Chaos Corona Forum

Chaos Corona for 3ds Max => [Max] General Discussion => Topic started by: kahein on 2014-02-28, 13:10:15

Title: CoronaSun Link To HDR
Post by: kahein on 2014-02-28, 13:10:15
Hi,
How can we link the rotation and angle of corona sun with wireparameter to the bitmap U and V offset.
I try to do it with the same method wich work with vray but with corona it doenst
Title: Re: CoronaSun Link To HDR
Post by: Ondra on 2014-02-28, 13:36:34
you mean standalone sun or the sun in daylight system?
Title: Re: CoronaSun Link To HDR
Post by: kahein on 2014-02-28, 14:17:42
stand alone sun
Title: Re: CoronaSun Link To HDR
Post by: Ondra on 2014-02-28, 14:33:07
its parameters are exported to maxscript, co it should be possible to do with some light scripting ;)
Title: Re: CoronaSun Link To HDR
Post by: Ludvik Koutny on 2014-02-28, 14:35:17
Actually it should be simply doable via wire parameter thingy :)
Title: Re: CoronaSun Link To HDR
Post by: kahein on 2014-02-28, 16:08:54
I link the sun rotation and sund height to u and v offset of bitmap but it just dont work
Title: Re: CoronaSun Link To HDR
Post by: kahein on 2014-02-28, 16:14:05
it stange because when i try with a simple box ( wire posX and posZ ) on the sun rotation and height, it work
Title: Re: CoronaSun Link To HDR
Post by: AnubisMe on 2014-03-04, 01:59:06
Try this http://www.peterguthrie.net/blog/2010/04/vraysun-and-hdri-sky-tutorial
Title: Re: CoronaSun Link To HDR
Post by: romullus on 2014-03-04, 12:10:15
I watched this tutorial out of curiosity and was shocked by such stupid inconvenient method of matching direct light with background image. I wonder, should i make video, showing a proper way of doing that. I may even include quick "wiring corona sun to hdri" example.
Title: Re: CoronaSun Link To HDR
Post by: kahein on 2014-03-04, 18:19:38
if you can do it please it would be very helpful
Title: Re: CoronaSun Link To HDR
Post by: romullus on 2014-03-04, 18:47:49
Youtube still processing it, but in a while, link should be ok.

Title: Re: CoronaSun Link To HDR
Post by: fellazb on 2014-03-04, 19:42:59
Thanks for the tutorial very straight forward solution you got there.

One thing is bugging me though, why do you really need a corona sun if your HDRI can also provide good shadowcasting? An anwser could be that a lot of HDRI's aren't good enough to produce sufficient shadows, but seeing this tutorial: http://www.ronenbekerman.com/hdr-image-based-lighting-3d-scene-setup/ (http://www.ronenbekerman.com/hdr-image-based-lighting-3d-scene-setup/) you can tweak the HDRI to produce these shadows.

So then again, what's the benefit of using a corona sun when an HDRI can do GI and shadowcasting?
Title: Re: CoronaSun Link To HDR
Post by: romullus on 2014-03-04, 20:04:57
Actually i almost never do the way i showed in my tutorial, because i have most of hdri's tweaked in photoshop :] I've learned this technique from Christian's Bloch's "HDRI Handbook". Excellent lecture, i might say: http://www.hdrlabs.com/book/index.html
However it has adventages, as well as disadvantages compare it to direct light method.

Btw, guy in that tutorial on ronenbakerman.com, has painted waaay to big sun.
Title: Re: CoronaSun Link To HDR
Post by: Ondra on 2014-03-04, 20:22:10
How big? If i remember correctly, the real size comes out at about 1 pixel for 1k map :D
Title: Re: CoronaSun Link To HDR
Post by: romullus on 2014-03-04, 20:40:55
Well, sun's angular diameter is about 0.5 degree. So for 10000x5000 pano, it would be ~14px.

Edit: btw, i compared it vs corona sun once and it matched perfectly :]
Title: Re: CoronaSun Link To HDR
Post by: blank... on 2014-03-04, 23:56:25
One thing is bugging me though, why do you really need a corona sun if your HDRI can also provide good shadowcasting?

If you have high quality HDRI (and you're satisfied with what you're getting), then no. Read about it here, Mental ray forum but never mind, i tested it with Corona and it works beautifully.

http://forums.cgarchitect.com/75415-mr-photons-ibl-fg-nothing-thime-better.html
Title: Re: CoronaSun Link To HDR
Post by: fellazb on 2014-03-05, 10:33:14
Thank you for the link.

So it all comes down to good quality HDRI's with a high EV value. I recently tried some HDRI from HRDmaps but couldn't get decent shadowcasting. When looking at the specs those only have an EV of 2 which is very low and therefor not highly contrasted for suitable shadows. They also produce a too pronounced color grading to the overall image...

I will look into the CG-source or Guthrie maps. If someone else can get some good info on this it would be highly appreciated. For now I stick to a Corona sun with a spherical backplate for the reflections.
Title: Re: CoronaSun Link To HDR
Post by: Midge on 2014-03-05, 11:59:36
I actually wrote a small piece on how Dynamic Range affects lighting with HDR's.

http://www.themantissa.net/blog/2014/2/1/the-importance-of-high-quality-hdr

It was interesting to see the effect visually between the different techniques.
Everything but the car was renderred with Corona. :)