matID render not respecting opacity on MixMaterial

[itsallgoode9]

When I render a matID and surfaces have opacity applied, the render shows the entire geometry and does not respect the opacity applied to the opacity map in the mix material. If I have a diffuse with an opacity map applied, it renders correctly in the matID pass, so I do not see why the mixMaterial renders without it. Is this intentional?

Below shows what is happening:
1. Final render. mixMaterial used to combine 3 materials is applied to geometry (one for paper, one for black text, one for gold foil) . and opacity
mask is used to "cut out" the label from the larger geo
2. shows geometry from viewport
3. matId render of when my MixMaterial is applied. Notice the matID just shows the whole geometry and doesn't respect my opacity map. This
should be the same shape as in image 1
4. matID render of diffuse material with same opacity map applied. notice it is the correct shape, matching the render in image 1
5. This is how I wish a matID would look when rendering a mixMat. it assigns a different matID to each one of the 3 materials combined through
the mixMaterial

[itsallgoode9]

any word from Octane team? Is this a bug or is this how it should function?

[roeland]

Yes, at the moment it works like this. Every input on a mesh will get one material ID. If some pins have the same material node attached they will get the same ID.

The material ID pass will not go inside materials and inspect mix materials, but it will consider the mix material one single material.

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Roeland

[itsallgoode9]

thanks for the response Roeland. I can't think of any situation where it would be useful to work in this manner. Is this something that could be changed in the next update? I mean, the renderer is already picking through the mixMaterial so it knows how to combine them, so it would be super helpful if the matId pass would do the same.

[roeland]

I can't think of any situation where it would be useful to work in this manner.

It depends on what you use the mix materials for. Sometimes treating a mix material as a single material makes the most sense. A lot of materials in liveDB are mix materials, but with a constant mix factor. For skin for example you may use a mix of a glossy material and a diffuse material with transmission. For an LCD screen you would mix an emitter and a glossy material. And worn out metal could be modelled with a mix material with a dirt texture as mix parameter.

Sometimes treating the mix input as different materials makes the most sense, like telling a bottle and the decal apart.

For the renderer unfortunately there is no real way to tell those two cases apart. The material ID pass only tells the material assignments on the mesh, and it can only assign one ID per material.

It's of course easy to add an option for that, but the hard part is adding it in a way it's actually useful for a lot of situations, and in a way it fits with the other features. A lot of things you can do with the material ID and object ID passes can now be done better with the render layers feature. For what would you use the output you'd like to have in image 5?

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Roeland

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Roeland

[itsallgoode9]

yeah that makes sense. I guess in my mind, all you would need would be an option box (possibly in the mix material node) to assign a mat ID to only the mix material or assign matID included materials. That would give you both options. I think you only need two options and that would cover all situations?

For my matID in image 5, I use something like that all the time so that I can have a ton of control for adjustments in photoshop without having to make selections by hand:

Client might decide the gold foil is the wrong tone of gold, so in photoshop I can adjust the color of only the gold foil
Client might say the embossing on black lettering isn't showing up well enough, so I can create an embossing layer on the black really quickly.
Adding textures overlays to specific finishes on the label. Maybe add alot of noise to the foil to make it look more like gold ink instead of foil.

That image can be used for a billion things for doing post work in photoshop thus saving a ton of time. Right now I have to create this matID by creating a matID texture in photoshop and applying it to a new material and re-rendering the image with a real diffuse lighting.

[roeland]

With the material ID pass users often get trouble because two adjacent areas with different materials end up having a similar colour, and this problem is hard to fix. Right now we are more looking into rendering layers to solve some of those problems.

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Roeland

[itsallgoode9]

yeah, i've run into that issue quite a few times. I know you said you're looking at render layers to fix this, but if that doesn't come through, just having the option of manually selecting the color of each material's matID is how Maxwell render handles it, which works well. I ONLY work with solid RGB and CMYK colors so that I can use each color's color channel mask in photoshop to get 100% accurate masks every time, even when there is overlapping DOF in the render.

I think that has been mentioned before in the render layers thread as one method of doing matID stuff but I thought i'd mention it just in case you weren't aware of this workflow. anyways, i'm excited to see what you guys figure out with the render layers!

[itsallgoode9]

hey Roeland, I've come to find out that i'm having problems getting the colors in my RGB mask texture to come out as 100% pure RGB channels. I have the camera set imager set to off, no color management and no matter what I do, the RGB color channels are not 100 B&W. Any ideas?