New user, problem with HDRI

[edonk]

Hi,
I'm on day 1 of my 30 day trial and so far I am very impressed. The only problem I have encountered so far is with trying to use a HDRI file to illuminate the scene. No matter what I try I get small to large blotches on the scene, a similar pattern to that of sun shining through tree leaves. Hopefully the image below will show you what I mean. Like I said I am on day 1 of my trial and no where near a competent user yet, I am working my way through the manual picking tips up as I go. Hopefully one of you guys can solve this one for me as I just dont see what I am missing by reading the manual.

[dalomar_cg]

Re: New user, problem with HDRI

This is actually something that we're trying to track down at the moment, and I'm not 100% sure what causes it. The apparent solution at the moment is to disable GI Refractive Caustics which can be done at the top of the Indirect Illumination rollout.

[edonk]

Re: New user, problem with HDRI

This is actually something that we're trying to track down at the moment, and I'm not 100% sure what causes it. The apparent solution at the moment is to disable GI Refractive Caustics which can be done at the top of the Indirect Illumination rollout.

Dalomar, I should have mentioned I already tried that after searching the forums for a solution before I made this post. The screenshot above was the best result I got after disabling it. Before disabling it the blotches were huge. This happens with all my commercial HDRI files. Until you find a fix is there anyway to get decent looking shadows in a scene because without HDRI I dont seem to get shadows at all?

[thomthom]

Re: New user, problem with HDRI

Are you using the background HDRI for GI lighting as well? If so; try making a copy resize it to 512-1024 pixels max and apply a heavy blur to it and use that as GI light.

[edonk]

Re: New user, problem with HDRI

Are you using the background HDRI for GI lighting as well? If so; try making a copy resize it to 512-1024 pixels max and apply a heavy blur to it and use that as GI light.

Hi ThomThom, the commercial HDRIs actually come with a lower res blurred version specially for this purpose. I am using the blurred one in the GI slot and the high res version in the background slot, is this the correct way to do it?

[thomthom]

Re: New user, problem with HDRI

Yea. I just mentioned it as I've had some noise appearing when I didn't use the smaller blurred HDRI.

[edonk]

Re: New user, problem with HDRI

Im actually getting some good results using the preset for external architectural render 'visopt' but how do I change the position of the sun (shadows) using this preset? It doesnt seem to match the position of the sketchup sun.

[Jackson_cg]

Re: New user, problem with HDRI

I'd agree with Thom- early on I used to try to use free HDRIs found on various sites for GI lighting, but the effect was invariably cr*p, very very splotchy results like your aimge. I realised that simple fake "studio" HDRIs with a more or less black background and 1, 2 or 3 very blurred light sources rendered well, but any HDRIs which were highly detailed (made from actual spherical panoramic photographs) just don't work. They're excellent for backgrounds and reflections, but aren't very useful when it comes to lighting. As Thom said, you can still use these HDRIs for GI by reducing them in size- in fact I've found you can reduce them down to just 200 x 100 px without any additional blur and they will produce good, clean results.



The first splotchy render below was rendered using a very high quality 6000 x 3000 px spherical HDRI like the one above.
The second image was rendered with exactly the same settings and the same HDRI, but reduced in size to just 200 x 100 px in Photoshop first. The remarkable thing is that even though the splotches are pretty much gone, the shadows are still as sharp as in the first one. Oh, and another thing- the original size HDRI was 51.9Mb- the tiny version I used to do the second render is just 64.7Kb! In other words, when it comes to HDRIs for backgrounds and reflections bigger is better, but for lighting they can (and often should) be tiny.

[Jackson_cg]

Re: New user, problem with HDRI

Im actually getting some good results using the preset for external architectural render 'visopt' but how do I change the position of the sun (shadows) using this preset? It doesnt seem to match the position of the sketchup sun.

I'm not sure how that visopt is setup, but for VRay to take the SU sun position/time/date into account you have to use the "sky" setting in the environment GI slot, or a blend of "sky" and an HDRI or LDRI.

[edonk]

Re: New user, problem with HDRI

Jackson, thankyou very much for your response. The blurred HDRI was already massively reduced to only 500px wide but reducing it further to 200x100 as per your example nearly shifted the entire blotch problem. I will experiment further to see if I can get rid of it entirely. Thanks for taking the time out to help me, cheers.

[edonk]

Re: New user, problem with HDRI

Hi guys just an update, it seems like reducing the HDRI blurred file down to 200x100 fixes all blotch problems completely no matter what HDRI I choose so maybe it needs to go in the hints and tips section?
Another question though, using an external HDRI I am having problems getting decent shadows, in fact I pretty much get no shadow information at all. Any ideas? Or have I got to do some photoshopping?

[Jackson_cg]

Re: New user, problem with HDRI

Great to hear!

Many HDRIs won't produce sharp, or even close to sharp shadows- another reason why usually more useful for studio setups than architectural external renders.

A way around this (other than making your own HDRIs with a tiny single light source) is to use a blend in the environment GI slot of VRay sky (which by default simulates a sun, controlled by SU's location, shadow, date and time settings) and a simple HDRI using a blend ratio of 0.99 or even 0.9999. This way you can keep the sharp shadows produced by the VRay sun, but the GI from the HDRI still contributes considerably to the render.

Of course you have to experiment a lot with the blend ratio as well as the rotation of the HDRI so the two GI sources (VRay sky and HDRI) don't conflict too much. An extreme example of getting these settings wrong can produce hard sun shadows from one side of a pillar while a softer HDRI shadow is coming from the other.

[edonk]

Re: New user, problem with HDRI

Thanks again Jackson, looks like I have some experimenting to do today! The reason I want to use HDRIs for the externals is purely for realistic reflections in glass panels. I just dont have time for that much postpro work.
I'm amazed at how fast Vray actually renders and the quality it can produce, if I can get all my usual workflow 'problems' resolved within my 30 day trial then it looks like I will be digging into the old wallet!

[edonk]

Re: New user, problem with HDRI

Just a quick update, the blend option works perfectly for external HDRIs and shadows - thanks again Jackson for helping me out.
The only thing left to figure out is why the position of the lighting from the HDRI never changes despite me changing the rotation of it in several tests. (no blending).
Also does the full commercial version come with a separate material editor?

[Jackson_cg]

Re: New user, problem with HDRI

Good to hear Thom's and my advice is working for you. Re: rotation having no effect on HDRI lighting- silly question, but the HDRI is loaded as a spherical environment isn't it? Are you rotating it by degrees, i.e. 45, 90, 180, etc? They're the only explanations I can think of for rotation having no effect on an asymmetrical HDRI GI environment.

AFAIK, the trial version is exactly the same as the licensed version- you make all material adjustments via the SU material editor combined with the VRay Material Editor.