Doc: Suggest to remove C API links and blank pages for core/imgcodecs/...

[Kumataro]

Describe the doc issue

Basically, C API has been deprecated/excluded at OpenCV4. ( https://github.com/opencv/opencv/wiki/Opencv4 ) It seems that there are some C API links and these linked C API pages are blank. I suggests to remove them.

Some modules has been fixed at 5.x branch. What style of pull request is appropriate?

• 2 pull requests
  • For 4.x ( calib3d, core, imgproc, imgcodecs, photo, video and videoio )
  • For 5.x ( calib, core, imgcodecs, photo, video and videoio)
• 3 pull requests
  • For common (core, imgcodecs, photo, video and videoio)
  • For additional 4.x (calib3d, imgproc and highgui)
  • For additional 5.x ( calib )
• 1 pull request ( do not fix to 4.x branch)
  • For 5.x ( calib, core, imgcodecs, photo, video and videoio)

module	4.x branch	5.x branch
calib		Needs
calib3d	Needs
core	Needs	Needs
imgproc	Needs
imgcodecs	Needs	Needs
highgui	Needs
photo	Needs	Needs
video	Needs	Needs
videoio	Needs	Needs

Fix suggestion

I think we can remove these links and pages.

• https://docs.opencv.org/4.x/d0/de1/group__core.html -> C structures and operations
• https://docs.opencv.org/4.x/d7/dbd/group__imgproc.html -> C API
• https://docs.opencv.org/4.x/d4/da8/group__imgcodecs.html -> C API
• https://docs.opencv.org/4.x/d7/dfc/group__highgui.html -> C API
• https://docs.opencv.org/4.x/dd/de7/group__videoio.html -> C API for video I/O
• https://docs.opencv.org/4.x/d7/de9/group__video.html -> C API
• https://docs.opencv.org/4.x/d9/d0c/group__calib3d.html -> C API
• https://docs.opencv.org/4.x/d1/d0d/group__photo.html -> C API

kmtr@kmtr-None:~/work/opencv$ git reset --hard
HEAD is now at 500c55a808 Merge pull request #25122 from unnonouno:pqueue
kmtr@kmtr-None:~/work/opencv$ git grep "C API" | grep "\@defgroup"
modules/calib3d/include/opencv2/calib3d.hpp:    @defgroup calib3d_c C API
modules/highgui/include/opencv2/highgui.hpp:    @defgroup highgui_c C API
modules/imgcodecs/include/opencv2/imgcodecs.hpp:    @defgroup imgcodecs_c C API
modules/imgproc/include/opencv2/imgproc.hpp:    @defgroup imgproc_c C API
modules/photo/include/opencv2/photo.hpp:    @defgroup photo_c C API
modules/video/include/opencv2/video.hpp:    @defgroup video_c C API
modules/videoio/include/opencv2/videoio.hpp:    @defgroup videoio_c C API for video I/O
kmtr@kmtr-None:~/work/opencv$ git grep "C structure" | grep "\@defgroup"
modules/core/include/opencv2/core.hpp:    @defgroup core_c C structures and operations

kmtr@kmtr-None:~/work/opencv5$ git reset --hard
HEAD is now at 1d1faaabef Merge pull request #24411 from alexlyulkov:al/dnn-type-inference
kmtr@kmtr-None:~/work/opencv5$ git grep "C API" | grep "\@defgroup"
modules/calib/include/opencv2/calib.hpp:    @defgroup calib3d_c C API
modules/imgcodecs/include/opencv2/imgcodecs.hpp:    @defgroup imgcodecs_c C API
modules/photo/include/opencv2/photo.hpp:    @defgroup photo_c C API
modules/video/include/opencv2/video.hpp:    @defgroup video_c C API
modules/videoio/include/opencv2/videoio.hpp:    @defgroup videoio_c C API for video I/O
kmtr@kmtr-None:~/work/opencv5$ git grep "C structure" | grep "\@defgroup"
modules/core/include/opencv2/core.hpp:    @defgroup core_c C structures and operations

[mshabunin]

@Kumataro , there is a PR which removes some of groups you mentioned: https://github.com/opencv/opencv/pull/25042/files#diff-3fe9ef1ff29a111bc7b5c61d62603ba3956f0969bc5df4781384e739341220f3

I think the best way to do it will be updating that PR with more changes, than waiting for it to be propagated to 5.x. And then we can finish leftovers in 5.x, e.g. calib.

Note: all legacy headers are excluded from the documentation by filename glob (*_c.h) https://github.com/opencv/opencv/blob/500c55a808ceaa2058e2d1c060c2269c40c0cc9a/doc/Doxyfile.in#L108

[Kumataro]

Thank you very much for your reply !

• Other modules(core,...) will be fixed by https://github.com/opencv/opencv/pull/25042 .
• In 5.x imgproc and highgui has been fixed at https://github.com/opencv/opencv/pull/22754 .

So I would like to create separate pull requests for patches for the calib3d module for 4.x and the calib module for 5.x.

[Kumataro]

This issue is completed, so I close it, thank you !