antialiasing problem

[aristocratic3d]

Hi,

I am a vray user. but I had to switch back to mental ray for this specific project.

 

Btw, my problem is, I see antialiasing problem in the metal material. However my set up is pretty high and scene is taking too long.

 

Please see my attachment and help me out.[ATTACH]37844[/ATTACH]

[brynmor530]

Which image filter are you using in the MR sample quality? From the pic you have posted it looks as though you are using 'Box'. Try changing it to Mitchell and adjust the width and height to suit your render size. 4 x 4 is a good start point. If that doesn't work try upping the minimal pixel sample to 1.

[aristocratic3d]

Hi,

I have tried your suggestion, but that did not work. I have attached my light and render setup both.

[ATTACH]37861[/ATTACH]

[ATTACH]37862[/ATTACH]

 

Please help me. I dont know why is it happening to me!

 

thanks in advance.

[aristocratic3d]

Hi,

there is nobody to help me? it has been a few days. Please help. I need to ensure my project.

 

Thanks in advance for the help.

[brynmor530]

Have you tired rendering at double the res? That way you can resize the image back to 950 x 425 in photoshop which should remove the antialiasing. More of a work around than a solution but I normally render at, at least 3 times your current render size. Your only other options are to increase the Mitchell sampling size and / or increase the minimum pixel sampling to 4. You'll see a render time hit but in all honesty probably not much improvement in the image quality.

 

Beyond that you'll have to look at your texture settings and the sample rates for things like reflections and AO.

[aristocratic3d]

I was thinking to render in double size too. But where is the reflection sample rate.

BTW, you right increasing sampling does not work.

 

Thanks for the reply

[brynmor530]

If you are using the MR Arch+Design material you can adjust the sampling for glossiness and adjust the reflection in the Main Material Pramaters box. If Glossiness is set to 1 this will be greyed out (Glossy Samples). Try setting glossiness to .99 or below and upping the samples. Under Indirect Illumination in Render Setup, you can also adjust the maximum number of reflections for all reflective materials. It in the section called Trace depth.

 

I've just tried a few very simple test renders and by increasing the Mitchell Filter to 5.0 for both width and height I can remove anitaliasing edges with samples per pixel set at min 1 max 16. Render size set to 950 x 425.

[mattclinch]

i suspect this is a clamping problem due to an 'overbright' background, as the same thing appears to be happening to your wood at the top.

 

master zap gave an excellent response in a thread a while back as to why this happens with bright windows or visible lights, but the same can be applied to an extremely bright background. i'll post it below.

 

This is actually completely "normal", although for most people, unexpected.

 

As a matter of fact, this effect happens in real life with real (digital) cameras too.

 

Here's the thing; Anti-aliasing is done by blending some subpixel samples.

 

Imagine a window, whose edge covers one quarter (1/4) of some pixel.

 

If we are rendering in low-dynamic range (i.e. not to floating point), mental ray clips each rays color to 1.0 (i.e. "white") *before* filtering.

 

This means that no matter HOW bright the window was (1.0, 10.0, 100.0 or 1000000.0) the ray gets clipped to 1.0 (white) and THEN blended with it's neigbours.

 

So for our example with a window that covers 1/4 of a pixel, the result is a 25% gray pixel, which is what you would expect for an anti-aliased white pixel covered to 25%.

 

However, in floating point rendering there is no clipping happening.

 

So if the intensity of the window was 10.0, and it covers 25% of the pixel, this is still a total intensity of 2.5 ... whiter than white (but still rendered on your screen as a "white pixel"! This is no less white than the "white" pixel that results from a pixel that is fully covered by the window. Even a pixel only covered 10% by the window still ends up "white". Yet the wall pixel beside it (covered 0% by the window) is dark. I.e. any pixel that even "touches" the window is full white. You get aliasing!

 

And this is completely normal. As a matter of fact, if you change the exposure in your HDR viewer you will see that when you get to the point where the window stops blowing out, your anti-aliasing comes back!

 

And yes, this would happen to a superbright pixel also in a real digital camera. However, intra-pixel bleed and glare tends to cover this up, it can sometimes be evident in a photographed image.

 

So... how do you get around it?

 

Well, there are two basic fixes:

 

a) Do what reality would do, and cover up the effect with glare.

 

In a real optical system, such superbrights would spill onto neighbouring pixels due to lateral scattering in the imaging surface (film, ccd, or retina of eye) or scattering inside the optical path (lenses, the optical goo inside the eye) and - to a much lesser extent and much less than people think - scattering in the atmosphere.

 

There are numerous shaders and tools to do this, from "glow" filters in photoshop, the Lume "Glare" shader that ships with max, Maya Glow, etc. etc. that all "does the job"... pick one. Use it. Enjoy.

 

b) Intentionally "pre-clamp" the rays before filtering with a lens shader.

 

This is the "best" way in the sense that it gives you your anti-aliasing back. However, be aware that this pretty much precludes you from doing any major exposure changes in post production, so you must already know that the exposure you have in your image is "ok" for how you plan to use it. I.e. the operation you do will pretty much keep blown-out things pegged as "white", and you will kill any detail in the overexposed region by doing so.

 

The problem with this is that doing the exposure in post is one of the main reasons of rendering to float in the first place! So it's a double-edged sword.

 

Anyway, there are multiple shaders to do this: One is the simple mib_lens_clamp shader which... well... just clamps. Duh.

 

A "nicer" and "more gentle" method is to use the mia_exposure_simple shader, which has a bit of control allowing you to do a "gentle clamp" (with the help of the "compression" feature), or the new mia_exposure_photographic (which does it's "gentle clamping" with the help of the "highlights_burn" paremeter). In either case use them in a "gamma=1" mode to keep the result in scene-reffered linear space (but "gently clamped"), since - I'm hoping - you are applying your display gamma in some later display step.

 

 

/Z

 

i would suggest that you try to reduce the overall intensity of your background whilst still getting it to render as white.

Edited June 28, 2010 by mattclinch

[pixelperfectg]

i suspect this is a clamping problem due to an 'overbright' background

I think so too.

 

FWIW in addition to the info Matt provided this issue is also explained in the 3ds Max help file:

http://area.autodesk.com/userdata/forum/r/rough_reflections.jpg