HDRI mapping question

[erikbroberg]

Hi,

 

I somewhat new to HDRI lighting and I have purchased a nice cityscape HDR. For some reason during my render, the light appears blotchy with small circles of brighter light. I am guessing this is the result of the texture not being mapped correctly in my GI and Background. I am unsure how to map this properly as well as to line it up to the sun/find the direction.

 

Thank you in advance

Erik

[Ismael]

http://www.peterguthrie.net/blog/2010/04/vraysun-and-hdri-sky-tutorial/

[Devin Johnston]

I've had this problem before, I think it's caused because the exposure values of the HDRI are too high. I've purchased several HDRI libraries, the current one I use comes with 10 different HDRI's but I can only use two of them due to this problem. The only way I've found to minimize it is to increase your GI settings but that starts to really affect render times. I'd love to get a definitive answer as to what causes this and how to fix it.

[erikbroberg]

Thank you for your replies. I have looked at the video, but I forgot to mention that I am using Rhino. In my settings, I have disabled the physical camera and sun and am using only the GI value to adjust the exposure of the HDRI which is at 1.0. To me, I think that for some reason the HDRI is too magnified. I wonder if there would be less of a problem if I could zoom out of the image. I am still trying to figure that out. Will also try a different HDRI, but they are pricey! I have also heard that using a gaussian blur in photoshop for the GI bitmap can help. I will attempt those things. If my response triggers any ideas please let me know.

Thank you in advance,

Erik

[jasonstewart]

It looks like the mapping of the HDRI is incorrect. I have never used Rhino but it should be set to spherical somehow. If that doesn't do the trick try using a lower resolution version of the HDRI and use the high res only for reflections and background.

[RyderSK]

Vray does importance sampling only through its dedicated lights, i.e. DomeLight here. Are you using domelight or simply putting HDRi inside environment/override slots ? Use only the former for actual lighting.

Vray DomeLight does importance sampling to specified texture resolution, by default 512px. It's not necessary to use manual sIBL approach and use blurred low-res HDRi.

Do you load your HDRi with correct gamma ? VrayHDRi map does it automatically for you, but it's 1.0 in any case.

 

Is your Vray setup correct ? Use the easiest 'Universal approach', it's 3-4 clicks. Detailed approach at Vray's web manual.

[erikbroberg]

THank you, I have used the dome light to light my scene and removed the HDR from the GI. However, the scale of my HDRI is way to high as the trees and buildings make my skyscrapers look miniscule. Is there a remedy for this? My dome light will not allow me to add a texture map to it for some reason.

Thank you

Edited July 16, 2014 by erikbroberg

[Stephen Thomas]

Yes, dome light is the way to go. The bright circles are a common artifact caused by using very high dynamic range in environment slot, as Devin suggests. As for the scale issue, that has got to be the number one HDRI-related question on this forum Since these images capture a full 360° view of the environment there is no way to change what you're seeing. Sure you could squash it vertically in photoshop or crop it so that ony the sky is visible, but if the HDRI captured a tree 10 feet away then there's no way of altering it to look a mile away.

 

That's why HDRI + matched backplate is the preferred option. Some you can definitely use for both, but generally it is purely there to provide more interesting colour and lighting to your scene as well as more realistic reflections.

[erikbroberg]

Hi Stephen,

What a helpful response! I am rather new to HDRI and have been trying to follow PG's tutorial, but for Rhino it is a bit different. What you say makes perfect sense as I have tried everything regarding scaling from FOV to cropping the HDRI in PSD. Now I have my HDRI in my domelight, but I am still seeing it in my Background, also when I put it soley in the Environment background map, it shows up at well. SO how would I use it just for the realistic lighting and reflection effects, but not be able to see it? Maybe adding a background will hide it? Or is there another option?

 

Thank you very much you have been helpful.

[Stephen Thomas]

Well I'm not sure about Vray for Rhino, but in 3dsmax you have the option to make dome light invisible. You can then either put background image in environment, map it to a plane, or add it in post-production.

[erikbroberg]

I thank you all for your detailed responses. I have realized that HDRI is not working for me at the moment after many long hours. My goal is to make my renders more realistic (HDRI or not) and I watched the Peter Guthrie video as well as others and my results are not as good as the sun system alone. I tried the HDRI in the dome light, in the GI, in the reflection background etc as well as in conjunction with the sun. My main problems are that the HDRI is zoomed in and I am not sure how to control the light (with the GI, with the sun, with the camera, the HDRI multiplier, or with the dome light scalar. I have attached my HDRI vs. my Sun system renders. I wish to make them more realistic for my final pinup so I welcome any SUGGESTIONS and at this point although I would like to incorporate the HDRI, I am not completely sold on it yet. Thank you very much in advance.

[Devin Johnston]

Erik as others have said the zoomed in look is a result of how the HDRI was shot, there's no way to adjust this you simply have to get different HDRI's that will work for you scene.

[Chris MacDonald]

The other day I found a "workaround" for getting an alpha of sorts when using an HDRI, and that is to include a "self illumination" render element (provided you don't have loads of self illuminated materials). Using this will render everything except the sky completely black, kind of like an inverse alpha channel.

[RyderSK]

Heh, that's pretty outside of box :- ). I am glad Vray3 solved this issue but, well, that took time.

What I always did was just use the same instance of HDRi map in environment as in invisible DomeLight.

[M V]

VR for Rhino 2.0 has domelight. If you are in the older 1.49 version that you cannot use an HDRI for environment lighting (this is why you have all those splotches).