New openCV detection sliders in Camera.html!

[brettfiedler]

Cross posting from Element/Slack:

When you're setting up your camera and calibrating papers, don't forget to check out the new Detection menu (on main branch or dev)! I can achieve much better projector/camera distances now (camera is sitting on top of projector rather than halfway in between).

Example picture shows a size of paper (half sheet) I couldn't previously get to work, especially with my lower resolution (720p) camera. Now it detects pretty well (if a little shakey)! You can gate out all of the spurrious "markers" (like my ring light would produce) with the Maximum Dot Area slider.