<div>Alpha is not "intuitive"! I thought the same thing once but I was wrong. -1 on forcing an alpha pass that's incorrect. Link to my old bug report<br></div><div><br></div><div><a href="http://projects.blender.org/tracker/?func=detail&atid=498&aid=32704&group_id=9">http://projects.blender.org/tracker/?func=detail&atid=498&aid=32704&group_id=9</a><br>
</div><div class="gmail_extra"><br></div><div class="gmail_extra">I'd recommend reading a good book on compositing like</div><div class="gmail_extra"><br></div><div class="gmail_extra"><a href="http://www.amazon.com/Science-Digital-Compositing-Second-Edition/dp/0123706386/ref=sr_1_1?ie=UTF8&qid=1355004081&sr=8-1&keywords=art+and+science+of+digital+compositing">http://www.amazon.com/Science-Digital-Compositing-Second-Edition/dp/0123706386/ref=sr_1_1?ie=UTF8&qid=1355004081&sr=8-1&keywords=art+and+science+of+digital+compositing</a></div>
<div class="gmail_extra"><br></div><div class="gmail_extra">We need to adapt our compositing tricks to the more modern ways of cycles and not the other way around :) So far I've managed to do everything I've needed (minus group lighting but that will come)</div>
<div class="gmail_extra"><br></div><div class="gmail_extra">don't get offended by this, just trying to help</div><div class="gmail_extra"><br clear="all">Daniel Salazar<br><a href="http://patazstudio.com" target="_blank">patazstudio.com</a><br>
<br><br><div class="gmail_quote">On Sat, Dec 8, 2012 at 1:47 PM, Brecht Van Lommel <span dir="ltr"><<a href="mailto:brechtvanlommel@pandora.be" target="_blank">brechtvanlommel@pandora.be</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
Hi,<br>
<div class="im"><br>
> So I would make the following suggestion to avoid the ambiguity:<br>
><br>
> 1- do as you said and switch key/premul based on output format (with a a<br>
> choice if the format allows both) in the output file settings.<br>
<br>
</div>Yes, probably there would be 3 choices: automatic, premul, key. I'm<br>
not sure about the design yet, it's probably not feasible to make the<br>
compositor keep track automatically of what the user did. I'm thinking<br>
there would be some settings that says if the compositor outputs<br>
premul or key, and based on that it could do automatic conversion to<br>
the file format then.<br>
<br>
So there would actually be 2 settings, but I would hope that in nearly<br>
all cases the compositor output type can be set to premul and file<br>
format to automatic. This should work for the cases where you use<br>
typical intermediate formats like OpenEXR and TIFF, and do final<br>
output either without alpha or with alpha in a web format like PNG.<br>
<div class="im"><br>
> 2- allow switching key/premul in renderlayers regardless of output<br>
> format , and make them a sane and consistent default (regardless of<br>
> output format chosen, maybe something suitable for openexr).<br>
<br>
</div>Not sure what you mean by this, where this switching would happen. But<br>
basically anything that comes out of a render engine is naturally<br>
premul. OpenEXR is always premul, and TIFF has metadata to indicate<br>
which alpha type was used. For intermediate formats premul seems the<br>
best option.<br>
<br>
Layers can be converted to key after rendering but there's no<br>
information to be gained there, and it would give some information<br>
loss for surfaces that are both emissive and transparent (though<br>
that's no so common, maybe for fire volumetrics or so). I think it<br>
would be good to make compositing nodes work by default with premul as<br>
a convention, so blur type nodes would have to do no conversion, and<br>
color correction nodes would optionally convert to key and back.<br>
<span class=""><font color="#888888"><br>
Brecht.<br>
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</div></div></blockquote></div><br></div>