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159 lines
6.5 KiB
Markdown
159 lines
6.5 KiB
Markdown
High level stitching API (Stitcher class) {#tutorial_stitcher}
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=========================================
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Goal
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----
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In this tutorial you will learn how to:
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- use the high-level stitching API for stitching provided by
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- @ref cv::Stitcher
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- learn how to use preconfigured Stitcher configurations to stitch images
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using different camera models.
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Code
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----
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This tutorial code's is shown lines below. You can also download it from
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[here](https://github.com/opencv/opencv/tree/master/samples/cpp/stitching.cpp).
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@include samples/cpp/stitching.cpp
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Explanation
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-----------
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The most important code part is:
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@snippet cpp/stitching.cpp stitching
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A new instance of stitcher is created and the @ref cv::Stitcher::stitch will
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do all the hard work.
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@ref cv::Stitcher::create can create stitcher in one of the predefined
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configurations (argument `mode`). See @ref cv::Stitcher::Mode for details. These
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configurations will setup multiple stitcher properties to operate in one of
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predefined scenarios. After you create stitcher in one of predefined
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configurations you can adjust stitching by setting any of the stitcher
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properties.
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If you have cuda device @ref cv::Stitcher can be configured to offload certain
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operations to GPU. If you prefer this configuration set `try_use_gpu` to true.
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OpenCL acceleration will be used transparently based on global OpenCV settings
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regardless of this flag.
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Stitching might fail for several reasons, you should always check if
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everything went good and resulting pano is stored in `pano`. See
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@ref cv::Stitcher::Status documentation for possible error codes.
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Camera models
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-------------
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There are currently 2 camera models implemented in stitching pipeline.
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- _Homography model_ expecting perspective transformations between images
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implemented in @ref cv::detail::BestOf2NearestMatcher cv::detail::HomographyBasedEstimator
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cv::detail::BundleAdjusterReproj cv::detail::BundleAdjusterRay
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- _Affine model_ expecting affine transformation with 6 DOF or 4 DOF implemented in
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@ref cv::detail::AffineBestOf2NearestMatcher cv::detail::AffineBasedEstimator
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cv::detail::BundleAdjusterAffine cv::detail::BundleAdjusterAffinePartial cv::AffineWarper
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Homography model is useful for creating photo panoramas captured by camera,
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while affine-based model can be used to stitch scans and object captured by
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specialized devices.
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@note
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Certain detailed settings of @ref cv::Stitcher might not make sense. Especially
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you should not mix classes implementing affine model and classes implementing
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Homography model, as they work with different transformations.
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Try it out
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----------
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If you enabled building samples you can found binary under
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`build/bin/cpp-example-stitching`. This example is a console application, run it without
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arguments to see help. `opencv_extra` provides some sample data for testing all available
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configurations.
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to try panorama mode run:
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```
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./cpp-example-stitching --mode panorama <path to opencv_extra>/testdata/stitching/boat*
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```
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to try scans mode run (dataset from home-grade scanner):
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```
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./cpp-example-stitching --mode scans <path to opencv_extra>/testdata/stitching/newspaper*
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```
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or (dataset from professional book scanner):
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```
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./cpp-example-stitching --mode scans <path to opencv_extra>/testdata/stitching/budapest*
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```
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@note
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Examples above expects POSIX platform, on windows you have to provide all files names explicitly
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(e.g. `boat1.jpg` `boat2.jpg`...) as windows command line does not support `*` expansion.
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Stitching detailed (python opencv >4.0.1)
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--------
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If you want to study internals of the stitching pipeline or you want to experiment with detailed
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configuration you can use stitching_detailed source code available in C++ or python
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<H4>stitching_detailed</H4>
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@add_toggle_cpp
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[stitching_detailed.cpp](https://raw.githubusercontent.com/opencv/opencv/master/samples/cpp/stitching_detailed.cpp)
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@end_toggle
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@add_toggle_python
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[stitching_detailed.py](https://raw.githubusercontent.com/opencv/opencv/master/samples/python/stitching_detailed.py)
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@end_toggle
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stitching_detailed program uses command line to get stitching parameter. Many parameters exists. Above examples shows some command line parameters possible :
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boat5.jpg boat2.jpg boat3.jpg boat4.jpg boat1.jpg boat6.jpg --work_megapix 0.6 --features orb --matcher homography --estimator homography --match_conf 0.3 --conf_thresh 0.3 --ba ray --ba_refine_mask xxxxx --save_graph test.txt --wave_correct no --warp fisheye --blend multiband --expos_comp no --seam gc_colorgrad
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Pairwise images are matched using an homography --matcher homography and estimator used for transformation estimation too --estimator homography
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Confidence for feature matching step is 0.3 : --match_conf 0.3. You can decrease this value if you have some difficulties to match images
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Threshold for two images are from the same panorama confidence is 0. : --conf_thresh 0.3 You can decrease this value if you have some difficulties to match images
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Bundle adjustment cost function is ray --ba ray
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Refinement mask for bundle adjustment is xxxxx ( --ba_refine_mask xxxxx) where 'x' means refine respective parameter and '_' means don't. Refine one, and has the following format: fx,skew,ppx,aspect,ppy
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Save matches graph represented in DOT language to test.txt ( --save_graph test.txt) : Labels description: Nm is number of matches, Ni is number of inliers, C is confidence
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Perform wave effect correction is no (--wave_correct no)
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Warp surface type is fisheye (--warp fisheye)
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Blending method is multiband (--blend multiband)
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Exposure compensation method is not used (--expos_comp no)
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Seam estimation estimator is Minimum graph cut-based seam (--seam gc_colorgrad)
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you can use those arguments on command line too :
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boat5.jpg boat2.jpg boat3.jpg boat4.jpg boat1.jpg boat6.jpg --work_megapix 0.6 --features orb --matcher homography --estimator homography --match_conf 0.3 --conf_thresh 0.3 --ba ray --ba_refine_mask xxxxx --wave_correct horiz --warp compressedPlaneA2B1 --blend multiband --expos_comp channels_blocks --seam gc_colorgrad
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You will get :
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For images captured using a scanner or a drone ( affine motion) you can use those arguments on command line :
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newspaper1.jpg newspaper2.jpg --work_megapix 0.6 --features surf --matcher affine --estimator affine --match_conf 0.3 --conf_thresh 0.3 --ba affine --ba_refine_mask xxxxx --wave_correct no --warp affine
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You can find all images in https://github.com/opencv/opencv_extra/tree/master/testdata/stitching
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