questions about using hdri sky dome in 3ds max (2016 now)

[SgWRX]

i think i've successfully used hdri images (from cg-source) for exterior scenes. i've done both with mrsun/sky using the hdri as a custom background map and with just a skylight and the hdri image.

 

1. in an hdri skylight only scene (no mrsun/sky in my case) you have your camera and set exposure. it seems that if you set your exposure to be generally bright enough overall, but have the sky in such a position that the sun and the nearby clouds it lights, are overblown and way too bright - just like over exposing a photograph.

 

is there a way to not over expose those areas (clouds/sun within the hdri map) but still keep the generally nice exposure on areas of the scene you would want?

 

2. some hdri sunset maps with the sun exposed (not burried behind clouds) have a very orange sunlight which in turn casts orange light on the scene. so lets say a white box in the direct sunlight looks orangish. is there a way to white balance the scene without affecting the "blue" parts of the sky, or affecting them to a lessor desgree? can it be done by white balancing the hdri map in photoshop? can it be done by white balancing using camera white balance or exposure control white balance?

 

thanks,

steve

[Francisco Penaloza]

When you use a skylight in mental ray you have the option to get the light from the environment or from an image or color.

In your case you can place an HDRI in your skylight and make a copy of it and place it on the environment slot, that way you can control the brightness of each one of them separated.

 

In the exposure control you can adjust your color balance, to an specific number (color temperature) or with the color picker. Of course this will affect the over all colors in your image, but you can adjust you sky colors back in post.

You can photoshop to neutralise a little the colors of your HDRI before render, this is OK. But one of the reason you want to use an HDRI as light source is exactly that, get not only the sun color but also the color cast and bleed of environment. Of course the is extreme cases that you'll need to adjust color, and that's OK too.

[SgWRX]

thanks. for white balance i've pretty much been doing that.

 

i did not think about doing the same hdri in both the enviornment and skylight separately. that's outstanding! thanks!

[SgWRX]

so this works out pretty well.

 

i was able to take the environment copy and edit in photoshop via exposure layer and a layer mask with gradient brush to "darken" the over exposed areas of the map (from cg-source). You can see a bit of a dark circle, so the mask will have to be more carefully created, but it gets the point across.

 

then, i dropped in the un-edited version of the hdri into the sky map.

 

is it better to use RGB levels or Output when adjusting the hdri maps? i have always tried both but they look like the produce the same results?

 

finally, looking the other direction, the environment map is reasonable in terms of brightness - typically it's too dark if you lower the bitmaps output to keep from blowing out the highlights which then requires re-adjustment in the settings. my point of looking at this is to be able to do a scene from other camera angles without having to re-adjust maps or exposures. i think it worked out pretty well so thanks again.

 

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Edited September 28, 2015 by SgWRX