From 20b040a77a1c703e126372419737d5645c6db3b2 Mon Sep 17 00:00:00 2001
From: Chi-Wei Lee <levi74108520963@gmail.com>
Date: Thu, 1 Oct 2026 14:58:31 +0800
Subject: [PATCH] util2d::getDepth(): use the mean for the neighbor depth
 tolerance (#1780)

When estimating a missing depth from its 4-connected neighbors, a
neighbor is accepted if it is within depthErrorRatio of the mean of the
neighbors accepted so far. The tolerance was computed from the running
sum instead of the mean, so it grew to 2x and then 3x the ratio for the
third and fourth neighbor, letting inconsistent depths into the average.

Co-authored-by: matlabbe <matlabbe@gmail.com>
---
 corelib/src/util2d.cpp       |  5 +++--
 corelib/test/test_util2d.cpp | 25 +++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/corelib/src/util2d.cpp b/corelib/src/util2d.cpp
index 052bb49d..584dd342 100644
--- a/corelib/src/util2d.cpp
+++ b/corelib/src/util2d.cpp
@@ -1029,8 +1029,9 @@ float getDepth(
 						}
 						else
 						{
-							float depthError = depthErrorRatio * tmp;
-							if(fabs(d - tmp/float(count)) < depthError)
+							float mean = tmp/float(count);
+							float depthError = depthErrorRatio * mean;
+							if(fabs(d - mean) < depthError)
 
 							{
 								tmp += d;
diff --git a/corelib/test/test_util2d.cpp b/corelib/test/test_util2d.cpp
index 1af87c95..deb0bd29 100644
--- a/corelib/test/test_util2d.cpp
+++ b/corelib/test/test_util2d.cpp
@@ -508,6 +508,31 @@ TEST(Util2dTest, GetDepthEstimationFromNeighbors16U) {
     EXPECT_NEAR(result, 1.5f, 1e-3f);
 }
 
+TEST(Util2dTest, GetDepthEstimationFromNeighborsRejectsOutlier) {
+    // Neighbors are visited as (2,1), (1,2), (3,2), (2,3). The last one is
+    // 25% away from the mean of the first three and must be ignored.
+    cv::Mat depth = cv::Mat::zeros(5, 5, CV_32FC1);
+    depth.at<float>(2, 1) = 1.00f;
+    depth.at<float>(1, 2) = 1.02f;
+    depth.at<float>(3, 2) = 0.98f;
+    depth.at<float>(2, 3) = 1.25f;
+
+    float result = util2d::getDepth(depth, 2.0f, 2.0f, false, 0.1f, true);
+    EXPECT_NEAR(result, 1.0f, 1e-5f);
+
+    cv::Mat depth16U = util2d::cvtDepthFromFloat(depth);
+    result = util2d::getDepth(depth16U, 2.0f, 2.0f, false, 0.1f, true);
+    EXPECT_NEAR(result, 1.0f, 1e-3f);
+
+    // Same with the default ratio (0.02): the last neighbor is 5% away.
+    depth.at<float>(2, 1) = 1.00f;
+    depth.at<float>(1, 2) = 1.01f;
+    depth.at<float>(3, 2) = 0.99f;
+    depth.at<float>(2, 3) = 1.05f;
+    result = util2d::getDepth(depth, 2.0f, 2.0f, false, 0.02f, true);
+    EXPECT_NEAR(result, 1.0f, 1e-5f);
+}
+
 TEST(Util2dTest, GetDepthOutOfBounds) {
     cv::Mat depth = cv::Mat::ones(5, 5, CV_32FC1);