Can't get right sky / room

[joevintage]

Hi i'm new ro c4d and corona.
I'm trying with a simple room project.
There a windows with glass material.
Corona sky + sun

With the sky multiplier set to 1 the room is correctly bright but the sky overexposed (completely white)
With rhe sky mult set to 0.1 the sky is light blue but the room to dark.
Any advice?
Thank you

[hog0]

hey there, first you should use a plane object just outside the window with a portal-material on it - that way you have less noise in less time rendering the image.

ok back to your question.. you can just leave the skymultiplyer by default and take a look at your camera and rendersettings.. there are several ways to get your desired effect on the scene.

assuming you are using a c4d camera with the corona camera tag on it - adjust the iso/f-stop/shutterspeed according to your needs. usually realworld numbers are a very good start to work from like, 100-200 iso / f-stop of 5,6 until ~8 (usually 5,6 does it for me for most scenes) / shutterspeed really depends on your overall lighting and reflection but you can try to start from 30/60 and work your way up.

for the actual rendersettings i would start at an exposure of maybe -4 to +4 (start on the negative end here -4,-3,-2..). for highlightcompression usually a value around 12 works for most of my scenes so just put in a 12 and basically ignore it ;). on the contrast setting i would start at something like -4 and again like the exposure work my way up slowly. you can also add bloom and other lens effects if you wish.

when rendering, use the Corona VFB (found under plugins corona tab or you can enable it inside the rendersettings by default). there you can adjust all above values exept the camer ones during or after your machine is rendering! that way you will find the desired effect pretty quick and can adjust your original rendersettings accordingly, so you wont have to play around with them very time after rendering :)

hope this helps!

edit:
maybe i didnt exactly get what you were trying to do but if you are trying to get the outside sky(maybe with clouds) visible through the window, then you should use a backplate with an image on it and just leave your settings as is for render01..

[joevintage]

Thankyou very much, i'll try everything.
2 questions:
Do i have to put the portal just inside the glass material? At which distance?
And for tue backplate with the sky image: jpg or hdri? Diffuse channel? And which distance from the window?
Thankyou very much

[hog0]

jpg in diffuse for the backplate is fine, you can adjust cororintensity by gamma/exposure/saturation/opacity.. whatever works for you :) and for the distance to the camera, usually i use a cylinder object section high enough to cover whats seen through the window and you should put it far enough away that the sun/skylight can actually get in, so further is better, just make the backplate big enough and your finde :)

abou the portal light, usually i put those inside the opening, exactly fitting, so for example your window is 160/100 cm, make the plane 160/100cm too and fit exactly inside the opening - there should be no objects cutting the portal, at least for me i get better results that way... basically in front of the window on the inside..

if you still have problems getting the light as you want, try placing area lights (low settings) behind the camera

[joevintage]

Thak you again.
How do u think is better to model the glass window? I used 2cm thick glass but i read it is better to use no thickness plan.
The other aspect i read is than is better to put the portal outside the window and not inside. I'll try to see the differences

[romullus]

Portals should always be outside your windows openings: https://coronarenderer.freshdesk.com/support/solutions/articles/5000501660-how-to-use-light-portals-in-corona-

[joevintage]

Thanks
At which distance fron the glasses?
And for the glasses, is it better using real tickness (2 cm) or just planes with no tickness?

[romullus]

Distance of portals from glass doesn't really matters as long as portals don't touch glass.

As for glass panes, many do it with single sided planes and assign material with thin glass. I for one prefer to make windows with two glass sheets that has thickness and assign ray switcher override material with normal glass material in all slots, except GI override - for that one i assign thin glass material.

[hog0]

as already mentioned above, there are usually two ways to render glass, the physical correct one with glass thickness and the flat plane object with thin-glass material on it.

for windows i am always using the thinglass one. less rendertimes for me after testing at least..

there is always a 3rd option, most ppl dont consider because its physically incorrect but works on about 40% of all scenes (including yours)
since you dont have any reflections/speculars showing up on your glass, nore does anything in your room reflect your window, try to simply turn off your glass. i know there are a lot of ppl arguing against it, but when rendering the right angle, where the glass really doesnt effect anything but rendertime, in my opinion shut it off.. or at least give it a try its just 2 clicks ;)

[joevintage]

Thank you Hog0. Switching off the glasses works well in this case..

I also tried to put a background sky mapped on a slice of a cylinder, and it works too.
The only problem is the the sun projects the shadow of the cylinder into the room. Maybe it is enough to set the cylinder to "non project shadows". I'll try this this evening.
Thank you again

PS: with the portal planes just outside the windows, the noise is less than an half.

[romullus]

You should exclude background object from contributing to GI. Here's how to do that: https://coronarenderer.freshdesk.com/support/solutions/articles/5000515605-how-to-create-background-material-in-corona-

[hog0]

here is a quick example how the backplate works - dont get in detail with the rendering its just a 5 min work..

no glass in windows, since there wont be any reflections..