
In this article I won't explain all the rules of modifying an object in linear perspective. There are a lot of tutorials about it, so you can look them up. Instead, I'll explain to you where these rules come from and why someone needed to invent them. The rules, after all, are only a way of describing a fascinating phenomenon, one present in nature since the day our brains started to process the signals from our eyes. After reading this article, your world will never be the same!
Perspective... So, What, Actually?
Forget about math and geometry. Go back in time and remember those days when you were traveling and observing the buildings and objects moving with you. Those closest to you were moving the fastest, and these in the background were scarcely changing position. And the furthest of them, the moon, wasn't moving at all—it was, and still is, always there, no matter where you go.But, of course, it was very silly of you to think the objects actually moved when you did. It was just an illusion, like how your monitor or a table looks skewed when you look at it from the side. Of course, it's a rectangle, so it's only an illusion. We're so used to these illusions that we don't see them any more, and if a child asks why the buildings move, or why a table is so skewed, for a while we may even not understand what they're talking about.

Size
How big is this object? Can you really tell?


Position
But where is our square? Is it far or is it close?




x
and y
to say where x
is. Unintuitive? Keep on reading. I'll explain it all later.Motion
Does this square move? Probably not, right?

You can tell whether something is moving by comparing it to another thing that isn't moving. The change of distance between them is the way you measure the speed. People used to believe that the Sun revolved around the Earth, and now we believe it's the opposite. The truth is neither of those is true—or they both are.
What Is True?
All these examples have one thing in common: a relation must occur for them to exist. Perspective is just a name for a relation between the observer and other objects. See? No math at all.You may think, "But objects are somewhere just like that, they don't wait for us to tell them they are there!" It may look unintuitive, but there are a lot of expressions created by humans in relation to us:
- If I need to move a lot to reach it, it's far.
- If my arms get tired quickly when I carry it, it's heavy.
- If I barely feel it in my hand, it's light.
- If it burns when touched by me, it's hot.
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| If (distance(my.position,x)) > 100*my.steps then x=far; else x=close; If (weight(x)) > my.strength then x=heavy; else x=light; If (temperature(x)) > my.temperature then x=hot; else if (temperature(x)) == my.temperature then x=normal; else x=cold; If (size(x)) > my.remembered_size_of_x then x=big; else if (size(x)) == my.remembered_size_of_x then x=normal; else x=small; |
What's interesting is that the expressions "far", "close", "big", "small", "heavy", "light", etc., change their meaning all the time depending on the variables. A remote control is far away from you when you need to get up to switch the channel (let's say, 3 meters), but at the same time a restaurant on the next street (300 meters) is close to you.
It may look like philosophy to you, something conceptual, one of many ways to describe reality. The fact is that all these things—size, position, distance, motion—are nothing but concepts. Imagine you're a kind of god and suddenly you can observe a world without it all! In fact, you can't imagine it—when trying, you're most likely "flying out of your body", but still being and observing everything from one point. We are our own references, and it's impossible—at least for a mentally healthy, sober person—to imagine the universe without any reference point. What's more, "feel", "touch", "observe", and other expressions like these imply an analyzing tool and analyzed object. We can't, in any way, sense objects without using us as a reference—as long as we are humans, we can't know what anything really is. Math is the closest we can get to its image, but the more accurate and complete it gets, the less people are able to understand it.
Every Sense Has Its Own Perspective
More specifically, perspective is a relation between a certain sense of a particular person and an object. Every sense may have a different perspective. That's where illusions come from—if an image received by one sense doesn't match the others (or our knowledge about it), we say it's not true. You can check it by closing your eyes in a small room with white walls. Spread your arms and you'll be surprised how tiny it became!We use vision as the most important sense, so we tend to imagine that reality is just like what we see. The world of darkness, when our eyes stay closed, is a different world that we like to call incomplete. The fact is that what we see is incomplete too—our eyes and brain process only a small fraction of all visual signals available. We live in a reality that exists only for us, and is similar—but not necessarily identical—among humans. We don't know what the world looks like. It's being rendered right in front of you with every move of your head. That's why objects around you change form when you move—it's not an illusion, they really do. Shapes and forms exist only in your head, as an interpretation of certain information processed by your brain. There's no "true" form, one not created by your brain. All of them—straight and skewed—are the same. Either you call them all illusions, or they're all true.

Perspective Makes the Image
I hope I didn't bore you with this lengthy explanation, but I think it's crucial to truly understand what I'll say next. As an artist you create an optical illusion—you use lines and patches of pigment to make people believe they're looking at something they know from reality. This illusion needs to take into account every single vision mechanism we know to be complete. You can't draw a bowl of apples, because, as we know now, we have no idea what it really is. You draw a seen bowl of apples—seen by someone's eyes.This is where it all begins. When you draw from a reference—be it a photo or reality—you simply copy the image you see in your head. That's why it's relatively easy to achieve amazing results from this—you only need good manual skills and hand-eye coordination, both simple to learn.
Most people see this process as "copying reality". Again, it's impossible to create a copy of a bowl of apples with your brush (A). You can only create a visual copy (3) of the image created in your mind (2) when looking at the bowl of apples (1).

- The image of an object is an interpretation of one's brain.
- The same brain will create a countless number of different images of the same object when the position of the eyes changes.


How Does Perspective Influence the Look of an Object?
It's still quite confusing, isn't it? Let's learn some more about depth.How is it possible you can see 3D in a 2D picture? The same way you can see depth with only one eye! In fact, binocular vision is the most useful at a very short range—you can use it to thread a needle or do some other precise tasks. For other cases, like distinguishing "close" from "far", we use our observations from the past. We know how big an apple is when we hold it in our hand, so when it's much smaller than this, it must be far. For a complete image, we also use eye accommodation, comparison, and light and shadow.
The observer has only one eye, as long as we don't have the technology to draw 3D pictures in an easily accessible way. But it doesn't really matter! When you see a 3D model on your screen, it's 2D. The illusion of depth is made when you start to rotate it. The same trick is used when you've got one eye—you move your head to change the perspective and suddenly depth is created. Why? Because 2D pictures have only one perspective. If you can easily switch between at least two of them along some common dimension, it becomes 3D for your mind. It's because in a 2D scene, an object can only move up-down and left-right, or across. When it moves in some other direction—towards or away from you—another dimension is added. This third dimension is depth.

There are perspectives that convey only two dimensions. Let's call them 2D perspectives. Since a sheet of paper is 2D too (at least from our perspective...), conveying only two dimensions on it is very intuitive. However, you can't get round the third dimension and expect it still to be readable! Drawing in a 2D perspective inevitably leads to a flat picture—something that maybe has a third dimension, but we can't know anything about it, so we assume it doesn't have any.


I've been there, too. But let's say it once again: an image is created when it's seen. When something is seen, a perspective is created automatically. Therefore, perspective is sewn into everything you draw. You can either learn it or not—but there's no way to avoid it.


How Does Perspective Work?
Finally, the part we've all been waiting for! We've already clarified that perspective is a crucial part of every drawing, not only technical ones. But where does it come from? How is a single perspective created? How and when does 2D perspective transform into 3D? And why do 3D objects on a 2D picture look distorted?Open your mind—this is something you might never have thought about. It will be counter-intuitive, because you've been using Euclidean geometry all your life, and, as we're going to learn soon, vision doesn't work that way. It's not easy to jump from one way of thinking to another after all these years, but it's certainly worth it!
Three Dimensions
Let's start with the explanation of dimensions. You may know 2D is flat and 3D is...well, 3D, but how does it work? What's the difference between flat and three-dimensional objects?Let's start with a probably shocking fact—objects aren't 2D, or 3D, or 5D—they're only immersed in dimensions and are perceived by us as a complete image made by parts from every dimension. That's why a cube can be a square, a square can be a line, and a line can be a point. We call an object "3D" if it exists in a third dimension as something more than a point.
Two Dimensions
It doesn't matter what we call the dimensions. What matters is that for us there are three of them. Let's start with two dimensions.This is a 2D sheet, right? We know it well. It has width and height, and that's all we need to draw anything flat.







The Mysterious Third Dimension
In 2D space we can go left, right, up, down, and everywhere in between. However, there's no "forward" and "away", no "close" and "distant" here. Distance will be our third dimension—when you move one 2D sheet under or over another, depth is created.
However, both a sheet of paper and your screen are 2D. We can't picture the third dimension here! The illustration below is just a concept, not a reflection of reality.



Human Field of Vision (FOV)
Our eyes aren't the most perfect of all the animals; they're actually pretty bad. Although with both eyes we have about 120 degrees field of vision, only in area 1 we can see sharp details and colors. In area 2, colors and blurry shapes are all that's left, and area 3 is mainly used to see motion only. However, our brain fills in gaps and we believe the image in our head is as good as a photo—with colorful, sharp details in every point. It also persuades us there's no blurry, double nose right in the center of our vision.



Here's a symbolic interpretation of a FOV in the simplest configuration (only one eye used, we don't need more).
- Glasses: I used them to show you where your eye is.
- Nose: it's always there, but your brain tells you it isn't.
- Sky: in this area everything is above your head.
- It's the area of your height.
- Ground: place objects here for them to stand steadily.
- Underground: if there's a hole in the ground, or the ground is actually water, you can make a good use of this area.
- The edge of your upper eyelid.
- The edge of your lower eyelid.
- Certain distance between the eye and the ground.



Scale
The most characteristic feature of perspective, objects getting smaller with distance, can be easily explained with the FOV cone.While the cone gets wider with distance, the size of every frame stays the same for our brain. When you look at something very close to you, you don't see that your field of view suddenly got smaller—you only notice that the object got bigger in comparison to it. Objects don't change when getting closer or farther, they only land on different frames. The bigger the frame, the smaller the object seems in comparison. That's why you can cover the whole world with a hand—at one point it's indeed able to cover the rest of the cone.

It also explains why the back side of a cube seems to move at a different speed than the front—they're both on different frames!

Default Size
Now we know why the size of an object changes with distance. But how can we determine the "default" size? At what point does the object look as big as it really is? If you've been reading carefully, you should know the answer—there's no such thing as a "real size". When you measure something with a ruler, you compare it to a model size of 1cm—a model that changes with distance too, so it's not constant for your eyes. There's no way to measure an object changing in perspective.However, there's a trick our eyes use to overcome this inconvenience. The first clue to estimate the size is to notice how big a part of the frame it takes.

Experience
This is the most basic one. You know that a building is big enough to store you inside, so when it looks too small for it, it must be far.
Comparison
Since the frames' size changes regularly, we can use proportions to estimate the size. It means that everything inside one frame will get smaller according to some kind of a factor that you can use in your equation to come back to the primary outcome. That's why we often use a human silhouette somewhere in the scene to stress the size of it. You can also use other well-known objects, like trees or mountains (when they're small in comparison to the main object, it must be huge), or grass (when it's huge, the main objects must be tiny).
Depth of Field
When using shallow DOF you're able to separate close objects from distant ones. An easy trick is to draw some negligible objects just in front of the observer and blur them, to show the distance between the observer and the scene. Even if you don't want to use blur, the areas out of focus should be less detailed.
Overlapping
One object can cover another only when it's closer to us than it. It speaks a lot about distance and it's the simplest, most intuitive method for creating depth.
Atmospheric Perspective
You can read more about it in my other article, but here's the point: The further something is, the more the color of the sky is being scattered between you and that object. It doesn't work when the air is very clear, but in most cases a bluer, lighter object = a distant object.
Distortions
If you looked carefully at our cone, you should notice an odd thing. The 2D planes aren't really flat—they're like shallow bowls. It means they're spherical like the Earth, and just as we can't create a perfect, undistorted 2D map, we can't create a 2D frame without distortion.The illustration below shows clearly that the line, although perpendicular to the sight line, lands on separate frames. As we know, the farther the frame, the smaller the object—so a part of the line will become smaller, making the line shorter and turned away from us!


Let's see how it works. When we want to see another side of the cube, we need to rotate it. However, at the same time the perpendicularity of the first one is being lost—both sides are sliced across multiple frames on a different distance (depth). Therefore, part of them looks shorter and more distant—they look rotated.

First you need to remember we've got two horizons—horizontal and vertical. We're so familiar with the horizontal horizon that we don't even notice the other one. But of course, that doesn't stop it from existing!





A
will look the closest to you, while the others will be observed as receding. 
A
lie on the same frame, so they're perceived from the same distance. However, between points B
and C
there's a difference in depth. For points E
and D
this difference is huge!

The higher the object over* the horizon, the more of its bottom** and the less of its front is visibleYou can now create analogous situations to this, with "*below" and "**top", or with "*to the left of" and "**right", etc. Just make the pairs of opposite sides and it will work! An addition to this lesson is:
The farther the line from the center, the shorter

The Flaws of Linear Perspective
Linear perspective is a simplification of everything we've been talking about. Let's see how it's possible.0-Point Perspective
In this perspective all the straight lines are parallel or perpendicular to each other. They don't converge at any point. This is the perspective we can observe when looking at the center area of our FOV, when the object stands in front of us.
1-Point Perspective
In this perspective all the lines that aren't parallel or perpendicular to each other converge at one point on the horizon. This is an effect similar to that observed in the center area, except in reality a slight distortion will occur. The objects need to stand perpendicularly to the sight line for this.
2-Point Perspective
In this perspective there are two points on the horizon where all the lines that are not parallel to each other converge. We can observe this effect when expanding the center area. Here the objects are allowed to be rotated.
3-Point Perspective
In this perspective there are no parallel or perpendicular lines. They all converge to one of the two points on the horizon or to the third point on the vertical horizon. This effect can be observed when looking peripherally, especially up/down (e.g. observing a high building). Rotation is welcome.Why Is It So Hard to Use?
There are two main reasons why linear perspective looks so counter-intuitive and stops you from spontaneous drawing.First, the vanishing points aren't about the position of the observer, but the objects in relation to them. Every object introduces its own vanishing points, so it's easiest to put them all in rows, so that they share the same VPs. If you prepare a single perspective grid and surrender all the objects to it, you'll get a stiff, man-made space—and lose control over the composition. On the other hand, the more vanishing points, the more chaos and work for you.


Conclusion
I agree, perspective isn't the easiest topic—but what is? If you want to be a great artist, there's no way to avoid things like this. If you haven't understood it yet, take your time, split it into parts and study them carefully. I strongly believe it's the base of everything about re-creating reality. Yes, it's hard—but believe me, after this, everything's easy!Perspective lets you draw a world seen from horseback, or dragonback, with the eyes of a tiny worm or a flying bird. It creates dynamism, motion, life. It turns a stiff frame into a vivid memory. If you want to breathe life into your pictures, stop thinking only about the pictured objects and focus on the observer too. Without them there would be no picture!
The first rule of linear perspective is: learn it so that you can discard it. I hope that after this lesson you don't feel like discarding anything—this is knowledge that will give you artistic freedom while obeying the rules of vision. Keep linear perspective for buildings and room plans—for everything else you just need to understand what's going on in your picture. You've just taken a great step towards being awesome!
