Open camera device by index through FFmpeg #27841
### Pull Request Readiness Checklist
resolves https://github.com/opencv/opencv/issues/26812
Example of explicit backend option (similar to `-f v4l2` from command line)
```
export OPENCV_FFMPEG_CAPTURE_OPTIONS="f;v4l2"
```
see https://trac.ffmpeg.org/wiki/Capture/Webcam for available options
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Use cairosvg for pattern rendering to get rid of double resize. #27906
Depends on https://github.com/opencv/ci-gha-workflow/pull/269
### Pull Request Readiness Checklist
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core: support 16 bit LUT #27890
Close https://github.com/opencv/opencv/issues/26899
### Pull Request Readiness Checklist
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Use `link_libraries` instead of `add_defintions` to link against Qt 6.9
and newer to avoid un-expanded generator expressions from Qt cmake files
being appended to linker flags when building the HighGUI module.
The actual bug is likely in how Qt cmake files end up with these
un-expanded generator expressions in the first place — see discussion in
https://bugreports.qt.io/browse/QTBUG-134774 — but the recommended way
to link against the library is to use `link_libraries` anyway, so this
fix should do the trick.
Fixes issue #27223.
Refactor minEnclosingCircle tests #27900
### Pull Request Readiness Checklist
Separate input points for tests
Before this, next input points depended on previous ones and it was not obvious which input points specific test checked
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.
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- Changed splitting logic to improved performance for all warp related functions in IPP HAL for multithreaded mode.
- Removed IPP 7.0 preprocessor condition from warp in IPP HAL, since unsupported.
- Added preprocessor condition to enforce IPP warp calls for custom builds.
2025-10-14T05:53:31.5387050Z C:\GHA-OCV-1\_work\ci-gha-workflow\ci-gha-workflow\opencv\modules\imgcodecs\src\bitstrm.cpp(156,57): warning C4244: 'argument': conversion from 'int64_t' to 'ptrdiff_t', possible loss of data [C:\GHA-OCV-1\_work\ci-gha-workflow\ci-gha-workflow\build\modules\imgcodecs\opencv_imgcodecs.vcxproj]
### Pull Request Readiness Checklist
Optional Known Foreground Mask for Background Subtractors #27810
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### Description
This adds an optional foreground input mask parameter to the MOG2 and KNN background subtractors, in line with issue https://github.com/opencv/opencv/issues/26476
4 tests are added under test_bgfg2.cpp:
2 for each subtractor type (1 with shadow detection and 1 without)
A demo shows the feature with only 3 parameters and with a 4th optional foreground mask for both core subtractor types.
Note: To patch contrib inheritance of the background subtraction class, empty apply method which throws a not implemented error is added to contrib subclasses. This is done to keep the overloaded apply function as pure virtual. Contrib PR to be made and linked shortly.
Contrib Repo Paired Pull Request: https://github.com/opencv/opencv_contrib/pull/4017
Enabled fp16 conversions, but disabled NEON FP16 arithmetics on Windows for ARM for now #27897
### Pull Request Readiness Checklist
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Fix charuco_board_pattern in generate_pattern.py #27876
### Pull Request Readiness Checklist
Fix#27871
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Fix QRCodeDetector::detectAndDecode crash #27877
### Pull Request Readiness Checklist
Fix#27807
The problem is that when we find closest points from hull, we can get same closest point for several different points
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.
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Fix invalid memory access in USAC #27865
### Pull Request Readiness Checklist
Fix#27863
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- [x] I agree to contribute to the project under Apache 2 License.
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Improved blur #27822
* Perform row and column filter operations in a single pass.
* Temporary storage of intermediate results are avoided.
* Impacts 32F and 64F inputs for ksize <=5.
### 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.
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Patch to opencv_extra has the same branch name.
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Add OPENCV_FFMPEG_SKIP_LOG_CALLBACK to preserve custom FFmpeg logging #27864
OpenCV’s InternalFFMpegRegister overwrites av_log_set_callback, blocking custom FFmpeg log handlers in statically linked apps.
Add `OPENCV_FFMPEG_SKIP_LOG_CALLBACK` to let applications keep their own logging.
### Pull Request Readiness Checklist
See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request
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Patch to opencv_extra has the same branch name.
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dnn: added neon intrinsics implementation of fastGEMM1T function #27785
### Pull Request Readiness Checklist
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- This PR improves the performance of the LSTM function on ARM64 targets.
- Added a NEON intrinsics implementation of the fastGEMM1T function and enabled its use in fully connected and recurrent layers file.
- As a result, ARM64 now benefits from vectorized matrix–vector multiplications, leading to measurable performance improvements in the LSTM layer.
- This change is limited to ARM64 and does not affect other architectures.
**Performance impact:**
- The optimization significantly improves the performance of lstm functions on ARM64 targets.
<img width="930" height="313" alt="image" src="https://github.com/user-attachments/assets/92e251cd-dc6c-4cda-9586-acc19bf16dfd" />
cudawarped
Alexander Smorkalov
MaximSmolskiy
Dmitry Kurtaev
s-trinh
Kumataro
xybuild
Atri Bhattacharya
Victor Getmanskiy
Dave Merchant
Alexander Smorkalov
xcm4
ashish-sriram
Peter Rekdal Khan-Sunde
pratham-mcw