Chaos Corona Forum
Chaos Corona for 3ds Max => [Max] I need help! => Topic started by: Techtrooper on 2021-03-01, 21:58:06
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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.
(https://i.imgur.com/UFnipnU.jpg)
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.
(https://i.imgur.com/Gk6JQZH.jpg)
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.
(https://i.imgur.com/UKPGiwQ.jpeg)
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.
(https://i.imgur.com/qjOMfv1.jpg)
15. Come here asking for help. Test scene attached. Help.
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Hi, I couldn't open your file since it was saved with an older version. I look at the problem, and my method would be the same as yours. Try to fake the room and lighting conditions, and use your backplate as a reflection map. It doesn't match as it is supposed to but sometimes it works. Maybe create a room just to block shadows and hide from camera and have a separate shadowcatcher plane.
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Maybe create a room just to block shadows and hide from camera and have a separate shadowcatcher plane.
That is exactly what I did. That dark square in the first photo is the plane with shadow catcher material. Room is another object that is hidden from camera.
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Hi Techtrooper,
Shadowcatcher material has a pretty straightforward usage. Though there are some intuitive and logical steps in the points you described, I think you made it more complicated that it needs to be.
And by the way, you can perspective match with CoronaCamera and it does have more functionality than a regular one which can relate to matching. Important thing is to have a not "Targeted" camera (untick in CoronaCamera) and you are ready to go. Just from my personal experience, which is most likely a 3Ds Max thing rather than a Corona related, sometimes it gets weird and just does not respond.
I have downloaded the scene and tested with your materials and maps.
Regarding, of course, what exactly you try to achieve, the solutions may vary. But here are some screenshots of renders and the scene, so you can see:
1. A simple shadowcatcher on the floor, no room boundaries
2. Shadowcatcher applied to the whole cage, Visible to camera enabled from object properties, no shell for the cage
3. Same with cage
4. Bonus with Torust knot
5. The material setup
Sun is being used in all the cases with CoronaSky.
Both the shadowcatcher and Direct visibility overrride have the CoronaToneMap applied as you see, to better link the background image and the scene (easier control).
You will find that the 2nd and 3rd versions are not that optimal, as it took long time to calculate the UHD Cache and it renders slowly because of the lighting.
The option with a plane of course works and renders much faster.
Hope this helps with what you want to do. In general, no faking or very little non-physical faking is required for compositing while using the Corona materials/maps.
If any questions are still left, feel free to post.