the file is used to # create a scalar or bump texture. r:red, g:green, # b:blue, m:matte, l:luminance, z:z-depth.. # (the default for bump is 'l' and for decal is 'm') For example, # says to use the red channel of bumpmap.tga as the bumpmap bump -imfchan r bumpmap.tga For reflection maps... -type sphere # specifies a sphere for a "refl" reflection map -type cube_top | cube_bottom | # when using a cube map, the texture file for each cube_front | cube_back | # side of the cube is specified separately cube_left | cube_right Vendor specific alterations Because of the ease in parsing the files, and the unofficial spreading of the file format, files may contain vendor specific alterations. According to the spec, options are supposed to precede the texture filename. However, at least one vendor generates files with options at the end. # bump multiplier of 0.2 bump texbump.tga -bm 0.2 Physically-based Rendering The creators of the online 3D editing and modeling tool, Clara.io, proposed extending the MTL format to contain the following parameters to represent the physically-based rendering parameters: Pr/map_Pr # roughness Pm/map_Pm # metallic Ps/map_Ps # sheen Pc # clearcoat thickness Pcr # clearcoat roughness Ke/map_Ke # emissive aniso # anisotropy anisor # anisotropy rotation norm # normal map (RGB components represent XYZ components of the surface normal) Further proposed extensions come from the DirectXMesh toolkit for Microsoft's DirectX engine, allowing the ability to define a model's pre-compiled RMA material. map_RMA # RMA material (roughness, metalness, ambient occlusion) map_ORM # alternate definition of map_RMA See also glTF OFF (file format) STL (file format) PLY (file format) is an alternative file format offering more flexibility than most stereolithography applications. References External links Appendix B1. Object Files (.obj), Advanced Visualizer Manual Mtl Specification Tools, libraries and example files FileFormat.Info: Wavefront OBJ File Format Summary CAD file formats 3D graphics file formats