Using alpha file to drive luminosity?

# 1 27-05-2005 , 01:19 PM

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I'm working on some skyscraper tests for a cityscape and have a question regarding the use of an alpha map to drive luminosity. I spoke to someone who has done this in LW and he sent a couple sample files for me to play with...one is the skyscraper texture file which I've plugged into a blinn's color node. The other is an alpha of the skyscraper file's windows which he basically said he was using to drive the painted windows' luminosity to give them a yellow glow. I've tried plugging this into various attributes like incandescence and via connection editor "Alpha is Luminance" into several things like Glow Intensity, Incandescence, etc. but still haven't gotten it right. Can someone point me in the right direction on how to do this?

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# 2 27-05-2005 , 03:37 PM

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uhhh... ambient? with some color correction on the file node?

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# 3 27-05-2005 , 03:49 PM

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could you post a small version of the map? there should be an easy way to do this..

my first thought would be to maybe do it separately so what I would do is an ID pass. So make a new lambert and make it's ambient value pure white and it's colour pure red 255 0 0. You then need to matte out the rest of the skyscraper geometry (are the windows and building separate?) so you may need to use the window aplha map to mask out the building. Then run that as a separate pass you can then use the red channel from the resulting image to control a blur/glow attribute in your compositing program... easier than re-rendering over and over again

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# 4 27-05-2005 , 06:45 PM

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I'm not at liberty to post the maps unfortunately but it's a very simple setup. All it is is the painted color map of a side of a building (grayish for the building and pale yellow for the windows). The other file is the alpha version (windows are various shades of white gray while the rest of the building is black)...similar to how youd prepare a file for bumpmapping or transparency.

I'm sure it would be easy in a compositing app to just load the alpha selections and color/blend them in but I'd like to be able to achieve the same thing in Maya. There has to be a way to use alpha to enhance or control the window color and glow amounts.

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# 5 28-05-2005 , 10:43 AM

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if you're using a maya glow then you can just put the greyscale map into the checker box beside the glow intensity in the shader. I just tried it with a black and white checkerboard and it worked like this:

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# 6 29-05-2005 , 04:37 AM

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I wasn't using glow but I did do some experimenting with it tonight. Not really what Im looking for, though. I'm going to do a bit more experimenting to see what I can up with....would defintiely be better to do this in post. I keep thinking more along the lines of what you'd do in photoshop...load an alpha, fill with a color and adjust layer modes. I'm sure I can get what I'm after messing around with utility nodes and whatnot...will just take some time.

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Using alpha file to drive luminosity?

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