What color is this?
You’re probably thinking, "it’s red!"
which, well, it is.
And what about this?
Why, it’s green, of course!
And what video on color would be complete without an appearance by our old friend blue?
We’ve been using these three colors to fool our eyes and brains into thinking that we’re
looking at a full-color image for over a century.
We can do this because of how our eyes and brains perceive color.
It’s all about ratios, and though it often seems a little freaky, we can mimic the effect
of any real color using just these three in controlled amounts.
But now that we have the luxury of bringing the primary colors of light into the real
world with bright, monochromatic LEDs, we can get a glimpse into just how wonderfully
strange our sense of color perception actually is.
In this video, we’re going to look at a series of demonstrations where objects in
the real world are lit using light from the digital world.
What we’ll find is that things can behave a little… unexpectedly when we play around
with light.
None of the footage in this video has been altered.
I promise no matter how weird some of this looks, I’m seeing the same things in person.
Let’s start with a brief overview of what it is we’re doing here.
I’m using these RGB studio lights to provide illumination.
I can control the ratio of red, green, and blue light they produce by adjusting their hue
and saturation parameters.
For the most part, we’ll be staying with a saturation of 100%, and this means we’ll
be cycling through the 3 primary colors, red, green, and blue, as well as various shades
of the three secondary colors that lie between them, yellow, cyan, and magenta.
When I need to, I can switch to standard phosphor-coated white LEDs
which provide a reasonable approximation
of true, full-spectrum lighting.
Yes, these lights really are G Bee’s knees.
In RGB mode, the light they produce is trichromatic, just like our vision, but each individual
color is monochromatic, meaning it’s comprised of a single wavelength.
And this is where the breakdown between the real and digital world can occur.
I’ll explain this in a little more detail shortly, but first let’s move on to a demonstration.
We’ll be spending much of this video, in the dark.
Here we have a kind of disappearing, color-changing ink.
This whiteboard, when lit with apparently yellow light, appears to have some red writing
on it.
Well, watch this.
Now it’s gone.
But it re-appears, now as a slightly more orange color, with the presence of some blue light.
Now watch as before your eyes the ink becomes a jet black.
It stays black even as the light grows brighter and we approach cyan, before the black turns
to red once more.
And finally, it’s gone again.
What’s happening here?
Well, the ink on this whiteboard is in fact red.
Switching to normal white lighting reveals that.
The red ink absorbs nearly all of the light coming from the green and blue LEDs, which
is why the ink appears black when the scene is anywhere between blue and green.
It doesn’t reflect any of that light back into the camera.
But in addition to absorbing the green and blue light, this red happens to be a near-perfect
match to the red produced by the light’s red LEDs.
And that’s why it disappears under red light.
The white of the whiteboard reflects pretty much all of the red light back to the camera,
as do most white objects, but so does the red ink.
And so, there’s very little contrast between the ink and the board, and the ink effectively
disappears.
Let’s move on.
What color is this can of spray paint?
It’s pretty hard to tell, isn’t it?
In fact, it’s impossible to tell.
Right now, this can of spray paint is being lit solely by the red LEDs, which means it’s
lit by a monochromatic light source.
Doing this fundamentally breaks our color vision because we rely on the mixing of colors
to determine what it is we’re seeing.
Under the same red light, let’s look at some construction paper.
This packaging says there are 8 colors here.
Well, what on Earth are they?
As far as I can tell, these are red, a darker red, a differently darker red, and uh,
more red.
I think there’s black, too, but I’m not sure.
With only one wavelength of light available in this scenario, there’s just no way to
know what it is you’re seeing.
Notice how we cannot tell what the colors are on these Rubik’s Cubes.
We can see that each color reflects the light back in different amounts, causing the stickers
to appear in different brightness levels, but they’re all just different shades of
the same red.
But, with this being a Rubik’s Cube, we know the colors are white, yellow, orange,
red, green, and blue.
We can make some educated guesses into which stickers are which colors.
The brightest are probably red, yellow, orange, and white, as these will reflect most or all
of the red light back into the camera.
The darkest are going to be blue and green.
Now we can be reasonably sure the darkest of them all is blue, as that’s farthest
from red, and the next darkest is green.
But as far as the bright colors?
That’s really anybody’s guess.
The brightest is probably white, but then again there look to be too many that we might
call white.
So white and at least one other color look kinda the same.
But which colors are they?
Well, let’s switch the light over to white and find out.
Oh, sorry, this one is actually monochromatic lemme, lemme get that out of here.
So, we were right about green and blue, but orange, white, and yellow all appear to be
the same.
Red was actually slightly darker, which you might not have expected given that we were
using red light.
This tells us that the hue of this red is actually not purely red, as it does absorb
some of the red we were throwing at it.
And if yellow and orange were reflecting the same amount of red light back as white, well
that again goes to show how strange our color perception is, and why monochromatic light
breaks it.
So how do we see in color?
Well, in our eyes, we don’t just have a bunch of plain photoreceptors.
We have some, known as rods, which just detect brightness, but those of us with typical trichromatic
vision also have three types of color-sensitive cells, called cone cells.
These are pigmented to filter the wavelengths of light that hit them.
Now, we often think of these cone cells as being sensitive to red, green, and blue light.
Which is broadly true, but their actual stimulation curves look like this.
Notice how the medium and long cones, which correspond to green and red, kinda, overlap
a lot, but the short cone is way over there.
Well, where they are along the spectrum doesn’t actually matter all that much.
What matters is that they respond differently to any given color.
Say we have a yellow-green wavelength right here.
Well, for this one color, and this one color only, the long and medium cones get equal
stimulation, and the blue cones get negligible stimulation.
This unique ratio allows our brains to interpret this color as yellow-green.
As we move towards red and head into yellow, now the medium cone gets progressively less
stimulated, and the long cone gets more stimulation.
So, our brains know this color is closer to red than it is green.
As we continue moving deeper into true red, the stimulation from the long cone starts
to taper off, but the medium cone is tapering off faster.
The important thing to remember is that any color at all along the visible spectrum will
cause a unique ratio of stimulation between these three cells, and so our brains know
what color that is.
And so, we can easily fool our eyes and brains into thinking we’re seeing any color at
all by using just three primary colors.
We need one of them to be way over here, so that the long cone gets a fair bit of stimulation,
but the medium cone doesn’t get all that much.
So we’ll use red.
We also need one to the left of the long-medium crossover, that way it stimulates the medium
cone more intensely than the long.
So we’ll use green.
And of course, we also need one way over here that stimulates the short cone a lot, but
doesn’t really influence the other two.
So we’ll use blue.
Now, to make a color like yellow-orange, we can simply mix red and green together, so
that there’s a lot of red and a bit of green.
This mixture causes the same stimulation that an actual yellow-orange object would.
Because there’s overlap between the three cone cells, all real colors just cause a unique
mix of stimulation between the three of them.
That includes, by the way, white, which is all three in close to equal amounts.
So, if we use three pure colors that allow us to selectively stimulate the three cells
with any given ratio, we can artificially reproduce all visible colors.
Our eyes simply don’t have a way to know they’re being fooled.
But while we can make any color appear by using just three colors in different ratios,
that doesn't mean that the world will look right without the whole spectrum to paint
the whole picture.
And unless we have a way to make the cone cells get stimulated in different ratios,
we can’t see color at all.
And with that in mind, let’s move onto some more demonstrations.
This scene contains many red objects.
But, under monochromatic blue light, you’d never know.
Watch what happens, though, when I add just the tiniest amount of red light.
Suddenly, the red pops into existence.
This is a pretty trippy effect in person, because it’s as if someone’s messing with
the RGB sliders of real life.
Until we have red light available, red objects appear, well, grey or black.
Even with green light, the same thing occurs.
Notice how with green and blue light together, we can start to see the yellow and oranges
of the Rubik’s Cube become distinct from the blue and green.
Still, though, the red objects remain completely dull.
Pure green light keeps them in the dark, just like blue.
Keep in mind that the green light is still stimulating the long cones a fair bit, but
without a third, longer wavelength to allow for comparison between the long and medium
cones, our brains cannot see red.
Plus, since the red objects in the scene aren’t reflecting any of that green light, they stay dull.
Add just a hint of red, though, and suddenly the scene explode into color.
Now, there is red light to be reflected, and more importantly for our eyes, there is red
light to be detected and compared with green and blue.
Here’s a different kind of color.
A game boy color.
Under blue light, this thing looks weird to say the least.
Now I’ll add a bit of red and green, alternately.
Compare the light on my hand to the light on the game boy, and you’ll see that overall,
I’m not changing the color in the scene much at all.
But the game boy drastically changes.
This game boy’s color, by the way, is dandelion.
Which is of course, to our eyes, a mixture of red and green.
An important thing to note is that, just like our eyes, the camera’s Bayer filter (which
actually separates subpixels into red, green, and blue elements) doesn’t filter red, green,
and blue perfectly.
There’s a lot of overlap.
And I can show it to you, even with only one wavelength to see.
You might assume that if light is a monochromatic green, then the camera’s blue and red subpixels
will never become active.
But this isn’t true.
If I overexpose the image, you’ll see that it starts turning white.
That happens because even though the light source is monochromatic, the red and blue
filters will still let some through, so the image starts to turn white with enough exposure.
The same thing happens with blue and red.
However, this doesn’t mean we can start to tell colors apart.
We still only have one wavelength illuminating the scene, which means the ratio of stimulation
in the camera’s subpixels stays the same.
The camera’s method of vision is surprisingly similar to our eye’s.
Well, as a matter of fact it’s built for our eyes.
And even under normal exposure levels, there is some green slipping in.
You might expect the image to turn black if I remove all of the red channel, but in fact
there’s a faint green image hiding underneath.
That green is actually helping to define the ultimate hue of the red we’re seeing on-screen.
Which brings me to my next demonstration.
We can have a monochromatic light source of any color, not just red, green, and blue.
With RGB lights, I can only produce yellow light by mixing red and green.
This then becomes a dichromatic color, and if I illuminate this scene with it, we can
actually tell some of the colors apart.
We can even kinda tell blue from green.
But, if I break out my yellow traffic light module (or amber, whatever), this is in fact
a monochromatic yellow.
This color looks quite similar to the yellow I’ve been making by mixing red and green,
but it’s actually very different.
So now, even though the green and red subpixels are both getting stimulation from the yellow
light, because it’s actually just yellow they always receive the same relative stimulation
no matter what’s in the scene.
Our eyes, and the camera, both see these two sources of light as essentially the same color,
but if we use them to illuminate the real world, and take a look at how they get reflected
back, we discover they’re actually very different.
And that brings us to what makes this whole ordeal so messy.
You may have heard of a term called the color rendering index, or CRI.
This describes how well an artificial light source reproduces the color of the objects
around us.
Incandescent lights, being a blackbody radiator, had a perfect CRI, just like the sun, but
more efficient LED and fluorescent light sources, indeed practically all light sources that
aren’t incandescent, don’t emit light as a perfectly uniform spectrum.
Now, as we know, one of the most common ways to mimic white light is to produce red, green,
and blue light, because, well, if you haven’t figured that out by now you’ve not been
paying much attention.
This works absolutely fantastically for creating a display device like the one you’re staring
at now.
Because it’s providing its own illumination, it doesn’t need to worry about how the red,
green, and blue channels interact with the objects around you.
It just needs to fool your eyes into thinking they’re looking at a full-color image.
And, well, displays are getting better and better, with incredibly lifelike colors, all
from just three colors of light.
Except for that one time Sharp got all weird with the yellow subpixel which was absolutely
unnecessary especially since nobody’s encoding color in an RGB-Y space, but I digress.
But the problem with using just three colors of light to illuminate the real world is that
this rarely looks right.
Think about that whiteboard earlier.
The red ink was invisible under red light.
This meant that it reflected practically all of the red light back.
Now, imagine I’m using these lights with red, green, and blue all working together.
This looks white to my eyes,
but when it gets reflected off of the objects around me, the
ratio of colors coming back can be way off.
In the case of the whiteboard, the red looks way too intense and bright.
Which makes sense.
If one third of the light from these lights is red, and the red ink reflects all of it,
it’s suddenly freakishly bright because, well, red is not one third of the color spectrum.
Under true white light, a much greater percentage of light gets absorbed, and the red appears
more dull, like it should.
As a quick note, this is the one demonstration where the camera couldn’t quite capture
what my eyes were seeing.
The difference in person is much more dramatic.
The problem here is that the ability to reduce the real world into three wavelengths of light
is not reversible.
If we have a truly white light source, then all the in-between colors get reflected as
they truly are.
Our eyes can see any wavelength of light because of all that overlap between the cone cells.
And indeed, cameras can see any wavelength of light, because their RGB bayer filters
also have overlap between them.
And so we can reproduce the stimulation real objects cause in our eyes with just three
wavelengths of light, but we cannot expect those three wavelengths to produce the same
stimulation ratios that they should when they hit and get reflected off of real objects
in the real world.
This can perhaps best be demonstrated by the color purple.
Purple is a rather strange color in general.
It, along with magenta, are what are called non-spectral colors.
If you look on the color spectrum, you’ll find violet just on the other side of blue,
but true violet is rather dull, and in fact we have a hard time seeing it.
Which is no surprise since it barely registers with any of our cone cells.
Purple and magenta are kinda similar to real violet, but in a sense, these colors exist
only in our minds.
That’s pretty wild, when you think about it.
Now obviously purple things exist in nature and we can see them with our eyes, so it’s
not like the color is imaginary.
But, it cannot be reproduced with a single wavelength of light.
We only see purple and magenta when our eyes receive blue and red stimulation,
but little green.
Therefore, purple and magenta objects absorb a fair bit of green light, but reflect both
red and blue.
And luckily, our brains have synthesized this combination of stimulation into magenta, and
not the average wavelength between them, as we do with yellow and cyan.
Otherwise, it would be another green.
Anyway, let’s take a look at our old friend Putt-Putt.
This particular anthropomorphic automobile is a rather vibrant shade of purple.
Now, using the phosphor-coated white LEDs, he looks pretty normal.
But when I switch to the RGB LEDs,
well not so much.
Under green light, he looks pretty dull.
Which we might expect, given that we can of course make purple by mixing red and blue
pigments, which will together absorb mostly green wavelengths.
When we add blue light, well now he just looks blue.
All into the cyan range, Putt-Putt looks just like a blue, and once we hit blue, well now
he looks kinda like a grey, as his white features become blue, and his body becomes a slightly
darker blue.
But here’s the weirder thing.
Add red, and now he really looks grey.
If I change the angle so you can see his tongue, yes cars have tongues, duh, his tongue is
bright red, but his body still looks grey.
And perhaps stranger still, replace the blue with some green and move into yellow territory
and he looks… burgundy?
A burnt red?
I don’t know exactly what this color is, but it is not purple.
Now, some of this is down to how our brains’ white balance works, as we are comparing his
white eyes to his body color, and in fact if we look in Photoshop we’ll see that what
looked grey to us is actually fairly purple.
It’s not the right purple, but it is purple.
And when you think about it, that makes perfect sense.
Assuming this shade of purple is just a darker magenta, then if lit with magenta light, his
body would appear to be the same hue as his white features, but at a reduced intensity.
Without any sort of color contrast, that reduction in intensity just looks … grey.
Grey is simply a darker version of white, and what is white in this scene, is actually
magenta.
This also explains why his tongue looks so vibrant.
His tongue is now the only thing actually changing the relative amounts of color being
reflected back.
Since it absorbs blue like a good red should, it’s now able to set itself apart from the
magenta mess that is everything else.
And of course, we can also explain why he looks red under yellow light.
His body will be absorbing most of the green coming from the lights, so the only thing
it reflects back is red.
It looks a little weird because of the fact that it does absorb some of the red just as
it absorbs some blue, so it looks darker than his tongue.
And our brains’ vain attempt to compensate for the yellow light and assume that’s real
white makes it look stranger, still.
Now we’re not quite yet done with Putt-Putt.
So far, I’ve been showing you how he looks under various colors of light.
But even under apparently white light, comprised of red, green, and blue, this purple color
simply does not get rendered correctly at all.
Notice how differently he looks under normal white light using the phosphor-coated LEDs,
compared to the false white made by the RGB LEDs working together.
Something about the way this purple absorbs wavelengths in the visible color spectrum
simply cannot be reproduced using a trichromatic RGB light source.
At least, not these lights.
So keep in mind that even though I can show you this royal purple on a screen using only
some red, some green, and some blue, I can’t just use those three colors in the real world
and expect to achieve the same result.
Now, before I leave you, well first of all that can of paint was yellow, sorry I forgot
to answer that earlier, but more importantly while setting these demos up I think I may
have accidentally discovered one of the most effective ways to understand color blindness.
Now, I’ve seen lots of simulated images online, but they’ve never really clicked
with me like this did.
The most common type of color blindness is red-green colorblindness.
There are varying degrees of this deficiency but in general it means that the green / medium
cones are either malfunctioning or not present.
Now, I have no way to turn down or otherwise stop the green cones in my eyes from working.
But, if I light the room I’m in with dichromatic magenta light, the effect is somewhat similar.
Now, it’s not like this is what a color-blind person sees.
Especially because the entire scene is intensely colored, and green objects, like this marker,
appear very dark, not simply similar to red.
But, for the first time, I truly felt like I could not distinguish red and green all
that well.
The snake figure, here, suddenly had its red and lime green become awfully similar.
Again, this is by no means accurate, look at how the green stickers on the Rubik’s
Cube look black, but it is certainly interesting to have the color information of the real
world become limited in ways I’ve never experienced.
Anyway, that’s it for now, I think.
I didn’t buy these lights assuming I was going to make a video about how strange RGB
lighting is, but playing around with them led to some interesting places.
And honestly, it’s helped me understand color vision even better than I did before.
Thanks for watching, and as always a huge thank you goes out to the people supporting
this channel on Patreon.
Thanks to the support of people like you, I can make bizarre little detours like these,
and I really enjoy it.
I hope you do, too.
If you’d like to join these people in supporting my work, you can check out the link in the description.
Thanks for your consideration, and I'll see you next time!
♫ trichromatically smooth jazz ♫
Hey!
It’s me!
But from the future!
Woah.
So many of you probably know this but if you didn’t, I have a second channel where I
sometimes upload rather random things, they tend to be kind of rambly, and I wanted to
let you know that following this video I want to have a more relaxed discussion about some
of the subtle differences between using true white lighting and RGB white lighting.
So if you want to check that out, there’s gonna be a link in the description as well
as a card on the end screen.
For now, I hope you’re enjoying this rather groovy looking Rubik’s Cube.
It's pretty groovy looking.
Groovy.