CD / Interlacing - YouTube

[On screen] WARNING: INTENSE STROBE EFFECT AT 2:03

Interlacing, huh? Super easy.

I'm gonna have a [audio stutter effect] field day with this.

If you think about it, we kinda got into television before it was finished being properly invented.

Broadcasting started in the 1930s,

but the first flatscreen displays that could show moving images in a normal continuous way,

didn't appear until almost the 21st century.

Before then, humans had to make do with the Cathode-Ray Tube.

In a CRT display, an electron emitter shot a stream of electrons at your face.

But there was a screen in the way, and the whole thing was in a vacuum tube,

so the electrons didn't bump into air molecules.

The TV transmission was decoded as fluctuations in the intensity of the electron beam,

and as it traveled forward, magnetic coils on the sides of the tube deflected it to scan

in a horizontal pattern down the screen.

This rapidly drawn pattern of lines, called the raster, generated the video image.

Some parts of the world went with 525 lines, others with 625.

Doesn't matter, it's not a competition --

Because if it was, Europe would be the winner and that's...

And anyway, this was just vertical resolution.

Analog television didn't really have horizontal resolution,

since those electron fluctuations across a line were continuous.

But electrons themselves don't look like much.

In order to make them visible, the screen was covered in a pattern of phosphor dots,

which lit up when bombarded by the electrons,

then dimmed back down on their own.

And this was an issue.

All this glowing and dimming had to happen instantly, over and over,

at a constant frame rate as high as 30 per second.

You couldn't use phosphors that glow longer than a frame,

because then the next frame couldn't be drawn in time.

But if they dim faster, as every consecutive line on the way to the bottom of the image gets drawn,

the lines making up the top are already disappearing!

Which in real time means -- flicker!

[Strobe effect, screaming]

The solution?

Draw every other line to get across the raster in half the time,

then go back and draw the missing lines in a second pass.

That way the refresh rate is doubled.

And even though only half the resolution of the image is on screen at one time,

the swap is so fast, the persistence of vision makes it look like a full resolution frame.

Brilliant! Let's move on with our lives.

But someone had another idea...

Since the two passes get displayed sequentially,

why don't we design video cameras to capture them sequentially too?

Instead of drawing the odd and even lines of a single moment in time,

we could use them to display two different moments, interlaced together as two fields of a single frame.

And sure, this was an ingenious way to increase the temporal resolution of video.

Frame rate was effectively doubled and this became the familiar look of

live news broadcasts, soap operas, and other shows recorded directly to tape.

It was also a convenient framework for adapting material shot in other frame rates,

through processes like 3:2 pulldown.

But none of it was long for this world...

Higher refresh rate CRTs were developed...

digital video capture and playback ran circles around the analog signal,

and eventually, high-definition flat screens completely changed the way moving images were displayed.

The entire broadcast system for which interlaced video was designed, got taken offline around 2009.

And even though interlacing is still part of HD standards, it has mostly become an artifact that gets in the way.

Modern progressive scan playback devices don't understand interlaced video,

and just show both fields as what they are:

tiny, single-pixel scan lines visible along the edges of moving objects.

So whether you're adding visual effects to interlaced footage,

or just exporting it for playback on a modern screen, the interlacing needs to be removed.

This can be done one of two ways: either by totally extracting one of the fields,

thereby cutting the vertical resolution of the video in half,

or by interpolating both fields - which looks a little better,

but can leave slight 'ghosting' artifacts.

Or I guess you can just not care and leave it as is.

Maybe having interlacing artifacts in your video is cool and retro now.

Maybe some people want to add fake interlace into their videos for style.

I should make a tutorial on how to do that.

Better yet! A plugin for which you could pay...

$800 once, or just $50 per month -- forever --

but you can cancel anytime after a minimum 2 year annual subscript--