Add RISC-V HAL implementation for cv::warp series #27119
This patch implements `cv_hal_remap`, `cv_hal_warpAffine` and `cv_hal_warpPerspective` using native intrinsics, optimizing the performance of `cv::remap/cv::warpAffine/cv::warpPerspective` for `CV_HAL_INTER_NEAREST/CV_HAL_INTER_LINEAR/CV_HAL_INTER_CUBIC/CV_HAL_INTER_LANCZOS4` modes.
Tested on MUSE-PI (Spacemit X60) for both gcc 14.2 and clang 20.0.
```
$ ./opencv_test_imgproc --gtest_filter="*Remap*:*Warp*"
$ ./opencv_perf_imgproc --gtest_filter="*Remap*:*remap*:*Warp*" --perf_min_samples=200 --perf_force_samples=200
```
View the full perf table here: [hal_rvv_warp.pdf](https://github.com/user-attachments/files/19403718/hal_rvv_warp.pdf)
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Fix minAreaRect and boxPoints docs (#26799) #27139
As requested from issue #26799 the docs regarding minAreaRect and boxPoints are extended specifying the order of the corners for boxPoints and the way the angle is computed for the rotated rect returned by minAreaRect
When WARP_INVERSE_MAP is used, accelerate the calculation with multi-threading #27108
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Find contours speedup #26834
It is an attempt, as suggested by #26775, to restore lost speed when migrating `findContours()` implementation from C to C++
The patch adds an "Arena" (a pool) of pre-allocated memory so that contours points (and TreeNodes) can be picked from the Arena.
The code of `findContours()` is mostly unchanged, the arena usage being implicit through a utility class Arena::Item that provides C++ overloaded operators and construct/destruct logic.
As mentioned in #26775, the contour points are allocated and released in order, and can be represented by ranges of indices in their arena. No range subset will be released and drill a hole, that's why the internal representation as a range of indices makes sense.
The TreeNodes use another Arena class that does not comply to that range logic.
Currently, there is a significant improvement of the run-time on the test mentioned in #26775, but it is still far from the `findContours_legacy()` performance.
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Added optional mask to cv::threshold #26842
Proposal for #26777
To avoid code duplication, and keep performance when no mask is used, inner implementation always propagate the const cv::Mat& mask, but they use a template<bool useMask> parameter that let the compiler optimize out unnecessary tests when the mask is not to be used.
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Threshold otsu doc update #27039
PR for #27038
(I had already done that, but encounters git madness after branch renaming)
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Add RISC-V HAL implementation for cv::pyrDown and cv::pyrUp #26958
This patch implements `cv_hal_pyrdown/cv_hal_pyrup` function in RVV_HAL using native intrinsics, optimizing the performance for `cv::pyrDown`, `cv::pyrUp` and `cv::buildPyramids` with data types `{8U,16S,32F} x {C1,C2,C3,C4,Cn}`.
Tested on MUSE-PI (Spacemit X60) for both gcc 14.2 and clang 20.0.
```
$ ./opencv_test_imgproc --gtest_filter="*pyr*:*Pyr*"
$ ./opencv_perf_imgproc --gtest_filter="*pyr*:*Pyr*" --perf_min_samples=300 --perf_force_samples=300
```
<img width="1112" alt="Untitled" src="https://github.com/user-attachments/assets/235a9fba-0d29-434e-8a10-498212bac657" />
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Fix getPerspectiveTransform for singular case #26926
### Pull Request Readiness Checklist
Fix#26916
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Update includes in filter.hpp #26850
Fixes :
```
identifier "Mat" is undefinedC/C++(20)
namespace "std" has no member "vector"C/C++(135)
```
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`step` and `maskStep` are used to increase/decrease `pImage`.
But it's done on unsigned type, relying on overflow, which is UB.
(step is size_t but seed.y is int and can be negative, the result
is therefore unsigned which can overflow)
Add cv::THRESH_DRYRUN flag to get adaptive threshold values without thresholding #26836
A first proposal for #26777
Adds a `cv::THRESH_DRYRUN` flag to let cv::threshold() compute the threshold (useful for OTSU/TRIANGLE), but without actually running the thresholding. This flags is a proposal instead of a new function cv::computeThreshold()
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Improve robustness for fitEllipseAMS #26810
### Pull Request Readiness Checklist
Related to #26694
Added functionality to add noise to points in degenerate cases and try again for `fitEllipseAMS`. `fitEllipseNoDirect` and `fitEllipseDirect` already have this
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Improve robustness for ellipse fitting #26773
### Pull Request Readiness Checklist
Related to #26694
Current noise addition is not very good because for example it turns degenerate case of one horizontal line into degenerate case of two parallel horizontal lines
Improving noise addition leads to improved robustness of algorithms
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- Updated the documentation of the putText function to clarify the behavior of the fontScale parameter.
- Explained how fontScale affects text rendering: magnifying (>1), minimizing (<1), and mirroring (<0).
Feature: weighted Hough Transform #21407
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Support C++20 standard #26590
Close https://github.com/opencv/opencv/issues/26589
Related https://github.com/opencv/opencv_contrib/pull/3842
Related: https://github.com/opencv/opencv/issues/20269
- do not arithmetic enums and ( different enums or floating numeric)
- remove unused variable
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