Author Topic: Avoiding Sky Pinching  (Read 1228 times)

2021-11-06, 21:50:47

BigAl3D

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So I'm testing a scene for a shot in a commercial. It is only lit with an HDRI in a Corona Sky object and no Sun since I was getting nice lighting and shadows. What is the best way to avoid the "pinching" of the sky in the reflections? This includes trashing this setup for something completely different.

Running v7 Hotfix 2.

2021-11-07, 00:07:52
Reply #1

Atlantis

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That's a strange behavior. What kind of HDR are you using? Did you try another one? Is the projection spheric?
You can also deactivate "visible in reflections" and use another sky just for the reflections.

2021-11-07, 00:26:54
Reply #2

BigAl3D

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Should've posted this before. Here's a screen grab of the HDRI I used. It's a free one from HDRI heaven I think. 16k, but I don't remember the f-stops. Set to spherical. I know in other cases of texturing a sphere, it's better to use hexahedron to avoid pinching of materials at the poles, but I don't see an option like that with the Sky Object. The other two projections, Cubic and Frontal produce odd results and no shadows.

2021-11-07, 12:51:21
Reply #3

ingemar

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That’s odd. As already mentioned, I would either try another HDRI or use a separate image for the reflections.

2021-11-07, 15:01:48
Reply #4

davetwo

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Hi.
The HDRI is fine and has no pinching - I just tested it (see screengrab). Works as both the old style C4D sky and also the new Corona sky model.

So...
Have you offset the scale or position?
Is there a Normals issue with the glass windscreens perhaps?


2021-11-07, 23:03:07
Reply #5

BigAl3D

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Yeah, pretty obvious the HDR isn't pinched, but I did offset the HDR on the U and the V so I could position the sun and shadows. If the V is offset enough, you will see the pinch. So this got me thinking. What happens if I rotate the Sky Object itself? To my surprise, this crazy idea worked. At least as a workaround. I was able to get the lighting almost exactly placed as before. Also, as you can see, the Normals appear to be "normal." Sorry, couldn't resist.

So what's the best way to get great outdoor lighting? Just HDRI? HDRI+Sun? Image for reflections, then a Sub Object?

2021-11-10, 20:58:29
Reply #6

BigAl3D

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Anyone have any pointers for realistic outdoor lighting? I'm sure at least the archviz crowd would know.
« Last Edit: 2021-11-11, 20:10:13 by BigAl3D »

2021-11-11, 05:36:45
Reply #7

Ealexander

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I've been playing with this very thing lately. Definitely check out this great blog/tutorial:

https://www.thecommonpoint.com/blog_hdri

It's for Max, but the principles are the same. I always just tossed an hdri in and cranked the exposure on the vdb up or down, but now I load it into a color correct node and use gamma and exposure to control it more finely. I also invested in some really high quality hdris:

https://www.pg-skies.net/

Using the Corona sky in physical mode with the sun object is nice too. It takes a bit to get used to it, but you can do nice things with practice. Just checking Volume Effect in the sky adds some nice distant haze without setup. Check out the volumetric article on that same blog.

Of course, you can mix and match and have one hdri for light and one for visual if you set the check boxes accordingly. I tend to just keep it simple though, easier to dial in and update. I think I tend to use hdri more for exterior and sky/sun for interiors, but the needs of each shot trumps all.

Also worth a warch, even though it's a few years old:


-evan

2021-11-11, 09:39:18
Reply #8

rojharris

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Most of the time I use a PG sky HDRI and always rotate the whole sky object. I never use the UV's as you don't get the control as they only go from 0-100% as opposed to 0-360 degrees. I also generally have one sky object for lighting and one for seeing the clouds etc set to a lower brightness so they look good by eye. Sometimes I use sun and sky if I want to use the nice new haze effect and can't be bothered to make a volume box, even then I'll add an HDRI in another object to use for clouds.


2021-11-11, 15:15:25
Reply #9

Ealexander

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I forgot to add, that yes, I too just rotate the whole sky system to place my sun in HDRIs. Shawn Astrom also makes some nice ones - I have a few of his kits.  Epic Sunsets is a great one. http://shawnastrom.com/store