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View Full Version : Mental Ray, Making objects invisible but still emit light.


motle3
04-20-2004, 08:13 PM
I am working on a project and I was told that you can hide an object from view while still having it emit light with mental ray's final gather.

I am working on an image with a television sceen that I want to have light up the room. SO have made 2 televisions.

an ultra bright version and

a regular brightness version

I need to hide the ultra bright one while keeping the regular one visible.

If anyone has any ideas I would greatly appreciate it.

I have posted the person's suggestions to me below

the part i don't comprehend is:

"So you have two TV screens with two versions of the same shader. One is super bright for creating the FG light and you make it invisible to normal rendering. The other is normal brightness and renders, but doesn't really affect the FG."

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If you need the TV to be brighter and light up the room more, open the attributes of the File texture node and set the Color Gain colour (under the Color Balence section) to something greater than white. To do that, change the colour palette mode to HSV (Hue, Saturation, Value) and change the Value to a number greater than 1 (like maybe 5). That Color Gain value can increase the intensity of the image as much as you like.

It's really great that most values/colours in Maya can be set to any infinite number, it's very usefull!

Now, by increasing the Color Gain, it's fine for a plain colour shader, but for an image it causes a lot of the detail in the image to be lost (not for the FG though, just the actual rendered shader). So you should probably create a second TV screen object and shader to be the rendered screen, and then turn off the Primary Visibilty for the super bright one that creates the FG light.

Get it? So you have two TV screens with two versions of the same shader. One is super bright for creating the FG light and you make it invisible to normal rendering. The other is normal brightness and renders, but doesn't really affect the FG.

Hehe, ask more questions if you need more answers!

The thread that contained the image I linked to before is here:

http://www.cgtalk.com/showthread.ph...hlight=interior

You should definitely check it out and make sure you get to the last page because.....wow! He ends up with GREAT images!

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thanks for any help

motle3

lazzhar
04-20-2004, 10:07 PM
If you turn the Primary Visibilty off you wont see the object in the rendering but it should respond to the FG shadows, reflections..etc

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