Bad anti-aliasing on bright glossy reflections and backgrounds

[Burnsyman9000]

Hello, I 've been using Vray for about 6 years and have noticed a new issue that first came up when I switched to Max 2010 and Vray 1.5SP4a. Before this I never had an issue with bad antialiasing in Vray. Basically any material that has a very bright reflection of Vray Sky and Sun seems to have a lot of aliasing on it. It also occurs when an object is set against a very bright background like in the second image. I've attached 2 sample images showing the problem I have. I use Vray Sun, Vray Physical Sky, Vray Physical camera and linear work flow. I've also attached some screen captures to my vray settings. As you can see I'm using pretty high setting and sampling rates and still have the problem. The ADMC image sampler is set to use the DMC sampler noise thres and is set to 0.001. It has min and max subdivs of 1 and 8. The subdivs on all glossy reflections in the materials are all set to between 25 and 40. I think these are all very high quality settings, so why do I have this aliasing problem? the only way I can get rid of it is by using an AA filter like quadratic or vray lanczos, but I never had to use any AA filters in the past and I don't like using them because they blur the image. Any help, pointers or links to other threads would be really appreciated. Thanks!

[Burnsyman9000]

also here are my camera and sun settings:

[sduck]

Have you tried checking sub-pixel mapping and clamp output in the V-ray: color mapping?

[Burnsyman9000]

I have a little but wasn't really happy with the results. The vray help files suggest keeping sub-pixel mapping off is more correct, and I found that using clamp output made my images look a bit muted and dull, like it took away some of the contrast and punch. Do many other users turn these settings on?

[sduck]

There are a ton of posts concerning AA and sub-pixel mapping. The problem arises in cases similar to your mullions being AA against the sky. Just as a test try a checking them and do a region render of your mullion area (interior looking out image). It might help.

[Burnsyman9000]

O.k. sweet, thanks sduck, I can see that this is helping a lot. On my interior scene looking out, sub-pixel mapping completely fixed the problem without even needing to clamp output. For some reason on the exterior is doesn't totally fix the aliasing, it did improved it a lot though. Here's the exterior without sub-pixel and no clamping, then with sub-pixel and clamped to 1.0.



Is there anything else I can do to help with the last bit of aliasing in this case? Higher ADMC image sampling, or do I have to start using AA filters to fix it?

One question about clamping the output. If I clamp it to 1.0, and then save as 32bit OpenEXR and add glows and DOF in after effects, won't the clamped output have an impact on those effects? Wouldn't it actually remove the hdr info from the exr and make it more like an 8bit image like tiff or jpg?

Thanks again for the help!

[sduck]

I am glad it is helping. If you will be doing post work with glows, then do not clamp the image. Concerning AA filters there are a ton of threads on the forum. Many suggest NOT to use the filters and render much larger then you need and reduce the image yourself.

Image sampling and settings are discussed in depth in Brian Smith's article --- Week 17: An In-Depth Look at Image Sampling

http://www.cgarchitect.com/news/newsfeed.asp?nid=3524

Lots of good information that would help with your exterior image issues.

[Burnsyman9000]

saaa-weeet, thanks, this helped a lot, really it was sub-pixel mapping that made all the difference, thanks again!