Video: What you never thought you might want

to know

… and some stuff you might actually care about

What shall we talk about?

A little theoryThe video signalPicture elementsColorspaces

… and some practiceVideo connectorsInterlaced vs progressiveAnalog vs digital

In theory

In the beginning was the cathode ray tube…

What’s a video signal?

A stream of images (“frames”) played at a constant rate

The frame rate must be high enough to fool the human brain into thinking that the motion is continuous (at least 15 frames per second)

... and then?

Woah, woah, hold up!What’s are these

“images” you keep mentioning?

An image is a matrix of picture elements, with a specific height and width

Each of these elements (or “pixels”) has a specific color

… and then?

Since the number of rows and columns is fixed, this is an approximation of the actual image

The more pixels you fit into a given space, the more accurate the image is and the higher the resolution

… and then?

So a pixel approximates a small sample of the image

What is a pixel?That depends. The

value of a pixel depends on the context, but in all cases it represents a color.

… and theeeen?

A color is a vector, and it only has meaning given the correct vector space (or rather, colorspace)

The common ones are…RGB (or sRGB)YUV/YPbPr/YCbCrCMYKHSB/HSV/HSLxvYCC

and then and then and then and then

In practice

Now comes the stuff you may care about

Video connectors

Legacy connections use analog video signaling:Pixels are sent over the

wire using an analog encoding scheme

Horizontal and vertical sync lines signal when a line or frame (respectively) begins and ends

There are dramatic differences in image quality between systems

Analog video connections

Composite video:• 1x RCA connector• Multiplexed signal• Crappy quality

S-Video:• 4-pin mini-DIN• Separate chroma/lumen signals• Passable quality

SCART:• Composite, Y/C or RGB video• Carries audio• Bidirectional

Interlaced video

What’s interlaced video?

Interlacing was invented to get better image quality out of CRTs with no cost

The technology is completely obsolete and is one of the worst holdovers from the analog era

Modern displays require deinterlacing or a progressive signal

Modern analog connections

Component video:• YPbPr colorspace• Progressive signal• Usually 3x RCA connectors

VGA connector:• D-sub 15 connector• Progressive signal• RGB + H/V sync• DDC data signal

A brave new world

Modern video signals are typically transmitted digitally

The core concepts have not changed (pixels, colorspaces)…

… but rather improved and expanded upon:New colorspace (xvYCC)Consumer Electronics

Control (CEC)24-bit, 192KHz audio

Questions?

(A)bort (R)etry (I)gnore?

To the infinity, and beyond!

There’s plenty to cover:Display technologiesMeasurements and calibrationDigital video artifactsCompression codecs

What would you like to hear about?...tomer@tomergabel.com