[Daniel Hruby]

What are the "appropriate" values for HDRI parameters? I recently did exterior shots using an HDRI background and I set all 4 intensity values to 100. I saw no effect of background intensity. Can anyone explain how these values should be set?

[Boris Ulzibat]

What are the "appropriate" values for HDRI parameters? I recently did exterior shots using an HDRI background and I set all 4 intensity values to 100. I saw no effect of background intensity. Can anyone explain how these values should be set?

I second this request! Have seen no difference with HDRI maps assigned from within Cinema4D.

[Daniel Hruby]

I also am not sure how Refraction of HDRI works in a rendering. Like an exterior elevation of a skyscraper- would you need to enable HDRI refraction? What would suffer? Would it save processing time to uncheck it?

And Illumination intensity? No shadows get cast from HDRI right? Because at 100% intensity, I get extremely soft or no shadows. I realize I can also enable sky and sun, but then the question becomes : How to achieve realism with two types of global lighting? Do I set illumation to 50% HDRI and try to match time of physical sky to the HDRI sun position? Or set it to 100%? Do I need to create some distant sun object? There does not seem to be much in the forum explaining the subtlties of mixing these two methods in a "physically accurate" way.

[michaelplogue]

I've begun to think that the HDR's are being converted to MXI's on the fly in the background - and losing the intensity data. I think that this would explain why it's almost impossible to get any sharp shadows. If you have an un-obscured sun (no clouds), you should be able to get pretty sharp shadows..... that is if the intensity values are working correctly.

I have also noted that each aspect (background, reflection, refraction, and luminosity) need to be adjusted separately in order to get them to work right.

[Daniel Hruby]

I havew tried playing with the 4 inensity settings. The only obvious affects are on Illumination (goes from dark to acceptable , but without shadows) and Reflection (glass reflections can be controlled in a realsitica manner at about 80%.

Background does not seem to have any change from 1 to 100. So why the parameter? And while Refraction is hard to spot, I assume its working like reflection.

I assume since these values only go to 100 that they are percentages. Why they are set to default 1 is curious. but it forces you to adjust each one at least.

[michaelplogue]

Agree. It takes quite a bit to ramp up the intensity for all four settings. It seems that (for the background at least), you see the greatest changes at the extremely low levels, and the higher you go, the less it seems to effect things.

[Daniel Hruby]

Yeah, it's complete guesswork for me at this point. Hopefully, someone will "enlighten" us with some information on this subject.

[giacob]

i wuoldnt hope that much...

[rivoli]

actually you can get sharp shadow out of an mxi illumination channel.. well, sort of.

this is a test with one of debevec's skyprobes hdris, which have an incredibly high range. as you can see from the preview the render would probably converge to a good solution.. after a while. this one reached sl 17 and it still has a long way to go, so I imagine that with more complex scenes it'd be a no go.



here's another approach, rendered with an older version, instead of using the illumination channel (which wasn't available at the time), I mapped a cube with an mxi texture and used it to lit the scene (the original hdri is almost black with a few artificial lights on):



once again, the result is not perfect (could use some more samples for starters), but it's getting there.

[Daniel Hruby]

Great! This is the sort of thing I am looking for. Thanks!

Can you post your intensity settings for the Illumation, Background, Reflection, Refraction?

[michaelplogue]

A while back, I had mapped an hdr/mxi to a large sphere to light my scene and provide a background image. I found that it was a lot less efficient (lower benchmark by at least 1/4) than using the environment channels. Also, as you increased the intensity, it cast light back upon itself, so the background got washed out.

[rivoli]

Can you post your intensity settings for the Illumation, Background, Reflection, Refraction?

the only channel I had enabled was the illumination one, was just curious to see if I could get any sort of sharp shadow out of it.
anyway, what I did was turn the original hdri into an mxi (if I loaded it into the ill channel without tuning, it gave me a way too strong illumination which was a bit of a hassle to expose), tweaked till it looked fine, and then left the intensity at 1,0 in the max's rollout.

here you can find the hdris I used:

http://gl.ict.usc.edu/skyprobes/

unlike these ones, most of the hdris you can find around the web are medium range at best, even the commercial ones. I guess that hdris with not very high values won't give good results no matter what.

I found that it was a lot less efficient (lower benchmark by at least 1/4) than using the environment channels. Also, as you increased the intensity, it cast light back upon itself, so the background got washed out.

it makes perfect sense, sure the emitter way is not the most convenient.

[Hervé]

the larger (bigger) the hdri, the faster it cleans in Maxwell...

Sachform last dvd are large and good.. (at least the demo free hdri)

hope this helps..

[acquiesse]

Thanks Hervé, good tip... Do you use the demo HDRs with the watermark?!

[Hervé]

yes I tried them a while ago..actually the croissant was lit by the demo with watermark.. except if you want it to show in the background, it's no problem..