Material Masking by
Ted Boardman
Ted Boardman
Who was that masked material?
Masking
is the process of hiding and revealing portions of a
pattern using the luminance values of another pattern or
map. The concept is simple, as is the fundamental
application, but by using masking upon masking you are
able to generate very complex materials that are convincing
to the viewer.
This column will
introduce you to the process of masking at both the map and
the material level in 3ds max or Autodesk VIZ, both programs share
the same capabilities. We will start with the simple
applications to see how masking functions, then work
into more complex examples including animated masks.
Grayscale
images generally function best as masks. It is the
Luminance value of a pixel that controls the masking
effect, white is opaque…black is transparent…levels of
gray are somewhere in-between. Color images may be used
as masks, but it is very difficult for most of us to
judge a particular luminance value of a color. For example,
green and yellow look very different, but might have the same
luminance values and would be ineffective as a mask.
As
with all topics in max or VIZ it is best to start
simply to get a feel for the functionality and controls,
then work into more complex applications. I will
include a VIZ 4 file for downloading that can be opened
in either VIZ 4 or 3ds max 4 and 5. For those of you with
previous versions of max or VIZ the descriptions should be enough
for you to build your own similar scenes and examples.
Where can masks be applied?
Masking can occur at either the map or the material level. If masks are applied at the map level the effect is only for that particular material component; Diffuse Color, Opacity, Reflections, etc. The material masking allows all components of materials to be hidden or revealed by the mask.
Where can masks be applied?
Masking can occur at either the map or the material level. If masks are applied at the map level the effect is only for that particular material component; Diffuse Color, Opacity, Reflections, etc. The material masking allows all components of materials to be hidden or revealed by the mask.
Two examples
of masking at map level would be the Mask map that allows one map
and one mask that allows the underlying Diffuse Color to show
through and the Mix map that allows two maps with an
optional mask. Another map type called Composite can be
used for masking effects that use image Alpha Channels
that will act as the masking agent. Alpha Channels will
be discussed later in the column.
At the material
level my favorite is the Blend material that allows two
materials with a mask. This allows you to reveal two
separate complete materials with different color, bumps,
reflections, for example, with the mask.
The
depth of masking is unlimited, for example you can have
a mask map within a mask map within a mask map or a
Blend material made of a material plus another Blend
material, each with it’s own mask. Like I said earlier,
though, start simply and build on your knowledge as you
become comfortable with the process.
Masking at map level
As mentioned, there are several methods for applying masks at the map level of a material and the one we’ll look at here will be the Mask map.
Masking at map level
As mentioned, there are several methods for applying masks at the map level of a material and the one we’ll look at here will be the Mask map.
The
scenario is a tile floor with solid red tiles
alternating with marble pattern tiles and can be
accessed by downloading Tile_viz4.max.
(Download zip file at end of article) The red color will be set
as the Diffuse and Ambient Color swatches of the material. A
Mask map is applied to the Diffuse Color slot and is
composed of a Perlin Marble map and a Checker mask. The
white areas of the Checker mask are opaque and show the
marble map. The black areas of the Checker mask are
transparent and reveal the underlying solid red Diffuse
Color. See Figure 1.
Figure 1:
The Material Editor shows a Mask map in Diffuse Color slot that
contains a map and a mask. The viewport and rendered image show
the effect of black and white masking of the map. Perlin
Marble shows in the white areas and diffuse red shows
in black areas.
This example
shows how the process works in a Diffuse Color example. In
the next example I use a Mask map in conjunction with a
Raytrace reflection map on a tile floor that can be
found in Wall_viz4.max. The scenario here is a ceramic
tile floor with Brick maps defining the color and the
bump pattern and a Raytrace map that causes the material
to reflect its surroundings.
In the Mask
map of the Reflection slot I have disabled the Bricks mask by
unchecking it in the Mask Parameters rollout causing the
reflection to be the same for both the tiles and grout.
See Figure 2.
Figure 2: The mask of the floor tile Reflection slot
has been disabled and you can see the reflection of the
cylinder is the same in the grout and tile.
By
applying the same Brick map I used in the Bump slot of
the material to a Mask map with a Raytrace map, the
reflections only occur in the white areas of the mask.
See Figure 3.
Figure 3: Enabling the Bricks mask reveals reflections
in the tile areas but not in the grout areas for a more
convincing floor material.
Masking
at the material component level offers a lot of
possibilities for experimentation. The same Reflection
masking as above could be used with Raytrace and a Noise
mask to give the illusions of puddles on a road
surface. A combination of Bricks map in the Bump slot
with a Gradient Ramp mask could create the illusion of a knurled
surface on a tool handle. Use your imagination and experiment.
Masking at the material level
Masking at the material level functions the same as at the map level but increases the control another notch. Each material can have widely varying attributes like color, shininess, and bumps, each revealed or hidden by the mask. In the example here I’ll use the Blend material with the optional mask.
Masking at the material level
Masking at the material level functions the same as at the map level but increases the control another notch. Each material can have widely varying attributes like color, shininess, and bumps, each revealed or hidden by the mask. In the example here I’ll use the Blend material with the optional mask.
The
scenario will be a wall that needs a combination of brick and stucco.
As in most projects the exact material placement will be
held in secret by the designer right up to the last
minute of the deadline. I want to be able to make last
minute changes quickly and easily. This is also using
the file Wall_viz4.max. (Download zip file at end of article)
Blend
material with masking allows us to do this nicely. I
create the Blend material with a Brick and a Stucco
material, each with different patterns, colors, and
bumps. I’ll use a Gradient Ramp mask that has been
adjusted for solid bands of black and white to reveal the two
materials exactly where I want them on the model.
This
wall example also illustrates a powerful feature of max
and VIZ called Map Channels. Because the patterns of
the brick, the stucco, and the mask repeat differently
over the wall surface I needed different mapping coordinates
for each map. The wall has three UVW Map modifiers each set to a
different Map Channel. The Gradient Ramp mask is set to
use Map Channel 1, the Brick map uses Map Channel 2, and
the Stucco map uses Map Channel 3 so that each pattern
may be adjusted independently. The Map Channel in the
UVW Map must match the Explicit Map Channel setting of
the map in the Material Editor.
The Gradient
Ramp map has been rotated in the W axis in the Coordinates
rollout for proper orientation on the wall. An
alternative would be to rotate the UVW Map modifier
Gizmo.
Figure 4 shows the Gradient
Ramp map and the rendered image shows the result of the
masking. Each material has it’s own color and bump
information.
Figure 4: A Blend material with a Gradient Ramp mask
reveals Brick or Stucco at the appropriate location.
A
simple change to the Gradient Ramp updates the position
of the materials with no other adjustments needed. See
Figure 5.
Figure 5: By adjusting the position of the flags
in the Gradient Ramp map used as the mask, you can quickly
reposition the location of the materials.
This
same wall material could have been used with a Noise
map to simulate a stucco wall with sections of plaster
fallen off to reveal bricks below. You could also create
the illusion of rust coming through a metal panel or
grassy areas with patches of rock and dirt.
Animated masks
Masks do not have to be static images or maps. Interesting effects can be created by using animated masks in the form of avi or mov files or as sequentially number still images. You might say that it sounds logical, but you don’t have a 2D animation program to create the animated maps. Don’t fear, it is easy to create animated masks in 3ds max or Autodesk VIZ.
In the file called Rope_viz4.max (Download zip file at end of article) is a section of coiled rope made by lofting a circle around a helix and applying a material to it. The task at hand is to make the rope disappear over time, not all at once, but from one end to the other.
Animated masks
Masks do not have to be static images or maps. Interesting effects can be created by using animated masks in the form of avi or mov files or as sequentially number still images. You might say that it sounds logical, but you don’t have a 2D animation program to create the animated maps. Don’t fear, it is easy to create animated masks in 3ds max or Autodesk VIZ.
In the file called Rope_viz4.max (Download zip file at end of article) is a section of coiled rope made by lofting a circle around a helix and applying a material to it. The task at hand is to make the rope disappear over time, not all at once, but from one end to the other.
The solution
here is to use a Blend material and a mask again. In the Blend material
is a rope material and a material that is completely
invisible. The opacity and glossiness of the material
have been set to 0. It is important to set the
glossiness to 0 to avoid a highlight on the invisible
portion of the rope.
The mask is
created in VIZ 4 by assigning a pure white material to a flat plane
and animating the plane moving from just off screen to
filling the viewport of a camera view. In this case it
is Camera02. The animation was rendered as an avi file
and used in the Mask slot of the Blend material.
Figure
6 shows the Blend material level in Material Editor and
the result of rendering frame 15 of 30 frames. Half the
rope that you see in the Camera01 viewport is invisible
in the rendered image. See Figure 6.
Figure 6
The
same technique could have been used to reveal a shiny
new material under an old crusty material over time or
to make a surface appear to bubble from the heat by
revealing the base material with same material with a
bump map added.
Note that it is
important in this case that the rope be created in max
or VIZ by lofting. Lofted objects are the only objects that generate
mapping coordinates that allow the patterns to follow the
curvature of the objects. For example the rope material
and the mask both follow the rope as it winds upward.
Alpha channel and masking
You will often hear the term Alpha Channel in conjunction with maps in max or VIZ. It refers to information that is stored in certain bitmaps that determine transparency. The most popular files types with alpha channels are tga, tif, and png.
Alpha channel and masking
You will often hear the term Alpha Channel in conjunction with maps in max or VIZ. It refers to information that is stored in certain bitmaps that determine transparency. The most popular files types with alpha channels are tga, tif, and png.
Computer
generated images are displayed in pixels, either on
screen or when printed. Since the early days of computer
graphics anti-aliasing has been used to smooth diagonal
lines and edges caused by stair-stepping across
squarish pixels.
Anti-aliasing is
done by blending the pixels at the edges of contrasting colors
to make the edge appear smoother. If a red diagonal line is
applied to a yellow background then some pixels are
quite red with a little yellow, some are half red, half
yellow, and others are quite yellow with a little red.
This smooths the transition when seen from a distance.
However,
if the red line is lifted from the yellow background
and composited onto a blue background the yellow
remnants look terrible and are worse than no
anti-aliasing. 32 bit files or files with 24 bits of
color and 8 bits of alpha channel use transparency pixels instead
of the background color to create the anti-aliasing effect.
Now when the red line with varying transparent pixels
are composited to another background there is no problem
and everything has clean edges that appear smooth.
Max
and VIZ both can take advantage of files with Alpha
Channel in the masks for a cleaner blend at either the
map or the material level. Workings on the examples in
this column don’t require Alpha Channel to work, but
keep it in mind if you are experiencing problems with
detailed masks in your explorations.
Summary
Masking gives you control of materials you never thought possible. The concept and application are simple at its base level, but by combining masks at different levels you can create materials that are complex yet easily edited.
Summary
Masking gives you control of materials you never thought possible. The concept and application are simple at its base level, but by combining masks at different levels you can create materials that are complex yet easily edited.
As a personal plug, if you
are a 3ds max 5 user, my new 3ds max 5 Fundamentals book
by New Riders Publishing is set to appear in late October or
early November. It is somewhat different than my previous
fundamentals book in that I focus on the many new max 5
features in a series of exercises that take you from a
medieval village to building a personal transporter, and
a trip to the fortune tellers. The exercises are
designed to be an interesting and informative way to learn uses
for max 5 features from modeling, to materials and radiosity
lighting, to collision detection and scene editing and
compositing.
In any case, good luck and have fun!
Ted
