How we see color - Colm Kelleher

Summary

This script explores the concept of physical color, explaining how light waves' frequencies determine color. It highlights the human eye's biology, particularly the role of cones detecting red, green, and blue light, which allows the brain to perceive a wide spectrum of colors, including yellow as a combination of red and green light. The script also touches on how our limited color detection in low light is due to rod cells and the practical application of color theory in TV manufacturing.

Takeaways

• 🌈 Light waves' colors are determined by their frequencies: violet for high frequencies and red for low frequencies.
• 🤔 The concept of 'physical color' suggests that color is an inherent property of light, independent of human perception.
• 👀 The combination of red and green light waves appears yellow to us due to how our eyes and brain process different frequencies.
• 🧬 Human color perception occurs in the retina, involving two types of light-detecting cells: rods and cones.
• 👁‍🗨 Rods are responsible for vision in low light, but cannot detect color, while cones are responsible for color vision.
• 🟥🟩🟨 There are three types of cone cells that correspond to red, green, and blue light frequencies.
• 🧠 The brain interprets signals from cone cells to create the perception of color, including mixed colors like yellow.
• 🌌 At night, when rods dominate, we can't perceive color because they only send a signal for light presence, not color.
• 🖥️ The principle that red, green, and blue light can be combined to create any color is utilized in TV manufacturing.
• 🎨 Our eyes have a limited number of color receptors, but this limitation allows for the creation of a wide spectrum of perceived colors.

Q & A

What is the physical basis for the color of an object?

The physical basis for the color of an object is the frequency of light waves it reflects. High-frequency light waves appear violet, low-frequency ones appear red, and the intermediate frequencies look yellow, green, orange, etc.

Why is the idea of physical color not the complete story?

The idea of physical color is not the complete story because it doesn't account for human perception. For example, when red and green light waves overlap, they create a yellow color, even though there is no yellow light present.

How does the human eye perceive color?

Color perception occurs in the retina, which contains light-detecting cells called rods and cones. Rods are for low-light vision, while cones are responsible for color vision, with three types corresponding to red, green, and blue.

Why does the overlapping of red and green light appear yellow?

The overlapping of red and green light appears yellow because the brain receives signals from both red and green cones, similar to how it would if actual yellow light were present.

How does the presence of only one type of rod cell affect night vision?

Having only one type of rod cell means that in low-light conditions, the brain can only receive signals for light or no light, which is why we cannot detect colors in the dark.

Why can the human brain be tricked into seeing any color?

The human brain can be tricked into seeing any color because it has only three types of cone cells. By combining the signals from these cones in the right way, it can perceive a wide range of colors.

What is the practical application of human color vision in television manufacturing?

In television manufacturing, instead of needing infinitely many colors, manufacturers only need to use red, green, and blue because the human brain can perceive a full spectrum of colors from these three.

How does the concept of 'red plus green equals yellow' relate to human color perception?

The concept of 'red plus green equals yellow' relates to human color perception because the brain interprets signals from red and green cones as yellow, whether from actual yellow light or a combination of red and green light.

What is the role of cones in color vision?

Cones play a crucial role in color vision by detecting specific frequencies of light and sending distinct signals to the brain, allowing us to perceive a wide range of colors.

How does the absence of a specific cone for yellow affect our perception of that color?

The absence of a specific cone for yellow does not affect our perception of that color because the brain interprets signals from red and green cones as yellow.

What is the significance of having three types of cone cells?

Having three types of cone cells allows humans to perceive a broad spectrum of colors by combining signals from red, green, and blue cones, which is known as the RGB color model.

Outlines

00:00

🌈 Understanding Color Perception

This paragraph introduces the concept of physical color, which is the idea that color is a property of light waves based on their frequency. High-frequency waves appear violet, while low-frequency waves appear red, with other colors like yellow, green, and orange falling in between. The paragraph then challenges this concept by pointing out that when red and green light waves overlap, they create the perception of yellow, even though there is no actual yellow light present. This leads into a discussion about the biological aspect of color perception, explaining that the human eye has different types of cells in the retina that detect light: rods for low light and cones for color. There are three types of cones, roughly corresponding to red, green, and blue light, which send signals to the brain to create the perception of color. The brain interprets the combination of red and green light as yellow, even though it's not a distinct frequency like the other colors mentioned.

Keywords

💡Light waves

Light waves are disturbances in the electromagnetic field that travel through space. They are characterized by their frequency, which determines the color we perceive. In the video, it's mentioned that high-frequency light waves appear violet, while low-frequency ones appear red, illustrating the relationship between frequency and color.

💡Frequency

Frequency refers to the number of wave cycles per unit of time, measured in Hertz (Hz). It's a fundamental property of light waves that determines their color. The video explains that different frequencies of light waves correspond to different colors, with violet at high frequencies and red at low frequencies.

💡Physical color

Physical color is the concept that color is an inherent property of light itself, independent of human perception. The video introduces this idea to contrast with how humans perceive color, which is a biological process rather than a purely physical one.

💡Retina

The retina is a light-sensitive layer of tissue located at the back of the eye. It contains cells that detect light and send signals to the brain. The video explains that color perception occurs in the retina, highlighting its importance in the process of seeing color.

💡Rods and cones

Rods and cones are the two types of photoreceptor cells in the retina responsible for vision. Rods are sensitive to low light levels but do not detect color, while cones are responsible for color vision. The video explains that there are three types of cones corresponding to red, green, and blue light.

💡Cones

Cones are specialized cells in the retina that detect color. There are three types of cones, each sensitive to different light frequencies corresponding to red, green, and blue. The video uses the example of yellow light to explain how the activation of red and green cones can create the perception of yellow.

💡Color mixing

Color mixing is the process by which different colors are combined to create new colors. The video discusses how mixing red and green light can appear yellow to the human eye, even though there is no actual yellow light present.

💡Signal

In the context of the video, a signal refers to the electrical impulse sent from the retina to the brain in response to light. The video explains how different signals from cones correspond to different colors perceived by the brain.

💡Low-light conditions

Low-light conditions refer to environments where there is little available light. The video explains that in such conditions, rod cells in the retina become active, which are not sensitive to color, hence why we cannot perceive color in the dark.

💡RGB

RGB stands for Red, Green, and Blue, the three primary colors of light used in electronic displays. The video uses the RGB model to explain how TVs can simulate a wide range of colors with just three types of light.

💡Perception

Perception is the process by which the brain interprets sensory information. The video discusses how our perception of color is a result of the brain interpreting signals from the retina, rather than a direct reflection of the physical properties of light.

Highlights

Light is a kind of wave, and color is related to the frequency of light waves it reflects.

High-frequency light waves appear violet, low-frequency appear red.

Intermediate frequencies correspond to yellow, green, orange, and other colors.

This idea is known as physical color, implying color is a property of light, not dependent on human perception.

The concept of physical color is incomplete without understanding human color perception.

Red and green light waves overlap to appear yellow, despite being different frequencies.

Light waves of different frequencies do not interact, yet our perception combines them.

The human eye's retina contains cells that detect light, called rods and cones.

Rods are for low-light vision, and there is only one type.

There are three types of cone cells corresponding to red, green, and blue light.

Cones send distinct signals to the brain based on the color they detect.

Yellow light activates both red and green cones, sending signals to the brain.

The brain interprets signals from red and green cones as yellow, regardless of actual light frequency.

In low-light conditions, rod cells take over, detecting only light or no light, not color.

Human vision can be tricked into seeing any color by combining red, green, and blue light.

This property is utilized in TV manufacturing, needing only red, green, and blue to simulate colors.

Transcripts

Translator: Andrea McDonough Reviewer: Bedirhan Cinar

You might have heard that light is a kind of wave

and that the color of an object

is related to the frequency of light waves it reflects.

High-frequency light waves look violet,

low-frequency light waves look red,

and in-between frequencies look yellow,

green,

orange,

and so on.

You might call this idea physical color

because it says that color is a physical property of light itself.

It's not dependent on human perception.

And, while this isn't wrong,

it isn't quite the whole story either.

For instance, you might have seen this picture before.

As you can see, the region where the red and green lights overlap is yellow.

When you think about it, this is pretty weird.

Because light is a wave, two different frequencies

shouldn't interact with each other at all,

they should just co-exist

like singers singing in harmony.

So, in this yellow looking region,

two different kinds of light waves are present:

one with a red frequency,

and one with a green frequency.

There is no yellow light present at all.

So, how come this region,

where the red and green lights mix,

looks yellow to us?

To understand this, you have to understand a little bit about biology,

in particular, about how humans see color.

Light perception happens in a paper-thin layer of cells,

called the retina,

that covers the back of your eyeball.

In the retina, there are two different types of light-detecting cells:

rods and cones.

The rods are used for seeing in low-light conditions,

and there is only one kind of those.

The cones, however, are a different story.

There three kinds of cone cells that roughly correspond

to the colors red,

green,

and blue.

When you see a color,

each cone sends its own distinct signal to your brain.

For example, suppose that yellow light,

that is real yellow light, with a yellow frequency,

is shining on your eye.

You don't have a cone specifically for detecting yellow,

but yellow is kind of close to green

and also kind of close to red,

so both the red and green cones get activated,

and each sends a signal to your brain saying so.

Of course, there is another way to activate

the red cones and the green cones simultaneously:

if both red light and green light are present at the same time.

The point is, your brain receives the same signal,

regardless of whether you see light that has the yellow frequency

or light that is a mixture of the green and red frequencies.

That's why, for light, red plus green equals yellow.

And, how come you can't detect colors when it's dark?

Well, the rod cells in your retina take over

in low-light conditions.

You only have one kind of rod cell,

and so there is one type of signal

that can get sent to your brain:

light or no light.

Having only one kind of light detector

doesn't leave any room for seeing color.

There are infinitely many different physical colors,

but, because we only have three kinds of cones,

the brain can be tricked into thinking it's seeing any color

by carefully adding together the right combination

of just three colors:

red, green, and blue.

This property of human vision is really useful in the real world.

For example, TV manufacturing.

Instead of having to put infinitely many colors in your TV set

to simulate the real world,

TV manufacturers only have to put three:

red, green, and blue,

which is lucky for them, really.