Color 5 (Human Perception)

Guide info#

Short: 6-8 minutes

TLDR - What this guide covers#

• Our eyes contain rods and cones which let us perceive color. Color blindness occurs when a cone malfunctions.
• Color relativity changes our perception of color based on the surrounding colors. This can lead to many unique visual illusions. As a result, there are also ‘impossible’ colors which exist only in our perceptions and not in reality.

1: The Human Eye

Before diving into color blindness and tetrachromacy, let’s talk about how the human eye normally functions and how we perceive color and light.

This is a diagram of an eyeball and how it takes in the visual information of an object.

The areas of interest here are the *retina *and the pupil. The pupil is responsible for the amount of light entering the eye. It shrinks in brightly lit areas to stop the eye from being overwhelmed, and it enlarges in dimly lit areas to take in more light and information.

The retina contains rods and cones which are the primary photoreceptor cells. The rods are located in the outer edges of the retina to allow more light to reach them, hence functioning better in low light areas. Rods only perceive the brightness of light, which is why it’s sometimes difficult to differentiate between hues.

The cones are the photoreceptors that allow us to perceive colors. They’re concentrated near the Fovea (see the diagram above) and function well in bright areas.

Humans typically have 3 different kinds of cones - red, green and blue - and as such are called ‘Trichromats’. These different cones are what let us see colors. Any kind of color blindness is the result of a malfunctioning cone.

There are 3 different kinds of color blindness. Abnormal green or red cones result in Deuteranopia and Protanopia, while an abnormal blue cone results in Tritanopia. Hence, people affected by color blindness are called dichromats, due to having 2 functioning cone cells.

There are some rare mutations which may result in people having 4 cones. However, most of the time, the fourth cone is malfunctional or a duplicate of another cone, making true tetrachromacy much rarer. Functional tetrachromats would have a yellow cone alongside the red, green and blue ones. This extra cone allows tetrachromats to see many more colors compared to trichromats.

Let’s try to visualize tetrachromacy. We’ll look at the work of a fine artist named Concetta Antico, who is a tetrachromat. It’s important to note that a fourth cone isn’t a prerequisite for being skilled with colors, nor is Antico’s talent solely due to her tetrachromacy. There are numerous visually impaired artists and GD creators who can produce brilliant works.

2: Color Relativity

While the human brain is quite skilled at processing colors, it’s not perfect. There are many quirks of our vision which arise because of how we see colors, as you’ll discover in this section.

Color Constancy#

Color constancy is when our eyes see a color as staying the same, even if the lighting changes. For example, we still see red strawberries as red, even if there’s a blue light shining on them.

Our brain perceives everything in this image as cyan, but it’s compensating for the cyan overlay, making us think we see the strawberries as red.

This is a very famous example of color constancy. In fact, all you have to do to find it on the internet is to search “gold and white”.

This dress has sparked debates online over whether it’s gold and white, or black and blue. Initially, people perceive it as gold and white due to the perception of being in a shadow. This image illustrates it well.

However, this is incorrect, and the dress is actually black and blue. Color constancy tricks our brains into thinking it’s under a shadow when it’s actually brightened. This becomes apparent when observing the bright, washed-out background.

Simultaneous Contrast#

Simultaneous Contrast is one of the most well known aspects of color relativity. It is the effect on our eyes when 2 of the same colors are perceived differently based on the surrounding colors.

There are many demonstrations of this; for example, this famous checkered board with a cylinder casting a shadow on it. In this image, we think square A is a dark square and square B is lighter, as they follow the same pattern as the light squares, and you can see there is a darker square next to them.

However, in reality, square A and square B are the exact same color.

Successive Contrast#

Successive contrast occurs when looking at one color influences how you view the following colors. This happens due to a process called adaptation, where the eyes adjust to take in more information with rods and cones.

Pause this video when it’s on the red and green circles, and stare at the black dots in the center for about 30 seconds. Afterwards, unpause the video. You’ll notice that you perceive the 2 orange circles to be slightly different colors.

When staring at the green circle for a while, the following orange circle will appear to be more saturated. When staring at the red circle, the orange circle that appears afterwards will look brighter than the more saturated circle. This is because successive contrast uses the complementary color of the initial color.

Green appears to be brighter than red, and it also happens to be its complement. This is why the orange circle seems more saturated after staring at the green circle.

Impossible Colors#

Impossible colors are a set of colors that cannot be seen normally. Some of these colors cannot be recreated realistically and some of them can be produced.

The first set of impossible colors are the imaginary colors. These colors are perceived by a combination of cone cells that cannot be achieved under normal circumstances.

Take the green or ‘medium’ cone cells, for example. It’s impossible to stimulate only the medium cone cell because its spectral sensitivity overlaps with that of the large and small cone cells. If you were to activate just the medium cone cell, you would perceive an impossibly green color often referred to as ‘Hyper green’.

The next type of impossible colors are called chimerical colors. They happen when you stare at a really bright color for a while and then look at a different color. Your eyes get overstimulated, and you see an after-image that’s the opposite of the original color.

Stare at the crosses in the circles for about 1 minute and then afterwards, stare at the crosses in the next square. You will briefly see an after-image appear above the other square.

Staring at the yellow circle and then looking at the black square, you will end up seeing a blue color called Stygian Blue. Stygian colors are types of color that are both impossibly dark and saturated.

If you stare at the green circle and then look at the white square, the resulting color will be a very bright red known as self-luminous red. Self-luminous colors happen when you stare at one color, then look at something bright. This creates an after-image of the opposite color, which looks super bright, even brighter than white.

If you stare at the cyan circle for long enough and then look at the orange square and the after-image it produces is a color known as hyperbolic orange. Hyperbolic colors are those that are more saturated than the purest of those colors.

Changed the channel name: Color 5: Human Perception

**Video: **https://youtu.be/P2r4Z5kbx7M?si=P8PvmVByUQ6W_Ocy&t=478

Credits#

Created by @etherail and @sku