cyptomatte questions and issue

[akos_kiss]

Hi!

I'm having a few issue - but mostly a bunch of questions- with the cryptomatte RE. Some of them are regarding the documentation, others are with the usage.

• I was wondering if there was a way to save the cryptomatte element separately in one exr or vrimg file? I have this option in octane and redshift. and sometimes its easier to use because if materials change in a project but the animation stays the same i can just reuse the cryptomatte i already have. Is there a reason that some render engines save the cryptomatte re separately and vray doesn't? Are there any advantages or disadvantages to this approach?
• When I save exr files containing cryptomatte re-s with the VR output system and i import them into After effects i get strange duplication when pre-composing the exr channels. The ORANGE layers are empty and only the red layers contaion the real information. This means that eighter AE reads and pre-comps the exr files wrongly or vray saves some empty layers? Anyone had this issue before?
• 

I have a few thing that i don't understand from the documentation: First of all the "node" is an arbitrary name for object, or geometry, as far as i can tell .) at least in layman's terms

One thing that caught my eye is:

• "Only requires a fixed number of additional render elements, typically four." what are those render elements? Are they necessary? what does this mean? are these extra layers that are unavailable in the exr?

The others sound way to technical for me

• Node name and Node name with hierarchy.
  • I get the same result in complex files where there is a bunch of parent and child relations, but id don't get what is the real differenc and when could it be usefull to use one over the other.
• Node material name – Creates mattes based on the materials in the scene.
  • Ok this sounds great but this still has the issu with layered materials and stacked materials just as the multimatte id re and others.
• Node asset/reference name – Creates mattes based on Cinema 4D References made within the scene. Note: This does not create mattes based on Cinema 4D Assets, only file references.
  • I have no idea what this means. Is this for xrefs? or imported alembic files? I've never hear of cinema 4d references. is this a name for something really basic i don't get?
• Node user attribute – Creates mattes from a property specified in the User Attribute field.
  • User Attribute – Specifies a user-defined attribute for creating ID mattes when ID type is set to V-Ray user attribute.
  • Ok, so i don't understand any of this regarding c4d. can anyone explain what does all this mean and how can i use vray attribtes and other user defined attributes? I could imagine this is something usefull but currently i have no ide how to make use of it. and If I'm correct this sentece says that the id type is node user attribute and if this id type is set to vray user attribute (this doesn't exist as an id type) then you can set custom ids? is this some kind reference loop I'm missing?
• Id Type Prefix – The text added to the beginning of the rendered file, when saved as a separate file (e.g. myrender.cryptomatte.exr).
  • I don't think this feature works. I've chose the node layer name id type and wrote "testid" and this string doesn't show up anywhere nor is it saved into a separate file ( first of i thought that this way i can save the specific cryptomatte re to a separate file but this was not the case) what are the use cases for this?
• Add Root Object Name – When ID Type is set to Sub object name, it specifies what information about the sub object names goes into the Cryptomatte manifest.The dag path and the sub object name(s) (e.g. MeshName.abc/ObjectName) is added to the manifest.
  • Again, i understand the principle, but i have no ide how should i use this information, or how could i use it in comp (fusion, nuke, ae)

I would like to know if there is a way to keep the cryptomatte elments consistent when developing a scene file. For example i would like to control the "ID"-s with the vray object properties tag and create cryptomatte based on the object id-s assigned with the object properties tag ( it would also be great if this respected the hierarchy or i could get id-s for childs of other object that have an other id) . So that i don't have to use a sea of multimatte id-s just one cryptomatte re. And if there was a way to get the id number from the the cryptomatte re it would be greate because i can have consistency and create a script to group my id-s however i want them. Is this far fetched?

Sorry if this was more of a rant and a cry for help but most of the forum doesn't cover these questions and i feel like there is probably a lot of potential that i'm missing, but i just don't understand the documentation without easy to understand examples .
Thanks for reading!

[akos_kiss]

Hi All!

Can anyone help me out with these question and some explanations regarding these settings? Or who should i contact?

[boyan]

Hey, akos.

Thank you for your questions! We should revise the material so that it sounds more reasonable in the near future. Meanwhile, I think the easiest way to handle your task is to use layer system with Cryptomatte.

Cheers,

[akos_kiss]

Hey boyan!
Thanks for the heads up! TBH honest I'am happy with little written explanations, there is no need to modify the documentation There is a bunch of examples for 3ds amx, maya and houdini on how to get the most out of the cryptomatte element. Unfortunately i couldn't figure out how to acces an utilize the more specific modes of the cryptomatte element and thats why i wrote out this lengthy post about it.

[akos_kiss]

Hi All!

I was wondering if someone could help with a few examples regarding the previously mentioned cryptomatte types.
It's been 5 months since the first post regarding these issues and i couldn't find any new info on these elements.

Can someone please, at least just reply in a forum post??? i don't care about the documentation anymore, but it would be great if at least someone could answer any of my questions...

1. This is a bit of a global question but how do i use the User attribute field in the cryptomatte RE settings? Are there any examples on how to use this in c4d? how can i set it up?
2. How do i use the Cryptomatte ID Type "Node User Attribute" ? How can i add custom attributes to an object that vray can read? I tried a types of user data field but none of them worked. I really neeed an example on how to set up custom user attributes because there is no information about this.
3. The remaining id types for the cryptomatte re are also not clear.
   1. What is Node Asset/ Reference name id type? in what situation shoul it be used? I assumed these were refering to instances, xrefs or alembic files in the scene, but non of those came back with any result. What is the supposed usecase and how should we use it?
   2. Sub object name. Is thi only good for vray proxies or vr scenes? no other elements worked for me.
   3. material path, this is a new one, and no info in the documentation. what is it for?

And Material stacking still doesn't work with the cryptomatte re.

[deyan.hadzhiev]

Hi akos_kiss, I will try to answer some of your questions, but keep in mind that I am not an expert on Cryptomatte.

This is a bit of a global question but how do i use the User attribute field in the cryptomatte RE settings? Are there any examples on how to use this in c4d? how can i set it up?

How do i use the Cryptomatte ID Type "Node User Attribute" ? How can i add custom attributes to an object that vray can read? I tried a types of user data field but none of them worked. I really neeed an example on how to set up custom user attributes because there is no information about this.

I'm answering both of this simultaneously because they are related. User Attributes are not yet available in V-Ray for Cinema 4D, but they are planned for the very near future and will be available soon. Once they are available you will be able to add a User Data entry on any object that is included in the render and it will be used by such User Attribute parameters. By the way - the User Attribute parameter in the Cryptomatte RE should be usable only when the ID type is "Node User Attribute" so this is something we will improve on our side.

What is Node Asset/ Reference name id type? in what situation shoul it be used? I assumed these were refering to instances, xrefs or alembic files in the scene, but non of those came back with any result. What is the supposed usecase and how should we use it?

You are on the right path with this one - that is its purpose. It should be used when you want objects using the same asset paths (like alembics or V-Ray proxies) to have the same ID in the Cryptomatte result. Unfortunately, this is not currently working in V-Ray for Cinema 4D and I have logged an internal issue for fixing this (VC4D-1780).

Sub object name. Is thi only good for vray proxies or vr scenes? no other elements worked for me.

Yes - this is used to have Sub Objects (as of separate hierarchy objects in V-Ray Proxy, Scene or Alembic) with the same name register with the same ID in the Cryptomatte RE.

material path, this is a new one, and no info in the documentation. what is it for?

You are right - this is something new that slipped in the list of IDs. Generally it is used to distinguish materials that are included from different composite assets (e.g. two distinct V-Ray scene nodes). Using the full path ensures that even if you have the same material name in both the assets, as long as they are from separate composite components, the Cryptomatte ID will be different.

I hope I answered your questions - please don't hesitate to ask more questions if you need further help.

[akos_kiss]

Hi deyan.hadzhiev
,
Thank you so much for the detailed and fast replies and explanations! This makes things a lot more clear, as i thought that these functions were implemented, but for some reason not advertised for c4d vray users.
Sorry for my late night grumpiness in the last post, but it was really keen on trying these features for some time and was adamant that there is some way to use these options, but there is no documentation for some reason.

The V-Ray cryptomatte implementation is already powerful, but when these missing features are added (especially the user attribute options) it will be a bliss to use!
Please keep us updated regarding these features!

Thank you again for the answers!