Interior scene with exterior HDRI

[JamesTaylor]

I'm not sure if this possible or recommended, but i'm wanting to light an interior scene with an exterior HDRI.

 

ie. the light from the HDRI comes in through a window or multiple windows to illuminate the room.

 

everything i've found so far illustrates how to light random shapes sat on a surface yet when i try the same method with objects in a room i can only illuminate areas which receive direct illumination, there is no bouncing of the light to create indirect illumination and light the remaining areas.

 

any suggestions, links etc. would be most welcome.

 

i have access to mental ray / vray / and scanline if it makes any difference.

 

thanks.

 

James

[IC]

In general terms Image Based Lighting is only for ambient light as only direct light (that from lights) can bounce enough to illuminate an interior.

 

Saying that, I don't know about individual render engine features, so there may be a way.

 

The way I light an interior like this is to use area lights in the windows which are the colour of the environment with additional area lights under floors and in walls to simulate different coloured light bounce/bleed.

The one under the floor is somewhere between the colour of the environment and the floor and so on.

 

Some omni type lights are normally required too.

[JamesTaylor]

Iain,

 

i'm wanting to use Global Illumination inorder to calculate the bounce effect, so i'm presuming, that the manner inwhich you set your lights up is for faking radiosty/GI, rarther than to speed up the processing of GI?

 

In relation to HDRI only being for ambient light does this suggest that it is not suitable for visualization of internal spaces pre build as capturing the HDRI image for any given room would require the space to be built inorder to capture the light information?

 

My reason for wanting to use an external HDRI image was that a sky and horizon type HDRI could be much more generic yet still produce high quality results.

 

I may be way off the mark with my presumptions as i'm still trying to get my head round the process!!

[IC]

I use the area light method to simulate the effect of strong ambient light coming through windows without a raytraced 'sun' light. It works really well in conjunction with radiosity as the colours bounce around the room from each light.

 

I think what you are talking about is the cinematic technique of duplicating lighting from existing rooms using HDR photography.

[JamesTaylor]

Do you know of any links that i can read about this?

[IC]

To be honest, I just pick things up from software forums, this forum and magazines like 3DWorld.

 

There's loads of HDR stuff on the web. Paul Debevec is a bit of a pioneer in the field. Read up on his work.

[Eric]

I don't see any reason why this shouldn't work.

 

To start, turn off the glass in your windows - this just helps to get the lighting level sufficient to light the space without worrying about if the glass is obstructing the light passing into the space.

 

You will probably need to increase the multiplier of the HDRI image to force it to project more light. Basically, this would be like bumping up the exposure time with a camera. The exterior HDRI image will become "blown out" or "over exposed" but that's because you're exposing your scene for an interior environment where lighting levels are much lower than exteriors. With a normal photograph, if you take a picture of the interior of a space, your exterior will be completely, or almost completely over exposed / bright white.

 

Once you have the lighting level where you want it, turn your glass back on and adjust its settings from there.

 

You may need to play with secondary bounce settings as well to force the light bounces to have a greater impact on the interior lighting.