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.
