CGTalk - glow reflection problem

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j00ey

07-28-2003, 09:15 AM

hi all
this is probably a really simple one [or not possible]
i want my heating elements to glow in the reflection in the flat perforated base plate similarly [but less intensely] to how they do when they themselves render.
i know in max only the raytracer will reflect / refract material or object ids and hence glow them in post processing. obviously maya doesn't work the same way as this is obviously all raytraced... but is there a way to achieve this? or is it an afx job?
thanks
j00ey

alexx

07-28-2003, 11:01 AM

glows should always be done in post.. - and yes: reflections cant glow when rendered in maya.
so i would suggest afterfx or any other post app..

just render out a mask pass for the elements you want to glow.

cheers

alexx

j00ey

07-28-2003, 11:16 AM

thanks alex

when you say render a mask pass, do you mean render just the elements with alpha [with matte material on the objects obscuring them, like the meat] and use that in afx?

also is there any way to isolate the elements' reflection and generate alpha from it? sounds unlikely, but just wondered.
thanks
j00ey

alexx

07-28-2003, 11:24 AM

yeah.. just render a black and white image.. the obscuring objects black and the glowing ones white.. you dont even need a proper alpha channel for that..

and yes.. you can render just the reflections with a trick:
you can set the primary visibility of the reflecting object to 0 (switch it off).

like that you can have the only the reflections visible but the object itself not..

before you are asking: no: maya does not have a reflection pass..

if you want to render reflections only:
render full image with reflections, then render the exact same image without raytracing, take both images in a compositing app and subtract the two.. now you only have the reflections..
now you can tweak them (e.g. blur) and in the end just add them over the image that you rendered without reflections before..

cheers

alexx

j00ey

07-28-2003, 06:47 PM

thanks alex
i'll do the glows as you say and try the primary visiblity trick you suggested.
i'll post a pic when meat etc is done
j00ey

alexx

07-28-2003, 06:53 PM

cool.. hope it works out for you :)

that is the way i would do it

cheers

alexx

TheWraith

07-28-2003, 07:38 PM

could it possibly work if you rendered out a pass without the glass? so that you have a nice rendering of the object glowing and not being reflected or refracted and then use that as a texture on the glass? maybe put it on an image plane if you needed it refracted or just throw it in the reflected color if you need it reflected only. hmm.... it sounds like it'll work in my head but i've never tried it before

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