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 <[email protected]>

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);