Hello everyone. I'm trying to place a CG object on an interior backplate. No HDRI!
I watched the tutorials about shadow catcher on Coronas YouTube channel, but still can't get it to work.
Here's my workflow.
1. Set backplate as viewport background, through Viewport configuration (Alt+B), not as an environment map like in the tutorial since I need that for the CoronaSky, since I have no HDRI.
2. Model a room, with the openings like in the image. Match the perspective. Set the room to be invisible to the camera.
3. Place Corona Sun in the scene and CoronaSky as environment map.
4. Place the Shadow catcher material and plug the backplate to the backplate node.
5. Test and see that the backplate is super dark. Plug the backplate into CoronaTonemapControl, turn everything off. Realize that this does nothing. Figure out you have to put CoronaCameraMod on the camera that you used and switch to Photographic exposure, than it works (you used standard free camera because perspective match tool doesn't work with Corona camera).
6. Test again and see that nothing looks right. Do some googling, find out that Corona sun doesn't have a "shadowcatcher illuminator" option.

7. Not a problem, replace it with a stupendously strong ordinary light and tick shadowcatcher illuminator.
8. Test again, see that things look better, but the shadow catcher is still clearly visible.

9.Try making it super large so it covers the whole scene, but it darkens the backplate visible inside the room and brightens the backplate not visible in the room.

10. Think about it for a while. Realize that the issue is that the shadow catcher is catching the shadows from the room it self. So, I guess, it performs as it should. But in this case, it's a problem.
11. Try to balance the exposure, light strength, sky strength... Give up after some time realizing you even might pull it of once, but it would be insane to try to do this for every image you have. (NOTE: this is just a test scene, here it could even work, but my actual scene has different lighting conditions and the shadow catcher is crazy visible! No amount of balancing helped to get it even close).
12. Decide to try "For compositing" option of the Shadow catcher and fake it in post with masking.
13. Set directly visible to black, switch Alpha mode in shadow catcher to "For compositing".
14. Look at it fail.

15. Come here asking for help. Test scene attached. Help.