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crazy light blotches on my hdri render


stayinwonderland
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hmm, interestig. Yes it is in the evironment slot. I guess this raises a question or two. Firstly, is it common practise to use a sun light + dome light when using HDRI? and secondly... although not a question but I'm thinking this means a whole lot more tweaking with the play between dome and sun. Or maybe it's beneficial to be able to control sky + ambient light seperately?

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Ok I've tried that. It certainly gets rid of the blotches but I'm getting a bit confused between juggling all the variables as two sources of light fight each other. I have areas that are in shadow but are somehow brightly lit.

 

Using the above image, I don't suppose you're able to advise on the general approach to multipliers for a) sun b) dome and c) the HRDI multipliers of 'overall' and 'render'? Like should the dome be very low in relation to the sun, should the hrdi multipliers be fairly low etc. Thanks :)

 

PS I've turned off shadow casting for the dome so I don't have multiple shadows. Does that sound good?

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If you've turned off shadow casting that could explain why your shadow areas are brightly lit! I wouldn't advise doing that. To be honest I hadn't noticed the seperate 'overall' and 'render' values before. From what I can see the only difference is that if you use the render one it doesn't change how it looks in the material editor, essentially they do the same thing. There are typical values for the Vray sun, but not so for HDRIs, which vary greatly in intensity. As a rule of thumb, if you are using a Vray Physical Camera you want to leave the sun value at 1 and adjust your camera exposure to suit. This does mean that you can end up with a very high multiplier on your HDRI, but don't worry too much about that. On the other hand if you are using a standard 3ds max camera, your sun intensity should be around 0.02 or so. Again, you will have to experiment with the particular HDRI you are using to find a balance. To keep things simple just leave the dome light multiplier at 1 and only adjust the HDRI multiplier in the map itself.

 

It's important to try and align your sun direction to the same spot it appears in the HDRI so they work with each other rather than contradicting. You can do this by eye in the perspective viewport. If you want to be a bit more scientific about setting them up to link to each others rotation value, Peter Guthrie has a good tutorial here: http://www.peterguthrie.net/blog/2010/04/vraysun-and-hdri-sky-tutorial/.

 

Hope that helps :)

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Thanks. I finally tweaked my scene to accommodate the extra dome light. Was very exhausting, took literally 5 hours of 30 second renders. I wouldn't choose this if those damn blotches didn't appear.

 

The linking of the sun to the HDR is vital too. That tutorial video is a bit too fast and with no audio or annotation it's just a little complex. I'm fairly sure there's a way to link the sun to a material... can't remember the details on that though.

 

Thanks for the info!

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