HDRI for exterior lighting - the very basics

[SgWRX]

i'm just starting to play around with HDRI lighting for exteriors. Mainly because I like the quality of the clouds/background image as opposed to doing it in post. I'd like to list a few things to see if i'm understanding all this HDRI business.

 

A)

 

1. I dropped an HDRI (thanks http://hdrmaps.com/ for a free sample) onto a skylight, then the same HDRI into the Environ Map of the background in (8) Environment and Effects.

 

1.1 When I loaded the HDRI map (.exr) I did not choose "color correction" where you can apparently set "black point", "white point", "exposure" etc.

 

2. I turned on mr Photo Exp Control, with Process Background and Env Maps checked. (settled on EV of 4.0)

 

3. I rendered and got a decent look, but _no_ shadows.

 

4. I had my default GI set to "Skylight Illuminatioin from Final Gather(FG)", but I switched this to "Skylight Illumination from IBL", re-rendered and got subtle shadows.

 

Is that all there is to it? Is this overly simplistic or am I missing something? Should I still be looking into using a Photometric light as a "Sun" for shadows and such?

 

B)

 

1. In comparison to a mrsun/mrsky system, it looks like in general, HDRI maps are not the same overall range. For example 1 HDRI image may require a mr Photographic Exposure value of 5EV another may call for 10EV etc... yet others may call for 0EV or 2EV. Am I understanding that?

 

2. Using an HDRI map in the "haze" map of the mr PhysicalSky shader, I found I would frequently get an error on render "encountered invalid pixel color, using black instead". Instead I put the HDRI in the "custom background" slot. However doing this, per Autodesk user manual and per my experience, the "custom background" HDRI is NOT visible in reflections of objects in the scene.

 

C)

 

1. In general, you are really stuck with the HDRI map you have as far as time-of-day. I think I found somewhere that one should really have a collection of HDRI's for sunset, sunrise (though they are similar), mid-day, late afternoon etc...

 

Thanks,

[SgWRX]

Oh - another thing:

 

If you adjust the skylight's output value, you then have to adjust the HDRI map's level to match it, so you don't end up with a "darker" sky than lit scene. Is there some other way to work with that? Otherwise it seems like you are "fixed" in terms of balancing the brightness of your background vs. the lit objects in the scene.

[jasonstewart]

This question would probably be better answered in your rendering engines section. I assume you are using Mental Ray?

[SgWRX]

yes, mentalray. yes actually i should have put it in that forum. can move?

[Zdravko Barisic]

...

 

3. I rendered and got a decent look, but _no_ shadows.

 

 

For shadows, go to mat editor, and your HDRI slot, make the HDRI gamma to 0.75 value, or similar, instead of default 1.0

Good luck!

[blank...]

Read this:

http://forums.cgarchitect.com/75415-mr-photons-ibl-fg-nothing-thime-better.html

[numerobis]

http://www.ronenbekerman.com/making-of-esherick-house-part-3/

[SgWRX]

thanks. good stuff. i was going to say, i can get decent but "flat" results now with a skylight (using the environment check, which i was not before). shadows, even with IBL mode GI are soft. I've tried a couple different maps but will keep playing around.

 

i like thorsten's enthusiasm! i need to look into mentalray string options for importons and irradiance.

 

i'm kind of surprised that one doesn't need to enable Final Gather anymore for the IBL/skylight(with environment checked) to work. is that new or was it always that way? back when i briefly looked at this it seemed that FG had to be used. maybe it's just 2014 with the IBL mode.

 

i was going to ask about setting white point. some HDRI's really give a strong blue tint to the render. well, without having mrPhotographic Exposure Control turned on, there's no way to set white point? i haven't tried the color correction, but i don't want the HDRI color corrected, i want the objects in the scene color corrected. but it seems that you can indeed use mrPhotographic Exp Cntl even with an HDRI.

 

sorry, yeah this is turning into a mentalray discussion. maybe moderator could move? thanks.

[Zdravko Barisic]

thanks. good stuff. i was going to say, i can get decent but "flat" results now with a skylight (using the environment check, which i was not before). shadows, even with IBL mode GI are soft. I've tried a couple different maps but will keep playing around....

 

I am still geting these flat images with HDRI, even going step by step through all steps. Do not know the secret yet.

Especially for daylight. Nightlight is not so flat, as it is night.

[SgWRX]

I am still geting these flat images with HDRI, even going step by step through all steps. Do not know the secret yet.

Especially for daylight. Nightlight is not so flat, as it is night.

 

 

 

 

 

1. download this sky (you have to register if don't have an account) it's free

http://www.cg-source.com/details_hdrisky.php?id=0086-03&pricat=sky

 

2. new scene in max

 

3. create a plane/teapot

 

4. create a skylight

 

5. open (8) 'Environment & Effects'

 

6. click on 'none' by 'Environment Map:"

 

7. find and click on 'bitmap'

 

8. in the 'select bitmap image file' dialog box, set 'gamma' to 'automatic' if max 2014 otherwise set 'gamma' to 'override' and choose 1.0

 

9. browse to the downloaded hdri, double-click the hdri, in the 'HDRI Load Settings', leave everything default EXCEPT check that the 'internal storage' is set to 'real pixels (32 bpp), then click 'ok'

 

10. create a standard skylight somewhere in your scene (next to teapot for example)

 

11. in the skylight settings, set the 'sky color' to 'use scene environment'

 

you're just about there.

 

12. open the material editor

 

13. drag the hdri from the 'environment & effects' slot into a material slot and choose 'instance'

 

14. make sure the hdri bitmap (now in the material editor slot) 'coordinates' is set to 'environ' and 'mapping' is set to 'spherical environment' (to display properly in my preview, i have to check 'texture', the un-check 'use real-world scale', the switch back to check 'environ'

 

at this point you can render and get shadows but this is where the goofiness comes in.

 

you can play with the 'output' of the hdri bitmap (instead of 1.0, set to 2.0 or 5.0) this will brighten the exposure of the scene.

 

you can also enable mrphotographic exposure control and play with physical scale, or just put the EV value to 0.0 or 1.0 etc... i haven't nailed it down yet.

 

but the gist of this is that it seems like we have to be careful which hdri iamges we choose.

 

EDIT: oh, you don't even need to have FG enabled. but you do have to have 'skylights & environment lighting (ibl)' set to 'skylight illumination from ibl'.

 

i've attached an image doing the above. but without mrphotographic exposure control. although in this image, i set the option "def. exposure' check-box along with the 'real pixels (32 bpp). it brightened it up without having to increase the bitmap's 'output' beyond '1.0'.

 

i also enabled the default 'glare' in the 'camera shaders' > 'output'

Edited August 30, 2014 by SgWRX

[Zdravko Barisic]

Thanks!!!

[SgWRX]

glad it worked for you!

 

looks like another thing we can do is use the hdri as the 'environment & effect' > 'environment map' in place of a mrphysical sky.

 

then all you have to do is try to match the mrsun (or any sun i'd guess) to the location of the sun in the hdri. also turn on FG or whatever indirect illumination you use.

 

but to do this, you have to play with the 'physical scale' > 'unitless' to get the sky balanced with the rendered objects.

 

the reason i tried this is, i used that same hdri inside a project and it seemed a little dark compared to what i was getting with the sun/sky. i still got shadows though, and was able to leave the FG turned off. if i increased the 'output' of the hdri, or changed settings when loading the hdri, i tended to get a brighter render but the clouds were starting to get blown-out to white. this is what happens in real-life.

 

i'll continue to look at this. i've seen some comments about tweaking with gamma/gain maps etc.

 

also, a cool thing is now that i'm able to get somewhat decent lighting (as long as i start with a new scene), i can now try out the environment blur and get really smooth blurred objects in my scene per zap's old blog post.

 

i say "as long as i start with a new scene" because i really think that the materials you use have to be balanced for the lighting you use. for example, i got used to using a mrsun/sky around 12:00 noon local time with a mrphysical exposure EV of around 13.5. i arrived at this by putting a standard white A&D material one glossy and one matte, then would render with different EV's until i got just a bit of "blow-out" on the white spheres in the highlights. and to clarify further, this is for materials i'm eye-balling to color/reflectance as opposed to using real reflectance and color data for a given material. some shades of grass for example, on a bright sunny day can tend to exposed as "middle-grey" or a little brighter/darker depending on your tastes in photography. at least that's my take on materials and lighting.

[blank...]

i like thorsten's enthusiasm! i need to look into mentalray string options for importons and irradiance.

 

You're missing the point, it's not about importons and irradiance, it's about high quality HDRI that you're using, if you want strong shadows.

 

i'm kind of surprised that one doesn't need to enable Final Gather anymore for the IBL/skylight(with environment checked) to work. is that new or was it always that way?

It's new, IBL will work without FG, but it is still recommended to use FG also, but much lower settings can be used.

 

It's new in a sense that native mr IBL is exposed in max 2014, but if you want to use it you really should use Thorstens Render optimizer. Much more control.

Edited September 1, 2014 by blank...