 | | | Paint F/X and objects with transparency....?? | Paint F/X and objects with transparency....?? 2003-12-01 - By Duncan Brinsmead
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Some effects are additive e.g. reflected light and glow effects. For these
you do not want to use luminance as alpha. Rather you should simply add the
values onto the image, i.e.
newColor = imageColor + raindropColor
However in your case it sounds like there is also some opacity to the
droplets( in which case you should see something, however faint, in the
alpha channel ).
What you can do in this case is the following, using the standard alpha
generated from the render against the black background(this assumes that the
render's alpha is correct):
newColor = imageColor * (1-raindropAlpha) + rainDropColor
If you are raytracing the droplets (I thought these were Paint Effects?) and
you want the scene reflected/refracted in them you could turn off primary
visiblity on all objects except the droplets and render. If one is
compositing the refractions in the droplets then they should be composited
such that the drops are fully opaque, ( it makes no sense to composite with
partial alpha if the droplet images contain what is behind them ).
Duncan
-- --Original Message-- --
From: maya-bounce@(protected) [mailto:maya-bounce@(protected)]On
Behalf Of zwp1@(protected)
Sent: Monday, December 01, 2003 12:39 PM
To: maya@(protected)
Subject: RE: Paint F/X and objects with transparency....??
Quoting Duncan Brinsmead <dbrinsmead@(protected)>:
> When there is no or little alpha it is not necessarily incorrect. Some
> objects are fully transparent, and yet add color to the scene. In the
> case
> of rain the drops are clear.. it is the specular and reflected
> component
> that adds color to the image. ( if you make a sphere fully transparent
> then
> stick a reflection map on it it will not show up in the alpha channel
> ).In
> these cases you can render against black then composite with an
> additive
> composite.. no alpha and thus no need to block what is behind, we simply
> add
> in some more light. It gets trickier when you have a mixture of
> incandescent
> or glowing transparent objects and opaque objects with antialiased
> alpha
> mattes ... sometimes you may need multiple compositing layers.
>
I was thinking about rendering against black and getting just the specular
highlights...then using the exact same images as a track matte/alpha. This
provided less than desireable results however b/c:
a.) I'm ONLY getting the specular when I render against black. I don't get
the
subtle curved in edges of the rain drop on the glass (the little bit of
shadow).
So basically it just looks like a sliver of white running down the glass
which
doesn't quite look right.
b.) I'm also not getting the curving/refracting of the image behind it.
So the effect doesn't quite add up...but I've come up with another slightly
more complex method to try out...I'll post it if it works (which would also
eliminate my paint f/x problem).
Thanks!
Z
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