Here
I will show you how I create a painted
metal surface worn by time with paint
chipping off, revealing older paintwork
underneath. I used a similar technique
for the BUB model seen in the gallery.
This
is the model I'll use, a clunky looking
part wating for some color.
After
applying a uvw modifier and arranging
in unwrap uvw I assign a grid texture
to the objects. The grid quadrats will
most probably be distorted so I manually
adjust the tiling to get the right
map aspect ratio and make the squares
quadratic. Turning on "Show Map in Viewport"
is quite helpful here. For this object
I needed 1.3 tiles to 1 so the aspect
ratio is 1.3 to 1. Now I take a snapshot
of the unwrapped meshes with Texporter
and save as a TIF file (TGA is fine too,
just make sure you get the alpha channel).
I wanted a map height of 800 pixels so
the width would be 800x1.3=1040
It's
not always neccesary to be this accurate
but I do this to prevent getting maps
distorted in one direction. Often you
can get away by just estimating the
texport aspect ratio as well.
Here
are the unwrapped meshes, ready to be
painted on. Within Photoshop I start out
by copying the alpha channel into a normal
layer and set it to Multiply. This way
the black wireframe will show but everything
that is white will be transparent, allowing
you to see what you're painting. This
layer will be the topmost one and always
locked to prevent accidental painting.
I
then put in a layer of yellow paint and
one of green paint, using several layered
photographic maps as a base and coloring
them.
The
result in Photoshop looks like the following
picture.
Now
with the wireframe picture as a guide
I start painting in where paint is to
be chipped off into a new layer using
black and white, highly contrasted
grunge photos with the clone stamp
tool and some careful handpainting
where it's needed.
I
then copy this layer into the alpha channel.
Using this as a selection I delete
the chipped paint off the green layer,
showing the underlying yellow layer. I
also added a subtle drop shadow to the
green layer to separate it a bit more
from the yellow.
Now
that the basic texture is done, lets start
dirtying it up. I create another layer
and set it to multiply. With a
very big, soft brush set to a mid brown
color I start adding dirt. Concentrate
this in nooks and corners
where dirt accumulates but also a bit
over the whole model for broad dirt. Keep
it soft and adjust the intensity by playing
with the layer transparency. You can also
break up the soft strokes with a grunge
texture.
Then
it's time to add wear to the surface.
This should mainly be kept along edges
but also within large surface areas like
the middle of the texture using
a broad brush.
This
might look good enough but if you've got
the time, why not add rust streaks, mud,
sootstains and what else your dirty heart
desires.
Next thing on the list is to add scratches
where all paint has come off to reveal
metal beneath. To remain flexible
I want to use a Mix Material in
Max for the paintjob and the metal. For
this I need a mask which I paint in Photoshop
with my Wacom set to brush width sensitivity.
With random strokes I paint the scratches
which turn out like this.
With
all the layers completed, the file
should look like this in Photoshop.
Now
it's time for the specular and
bumpmaps. The reason why I've
kept every color and effect in a separate
layer in Photoshop is because this makes
it easy to derive the spec and bumpmaps
from them. You could of course also
just reuse the diffuse map but in this
and many other cases it would't work:
the yellow paint is beneath the green
but if you'd use the diffuse as a bumpmap,
the yellow, being a lighter color, would
be above the green. You also don't want
the dirt and wear layers to influence
the bumpmap. It also wouldn't work as
a specular texture because we want both
colors to have about the same shinyness.
So I adjust each layer separatly using
brightness/contrast and hue/sat/lightness,
hiding the dirt and wear layers for
the bumpmap.
By
using Actions in Photoshop it's
fairly easy to record these settings
and apply them to other files which
I will do later with the other object.
Here are the resulting maps.
I
then create textures for the other part
using the same steps as above and use
the Action I created to make the bump
and speculars.
Now let's get back to Max again and
start assigning those maps.
I
use the same shinyness map in
both Specular Level and Glossyness
slots and use Output -> Output
Levels (or RGB Levels) in the Texture
Map submaterial to adjust
the shine. Since 3ds max4 supports Wiring
I wire the Output Levels of the two
objects to each other so that any change
to one will affect the other. This is
a great thing that would have saved
me some tears had I been able to do
that in earlier projects.
I create a metallic looking material
using a bitmap texture, a high
Specular Level and a very low
Glossyness.
Now
each object's material is split into
a Mix Material. The painted surface
come into one slot, and in the other
slot comes a reference of the
metal material. This way it's easy to
change the metallic look globally. As
a mask we use the scratch textures
we painted before.
Let's
have a look at the objects in good light.
It's very helpful to have some basic
lighting set up while tweaking materials
as opposed to using the standard max
2-light setup. This way you'll better
see how the materials react.
Here
are some renders of the diffuse color
alone, with bump and specular and then
with the scratches added. The scratches
are subtle but add a neat touch when
light makes the metal shine differently
beneath the paint. Because if the broad
but strong metallic speculars and the
dark texture, the metal will be lighter
than the paint in light but darker in
shadows.
You
can also download the scene with all materials
in full size as well as a PSD file
(Photoshop 6, resized to save space)
of the tutorial object and an animation
(DivX) of the objects spinning.
