Alpha channel for editing background in Rendering 32 bit .EXR vray 3ds max

[torstenmiddelkoop]

Hi guys,

 

I have some difficulty with my render in postproduction in photoshop.

I rendered an exterior with lots of trees. I use vray sun and sky. The render output is 32 bit .EXR. Now when i open the rgb color i need to get rid of the sky background. I would also like to keep the transparancy of the leaves. If i look in the channels i can see an alpha channel, but clicking on it only makes it pop up pink. The goal is to put in a background myself in postpro.

 

The hard way that i did in previous works is selecting the black parts of the alpha render pass and delete this part from the rgbcolor. Problem with this is that i don't have the translucency in the leaves and also white borders around the cut out rgbcolor pass.

 

Does any one of you know how to tackle this problem?

[Corey Beaulieu]

Holding Ctrl while you LMB on the Alpha Channel should load that into your selection. Then add a mask to the layer or folder you want the sky removed from.

[torstenmiddelkoop]

Hi Corey,

 

Yes I know that method. But you will end up with white borders around your edges. I hoped that when i import 32 bit in photoshop it would automatically delete my background. If i import it i can choose for Alpha Channel Data: "as transparency"or "as alpha channel". But neither of them give me an image without the background.

[Corey Beaulieu]

Sorry. I didn't want to assume anything. I figured that was too simple an answer.

 

Generally speaking, in a sky replacement, you will likely always get a small bit of fringing. This would be due to the the fact that the edges of your 3D object colors are premultiplied against the old sky color. This will leave an artifact of color and can be very annoying. Your best bet if you know you want to replace the sky is to use you sky image for reflections only and not the visible background. An alpha channel that is premultiplied against black will only filter the edges and leave you able to slip any sky behind your render without any halo effect.

 

I've certainly rendered against a visible sky and I do know what you are talking about, but the sky I have replaced it with is generally pretty close so the halo is not noticeable. Are you getting something more egregious than that? Like you use the Magic wand tool on it and it isn't getting a good selection?

[jasonstewart]

Layer>Matting>Defringe may help but seems Corey has the best solution going forward. You will need to collapse the Alpha mask before using Defringe just so you know.

[torstenmiddelkoop]

Hi Corey and Jason,

 

Rendering against a black background seems a good option indeed. But sometimes i need to have a sky already when i do edits in 32 bit format, like glow or diffusion.

Seems there is no perfect solution.

 

Thanks guys

[rogue3d]

May not be as bad as you think. Try converting it to a 16 bit image and see if the halos are as noticeable. I've noticed that this effect is more exaggerated in 32 bit. Not the best solution but might be workable without a rerender.