Lecture 3-Video Signals Flashcards
In analogue video signals, what is field dominance?
What does a field include?
Which way does the scan move?
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
What is horizontal blanking?
Beam turned off at end of line
What is horizontal retrace?
Beam moved left to the next alternate line
What scan does digital use?
Progressive scan- each line is drawn in sequence top to bottom
What is PAL for analogue video signal standards?
Phase Alternating Line 50Hz 25fps UK, most of Europe 625 scan lines
What is NTSC video signal standards for analogue?
National Television System Committee 6oHz electrical system 29.97 fps US and Japan Uses 525 scan lines
What is SECAM video signal standards for analogue?
Sequential Couleur a Memorie 50Hz 25fps France, Russia 625 scan lines
What resolution does SD have?
PAL and SECAM: 720 x 576
NTSC: 720 x 480
What is HD resolutions for picture area?
Progressive: 1,280 x 720 (720p)
Interlace: 1,920 x 1,080 (1080i)
Progressive: 1,920 x 1080 (1080p)
What is the Back Porch?
Area prior to the active video that contains colour burst information.
What is colour burst?
A reference signal that is transmitted to the receiver to derive colour information. If not present the signal is black and white.
What is the colour subcarrier? What does it combine with?
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.
How are analogue channels and digital sub channels broadcasted?
Analogue- different frequencies
Digital- same frequency and combined via digital compression techniques.
How do streaming and download services transmit?
Phone network or through dedicated cables.
What is luminance and its sum?
Represents the amount of white or brightness, it is the sum of all colour components (Y)
Y= R+G+B
Define Chrominance:
The colour information within a signal, it is a measure of each colour component. R and B are measured or sampled, G is calculated.
Why do we care about video signals?
To verify exposure, colour reproduction, to ensure compliance with broadcast standards (luminance and chrominance limits and ‘illegal colours’), to troubleshoot signal issues.
What are waveform monitors used for, and what are they measured in?
Measure luminance, IRE units, clipping point refers to the top level that is pure white.
What is Super Black?
Black signal at 3.5 IRE
What is low pass, CHRM and flat in waveform monitors?
Low pass: shows luminance only
CHRM: shows chrominance only
Flat: shows composite signal
What is a vectorscope?
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.
What luminance levels should video signals be?
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.
What are Chrominance limits?
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
What are histograms used for?
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.
