Primary, Secondary, and Tertiary Shapes
By Neil Blevins
Created On: Sept 28th 2006
Updated On: Aug 2nd 2020

Go here to read this tutorial in Indonesian.

Go here and here for a fantastic talk on the subject by Gleb Alexandrov.

Introduction

This theory in composition goes by many names...

• Primary, Secondary, and Tertiary Shapes
• Big, Medium, Small
• 70 / 30 rule
Whatever the name, the idea is the same, 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.

You have two choices with this lesson, watch me discuss the issue in the video below, or read the full text.

A Definition

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 on top of, or help make up the primary shapes.

Tertiary shapes are again smaller than the secondary shapes, they are the tiny details that add visual interest.

Here's three 2D diagrams showing primary, secondary and tertiary shapes in a fake composition. These 2d rules work exactly the same in 3 dimensions.

Here's another similar diagram...

The Important Questions

Now that you know what primary, secondary and tertiary shapes are, here's 3 important questions...

1. Does my composition have all 3 types?
2. How big should each shape should be?
3. Where in the composition should they go?
Do I Have All 3 Types?

This is pretty straight forward. Does your composition have all 3 of these details? If not, let's say it only has large and medium details, it may be time to add some smaller ones to balance things out. Or if everything is super detailed without any larger shapes, time to add some of those.

What Size Should The Shapes Be?

What should the size of these details be? That depends heavily 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.

So these could be primary, secondary and tertiary shapes sizes....

But so can these...

And these...

Of course, not all details should be the same size, it's more like a range of sizes. So for example, if you have 3-4 secondary shapes in the image, they don't have to be and frequently should not be exactly the same size. This is related to the 70 / 30 rule. If you have a large primary shape, and you want to break it up into 2 secondary shapes, it is more pleasing to break it up into one shape that is 70% of the size, and one shape that's 30% of the size, then two secondary shapes that are both 50% of the original size.

The same works for tertiary shapes. If you break up a secondary shape into multiple tertiary shapes, consider breaking it up into a bunch of tertiary shapes that are 30% the size of the secondary shapes.

Where Should They Go?

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, if you are a 3d artist just starting out, and need a dirt ground, you're likely to make an image like this by placing a standard procedural pattern on a ground plane...

This does not provide the eye any spot to rest, and hence doesn't look very natural. 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.

A Photographic Example

Remember that noisy ground plane above? Let's fix it by looking at a photo of a real dirt ground. Notice the variety in the patterns.

A 3D Example

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.

Examples From My Artwork

Here's a few paint-overs of some images that I made in the past, showing off the primary, secondary and tertiary shapes...

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.

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.

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.

Robot Example

Here's an example of a floating loader robot.

Now let's look more closely at the distribution of detail.

Sometimes, 3 reads (or sizes of shapes) aren't enough. In this example, I split it one step further with 1st read being the largest shapes (primary shapes), 2nd is more support shapes that make up the primary shapes (secondary shapes), 3rd is another level below that (tertiary shapes), and 4th read shapes are the super tiny detail.

Conclusion

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 around the image and not all clumped in one area.
• 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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