Gi Colour Bleed Changes

[stu]

Somewhere between version 6 and 7 of houdini the behaviour of the VEX Global Illumination light shader changed. Ambient light use to contribute to the colour bleed in the irradiance solution. ie. If the only light sources in the scene was a light referencing the VEX Global Illumination shader and an ambient light, you would get colour bleeding between surfaces.

Not any more.

Now the only colour bleed being generated is that created through the bounce of a direct light source. If you're using an ambient light generate a bounce light pass to be multipled by an occlusion pass, you won't get any colour bleeding unless the surfaces are being struck by a direct light source.

Why did this change?

Also, why don't I get colour bleed if the only light source in the scene is the VEX Global Illumination light? I would expect it.

Here's an example:

The scene has two lights - a direct light and a VEX GI light with full irradiance turned on (and cranked up to illustrate the point). The direct light is hitting the cube from the right, so we get colour bleed on that side of the cube and floor. There isn't any colour bleed on the indirectly illuminated surfaces.

stu

[jedijones]

Hi Stu,

did you sort out the colour bleed problem? Im having the same problem. Could you post the hip file for me to study please.

thanks jj

[stu]

Hi jedijones,

Someone who knows A LOT about mantra is looking into it.

[Dennis Sedov]

Any news on this? I really like the way renderman ambient light shader works giving color bleeding.

Hi jedijones,

Someone who knows <span style='font-size:21pt;line-height:100%'>A LOT</span> about mantra is looking into it.

[stu]

Any news on this? I really like the way renderman ambient light shader works giving color bleeding.

Wow, this is back from the dead. The word was that indirect illumination was only contributed from the other legitimate light sources in the scene. If you do a search for the Lego scene that I posted about a hundred years ago, you'll see the hack that I used to get around the problem. If you want indirect bounces from what is correctly referred to as "global illumination", PBR is the way to go.

[Dennis Sedov]

Wow, this is back from the dead. The word was that indirect illumination was only contributed from the other legitimate light sources in the scene. If you do a search for the Lego scene that I posted about a hundred years ago, you'll see the hack that I used to get around the problem. If you want indirect bounces from what is correctly referred to as "global illumination", PBR is the way to go.

How funny. I just looked at the post date above and it goes back to 2005 =) Will look next time, before bringing stuff from the grave =)