Alpha with sky or background object question

[Katachi]

This is a restriction in c4d. I reported it...I think 1 year ago. Hope to see this flattened soon. Anyway, did you try using transparency instead of alpha? (I remember this didn´t work either...however, worth a try as I´m not sure anymore)

And why not using no background at all. Then go to PS and composite with a white bg. Create a PS action for it, then process the whole sequence if it´s an animation.

HTH

[govinda]

It's been a bug all this time, eh? I just speculated that it was premultiplying with the hue used in the background object, even if you use 'straight' as an alpha setting iirc.

[joeski4d]

Thanks for the info... At least I know it's a bug now and not something I was doing wrong.

Replacing the black background in PS with white doesn't work because some of the black remains present in the transition from blue to white (darkens the glow effect).

I guess I'll just have to create object buffers and render some separate passes and composite....

thanks again,

Joe

[Cartesius]

Long standing issue with C4D: Sky and Background kills alpha. Would a big Plane placed behind your objects, with either full white Luminance or 100% white Color combined with a comp tag work in your situation?

/Anders

[georgedrakakis]

thanks for the info, too!
long time i was dealing with a procedural-roof-shader. (http://studiomoccoro.googlepages.com/roof_tiles_1.jpg/roof_tiles_1-full;init:.jpg)
i quit it, cause i thought that displacement and alpha don't get along together.
i've just opened the file and i saw a sky-object for background.
now it's time to set-up the rigdes :)
thanks again!

[joeski4d]

Long standing issue with C4D: Sky and Background kills alpha. Would a big Plane placed behind your objects, with either full white Luminance or 100% white Color combined with a comp tag work in your situation?

/Anders

Thanks, yes I think just using some object buffers with the sky object should do the trick. Not a big deal, but it does add some extra steps... this would have been much quicker if it wasn't for the bug... now I know.

[specs2]

i'm facing that problem at work all the time. we work around that, by rendering the object twice, once with sky and once without. then, you copy the alpha channel from the version without the sky to the version with the sky.
try, if this works for you.

[chromecity]

I just ran into this for the first time tonight. Apparently, I hadn't used alpha & sky & background together before. What was weird about it in my case was that at first it was rendering just fine. Then for no known reason it just suddenly started to ignore the alpha (although the OpenGL viewport previews and material swatches still looked correct). In my case, the alpha was just to matte certain areas 100% out, so I was able to use a compositing tag on the sky to tell it to exclude the objects with those materials and since the sky effects weren't really noticeable on those particular objects anyway, that worked fine. Definitely had me perplexed for a while though.

[williamsburroughs]

Replacing the black background in PS with white doesn't work because some of the black remains present in the transition from blue to white (darkens the glow effect).

Joe

Import the same image into Photoshop and apply the following:
Layer > Matting > Remove Black Matte

This should take away the fringe of Black in the Alpha Channel.

I usually apply this whenever importing 3D composite elements into Photoshop.

Hope this helps.

[pasto]

What about exclusion (compositing tag) ?
Just exclude your plane object from the sky.

[Navstar]

If you use After Effects, try the free Unmult plug-in from Red Giant Software.

edit: that works with images on black backgrounds only. You could run Invert RGB, then Unmult, then Invert RGB again.

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