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mtl文件（Material Library File）是材质库文件，描述的是物体的材质信息，ASCII存储，任何文本编辑器可以将其打开和编辑。一个.mtl文件可以包含一个或多个材质定义，对于每个材质都有其颜色，纹理和反射贴图的描述，应用于物体的表面和顶点。
以下是一个材质库文件的基本结构：
newmtl mymtl_1
材质颜色光照定义
纹理贴图定义
反射贴图定义
newmtl mymtl_2
材质颜色光照定义
纹理贴图定义
反射贴图定义
newmtl mymtl_3
材质颜色光照定义
纹理贴图定义
反射贴图定义
……
注释：每个材质库可含多个材质定义，每个材质都有一个材质名。用newmtl mtlName来定义一个材质。对于每个材质，可定义它的颜色光照纹理反射等描述特征。主要的定义格式如下文所示：
////////////////////////////////////////////////
材质颜色光照
1。环境反射有以下三种描述格式，三者是互斥的，不能同时使用。
Ka r g b ——用RGB颜色值来表示，g和b两参数是可选的，如果只指定了r的值，则g和b的值都等于r的值。三个参数一般取值范围为0.0~1.0，在此范围外的值则相应的增加或减少反射率;
Ka spectral file.rfl factor ——用一个rfl文件来表示。factor是一个可选参数，表示.rfl文件中值的乘数，默认为1.0;
Ka xyz x y z ——用CIEXYZ值来表示，x，y，z是CIEXYZ颜色空间的各分量值。y和z两参数是可选的，如果只指定了x的值，则y和z的值都等于r的值。三个参数一般取值范围为0~1。
2。漫反射描述的三种格式：
Kd r g b
Kd spectral file.rfl factor
Kd xyz x y z
3。镜反射描述的三种格式:
Ks r g b
Ks spectral file.rfl factor
Ks xyz x y z
4。滤光透射率描述的三种格式：
Tf r g b
Tf spectral file.rfl factor
Tf xyz x y z
5。光照模型描述格式：
illum illum_#
指定材质的光照模型。illum后面可接0~10范围内的数字参数。各个参数代表的光照模型如下所示：
--------------------------------------------------------------
光照模型 属性
0 Color on and Ambient off
1 Color 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 and Ray trace on
6 Transparency: Refraction on
Reflection: Fresnel off and Ray trace on
7 Transparency: Refraction on
Reflection: Fresnel on and Ray trace on
8 Reflection on and Ray trace off
9 Transparency: Glass on
Reflection: Ray trace off
10 Casts shadows onto invisible surfaces
--------------------------------------------------------------
6。渐隐指数描述
d factor
参数factor表示物体融入背景的数量，取值范围为0.0~1.0，取值为1.0表示完全不透明，取值为0.0时表示完全透明。当新创建一个物体时，该值默认为1.0，即无渐隐效果。
与真正的透明物体材质不一样，这个渐隐效果是不依赖于物体的厚度或是否具有光谱特性。该渐隐效果对所有光照模型都有效。
d -halo factor
指定一种受观察者影响的渐隐效果。例如，对于一个定义为 d -halo 0.0的球体，在它的中心是完全消隐的，而在表面边界处将逐渐变得不透明。
其中factor表示应用在材质上的渐隐率的最小值。而材质上具体的渐隐率将在这个最小值到1.0之间取值。其计算公式为：
dissolve = 1.0 - (N*v)(1.0-factor)
7。反射指数描述
Ns exponent
指定材质的反射指数，定义了反射高光度。
exponent是反射指数值，该值越高则高光越密集，一般取值范围在0~1000。
8。清晰度描述
Sharpness value
指定本地反射贴图的清晰度。如果材质中没有本地反射贴图定义，则将此值应用到预览中的全局反射贴图上。
value可在0~1000中取值，默认60。值越高则越清晰。
9。折射值描述
Ni ptical density
指定材质表面的光密度，即折射值。
ptical density是光密度值，可在0.001到10之间进行取值。若取值为1.0，光在通过物体的时候不发生弯曲。玻璃的折射率为1.5。取值小于1.0的时候可能会产生奇怪的结果，不推荐。
////////////////////////////////////////////////
纹理映射
纹理映射可以对映射的相应材质参数进行修改，这个修改只是对原有存在的参数进行叠加修改，而不是替换原有参数，从而纹理映射在物体表面的表现上有很好的灵活性。
纹理映射只可以改变以下材质参数：
- Ka (color)
- Kd (color)
- Ks (color)
- Ns (scalar)
- d (scalar)
除了以上参数，表面法线也可以更改。
纹理文件类型可以是以下几种：
1.纹理映射文件
.mpc：颜色纹理文件color texture files ——可改变Ka，Kd，Ks的值
.mps：标量纹理文件scalar texture files——可改变Ns，d，decal的值
.mpb：凹凸纹理文件bump texture files——可改变面法线
2.程序纹理文件：
程序纹理文件是用数学公式来计算纹理的样本值。有以下几种格式：
.cxc
.cxs
.cxb
以下是mtl文件中对于纹理映射的描述格式：
1.map_Ka -options args filename
为环境反射指定颜色纹理文件(.mpc)或程序纹理文件(.cxc)，或是一个位图文件。在渲染的时候，Ka的值将再乘上map_Ka的值。
而map_Ka的可选项参数有以下几个：
-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
2.map_Kd -options args filename
为漫反射指定颜色纹理文件(.mpc)或程序纹理文件(.cxc)，或是一个位图文件。作用原理与可选参数与map_Ka同。
3.map_Ks -options args filename
为镜反射指定颜色纹理文件(.mpc)或程序纹理文件(.cxc)，或是一个位图文件。作用原理与可选参数与map_Ka同。
4.map_Ns -options args filename
为镜面反射指定标量纹理文件（.mps或.cxs）。可选参数如下所示：
-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
5.map_d -options args filename
为消隐指数指定标量纹理文件（.mps或.cxs）。作用原理和可选参数与map_Ns同。
6.map_aat on
打开纹理反走样功能。
7.decal -options args filename
指定一个标量纹理文件或程序纹理文件用于选择性地将材质的颜色替换为纹理的颜色。可选参数同map_Ns。
在渲染期间， Ka, Kd, and Ks和map_Ka, map_Kd, map_Ks的值通过下面这个公式来进行使用：
result_color=tex_color(tv)*decal(tv)+mtl_color*(1.0-decal(tv))
其中tv表示纹理顶点，result_color是Ka,Kd和Ks的综合作用值。
8.disp -options args filename
指定一个标量纹理文件或程序纹理文件实现物体变形或产生表面粗糙。可选参数同map_Ns。
9.bump -options args filename
为材质指定凹凸纹理文件（.mpb或.cxb）,或是一个位图文件。
可选参数可为：
-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
以上各参数含义可见原文。
////////////////////////////////////////////////////////
反射贴图
在.mtl文件中的定义格式为：
1.refl -type sphere -options -args filename
指定一个球体区域将指定的纹理反射映射至物体。filename为一个颜色纹理文件，或可以映射的位图。
2.refl -type cube_side -options -args filenames
指定一个立方体区域将指定的纹理反射映射至物体。可以通过以下方式来指定纹理位置：
refl -type cube_top
refl -type cube_bottom
refl -type cube_front
refl -type cube_back
refl -type cube_left
refl -type cube_right
“refl”可以单独使用，或配合以下参数使用。使用时将参数置于“refl”和“filename”之间。
-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
////////////////////////////////////////////////////////
实例：
newmtl my_mtl
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 19713
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
refl -type sphere -mm 0 1 clouds.mpc
////////////////////////////////////////////////////////
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
5. Material Library File (.mtl)
Material library files contain one or more material definitions, each
of which includes the color, 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 organized as shown below.
newmtl my_red
Material color
& illumination
statements
texture map
statements
reflection map
statement
newmtl my_blue
Material color
& illumination
statements
texture map
statements
reflection map
statement
newmtl my_green
Material color
& illumination
statements
texture map
statements
reflection map
statement
Figure 5-1. Typical organization 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
color, 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 chapter, the statements are described
in the system-assigned order.
Format
The following is a sample format for a material definition in an .mtl
file:
Material
name
statement:
newmtl my_mtl
Material
color 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.
Syntax
The folowing syntax describes the material name statement.
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 color and illumination
The statements in this section specify color, transparency, and
reflectivity values.
Syntax
The following syntax describes the material color 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 r g b
The Ka statement specifies the ambient reflectivity using RGB values.
"r g b" are the values for the red, green, and blue components of the
color. 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 relectivity accordingly.
Ka spectral file.rfl factor
The "Ka spectral" statement specifies the ambient reflectivity using a
spectral curve.
"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.
Ka xyz x y z
The "Ka xyz" statement specifies the ambient reflectivity using CIEXYZ
values.
"x y z" are the values of the CIEXYZ color 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 r g b
The Kd statement specifies the diffuse reflectivity using RGB values.
"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 relectivity accordingly.
Kd spectral file.rfl factor
The "Kd spectral" statement specifies the diffuse reflectivity using a
spectral curve.
"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 x y z
The "Kd xyz" statement specifies the diffuse reflectivity using CIEXYZ
values.
"x y z" are the values of the CIEXYZ color 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 r g b
The Ks statement specifies the specular reflectivity using RGB values.
"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 relectivity accordingly.
Ks spectral file.rfl factor
The "Ks spectral" statement specifies the specular reflectivity using a
spectral curve.
"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 x y z
The "Ks xyz" statement specifies the specular reflectivity using CIEXYZ
values.
"x y z" are the values of the CIEXYZ color 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 specifiec colors 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 r g b
The Tf statement specifies the transmission filter using RGB values.
"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 relectivity accordingly.
Tf spectral file.rfl factor
The "Tf spectral" statement specifies the transmission filterusing a
spectral curve.
"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 x y z
The "Ks xyz" statement specifies the specular reflectivity using CIEXYZ
values.
"x y z" are the values of the CIEXYZ color 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
summarized below; for complete descriptions see "Illumination models" on
page 5-30.
Illumination Properties that are turned on in the
model Property Editor
0 Color on and Ambient off
1 Color 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 and Ray trace on
6 Transparency: Refraction on
Reflection: Fresnel off and Ray trace on
7 Transparency: Refraction on
Reflection: Fresnel on and Ray trace on
8 Reflection on and Ray trace off
9 Transparency: Glass on
Reflection: Ray trace off
10 Casts shadows onto invisible surfaces
d factor
Specifies the dissolve for the current material.
"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 factor
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 center and will
appear gradually more opaque toward its edge.
"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" on page 5-30.
Ns exponent
Specifies the specular exponent for the current material. This defines
the focus of the specular highlight.
"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 value
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.
"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 map introduce aliasing effects
in flat surfaces that are viewed at a sharp angle
Ni optical_density
Specifies the optical density for the surface. This is also known as
index of refraction.
"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 (color)
- Kd (color)
- Ks (color)
- 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:
- color texture files (.mpc)
- scalar texture files (.mps)
- bump texture files (.mpb)
Color textures. Color texture files are designated by an extension of
".mpc" in the filename, such as "chrome.mpc". Color textures modify the
material color 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 formulas 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 chapter 9, "Procedural Texture Files (.cxc, .cxb. and .cxs)".
Syntax
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 -options args filename
Specifies that a color texture file or a color procedural texture file
is applied to the ambient reflectivity of the material. During
rendering, the "map_Ka" value is multiplied by the "Ka" value.
"filename" is the name of a color texture file (.mpc), a color
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 chapter 8, "Spectral Curve File (.rfl)".
The options for the "map_Ka" statement are listed below. These options
are described in detail in "Options for texture map statements" on page
5-18.
-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
map_Kd -options args filename
Specifies that a color texture file or color procedural texture file is
linked to the diffuse reflectivity of the material. During rendering,
the map_Kd value is multiplied by the Kd value.
"filename" is the name of a color texture file (.mpc), a color
procedural texture file (.cxc), or an image file.
The options for the map_Kd statement are listed below. These options
are described in detail in "Options for texture map statements" on page
5-18.
-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
map_Ks -options args filename
Specifies that a color texture file or color procedural texture file is
linked to the specular reflectivity of the material. During rendering,
the map_Ks value is multiplied by the Ks value.
"filename" is the name of a color texture file (.mpc), a color
procedural texture file (.cxc), or an image file.
The options for the map_Ks statement are listed below. These options
are described in detail in "Options for texture map statements" on page
5-18.
-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
map_Ns -options args filename
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.
"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. These options
are described in detail in "Options for texture map statements" on page
5-18.
-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
map_d -options args filename
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.
"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. These options
are described in detail in "Options for texture map statements" on page
5-18.
-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
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 -options args filename
Specifies that a scalar texture file or a scalar procedural texture
file is used to selectively replace the material color with the texture
color.
"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_color=tex_color(tv)*decal(tv)+mtl_color*(1.0-decal(tv))
where tv is the texture vertex.
"result_color" is the blended Ka, Kd, and Ks values.
The options for the decal statement are listed below. These options
are described in detail in "Options for texture map statements" on page
5-18.
-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
disp -options args filename
Specifies that a scalar texture is used to deform the surface of an
object, creating surface roughness.
"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. These options are
described in detail in "Options for texture map statements" on page 5-
18.
-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
bump -options args filename
Specifies that a bump texture file or a bump procedural texture file is
linked to the material.
"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. These options are
described in detail in "Options for texture map statements" on page 5-
18.
-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
Options for texture map statements
The following options and arguments can be used to modify the texture
map statements.
-blenu on | off
The -blendu option turns texture blending in the horizontal direction
(u direction) on or off. The default is on.
-blenv on | off
The -blendv option turns texture blending in the vertical direction (v
direction) on or off. The default is on.
-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 value
The -boost option increases the sharpness, or clarity, of mip-mapped
texture files -- that is, color (.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 on | off
The -cc option turns on color correction for the texture. You can use
it only with the color map statements: map_Ka, map_Kd, and map_Ks.
-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 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 base gain
The -mm option modifies the range over which scalar or color 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 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 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 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 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 color 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 color texture file or a color 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.
Syntax
The following syntax statements describe the reflection map statement
for .mtl files.
refl -type sphere -options -args filename
Specifies an infinitely large sphere that casts reflections onto the
material. You specify one texture file.
"filename" is the color texture file, color procedural texture file, or
image file that will be mapped onto the inside of the shape.
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 color texture files, color 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" on page 18.
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
colorizes objects that are seen through it. Filtering is done according
to the transmission color 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 colors have been set to black. Only the transmission color
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
color is set to "ident" to preserve the texture's true color. When
applied to an object, this texture map will affect only the ambient and
diffuse regions of that object's surface.
The color 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 color is set to "ident" to preserve the texture's true color.
When applied to an object, it affects both the color of the object's
surface and its apparent bumpiness.
The color 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 color is set to "ident" to preserve the
texture's true color. 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 color is set to "ident" to preserve the
texture's true color.
In this example, the original image of the logo is off-center 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 color is set to "ident" to preserve the
texture's true color.
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 color illumination model. The color is the
specified Kd for the material. The formula is:
color = Kd
1 This is a diffuse illumination model using Lambertian shading. The
color includes an ambient constant term and a diffuse shading term for
each light source. The formula is
color = 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 color includes an ambient constant term, and a
diffuse and specular shading term for each light source. The formula
is:
color = 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 color includes an ambient
constant term and a diffuse and specular shading term for each light
source. The formula is:
color = 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:
color = 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 color
samples. The formula is:
color = 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:
color = 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:
color = 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:
color = 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 4without
ray tracing. The formula is:
color = 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.
color = Pixel color. The pixel color of a shadowmatte material is
always black.
color = 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 matte channel of the image, 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 traveling
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.