i have a question:
is it possible to measure reflectance function within 3d package (like 3dsmax)?
i’m asking, because many times i tried to achieve photorealism with shaders and in most cases i do not have enough control for it, for example velvet: every tutorial sas “just apply fall off map”, ok, for rounded surfaces it looks fine, but for, lets say, box with small chamfer it looks like crap, i read many article about measuring brdf in real life, its done with rare and expansive equipment that i obviously don’t have, so i thought: why do i need it? i can build the surface (for velvet that would probably be something very furry) in my 3d package and then calculate its reflectance for a regular model (sort of baking a texture), the question is HOW CAN I DO THAT?
is there any plugins for it?
Short answer: not that I’m aware of, no.
It is possible to do this, and it’s something I’ve been wanting to write for a long time, but haven’t had the time so far.
Thanks for the answer playmesumch00ns, i hope some day you will find time and write the plugin, so if i’m unable to measure brdf, can i at least use brdf data that someone else calculated? I mean is there any library of shaders with measured brdfs in the internet that i can use in Max (vray , mental ray)?
Maybe I’m wrong, but there’s an advanced BDRF, and simplified - like in max, vray and so on.
And materials may substantially differ in different conditions:weathering, wearing, getting wet, admixtures, differences in lighting conditions, exposure, almost infinite. So, you need some general guides for common materials, and then adjust by your eye. Maybe maxwell can be your choice as long it gives quite realistic results and works by another algorithm of materials.
You can try those schemes to start from:
reflection:4-5%\100(fresnel - towards-away)
refration: 1.5-1.8, depends from type
refraction: 1.33(the majority of transparent liquids)
(Plastic 1.46 - 1.55
linoleum, laquered floor(гhybrid materials, layered)
reflection: 5%\50)(laquered furniture)
typical wooden laquered floor
reflection(total):75%(linoleum a bit less)
diffuse is less saturated than plastic’s, more pale
only metals have colored reflection
diffuse:black(chrome), worn - a bit lighter(alluminium)
some more refraction indexes:
Rubber, Natural 1.51
Eye, Aqueous humor 1.33
Eye, Cornea 1.38
Eye, Lens 1.41
Eye, Vitreous humor 1.34
Emerald 1.560 - 1.605
There are BRDF databases like the CUReT database: http://www1.cs.columbia.edu/CAVE//software/curet/
However I don’t know if there are any shaders available for using these sort of data. There are also companies who will calculate a BRDF for you from a given material sample if you have something particular in mind.
thanks, but this is kind of general material properties, i’m trying to achieve the look of surface, caused by it’s micro texture, things that eye is unable to see, but that make the material look diffuse, isotropic, anisotropic, rough etc.
thanks for the link, i heard that in Matrix movie they calculated brdf for clothes with reflectometer from NASA, and used this data in mental ray, do you have an idea what shader they used, is it possible to find it somewhere?
Yes, I understand what you mean, but in vray and I guess mental ray those are simplified and generalised versions without a possibility to use a custom external data.
Yes there was a lot of hoo-hah about their lightstage stuff and they hired a gonioreflectometer to measure material samples.
I heard from someone on the production that they never ended up using it, which is why for all the fancy-pants wizardry the cloth looked like a blinn. Because it was a blinn.
I would assume the shader that they used (for the tests at least) would have been custom-written at ESC, and probably would just have read a massive lookup table, or some compressed version of the data. Either way, without the reflectometer measurements (not cheap), it would be pretty useless.
Slightly off topic… but I’ve been dying to ask that for a while??
What is BRDF??
I know what the term BRDF stands for, But…
Some use the term to refer to the common reflectance models “Lambert, Blinn… etc”.
Some Use it to refer to custom written “illuminance” loops.
and Some use it to refer to data measured from real samples and some fancy stuff that I have no idea what it means!!
minaragaie take a look at these link :
and the paper about cloth brdf in matrix :
I found a very cute shader for max - Moodee, you can download it at maxplugins.de, made some tests with velvet, i used shellac with rough oren-nayar-blinn as base and Moodee as coated with custom reflectivity (specular) curve, unfortunatly it works only in scanline, does anyone know any shader for mental or vray that has such control over the reflectivity (not only specular)?
thanks alot popol… I kindda knew most of it already… I was asking more about the common usage of the word in the industry. my bad the question wasn’t clear enough.
anyway… it’s slightly off topic so I’ll give it a rest not to hack this thread
Great information here!
You guys are great.
One question though, in the above examples you give numbers like this-
what does the \100 mean?
It is a fresnel rate of reflection towards\away from the point of view, or “front\side” in a falloff map type in 3ds max, which is usually used in the Vray material in reflection slot. Or if you use Mental ray the Arch&design shader, it is BRDF -custom reflectivity function - 0 deg refl(front)\90 deg refl(side).
Thanks for all this great info!
I don’t know how I’ve managed to not spend much time in this section since becoming a member.
2 threads in this section have given me more information in the last few days than most other sections have in the last few months.
I’m gonna add these values into the pdf about CG science then.
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