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Hi there :) I'm curious why baking using the Combined Bake Type doesn't bake the metallic values next to baking diffuse and shadows/lights.

Are there any special settings that I missed or is there a completely different way to do this?

Note: I'm not trying to bake the Metallic map, I already did and will use that together with the Combined map if I don't find a way to only use one map but I can't imagine that this would be impossible to do in blender.

Thanks!

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The general thing in 3D that makes a metal metallic, is that it has a black diffuse and a tinted glossy component (along with an altered Fresnel response, but that's tunable.) This corresponds to the physical reality of an ideal metal: photons do not pass through its surface to bounce around and reflect diffusely from deep within; they only ever reflect off of its surface, or they are absorbed.

Because of this, a metallic object has no diffuse component, only a glossy component. Any diffuse bake of a fully metallic material will give you black, because a metal's diffuse component is black. If you have a metal mix, you'll just get a darker version of your base color, because all that an interpolated metalness is doing is interpolating between a full metal and a full non-metal.

In general, baking glossy components doesn't make a lot of sense, because they're view dependent-- unlike diffuse, they depend on where the camera is; they point at the reflection of the incoming vector over the surface normal. So any real glossy bake might as well be a render instead of a bake: they're only ever going to be valid for a single camera position*. Because metals are glossy and thus view dependent, no bake is going to capture their response.

Most engines are going to include a metallness-based material, in which case there's no need to bake metalness into diffuse-- you just bake it into metalness, by plugging your metalness value into emission and baking a new texture (from an emission bake rather than a diffuse bake, of course.) Then you can use your metalness texture as your metalness in whatever engine you are using.

*There are times when it's useful to bake view-dependent effects into a fixed texture, but unfortunately, Blender doesn't do that, or rather, doesn't do it very well; as far as I can tell, it always use the surface normal as the sample->camera vector. Maybe if Eevee baking is ever implemented, we'll see the potential for Blender to do some view-dependent baking.

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  • $\begingroup$ I appreciate the time you took to reply and write everything out in detail! It's a specific project I'm working on and I need the Metallic to be baked in regardless of the angle the model is being looked at like you mentioned at the end. I use a studio light setup for this (so that the reflections don't look odd) and I've used Octane in the past to achieve this so I was curious if Cycles had a similar option. Thank you! $\endgroup$
    – tzarica
    Jul 29, 2023 at 11:30
  • $\begingroup$ @tzarica If somebody needed a view-dependent bake, I'd recommend rendering it and then painting it onto the mesh (or possibly baking the render from projected uv to real uv.) It'd take at least two renders. You could mix between the renders by the ratio of light from suns with the cameras' orientations. $\endgroup$
    – Nathan
    Jul 29, 2023 at 14:07
  • $\begingroup$ I'm definitely playing around more with this. Thanks @Nathan! $\endgroup$
    – tzarica
    Jul 30, 2023 at 19:17
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There is no metallic pass to bake in the first place.

Metallic data in the Principled BSDF shader influences the material's Diffuse and Glossy passes. Metallic isn't a pass in rendering, it's a type of data processed by the Principled BSDF into the render.

Combined type baking calculates render passes, the components of the "final render result" in a way. If none are excluded, it's basically baking the final render result as is.

More info:

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  • $\begingroup$ Thank you for taking the time to reply to the question and add the links, appreciate it! I'm aware that Metallic isn't a pass but under the bake options you can tick Glossy and I was wrongly assuming that that would bake the metallic values as well. I'm trying to do what @Nathan suggested in his comment but looks like there's no option for that for now so I will be using a Metallic map like you're saying :) $\endgroup$
    – tzarica
    Jul 29, 2023 at 11:36

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