Lecture 3-Video Signals

Question 1

In analogue video signals, what is field dominance?
What does a field include?
Which way does the scan move?

Answer 1

Which field starts first- even or odd.
A field includes half of the vertical resolution but all of the horizontal resolution.
Scan moves from left to right

Question 2

What is horizontal blanking?

Answer 2

Beam turned off at end of line

Question 3

What is horizontal retrace?

Answer 3

Beam moved left to the next alternate line

Question 4

What scan does digital use?

Answer 4

Progressive scan- each line is drawn in sequence top to bottom

Question 5

What is PAL for analogue video signal standards?

Answer 5

Phase Alternating Line
50Hz
25fps
UK, most of Europe 
625 scan lines

Question 6

What is NTSC video signal standards for analogue?

Answer 6

National Television System Committee
6oHz electrical system 
29.97 fps
US and Japan
Uses 525 scan lines

Question 7

What is SECAM video signal standards for analogue?

Answer 7

Sequential Couleur a Memorie
50Hz
25fps
France, Russia
625 scan lines

Question 8

What resolution does SD have?

Answer 8

PAL and SECAM: 720 x 576

NTSC: 720 x 480

Question 9

What is HD resolutions for picture area?

Answer 9

Progressive: 1,280 x 720 (720p)
Interlace: 1,920 x 1,080 (1080i)
Progressive: 1,920 x 1080 (1080p)

Question 10

What is the Back Porch?

Answer 10

Area prior to the active video that contains colour burst information.

Question 11

What is colour burst?

Answer 11

A reference signal that is transmitted to the receiver to derive colour information. If not present the signal is black and white.

Question 12

What is the colour subcarrier? What does it combine with?

Answer 12

Contains colour info for the line. Combines with the main picture signal to create a composite signal. Component signals separate the information, always higher quality than composite.

Question 13

How are analogue channels and digital sub channels broadcasted?

Answer 13

Analogue- different frequencies

Digital- same frequency and combined via digital compression techniques.

Question 14

How do streaming and download services transmit?

Answer 14

Phone network or through dedicated cables.

Question 15

What is luminance and its sum?

Answer 15

Represents the amount of white or brightness, it is the sum of all colour components (Y)
Y= R+G+B

Question 16

Define Chrominance:

Answer 16

The colour information within a signal, it is a measure of each colour component. R and B are measured or sampled, G is calculated.

Question 17

Why do we care about video signals?

Answer 17

To verify exposure, colour reproduction, to ensure compliance with broadcast standards (luminance and chrominance limits and ‘illegal colours’), to troubleshoot signal issues.

Question 18

What are waveform monitors used for, and what are they measured in?

Answer 18

Measure luminance, IRE units, clipping point refers to the top level that is pure white.

Question 19

What is Super Black?

Answer 19

Black signal at 3.5 IRE

Question 20

What is low pass, CHRM and flat in waveform monitors?

Answer 20

Low pass: shows luminance only
CHRM: shows chrominance only
Flat: shows composite signal

Question 21

What is a vectorscope?

Answer 21

Measure chrominance, graticule measures phase angle and magnitude which represent saturation. Target boxes indicate compliance with standards.
Calibrated with colour bars before use.
Rotate: ensures the reference phase angle is aligned, gain cal ensures the reference magnitude is aligned.
Used for grading and colour correction. Adjust Hue Saturation and value.

Question 22

What luminance levels should video signals be?

Answer 22

No signal below 0 IRE for PAL. No signal above 100 IRE (all standards). Black level should always be 0 for PAL and for Digital.

Question 23

What are Chrominance limits?

Answer 23

8 bit- super black 1-15 not used
Super white 236-254 not used
No data with a value of 0 or 255 is allowed

Question 24

What are histograms used for?

Answer 24

Show the amount of component based on luminance. Black is on the left, white on the right, the higher the peak the more pixels that contain that value.