Why am I getting such poor anti-aliasing with regards to backgrounds ?

[JezUK]

Something which I must get to the bottom of because I get this issue quite a lot - I need to know the solution !

This is showing a cropped part of an exterior render (I've popped this into Photoshop and used a pale green to show the issue as best as I can) - the issue is bad when I put a sky backplate and those trees on the left look awful when that sky background is in place.

It happens not only on the trees, but also on those hedges and the edges of the building outline etc.

Please can someone tell me what the problem is and what the solution is as well ?

It's not the models because, as you can see, it happens to anything, including the building I modelled myself (trees are Laubwerk, hedge work was made using AutoHedge).

Many thanks.

[Moriah]

You have to render with a black background, else you'll have issues with alpha premultiplication, which seems to be the case.

[glorybound]

After a decade I have yet to be able to comp a sky in Photoshop. That white border is always there.

[kosso_olli]

After a decade I have yet to be able to comp a sky in Photoshop. That white border is always there.

Render against black background, not against V-Ray Sky or anything with color.

[glorybound]

That is one of the first things I have tried

[Dubbie99]

This is because photoshop does its maths completely wrong, so you will always get fringing.
You need to comp in an application that knows that 1 + 1 = 2
If you have no choice, then a workaround is to unpremultiply your render after rendering it. Then when you comp it in photoshop it might look ok.
It will only support opaque object though. Anything additive or self illuminated will be wrong.

Adobe is to blame here. They won't fix it because everyone has gotten used to everything they do being wrong.

[Oleg_Budeanu]

You can do basic compositing in Natron - it's free and it's doing math correctly. After compositing background - you can get back to PS and do the rest.

[JezUK]

You have to render with a black background, else you'll have issues with alpha premultiplication, which seems to be the case.

Thank you so much - that worked like a charm

[JezUK]

You can do basic compositing in Natron - it's free and it's doing math correctly. After compositing background - you can get back to PS and do the rest.

Thanks Oleg, anything free and I'm in

[Pixelcon]

Load your background into the VFB as a background layer. Check 'save in image'.

[JezUK]

Load your background into the VFB as a background layer. Check 'save in image'.

Hmmm, I was using my background in the VFB - I'll take another look re 'save in image'.

Thanks

Still, the black background worked very well for me.

[Pixelcon]

That's what I was doing - and is why it doesn't work.

Trust me, as others have said, it's the black background trick that is the solution.

I'm doing exactly what I explained and it works flawlessly. Rendering to black doesn't work 100% perfectly. It still leaves an ever so small black fringe which the vfb trick does not do. I don't really know what to tell you other than 'It works for me'.




PS's defringing options might LOOK like a workaround but they destroy any fine details (like thin branches).

[JezUK]

I'm doing exactly what I explained and it works flawlessly. Rendering to black doesn't work 100% perfectly. It still leaves an ever so small black fringe which the vfb trick does not do. I don't really know what to tell you other than 'It works for me'.




PS's defringing options might LOOK like a workaround but they destroy any fine details (like thin branches).

Hi James,

Sorry, you'll see I'd since rephrased my reply before your set of images

After I posted that initial reply towards you, I'd remembered that maybe I hadn't checked "Save in Image" (don't remember doing so) - so I'll definitely give your solution a try at the next opportunity.

But the black background worked for me and has been posted also by others as the solution including the authors of PSD-Manager - so I went with that option (as your solution came after I was done).

Either way, thanks again, I'm confident that if I follow your exact procedure, including "save in image", then it'll work just as you describe

[Joelaff]

Remove Black Matte has been in Photoshop since at least version 2. I think I recall it was even in the Pre-1.0 betas.

This is specifically designed to unmultiply an image premultiplied on a black background— which is what you want. Defringe may or may not look good, but it is not specifically for this purpose.

Perhaps render to EXR premultiplied on black, then Remove Black Matte with the image still in floating point linear gamma (dark to the eye). Then convert to sRGB or whatever you want for display gamma. (E.g. add gamma 2.2 or 2.4).

I think the difference between VFB and PS with remove black matte is likely the gamma at which this is applied.