For newbies: HDRI lights settings

joel ruiz c

joel ruiz c

Active member
I just discovered one very important thing about HDRIs. What is a bit frustrating about the manual is the lack of samples and barely any explanations about how things work.

I was downloading a few more HDRI's from HDRI Haven and I kept seeing how my renders didn't look like the sample renders in that page. Some of the sample renders have strong, sharp shadows and all I got in C3D were soft shadows. Colors were mostly consistent, but the quality of the light was always soft in C3D. I was rendering the sample scene pictured below with every map I had downloaded from that page, and all of them had soft lighting.

So I started playing with the parameters, going a bit crazy with the numbers to see what I got. That's when I discovered "Clamp".

All the manual says about it is:

  • Clamp: Pixels in the HDRI with a very high intensity (for example in the sun) can cause serious noise in combination with ambient occlusion or radiosity renderings. The artifacts can be easily reduced by clamping the high intensities. Don't set the clamp value to low however, or you will lose all the benefits of using an HDRI.
That's it. While it is useful information, it doesn't say it affects the contrast of the light, the hardness or softness of the shadows, you don't get the full spectrum with the default setting of 10. I went crazy and set a value of 1000.. and I saw what I was looking for!

So, to all newbies like me haha.. if you are wondering why you don't get all the lighting from an HDRI map.. it is that damned clamp value. Set it to 1000. Or 100,000. It BARELY affects render times with Falcon, and you get all the glorious light from your HDRI map :)

I need to start over and render all of my samples again, this time with a clamp value of 1000.

No other lights used in these samples. SPP set to 500, Clamp 1000, Intensity set to 2 in all of my samples, you can check them HERE.







 
Hey I'm glad this helps more than one :)

I said "set it to 1000 or 100,000" well no.. I'm still playing with that thing. I'm thinking the sweet spot varies from map to map, but so far it seems to be between 5,000 to 10,000 if you want all the info without over blowing things. Caustics look better too but that was expected. I'm rendering a scene with glass right now (my cups lol), it looks nice but still a while before it's done.
 
HDRI clamping should be set to zero (= no clamping at all) and only adjusted with a number when a noise/firefly problem arises IMHO.
If it is too bright, intensity can be lowered.
 
I know that ideally it should be set to zero, but I have found with many maps that then the hard shadows become pitch black.. not pretty. So I think the clamp value is very useful to fine tune the final result. 10 is absolutely not enough, you just get basic lighting from the map globally. Zero (no clamping) is too much and somehow you miss info in the shadows (hard shadows are black, no detail). What I have found is that you should allow the map to give you much more info than with clamp set to 10, but not as much as with no clamping. So I have found that a value from even 1000 to 10,000 is enough and you get the most out of the map. Of course it may vary from map to map.
 
Well the HDRI I'm using in this old scene doesn't change at all in Falcon or Cheetah.

HDRI- Church_HarvestLobby

I tried zero and 5,000 with no change. In all renders HDRI intensity was set at 2 with no other lights.

I was surprised Falcon didn't handle the reflection of the cheetah face and syrup bottles.
The face reflection was not planned when I originally set this up years ago,
It was itself a pleasant surprise. I was hoping Falcon would render it as well.

Falcon No Clamp HDRI
Falcon No Clamp.jpg


Falcon 5K Clamp HDRI
Falcon 5k Clamp.jpg


Cheetah AO No Clamp HDRI
Cheetah No Clamp.jpg


Cheetah AO 5K Clamp HDRI
Cheetah 5k Clamp.jpg
 
About the reflection, that's strange. But even the golden reflections in the Cheetah badge are different, it is as if Falcon is not picking up a lot of reflections. I can see the bottles and the badge in the wall, but very faint.
--
About the lighting..
How does it look with the default value of 10?

I don't have that map, is it from HDRI Haven? I think not?

I think it depends on the quality of the map. The maps at HDRI Haven are of very high quality and have a very large dynamic range (check the EV number when downloading from the page), I think your map doesn't have much of a dynamic range.

Look how different these renders are, it's unbelievable..

Clamp 5000

Here you can see the light coming from an incandescent light bulb in the ceiling, the shadows and the yellowish coloring come from it.
--

Clamp 10

Here you only see the strongest lighting from the window, any other light source from the map is gone. It changes everything.

I'm rendering this scene with no clamping at all (set to zero).. I will post it when done.
 
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That's quite a difference, and the hardening of the shadow is great.
I get no difference with a setting of 10.
I get a little difference with 100000 on one of my outdoor HDRIs, but no shadow hardening.
 
It depends completely on the map. If the guy took the photos in an area with a harsh light (direct sun or other light source) you'll get hard shadows. On top of that, if the photographer captured a large dynamic range you'll see everything, if he didn't you might see no difference.

Try a map like san giuseppe bridge from HDRI Haven.. you'll get nice long hard shadows as well as soft shadows (set clamp to 10,000)

https://hdrihaven.com/hdri/?c=outdoor&h=san_giuseppe_bridge

This one is san giuseppe bridge


BTW, all maps I download from that page I select the 8K version, that's big enough for me. The 16k version are too large lol.. I want to download all maps but not to use a hard disk just for maps haha
 
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Here's a render with clamp = 0. It gets more noisy (spp = 0), and it is not very different from clamp = 5000, so the sweet spot for this particular map (Cayley Interior) is 5000 or less.

 
Here's another map that's a bit more challenging but it has great possibilities Piazza Martin Lutero it has very harsh lighting but lots of dynamic range.

Clamp=10 (default), Intensity=1 (default)

The clamp value is too low, so it's not letting the map to give all the dynamic range it has.

Clamp=0 (no clamp), Intensity=1

Too harsh, shadows would look black if not becuse the light is bouncing among the cups.

Clamp=20,000, Intensity=3

Good compromise I think, of course it depends on what you want.
 
I have a number of HDRIs from HDRI Haven, had them for some time,
but none of the ones I picked out work this way, no matter the size.
I guess It's the luck of the draw. Did you try- umhlanga sunrise?

I tried Cayley Interior and that worked well even with the smaller versions. Now I see what your driving at.

In this animation I rotated the HDRI 180 degrees and animated the Clamp value from 10.0 to 5K.
The HDRI environment in Cayley Interior has two main light sources-
The sunlight coming in the window and the incandescent from above.
With the Clamp value at ten, all you see is the diffused sunlight, but no trace of the incandescent.
At just above ten you clearly see the shadows from the two light sources.
And the warm color of the incandescent light gets stronger. Very cool-:cool:

 
It depends on the map. When the map has only one light source, and when that light source is very large (overcast sky for example) you won't see much of a difference, as the light from that map is supposed to be soft anyway. But when you have multiple lights in a map varying in power, you start seeing them appear when you increase the clamp value. They affect color temperature too.

I don't remember which map, but it was a sunset or a sunrise. The sun was of course warm, but the sky above was blue. With a clamp setting of 10 the render had a cool temperature, but as you increase the clamp value the temperature shifts towards warmer tones. With no clamping the scene is very warm because of the setting (or rising) sun.. that's a lot of change.
 
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