[Bf-committers] Render and Scene Panel Audit?

[Brecht Van Lommel]

Hi,

This all goes back to solving the premul/key alpha problem properly,
I've written about this on the wiki before. It's pretty clear what
needs to be done, but just like color management it's a big
undertaking.
http://wiki.blender.org/index.php/Dev:Source/Image/Color

Basically:

* Alpha mode should be turned into a transparent on/off setting, same
as Cycles. If it's off there is no alpha, if it's on it's
premultiplied.
* RGB/RGBA is a file saving option, does not belong in the shading
panel. This option should default to RGBA and save alpha if it is
available. With the current Sky rendering that is not ideal, but if we
have a transparent on/off switch it makes sense.
* File formats should automatically convert premul <=> key alpha based
on whatever the standard is for that file format. So PNG key, EXR
premul, etc.

I've also moved the Color Unpremultiply option to the color management
panel now. I think Sergey and I agreed on that but forgot to do it.

Brecht.

On Thu, Sep 27, 2012 at 2:09 AM, Guillermo Espertino (Gez)
<gespertino at gmail.com> wrote:
> El 26/09/12 18:38, Troy Sobotka escribió:
>> Suggestions:
>>
>> 1) Migrate Alpha to the Output panel where the other alpha oriented
>> output factors are stored.
>> 2) Migrate Color Unpremultiply to either the Output panel or the Color
>> Management panel.
> Also I think the "sky" option should be re-evaluated. Being the default,
> it does more harm than good, because it's completely useless for
> compositing, and RGBA images created with it will have all its
> semi-transparent pixels contaminated with the sky color, rendering them
> useless for using in other applications without some sort of background
> color removal (like After Effect's "premultiplied with color" option in
> the interpret footage dialog).
> In my opinion the sky background should be an option attached to the
> type of output. If it's RGBA, then sky is useless. If it's RGB without
> an alpha channel, then sky could be an option.
>
> There has to be a way to simplify the workflow, and make more
> straightforward to choose RGB or RGBA outputs, use composite nodes or
> not. That's the key of the problem: The only case when the sky option is
> useful is when the output won't have an alpha channel, so that option
> should be visible only when the output is RGB.
> Currently we have a default with RGB and Sky, and if you want to export
> a proper RGBA file you have to change two options, not one (and if you
> forget one of them and throw a long render you're screwed).
> And if you want to use the compositor you have to activate yet another
> option!
> It's three steps for something that should probably the default behavior.
>
> I haven't thought about this thoroughly, but what about just removing
> the alpha options from the shading panels and leave only the RGB and
> RGBA options there, showed in a more prominent way?
> If the user chooses RGB, it will use the sky background. If the user
> chooses RGBA, it will use the alpha "mode" set in the color preferences
> (premultiplied/straight)* and the "use composite nodes" option will be
> used (and probably the switch could go away too).
> I mean, why do we have to activate that option? What's the problem of
> having it always active when RGBA output is used?
>
> *) Maybe the alpha association should be set in the color management
> panel or even in the user preferences. Having it near the file output in
> the render panel can be misleading and lead users to think that it's an
> option that governs the alpha association of the output file.
> It should be perfectly clear that the option defines the default
> behavior for the alpha association in rendering, which is something that
> can be changed during compositing.
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