bool need_labels = _labels.needed();
 
-    CV_Assert( src.type() == CV_8UC1);
+    // CV_Bool is a 1-byte mask type (added in 5.0) and is only ever zero-tested
+    // here, so accept it wherever a CV_8UC1 mask was accepted. See #29596.
+    CV_Assert( src.type() == CV_8UC1 || src.type() == CV_BoolC1);
 
     _dst.create( src.size(), CV_32F);
     Mat dst = _dst.getMat();
diff --git a/modules/imgproc/test/test_distancetransform.cpp b/modules/imgproc/test/test_distancetransform.cpp
index c1d2e8c34a..6d73dec8fc 100644
--- a/modules/imgproc/test/test_distancetransform.cpp
+++ b/modules/imgproc/test/test_distancetransform.cpp
@@ -209,4 +209,49 @@ TEST(Imgproc_DistanceTransform, ipp_deterministic)
     }
 }
 
+// See https://github.com/opencv/opencv/issues/29596
+// cv::Mat_<bool>::depth() returns CV_Bool in 5.0, where it was CV_8U in 4.x, so
+// distanceTransform started rejecting boolean masks. CV_Bool is a 1-byte type
+// whose values are only ever zero-tested here, so the result must match the one
+// produced by an equivalent CV_8UC1 mask.
+TEST(Imgproc_DistanceTransform, bool_mask_29596)
+{
+    Mat_<bool> mask(7, 7, true);
+    mask(3, 3) = false;
+    mask(0, 6) = false;
+
+    Mat_<uchar> ref(7, 7, (uchar)255);
+    ref(3, 3) = 0;
+    ref(0, 6) = 0;
+
+    ASSERT_EQ(mask.depth(), CV_Bool);
+
+    // CV_32F output: 3x3 and 5x5 kernels, plus the precise (trueDistTrans) path
+    const int maskSizes[] = { DIST_MASK_3, DIST_MASK_5, DIST_MASK_PRECISE };
+    for (size_t i = 0; i < sizeof(maskSizes)/sizeof(maskSizes[0]); i++)
+    {
+        Mat dist_bool, dist_ref;
+        ASSERT_NO_THROW(distanceTransform(mask, dist_bool, DIST_L2, maskSizes[i]));
+        distanceTransform(ref, dist_ref, DIST_L2, maskSizes[i]);
+        EXPECT_EQ(cv::norm(dist_bool, dist_ref, NORM_INF), 0) << "maskSize = " << maskSizes[i];
+    }
+
+    // CV_8U output path (distanceTransform_L1_8U -> distanceATS_L1_8u)
+    {
+        Mat dist_bool, dist_ref;
+        ASSERT_NO_THROW(distanceTransform(mask, dist_bool, DIST_L1, DIST_MASK_3, CV_8U));
+        distanceTransform(ref, dist_ref, DIST_L1, DIST_MASK_3, CV_8U);
+        EXPECT_EQ(cv::norm(dist_bool, dist_ref, NORM_INF), 0);
+    }
+
+    // labels overload
+    {
+        Mat dist_bool, labels_bool, dist_ref, labels_ref;
+        ASSERT_NO_THROW(distanceTransform(mask, dist_bool, labels_bool, DIST_L2, DIST_MASK_5));
+        distanceTransform(ref, dist_ref, labels_ref, DIST_L2, DIST_MASK_5);
+        EXPECT_EQ(cv::norm(dist_bool, dist_ref, NORM_INF), 0);
+        EXPECT_EQ(cv::norm(labels_bool, labels_ref, NORM_INF), 0);
+    }
+}
+
 }} // namespace