sky portal intensity

[Dave Buckley]

when using multiple sky portals at various windows to light an interior, should the intensities of the sky portals be adjusted???

 

at the minute i have them all set at 1.0

[Tommy Burns]

Up to yourself really sometimes they are just to strong thats what I do anyway.

[MasterZap]

when using multiple sky portals at various windows to light an interior, should the intensities of the sky portals be adjusted???

 

at the minute i have them all set at 1.0

 

They should all be at 1.0 for physical correctness.

 

/Z

[Dave Buckley]

ok so technically for physical correctness, if i have a building in its correct geographic location and modelled to the correct scale. if i then place a daylight system with mrsun and mrsky and mrphysical sky and sky portals at every window, if i then enable mr photographic exposure and choose the preset interior setting - your telling me that all i need to do is enable final gather and all the lighting will be physically correct???

 

i'm not sayin i don't believe you but half of my sky portals are way to intense on the scene even if i do everything as above

[AJLynn]

It's because of the camera exposure - when you take a shot in an interior in daylight, what's outside the windows gets blown out. You see it in photos all the time. If you want to to not get blown out you need to make changes that will not be technically accurate (but we do it all the time anyway).

[Dave Buckley]

thanks just as i thought

 

slight problem though, the burn spinner doesn't go into negative values???

 

obviuosly something wrong with my scene

[MasterZap]

i'm not sayin i don't believe you but half of my sky portals are way to intense on the scene even if i do everything as above

 

Are you saying they emit too much light, or that they are blown out visibly?

 

If the former, well, your exposure must be off.

 

If the latter, well, read on:

 

Here's the thing: Our eyes have built in tonemappers, and we are really poor at judging absolute intensity. So we can stand inside a room, lit only by light from outside the room (through a window) and see stuff both indoors and outdoors.

 

Try that with a camera; either your indoors are pitch black, or your windows are blown out. That's just life, with real photography.

 

Luckily, the portals have a built in feature to get around this unfortunate reality of physics: Go to the advanced rollout you'll see a "Transparency" setting. Set it to some dark color. This will not affect the light, only what you see through the portals. It's a faux trick to behave like your eyes - it makes the great outdoors darker to the camera, but still lets all of the lighting in.

 

/Z

[Dave Buckley]

well blow me down

 

you learn something everday

 

thanks once again for another great bit of info

 

i have been wanting something like that for ages because i want to create interiors in mental ray that match vray style interiors, and the vray ones always have nice images outside the windows and i just love that style but have always wondered how to do it with MR thanks again

[DavidR]

i have been wanting something like that for ages because i want to create interiors in mental ray that match vray style interiors, and the vray ones always have nice images outside the windows and i just love that style but have always wondered how to do it with MR thanks again

 

Vray will blow out the windows if your exposure is physically correct; the Vray renders you've seen have almost certainly been doctored.

[AJLynn]

Transparency... never thought of that, but it makes perfect sense. Excellent tip, thanks.

 

I've also been working with these issues. I recently did an image that's a section cut through a facade and shows interior and exterior including the building behind. Huge pain in the ass to get the lighting just right and it ended up being a big ol' kludging of sun/sky intensity, interior light intensity, exposure control and FG multiplier but it did work, and looked darn good (after a bit of Photoshop) - gotta love the mental ray.

[Dave Buckley]

aj post the render, it sounds interesting

[AJLynn]

Okay. It's kind of quick and WIP and sorry for the blur but you get the idea.

[Dave Buckley]

thats really really good mate, congrats,

 

but what is the blur hiding????

 

and any hints or tips on how the interior/exterior lighting setups were

 

i can never get my photometric lights to look like that

 

 

(going back to my original problem - does the fact the light portals are behind glass have much effect on how blown out it will be "reflections maybe?)

[AJLynn]

The blur is hiding some identifying markings, of course - you're not supposed to know exactly what it is.

 

The lighting setup was... hang on, maybe I still have this in a file I can find... damn, this is so crude it's actually embarrassing...

 

The sun has a multiplier of 0.03, sky is 0.05, camera is target with clipping and there's exposure control with EV=9. The track lights are from the internet, ERCO.73200.023.142 with the corresponding IES file and in Light Lister their dimmer is at 1200.

 

The sun has photon targeting turned on and its GI Photons are set to 100 under the mental ray Indirect Illumination tab. GI is turned on and the average photons per light is 1500. FG is set to draft with multiplier at 1.5 and there are sky portals with default settings.

 

All the materials are A&D and most have some kind of glossy reflection.

 

Basically I'm throwing more of my computer's time at the problem than my own - I figure I could have optimized it more but I didn't feel like it.

[Dave Buckley]

ok but if your sun and sky settings are soooo low, then how does the exterior look so sunny?

 

and also how does the render look so crisp when you only have a draft setting for fg???

[AJLynn]

When you use GI+FG you don't need your settings for either to be so high. And the exterior looks sunny because those are the sun/sky settings appropriate to my camera's exposure - basically I had perviously done another render in the interior where the sun/sky were at 1.0 (the outside was blown out but that was ok) and I had made the adjustments in the exposure control and interior light dimmers to get everything looking nice. Then when I wanted the section (this is design process stuff, in an architecture firm, and it was an impromptu thing) I adjusted the sun to balance it to the interior lights then made some tweaks in the exposure settings, and Photoshopped the levels to make it what I wanted. In the Photoshop file the top layer is Levels set to 5/1.2/235.

 

I did say it was crude...

[Dave Buckley]

problem with zap's solution to my initial question

 

when you change the transparency colour, you still can't see the environment through the sky portal, it is now just black ?? i have a panoramic bitmap in my environement slot but nothing is showing. The blown out effect is fixed however so and

 

and aj it maybe crude, but these are tips that help people like me out when we struggle for ages to get the result that i want, we may not think to do it like that although it works for what we want

[Justin Hunt]

sounds like you have turned the transparency down too much.

 

Here is a basic test , two portals one with transparency one without, mrsun and sky, photographic exposure @ ev 12 , GI and FG

 

Portal transparency colour value @ 1 (white), 0.5 (grey) and 0 (black) and last one has a pink colour

 

Notice how the light doesnt change, only the intensity of the mrphysical sky.

Notice how the pink tinted the sky but not the lighting

Notice that the portal lights dont quite fit in the window (Im lazy) and how the sky "outside" the portal is still blown out

 

jhv

[siliconbauhaus]

zap should add that tip to his blog

[Justin Hunt]

It was mentioned on my mentalray.com as well

 

jhv