Faking GI with an ambient light and vray dirt

[tricky]

I'm experimenting with rendering an architectural scene (both exterior and interior with quite a lot of glazed windows) without GI and was after a few tips and suggestions.

I have created a vrayambient light and added a VRayDirt map to the light map. I have also added a VRay sun and stuck the Vraysky in the reflect/refract environment overide.

I am using a physical camera at the moment (is this the right way to go) and have checked the ambient light compensates for exposure. The intensity of the ambient light doesn't seem to make any difference to the brightness of my render. It seems that to affect the brightness, I need to change the colour of the occluded swatch in the dirt map to something less than black. The radius of the dirt is 10m (I think this is the default). All other settings on the dirt map are the same.

It seems that changing the exposure of the camera only affects the parts of the render that are affected by the vraysun - not the bits 'in shadow'.

Is this the right way to go?

[vlado]

In the VRayDirt texture that you have put in the ambient light, turn on the "environment occlusion" option and put the VRaySky texture either in the GI environment slot in the rendering settings, or in the regular 3ds Max environment slot.

Best regards,
Vlado

[vlado]

Here's an example.

Best regards,
Vlado

[super gnu]

ha.. you learn something every day. i was never sure what "environment occlusion" was for.

[tricky]

Here's an example.

Best regards,
Vlado

Thanks Vlado. Very useful. What should the radius of the dirt be set to? Is it something that is scene dependant?

[vlado]

The radius depends on your scene and what kind of effect you are after, so you'll have to do a few tests.

Best regards,
Vlado

[tricky]

The radius depends on your scene and what kind of effect you are after, so you'll have to do a few tests.

Best regards,
Vlado

OK - I will have a play around.

Who needs GI???

[Morbid Angel]

the issue with amb occlusion method tricky, if you have strong sunlight hit on the wall, there won't be any spill from that in the interior.

[tricky]

the issue with amb occlusion method tricky, if you have strong sunlight hit on the wall, there won't be any spill from that in the interior.

Yeah - I realise that there are some pretty significant compromises that will need to be made. There is also something really nice and simple about sticking a sun, a sky and a physical camera in there and simply controlling the exposure of the camera (like in the real world) to get things looking nice. Faking it is actually more work! We are gearing up for an animation and weighing up the pros and cons of GI vs Fake.

(What would be nice is if you could use this 'Fake GI' approach and tell the primary 'hot' areas where direct sunlight hits to be low quality secondary lights that take on that colour and emit light from those areas alone (essentially creating coloured vray plane lights wherever the direct sun hits). You could control intensity and some sort of 'size threshold' to those areas so only plane lights are created over a certain size only.)

[hoppergrass]

years ago I did a test with something similar, if I remember correctly, I plugged two different AO's into a fall off map set to light and shadow, with the light having brighter AO colours and shadow having darker AO colours.

It worked well to give the appearance of light bouncing off surfaces, as long as you didn't study the image too closely
interestingly it took longer to render than a very low value GI solution which also looked better.

[AlexP]

Yeah - I realise that there are some pretty significant compromises that will need to be made. There is also something really nice and simple about sticking a sun, a sky and a physical camera in there and simply controlling the exposure of the camera (like in the real world) to get things looking nice. Faking it is actually more work! We are gearing up for an animation and weighing up the pros and cons of GI vs Fake.

(What would be nice is if you could use this 'Fake GI' approach and tell the primary 'hot' areas where direct sunlight hits to be low quality secondary lights that take on that colour and emit light from those areas alone (essentially creating coloured vray plane lights wherever the direct sun hits). You could control intensity and some sort of 'size threshold' to those areas so only plane lights are created over a certain size only.)

Interested to see your results of this if you are able to post any

[tricky]

years ago I did a test with something similar, if I remember correctly, I plugged two different AO's into a fall off map set to light and shadow, with the light having brighter AO colours and shadow having darker AO colours.

It worked well to give the appearance of light bouncing off surfaces, as long as you didn't study the image too closely
interestingly it took longer to render than a very low value GI solution which also looked better.

Interesting. The problem with GI comes when we want to animate anything other than a camera. It would be great to have some alternative that fakes GI to a point but is animation friendly.

[super gnu]

(What would be nice is if you could use this 'Fake GI' approach and tell the primary 'hot' areas where direct sunlight hits to be low quality secondary lights that take on that colour and emit light from those areas alone (essentially creating coloured vray plane lights wherever the direct sun hits). You could control intensity and some sort of 'size threshold' to those areas so only plane lights are created over a certain size only.)

there used to be a plugin to do similar this with point lights in MAx, before GI was practical.. Enlight.