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Rafael Muñoz Salinas
cc1ab3e3ac
imgproc: add findTRUContours - lock-free parallel contour extraction #28773 Integrates the TRUCO algorithm (Threaded Raster Unrestricted Contour Ownership, @cite TRUCO2026) as a transparent fast path inside `cv::findContours`. No API change is required: existing code automatically benefits when `mode=RETR_LIST` and no hierarchy output is requested. ### How it works When `mode=RETR_LIST` and the caller does not request hierarchy, `findContours` delegates to the TRUCO parallel engine instead of Suzuki-Abe. All ContourApproximationModes are supported; approximation is applied in parallel after extraction. In all other cases the original Suzuki-Abe path is used unchanged. ### Key design ideas - Row-strip domain decomposition parallelised via `cv::parallel_for_` - Start-point ownership rule + speculative downward tracing eliminate tile stitching and synchronisation primitives (lock-free) - 8-bit state space instead of the 32-bit integer labeling required by Suzuki-Abe, giving higher SIMD throughput and lower memory-bandwidth pressure - Paged contour buffer (`TRUCOPagedContour`) avoids heap reallocation on the hot tracing path - SIMD-accelerated row scanning via `cv::v_uint8` intrinsics - Thread count controlled globally via `cv::setNumThreads()`, consistent with OpenCV conventions ### Output correctness Significant effort has gone into ensuring the output is identical to the original `findContours` in every respect: same contour set, same ordering, and same approximation results for all methods. A dedicated test suite (`test_contours_truco.cpp`) verifies exact match against Suzuki-Abe across all four `ContourApproximationModes` and thread counts from 1 to 39, using noise images, circles, nested rectangles, and mixed scenes. ### Performance vs. Suzuki-Abe (from submitted paper) - single-thread: ~1.8–1.9× faster (8-bit SIMD advantage) - 20 threads: ~14–20× faster on i7-13700H (6P+8E, 20T) - 20 threads: ~10–12× faster on Xeon Silver 4510 (12C/24T) ### 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. - [x] The feature is well documented and sample code can be built with the project CMake
