Analog Video

Broadcast

Yossi Cohen

VDroid

Agenda� Introduction to Color Spaces

� Connectors

� Video Broadcast Standards

� NTSC

� PAL

� Audio Standards

� NICAM

� BTSC

� EIAJ

� A2

� Transmission Path

� Reception Path

INTRO TO ANALOG TV

Color Spaces

Connectors

Broadcast Standards

Color Representation� The most simple way to represent color is by using RGB representation.

� The color space will look like:� This is usually the color space used for:� Display output� Sometimes as camera input

� For video compression & video transport other color spaces are used.

� In those color spaces luminance is separated from the color channel:

� In the diagramed we see the YUV space

� Reasoning is the number and sensitivity of the light sensing cells (rods) in the eye in comparison to color sensing cells (cons)

R

GB

R

B

G

YU

V

I

Q

Color Models in Video

�In Europe, video broadcast uses PAL or SECAM coding, uses the YUV color model.

�A matrix transform YIQ is used to transmit TV signals in North America and Japan. (NTSC) This coding also makes its way into VHS video tape coding in these countries since video tape technologies also use YIQ.

�Digital video uses a matrix transform called YCbCr that is closely related to YUV.

�Recently NV12 format has gained popularity

YUV Separation

YUV Color Model

�YUV codes a luminance signal (for gamma-corrected signals) equal to Y , the “luma".

�Chrominance refers to the difference between a color and a reference white at the same luminance. (U and V)

The transform is:

YIQ Color Model

YIQ is used in NTSC color TV broadcasting.

Again, gray pixels generate zero (I;Q)

chrominance signal.

I and Q are a rotated version of U and V .

The transform is:

YUV / YIQ relationship� We can easily see that the difference between YIQ & YUV spaces is a 33 degree offset of the IQ plane

Analog TV Connectors

� Analog TV connectors have a tradeoff between

� Number of Pins & wires

� Quality of video

� Using one wire to deliver luminance and color leads to interferences between the luminance and color components while using three wires or more just for the video is not convenient.

� Those problems are solved in new digital video connection standards like:

� DVI (obsolete)

� HDMI 1.4

Composite Video

� CVBS - Composite Video, Blanking, and Sync

� Composite Video uses only ONE wire to transfer the mix of:

� Video color signals (chrominance)

� Luminance signals

� Since color and intensity are wrapped into the same signal, some interference between the luminance and chrominance signals is inevitable.

S-Video � S-Video uses two wires, one for luminance and another for a composite chrominance signal.

� This limits the crosstalk between the color information and the gray-scale information.

� Humans are able to differentiate spatial resolution in grayscale images with a much higher acuity than for the color part of color images.

� As a result, we can reduce color information since we can only see fairly large blobs of color, so it makes sense to send less color detail.

Component Video� Component uses three separate video signals for R,G,B

planes.

� Each color channel is sent as a separate video signal.

� Most computer systems use Component Video, with separate signals for R, G, and B signals.

� Provides the best color reproduction since there is no “crosstalk“ between the three channels.

� Component video, requires more bandwidth and good synchronization of the three components than composite/S-Video .

ANALOG BROADCAST

STANDARDS

Broadcast Standard

� The main Analog Broadcasting standards are:

� NTSC

� PAL

� SECAM

� They differ in:

� Resolution

� Frame Rate

� Color scheme

� Modulation methods

� Channel BW

� Carrier Distances

NTSC• NTSC (National Television System Committee) TV standard is mostly used in North America and Japan.

▫ 4:3 aspect ratio

▫ 525 scan lines

▫ 30 frames per second (fps)

• NTSC follows the interlaced scanning system, and each frame is divided into two fields, with 262.5 lines/field.

• The horizontal sweep frequency is 525 X 29.97 = 15,734 lines/sec,

• Line swept cycle is 63.6u second.

• The horizontal retrace takes 10.9 u sec, this leaves 52.7 sec for the active line signal during which image data is displayed

NTSC video is an analog signal with no fixed horizontal

resolution. Therefore one must decide how many times to

sample the signal for display: each sample corresponds

to one pixel output.

A “pixel clock" is used to divide each horizontal line of

video into samples. The higher the frequency of the pixel

clock, the more samples per line there are.

Different video formats provide dierent numbers of

samples per line,

NTSC

NTSC Color Modulation

� NTSC uses the YIQ color model, and the technique of quadrature modulation is employed to combine (the spectrally overlapped part of) I (in-phase) and Q (quadrature) signals into a single chroma signal C:

� C = I cos(Fsct) + Qsin(Fsct)

� This modulated chroma signal is also known as the color subcarrier, whose magnitude is qI2 +Q2, and phase is arctan(Q/I). The frequency of C is Fsc 3.58 MHz.

� The NTSC composite signal is a further composition of the luminance signal Y and the chroma signal as defined below:

� composite = Y +C = Y +I cos(Fsct) + Qsin(Fsct) (5:2)

PAL

� PAL (Phase Alternating Line) is a TV standard widely used in Western Europe, China, India, and many other parts of the world.

� 4:3 Aspect Ratio

� 625 scan lines

� 25 frames/second

� YUV Color space

� 8 MHz channel

� 5.5 MHz to Y

� 1.8 MHz each to U and V.

� Color subcarrier frequency is fsc 4.43 MHz.

Analog Video Signal� B/W Sync Pulse

� Luminance values � signal levels at 0-4.2MHz

� Color Burst � Color Sync ~9-10 cycles

� Color subcerrier at 3.85MHz (NTSC)

� Completing color values� Hue – Color Phase

� Saturation – Color Amplitude

Audio and Video modulation� For NTSC

� Total channel bandwidth is 6MHz

� Luminance signal 0 - 4.2MHz

� Color sub-carrier at 3.58MHz

� Audio sub-carrier at 4.5MHz.

Video sub-standards

� Standards defines:

� Scan time

� Resolution

� signal

� The sub-standards (B,GH, DK, M, N, L, I etc)

� Modulation depth

� Modulation type

� Frequency map of the modulated channel

Audio Modulation Methods

� Mono AM

� BTSC / MTS

� EIA-J

� A2 / Zweikanalton

� NICAM

Overview

� Legacy TV only has monaural sound capabilities which receives a single L+R channel

� Later audio system delivered stereo capabilities while supporting the legacy TVs:

� Must provide the legacy mono channel

� Add Stereo of L-R using new technique & Bandwidth

BTSC

� BTSC includes:� Normal Mono is FM modulated over L+R

� BTSC adds Stereo Channel by adding AM L-R

� SAP – Secondary Audio Channel (like subtitles)

� Optional Professional channel

Source: Video Demystified

EIAJ

� Stereo Broadcast standard in Japan

� Used in conjunction with NTSC-J, similar to BTSC

� Uses FM instead of AM for the L-R Modulation

� Differentiate between dual mono and single stereo using a 3.5FH subcarrier AM modulated (for 1/0)

A2

� Instead of L+R and L-R transmission, A2 FM modulates two separate L+R, R channels

� This enables

� Better L/R crosstalk performance

� Transmission of two separate mono channels (second lang.)

Source: Video Demystified

NICAM

� NICAM is used for Digital Audio broadcast.

� NICAM uses an “A-Law Like” commanding algorithm.

� NICAM Supports

� One digital stereo sound channel.

� Two completely different digital mono sound channels.

� One digital mono sound channel and a 352 kbit/s data channel.

� One 704 kbit/s data channel.

� NICAM scrambles bits to resemble white noise and provides parity check

BTSC EIAJ A2 NICAM

Mono V V V V

Stereo V V V V

Dual Mono V V V

SAP V

Data V

Simplified Broadcast Path (Mono)

Video AM

Modulator

FM

Modulator

Mono Audio

HF

ModulatorConditioning

Audio IF Freq

+

Channel carrier freq

(~650MHz)

Video IF carrier freq

(30-40MHz)

41.25MHz

Audio Video

666MHz

videoAudio

Broadcast Path

� Conditioning

� Back porch clamping

� White clamping

� LPF Filtering

� IF Modulation

� Fixed IF Frequency per standard

� Carrier Modulation

� Frequency changes according to channel

Signal Conditioning

� Back Porch Clamping� -1.25MHz in NTSC

� Reduce Channel BW

� White Clamping� 10%-90% of max signal

� Prevents over modulation / Buzzing

� Chroma is added� 3.58MHz in NTSC

� Low Pass Filtering � 4.2MHZ in NTSC

FV Back Porch

clamping

chroma

Back Porch

clamping

LPF

chroma

Modulation

� Video is AM modulated to IF freq

� 45.75MHz in NTSC*

� and mixed with modulated Audio

� 41.25MHz in NTSC

� The Signal is later modulated to HF

� Example of 666MHz channel

664.25MHz 668.75MHZ

41.25MHz 45.75MHz

Audio Video

video Audio

*For non-NTSC IF Frequency check backup slide

Simplified Reception Path

Analog

Tuner

Video

Digitizer

(HDMI)

Audio

Demodulator

SIF

Processor

Display

SpeakersCVBS

666MHz

videoAudio

I2S (Digital)

L,R (Analog)

Thank you!

• Video Expert

• Lectures on Video / Android / VoIP

• Android Native Developer

More About me:

Yossi Cohen

yossicohen19@gmail.com

+972-545-313092