Primary, Secondary, and
Tertiary Shapes
By Neil Blevins
Created On: Sept 28th 2006
This lesson is all about Primary, Secondary
and Tertiary shapes, what they are and how to use them. This concept is
also sometimes referred to as "Big, Medium, Small", as in, if your
image
has a nice distribution of big (primary), medium (secondary) and small
(tertiary) shapes, the resulting image will tend to be more pleasing to
the eye.
First, a definition. Primary shapes are your big shapes. If you
squint at an image, the details tend to disappear and you're left
with only your big shapes.

Secondary shapes are the smaller shapes that either sit ontop of, or
help make up the primary shapes.
Tertiary shapes are again smaller than the secondary shapes.
Here's three 2D diagrams showing primary, secondary and tertiary
shapes
in a fake composition. Even though this is 2d, the exact same rules
apply to 3d.

First off, what should the size of these details be? Well, that
depends on personal taste. I like having the primary details being
huge, almost the size of the image itself. And I like Tertiary details
being really small, sometimes the size of a pixel or two. From there
you can decide the appropriate size for the Secondary Details. Of
course, not all details should be the same size, it's more like a range
of sizes, so not all secondary details should be the same size, but
should be in a similar range.
So these could be primary, secondary and tertiary shapes....

But so can these...

And these...

Next comes the distribution of these details. Take a look at this
image, it has all 3 levels of detail, but the tertiary shapes are in
one uniform block...

Many images suffer from this problem, huge blocks of small
repeating patterns. For example, you get this effect if you place a
procedural noise with no variation on a surface.

This does not provide the eye any spot to rest. So in general you
want to vary the placement of your tertiary details so that they are
more
random, and have several areas of detail, and several areas of no
detail.

Notice how this is easier to digest. The eye can look at the
detailed lower right corner, then move to the center of the image and
rest there for a moment (in the big area of little detail) before
looking at more tertiary details elsewhere.
This is another reason why natural patterns generally look better
than out of the box procedural patterns. Natural patterns tend to have
areas of lots of
detail, and areas of very little detail, and they're placed in a more
random fashion. Of course, through mixing and what not, you can get a
more "organic" quality from procedurals, but procedurals right out of
the box generally don't give you that kind of variety. See my Complex
Shaders Using Procedurals, The Green Tongue lesson for a discussion
on how to get more variety from your
procedurals.
Here's a photo of a rock in greyscale. Notice the variety in the
patterns.

Here's another example of building up shapes. First, lets start
with a cylinder, maybe this will be a pipe for a robot.

Now lets place some secondary shapes, rings around the pipe.
Now that's more interesting, but the regular pattern is kind of
boring. Lets vary the position of the secondary rings...
Better, but all the secondary shapes are the same size, lets vary
the sizes a bit...
Looking better. We now have variety in the sizes of the secondary
shapes, and we have areas with lots of secondary shapes, and areas
with no secondary shapes. Lets add a few tertiary shapes...
Now we have a well balanced composition.
Here's a few paint overs of some of my images showing the primary,
secondary and tertiary shapes...

Click here
for the original...
In this case, the giant tower is the primary
shape (a cylinder). That shape is made up of many secondary shapes,
pipes and large
pieces of concrete, and the entrance. The tertiary shapes are the tiny
ships, and tiny
lights along the surface of the tower, many of which are just a few
pixels large.
This helps give the piece a good sense of scale.
Click here
for the original...
The primary shape is the shape made by the
creature against the background. Then there's some larger tentacles,
which are secondary shapes. Then there are more tiny tentacles, and
grass, etc., which are tertiary shapes. If the image had no tertiary
shapes, it would feel like something's missing.

Click here
for the original...
Robots are a great opportunity for practicing "Big, Medium, Small".
In this image, the larger shape of the creature is the primary
shape. Then that has secondary shapes on it like the front panel or
eye. Then those have tiny tertiary shapes on them as well, such as
nuts, panel lines, small raised panels, etc. Also note that there
aren't tertiary shapes everywhere on the secondary shapes, there are
areas of lots of detail, and areas of no detail. Also notice just how
small some of the tertiary shapes are compared to the secondary shapes.
To summarize, when making your images...
- Have large, medium, and small shapes.
- Have variety to the size of shapes in each of the three
categories.
- Make sure these details are placed somewhat chaotically to avoid
obvious patterns.
- And make sure there are areas of lots of details, and areas of
almost no details.
And remember, just because these are the rules doesn't mean you
necessary have to follow them. But if you don't follow
them, you need to be aware that you're not following them, and what
sort of affect that will have on the viewer.
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Blevins,
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