Bassam: that sounds nice, what about image input nodes? convert all to premul based on image type?<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 6:52 PM, Bassam Kurdali <span dir="ltr"><<a href="mailto:bassam@urchn.org" target="_blank">bassam@urchn.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi Brecht, then it's perfect,<br>
<br>
- output files dictate the choice,<br>
<br>
- renderlayers are always premul.<br>
<br>
I had been initially scared you meant the renderdlayers themselves would<br>
end up switching their alpha between key and premul based on the output<br>
file choice!!<br>
<br>
Suggestions for the renderlayer nodes: a convenience 'key alpha' check<br>
box that does a convert to key alpha if checked, removing the need for<br>
the extra node... benefits:<br>
<br>
1- removes need for an extra node in some setups.<br>
2- communicates to the user that the renderlayer is (unless you check<br>
it) with premul alpha.<br>
<div class="HOEnZb"><div class="h5"><br>
<br>
On Sat, 2012-12-08 at 20:47 +0100, Brecht Van Lommel wrote:<br>
> Hi,<br>
><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>
> 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>
><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>
> 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>
><br>
> Brecht.<br>
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