Merge pull request #27305 from chengolivia:add-check-sgbm-nondeterminism

chengolivia · web-flow · commit 250b5003ee74 · 2025-05-17T10:19:09.000+03:00
Add image dimension check to avoid StereoSGBM non-determinism #27305 Addresses #25828 Users noticed that StereoSGBM would occasionally give non-deterministic results for `.compute(imgL, imgR)`. I and others traced the cause to out-of-bounds access that was not being caught when the input images were not wide enough for the input block size and number of disparities to StereoSGBM. The specific math and logic can be found in the above issue's discussion. This PR adds a CV_Check to make sure images are wider than 1/2 of the block size + the max disparity the algorithm will search. The check was only added to the regular `compute` method for StereoSGBM and not to the other modes, as I did not observe the non-deterministic behavior with the other compute modes like HH. In addition, this PR adds a test case to Calib3d to make sure the check is being thrown in the problem case and that the results are deterministic in the good case. ### 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 - [x] The PR is proposed to the proper branch - [x] There is a reference to the original bug report and related work - [x] 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
diff --git a/modules/calib3d/src/stereosgbm.cpp b/modules/calib3d/src/stereosgbm.cpp
@@ -508,6 +508,9 @@ static void computeDisparitySGBM( const Mat& img1, const Mat& img2,
     int SW2 = params.calcSADWindowSize().width/2, SH2 = params.calcSADWindowSize().height/2;
     int npasses = params.isFullDP() ? 2 : 1;
 
+    CV_CheckGT(width - (params.minDisparity + params.numDisparities), params.calcSADWindowSize().width/2,
+     "Your input images are too small for your window size and max disparity, and will result in non-deterministic SGBM results");
+
     if( minX1 >= maxX1 )
     {
         disp1 = Scalar::all(INVALID_DISP_SCALED);
diff --git a/modules/calib3d/test/test_stereomatching.cpp b/modules/calib3d/test/test_stereomatching.cpp
@@ -920,6 +920,38 @@ class CV_StereoSGBMTest : public CV_StereoMatchingTest
 
 TEST(Calib3d_StereoSGBM, regression) { CV_StereoSGBMTest test; test.safe_run(); }
 
+TEST(Calib3d_StereoSGBM, deterministic) {
+    cv::Ptr<cv::StereoSGBM> matcher = cv::StereoSGBM::create(16, 11);
+
+    // Expect throw error (non-determinism case)
+    int widthNarrow = 28;
+    int height = 15;
+
+    cv::Mat leftNarrow(height, widthNarrow, CV_8UC1);
+    cv::Mat rightNarrow(height, widthNarrow, CV_8UC1);
+    randu(leftNarrow, cv::Scalar(0), cv::Scalar(255));
+    randu(rightNarrow, cv::Scalar(0), cv::Scalar(255));
+    cv::Mat disp;
+
+    EXPECT_THROW(matcher->compute(leftNarrow, rightNarrow, disp), cv::Exception);
+
+    // Deterministic case, image is sufficiently large for StereSGBM parameters
+    int widthWide = 40;
+    cv::Mat leftWide(height, widthWide, CV_8UC1);
+    cv::Mat rightWide(height, widthWide, CV_8UC1);
+    randu(leftWide, cv::Scalar(0), cv::Scalar(255));
+    randu(rightWide, cv::Scalar(0), cv::Scalar(255));
+    cv::Mat disp1, disp2;
+    for (int i = 0; i < 10; i++) {
+        matcher->compute(leftWide, rightWide, disp1);
+        matcher->compute(leftWide, rightWide, disp2);
+        cv::Mat dst;
+        cv::bitwise_xor(disp1, disp2, dst);
+        EXPECT_EQ(cv::countNonZero(dst), 0);
+    }
+
+}
+
 TEST(Calib3d_StereoSGBM_HH4, regression)
 {
     String path = cvtest::TS::ptr()->get_data_path() + "cv/stereomatching/datasets/teddy/";

Original file line number	Diff line number	Diff line change
`@@ -508,6 +508,9 @@ static void computeDisparitySGBM( const Mat& img1, const Mat& img2,`
`508`	`508`	`int SW2 = params.calcSADWindowSize().width/2, SH2 = params.calcSADWindowSize().height/2;`
`509`	`509`	`int npasses = params.isFullDP() ? 2 : 1;`
`510`	`510`
	`511`	`+ CV_CheckGT(width - (params.minDisparity + params.numDisparities), params.calcSADWindowSize().width/2,`
	`512`	`+ "Your input images are too small for your window size and max disparity, and will result in non-deterministic SGBM results");`
	`513`	`+`
`511`	`514`	`if( minX1 >= maxX1 )`
`512`	`515`	`{`
`513`	`516`	`disp1 = Scalar::all(INVALID_DISP_SCALED);`