Composite Video signal::
The composite video waveform contains all the information needed for complete CRT picture, line by line and field by field. The signal is used in picture tube to reproduce picture on the scanning raster. The composite video consists of video information plus blanking and sync pulses needed for synchronized reproduction. 2 Important characteristics of composite video signal are polarity and the amplitude. Video signal can have 2 polarities:
1. A positive sync polarity, with the sync pulses “up”
2. A negative sync polarity
Component video: Higher-end video systems make use of three separate video signals for green, red, and blue image planes. Each color channel is sent as a separate video signal.
(a) The most computer systems use Component Video, with separate signals for R, G, and B signals.
(b) For any of the color separation scheme, Component Video gives the best color reproduction since there is no \crosstalk” between the three channels.
(c) This is not the case for S-Video or Composite Video, dis- cussed next. Component video, however, requires more bandwidth and good synchronization of the three components.
Composite video – color (\chrominance”) and intensity
(\luminance”) signals are mixed into a single carrier wave.
a) Chrominance is composition of 2 color components (I and Q, or U and V).
b) In NTSC TV, e.g., I and Q are combined into a chroma signal, and a color subcarrier is then employed to put the chroma signal at the high-frequency end of the signal shared with the luminance signal.
c) Chrominance and the luminance components may be separated at the receiver end and then the two color components can be further recovered.
d) When connecting to the TVs or the VCRs , Composite Video uses only 1 wire and video color signals are mixed, not it sent separately. Audio and the sync signals are additions to 1 signal.
Advantages of digital representation for video are many.
(a) Video can be stored on digital devices or in the memory, ready to be processed (noise removal, cut and paste, etc.), and
integrated to the various multimedia applications;
(b) Direct access is possible, which makes nonlinear video editing achievable as a simple, rather than a complex,
(c) Repeated recording does not degrade the image quality;
(d) Ease of the encryption and the better tolerance to channel noise.
vestigial side band signal:
To conserve spectrum space commercial television uses a transmission mode known as Vestigial sideband.A Component video signal,containing frequency components from dc to 4MHz,is amplitude modulated into a carrier.The resulting sum and difference friquencies occupy an 8MHz bandwidth.
Q1: What is SECAM?
Ans: SECAM stands for Syst_eme Electronique Couleur Avec M_emoire,
the third major broadcast TV standard.SECAM also uses 625 scan lines per frame, at 25 frames per
second, with a 4:3 aspect ratio and interlaced Fields.
Q2: What is the difference between SECAM and PAL ?
Ans: They differ slightly in their color coding scheme:
(a) In SECAM, U and V signals are modulated using the separate color subcarriers at the 4.25 MHz and the 4.41 MHz respectively.
(b) They are sent in alternate lines, that is only 1 of the U or V signals will be sent on each scan line.
Q3: What is the total width of PAL?
Ans: T he total width of PAL is 8.0 MHZ.
Q4: What are the services provided by FCC?
Ans: The services provided by FCC will include:
SDTV (Standard De_nition TV): the current NTSC TV or higher.
EDTV (Enhanced De_nition TV): 480 active lines or higher
HDTV (High De_nition TV): 720 active lines or higher.
Q5: Explain Color Model and Modulation of NTSC ?
Ans: NTSC uses YIQ for the color model, and the technique of quadra-
ture modulation is employed to combine (the spectrally
overlapped part of) I (in-phase) and Q (quadrature) signals
into a single chroma signal C. This modulated chroma signal is also known as the color
subcarrier, The NTSC composite signal is a further composition of
luminance signal Y and chroma signal.