how do you assign a light to specific objects?

tmtmtm_f56c8d4bda

I'm using Iray and want to have a dedicated light emitting mesh be used only by specific surfaces. In octane I can set layers. How can you do this in Studio/Iray?

Richard Haseltine

Use Light Path Expressions with the Canvasses feature, in its own tab under the Advanced tab of Render Settings

Tobor

Do you mean you only want certain surface areas of your object to emit light? For that, you can probably use the geometry editor and assign a new surface. Make just that one emitting.

mjc1016

Tobor said:

Do you mean you only want certain surface areas of your object to emit light? For that, you can probably use the geometry editor and assign a new surface. Make just that one emitting.

And/or masks...sometimes on things like consoles/panels masks are the only way to do it.  They may be one big polygon and have no easy way of creating a new surface.  So a mask is made (black and white image...black = off/white = on) with the buttons/indicators/etc colored in white and everything that isn't supposed to cast light as black.

tmtmtm_f56c8d4bda

I gues I'm not good at expplaining it.

 

I have a plane emitting red light and the environment. I have a cube and a sphere. I want the sphere to be lit red and the cube only lit by the environment. 

Richard Haseltine

My answer applies to that.

tmtmtm_f56c8d4bda

I have a plane emitting red light and the environment. I have a cube and a sphere. I want the sphere to be lit red and the cube only lit by the environment. 

Richard Haseltine said:

My answer applies to that.

Thank you Richard. Crap, now I have another whole universe of things to learn... canvas types and nodes - clueless.

 

Is this easily explained? Any chance you might be able to give me some pinters? Thank you.

fastbike1

If you mean lit by the red plane as opposed to internally lit red, the cube will need to have the red light from the plane blocked in some fashion. Iray is a physically based render engine. Light pretty much behaves like real light.

You said light emitting mesh in the OP, for which case you to use the Daz Uber Iray Emissive shader and set the emission color to your desired value.

kitakoredaz

So already richard suggested,  we can controll which light source , what render,, or which light path (diffuse,  specular,  glossy  etc) we need , by canvas setting of I ray.

then composit rendered each canvas image (as EXR, or render one by one as PNG) by paint aprication, which can manage those layer. 

 

 I sometimes use LPE and canvas setting, and your question is good chance to test and learn. again

1 I set scene, with simple HDR environment light source, and make one red mesh light by primitive  plane ,  now I re-name the planelight as "RedEmitterPlane" in daz studio scene tab.

2  locate ,"cube" and "sphere" in the simple room.  then I make canvas1. .   it is "default full render" , and DAZ seems name it as "beauty"type of iray  Canvas.

I render pic of current scene (canvas1 beauty). 

 

3  next I need to set canvas2  I do not know your detail of what you need, then you may change setting, but I set canvas2 , and set type as LPE.

then I plan, canvas2 render scene without sphere , (it become mask)  and without "RedEmitterPlane" light effect.  (though there is still plane mesh , but I set it un-viisible by shader setting and it can not cast shadow too, I do not need to mask shape,  about the light soruce. ), and this scene (cube)  only emitted by HDR enviroment image.. 

then canvas2  LPE need to code like that,    <L[^'RedEmitterPlane']> .*[^'sphere']E 

 

4 finally I need canvas3,  it need to render only sphere  emitted by both HDRI and red meshplane light (if you need, you can emit only by red light plane, without HDRI,, but when I test, I feel the red is too strong,, then I emit with enviroment light too)

canvas3 LPE  is L.*['sphere']E 　

or you can tweak it as <L['RedEmitterPlane']>.*['sphere']E （if you hope, sphere only emitted by red plane mesh light)

5 I render all canvas, as PNG,, then I may composit canvas2 and canvas3,,, but if you have spme 2d photo tool which can manage exr, or compositor,, you can play with exr too.

(after you set canvas,, then render beauty,, and save the image to the directory,,  ds should make all canvas exr on the directory. (then you may need render the canvas1 only,, to get exr)

 

it is simple introduce and test of LPE for you,, you may need to get Nvidia LPE documents,,, in Nvida iray forum ,,,

https://forum.nvidia-arc.com/showthread.php?13657-Light-Path-Expressions

and this official iray  blog may help you,, 

http://blog.irayrender.com/post/76948894710/compositing-with-light-path-expressions

and I know some daz user already show good tutoriall aboout LPE,, in daz studio forum,,  you may serch it too.

==========

 I feel,, blender cycle llight path, with using render lyaer, have more flexbility,, we can divide, or mix k each light path directly,, f

rom one rendered full. exr with setting composit Light path  nodes,,

I do not think, current  iray and ds canvas offer such flexbillity.  to make more complex compsit, I feel ,I must need to set,, many canvas for each light path and obj,,,,etc,,.. Can I expect daz will  offer composit tool for ds iray canvas  ,, like shader mixer?  

 

tmtmtm_f56c8d4bda

@kitakoredaz, thank you so much for the detailed description and images. Really big help!