Make cv::VideoCapture::get return cv::CAP_PROP_UNKNOWN (-1) for unsupported properties #21337
The return value indicating an unsupported property is not consistent across backends.
I stumbled on this issue because my code was determining if a property value is valid if it's non-zero (like the documentation says), which worked fine on macOS, but not on Android.
For example, auto-exposure is not supported on macOS, so get() returns 0. But it is supported on Android and 0 means auto-exposure is off.
I think -1 is the better return value to indicate unsupported properties.
I made changes to all the backends. I think I got every case. This breaks API compatibility for some backends, so I based this on branch 3.4.
- [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 other license that is incompatible with OpenCV
- [x] The PR is proposed to proper branch
- [ ] There is reference to original bug report and related work
- [ ] 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
❗ Potential conflicts with #25958
C-API cleanup: highgui, videoio #26025❗ Merge with: opencv/opencv_contrib#3780
This PR removes usage of C-API from highgui and videoio modules. Only source code is affected, tests were not using obsolete API.
It should be possible to backport these changes to 4.x branch preserving removed public headers and source files (`*_c.h` and `*_c.cpp`).
#### Checklist
I tried to verify as many backends as possible, though these checks were not as thorough as I'd like them to be. Below is the checklist covering all modified backends with their statuses.
> 🔹 - small changes
> 🟢 - consider working
> ⚪ - considered untested
##### highgui
Pass | Backend | Local check | CI check
-----|---------|-------------|---------
🟢 | GTK2 | build + test, plugin build | build + test ❔🟢 | GTK3 | build + test, plugin build | build + test
🟢 | QT | build + test, plugin build |
⚪ | Wayland 🔹 | |
🟢 | WIN32 🔹 | | build + test
🟢 | Cocoa 🔹 | | build + test
⚪ | WinRT | |
##### videoio
Pass | Backend | Local check | CI check
-----|---------|-------------|---------
🟢 | Android Camera/MediaNDK 🔹 | | build
🟢 | Aravis | build |
🟢 | AVFoundation OSX | | build + test
⚪ | AVFoundation iOS | | build
🟢 | DC1394 | build |
🟢 | DShow 🔹 | | build
🟢 | FFMpeg | build, plugin build | build + test
🟢 | GPhoto 🔹 | build |
🟢 | GStreamer | build, plugin build | build + test
🟢 | Images | build | build + test
🟢 | MSMF 🔹 | | build + test
🟢 | OpenNI | build |
🟢 | PVAPI | build |
🟢 | V4L | build + test | build
🟢 | XIMEA | build |
🟢 | XINE 🔹 | build |
#### Notes
- local linux build checks performed using [this framework](https://github.com/mshabunin/opencv-videoio-build-check)
- minor extra changes made in both `cap_avfoundation*.mm` to make them slightly more synchronized - it would be better to combine them into a single one in the future
- configurations with plugins have been build but not tested
- **moved unrelated changes to separate PRs** ~two issues have been fixed in separate commits:~
- ~imgproc: missing `cv::hal::` color conversion functions has been used in MediaSDK backend~
- ~videoio/V4L: wrong color conversion mode caused bad colors for NV12 camera input format (RGB instead of BGR)~
It would be nice to check following functionality manually:
- [ ] OSX: camera input
- [ ] iOS: camera and file input
- [ ] WinRT: build, some testing
- [x] Linux/Wayland: build
(use "git reset HEAD <file>..." to unstage)
modified: modules/java/generator/gen_java.py
modified: modules/videoio/include/opencv2/videoio.hpp
modified: modules/videoio/include/opencv2/videoio/videoio_c.h
modified: modules/videoio/src/cap_dshow.cpp
modified: modules/videoio/src/cap_pvapi.cpp
Following changes have been made:
1. Some minor bugs have been removed.
2. In the PvAPI module the option CAP_PROP_MONOCROME has been removed because
this option does not make sense and causes an error if a color camera is used.
3. Instead the new option CAP_PROP_PVAPI_PIXELFORMAT has been added which allows
to activate the different pixel formats (color modes) of an AVT camera.
4. Since there were two identical defines
CAP_PROP_MONOCROME = 19
CAP_PROP_MONOCHROME = 19
which were also used in the other module DSHOW, the first one with an orthographic
error has been removed in favor of the second one.
Mansour Moufid
Maksim Shabunin
Alexander Alekhin
Prof. Dr. Rudolf Haussmann
Artur Wieczorek
Vadim Pisarevsky
Nick D'Ademo
Low Chin Kian
vbystricky