tiff: use a per-TIFF error handler #27927
libtiff 4.5 introduced [per-TIFF error handlers](https://libtiff.gitlab.io/libtiff/functions/TIFFOpenOptions.html). This PR removes the global OpenCV error handlers and uses per-handle error handlers. This reduces any risks associated with modifying global state, e.g. if another library also tries to set the global error handlers and OpenCV clobbers them.
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Open camera device by index through FFmpeg #27841
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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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Update Gao P3P with Ding P3P #27736
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---
The current Gao P3P implementation does not cover all the degenerate cases, **see last line** in: 6d889ee74c/modules/calib3d/src/p3p.cpp (L211-L221)
See also:
- https://github.com/opencv/opencv/issues/4854
---
<details>
<summary>OBSOLETE</summary>
To fix this, the USAC P3P from OpenCV 5 is used instead: 7e6da007cd/modules/3d/src/usac/pnp_solver.cpp (L282)
---
## Some results
### Old P3P vs new
In the following video, I have tried to highlight the viewpoints which cause issues:
https://github.com/user-attachments/assets/97bec6a6-4043-4509-b50e-a9856d6423bd
| | Old P3P | New P3P |
| -------- | ------- | ------- |
| Mean (ms) | 0.045701 | 0.024816 |
| Median (ms) | 0.025146 | 0.023193 |
| Std (ms) | 0.028953 | 0.006124 |
### New P3P vs AP3P
https://github.com/user-attachments/assets/eaeb21dc-3ffd-4b6c-9902-4352f824aa45
The AP3 method is superior both in term of accuracy and computation time:
| | New P3P | AP3P |
| -------- | ------- | ------- |
| Mean (ms) | 0.043750 | 0.023442 |
| Median (ms) | 0.023193 | 0.021484 |
| Std (ms) | 0.039920 | 0.005265 |
### New P3P vs AP3P (range test)
https://github.com/user-attachments/assets/572e7b7a-2966-4bed-8e0c-b93d863987dc
The implemented P3P method does not work well when the tag is small, at long range.
| | New P3P | AP3P |
| -------- | ------- | ------- |
| Mean (ms) | 0.031351 | 0.025189 |
| Median (ms) | 0.022217 | 0.020996 |
| Std (ms) | 0.024920 | 0.009633 |
---
- I have tried to simplify the P3P code, hope I did not break the implementation code
- calculations are performed using double type for simplicity.
- code such as the following are redundant and no more needed and should be replaced by `cv::Rodrigues`:
6d889ee74c/modules/calib3d/src/usac/pnp_solver.cpp (L395)
</details>
core: support 16 bit LUT #27890
Close https://github.com/opencv/opencv/issues/26899
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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
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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
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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]
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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
Fix QRCodeDetector::detectAndDecode crash #27877
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Fix#27807
The problem is that when we find closest points from hull, we can get same closest point for several different points
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Fix invalid memory access in USAC #27865
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Fix#27863
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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.
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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.
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dnn: added neon intrinsics implementation of fastGEMM1T function #27785
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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" />
