[mighty_haav]

I'd like to have something like this: http://www.v-ray.com/features/new-skin-shader/

Why is it so hard to get Maxwell to render skin (in a reasonable amount of time)? I'm new to Maxwell and I thought that "physically correct" means you can render everything physically correct. But while this is true for archviz it seems to be really difficult to use Maxwell for characters.

Regards,
Michael

[eric nixon]

'Physically correct', only applies to opaque surfaces and homogenous substances. Many partailly transparent objects such as foodstuffs or animals are not homogenous. This is the essential problem.

[numerobis]

... everything physically correct. But while this is true for archviz ...

not really... with the limitations of AGS, caustics through dielectrics and only theoretically possible dispersion......

[Mihai]

Why is it so hard to get Maxwell to render skin

And in reality, what is "skin" for you? Define that please.

Here is one (simplified) definition:



So, have you modeled that stuff? What shader should each of those parts have? Now in this newly discovered context, read what you wrote here:

I thought that "physically correct" means you can render everything physically correct.

[eric nixon]

And then consider how the geo would look in order to comply with the 'russian dolls' principle of multiple transparent parts. And then consider the render time!!!

So the only answer is for NL to code a BIASED skin shader using black magic math, which doesnt break the rest of the algorithm.

Maybe 'cg people' is actually a dead end creatively, a bit like cg vegetation but more of a dead end... I can see why clients ask for it though.

[mighty_haav]

Mihai, what do you want to say by posting that image? Do you want to say that Maxwell is unable to produce any "real" looking characters without modelling every single cell of a human being in a detailed way that no client on this planet is willing to pay for? Serious?

I mean: Maxwell is a tool to produce desired results. And it should do that fast. Do you really want me to tell my clients: "Oh, sorry, you'll have to wait another 2 month until I've modelled the last veins and another few millions of cells ..."? Not really.

So you've got all this nice stuff to "fake" reality like Maxwell hair/fur, Maxwell grass, Maxwell sea ...
It's really time for Maxwell skin now!

Regards,
Michael

[seghier]

what i like in maxwell render that maxwell team always find the best solution to get the best result ; thay think about what the users need.
maxwell need special skin material with quick setup of textures ; it's not easy to create skin material using translucent material

[Nasok]

Well I'm super MAxwell's team will come up with special "skin" preset in material constructor .. It is definitely possible to simulate realistic skin with scattering and al that fancy look and feel - it's just ton that obvious on how to tweak the standard material to get the desired look.

So I guess .. it could be very simple input from MAxwell's team on giving the "default skin" preset in Material "wizard" so you could understand the workflow and tweak as desired.

[Mihai]

I thought that "physically correct" means you can render everything physically correct.

Michael, I wanted to draw attention to that statement above and make you realize it has no meaning to look at reality in this way. Glass, plastic, metals, you can say these are substances. Maxwell can render them very accurately because they are a homogeneous medium, and there are very clear rules about how these homogeneous substances interact with light. So in this case your assumption would make sense.

Now, is "skin" a substance? You might as well be asking, why is it so hard for me to render a kiwi? I thought it could render everything physically correct. Just pointing out that you are right to ask for a dedicated skin shader that will try as best it can to mimic all the different structures that really make up skin, but if you thought by physically correct, it suddenly means Maxwell can render "everything", your thinking will lead you to many more dissapointments.

Why is it hard to get a realistic skin "look" in Maxwell? Because the volumetric Sss material is designed to mimic a homogenous translucent material, and not all the stuff you can find in "skin". While you can get close to some sort of skin look, it's difficult to control and since it's fully volumetric, can also take some time to render.

[rusteberg]

I've never tried skin with maxwell before, so I found this model: http://www.turbosquid.com/FullPreview/I ... /ID/739758 and gave it a try just using the maps that came with the model...

[Fernando Tella]

Good attempt!

I think the key when rendering skin is on the textures more than the shaders.

I mean, Maxwell has an universal shader that works for everything; that should do the job.

[Mihai]

I'm talking to myself....

When the look of something comes more from the structure, than the substance itself, you can't really do it with a general shader.

[rusteberg]

sooooo, then why even bother with trying to render organics at all? why bother rendering anything for that matter since everything is organic and has an infinite material structure which as you say "you can't really do with a general shader"?

in this case why would a double sided material even be relevant for an organic leaf structure?



don't take it personally Mihai....

[eric nixon]

When making leaves or grass blade mxm's I actually try to include the effect of the upper palisade cells - because the cell walls are packed together vertically, less light is scattered sideways. I use the assymetry value to describe that more light is scattered inwards and a little bit is scattered outwards, but v. little is scattered sideways.

Anyway your post is just a distraction because leaves are thin. The issue of rendering non-homogenous VOLUMES remains. I noticed that Thea render (hopelessly academic renderer) has made some advances in this area with the ability to include procedural volumetric 'maps' to control sss density and colouring.

I hope we see that functionality one day.

[Mihai]

in this case why would a double sided material even be relevant for an organic leaf structure?

Well for one as Eric points out a leaf has much less volume to describe and compared to the distinct layers of skin that can go several mm deep and contribute to the final look of the skin - it's easier. Double sided materials simply make it a little easier to create realistic leafs for the simple reason that it allows you to increase the realism by using two different textures - as leafs usually have one side rougher veiny looking and the other shiny smoother looking.

But when it comes to describing a complex structure and volume of several mm thick - trying to make this somewhat believable with a general volumetric sss that's ment to render accurately homogeneous materials is not an easy task, if possible at all. Its limitations become much more apparent compared to trying to render a thin surface such as a leaf. Besides needing a description of the various layers of skin, and veins and fat that make up its volume, you also need a way for the light to stop at a certain depth and start bouncing back, you know, we have bones and stuff, and that also contributes to the final look. This is yet another thing which the volumetric general sss material isn't capable of doing. You give it a head model - it's going to handle it as a giant piece of some sort of sss material. So, unless you start also modelling the bones beneath the skin, you need a dedicated skin shader which tries to mimic this, among other things.