Chaos Corona Forum
Chaos Corona for 3ds Max => [Max] I need help! => Topic started by: dj_buckley on 2019-02-26, 08:45:36
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Can anyone with a bit of technical knowledge explain why some HDRI's are way too strong in reflections and some are way to dull.
For example, I often find getting the lighting/exposure right with PGSkies results in super bright reflections, but yesterday I was experimenting with the Poliigon HDRI's and found the opposite. Once lighting and exposure looked correct, the reflections were incredibly dull?
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Can anyone with a bit of technical knowledge explain why some HDRI's are way too strong in reflections and some are way to dull.
For example, I often find getting the lighting/exposure right with PGSkies results in super bright reflections, but yesterday I was experimenting with the Poliigon HDRI's and found the opposite. Once lighting and exposure looked correct, the reflections were incredibly dull?
Everything is physically based. Some HDRIs have a strong highlight, but weak surrounding in comparison (eg. direct sun light). If you expose for the sun, the surrounding get's very dark in comparison and seems to reflect weaker, because you turned exposure way down.
To combat this you can use HDR Compression on the image before piping it into the environment, thus the sun get's less bright and the surrounding instead appears more clearly.
This dynamic changes from image to image, as each image has a different... dare I say it... dynamic range.
Also be very careful when importing HDRs with how the Gamma is layed out. Usually you have to import with gamma 1.0, but I have seen HDRs exported with a gamma curve and when you import them in 3dsMax with gamma 1.0 they appear utterly dark everywhere where it isn't a bright spot.
If that doesn't clear it, post some screenshots of the offending scene, so we can nail down exactly what is happening.
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If you look at the example Max files that come with PG Skies, the Highlight compression is set to 20, and the contrast to 3. I believe this is how they combat the bright reflections.
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If you look at the example Max files that come with PG Skies, the Highlight compression is set to 20, and the contrast to 3. I believe this is how they combat the bright reflections.
Yep, HC set to 20 would literally destroy an image full of textures too. It would be way too flat
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If you look at the example Max files that come with PG Skies, the Highlight compression is set to 20, and the contrast to 3. I believe this is how they combat the bright reflections.
Yep, HC set to 20 would literally destroy an image full of textures too. It would be way too flat
Which is why you should compress the brightness of the HDRi before it lands in the environment, not in the VFB.
The Colors stay the same, the brightspots just get less bright.
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I guess a cause could be that the dynamic range isn't identical across all HDRs, especially when they come from different sources. A sun spot with lower dynamic range would result in less intense sunlight in the rendering, higher dynamic range would result in a much brighter sunlight, hence the changing 'contrast' which is probably more a thing of proper (or improper) dynamic range balance between sky and other elements in the HDR.
Also, sun intensity changes quite a lot with different angles over horizon, this can be another reason.