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MTL material format (Lightwave, OBJ)

Excerpt from FILE FORMATS, Version 4.2
October 1995
Documentation created by: Diane Ramey, Linda Rose, and Lisa Tyerman
Copyright 1995 Alias|Wavefront, Inc.
All rights reserved

Material Library File (.mtl)

Material library files contain one or more material definitions, each of which includes the colour, texture, and reflection map of individual materials. These are applied to the surfaces and vertices of objects. Material files are stored in ASCII format and have the .mtl extension.

An .mtl file differs from other Alias|Wavefront property files, such as light and atmosphere files, in that it can contain more than one material definition (other files contain the definition of only one item).

An .mtl file is typically organised as shown below:

newmtl my_red
        Material colour & illumination statements

        Texture map statements

        Reflection map statement

newmtl my_blue
        Material colour & illumination statements

        Texture map statements

        Reflection map statement

newmtl my_green
        Material colour & illumination statements

        Texture map statements

        Reflection map statement

Figure 5-1.  Typical organisation of .mtl file

Each material description in an .mtl file consists of the newmtl statement, which assigns a name to the material and designates the start of a material description. This statement is followed by the material colour, texture map, and reflection map statements that describe the material. An .mtl file map contain many different material descriptions.

After you specify a new material with the newmtl statement, you can enter the statements that describe the materials in any order. However, when the Property Editor writes an .mtl file, it puts the statements in a system-assigned order. In this section, the statements are described in the system-assigned order.

The following is a sample format for a material definition in an .mtl file:

Material name statement:
        newmtl my_mtl

Material colour and illumination statements:
        Ka 0.0435 0.0435 0.0435
        Kd 0.1086 0.1086 0.1086
        Ks 0.0000 0.0000 0.0000
        Tf 0.9885 0.9885 0.9885
        illum 6
        d -halo 0.6600
        Ns 10.0000
        sharpness 60
        Ni 1.19713

Texture map statements:
        map_Ka -s 1 1 1 -o 0 0 0 -mm 0 1 chrome.mpc
        map_Kd -s 1 1 1 -o 0 0 0 -mm 0 1 chrome.mpc
        map_Ks -s 1 1 1 -o 0 0 0 -mm 0 1 chrome.mpc
        map_Ns -s 1 1 1 -o 0 0 0 -mm 0 1 wisp.mps
        map_d -s 1 1 1 -o 0 0 0 -mm 0 1 wisp.mps
        disp -s 1 1 .5 wisp.mps
        decal -s 1 1 1 -o 0 0 0 -mm 0 1 sand.mps
        bump -s 1 1 1 -o 0 0 0 -bm 1 sand.mpb

Reflection map statement:
        refl -type sphere -mm 0 1 clouds.mpc

Material Name

The material name statement assigns a name to the material description:

newmtl name

Specifies the start of a material description and assigns a name to the material. An .mtl file must have one newmtl statement at the start of each material description.

name is the name of the material. Names may be any length but cannot include blanks. Underscores may be used in material names.

Material colour and illumination

The statements in this section specify colour, transparency, and reflectivity values.

The following syntax describes the material colour and illumination statements that apply to all .mtl files:

Ka r g b
Ka spectral file.rfl factor
Ka xyz x y z

To specify the ambient reflectivity of the current material, you can use the Ka statement, the Ka spectral statement or the Ka xyz statement.

Tip

These statements are mutually exclusive. They cannot be used concurrently in the same material.

Ka:

The Ka statement specifies the ambient reflectivity using RGB values:

Ka r g b
  • r g b are the values for the red, green and blue components of the colour.
  • The g and b arguments are optional. If only r is specified, then g and b are assumed to be equal to r.
  • The r g b values are normally in the range of 0.0 to 1.0. Values outside this range increase or decrease the reflectivity accordingly.
Ka spectral:

The Ka spectral statement specifies the ambient reflectivity using a spectral curve:

Ka spectral file.rfl factor
  • file.rfl is the name of the .rfl file.
  • factor is an optional argument.
  • factor is a multiplier for the values in the .rfl file and defaults to 1.0 if unspecified.
Ka xyz:

The Ka xyz statement specifies the ambient reflectivity using CIEXYZ values:

Ka xyz x y z
  • x y z are the values of the CIEXYZ colour space.
  • The y and z arguments are optional. If only x is specified, then y and z are assumed to be equal to x.
  • The x y z values are normally in the range of 0 to 1. Values outside this range increase or decrease the reflectivity accordingly.
Kd r g b
Kd spectral file.rfl factor
Kd xyz x y z

To specify the diffuse reflectivity of the current material, you can use the Kd statement, the Kd spectral statement, or the Kd xyz statement.

Tip

These statements are mutually exclusive. They cannot be used concurrently in the same material.

Kd:

The Kd statement specifies the diffuse reflectivity using RGB values:

Kd r g b
  • r g b are the values for the red, green, and blue components of the atmosphere.
  • The g and b arguments are optional. If only r is specified, then g and b are assumed to be equal to r.
  • The r g b values are normally in the range of 0.0 to 1.0. Values outside this range increase or decrease the reflectivity accordingly.
Kd spectral:

The Kd spectral statement specifies the diffuse reflectivity using a spectral curve:

Kd spectral file.rfl factor
  • file.rfl is the name of the .rfl file.
  • factor is an optional argument.
  • factor is a multiplier for the values in the .rfl file, and defaults to 1.0 if not specified.
Kd xyz:

The Kd xyz statement specifies the diffuse reflectivity using CIEXYZ values:

Kd xyz x y z
  • x y z are the values of the CIEXYZ colour space.
  • The y and z arguments are optional. If only x is specified, then y and z are assumed to be equal to x.
  • The x y z values are normally in the range of 0 to 1. Values outside this range increase or decrease the reflectivity accordingly.
Ks r g b
Ks spectral file.rfl factor
Ks xyz x y z

To specify the specular reflectivity of the current material, you can use the Ks statement, the Ks spectral statement, or the Ks xyz statement.

Tip

These statements are mutually exclusive. They cannot be used concurrently in the same material.

Ks:

The Ks statement specifies the specular reflectivity using RGB values:

Ks r g b
  • r g b are the values for the red, green, and blue components of the atmosphere.
  • The g and b arguments are optional. If only r is specified, then g, and b are assumed to be equal to r.
  • The r g b values are normally in the range of 0.0 to 1.0. Values outside this range increase or decrease the reflectivity accordingly.
Ks spectral:

The Ks spectral statement specifies the specular reflectivity using a spectral curve:

Ks spectral file.rfl factor
  • file.rfl is the name of the .rfl file.
  • factor is an optional argument.
  • factor is a multiplier for the values in the .rfl file and defaults to 1.0 if not specified.
Ks xyz:

The Ks xyz statement specifies the specular reflectivity using CIEXYZ values:

Ks xyz x y z
  • x y z are the values of the CIEXYZ colour space.
  • The y and z arguments are optional. If only x is specified, then y and z are assumed to be equal to x.
  • The x y z values are normally in the range of 0 to 1. Values outside this range increase or decrease the reflectivity accordingly.
Tf r g b
Tf spectral file.rfl factor
Tf xyz x y z

To specify the transmission filter of the current material, you can use the Tf statement, the Tf spectral statement, or the Tf xyz statement.

Any light passing through the object is filtered by the transmission filter, which only allows the specific colours to pass through. For example, Tf 0 1 0 allows all the green to pass through and filters out all the red and blue.

Tip

These statements are mutually exclusive. They cannot be used concurrently in the same material.

Tf:

The Tf statement specifies the transmission filter using RGB values:

Tf r g b
  • r g b are the values for the red, green, and blue components of the atmosphere.
  • The g and b arguments are optional. If only r is specified, then g and b are assumed to be equal to r.
  • The r g b values are normally in the range of 0.0 to 1.0. Values outside this range increase or decrease the reflectivity accordingly.
Tf spectral:

The Tf spectral statement specifies the transmission filter using a spectral curve:

Tf spectral file.rfl factor
  • file.rfl is the name of the .rfl file.
  • factor is an optional argument.
  • factor is a multiplier for the values in the .rfl file and defaults to 1.0, if not specified.
Tf xyz:

The Tf xyz statement specifies the transmission filter using CIEXYZ values:

Tf xyz x y z
  • x y z are the values of the CIEXYZ colour space.
  • The y and z arguments are optional. If only x is specified, then y and z are assumed to be equal to x.
  • The x y z values are normally in the range of 0 to 1. Values outside this range will increase or decrease the intensity of the light transmission accordingly.
illum illum_#:

The illum statement specifies the illumination model to use in the material. Illumination models are mathematical equations that represent various material lighting and shading effects.

illum_# can be a number from 0 to 10. The illumination models are summarised below; for complete descriptions see Illumination models.

Illumination model Properties turned on in the Property Editor
0
Colour on and Ambient off
1
Colour on and Ambient on
2
Highlight on
3
Reflection on and Ray trace on
4
Transparency: Glass on
Reflection: Ray trace on
5
Reflection: Fresnel on, Ray trace on
6
Transparency: Refraction on
Reflection: Fresnel off, Ray trace on
7
Transparency: Refraction on
Reflection: Fresnel on, Ray trace on
8
Reflection on, Ray trace off
9
Transparency: Glass on
Reflection: Ray trace off
10
Casts shadows onto invisible surfaces
d:

Specifies the dissolve for the current material:

d factor
  • factor is the amount this material dissolves into the background.
  • A factor of 1.0 is fully opaque. This is the default when a new material is created.
  • A factor of 0.0 is fully dissolved (completely transparent).

Unlike a real transparent material, the dissolve does not depend upon material thickness nor does it have any spectral character. Dissolve works on all illumination models.

d -halo:

Specifies that a dissolve is dependent on the surface orientation relative to the viewer. For example, a sphere with the following dissolve, d -halo 0.0, will be fully dissolved at its centre and will appear gradually more opaque toward its edge.

d -halo factor

  • factor is the minimum amount of dissolve applied to the material.

  • The amount of dissolve will vary between 1.0 (fully opaque) and the specified factor. The formula is:

    dissolve = 1.0 - (N*v)(1.0-factor)

For a definition of terms, see Illumination models.

Ns:

Specifies the specular exponent for the current material. This defines the focus of the specular highlight.

Ns exponent
  • exponent is the value for the specular exponent.
  • A high exponent results in a tight, concentrated highlight.
  • Ns values normally range from 0 to 1000.
sharpness:

Specifies the sharpness of the reflections from the local reflection map. If a material does not have a local reflection map defined in its material definition, sharpness will apply to the global reflection map defined in PreView.

sharpness value
  • value can be a number from 0 to 1000. The default is 60.
  • A high value results in a clear reflection of objects in the reflection map.

Tip

Sharpness values greater than 100 may introduce aliasing effects in flat surfaces that are viewed at a sharp angle.

Ni:

Specifies the optical density for the surface. This is also known as index of refraction.

Ni optical_density
  • optical_density is the value for the optical density.
  • The values can range from 0.001 to 10.
  • A value of 1.0 means that light does not bend as it passes through an object.
  • Increasing the optical_density increases the amount of bending.
  • Glass has an index of refraction of about 1.5.
  • Values of less than 1.0 produce bizarre results and are not recommended.

Material texture map

Texture map statements modify the material parameters of a surface by associating an image or texture file with material parameters that can be mapped. By modifying existing parameters instead of replacing them, texture maps provide great flexibility in changing the appearance of an object's surface.

Image files and texture files can be used interchangeably. If you use an image file, that file is converted to a texture in memory and is discarded after rendering.

Tip

Using images instead of textures saves disk space and setup time, however, it introduces a small computational cost at the beginning of a render.

The material parameters that can be modified by a texture map are:

  • Ka: Colour
  • Kd: Colour
  • Ks: Colour
  • Ns: Scalar
  • d: Scalar

In addition to the material parameters, the surface normal can be modified.

Image file types

You can link any image file type that is currently supported. Supported image file types are listed in the chapter "About Image" in the "Advanced Visualizer User's Guide". You can also use the im_info - a command to list Image file types, among other things.

Texture file types

The texture file types you can use are:

  • Mip-mapped texture files: .mpc, .mps, .mpb
  • Compiled procedural texture files: .cxc, .cxs, .cxb
Mip-mapped texture files

Mip-mapped texture files are created from images using the Create Textures panel in the Director or the texture2D program. There are three types of texture files:

  • Colour texture files: .mpc
  • Scalar texture files: .mps
  • Bump texture files: .mpb
Colour textures:

Colour texture files are designated by an extension of .mpc in the filename, such as chrome.mpc. Colour textures modify the material colour as follows:

  • Ka: Material ambient is multiplied by the texture value
  • Kd: Material diffuse is multiplied by the texture value
  • Ks: Material specular is multiplied by the texture value
Scalar textures:

Scalar texture files are designated by an extension of .mps in the filename, such as wisp.mps. Scalar textures modify the material scalar values as follows:

  • Ns: Material specular exponent is multiplied by the texture value
  • d: Material dissolve is multiplied by the texture value
  • decal: Uses a scalar value to deform the surface of an object to create surface roughness
Bump textures:
Bump texture files are designated by an extension of .mpb in the filename, such as sand.mpb. Bump textures modify surface normals. The image used for a bump texture represents the topology or height of the surface relative to the average surface. Dark areas are depressions and light areas are high points. The effect is like embossing the surface with the texture.
Procedural texture files

Procedural texture files use mathematical formulae to calculate sample values of the texture. The procedural texture file is compiled, stored, and accessed by the Image program when rendering. For more information, see Procedural Texture Files.

The following syntax describes the texture map statements that apply to .mtl files. These statements can be used alone or with any combination of options. The options and their arguments are inserted between the keyword and the filename.

map_Ka:

Specifies that a colour texture file or a colour procedural texture file is applied to the ambient reflectivity of the material. During rendering, the map_Ka value is multiplied by the Ka value.

map_Ka -options args filename

filename is the name of a colour texture file (.mpc), a colour procedural texture file (.cxc), or an image file.

Tip

To make sure that the texture retains its original look, use the .rfl file ident as the underlying material. This applies to the map_Ka, map_Kd, and map_Ks statements. For more information on .rfl files, see Spectral Curve File (.rfl).

The options for the map_Ka statement are listed below:

-blendu on | off
-blendv on | off
-cc on | off
-clamp on | off
-mm base gain
-o u v w
-s u v w
-t u v w
-texres value

These options are described in detail in Options for texture map statements.

map_Kd:

Specifies that a colour texture file or colour procedural texture file is linked to the diffuse reflectivity of the material. During rendering, the map_Kd value is multiplied by the Kd value.

map_Kd -options args filename

filename is the name of a colour texture file (.mpc), a colour procedural texture file (.cxc) or an image file.

The options for the map_Kd statement are listed below:

-blendu on | off
-blendv on | off
-cc on | off
-clamp on | off
-mm base gain
-o u v w
-s u v w
-t u v w
-texres value

These options are described in detail in Options for texture map statements.

map_Ks:

Specifies that a colour texture file or colour procedural texture file is linked to the specular reflectivity of the material. During rendering, the map_Ks value is multiplied by the Ks value.

map_Ks -options args filename

filename is the name of a colour texture file (.mpc), a colour procedural texture file (.cxc), or an image file.

The options for the map_Ks statement are listed below:

-blendu on | off
-blendv on | off
-cc on | off
-clamp on | off
-mm base gain
-o u v w
-s u v w
-t u v w
-texres value

These options are described in detail in Options for texture map statements.

map_Ns:

Specifies that a scalar texture file or scalar procedural texture file is linked to the specular exponent of the material. During rendering, the map_Ns value is multiplied by the Ns value.

map_Ns -options args filename

filename is the name of a scalar texture file (.mps), a scalar procedural texture file (.cxs), or an image file.

The options for the map_Ns statement are listed below:

-blendu on | off
-blendv on | off
-clamp on | off
-imfchan r | g | b | m | l | z
-mm base gain
-o u v w
-s u v w
-t u v w
-texres value

These options are described in detail in Options for texture map statements.

map_d:

Specifies that a scalar texture file or scalar procedural texture file is linked to the dissolve of the material. During rendering, the map_d value is multiplied by the d value.

map_d -options args filename

filename is the name of a scalar texture file (.mps), a scalar procedural texture file (.cxs), or an image file.

The options for the map_d statement are listed below:

-blendu on | off
-blendv on | off
-clamp on | off
-imfchan r | g | b | m | l | z
-mm base gain
-o u v w
-s u v w
-t u v w
-texres value

These options are described in detail in Options for texture map statements.

map_aat on:

Turns on anti-aliasing of textures in this material without anti-aliasing all textures in the scene.

If you wish to selectively anti-alias textures, first insert this statement in the material file. Then, when rendering with the Image panel, choose the anti-alias settings: shadows, reflections polygons, or polygons only. If using Image from the command line, use the -aa or -os options. Do not use the -aat option.

Image will anti-alias all textures in materials with the map_aat on statement, using the oversampling level you choose when you run Image. Textures in other materials will not be oversampled.

You cannot set a different oversampling level individually for each material, nor can you anti-alias some textures in a material and not others. To anti-alias all textures in all materials, use the -aat option from the Image command line. If a material with map_aat on includes a reflection map, all textures in that reflection map will be anti-aliased as well.

You will not see the effects of map_aat in the Property Editor.

Tip

Some .mpc textures map exhibit undesirable effects around the edges of smoothed objects. The map_aat statement will correct this.

decal:

Specifies that a scalar texture file or a scalar procedural texture file is used to selectively replace the material colour with the texture colour.

decal -options args filename

filename is the name of a scalar texture file (.mps), a scalar procedural texture file (.cxs), or an image file.

During rendering, the Ka, Kd, and Ks values and the map_Ka, map_Kd, and map_Ks values are blended according to the following formula:

result_colour = tex_colour(tv)
        * decal(tv)
        + mtl_colour
        * (1.0-decal(tv))

where tv is the texture vertex.

result_colour is the blended Ka, Kd, and Ks values.

The options for the decal statement are listed below:

-blendu on | off
-blendv on | off
-clamp on | off
-imfchan r | g | b | m | l | z
-mm base gain
-o u v w
-s u v w
-t u v w
-texres value

These options are described in detail in Options for texture map statements.

disp:

Specifies that a scalar texture is used to deform the surface of an object, creating surface roughness.

disp -options args filename

filename is the name of a scalar texture file (.mps), a bump procedural texture file (.cxb), or an image file.

The options for the disp statement are listed below:

-blendu on | off
-blendv on | off
-clamp on | off
-imfchan r | g | b | m | l | z
-mm base gain
-o u v w
-s u v w
-t u v w
-texres value

These options are described in detail in Options for texture map statements.

bump:

Specifies that a bump texture file or a bump procedural texture file is linked to the material.

bump -options args filename

filename is the name of a bump texture file (.mpb), a bump procedural texture file (.cxb), or an image file.

The options for the bump statement are listed below:

-bm mult
-clamp on | off
-blendu on | off
-blendv on | off
-imfchan r | g | b | m | l | z
-mm base gain
-o u v w
-s u v w
-t u v w
-texres value

These options are described in detail in Options for texture map statements.

Options for texture map statements

The following options and arguments can be used to modify the texture map statements.

-blendu:
-blendu on | off

The -blendu option turns texture blending in the horizontal direction (u direction) on or off. The default is on.

-blendv:
-blendv on | off

The -blendv option turns texture blending in the vertical direction (v direction) on or off. The default is on.

-bm:
-bm mult

The -bm option specifies a bump multiplier. You can use it only with the bump statement. Values stored with the texture or procedural texture file are multiplied by this value before they are applied to the surface.

mult is the value for the bump multiplier. It can be positive or negative. Extreme bump multipliers may cause odd visual results because only the surface normal is perturbed and the surface position does not change. For best results, use values between 0 and 1.

-boost:
-boost value

The -boost option increases the sharpness, or clarity, of mip-mapped texture files -- that is, colour (.mpc), scalar (.mps), and bump (.mpb) files. If you render animations with boost, you may experience some texture crawling. The effects of boost are seen when you render in Image or test render in Model or PreView; they aren't as noticeable in Property Editor.

value is any non-negative floating point value representing the degree of increased clarity; the greater the value, the greater the clarity. You should start with a boost value of no more than 1 or 2 and increase the value as needed. Note that larger values have more potential to introduce texture crawling when animated.

-cc:
-cc on | off

The -cc option turns on colour correction for the texture. You can use it only with the colour map statements: map_Ka, map_Kd, and map_Ks.

-clamp:
-clamp on | off

The -clamp option turns clamping on or off. When clamping is on, textures are restricted to 0-1 in the uvw range. The default is off.

When clamping is turned on, one copy of the texture is mapped onto the surface, rather than repeating copies of the original texture across the surface of a polygon, which is the default. Outside of the origin texture, the underlying material is unchanged.

A postage stamp on an envelope or a label on a can of soup is an example of a texture with clamping turned on. A tile floor or a sidewalk is an example of a texture with clamping turned off.

Two-dimensional textures are clamped in the u and v dimensions; 3D procedural textures are clamped in the u, v, and w dimensions.

-imfchan:
-imfchan r | g | b | m | l | z

The -imfchan option specifies the channel used to create a scalar or bump texture. Scalar textures are applied to:

  • Transparency
  • Specular exponent
  • Decal
  • Displacement

The channel choices are:

  • r: Specifies the red channel
  • g: Specifies the green channel
  • b: Specifies the blue channel
  • m: Specifies the matte channel
  • l: Specifies the luminance channel
  • z: Specifies the z-depth channel

The default for bump and scalar textures is l (luminance), unless you are building a decal. In that case, the default is m (matte).

-mm:
-mm base gain

The -mm option modifies the range over which scalar or colour texture values may vary. This has an effect only during rendering and does not change the file.

base adds a base value to the texture values. A positive value makes everything brighter; a negative value makes everything dimmer. The default is 0; the range is unlimited.

gain expands the range of the texture values. Increasing the number increases the contrast. The default is 1; the range is unlimited.

-o:
-o u v w

The -o option offsets the position of the texture map on the surface by shifting the position of the map origin. The default is 0, 0, 0.

  • u is the value for the horizontal direction of the texture
  • v is an optional argument
    v is the value for the vertical direction of the texture
  • w is an optional argument
    w is the value used for the depth of a 3D texture
-s:
-s u v w

The -s option scales the size of the texture pattern on the textured surface by expanding or shrinking the pattern. The default is 1, 1, 1.

  • u is the value for the horizontal direction of the texture
  • v is an optional argument
  • v is the value for the vertical direction of the texture
  • w is an optional argument
    w is a value used for the depth of a 3D texture
    w is a value used for the amount of tessellation of the displacement map
-t:
-t u v w

The -t option turns on turbulence for textures. Adding turbulence to a texture along a specified direction adds variance to the original image and allows a simple image to be repeated over a larger area without noticeable tiling effects.

Turbulence also lets you use a 2D image as if it were a solid texture, similar to 3D procedural textures like marble and granite.

  • u is the value for the horizontal direction of the texture turbulence
  • v is an optional argument
  • v is the value for the vertical direction of the texture turbulence
  • w is an optional argument
  • w is a value used for the depth of the texture turbulence

By default, the turbulence for every texture map used in a material is uvw = (0,0,0). This means that no turbulence will be applied and the 2D texture will behave normally.

Only when you raise the turbulence values above zero will you see the effects of turbulence.

-texres:
-texres resolution

The -texres option specifies the resolution of texture created when an image is used. The default texture size is the largest power of two that does not exceed the original image size.

If the source image is an exact power of 2, the texture cannot be built any larger. If the source image size is not an exact power of 2, you can specify that the texture be built at the next power of 2 greater than the source image size.

The original image should be square, otherwise, it will be scaled to fit the closest square size that is not larger than the original. Scaling reduces sharpness.

Material reflection map

A reflection map is an environment that simulates reflections in specified objects. The environment is represented by a colour texture file or procedural texture file that is mapped on the inside of an infinitely large space. Reflection maps can be spherical or cubic. A spherical reflection map requires only one texture or image file, while a cubic reflection map requires six.

Each material description can contain one reflection map statement that specifies a colour texture file or a colour procedural texture file to represent the environment. The material itself must be assigned an illumination model of 3 or greater.

The reflection map statement in the .mtl file defines a local reflection map. That is, each material assigned to an object in a scene can have an individual reflection map. In PreView, you can assign a global reflection map to an object and specify the orientation of the reflection map. Rotating the reflection map creates the effect of animating reflections independently of object motion. When you replace a global reflection map with a local reflection map, the local reflection map inherits the transformation of the global reflection map.

The following syntax statements describe the reflection map statement for .mtl files.

refl:

Specifies an infinitely large sphere that casts reflections onto the material. You specify one texture file.

refl -type sphere -options -args filename

filename is the colour texture file, colour procedural texture file, or image file that will be mapped onto the inside of the shape.

refl:
refl -type cube_side -options -args filenames

Specifies an infinitely large sphere that casts reflections onto the material. You can specify different texture files for the top, bottom, front, back, left, and right with the following statements:

refl -type cube_top
refl -type cube_bottom
refl -type cube_front
refl -type cube_back
refl -type cube_left
refl -type cube_right

filenames are the colour texture files, colour procedural texture files, or image files that will be mapped onto the inside of the shape.

The refl statements for sphere and cube can be used alone or with any combination of the following options. The options and their arguments are inserted between refl and filename:

-blendu on | off
-blendv on | off
-cc on | off
-clamp on | off
-mm base gain
-o u v w
-s u v w
-t u v w
-texres value

The options for the reflection map statement are described in detail in Options for texture map statements.

Examples

1. Neon green

This is a bright green material. When applied to an object, it will remain bright green regardless of any lighting in the scene:

newmtl neon_green
Kd 0.0000 1.0000 0.0000
illum 0

2. Flat green

This is a flat green material:

newmtl flat_green
Ka 0.0000 1.0000 0.0000
Kd 0.0000 1.0000 0.0000
illum 1

3. Dissolved green

This is a flat green, partially-dissolved material:

newmtl diss_green
Ka 0.0000 1.0000 0.0000
Kd 0.0000 1.0000 0.0000
d 0.8000
illum 1

4. Shiny green

This is a shiny green material. When applied to an object, it shows a white specular highlight.

newmtl shiny_green
Ka 0.0000 1.0000 0.0000
Kd 0.0000 1.0000 0.0000
Ks 1.0000 1.0000 1.0000
Ns 200.0000
illum 1

5. Green mirror

This is a reflective green material. When applied to an object, it reflects other objects in the same scene.

newmtl green_mirror
Ka 0.0000 1.0000 0.0000
Kd 0.0000 1.0000 0.0000
Ks 0.0000 1.0000 0.0000
Ns 200.0000
illum 3

6. Fake windshield

This material approximates a glass surface. Is it almost completely transparent, but it shows reflections of other objects in the scene. It will not distort the image of objects seen through the material.

newmtl fake_windsh
Ka 0.0000 0.0000 0.0000
Kd 0.0000 0.0000 0.0000
Ks 0.9000 0.9000 0.9000
d 0.1000
Ns 200
illum 4

7. Fresnel blue

This material exhibits an effect known as Fresnel reflection. When applied to an object, white fringes may appear where the object's surface is viewed at a glancing angle.

newmtl fresnel_blu
Ka 0.0000 0.0000 0.0000
Kd 0.0000 0.0000 0.0000
Ks 0.6180 0.8760 0.1430
Ns 200
illum 5

8. Real windshield

This material accurately represents a glass surface. It filters of colourises objects that are seen through it. Filtering is done according to the transmission colour of the material. The material also distorts the image of objects according to its optical density. Note that the material is not dissolved and that its ambient, diffuse, and specular reflective colours have been set to black. Only the transmission colour is non-black.

newmtl real_windsh
Ka 0.0000 0.0000 0.0000
Kd 0.0000 0.0000 0.0000
Ks 0.0000 0.0000 0.0000
Tf 1.0000 1.0000 1.0000
Ns 200
Ni 1.2000
illum 6

9. Fresnel windshield

This material combines the effects in examples 7 and 8:

newmtl fresnel_win
Ka 0.0000 0.0000 1.0000
Kd 0.0000 0.0000 1.0000
Ks 0.6180 0.8760 0.1430
Tf 1.0000 1.0000 1.0000
Ns 200
Ni 1.2000
illum 7

10. Tin

This material is based on spectral reflectance samples taken from an actual piece of tin. These samples are stored in a separate .rfl file that is referred to by name in the material. Spectral sample files (.rfl) can be used in any type of material as an alternative to RGB values.

newmtl tin
Ka spectral tin.rfl
Kd spectral tin.rfl
Ks spectral tin.rfl
Ns 200
illum 3

11. Pine Wood

This material includes a texture map of a pine pattern. The material colour is set to ident to preserve the texture's true colour. When applied to an object, this texture map will affect only the ambient and diffuse regions of that object's surface.

The colour information for the texture is stored in a separate .mpc file that is referred to in the material by its name, pine.mpc. If you use different .mpc files for ambient and diffuse, you will get unrealistic results.

newmtl pine_wood
Ka spectral ident.rfl 1
Kd spectral ident.rfl 1
illum 1
map_Ka pine.mpc
map_Kd pine.mpc

12. Bumpy leather

This material includes a texture map of a leather pattern. The material colour is set to ident to preserve the texture's true colour. When applied to an object, it affects both the colour of the object's surface and its apparent bumpiness.

The colour information for the texture is stored in a separate .mpc file that is referred to in the material by its name, brown.mpc. The bump information is stored in a separate .mpb file that is referred to in the material by its name, leath.mpb. The -bm option is used to raise the apparent height of the leather bumps.

newmtl bumpy_leath
Ka spectral ident.rfl 1
Kd spectral ident.rfl 1
Ks spectral ident.rfl 1
illum 2
map_Ka brown.mpc
map_Kd brown.mpc
map_Ks brown.mpc
bump -bm 2.000 leath.mpb

13. Frosted window

This material includes a texture map used to alter the opacity of an object's surface. The material colour is set to ident to preserve the texture's true colour. When applied to an object, the object becomes transparent in certain areas and opaque in others.

The variation between opaque and transparent regions is controlled by scalar information stored in a separate .mps file that is referred to in the material by its name, window.mps. The -mm option is used to shift and compress the range of opacity.

newmtl frost_wind
Ka 0.2 0.2 0.2
Kd 0.6 0.6 0.6
Ks 0.1 0.1 0.1
d 1
Ns 200
illum 2
map_d -mm 0.200 0.800 window.mps

14. Shifted logo

This material includes a texture map which illustrates how a texture's origin may be shifted left/right (the "u" direction) or up/down (the "v" direction). The material colour is set to ident to preserve the texture's true colour.

In this example, the original image of the logo is off-centre to the left. To compensate, the texture's origin is shifted back to the right (the positive "u" direction) using the -o option to modify the origin.

Ka spectral ident.rfl 1
Kd spectral ident.rfl 1
Ks spectral ident.rfl 1
illum 2
map_Ka -o 0.200 0.000 0.000 logo.mpc
map_Kd -o 0.200 0.000 0.000 logo.mpc
map_Ks -o 0.200 0.000 0.000 logo.mpc

15. Scaled logo

This material includes a texture map showing how a texture may be scaled left or right (in the "u" direction) or up and down (in the "v" direction). The material colour is set to ident to preserve the texture's true colour.

In this example, the original image of the logo is too small. To compensate, the texture is scaled slightly to the right (in the positive "u" direction) and up (in the positive "v" direction) using the -s option to modify the scale.

Ka spectral ident.rfl 1
Kd spectral ident.rfl 1
Ks spectral ident.rfl 1
illum 2
map_Ka -s 1.200 1.200 0.000 logo.mpc
map_Kd -s 1.200 1.200 0.000 logo.mpc
map_Ks -s 1.200 1.200 0.000 logo.mpc

16. Chrome with spherical reflection map

This illustrates a common use for local reflection maps (defined in a material).

This material is highly reflective with no diffuse or ambient contribution. Its reflection map is an image with silver streaks that yields a chrome appearance when viewed as a reflection.

ka 0 0 0
kd 0 0 0
ks .7 .7 .7
illum 1
refl -type sphere chrome.rla

Illumination models

The following list defines the terms and vectors that are used in the illumination model equations:

Term Definition
Ft
Fresnel reflectance
Ft
Fresnel transmittance
Ia
Ambient light
I
Light intensity
Ir
Intensity from reflected direction
(reflection map and/or ray tracing)
It
Intensity from transmitted direction
Ka
Ambient reflectance
Kd
Diffuse reflectance
Ks
Specular reflectance
Tf
Transmission filter
Vector Definition
H
Unit vector bisector between L and V
L
Unit light vector
N
Unit surface normal
V
Unit view vector

The illumination models are:

0:

This is a constant colour illumination model. The colour is the specified Kd for the material. The formula is:

colour = Kd
1:

This is a diffuse illumination model using Lambertian shading. The colour includes an ambient constant term and a diffuse shading term for each light source. The formula is:

colour = KaIa + Kd { SUM j=1..ls, (N * Lj)Ij }
2:

This is a diffuse and specular illumination model using Lambertian shading and Blinn's interpretation of Phong's specular illumination model (BLIN77). The colour includes an ambient constant term, and a diffuse and specular shading term for each light source. The formula is:

colour = KaIa
        + Kd { SUM j=1..ls, (N*Lj)Ij }
        + Ks { SUM j=1..ls, ((H*Hj)^Ns)Ij }
3:

This is a diffuse and specular illumination model with reflection using Lambertian shading, Blinn's interpretation of Phong's specular illumination model (BLIN77), and a reflection term similar to that in Whitted's illumination model (WHIT80). The colour includes an ambient constant term and a diffuse and specular shading term for each light source. The formula is:

colour = KaIa
        + Kd { SUM j=1..ls, (N*Lj)Ij }
        + Ks ({ SUM j=1..ls, ((H*Hj)^Ns)Ij } + Ir)

Ir = (intensity of reflection map) + (ray trace)
4:

The diffuse and specular illumination model used to simulate glass is the same as illumination model 3. When using a very low dissolve (approximately 0.1), specular highlights from lights or reflections become imperceptible.

Simulating glass requires an almost transparent object that still reflects strong highlights. The maximum of the average intensity of highlights and reflected lights is used to adjust the dissolve factor. The formula is:

colour = KaIa
        + Kd { SUM j=1..ls, (N*Lj)Ij }
        + Ks ({ SUM j=1..ls, ((H*Hj)^Ns)Ij } + Ir)
5:

This is a diffuse and specular shading models similar to illumination model 3, except that reflection due to Fresnel effects is introduced into the equation. Fresnel reflection results from light striking a diffuse surface at a grazing or glancing angle. When light reflects at a grazing angle, the Ks value approaches 1.0 for all colour samples. The formula is:

colour = KaIa
        + Kd { SUM j=1..ls, (N*Lj)Ij }
        + Ks ({SUM j=1..ls,
             ((H*Hj)^Ns)Ij Fr(Lj*Hj,Ks,Ns)Ij}
           + Fr(N*V,Ks,Ns)Ir})
6:

This is a diffuse and specular illumination model similar to that used by Whitted (WHIT80) that allows rays to refract through a surface. The amount of refraction is based on optical density (Ni). The intensity of light that refracts is equal to 1.0 minus the value of Ks, and the resulting light is filtered by Tf (transmission filter) as it passes through the object. The formula is:

colour = KaIa
        + Kd { SUM j=1..ls, (N*Lj)Ij }
        + Ks ({ SUM j=1..ls, ((H*Hj)^Ns)Ij } + Ir)
        + (1.0 - Ks) TfIt
7:

This illumination model is similar to illumination model 6, except that reflection and transmission due to Fresnel effects has been introduced to the equation. At grazing angles, more light is reflected and less light is refracted through the object. The formula is:

colour = KaIa
        + Kd { SUM j=1..ls, (N*Lj)Ij }
        + Ks ({ SUM j=1..ls, ((H*Hj)^Ns)Ij
                Fr(Lj*Hj,Ks,Ns)Ij}
              + Fr(N*V,Ks,Ns)Ir})

        + (1.0 - Kx)Ft (N*V,(1.0-Ks),Ns)TfIt
8:

This illumination model is similar to illumination model 3 without ray tracing. The formula is:

colour = KaIa
        + Kd { SUM j=1..ls, (N*Lj)Ij }
        + Ks ({ SUM j=1..ls, ((H*Hj)^Ns)Ij } + Ir)

Ir = (intensity of reflection map)
9:

This illumination model is similar to illumination model 4 without ray tracing. The formula is:

colour = KaIa
        + Kd { SUM j=1..ls, (N*Lj)Ij }
        + Ks ({ SUM j=1..ls, ((H*Hj)^Ns)Ij } + Ir)

Ir = (intensity of reflection map)
10:

This illumination model is used to cast shadows onto an invisible surface. This is most useful when compositing computer-generated imagery onto live action, since it allows shadows from rendered objects to be composited directly on top of video-grabbed images. The equation for computation of a shadowmatte is formulated as follows:

colour:

Pixel colour. The pixel colour of a shadowmatte material is always black.
colour:

Black
M:

Matte channel value. This is the image channel which typically represents the opacity of the point on the surface. To store the shadow in the image's matte channel, it is calculated as:

M = 1 - W / P

where:
P:

Unweighted sum. This is the sum of all S values for each light:

P = S1 + S2 + S3 + .....
W:

Weighted sum. This is the sum of all S values, each weighted by the visibility factor (Q) for the light:

W = (S1 * Q1) + (S2 * Q2) + .....
Q:

Visibility factor. This is the amount of light from a particular light source that reaches the point to be shaded, after travelling through all shadow objects between the light and the point on the surface.

  • Q = 0 means no light reached the point
    to be shaded; it was blocked by shadow objects,
    thus casting a shadow.
  • Q = 1 means that nothing blocked the light,
    and no shadow was cast.
  • 0 < Q < 1 means that the light was partially
    blocked by objects that were partially dissolved.
S:

Summed brightness. This is the sum of the spectral sample intensities for a particular light. The samples are variable, but the default is 3:

S = samp1 + samp2 + samp3