HD-SDI, HDMI, and Tempus Fugit

Home , Color depth, Color space, Serial Digital Interface, SMPTE 372M, XvYCC

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By Steve Somers, Vice President of Engineering

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

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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. Since I feel good about that. I’d feel even better for cable loss at one half the clock rate horizontal and vertical synchronization if we had displays that could show all

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HD-SDI, HDMI, & Te m p u s F u g i t — continued those colors, but that’s another discussion have long used 120 Hz refresh rates, so for another time. At least we know that is now supported. The Rules of Deep Color that we can collect the colors, assign a • Support for deep color modes is optional. number to them, and store them away in Another item not to be overlooked by all • Only HDMI version 1.3 supports deep color. a large hard drive for future use… a kind of us in the A/V community is the auto- • 30, 36, and 48 bpp are deep color modes. of cryogenic color storage, figuratively magic audio/video lip sync feature. Lip • Devices discover pixel depth support via the speaking, to be thawed at a future date sync is one of those things we don’t talk E-EDID interface. by the LED and the laser. Surely, the good about, but its preponderance is lurking • A device’s failure to indicate pack pixels initiates ol’ days are yet to come. within every high-end A/V system design. 24-bit mode. Typically, the video is delayed significantly • RGB 4:4:4 deep color always supported. d Nearby is a summary listing the salient by the processing encountered in most • YCBCR 4:4:4 deep color support optional. new features offered by version 1.3. Of scaling and switching systems. The effect • YC C 4:2:2 does not support deep color. all the new features, the ones most likely is compounded if additional scaling occurs B R to be noticed by most consumers are in the display as well as externally. Audio the improved color depth and the small could lag video by as much as three or form factor connector. The new mini- four frames… a condition quite noticeable 24 bpp. The new interface must operate connector debuted recently on some to the viewer. Many video processors at least twice as fast, hence 340 MHz, to camcorders as the new interface for direct control or include built-in compensation support up to 48 bpp. With the increased connection to your home HDTV system. for this lag, but depending on the A/V clock rate, version 1.3 lays out the Like USB, devices having the new physical system design, lip sync error may creep in. interleaving details that support orderly interface will provide a short cable with fragmentation, packing, and movement the standard HDMI connector on one Pixel Packing 101 of the additional pixel information for end and the new mini on the other end But, let’s get back to the deal closers… each of the new pixel depths (30, 36, to facilitate direct digital connection to a more resolutions and greater color depth. and 48) beyond the standard 24. Did I display system. At slightly more than double the previous say “fragmentation”? That’s right; there transmission rate, version 1.3 widens IS matter smaller than one pixel. The support for high resolution progressive HDMI 1.3 is rampant with partial pixels HDMI version 1.3 Feature List scan rates along with the greater color tucked together within all the nooks • Higher speed: from 165 MHz to 340 MHz depth. A comprehensive list of supported and crannies of the three data channels. (4.95 Gbps to 10.2 Gbps) rates is covered in Consumer Electronics Pixel packing and keeping track of partial • Deep color (24, 30, 36, 48 bit depth) for RGB Association document CEA-861-D. For pixels is not only very interesting, but and YC C B R example, the regular single-link HDMI, definitely recommended study for anyone • Increased resolution range or DVI, supports 1920x1080 progressive experiencing difficulty falling asleep in the • Higher frame rates to 120 Hz scan high definition video at 24 bits per evening. • New, lossless audio formats pixel, bpp. To review, 24 bpp means • Automatic audio/video lip sync that each of the three color channels Color Space — “The Final Frontier” (R, G, B) are assigned 8 bits, or 256 levels. Color depth and color space are not • New mini-connector for small electronics like cameras If we multiply 256 to the third power, the same thing. Color depth refers to a • Broader color space – “xvYCC” as described in we achieve the 16.7 million colors. To method for dividing a range of color, the IEC61966-2-4 achieve any of the greater color depth red channel for example, into smaller • Two classes of interconnect cable values, more pixel information must be graduated increments so as to attain transmitted. smoother, shaded tonal appearance on a display device. The less noticeable, but important The version 1.3 specification chapter features are the higher interface speed, 6 illustrates the methodology for Color space describes the overall range of from 4.95 Gbps to 10.2 Gbps, which will increasing clock rate and packing pixels to colors within the realm of human vision support higher visual resolutions along achieve the additional data throughput. that a system can reproduce. Humans with lossless audio formats like Dolby® If you think about it a moment, it’s are capable of seeing more colors than TrueHD and DTS-HD Master Audio™. straightforward in that the existing our existing visual display systems can Systems providing 3D viewing capability interface operates at 165 MHz to support show us. The quest continues for larger

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Green version for portable devices. Refer to television video rates, including standard

xvYCC Color Space Figure 2, which shows approximately 33% definition and high definition through miniaturization compared to Type A. Table 1080i and 1080p at 30 Hz frame or below 4-13 in the HDMI 1.3 specification lists the operating at 24 bpp, are serviced by the HDTV Color Space pin alignment between Type A and Type 74.25 MHz clock rate. This means that the C as they are not pin-to-pin compatible supposedly cheaper, existing Category 1 in the interest of Type C connector cable will suffice. The higher performance Red design optimization. Some new digital cable is therefore required to realize any of camcorders utilize the Type C connector so the deep color rates. that the user may plug directly into HDMI-

Blue equipped displays for that high quality Attenuation limit charts and eye diagram

direct digital RGB or YCBCR video rush. masks provide the tools to guide Figure 1: Conceptual presentation of the expanded xvYCC the cable designer between the two color space compared to the sRGB color space (not to scale). categories. It is obvious that, since cable length cannot be tied to the specification, color space and the ability to display it. we are highly dependent on the cable HDMI version 1.3 takes a new step in manufacturer to accurately design, that direction denoted as “xvYCC”, or test, and label the cable assemblies Extended-gamut YCC color space. The appropriately for the given length sold. IEC 61966-2-4 defines this color space for While a short length of a particular cable video applications. Chapter 4.3 of the IEC type may perform to Category 2, it does standard describes xvYCC as an extension not mean that a longer version of the

of ITU-R BT709-5, but extends the gamut Figure 2: Relative size comparison between Type A (left) same cable type will perform to Category of that standard much wider. The concept and the new Type C (right). Type C is about 33% smaller. 2. As cable length increases, we all know is illustrated in Figure 1 where the outer that attenuation effects limit performance boundary of the color space “wedge” Interface cabling continues to boggle the rapidly. For critical applications, represents the limits of human visual senses. The first thing we need to take care A/V designers should pre-test cables capacity and the triangles represent the of here is this: the HDMI specification only regardless of category labeling. available colors within a region defined by provides us with the electrical performance primary red, green, and blue tristimulus requirements for a functional interface. Tempus Fugit — Time Flies values for a given color space. The larger It does NOT specify cable design or cable Well, it certainly has. While being a glimpse the triangle, the more vivid are the length maximums. Everyone has but their of the expanding HD-SDI arena and HDMI perceived colors. Note that the HDTV own ingenuity using available raw cable version 1.3 new offerings, this article locks (ITU-R 709) color space and the sRGB materials and active electronics to solve the in time a small moment where we discuss color space used in computer applications distance issues. However, version 1.3 does the new, yet dream about what might be and by most all JPEG-based digital establish two classes of cable assemblies in store for our future. Likely a year or two cameras are the same color space. This called Category 1 and Category 2. These from now I’ll need to revisit some aspect of means that images in the sRGB space will “category” designations have nothing these interface topics. Oh, don’t forget to directly match the color space of displays to do with the same nomenclature used download your own free copy of version capable of displaying the HDTV space. for network cabling. Version 1.3 outlines 1.3 at www.hdmi.org … all 276 pages of detailed electrical design and testing it. It will be some time before all devices Getting Physical requirements for both categories with make full use of version 1.3. Chapter 4 of the HDMI specification 1.3 Category 1 cables supporting HDMI clock defines the physical layer, or the connector frequencies to 74.25 MHz and Category 2 Meanwhile, I’ve got to figure out how and cable interface. In the connector cables supporting the entire specification we’re going to make a cable that supports department, there are now three types: through 340 MHz. So, what does this 340 MHz and a 10.2 Gbps data rate for A, B, and C. Type A is the popular 19-pin mean to us? Table 4 of the CEA-861 any reasonable distance. So, while I’m off version in widespread use. Type B is the companion standard lists all the supported the street working on that, pay attention lesser known 29-pin dual link connector. resolution rates and the corresponding to those new HDMI cable assemblies. Don’t And, Type C is the new compact 19-pin clock rate required for the HDMI. All buy anything with peel-off category labels!