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Welcome back to Reality!.
In this article we’ll be covering more principles of photorealism. Remember
the Principles of 3D photorealism we discussed in the last article? Well,
in case you don't, here they are again.
The 10 Principles of Photoreal 3D:
- Clutter & Chaos
- Personality & Expectations
- Believability
- Surface Texture
- Specularity
- Dirt, Dust and Rust
- Flaws, Scratches and Dings
- Beveled Edges
- Object Material Depth
- Radiosity
We discussed the first
three principles in the last issue so we’ll be covering steps 4-6 in this
one. Before we get started, let’s revisit our example image and the background
behind it. Take a look at Figure 1.1.
'Dwellers'
is a 3D animated short film currently in production at Komodo Studio, a
3D studio in Southern California. It's about a race of cognitive thinking
robotic creatures that were created by an old toy maker named Papagaio.
Papagaio created the first Dweller, Gizmo, in his basement workshop. To
make a short story even shorter, Papagaio built Gizmo out of discarded
junk and parts he scavenged from both new and old items. The Dwellers are
built from actual real-world parts. This helps to establish their photoreal
credibility. This also helps determine the modeling and surfacing attributes
not to mention the mechanics of motion.
Figure 1.1 Photorealism applied!
Figure
1.1 shows Gizmo on Papagaio's workbench where he was created. The scene
takes place at around 1AM in the basement of Papagaio’s house. He doesn't
want anyone to find out about the Dwellers so he only uses a shop light
to illuminate the workbench. He's just finished adding the circuit board,
which is Gizmo's brain. The scene has captured the moment at which Gizmo
comes to life.
Now that we've refreshed
our memories, let's take a look at few more Principles of Photoreal 3D
and see how they were applied to the 'Dwellers' image.
PRINCIPLE 4: SURFACE TEXTURE
All real-world objects
have surface texture. Now don't confuse the term 'texture' with the reference
commonly used in the 3D industry. Texture does not mean the coloration
of the object. In fact, the proper term for texture is the roughness or
smoothness of the object surface. It's the surface attribute that you can
feel. All objects have some form of surface texture, including the smooth
ones.
A common problem with
the 3D objects surfacing is that they are almost always too smooth. Frequently
you will see polished wood that's as smooth as glass. This just isn't realistic.
The varnish will conform to the natural texture of the wood's grain, leaving
very subtle variations in the varnish texture. The only way to get smooth
varnish is to coat the wood with several layers and then sand the final
layer smooth. This just isn't done unless you want to mortgage your house
to buy a wooden desk.
You could hypothesize
that the wood is an artificial veneer but then nobody would want to admit
to using artificial wood in their scene. You could try sanding the wood
until it is completely smooth, but this wouldn't work well either. Wood
has a natural grain. To completely remove any surface texture, you would
have to sand all the wood away; this just isn't a very practical solution.
Keep in mind just because you can't feel a texture it doesn't mean it's
not there. The texture may be too subtle to feel, but it will definitely
show up in the object's specularity - particularly if the object is animated.
Another factor of varnished
wood is the very subtle bump that the varnish itself creates. When the
varnish dries there are very tiny air bubbles trapped under the surface,
you can’t see these from any distance but if you plan to shoot a close-up
of an object on a varnished table, you’ll need to add the varnish bump.
Once again, you won’t really see the bump but you will see the visual impact
on the specularity and reflectivity of the wood.
Take a look at Figure
1.2. This is a close-up shot of the tools on Papagaio's workbench. You
can see a subtle bump texture on the wrenches against the wall. Shop tools
are primarily made of chrome alloy. Chrome alloy usually has a slightly
rough surface that is quite often brushed. There are also many chrome alloys
that have an irregular bumpiness to their surface. This texture is essential
for the tools to appear photo realistic. There is also a very subtle brushed
bump map on the neck of the light. This texture is not really obvious in
a still shot, but it’s very apparent when the neck is animated. It affects
both the specularity and the reflection. Of course, there is a subtle texture
on the wood. You have to look close, but you will see small lines between
the larger grain lines. This is that tiny texture that can’t be felt but
can be seen upon close inspection. While this texture isn’t necessary for
distance shots it becomes an important part of close-in shots.
I
know I've been picking on wood, but it's not the only surface that requires
a bump map. You'll need to add surface texture to all the photoreal objects
in your scene. Particularly surfaces like plastic, rubber, metals, fabric,
and even paper. Take a look at any multimedia component in your house.
You'll notice the plastic has a minor roughness to its surface. If you
don't incorporate that texture into the 3D rendered version of that object,
it won't be photorealistic. Even smooth plastic objects have minor surface
distortion that impacts their specularity. Specularity is a critical element
of surface realism. It's also the 5th Principle of Photoreal 3D.
Figure 1.2 Real-World objects have surface texture.
PRINCIPLE 5: SPECULARITY
Simply put, specularity
is the reflection of the light source on the object’s surface. it’s a bright
spot that the human eye uses to determine the surface’s shininess and hardness.
Specularity is a very important aspect of photoreal 3D. it’s necessary
to add specularity to mimic the real-world attributes of the surface. Without
specularity, the object would appear dull, soft and flat. While this may
be good for cloth it doesn’t do much for metal or plastic. Specularity
and surface texture work together to simulate real-world surfaces. For
example: Plastic has a rough surface texture. When specularity is applied,
it adds specular highlights to the tops of the surface bumps. This does
2 things, it gives the surface bump a 3D feel and provides you with a visual
reference for hardness.
Let’s take a look at
how specularity impacts the model photorealism in the workbench scene.
Take another look at Figure 1.2. Notice how there is a soft white spot
on the leading edge of each segment in the light’s neck. This subtle specular
highlight is essential for the photorealism of the object. The light’s
neck is made of chromed aluminium, which, like all metals, has a low specular
level because it reflects light. The subtle specular highlight helps the
human eye identify the surface as metal.
Just behind the lights
neck you’ll see the head of a crescent wrench. you’ll notice a very subtle
specular highlight on peaks of the rounded parts. The wrench has a lower
specular level than the light neck because it’s a different metal surface.
The wrench is made of chromed alloy, which has a lower specular level and
a rough surface texture. The low specular level spreads the highlight over
the surface of the object, which is then softened by the rough surface
texture.
Take a look at the open-end
wrench to the left of the light neck. It too is made of chrome alloy, so
the specularity is spread out over the surface. The entire head of the
wrench is covered in a soft specular highlight because it’s a flat surface
that is parallel to the light source. This is a case where the surface
texture is necessary to maintain the photorealism of the metal surface.
Without a texture, the surface would be completely washed-out by the specular
highlight, covering all the surface attributes. The specular highlight
is broken-up by the surface texture, which helps maintain the integrity
of the surface.
While specularity is
important to simulate many real-world textures, there are cases where you
don’t want parts of an object to be specular. For instance: You would want
metal to be specular but what if it was covered in corrosion? Corrosion
isn’t normally specular. Therefore you would need to make the metal specular
but not the corroded areas. This is accomplished with specular image maps,
which we will discuss in Part III: Photoreal Surfacing Technique. Although,
there are occasions where the corrosion would be specular due to humidity
or water. In these cases you would need to add specularity to the corrosion.
As you can see, it’s important to identify the environmental conditions
of the scene to properly apply specularity. While we’re on the subject
of corrosion, let’s take a look at the 6th Principle of Photoreal 3D: Dirt,
Dust and Rust.
PRINCIPLE 6: DIRT, DUST AND RUST
Dirt, dust and rust
are very important aspects of an object’s surface, which are commonly referred
to as Aging. There are very few clean surfaces in reality. Just look around
your home or office and you’ll find most everything is covered in dust.
If you have small children, it’s likely that you have stains on the carpet
and handprints on the walls. I’m willing to bet that your glass tabletops
have smudges and there might even be cobwebs in the ceiling corners. If
you have brass, copper or silver items they are likely to be tarnished.
I haven’t seen a TV yet that doesn’t have a layer of dust on the screen.
Picture tubes are dust magnets! You can’t see it while the TV is on but
when you turn it off, well, it's not a pretty sight.
It's not that we are
lazy and don't clean our houses. It's just a fact of life, dirt is everywhere
and we can't escape it -- unless we live in a plastic bubble. Yet it seems
nearly every 3D scene created has somehow captured the precise moment after
which it was visited by Mr. Clean. that’s a whole lot of great timing.
Spotless scenes just aren’t natural. It may look great but it doesn’t look
realistic. it’s important to add aging to your scenes. The level of aging
depends on the scene’s background. If you are creating a factory scene
you should bury everything in a layer of dirt and grime. If you are rendering
a hospital operating room you can probably get away with making the scene
spotless Ð well, one would hope it would be spotless. You need to consider
the environment of the scene when planning your surfaces.
Let’s take a look another
look at the workbench scene in Figure 1.1 and see where the aging was added.
Remember when we discussed Papagaio’s personality? he’s an intelligent
inventor, and that makes him neat with a tendency to get a little disorganized.
His personality needs to be reflected in the scene’s surfaces. Notice how
the workbench is covered in burn marks and dirt stains. Even though Papagaio
is neat, it would be nearly impossible to avoid making stains on the workbench.
you’ll notice they aren’t huge stains, just a little dirty. This is a reflection
of Papagaio’s personality. We need to zoom in to the picture more to see
some of the aging detail.
Figure 1.3 Real-World objects have surface texture.
Take
a look at image 1.3. This is a close-up of gizmo’s oil can body. you’ll
notice the top of the can is covered in rust and corrosion. This is a very
important element of the scene. It justifies a great deal of the dirt in
the rest of the scene. We have to assume that Papagaio has been handling
Gizmo. If so, the rust and corrosion has likely rubbed off on his hands.
This dirt will be transferred to the objects Papagaio handles. You can
see evidence of this by looking back at figure 1.1. Here you can see that
the rust and corrosion from Papagaio’s hands has rubbed off on the soldering
iron grip. You can see that he handled the duct tape because there is grime
on the left side and dirt on the center roll.
Let's explore the workbench
scene a little more to see if we can find additional evidence of Papagaio’s
grimy grasp. Take a look at Figure 1.4. Here we have a close-up of the
reference book. Notice how there are dirt stains on the cover. This is
another subtle sign of aging, but it’s important to ensure the scene makes
sense. A spotless book on a cluttered and dirty workbench would stand out
like a sore thumb. You need to sit back and examine a scene after you have
staged it, to determine where and how to apply the aging.
Figure 1.4 Only certain objects will be affected by the aging source.
Keeping with the idea
that Papagaio is spreading the dirt with his hands, there is another object
in the scene that needs some specific aging. Take a look at Figure 1.5.
Here we have a close-up of the camera box. Since the camera box is open,
we have to assume Papagaio handled it. Therefore it needs to have dirty
fingerprints. If you look close you’ll see a couple fingerprints around
the opening on the right side of the box, and a couple on the opposite
side where he held the box while opening it. These may be subtle details
but they add an extraordinary amount of photorealism to the scene.
Figure 1.5 You need to follow the aging source through the scene.
It’s this attention to detail that makes the scene photoreal. If you take
a closer look at Figure 1.1 you’ll notice that there are grime and dirt
marks on all of the tools that Papagaio has handled.
As you can see, aging
is a critical aspect of a photo realistic 3D scene. Before you add the
aging, take some time to explore your scene to find out what kind of aging
to add, where it is coming from, and how it’s being spread. It may seem
like a lot of work but it’s actually a lot of fun. How often do you get
the opportunity to make a mess without having to clean it up? If you’re
like me, it’s not often enough.
Get more Bill Fleming - look for his books in the cadmonkey.com bookstore.
Part I - Principals 1 - 3
Part III - Principals 7 - 10
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