RGL
Realistic Graphics Lab
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Ma­ter­i­al Data­base — Fre­quently Asked Ques­tions

Fea­tures

The ma­ter­i­al data­base provides broad cov­er­age of com­mon and more spe­cial­ized ma­ter­i­als, in­clud­ing iso­trop­ic and an­iso­trop­ic BRD­Fs of metals, pa­per, car paints, or­gan­ic samples, fab­rics, etc. Each ma­ter­i­al is avail­able in a spec­tral ver­sion that cov­ers the 360(UV) - 1000nm (NIR) range with ~4nm sample spa­cing, as well as a RGB ver­sion for com­pat­ib­il­ity with ren­der­ers that do not sup­port col­or spec­tra. The rep­res­ent­a­tion is ex­tremely com­pact, re­quir­ing ap­prox­im­ately 16KiB and 544KiB per chan­nel for iso­trop­ic and an­iso­trop­ic ma­ter­i­als, re­spect­ively. Fur­ther­more, it provides a nat­ur­al im­port­ance sampling op­er­a­tion that does not re­quire nu­mer­ic­al fits or com­plex ad­di­tion­al data struc­tures. Tech­nic­al de­tails on the un­der­ly­ing para­met­er­iz­a­tion and meas­ure­ment meth­od­o­logy are avail­able in the pa­per

An Ad­apt­ive Para­met­er­iz­a­tion for Ef­fi­cient Ma­ter­i­al Ac­quis­i­tion and Ren­der­ing
by Jonath­an Dupuy and Wen­zel Jakob
In ACM Trans­ac­tions on Graph­ics (Pro­ceed­ings of SIGGRAPH Asia 2018)

The meas­ure­ment device and its cap­ab­il­it­ies are de­scribed here.

Fu­ture plans

We plan to con­sid­er­ably ex­tend the data­base in the fu­ture so that it even­tu­ally con­tains hun­dreds of ma­ter­i­als that densely cov­er the space of real-world ma­ter­i­al ap­pear­ance. Out­side help is wel­come: if you have in­ter­est­ing samples, we'd love to meas­ure them. See be­low for de­tails.

Stan­dalone view­er

BRDF files can be in­ter­act­ively viewed and ana­lyzed us­ing the Tekari view­er cre­ated by Ben­oît Ruiz. Tekari plots the BRDF and sample loc­a­tions with re­spect to dif­fer­ent in­cid­ent angles and/or wavelengths, us­ing a vari­ety of power­ful visu­al­iz­a­tion tools. Click the fol­low­ing link to down­load pre­com­piled 64-bit ex­ecut­ables for OSX, Win­dows, and Linux. To open a ma­ter­i­al, simply drag & drop the “_spec.bsdf” file onto the ap­plic­a­tion, or provide the fi­le­name as a com­mand line ar­gu­ment. Note while Tekari is an open source pro­ject, it de­pends on a com­pon­ent, whose source code is not yet avail­able (hence the pre­com­piled bin­ar­ies). 

C++ and Py­thon API

We've re­leased a ref­er­ence BRDF im­ple­ment­a­tion, which provides the stand­ard op­er­a­tions needed by most mod­ern ren­der­ing sys­tems: BRDF eval­u­ation, sampling, and a routine to query the un­der­ly­ing prob­ab­il­ity dens­ity. The re­pos­it­ory also con­tains a plu­gin for the Mit­suba ren­der­er and Py­thon code to load the data files in­to NumPy, which is use­ful for visu­al­iz­a­tion and sys­tem­at­ic ana­lys­is of the data­base con­tents.

Raw data

A go­nio-pho­to­met­er typ­ic­ally can­not meas­ure all angle com­bin­a­tions due to op­tic­al and mech­an­ic­al lim­it­a­tions (for in­stance, the sensor oc­cludes the light source at cer­tain angles). Our meas­ure­ment pipeline de­tects such cases and ex­tra­pol­ates the miss­ing data from oth­er meas­ure­ments. To provide trans­par­ency on what parts of the data cor­res­pond to ac­tu­al meas­ure­ments, we provide “raw” data files con­tain­ing an ex­tremely verb­ose log of the en­tire ac­quis­i­tion pro­cess in Py­thon pickle format.

Un­der­stand­ing the visu­al­iz­a­tions

Click­ing on the ma­ter­i­al re­veals a num­ber of visu­al­iz­a­tions:

Slice (meas­ured): The first im­age shows an RGB rendi­tion of what was meas­ured by the spec­tro­met­er. Note that the data typ­icaly has ex­tremely high-dy­nam­ic range, hence some de­tail in the black may simply be in­vis­ible. Red pixels cor­res­pond to wasted space of the dis­cret­iz­a­tion. The black column on the left is a re­gion that could not be meas­ured.

Slice (pro­cessed): This plot con­tains the same data, but after post-pro­cessing. The black re­gions on the left were filled in, and the data was scaled by the Jac­obi­an of the para­met­er­iz­a­tion (see the pa­per for de­tails). This has the ef­fect of mak­ing the rep­res­ent­a­tion sig­ni­fic­antly easi­er to in­ter­pol­ate. The bot­tom row shows spec­tral curves in the 360..1000nm range cor­res­pond­ing to the row above.

Para­met­er­iz­a­tion: shows in­cid­ent and out­go­ing angles, for which the ma­ter­i­al was meas­ured.

NDF: Our meth­od heav­ily re­lies on the ma­ter­i­al's retrore­flect­ive re­ponse. This plot shows the ex­trac­ted nor­mal dis­tri­bu­tion and the res­ult­ing backs­cat­ter­ing (the­ory & ac­tu­al).

Meas­ured angles: 2D visu­al­iz­a­tion of the meas­ured el­ev­a­tions (left) and azi­muths (right)

Li­cens­ing con­di­tions

Un­less oth­er­wise noted, all ma­ter­i­al data is li­censed un­der the Cre­at­ive Com­mons Zero (CC0) li­cense.

Meas­ure­ment ser­vice

We plan to con­sid­er­ably ex­tend the data­base in the fu­ture and would be happy to meas­ure samples provided by you for free. Please reach out to us if this sounds in­ter­est­ing. There are a few strings at­tached:

Changelog

We routinely add ad­di­tion­al ma­ter­i­als to the data­base. More sig­ni­fic­ant changes will be lis­ted here.