iray Matte Objects

[dlevesque]

hi, can't find a way to attach the pdf, i've uploaded it on scribd which unfortunately downsamples the images but i think it should be readable, let me know

http://www.scribd.com/danielefoggiat...nvironment-Obj

Thanks.

The goal of iray's matte objects is to make it appear as if the CG objects and matte objects are part of the same scene, i.e. making that faucet look like it's actually on that ground. The faucet will therefore always reflect the ground.

At first glance, it seems to me that what you want is to composite two different layers, a faucet render and a shadow render, without either having any effect whatsoever on the other. That's something that classical matte workflows do provide, but not something that iray provides: iray embeds matte objects within its path tracing logic, rather than implementing matte objects as some sort of compositing operation.

But there's one problem I can solve: that of the background color affecting the ground color. What you really want is to replace the background color by white (or red), without affecting the rendered result. That's OK, but it should be done in Photoshop as a post-render step because everything you provide to iray will affect the render. The background is used by iray as the matte color... You need to set the "Render for Compositing" flag, in the iray matte environment shader, and avoid overriding the background color entirely. This will cause the background to render black, without affecting the color of the ground. You can then use Photoshop to composite the white background at post-render, using the alpha channel.

Does this help?

daniel
iray dev

[conradbenzin]

ok, i see your point, what i think is weird though is that the ambient is being reflected only if i have the enable ground plane checkbox set to on or matte objects which seems to me to be "simply" colorized-mapped and not transparent, the ground plane will be reflected on the object which i thought being matte means also non reflected because if i can exclude it from the direct rays it should be also excludible from indirect ones (reflections, correct me if i'm wrong), well to "skip" this problem i could make a plane and make it matte as obj which will reflect just a little in the object but if i set the environment it makes no sense for me to see it in the reflection...in fact if i set the environment say red in the background switcher the object is not affected at all. about the rendering for compositing i'll try and report back...i've tried days before but i'll recheck.

thanks
Daniele

[conradbenzin]

here i am, i tried what you told me about the render for compositing but the problem is the same as the 4th test render..the ground plane is being reflected and so the biggest problem is still here...comp_gplane.jpgcomp_no_gplane.jpg
so any chance we'll get in the future an option to exclude an object from reflection? i think it would be valuable also for many non archiviz scenarios

thanks
DAniele

[dlevesque]

That's what I suspected. Yet that behaviour is as intended.

The ground plane isn't actually transparent: it resolves to a pre-shaded value, that of environment projected from the camera view. So reflections of the ground plane are meaningful, and probably not what you'd like them to be. Yet what you're trying to achieve isn't actually what iray's matte object workflow was intended for... A faucet floating in space, casting a shadow on an otherwise invisible plane isn't physically plausible. This workflow is more akin to the realm of mental ray's special effects "render whatever your mind can imagine" type of workflow.

Adding a reflection exclusion feature to iray would break it in ways difficult to imagine. The beautiful thing with physically-based rendering algorithms is that they all fit together like puzzle pieces. But if you break one rule (e.g. add reflection exclusion), the rest falls like dominoes.

What iray could do very well is place that faucet in a photo of a kitchen counter, and you wouldn't believe that the faucet wasn't part of the photo in the first place!

cheers
daniel

[conradbenzin]

Adding a reflection exclusion feature to iray would break it in ways difficult to imagine...the rest falls like dominoes


i understand

thanks
daniele

[wulften]

Hi,

I've just tried to use the plugin in max 2013 and I have ran into a problem. I'm trying to composite a basic scene (ground plane, with a teapot and box sat on top), it's lit with a HDRI map and a single photometric target light so there are harsh shadows from the teapot casting onto the floor and onto the box next to it. The problem appears to be that when I assign the box and plane to the 'matte object' list they only receive shadows from the HDRI/GI solution. The shadows from the spotlight disappear.

If I remove them from the matte object list then the shadows appear again (but of course so do the objects). This makes it impossible to composite. I figure this is pretty basic so I must be doing something wrong. Can anyone help?

[dlevesque]

Hi,

I've just tried to use the plugin in max 2013 and I have ran into a problem. I'm trying to composite a basic scene (ground plane, with a teapot and box sat on top), it's lit with a HDRI map and a single photometric target light so there are harsh shadows from the teapot casting onto the floor and onto the box next to it. The problem appears to be that when I assign the box and plane to the 'matte object' list they only receive shadows from the HDRI/GI solution. The shadows from the spotlight disappear.

If I remove them from the matte object list then the shadows appear again (but of course so do the objects). This makes it impossible to composite. I figure this is pretty basic so I must be doing something wrong. Can anyone help?

Try tweaking the "Environment Shadow Mixer", as described in the blog post:

http://blog.irayrender.com/post/2165...n-3ds-max-2013

daniel

[juang3d]

Hi.

I have a question regarding this shader.

I know iRay is not supported in Maya, but i'm testing it with very good results so far (i own a maya and a max license).

I tried this shader, with the included include file, so far is working great, i had to figure out how to insert matte objects, but is pretty simple, just input the "Inst Obj Groups[0]" from the mesh node of the object into the "Matte Objects[0]" of the matte shader node and it works pretty well.

Now i'm stucked with one simple thing, the environment map, there is no way to make it work.

If i use the physical sky in the environment slot of the camera, it works pretty well, but if i use it in the environment map of the shader, it doesn't works.

Can someone tell me what should i put there to get an environment? i want to use an HDR or EXR to illuminate the scene, it works without the matte environment, how can i do that?

Thanks.

Cheers.

[rlevene]

Hi, I am starting to test iray and I am wondering how did you get the matte object to work with refraction as seen in the car table top example video.

Many thanks,

Richard

[dlevesque]

Hi, I am starting to test iray and I am wondering how did you get the matte object to work with refraction as seen in the car table top example video.

Many thanks,

Richard

I modeled the glass and water with appropriate (refracting) materials, then flagged the glass+water as a matte object. The rest is automatic .

daniel