View Full Version : Illumination Baking
08-03-2005, 01:42 AM
I'm having a little trouble baking illumination only from a radiosity scene.
What I want to achieve is a coloured image that contains an illumination map for a surface. I then want to be able to apply the map to the object so that my colour textures are affected by the illumination map.
What I've done is use surface baker set to illumination only to bake out the illumination map. This seems to work nicely. If I was only interested in white objects I'd be fine..
The problem comes when the object needs to have a colour map applied to it as well. I set the luminosity to 100% (diff and spec to 0%). Then I apply the illumination map as the top layer in the color channel set to multiply.
For some reason in my tests the result is always brighter that a straight unbaked radiosity render. For the life of me I can't work out what I'm doing wrong.
I've attached images of the plain radiosity render, the illumination map and the resulting render. The yellow grid is the color texture, and the red arc is coloured illumination from the radiosity.
could somebody explain what's going wrong as this is really frustrating me,
08-03-2005, 02:16 PM
I am kinda confused on how you are combining your layers. Are you combining them in Photoshop or lightwave? Do you want to end up with a map that will go onto a model or do you need if for something non-3d.
08-03-2005, 03:11 PM
the plan is basically to render out a lower resolution illumination map that I can then apply to the model in lightwave. I wanted to bake the illumination seperately to the color channel for the surface so that higher detail in the colour channel can be rendered in the final animation.
To do this I currently add the baked out illumination map (which includes colour information due to lighting and bounces) in at the top of my colour texture stack, and setting the blend mode for the layer to multiply.
My understanding was that with the luminosity for the surface at 100% this should produce an identical effect to the surface being lit by the radiosity solution.
08-03-2005, 04:24 PM
I could well have the wrong end of the stick . . . but have you made sure that your object on which you have the backed illumination is not also being "re-lit" by further radiosity or other lights still active in your scene.
08-03-2005, 04:45 PM
Yup, no other lighting should be affecting the surface. The illumination matches incredibly closely if I try the same test with simple white object and setting the colour channel to only be the illumination map.
The problem occurs when I set the top colour layer to multiply, for some reason multiplying the top layer doesn't seem to work like a proper multiply operation as it does in say photshop.
It seems that I can probably get around it by setting the gamma for my image map to about 0.5 in the image editor. That gives me a pretty close match to the original render.
08-03-2005, 04:52 PM
Again just a maybe ... but is your ambient set to "0"?
08-03-2005, 05:03 PM
Doesn't make any difference at all (I tried just in case) since the diffuse and specular are set to 0% no lighting has any effect on the way the surface is rendered when I'm applying the illumination map.
I'm sure it's down to the strangeness that is lightwave layer blend modes,
08-03-2005, 06:49 PM
If you combine the layers in photoshop does it look better? When I do this I usually combine my layers in PS untill I get exactly what I want.
What is it that needs to look exactly like it does before baking? Do you have any room at all that would let you get away with the difference?
08-04-2005, 01:18 AM
Looks like you were right about the gamma settings. I found this
UPDATE 04/26/03: As most LightWavers know, most of the mathematical layer blending modes, including Multiply which is used here, do not actually work the way they should. Multiply, for example, yielded rather washed out results in this hack versus actual radiosity. Fortunately, the inaccuracy turns out to be a gamma applied in the multiply operation. It has no business being there any more than the "slide" belongs in the Texture Channel... but it's there, and we have to work around it by adding a counter-gamma in Image Editor of 0.52 (noted in Step 4).
08-04-2005, 08:51 AM
Uncon: Strangely it hadn't occured to me to combine the layers outside LW. I probably could combine the layers in DFX+ since its an animation I'm working on. Unfortunately there's more than the one surface involved, so I'd end up rendering out more passes than I'd really like to consider.
Cyphyr: cool, thanks for digging that up, I had a quick google around on the subject but couldn't seem to find anything relevant. It's nice to know someone else has hit the same problem. It's also very handy that it gives a value for the gamma correction.
08-04-2005, 08:51 AM
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