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Author Topic: Plastic looks of 3D vs fractals and reflections  (Read 571 times)
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Alef
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« on: September 29, 2017, 05:21:06 PM »

Well I used to get bored with 3D and it's plastic looks. This is no way a property just of 3D fractals. To examine 3D in turned on TV and looked on few cartoon channels for kids.  They alll are plastic.

Many fractals have small holes so sometimes are "sandstone", "chalky" so they don't feel so plastic.


So I searched the wikipedia pages to search for light effects and properties.

Article with lots of text blablabla, but it gives some hints:
https://en.wikipedia.org/wiki/Transparency_and_translucency





And more interesting article with lots of beautifull pics:
https://en.wikipedia.org/wiki/Lustre_(mineralogy)






3D typical plastic boy


Waxy lustre of jade:


Lustre of this object needs to be examined more closely:


Mineral with silky lustre:


So it seems that all of these effects depends on translucency and light reflection by micro structures. All of the mineral properties of "silky", "greasy", "waxy", "pearly", "metallic looks" or "asterism" is based on non-ideal reflection of light.
Plastics have ideal chemical structure. And most of equations for reflections on material is for ideal solids. Aka "quation of ideal gas". Then only other ideal is metallic shine.


I realy don't have any advanced 3D software. (I don't have it at all). But if they would have "waxy" reflections probably humans in 3D cartoons would not look so plastic.

I think some random scatering of reflected light (I meant shine from light not reflection of objects) and slight reflection of light deeper into the solids could simulate more natural looks.

Of corse opalescent mandelbulb would be just wonderfull. But all of the properties of light like reflections according to spectrum and all the spectral effects of light would be mutch too hard to program.

Bismuth is magical element. Metallic lustre:

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hobold
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« Reply #1 on: September 30, 2017, 09:25:24 AM »

Collection of relevant buzzwords for further googling:

These days the "plastic" look of computer generated imagery is mostly caused by not wanting to spend more time and money on cheap TV cartoons. The state of the art in computer graphics is "physically based rendering", meaning that the software accurately models the physics of light in as much detail as the user of that software desires.

The effects that you observed are modelled with something known as "Bi-Directional Reflectance Distribution Function", usually abbreviated to "BDRF". If the BDRF is allowed to vary with wavelength, then materials like Bismuth are covered as well ("spectral rendering").

Translucency is caused by light traveling through solid matter and being scattered there. Even material that we think of as opaque can permit light to travel a short distance through it, without being completely absorbed. If that light happens to exit that same surface again in a nearby place, there is a substantial influence on the overall look of that material. The most common application of this is "subsurface scattering" to more accurately model the look of human skin.

Translucency in general is a subset of light interacting with the medium it's travelling through. Effects like mist, fog, "god rays" / "volumetric shadows", are all caused by light _not_ travelling unimpeded in a straight line.

And finally there is the modelling of the wave nature of light, to render interference or diffraction. These effects are usually subtle and rare. To my knowledge, no professional rendering software implements general wave rendering. However, things like soap bubbles and iridescent butterfly wings are everyday phenomena, so the renderers usually provide some tricks to approximate the effect in plausible ways.
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Alef
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« Reply #2 on: October 10, 2017, 01:32:49 PM »

Thnx, nice explanation.

Well, probably they just use hardware rendering with no sutch things and are at most interested in economy of speed. Some of them financialy realy aren't so cheep as they looks;) Bismuthy chrystal is not the best thing to show spectral effects. It is just beautifull.
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lycium
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« Reply #3 on: October 10, 2017, 02:06:43 PM »

Small correction: the abbreviation for bidirectional reflectance distribution function is BRDF, not BDRF (maybe helps when searching for more info).
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Alef
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« Reply #4 on: October 10, 2017, 02:38:00 PM »

wink
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hobold
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« Reply #5 on: October 10, 2017, 04:41:01 PM »

Small correction: the abbreviation for bidirectional reflectance distribution function is BRDF, not BDRF (maybe helps when searching for more info).
Thanks! I am just an interested dilettante, trying to guide other laymen to a point where they can begin asking the right questions.
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Alef
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« Reply #6 on: October 17, 2017, 04:40:32 PM »

Trying to guide developers to these direction tease
https://en.wikipedia.org/wiki/Bidirectional_reflectance_distribution_function

Among them are:
"Phong reflectance model, a phenomenological model akin to plastic-like specularity."

and

Cook–Torrance model, a specular-microfacet model (Torrance–Sparrow) accounting for wavelength and thus color shifting.

and

The Oren–Nayar reflectance model, developed by Michael Oren and Shree K. Nayar, is a reflectivity model for diffuse reflection from rough surfaces. It has been shown to accurately predict the appearance of a wide range of natural surfaces, such as concrete, plaster, sand, etc



To make it more hard  huh? they alsou have BSDF
https://en.wikipedia.org/wiki/Bidirectional_scattering_distribution_function



 huh?
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Alef
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« Reply #7 on: October 18, 2017, 04:26:39 PM »

It should be it:

Quote
BSSRDF (Bidirectional scattering-surface reflectance distribution function or B surface scattering RDF) describes the relation between outgoing radiance and the incident flux, including the phenomena like subsurface scattering (SSS). The BSSRDF describes how light is transported between any two rays that hit a surface

https://en.wikipedia.org/wiki/Subsurface_scattering

Direct surface scattering (left), plus subsurface scattering (middle), create the final image on the right.
Actualy I can't say that this feels realistic. It somehow reminds skin not mineral.


This is better.  If slight fractality and natural imperfection would be added this would look just like real marble statue. Subsurface scattering:


Alsou

Quote
Acquisition of the BSDF over the human face in 2000 by Debevec et al. was one of the last key breakthroughs on the way to fully virtual cinematography with its ultra-photorealistic digital look-alikes.
The team was the first in the world to isolate the subsurface scattering component (a specialized case of BTDF) using the simplest light stage on a modest computer. The team utilized the existing scientific knowledge that light that is reflected and scattered from the air-to-oil layer retains its polarization while light that travels within the skin loses its polarization.

Ha ha, these names is like BSDM

There is some scientical papers about this. If they are needed they can be accesed by first ever piratic scientic site Sci Hub . This seems legitimate becouse some scientis had called a species in name of creator of that site. "  Idiogramma elbakyanae Khalaim, sp. n.  The species is named in honour of Alexandra Elbakyan (Kazakhstan/Russia), creator of the web-site Sci-Hub, in recognition of her contribution to making scientific knowledge available for all researchers."
https://jhr.pensoft.net/articles.php?id=12919


« Last Edit: October 20, 2017, 04:18:47 PM by Alef » Logged

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