How We See Part 1: Optical Illusions

In order to understand why and how to retouch, it’s important to understand how we process visual information. There’s no denying that our visual system is remarkable, but it’s far from perfect. It’s incredibly easy to trick. Our brains don’t always interpret what’s in front of us correctly. Our perception is influenced by a number of different things, so that what we see isn’t always what’s there. So, let’s have some fun and take a look at some optical illusions!

Zöllner illusion

Zollner Illusion

These lines are actually parallel. You can also see a dynamic demonstration of this illusion.

Pinna’s Illusory Intertwining Effect

Pinna's Illusory Intertwining Effect

These circles are actually perfectly concentric. It’s easy to throw our visual system off balance.

The Checkershadow Illusion

Checker Shadow Illusion


Squares A and B are the same shade. The proof:


Checker Shadow Illusion Proof

Correct tone and color are the lifeblood of a good photograph. Knowing how people will interpret them is very important.

Poggendorff Illusion

Poggendorff Illusion

We perceive the blue line as connected to the black one, but it’s actually the red line. I’ve moved limbs and strands of hair because of this effect.


Simultaneous Contrast Illusion

The background is a gray gradient. We perceive the smaller rectangle to also be a light to dark gradient, but actually it is one color.

 Ebbinghaus IllusionThe orange dot on the left seems smaller than the one on the right, but they are the same size.

 thaumatropeAnd of course, because I love all old things, I have to conclude this post with the traditional thaumatrope, which is a set of two images on two sides of a piece of paper that you can twirl around on strings to create the illusion of a single image. Classic example: bird in a cage.

So, why is this significant for retouching?

Retouchers need to understand, on at least a surface level, how the brain interprets visual information. People can look at a photograph of something and see all sorts of strange visual phenomena. We need to correct for that in one direction or the other. We can either remove aberrant, confusing visual effects or create illusions to compensate for shortcomings in a photo. One thing I often notice in skin is when pores or light start to create strange, distracting patterns or channels. Have you ever stared at clouds or a stucco wall and started to see pictures? Same effect. We would never notice that in real life. That’s an example of an illusion we need to correct for. Another weird one is limbs that go behind objects and then emerge again at seemingly totally different angles, much like in the Poggendorff illusion. They look like they don’t line up at all! That needs fixing so that the poor person in the photo doesn’t look like they’ve dislocated something. Tonal and color illusions can also completely run amok, especially in mixed lighting, and are a major part of retouching that we always need to be aware of . There are many examples of day to day illusions and they aren’t just limited to photos. We encounter them in life as well. We just don’t notice them as readily because life moves so quickly. There’s no freeze frame without a camera.

Ultimately, optical illusions remind us that experience isn’t always the same as the reality. We are constantly bombarded with all sorts of subtle optical illusions. When looking at a still photograph, we have more time to pick apart those illusions, much like we can pick apart the above illusions when we sit and consider them. Armed with knowledge about how we see, retouchers can bring a photo closer to our day to day experience of a person, place or thing. Sure, sometimes we want the cold, hard, facts about a scene, and sometimes it can be fun to spot all those things we can’t see in the blink of an eye–it can be a game–but art, in the end, is about the human experience, not always cold, hard documentarian facts. Properly armed with the laws of visual science, we can use our understanding of how we see to bring a photograph more in line with how people really visually experience things on a day to day basis.

You may be wondering at this point why we don’t process optical illusions as the norm when we’re looking at things in our day to day lives. We’ll be talking about a meaty subject next week that may explain some of those compensatory mechanisms in How We See Part 2: Gestalt Psychology.

And really, if you’d like to learn more about how we process visual information, I really highly recommend this book. It goes into great detail about our visual systems and psychology. I consider it a must-read for any artist and retouchers in particular: (affiliate link)