[Bf-cycles] Alpha pass independent from transparent option

Adriano Oliveira adriano.ufrb at gmail.com
Sat Dec 8 19:45:40 CET 2012

Dear Riakiotakis,

Alpha without transparency is not incorrect, it is just one more option for
composing that I would like to have.

Consider this scenario: In a outdoor render, I have ground, buildings and
trees (leaves have oppacity masks), and a sky. In the composition I want to
compose the render with an AO pass. Without an alpha to mask AO, the sky
would get black. I canot use masks based on objectID, due to leaves

In this case, using alpha mask is just fastest and the fring pixels are no
matter at all.

Adriano A. Oliveira

2012/12/8 Antony Riakiotakis <kalast at gmail.com>

> >
> > I understand the risk, but this option is usual in many renders, like
> Vray.
> > The alpha is just an information that can be used in compositions. Some
> > times is good to have alpha mask just to saturate a non-trasparent
> > background, without the need of complex render layers, for example.
> >
> > I think it is more intuitive that the alpha slot in render layer always
> give
> > alpha mask, no matter the trasnparent status.
> >
> It's not a risk, it's incorrect behaviour. In your use case, any alpha
> mask will take non-background colours in the result. The colours at
> the edges of the background will be incorrect.
> Intuitive != correct.
> Also, "many others do something" != "it is right"
> >
> > I believe in freedom :D
> >
> As opposed to slavery in correctness? Freedom to be lazy is acceptable
> I guess. I also get bored when I need to setup render layers. But such
> grand proclamations are a bit out of context I think.
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