Zdepth Recognised In Scanline Render Node

[maya-man]

Hello,

Hopefully I've phrased that title correctly. I did a basic test with a character walking through a room in Maya and I exported the room (as obj) and the camera to Nuke. The character was rendered with a basic beauty pass and a z pass, using mental ray. I actually took the z into shake, put z into the rgb and output it as something nuke could read (floatingpoint exr) then shuffled it back into z - maybe not the best way to go but the depth values were still there.

My aim is to feed the character pass into the BG input of the render node so that the character is correctly z-composed with the room. The online help tips say this is possible if there is z in the BG image. I haven't been able to get this working...is it broken in the current build, am I doing something wrong, or is there a better way of approaching this with other nodes? I'm looking for a semi-automagic solution if at all possible...

Thanks

Michael

[user_deleted]

Hi Michael,

I've never used this feature. Are you saying that the render node is supposed to act as a ZMerge node if the bg image has a z buffer?
I If so you're right, it doesn't work

Just use a ZMerge node instead to merge your character render with the render node's output.
However, you'll have to make sure both z values (maya's and nuke's) are using the same logic.
In Nuke, the z value is 1/distance (objects close to camera have higher values than objects further away) so if the stuff coming from Maya is the same you're fine, if not you might have to reverse one of the z buffers first first and set up the ZMerge accordingly.
Also make sure th Maya z buffer is not normalized.

cheers,
frank

[maya-man]

Frank,

Thanks for the pointers. I will try a zmerge. If you check the render node tooltip help (the yellow boxes hovering over the question mark) then it tells you that a z file in the bg input will be recognised. However it does seem better to do the zcomp outside the render node, even if it did work! As far as the z values I will keep my eye on that. I actually tried mentalray .zt from the framebuffer but will try a regular .iff from maya. Ultimately if this works out nicely I will try a z file from either prman or 3delight so this may be different again.

Actually, just another question, with a zmerge, is it not necessary to have two zfiles as input? Or does it recognise the z information in a nuke 3D scene? I'll have a look at this asap. I did not know of a way to render a z file from an existing nuke 3D scene.

Michael

[user_deleted]

Or does it recognise the z information in a nuke 3D scene<<
yes, the scanline render node by default produces z values if that's what you mean.

[maya-man]

Thanks again. I got this working fine with two intersecting Nuke 3D primitives split off into separate scanline renders then recombined with a zmerge. Obviously there are issues with aliased edges but I've been able to break out the composite a bit more to deal with that. However now I'm realising that it's tricky to blur an occluded zcomposed object in any way, ie soften the edges or add vector motion blur and get the foreground zmerged pixel to correctly occlude this. I'm thinking that using matte ID's, garbage mattes, perhaps zslices etc and just A over B will resolve this, but it may be more trouble than it's worth compared to rendering the approriate passes from 3D...I'll see what I can come up with.

Michael

[maya-man]

Just an update on this for anyone interested: By taking a 3delight z file and using a color expression of 1/Z I can easily comp with Nuke's z output. In my simple test I have a character walking around an object in a room and they both occlude each other at different points. The character is rendered from 3delight and the rest is imported geometry. The basic z comp is aliased edges but it outputs a new alpha that is a good starting point for a clean matte. So I re-instated the characters original alpha and then stencilled out the needed part from the new alpha. Before this I softened the zcomp alpha edge. At the bottom of the tree I just over'd the elements.
Also I unpremulted the character alpha at the start (better to render straight alpha instead though).

I can see how the result can be useable although I haven't gotten into adding motion blur yet.

Cheers
Michael