In this video, I’d like to revisit a concept from my television series.
I created this thumbnail for my video explaining analog color TV,
and it’s been causing debate ever since.
Though I had hoped my video on Trinitron would help illustrate my point and put the debate
to rest, there was and is still much debate in the comments.
It seems this debate comes mostly from semantics, and I’ll admit I see a gap in my explanation.
So let’s try again.
This is the TV in my kitchen.
Like any TV on sale today, it produces an image by manipulating the brightness of many
thousands (and these days millions) of individual picture elements called pixels, which is actually
just short for picture element.
There are a few different technologies in use these days, but at their core their job
is to produce a set brightness value for the red, green, and blue components of each pixel.
These are called subpixels, and in many LCD panels each subpixel is actually further divided
into sub-sub pixels.
This probably increases the total number of discrete brightnesses each color can make,
and thus allows for more precise control over the panel and a larger number of possible colors.
Someone please correct me if that’s not what the subdivisions do.
The combination of red, green, and blue can create what appears to our eyes to be any color,
because the way we perceive color (for those of us with normal trichromatic color
vision, anyway) is through the ratio of stimulation between the three different cone cells in
our eyes.
Their primary sensitivities are red, green, and blue, so by using just these three colors,
we can activate the cone cells in any given ratio and thus produce any apparent color.
This biology hack is the result of the overlapping sensitivities of each cone cell.
For example, yellow light stimulates both the red and green cone cells in your eyes
roughly equally, as both of these cells can detect this wavelength of light.
This means that to recreate what we see as yellow light, we don’t need to actually
reproduce the same wavelength of light.
Instead, we can artificially stimulate the red and green cone cells with just red and
green light, and so long as the red and green cells receive the same relative stimulation
as they did with honest-to-goodness yellow light, the brain can’t tell the difference
and thinks it’s yellow.
Simply outputting red, green, and blue light can produce any color to our eyes because
when combined, it can produce the same ratios of stimulation between the three cone cells
that any real color would.
Anyway, the microprocessors inside this television are working together to make it all...happen,
and the main image processor can tell the panel exactly what to do.
The image on screen is coming from a Chromecast, and through the HDMI port on the television,
the Chromecast can tell it exactly what each pixel needs to do to make this image, and
the drivers inside the TV will make that happen.
We can define the resolution of this display by counting how many pixels there are along
each edge.
I’d rather not actually do that, so I’ll just recite the specs here and tell you that
there are 1,366 pixels along the bottom and 768 pixels along the sides, yes I know that’s
not 720P but that’s the panel that’s in here, and that means that there are 1,049,088
pixels on this screen.
Generally, resolution is defined as X by Y, so we’d say this panel has a resolution
of 1366 by 768.
Now take a look at an old school CRT television.
Get nice and close to it and you’ll find what appear to be pixels.
There’s a neat division between red, green, and blue.
The borders are defined, and it’s forming a grid, almost.
But, you would be running a fool’s errand if you attempted to count the number of these
“pixels” along the edges to determine this TV’s resolution.
That’s because these aren’t pixels, and they don’t define its absolute resolution.
To understand why, you need to look at a black and white television.
Oh how convenient, a black a white television.
Now with the set turned off, you can’t see any structure to this screen.
Going back to the LCD TV, even when it’s off, that grid of pixels is still there.
You need to shine a bright light onto it to see them, but the pixels are there as physical
parts of the screen.
But on this little CRT, there’s no grid to be seen.
Let’s switch it on.
With an image now on screen, you should be able to see a series of lines.
In analog video, this is how the image is drawn.
See, the CRT only has one “pixel” to deal with.
At the rear of the picture tube is an electron gun which is projecting a single point of
light at the screen.
Then, electromagnets in the deflection yoke move this point around the screen very rapidly
in a pattern called a raster.
By varying the brightness of the point of light as it moves around the screen, an image
can be made.
The image is drawn as a series of stacked horizontal lines.
In the US, roughly 480 lines are visible on the screen at once, drawn as two fields of
240 lines 60 times per second as interlaced video.
This is why standard definition is defined as 480i here in the States.
I’ve made a video explaining how analog television works in greater detail, which
can you find up above now or down below later.
Now, this TV has no idea what it’s doing.
It doesn’t have a microprocessor.
It doesn’t have an HDMI port.
It doesn’t have any digital circuitry of any kind.
All it’s doing is looking for two pulses in the video signal, the horizontal blanking
interval and the vertical blanking interval, in order to draw the image in the same place
on the screen and not have it roll around like this.
The nature of this signal is analog, and really all the signal does is tell the TV how bright
to make the image.
It’s just timed really really well so that each individual part of the screen is drawn
with the correct brightness, as the position of the point of light is determined by the
length of time that has elapsed from the start of the frame.
And to be clear, we’re dealing with tiny fractions of a second since the beam moves
incredibly quickly.
So then, here’s the challenge.
Where are the pixels?
Well, there aren’t any!
If I change the channel and we take a look at snow, you’ll see that there is no regularity
whatsoever in this noise.
If this image was defined by a grid of discrete picture elements, the borders between white
and black sections should form columns of some sort, or at the very least there should
be some clear vertical structure visible.
But there isn’t.
They appear completely randomly within the line.
I can tell you exactly where the line is, but I can’t define any separation within
the line itself.
That’s completely arbitrary.
Now here’s where the color CRT comes into play.
Specifically one like this.
This is a GE television, using a slot-mask CRT.
Up close, it appears to have a similar grid structure to the LCD TV in my kitchen.
So then, why aren’t these pixels?
They’re what make up the image, right?
Well, no, they aren’t.
These are actually called phosphor dots.
What they do is create specific targets for the red, green, and blue electron beams to hit.
See to make a color image, we need to make a red, green, and blue image, and they need
to be merged together somehow to appear as one.
In the early days of color TV, there were all sorts of ideas being explored on how to
produce an RGB image.
I’ll throw another card up on my playlist on Television, because if this is the sort
of thing that interests you you can take quite the nerdy deep dive.
A color CRT is functionally identical to a black and white CRT, but it draws three separate
images at once.
Think of it like three picture tubes, one red, one green, and one blue, combined into
a single picture tube.
This combined tube has an electron gun for each color, but of course we also need a way
to separate the colors in order to drive each one on its own.
That’s what the phosphor dots do.
They separate the face of the tube into a mosaic of red, green, and blue dots.
The earliest color TVs used a pattern of phosphor dots that looked like this.
These dots line up with a simple metal sheet just behind them.
Let me show you what it does.
Here I have a green flashlight.
If I shine it at this poster board, it creates a flood of green light.
But if I place a mask in front of it with a single hole, now the light can only make
it through in a straight line between the flashlight and the hole, which produces just
a dot on the poster board.
Now, here’s a red flashlight.
Watch what happens when I put it next to the green flashlight.
Because the red flashlight is in a slightly different position from the green one, the
light it makes can’t take the same path as the green light.
It will go through the hole at a different angle, so the dot it produces appears next
to the green one.
Now if I add a third, blue flashlight and put it in between the red and the green just
above them, a blue dot appears below the red and green dots.
If I take the mask away, it creates just a wash of white light.
But with the mask in place, it produces three small dots of light in the same arrangement
as the flashlights themselves, though it’s mirrored and upside down.
If I add a second hole the to mask, the same pattern appears right next to the first set
of dots.
If I keep going and make a bunch of small holes in this offset pattern, what we get
is a mosaic pattern of red, green, and blue dots.
This is happening because the flashlights are arranged in a triangle, and at every hole
in the mask the beams converge and cross over to project the opposite image on the screen.
Notice how similar this pattern is to this color CRT.
See, if I aim these three flashlights together at the poster board, their beams just blend
together and make what appears to be white.
This is what would happen if we used a color CRT without a mask.
But if I place the mask in front of it, which is just a piece of aluminum foil with some
holes punched in it, suddenly a pattern just like the phosphor dots appears.
Now, the red beam can only hit specific parts of the screen, and the blue and green beams
can’t hit those points.
Because the light sources are physically separated, they can only make their way through the holes
at specific angles.
The mask puts the red targets in the shadow of the blue and green beams.
The mask casts a shadow on the targets.
Wait a minute,
shadow mask!
What’s important to realize here is that the mask is what’s creating the pattern
of dots.
The flashlights are firing indiscriminately at the mask, but the mask will always force
each beam into the correct location on the other side.
This means that no matter what sort of pattern of light the beams or flashlights are creating,
it will always appear as a series of dots on the other side.
So if we go back to our picture tube, what you see as a viewer are the phosphor dots
which are the targets for each individual color electron beam.
Inside the tube, directly behind them, is the metal sheet with holes in it, which always
ensures the color components stay separated and project onto the phosphor dots in the
correct orientation.
But the key here is that they do not change how the image is drawn.
Just like the black and white television, this TV is stacking horizontal lines.
In fact, these two televisions are receiving the same exact signal.
The difference is that the color TV can recover the color information that’s superimposed
in the signal through quadrature amplitude modulation--
Don’t worry too much about the specifics of that--
and it can then adjust the relative intensities of the three color components.
But since that means it’s effectively drawing drawing three different sets of lines at once,
it needs a way to keep the colors from crossing over.
That’s what the shadow mask does.
Remember, even though the flashlights were just blasting away at the mask, the mask made
sure each part was separated into little dots on the other side.
From this side of the picture tube, it’s just like taking a black and white CRT, then
drawing a grid on top of it, and then coloring each little cell in with red green or blue.
The only functional difference between a true color CRT and a black and white CRT with lines
and colors drawn on top is that the mask behind the phosphor dots of the color picture tube
ensures the colors stay separated, and thus allows for individual control of each color.
Now, this style of shadow mask makes it hard to even define what could be a pixel.
Assuming each pixel contains one red, one blue, and one green dot, well first of all
they’re triangular, but then each one changes orientation as you move on and really it’s
just a mess but this style of CRT, which uses a slot-mask display, does make a pattern that
really looks like there are pixels.
These CRTs arrange the electron guns in a line, and rather than use a mask with round
holes they use a mask with small slots.
This allows more of the beam energy to pass through the mask and makes a brighter image.
And here’s where the semantics comes in.
I’ll grant you that the picture is “made up of” these groupings of phosphors.
You could say that they are elements of the picture, and thus are pixels.
But this ignores the fact that they are only there as a side-effect of the need for color
separation.
They are in front of what makes the image, and are not the actual building blocks of
the image.
To put it another way, here’s a window screen.
If I put it in front of this album cover, does that become a pixel?
Have I pixellated the image by placing a grid in front of it?
Or have I simply compartmentalized parts of the image into little square cells?
And here’s the part that I think is hardest to understand.
The phosphor dots do not in any way define the maximum amount of detail that can be displayed
on the screen.
That may sound silly, but hear me out.
All they really do is define the maximum color resolution of the display.
Let’s go back to this CRT.
I’ve only shown it in close-up because this is a laughable little 5 inch color TV boombox
from some point in the 1980’s.
The dot pitch, that’s the fineness of the dots, is very poor on this TV.
I mean, you can’t really blame it, as it’s only got 5 inches to work with.
This means it can’t display much color detail, but it can display as much brightness detail
as any television.
Let me boot up Kingdom Hearts.
[PS2 Game Start noise]
OK, so take a look at the menu in the bottom left corner.
If we look at the black and white TV, we can see that there are about 10 or 12 lines defining
the height of the letter M in Magic.
If we count the number of dots along the height of the M, we also get about 10, maybe 11.
But, each cluster of three color dots spans the height of two lines.
We appear to have only half the color resolution as we do brightness resolution in this CRT.
Look at how infrequently a red dot appears among blue and green.
That’s they key here, we’re not getting a lot of complete RGB clusters among the word
Magic, but we can still clearly see the shape of the word Magic.
You can even see the how the center of the A is darker than the rest, but only this one
red dot is actually darker.
But the thing is, from a normal viewing distance, you can’t really tell how poor the color
resolution is.
Once you’re far enough away that you can’t discern the individual phosphor dots, the
image appears more or less normally.
This is in contrast to a digital LCD panel, where the pixels themselves define the shape
of an image.
If I want to draw a letter M using a grid of 10 X 10 pixels, well I can say how bright
I want each pixel to be.
Then I can tell the display what to do with each of these 100 pixels to make an M. But
in the case of a CRT, it’s drawing the M like this, in Lines.
That shape is then forced into the grid of phosphor dots, and wherever it lands will
tell you which dots get lit up.
And that’s the key difference.
In digital video, the pixels define the shape of the image, logically.
In analog video, the shape of the image defines which phosphor dots are lit.
You can see this effect with the small TV.
This screen really suffers where very small, colored elements appear.
If I open the pause menu and look at these stats, some of it is very hard to read.
That’s because this text is colored green, so the blue and red guns pretty much
don’t fire when drawing it.
Since the green dots are so far apart and this text is so small, if the text to be drawn
lies between the green dots, it just won’t get drawn.
It’s not like the gun isn’t firing, it’s just that for the entire section here, the
text is in the shadow of the green gun, so none of its energy is able to light up the screen.
And that’s the point I’m trying to make when I say “these are not pixels”.
These two TVs are displaying the same image and they both have 480 lines of resolution.
But this little CRT has fewer phosphor dots, so it can’t recreate color as precisely
as the larger TV.
But that doesn’t mean it’s not conveying the same 480 lines of resolution.
It is, just in brightness only.
It loses detail in the color department, and as a side-effect it can’t reproduce some
fine color details.
A CRT television has no control over how the three electron beams interact with the mask.
The combined beam can land and will land wherever it wants, and it’s then up to the mask to
separate the color components.
The clusters of phosphor dots are there just because they need to be.
They can be a different size, a different shape, and some TV’s don’t even split
them up beyond vertical stripes.
Trinitron.
As a final point, which I think is at the crux of the issue, in an LCD, OLED, Plasma,
or any sort of digital display, the grid of pixels is an active matrix.
The display has an electrical connection to each one of them, and can talk to it.
The shadow mask and phopshor dots are a passive component of the CRT.
They don’t get addressed.
They don’t have an electrical connection.
They’re just there.
Sure, the TV does “control” which ones get lit up, but it’s not done with logical
control or any precision whatsoever.
Just like the black and white CRT, wherever the beam lands is what part gets lit up.
Now this isn’t to say that an analog TV can’t produce an image made of pixels.
Surely it can, it's just making small squares.
And in fact that’s what it's been doing throughout all of this video.
A PlayStation 2, DVD player, Roku box, or any digital source with a composite output
will take its logical 640X480 digital grid and convert that to the 480 horizontal lines
to drive the TV.
But I guarantee you those ethereal pixels in the logic circuits of the digital source
won’t be lining up nicely with these phosphor dots.
They simply don’t need to.
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