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Merge pull request #27992 from asmorkalov:as/HoughLines_bias

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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
This commit is contained in:
Alexander Smorkalov
2025-11-12 11:30:14 +03:00
committed by GitHub
parent adaa369bb1
commit a31a52adef
3 changed files with 65 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files
modules/imgproc/src/hough.cpp
+1 -1
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@@ -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<float>(min_theta) + n * theta;
if (type == CV_32FC2)
{
modules/imgproc/src/opencl/hough_lines.cl
+1 -1
View File
@@ -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);
modules/imgproc/test/test_houghlines.cpp
+63
View File
@@ -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<cv::Vec2f>(0)[0], 1e-5);
EXPECT_NEAR(0, lines.at<cv::Vec2f>(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<cv::Vec2f>(0)[0], 1e-5);
EXPECT_NEAR(0, lines.at<cv::Vec2f>(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<cv::Vec2f>(0)[0], 1e-5);
EXPECT_NEAR(0, lines.at<cv::Vec2f>(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<cv::Vec2f>(0)[0], 1e-5);
EXPECT_NEAR(0, lines.at<cv::Vec2f>(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<cv::Vec2f>(0)[0], 1e-5);
EXPECT_NEAR(CV_PI/2., lines.at<cv::Vec2f>(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<cv::Vec2f>(0)[0], 1e-5);
EXPECT_NEAR(CV_PI/2., lines.at<cv::Vec2f>(0)[1], 1e-5);
}
TEST(WeightedHoughLines, horizontal)
{
Mat img(25, 25, CV_8UC1, Scalar(0));