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A Mental Ray question...

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I have seen this effect many times in Second Life, for example, in chains, necklaces, etc..

That texture that makes metals more realistic ...  I have tried with mental ray, but the result to the bake time is a black texture... and I doubt that this effect is achieved manually with photoshop and the shadow maps...


Any suggestions? ...or do something that has been overlooked to continue?

Example in Maya Autodesk 2011: Rendered Image

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Hi, Normaly to do those kind of effect you need to use a Hdri Image..I've seen some to sale on the market place so i do imagine you can set a Hdri image to oject but i don't know yet enough about Sl to explain, sorry. But i think you can dig in that direction.

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I'm guessing you're trying to do image based lighting?  If so, it's a big subject, so be prepared to do a lot of reading, and lot of tinkering, before you'll be able to get a solid handle on it.  For starters, you're going to need to know how to work with HDR images, how to set them up as light sources in Maya/MR, how to best light a scene so that the IBL is harmonious with all the other lights, and how to create appropriate materials that respond well to the lighting scheme you're using.  This isn't something you'll be able to tackle after reading just a single tutorial or forum post.  It's gonna be a somewhat hefty learning curve.

This tutorial might be a good place for you to start.  It's older, but it's the best one I was able to find quickly that you can access without a subscription to Lynda or Digital Tutors.  (If you're serious about REALLY learning this stuff, such subscriptions are sooooo worth it, by the way.)  Some of what it covers is outdated technique, since there are options now that didn't exist then, but it all still works.  Remember, it's just for starters.


As for what's going on in your rendered example, I'm not sure why you referred to it as "black".  The chain material may be darker than you'd intended, but it's anything but black.

One reason the chain is dark is because half of it is reflecting the darkness below the model.  I can't tell from the image if you've got a dark gray ground plane underneath, or if it's just empty space, and you've got your camera background set to that color.  Either way, you can't expect chrome to look bright when it's reflecting a dark color like that. 

The reflected sky does look darker than it would if the chain were a true chrome.  It looks more like gun metal, with a deep gray natural hue.  There are many ways to change that.  Among the simplest is to set the material's color to a lighter shade of gray (I'm assuming it's default 50% gray right now), and/or to increase the amount of light the surrounding dome is emitting.


A few side notes:

1.  If your goal is to create realistic chain, I might suggest you ask yourself when was the last time you saw a RL chain made from mirror-polished chrome like that?  I'm not sure I've ever seen one.  Chain links tend to be non-reflective.  They're often highly specular, of course, but they're very rarely reflective. Even jewelry chains, with their smooth-finished links, aren't particularly mirror-like.

If a chain were mirror-finished, it wouldn't stay that way for long.  Chain links rub against each other, constantly scratching and scuffing each other up.  Decorative chains and jewelry chains do it to less of a degree than industrial chains, of course, but they still do it.

So you know, a super easy way to make nicely specular metallics is to connect an ambient occlusion shader to the specular color channel of a Blinn material.  Put a few pin lights around the scene, set to emit only specular light, to give the specular highlights something to pop off of.  Set the material's reflectivity very low, adjust all other channels to your liking.  Presto, believable shiny metal, in just seconds.


2.  What's the poly count of each of those links?  They look really high.  I take it since you put this thread in the building forum instead of the mesh forum, they're sculpties?  If so, you've got 2048 polys per link, if you're using a 64x64 sculpt map.   How many links are going to be in the whole chain?   If it's 50, that's a million polys, absolutely insane.  If it's 25, that's half a million, still completely ludicrous.  If it's 10, that's still over 20,480 polys, roughly the equivalent of three full avatars.

I'd STRONGLY recommend you use mesh for this.  By eliminating all the extra faces that sculpties force you to use, you can make a VERY good looking chain link for around 250 polygons.  That gives you almost 10 links for the rendering cost of a single sculpty.  These, for example, are just 288 polys each:


I made links in the image above in about 10 seconds, created the material with just a few clicks (as described in the previous point), and rendered very quickly, just as an example.  The whole thing took maybe two minutes, including render time.  If I were doing it for real, I would have spent a little more time getting the highlights and the subtle reflections exactly right.  I also would have added imperfections like corrosion, scuffs and scrapes, maybe even some stamp-engraved text, like you'd find on RL chain links.  

Quite obviously, I didn't use IBL for the rendering.  The example was simply meant to show that you can make a good chain link model with a low poly count.  I wanted it to render as quickly as possible, with minimal fuss.  If I wanted to spend more time on it, I certainly could IBL it.


3.  Mental Ray is very powerful, and can do an amazing job, but its got its own quirks, which make setup complicated.  This is one of the reasons I use Turtle.  Everything is just so much easier with Turtle.  But if MR is all you've got, it will certainly do the job.  Just be prepared to spend a good deal of time with it.


4.  If you're trying to do IBL from an image that is not HDR, forget about it.  You'll never get realistic results from a standard RGB image.  There just aren't enough values in 8-bits per channel to make it work.

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Wow.. before say anything, I can only say thank you, good explanation, and logical.

After several tests, The result has been more consistent with the material Pong E, with low reflections and full specular, and ignoring Mental Ray, of course.
I have also tried Binn, but it is not like the example you have given me ... I guess I need practice.


Here is my result ... I hope to keep improving ... and tinkering with Maya... one day must come out.





Using Blinn with ambient occlusion (3 Spot lights, and 1 ambient light).

Relatively good result in rendering

Black Texture in SL

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Looks like you're making good progress.

So you know the rule of thumb for the three most commonly materials is this.  Lambert = matte, Blinn = metal, Phong = glass.  For the latter two, that's not set in stone, of course.  You can make a Blinn look glassy, or a Phong look metallic, or you can make either one of them look like plastic, or polished marble, or what have you.  It's just that Blinns tend to lend themselves pretty easily to kind of surface sheen we see in metals, and Phongs are more easily equipped for a deep gloss type of look. 

Phong E is a smplified version of Phong, with generally sofer specular highlights.  It renders faster than the regular Phong, but is less flexible.

You might also want to consider anisotropic, if you want more of a brushed metal look.


It's hard to tell what went wrong in your last image.  It could be as simple as a texture placement/rotation issue in SL.  I notice the chain itself appears to be upside down from how it is in the rendering.  It could also be a normals problem in your Maya model.  Or perhaps you baked specular only, with no diffuse light.

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