Color Illusions

Apples illustrating color illusions, by Benjamin Lawless

How Color Can Play Tricks With Your Eye

Color is one of those elusive subjects; it is very difficult to communicate precisely. Many variables, from lighting conditions to the surrounding environment to the age of the viewer, have an effect on the way we perceive color. Some variables in particular change the way colors are perceived when prints become large. In this article I show you some visual aids to demonstrate how a color can be perceived differently simply by changing the surroundings.

The Luminance Illusion

Lets start with a simple grayscale example. The image below demonstrates how our perception of depth and shadow effects the way we perceive color. To be more precise, the following illusion will show how the eye perceives the luminance of an object different from the actual luminance values. Press “Play” to reveal the illusion.

The Cornsweet illusion: our eyes perceive the luminance of the top and bottom object as different, when they are actually the same luminance, or brightness.

You will see that the top and bottom grey are actually the same value! This effect is know as the Cornsweet illusion. You can read more about it here at Wikipedia.

Discounting the Illuminate

This next illusion demonstrates how the surrounding lighting environment changes the way we perceive color. The cube on the left is lit by a yellow light, the cube on the right is lit by a blue light. Slide the bottom slider to reveal the illusion. Clicking “Revealing Color Table” will show swatches of the colors used in the cube surrounded by white light, thus revealing their true color values.

Color Constancy: “…a feature of the human color perception system which ensures that the perceived color of objects remains relatively constant under varying illumination conditions” —source: Wikipedia.


As you can see the "blue" squares on the left and the "yellow" squares on the right are actually both neutral grey. The surrounding environment causes us to perceive them as having a color. This is known as Color Constancy, where the eye adjusts to varying lighting conditions allowing us to perceive colors as relatively constant. This is why the yellow squares of the left image still look yellow in the right image, even though they are actually grey in the right image.

The Same-Color Illusion

Our last illusion demonstrates something a little simpler and more subtle. Click "Play" to see it in action.

This demonstration shows that two spectrally-identical circles will be perceived differently when surrounded by different backgrounds.

The two circles pictured above are the same color. By coloring the surrounding space with slightly different colors we change the circles perceived color. For all the graphic designers reading this: imagine that the circles represent your customer’s Pantone™ swatch (which they chose from a color pallet previewed on a white background). Your printer might match the color dead-on, but because of the surrounding environment, each will be perceived incorrectly.

Conclusion

Hopefully this helps you understand how our eyes can perceive colors differently under varying conditions. If you are interested in reading more on this subject I suggest you check out the following resources:

Purves Lab: This is where the sample images you saw above came from. Purves lab is a wealth of information and examples about how we perceive color.

Wikipedia: Visit the Optical Illusions category at Wikipedia for a collection of illusions and their explanations.



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Article written by Jon Beebe.