From a31a52adefb488f5b8c2f661525f90b87f35a22b Mon Sep 17 00:00:00 2001 From: Alexander Smorkalov <2536374+asmorkalov@users.noreply.github.com> Date: Wed, 12 Nov 2025 11:30:14 +0300 Subject: [PATCH] Merge pull request #27992 from asmorkalov:as/HoughLines_bias Fixed standard HoughLines output shift for rho. #27992 Closes: https://github.com/opencv/opencv/issues/25038 Replaces: https://github.com/opencv/opencv/pull/25043 Merge with https://github.com/opencv/opencv_extra/pull/1288 The original implementation introduces systematic shift (-rho/2) for odd indexes. Integer division just gives proper rounding. ### 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 - [ ] The PR is proposed to the proper branch - [ ] There is a reference to the original bug report and related work - [ ] 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/src/hough.cpp | 2 +- modules/imgproc/src/opencl/hough_lines.cl | 2 +- modules/imgproc/test/test_houghlines.cpp | 63 +++++++++++++++++++++++ 3 files changed, 65 insertions(+), 2 deletions(-) diff --git a/modules/imgproc/src/hough.cpp b/modules/imgproc/src/hough.cpp index 39bdecf2ea..b418b046bc 100644 --- a/modules/imgproc/src/hough.cpp +++ b/modules/imgproc/src/hough.cpp @@ -228,7 +228,7 @@ HoughLinesStandard( InputArray src, OutputArray lines, int type, int idx = _sort_buf[i]; int n = cvFloor(idx*scale) - 1; int r = idx - (n+1)*(numrho+2) - 1; - line.rho = (r - (numrho - 1)*0.5f) * rho; + line.rho = (r - (numrho - 1)/2) * rho; line.angle = static_cast(min_theta) + n * theta; if (type == CV_32FC2) { diff --git a/modules/imgproc/src/opencl/hough_lines.cl b/modules/imgproc/src/opencl/hough_lines.cl index 907811cded..5ae4171fcb 100644 --- a/modules/imgproc/src/opencl/hough_lines.cl +++ b/modules/imgproc/src/opencl/hough_lines.cl @@ -162,7 +162,7 @@ __kernel void get_lines(__global uchar * accum_ptr, int accum_step, int accum_of if (index < linesMax) { - float radius = (x - (accum_cols - 3) * 0.5f) * rho; + float radius = (x - (accum_cols - 3) / 2) * rho; float angle = y * theta; lines[index] = (float2)(radius, angle); diff --git a/modules/imgproc/test/test_houghlines.cpp b/modules/imgproc/test/test_houghlines.cpp index 02eb2d4379..82b2864b13 100644 --- a/modules/imgproc/test/test_houghlines.cpp +++ b/modules/imgproc/test/test_houghlines.cpp @@ -340,6 +340,69 @@ TEST(HoughLines, regression_21983) EXPECT_NEAR(lines[0][1], 1.57179642, 1e-4); } +TEST(HoughLines, regression_25038_vertical) +{ + cv::Mat img = cv::Mat::zeros(8, 8, CV_8UC1); + img.col(3).setTo(255); + + cv::Mat lines; + cv::HoughLines(img, lines, 0.5, CV_PI/4., 2); + EXPECT_EQ(1, lines.cols); + EXPECT_EQ(1, lines.rows); + EXPECT_EQ(2, lines.channels()); + EXPECT_NEAR(3, lines.at(0)[0], 1e-5); + EXPECT_NEAR(0, lines.at(0)[1], 1e-5); + + cv::HoughLines(img, lines, 0.05, CV_PI/4., 2); + EXPECT_EQ(1, lines.cols); + EXPECT_EQ(1, lines.rows); + EXPECT_EQ(2, lines.channels()); + EXPECT_NEAR(3, lines.at(0)[0], 1e-5); + EXPECT_NEAR(0, lines.at(0)[1], 1e-5); +} + +TEST(HoughLines, regression_25038_even) +{ + cv::Mat img = cv::Mat::zeros(8, 8, CV_8UC1); + img.col(4).setTo(255); + + cv::Mat lines; + cv::HoughLines(img, lines, 0.5, CV_PI/4., 2); + EXPECT_EQ(1, lines.cols); + EXPECT_EQ(1, lines.rows); + EXPECT_EQ(2, lines.channels()); + EXPECT_NEAR(4, lines.at(0)[0], 1e-5); + EXPECT_NEAR(0, lines.at(0)[1], 1e-5); + + cv::HoughLines(img, lines, 0.05, CV_PI/4., 2); + EXPECT_EQ(1, lines.cols); + EXPECT_EQ(1, lines.rows); + EXPECT_EQ(2, lines.channels()); + EXPECT_NEAR(4, lines.at(0)[0], 1e-5); + EXPECT_NEAR(0, lines.at(0)[1], 1e-5); +} + +TEST(HoughLines, regression_25038_horizontal) +{ + cv::Mat img = cv::Mat::zeros(8, 8, CV_8UC1); + img.row(3).setTo(255); + + cv::Mat lines; + cv::HoughLines(img, lines, 0.5, CV_PI/4., 2); + EXPECT_EQ(1, lines.cols); + EXPECT_EQ(1, lines.rows); + EXPECT_EQ(2, lines.channels()); + EXPECT_NEAR(3, lines.at(0)[0], 1e-5); + EXPECT_NEAR(CV_PI/2., lines.at(0)[1], 1e-5); + + cv::HoughLines(img, lines, 0.05, CV_PI/4., 2); + EXPECT_EQ(1, lines.cols); + EXPECT_EQ(1, lines.rows); + EXPECT_EQ(2, lines.channels()); + EXPECT_NEAR(3, lines.at(0)[0], 1e-5); + EXPECT_NEAR(CV_PI/2., lines.at(0)[1], 1e-5); +} + TEST(WeightedHoughLines, horizontal) { Mat img(25, 25, CV_8UC1, Scalar(0));