AxF File

AxF (Appearance eXchange Format) files are textured appearance property files generated with X-Rites measurement devices. Speos supports the SVBRDF model.

Description

Speos can simulate high quality environment lighting and material appearance.

However, Speos has a gap to create very realistic materials which require high level of details, as it can be tedious and time consuming. To overcome this gap, Speos can now use physically based rendering (PPR) models with AxF SVBRDF models.

Appearance VS BRDF

Appareance concept is different from traditional optical properties.
  • An appearance material is not used to make pure photometric measurements. The goal of appearance materials is to be able to visualize the material the most realistic way possible when simulating textures.
  • A BRDF is fully spectral, can extend from infrared to ultraviolet, respects the energy conservation, and respects the pinciple of Helmholtz reciprocity (same result in Direct and Inverse simulations). The goal is to make photometric analysis.

SVBRDF Model

SVBRDF model is a file format developed by X-Rite, company specialized in the color measurement. SVBRDF is a mathematical model that store data about how a material reflects light from different angles with few parameters. Each parameter is stored in a texture (1 texture for the diffuse parameter, 1 texture for the normal parameter, 1 texture for the specular parameter, 1 texture for the roughness parameter, 1 texture for the anisotropy parameter), allowing to get the spatial variation and so the material appearance to change across its surface.



SVRBDFs are RGB most of the time, can be energy preserving but not energy conserving, and do not usually respect the Helmholtz reciprocity, unlike standard BRDF files. As a consequence, the purpose of SVBRDF models are purely visual rendering appearance. They are not meant to be used for photometry analysis.

In Speos

SVBRDF models are contained in *.axf files. As of version 2025 R1, a new Surface Property type, Appearance, is available when applying a texture.

Example



  1. Material capture using MA-T12 X-Rite tool
  2. Speos definition of a texture using the *.axf file generated out of the capture
  3. Live Preview rendering

Speos/AxF Compatibility

Note:
  • AxF models are CPU and GPU compatible.
As of version 2025R1, Speos manages SVBRDF microfacet models with the support of all maps from AxF 1.5 model:
  • GGX SVBRDF (1.5) with diffuse color, normal, specular color and specular lobe textures
  • RGB or Spectral
  • Anisotropy
The following content is ignored with warning upon use:
  • Alpha (transparency)
  • Sheen
  • Displacement map
  • Clear Coat
The following models are not be supported and return an error:
  • Carpaint
  • Volume

Tools to generate AxF files

AxF can be generated with 3 tools from X-Rite:
  • the TAC7 (lab size for any purpose):
    • Bench size
    • Fully detailed AxF
    • 0°, 22.5°, 45°, 67.5° capture incidences
    • Sample size: 130mm
  • the MA-T12 (portable, more for glossy materials)
    • Portable with Li-ion battery
    • CarPaint, Spectral SVBRDF
    • Wavelength range: 400-700nm, 10nm
    • 40px/mm (1016dpi)
    • Sample: 9mm*12mm
  • the MetaVue (portable, more for textiles)
    • Compact Benchtop
    • Spectral SVBRDF, Specular as single values (60° gloss sensor)
    • Wavelength range: 400-700nm, 10nm
    • 11.5px/mm (292dpi)
    • Sample: 12mm