Transparent object emitting light?

[Anonymous]

Hello,

I have an object in Maya 2017 with a Lambert shader and transparency. I want the object to have no shadows, no illumination, no reflection, no refraction, no anything but a sanitary object with transparency not seen by anything else, not seeing anything else, and not producing any render characteristic except itself.

I am rendering with Mental Ray.

I have turned every parameter I can possibly imagine, and related to Mental Ray, off in the Object, the Shape, and the relevant Shader. the only render parameters on are Primary Visibility, Double Sided, Visible in Transparency, and Transmit Transparency. Yet it still appears to be producing either shadows or some form of secondary illumination or occlusion. If I hide the object these rendering characteristics are not in the image. If the object is visible they are there.

I need this one specific object to render in the scene, but independent and exclusive of any of the scene shading. Basically a Constant shaded object that is transparent, but that does not affect the scene nor is affected by the scene. 

It needs to intersect with other objects so rendering it as separate layer or pass is out of the question.

Is this possible? I'm sure I must be overlooking something terribly obvious.

Joey

[mspeer]

Hi!

"Visible In Transparency" in conjunction with "Double Sided" may be the problem.

Please add more details, screenshot(s) and a scene-file.

[Anonymous]

Unfortunately that's not it. Tried every combination of off/on for those two parameters and no change.

In fact after a day and a half I cant ascertain what the issue is.

The one thing that is happening though is that some objects (not all) behind the transparent part of the foreground object are rendering darker than they should.

Essentially I have a plane with a lambert shader and a ramp feeding into the Transparency of that shader. On one side of the plane it is transparent, on the other side opaque. Objects behind the transparent side render really dark for no apparent reason. I can set Primary visibility of the plane off, the plane doesn't render but the objects in the back still render darkly behind the plane object. If I hide the plane it all goes away.

If I turn all shadow production off for the entire scene all shadows go completely away, but the objects behind transparency still render darker than they should.

I'm stumped.

Joey

[damaggio]

Try lambert shadow attenuation to zero...: although you should be using mr shaders only.

[Anonymous]

Tried that no difference.

As for the mental Ray shaders I had tried them too. In particular the mib_opacity shader among a bunch others. But I get the same results.

Incidentally I built this rig outside this scene and tested it there but it gave no problems. I imported it into this scene and I see the issue here.

I've been unable to replicate it outside this scene.

Thanks

Joey

[damaggio]

Well if you want to really solve this you have to upload a screen file already pointed out earlier by mspeer.

[damaggio]

Scene file I mean

[Anonymous]

Sorry.

Scene file is out of the question. Its over 1GB in file size.

I've tried replicating the problem in something small enough to share, but so far I've had no luck replicating it.

I'll try again.

Joey

[Anonymous]

Ok, I was able to perform a reduction on the scene to bare elements and retain the problem. The scene is enclosed.

Everything but the light, sky, camera and object/material with the ramp transparency have been removed and replaced with analogs. Everything else I can get my hands on has been removed, or frozen, which mean none of those thing removed are promoting the problem.

The anomaly occurs most predominantly in the transparent side of the ramp applied to the pyramid. At first it seems to be occurring only in the transparency but the anomaly is also affected by distance.

Further, if I hide the pyramid and render, you will find that significant contributions to the render are removed on multiple objects in the scene compared to rendering the file with the pyramid present.

I don't want this object to do that. It should not respond to anything, and should not affect anything. It needs to have constant shading with the transparency ramp, only primary visibility, affect nothing else in secondary nor receive anything in secondary.

I have gone as far as to turn all shadows off globally and it still persists.

Any insight as to what I have missed here would be greatly appreciated!

Thanks

Joey

[Anonymous]

Its in the Global Illumination.

I turned Indirect Diffuse (GI) Mode OFF in "Render Settings>Quality>Adv Light Sampling"

I then turned Emit Environment Light ON in "Render Settings>Scene>Environment"

It then renders somewhat as expected. Is there no way to make MR ignore all GI for the object?

Joey

[mspeer]

Hi!

I came to the same conclusion. But it's more than just not being able to exclude an object from GI Rendering (GI Next), for Indirect Lighting the Transparency or Refraction of an object is completely ignored. There is a shadow even if the object is 100 % Transparent, this is a bug or missing feature.

If you change to "old" Final Gather you have to set in Final Gather Tracing a value of "2" or higher for Refractions to make it work, but currently GI Next seems to ignore Refractions.

Please report this problem to NVIDIA in the Mental Ray for Maya Forum.

But before anyone starts shouting then use Arnold, for Arnold it's the same (at default settings), you have to enable Advanced -> Caustics in Material first to make this work.

[Anonymous]

Then I'll have to ignore GI for the time being.

I'll post the condition to the Mental Ray for Maya Forum shortly.

Thanks!

Joey