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HD-SDI, HDMI, and Tempus Fugit

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TECHNICALL Y SPEAKING... By Steve Somers, Vice President of Engineering HD-SDI, HDMI, and Tempus Fugit D-SDI (high definition serial digital interface) and HDMI (high definition multimedia interface) Hversion 1.3 are receiving considerable attention these days. “These days” really moved ahead rapidly now that I recall writing in this column on HD-SDI just one year ago. And, exactly two years ago the topic was DVI and HDMI. To be predictably trite, it seems like just yesterday. As with all things digital, there is much change and much to talk about. HD-SDI Redux difference channels suffice with one-half 372M spreads out the image information The HD-SDI is the 1.5 Gbps backbone the sample rate at 37.125 MHz, the ‘2s’ between the two channels to distribute of uncompressed high definition video in 4:2:2. This format is sufficient for high the data payload. Odd-numbered lines conveyance within the professional HD definition television. But, its robustness map to link A and even-numbered lines production environment. It’s been around and simplicity is pressing it into the higher map to link B. Table 1 indicates the since about 1996 and is quite literally the bandwidth demands of digital cinema and organization of 4:2:2, 4:4:4, and 4:4:4:4 savior of high definition interfacing and other uses like 12-bit, 4096 level signal data with respect to the available frame delivery at modest cost over medium-haul formats, refresh rates above 30 frames per rates. distances using RG-6 style video coax. second, and larger picture formats. Defined in SMPTE (Society of Motion Applications like digital cinema demand Picture and Television Engineers) 292M, More Bits is More Better the uncompressed, 12-bit 4:4:4 structure; this standard just underwent an update in SMPTE addressed this demand with meaning that each channel is full late 2006. The technical data is essentially SMPTE 372M, which describes a dual-link bandwidth RGB or component format the same, but the standard’s relationship application of HD-SDI capable of 4:4:4 with 12-bit depth per color. According to to other SMPTE standards is now clarified delivery; i.e. two coax cables supporting Table 1, a wide variety of frame rates may via a roadmap within the new release. separate, but coordinated, interfaces be accommodated, but digital cinema with each delivering 1.485 Gbps for a typically utilizes the 24 frame progressive And so it goes, but the real reason to total bandwidth of 2.970 Gbps. This mode listed so as to preserve the film discuss HD-SDI today is to introduce adaptation supports component and RGB look. Since this standard is an extension you to some of its variations. Why? The sources of 10-bits and 12-bits as well as of SMPTE 292M, the original HD-SDI variations are taking on new meaning an “alpha” channel. The alpha channel format, its versatility is utilized for some as the industry encounters the need provides support for chroma keying and digital cinema interfacing installations; for higher color depth and expanded background clipping mattes. When the although at this time, the digital cinema transmission bandwidth. The digital alpha channel is present, the sampling infrastructure is still under considerable cinema industry is well aware of the structure is referred to as 4:4:4:4. SMPTE development and change. new flavors of HD-SDI and, in some applications, uses its variants to feed the voracious data appetite of the digital cinema projector. Signal format sampling structure/ Frame/Field Rates pixel depth SMPTE 292M describes the basic 1.485 4:2:2 (Y'C' C' ) / 10-bit 60, 60/1.001 and 50 progressive Gbps serial digital interface capable of B R 4:4:4 (R'G'B'), 4:4:4:4 (R'G'B'+ A) / 10-bit supporting high definition 10-bit, 1024 30, 30/1.001, 25, 24, and 24/1.001 progressive, PsF levels, component video in the 4:2:2 4:4:4 (R'G'B') / 12-bit 4:4:4 (Y'C' C' ), 4:4:4:4 (Y'C' C' + A) / 10-bit 60, 60/1.001, and 50 fields interlaced sampling format. This is digital component B R B R 4:4:4 (Y'C' C' ) / 12-bit with the luminance channel having full B R 4:2:2 (Y'C' C' ) / 12-bit bandwidth sampling at 74.250 MHz, B R the ‘4’ in 4:2:2, while the two chroma Table 1: Source signal formats from SMPTE 372M-2002 18 ExtroNews 18.2 Summer 2007 TECHNICALL Y SPEAKING... TECHNICALL Y SPEAKING... Reference Mapping Image Signal Format Sampling/Pixel SMPTE Frame/Field Rates Structure Format Depth Standard 1 274M 1920 x 1080 4:2:2 (Y’C’BC’R) / 10-bit 60, 60/1.001, 50 frame progressive 296M 4:4:4 (R’G’B’), 4:4:4:4 (R’G’B’+ A) / 10-bit 60, 60/1.001, 50 frames progressive 1280 x 720 4:4:4 (Y’C’BC’R), 4:4:4:4 (YC’BC’R+A) / 10-bit 30, 30/1.001, 25, 24, & 24/1.001 frames progressive 2 274M 4:4:4 (R’G’B’), 4:4:4:4 (R’G’B’+ A) / 10-bit 60, 60/1.001, 50 frames interlaced 1920 x 1080 4:4:4 (Y’C’BC’R), 4:4:4:4 (YC’BC’R+A) / 10-bit 30, 30/1.001, 25, 24, & 24/1.001 frames progressive 3 274M 4:4:4 (R’G’B’) / 12-bit 60, 60/1.001, 50 frames interlaced 1920 x 1080 4:4:4 (Y’C’BC’R) / 12-bit 30, 30/1.001, 25, 24, & 24/1.001 frames progressive 4 274M 30, 30/1.001, 25, 24, & 24/1.001 frames progressive 1920 x 1080 4:2:2 (Y’C’BC’R) / 12-bit 60, 60/1.001, 50 fields interlaced Table 2: Source Image Format Relationships from SMPTE 425M SMPTE Dynamic Duo: 424M and 425M moves from 743 MHz to 1.485 GHz. timing occupied about 20% of the total Dual-link HD-SDI is certainly a step Essentially, the loss is about double for the timing allotment, re-use of this valuable forward, but it demands that the same distance with the same cable; or, we timing slot allows a significant amount of interfacing devices be capable of can transmit the signal half as far. additional data to be transmitted within managing a certain amount of timing the HD-SDI or HD-SDTI. skew that can occur as the signal travels In SMPTE 425M, both 10-bit and through two separate cable pathways. It is 12-bit signals map into the 3 Gbps stream. SMPTE 349M takes the transport imperative that cable length be managed Table 2 summarizes the scope of image concept back into the standard definition closely to guard against increased skew formats handled in this dual-rate standard. production environment for support of time. Signal timing difference at the The mapping structure supports various 525 and 625 line video. Instructions are source must not exceed 40 nanoseconds. rates from 4:2:2 10-bit component up provided for the repacking of standard Wouldn’t it be nice if we could manage to 4:4:4 12-bit component and RGB. definition into the HD-SDI transport space. the two data streams on one cable? Increasing the bit depth improves the Further, this standard sets the structure image’s dynamic range. for transport of a variety of video data SMPTE 424M and 425M do just that. Both including MPEG-2 encoded video. standards describe attributes of the new Video Blanking Recycled 3 Gbps HD-SDI often referred to as “dual You might recall from the past HD-SDI New Song: “What kind of HD-M-I?” rate”. SMPTE 424M describes the physical article some discussion on the SMPTE Yes, Mr. Sinatra would be asking himself interface while SMPTE 425M details image 348M transport version called HD-SDTI, just that if he were around to install and format mapping. Just think of 424M high definition serial digital transport connect his own flat screen TV today. The being two regular 10-bit HD-SDI data interface. HD-SDTI is geared for general big news is that HDMI version 1.3 finally streams alternating, or time-multiplexed, purpose data hauling at 1.5 Gbps. In the released along with an additional smaller, onto one cable. In order to transmit the new release of SMPTE 292M, the roadmap adroit connector and a color depth same information as two separate HD- shows this transport interface tied in to increase from a paltry 16,777,216 colors SDI streams, the clocking rate is simply the taxonomy through SMPTE 291M, also to 68,719,476,736 colors. Yes, folks, doubled. This arrangement is called a updated in 2006, which describes how to 68.7 Gigacolors. One could fixate into a “virtual interface” within 424M. The format data for use within the ancillary comma coma reading numbers like that. connectivity via 75 ohm RG-6 style coax data space supplied in all television serial Can you imagine what a jump all the way with BNC connectors and loss budget digital standards. The ancillary space to version 2.0 might bring? Welcome to is the same as with the original SMPTE is the time interval previously devoted Gigacolors. 292M for the standard HD-SDI. The only to horizontal and vertical blanking in difference is that our -20 dB calculation the analog television system.
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