It’s 1953. The National Television Standards Committee (NTSC) has releaseda comprehensive set of technical parameters for color televisionbroadcasting and display. Everything from the specific mathematical valuesfor color and luminance components to phosphor color coordinates iscontained in this document. The only problem is that no monitors exist withenough resolution, correct phosphors, and sufficiently accurate colordecoding to show an NTSC signal-a problem that will not be overcome fornearly two decades.
It’s 1999. Digital television is coming, and broadcasts have commenced inmajor markets. Studios are purchasing equipment for HDTV acquisition,editing, and postproduction. A comprehensive standard is in place, thanksto the efforts of the Grand Alliance and the Advanced Television StandardsCommittee. Once again, the parameters of color encoding and decoding,compression, bandwidth, and color phosphor coordinates are clearly spelledout.
And once again, very few broadcast, studio, postproduction, and consumervideo monitors exist that can accurately show a 1920 x 1080i HDTV signal.Yes, they can get the colors decoded correctly. Yes, they use the specifiedphosphors. And all of them have the proper 16:9 image aspect ratio. Whatmost of these monitors do not have is a fine enough CRT dot pitch toresolve 1920 pixels along 1080 vertically scanned picture lines-if they caneven resolve the 1080 scan lines.
A Question of PitchThere are many technical hurdles to designing and manufacturinghigh-resolution, direct-view CRT monitors. Fortunately, phosphor accuracy,color decoders, and scan-rate compatibility are not big issues anymore. TheHDTV color gamut essentially follows the SMPTE C and CCIR-601 color space.Microprocessor technology and retention of a component color system (Y, Pb,Pr) will ensure accurate color decoding, and multi-scan monitor technologyis “old hat.”
The big trade-off comes when you must choose between image brightness anddot size, or “pitch,” of the CRT’s electron gun. Computer monitors can havedot pitches as low as .22mm, making it relatively easy to map out 1024 x768, 1280 x 1024, 1600 x 1200, 1920 x 1080 and other high-resolutiondisplay formats. The price that we pay for this added resolution? Smallscreen sizes.
Studio and group viewing calls for a larger-screen broadcast monitor.Generally, broadcast-quality monitors with picture sizes larger than 21″employ CRTs with coarse dot pitch aperture grills, which range from .6mmall the way to 1mm. While these monitors have picture scan rates compatiblewith a wide variety of video and computer signals, they do not displayimages with the same degree of resolution as computer monitors.
Do the MathHere’s some simple math to better illustrate the problem. Let’s say we areusing a 20″ 4:3 computer monitor with a dot pitch of .25mm to work at 1024x 768 (XGA) resolution. Assuming the images we view on that monitor haveall the detail we want, we’d have to find a 27″ 4:3 monitor with a dotpitch of .31mm or a 37″ 4:3 monitor with .54mm dot pitch to view the sameimages with the equivalent resolution.
One problem, though: No such monitors exist! With .75mm dot pitch (a commonaperture grill size), we would need a 65″ diagonal picture tube to see allthe detail displayed on the 20″ monitor. But the largest picture tubescurrently manufactured measure only 37″ diagonally. The problem worsenswhen viewing image details near the edge of the picture tube. Here, thedeflection angle of the electron gun is quite severe, causing the dot shapeto elongate and distort. This results in a larger spot size and furtherdegrades picture resolution.
Confused about dot pitch? Think of an artist attempting to produce somevery fine calligraphy with only crayons or felt-tip markers instead of afine-point pen. The end result certainly looks like script with plenty ofelaborate curves and filigrees, but none of it is legible-the “dot pitch”is just too coarse to capture all the subtleties of script lettering.
Newer picture tubes with .6mm dot pitch are specified as having SVGA (800 x600) resolution and are now beginning to find their way into broadcastmonitor applications. However, even with a .6mm dot pitch, our broadcastmonitor’s optimal picture tube size would have to measure about 52″diagonally, which is still too large to manufacture. So, we compromise byworking with what is available and toss away some picture resolution in theprocess.
The truth is, 4:3 broadcast monitors in the 25″ to 37″ range with .7mm to.8mm dot pitch have just enough resolution to handle 525-line NTSC (analogor digital), plus 640 pixel x 480 pixel computer images. (At least onemanufacturer of monitors-Sony-recognized this fact some time ago andstarted building scan converters into 27″ 4:3 presentation monitors toconvert higher resolutions down to VGA.)
Wider is Better?It should come as no surprise that many of the new 16:9 HDTV video monitorshave the same resolution limitations as conventional 4:3 monitors. Flipthrough data sheets, and you will see that many evaluation and viewingmonitors have a published specification of 700 (4:3) to 1000 (16:9) TVlines horizontally. This is about one-third to one-half the resolutionneeded to correctly show a 1920 x 1080 signal and one-half to three-fourthsthe required resolution for a 1280 x 720 signal.
Things are not that much better on the consumer side. Even the newestdirect-view consumer HDTV sets are using picture tubes with only .6mm dotpitch and yield a maximum resolution of 800 pixels/lines. These sets do afine job with 480p signals, but they display less than one-half of thetotal resolution in a 1080i picture. Older sets are still hamstrung with.7mm to .8mm dot sizes.
Even rear-projection TVs and monitors are handicapped by using 7″ CRTs,which are primarily used for projecting video and VGA (640 x 480) pictures.The industry consensus is that it takes at least 9″ tubes in a CRT videoprojector to do justice to a 1080i image, but such tubes add considerablesize, weight, and cost to a projection system. The cheapest consumer-model,rear-projection HDTV set using 9″ tubes (Philips’ 64PP9901) costs about$10,000.
What all of this means is that we are rolling out a high-resolution TVsystem that exceeds the capacity of most devices used to display it! Anaverage viewer will not see a tremendous difference between 480p and 720pmaterial as a result-most monitors are incapable of showing all the extradetail. The use of set-top boxes that work at only two resolutions (1080ior 480i/p) and down-convert 720p decoded signals to 480p will furthercompound the problem.
This situation is not lost on many in the broadcast industry. The leap inimage quality just from analog 525-line video to digital 480p issubstantial for most viewers. There is even a school of thought that says720p images are effectively as good as 1080i, given the loss of resolutiondue to interlacing and the fact that most displays cannot do 1080i justice.This is part of the reason for ABC’s decision to transmit in the 720pformat (a signal that many set-top HDTV decoders will down-convert to 480panyway).
As a result of this resolution conundrum, there is a considerable “buzz”about plasma display panels (PDPs), large-screen monitors that can hang ona wall or sit discretely on small tabletops. Newer 50” models from Pioneer(PDP-v502x) and NEC (PlasmaSync 5000W) have defined pixel resolutions of1280 x 768 and 1365 x 768, respectively. This makes both models immediatelycompatible with 720p signals as well as 480p and allows 1080i broadcasts tobe shown with about 33-percent compression. However, the pixel sizes onmany plasma displays are quite large-just under 1mm for the largestPDPs-and can result in a noticeable pixel structure.
A different problem faces manufacturers of rear-projection LCD and DLPmonitors. Current models are only capable of XGA (1024 x 768) resolution,with 1280 x 1024 (720p compatible) not expected until next year. Atpresent, neither Sony nor Epson have plans to produce 1920 x 1080liquid-crystal panels, while Texas Instruments has only made a handful ofprototype 1920 x 1080 digital micro-mirror devices. However, TI hasannounced partnerships with Hitachi and Mitsubishi to build all-digitalHDTV sets for home use, presumably using 1280 x 1024 (16:9) DMDs.
Current OfferingsWhere is still a need for HDTV monitors, even if they cannot handle all thepicture resolution. Several evaluation and presentation-quality models arenow available. Many of the smaller picture sizes (20″ and under) are usinga fine-pitch picture tube similar to that found in a desktop computermonitor, but they are really intended for single-user viewing. The largermodels (22″ and up) have coarser resolution, but they can be located somedistance from the viewer.
While the original NTSC specification called for a viewing distance ofseven-times the screen height, 1080 signals are optimally viewed atthree-times the screen height. This means that facilities installing HDmonitors into existing editing, post, and graphics suites must either movethe monitors closer to viewers to get the full benefit of the addedresolution or upgrade to larger monitors.
For now, the majority of presentation-quality HDTV monitors measure between22″ and 30″ diagonally and deliver optimum viewing distances of about fiveto seven feet. If you are in the market for HDTV monitors, be careful-somemodels use 4:3 tubes with masking to yield a 16:9 image. The process islike viewing letterboxed DVDs on a standard 4:3 television. Look forresolution specifications-if it goes up in 16:9 mode, chances are it uses awidescreen picture tube. If they go down, it’s a 4:3 tube.
Sony’s new BVM-D series digital studio/field monitors are available insizes from 8″ to 22.5″ and are digital-ready with no external decoder cardsrequired. The BVM-D9H1U/H5U AC/battery 4:3 monitors have 8″ viewable areasand are compatible with 480i/p, 720p, and 1035i/1080i signals, althoughtheir resolutions are specified at only 340 TV lines in 16:9 mode (450lines in 4:3). Sony’s BVW-D14H1U/H5U 13″ monitors claim 600 TV lines ofresolution (800 lines in 4:3) while showing everything from 480i to 1080i.
The BVW-D20F1U evaluation monitor has a claimed resolution of 700 TV linesin 16:9 mode (900 in 4:3), while the BVM-D24E1WU evaluation monitor boastsof 1000 widescreen TV lines. You should note that all but the last monitoruse conventional 4:3 tubes with a hard bezel mask to get a 16:9image-widescreen images are letterboxed to fit the screen width, while 4:3images fill the frame top to bottom. Only the BVM-D24E1WU uses a true 16:9picture tube, which accounts for the increase in picture resolution when inwidescreen mode.
For HDTV production, Sony offers the HDM-series evaluation and PHM-seriesviewing monitors. The PHM-14M8U, HDM-14E5U, and HDM-14E1U all feature 12″screens rated at 700, 700, and 600 TV lines, respectively. Unlike theD-series, these monitors can only accept 480p or 1035i/1080i signals. The17″ HDM-20M8U viewing monitor and HDM-20E1U evaluation monitor sport 700and 850 lines of resolution with 480p and 1035/1080i compatibility, whilethe HDM-2830/4 evaluation monitor specs at 1000 TV lines (again 1035/1080iand 480p compatible).
Want plasma? Sony’s PFM-500A1WU 42″ PDP has a native pixel resolution of852 x 480 and can show both 720p and 1080i as well as 480p and VGA throughSXGA computer graphics. (Ditto the improved-contrast PFM-500A2WU 42″ panel,which is also 852 x 480 native.) For increased resolution, Sony now offersthe 42″ PFM-510A1WU with 1024 x 1024 non-square pixels and full 1035/1080i,720p, and 480p plus computer compatibility.
Panasonic has rolled out a few new models for digital and HD production.The DT-M3050W 30″ DTV color monitor uses a super-flat picture tube with adot pitch of .7mm and a claimed resolution of 640 TV lines in HD mode. It’san analog monitor that accepts decoded 480i/p, 720p, and 1080i signals. Forthose with a few more dollars to spend, Panasonic offers the AT-H3015W 30″HDTV master monitor. It sports a .36mm dot pitch and claims 1000 lines ofresolution. Digital convergence and full 480-to-1080 compatibility arestandard.
Other Panasonic monitors are good for less-critical viewing of DTV and HDsignals. The DT-2750MS presentation monitor has a 27″, 4:3 screen and 600TV lines (800 x 600) of resolution, adequate for 480p applications. Forportable use, the BT-S915DA 4:3 9″ monitor will accept analog Y/Pb/Prsignals or SDI input via an optional ET-SD06U interface and will letterbox1080i and 720p material. It claims 300 TV lines of resolution with a .5mmdot pitch CRT.
Panasonic has also gone “flat” with the PT-42P1 42″ plasma panel. It has anative pixel count of 852 x 480 and is compatible with both DTV and HDTVsignals, although the maximum native vertical image resolution is only 480lines (33-percent reduction from a 1920 x 1080 signal). At this year’s NABand INFOCOMM, Panasonic showed a prototype 60″ plasma monitor with nativeresolution of 1366 x 768 pixels-adequate for scaled displays of 1080material and a one-to-one match for viewing 1280 x 720p programs. Contrastand brightness are considerably improved over older PDPs.
Princeton Graphics, long known for high-quality computer monitors,introduced a monitor specifically designed for HDTV viewing. The companyfirst aimed the AF 3.0 HD 32″ monitor (30″ viewable) at the consumermarket, but it is also perfectly at home in studio and broadcast HDapplications. It sports a.6mm dot pitch and 600 TV lines (800 x 600) ofresolution and is compatible with decoded 1080i, 720p, and 480i/p signalsas well as VGA, SVGA, and XGA computer graphics. A built-in line doublerconverts 525/625 inputs and 480i to 480p.
Barco-a name long associated with high-quality monitors-has one HD and afew digital offerings as well. The ADVM-28, -20, and -14 models are all 4:3hybrid digital/analog monitors and are capable of accepting direct SDinputs. While not compatible with DTV signals, they are useful formonitoring the down-converting/up-converting of HD material to 480i ordirect viewing of multiple 480i feeds. The ADVM-28 uses a .8mm dot pitchCRT, while the ADVM-20 and ADVM-14 are rated at .26mm dot pitch/1000 TVlines and .28mm dot pitch/750 TV lines, respectively.
Barco also offers the HDM-5049 17″ 16:9 monitor, a true HDTV-compatibledisplay with analog signal inputs. It uses a .26mm dot pitch CRT and claims1200-plus lines of resolution. In addition to compatibility with 480i/p,720p, and 1080i signals, Barco claims that the internal synch (30kHz to82kHz) and bandwidth (135mHz) are sufficient to handle 1080p inputs,although the calculated bandwidth of a 1080p signal is somewhere around180-plus mHz.
Finally, JVC has gone high-def with the DT-V2000SU 4:3 broadcast/editmonitor, a 20″ display that is compatible with analog 480i/p, 720p, and1080i formats. Resolution is specified at 900 TV lines in 4:3 mode and 700TV lines in 16:9. It can also display computer signals from VGA to XGA. Fortrue 16:9 imaging, JVC also offers the HV-M300VSU production monitor with a32″ screen. It has a dot pitch of about .68mm and claims 550 TV lines ofresolution (800 x 600 pixels) in 16:9 mode. Two separate sets of Y/Pb/Pr orRGB inputs are standard for viewing 480, 720, or 1080 content.
JVC has also introduced a plasma product, the GD-V425PZW. Like most 42″PDPs, it supports wide VGA resolution (852 x 480 pixels) and can show 720pand 1080 with some compression in detail. It also supports both RGB andY/Pb/Pr inputs. Although JVC has based the GD-V425PZW on a FujitsuElectronics glass panel array, the company has done some work on thedriving electronics to improve video quality, contrast, and colorsaturation.