AgendaIntroduction to Color SpacesConnectorsVideo Broadcast Standards NTSC PALAudio Standards NICAM BTSC EIAJ A2Transmission PathReception Path
INTRO TO ANALOG TVColor SpacesConnectorsBroadcast Standards
Color RepresentationThe most simple way to represent Gcolor is by using RGB representation. BThe color space will look like:This is usually the color space usedfor: Display output Sometimes as camera inputFor video compression & video Rtransport other color spaces are used. GIn those color spaces luminance isseparated from the color channel: BIn the diagramed we see the YUVspace I U YReasoning is the number andsensitivity of the light sensing cells V(rods) in the eye in comparison to colorsensing cells (cons) Q R
Color Models in VideoIn Europe, video broadcast uses PAL or SECAM coding,uses the YUV color model.A matrix transform YIQ is used to transmit TV signals inNorth America and Japan. (NTSC) This coding alsomakes its way into VHS video tape coding in thesecountries since video tape technologies also use YIQ.Digital video uses a matrix transform called YCbCr that isclosely related to YUV.Recently NV12 format has gained popularity
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 relationshipWe can easily see that thedifference between YIQ &YUV spaces is a 33 degreeoffset 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-VideoS-Video uses two wires, one for luminance and anotherfor a composite chrominance signal.This limits the crosstalk between the color information andthe gray-scale information.Humans are able to differentiate spatial resolution ingrayscale images with a much higher acuity than for thecolor part of color images.As a result, we can reduce color information since we canonly see fairly large blobs of color, so it makes sense tosend less color detail.
Component VideoComponent uses three separate video signals for R,G,Bplanes.Each color channel is sent as a separate video signal.Most computer systems use Component Video, withseparate 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 goodsynchronization of the three components thancomposite/S-Video .
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
NTSCNTSC video is an analog signal with no fixed horizontalresolution. Therefore one must decide how many times tosample the signal for display: each sample correspondsto one pixel output. A “pixel clock" is used to divide each horizontal line ofvideo into samples. The higher the frequency of the pixelclock, the more samples per line there are.Different video formats provide dierent numbers ofsamples per line,
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 SignalB/W Sync PulseLuminance values signal levels at 0-4.2MHzColor Burst Color Sync ~9-10 cycles Color subcerrier at 3.85MHz (NTSC)Completing color values Hue – Color Phase Saturation – Color Amplitude
Audio and Video modulationFor 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
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
BTSCBTSC 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)
A2Instead of L+R and L-R transmission, A2 FM modulates twoseparate L+R, R channelsThis enables Better L/R crosstalk performance Transmission of two separate mono channels (second lang.) Source: Video Demystified
NICAMNICAM 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 andprovides parity check
BTSC EIAJ A2 NICAMMono V V V VStereo V V V VDual Mono V V VSAP VData V
Simplified Broadcast Path (Mono) Audio IF Freq Mono Audio FM Modulator Audio Video 41.25MHz Video AM + HF Conditioning Modulator Modulator Audio video 666MHz Video IF carrier freq Channel carrier freq (30-40MHz) (~650MHz)
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 FV Back Porch Back Porch Clamping 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 chroma Low Pass Filtering 4.2MHZ in NTSC chroma BackLPF Porch clamping
Modulation Video is AM modulated to IF Audio Video freq 45.75MHz in NTSC* and mixed with modulated Audio 41.25MHz 45.75MHz 41.25MHz in NTSC The Signal is later modulated to HF Example of 666MHz channel video Audio 664.25MHz 668.75MHZ*For non-NTSC IF Frequency check backup slide
Simplified Reception Path Audio video 666MHz SIF Audio I2S (Digital) Display Demodulator Analog L,R (Analog) Tuner Processor CVBS Video Digitizer Speakers (HDMI)
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