daveb867

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

They should all be at 1.0 for physical correctness.

/Z

__________________
mentalraytips.blogspot.com - mr Zap Andersson - a completely mental shader guy

daveb867

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).

daveb867

thanks just as i thought

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

obviuosly something wrong with my scene

MasterZap

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

__________________
mentalraytips.blogspot.com - mr Zap Andersson - a completely mental shader guy

daveb867

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

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.