HOW TO BUY A TV MONITOR FOR DESKTOP VIDEO
Television is a little different from computer imagery. Those who have converted their text and graphics to video have quickly discovered that the colors are different, thin lines tend to vibrate, and the picture is much fuzzier than the one on their computer screen. Some of the most beautiful CRT art goes to pieces when transformed into the fuzzy world of NTSC (National Television Standards Committee) video, the kind recorded on VCRs and broadcast to your home. For this reason, many computer videographers compose their work with two monitors, a CRT to show clearly what the computer is doing, and a video monitor to show the results as they will be seen by the TV viewer. Composing on a video monitor helps the artist maintain realistic goals about color and detail.
There are really two kinds of TV monitors, those that make the picture look good (designed for the viewing audience), and those that tell the truth (helpful to those analyzing their pictures to make them the best possible). We will focus on the latter, the kind of monitor videographers use to measure the quality of their video signal, both the visible and the invisible parts.
Because analog NTSC video devices are prone to drift out of adjustment, it is necessary to calibrate the signal and the TV monitor frequently. It is also necessary to pay attention to hidden parts of the TV picture, such as the sync (the black bar you see when you misadjust the vertical or horizontal hold on your TV set).
Here are some features to look for when buying a video monitor. Your particular needs will determine which of these features will be most important to you. There is usually a trade-off between quality, size, features, and price. A large screen monitor with a sharp picture with high color accuracy and many automated controls will cost over $3000. A small monitor used simply to observe (not analyze) your work may cost as little as $400. Other trade-offs involve how the monitor is used. Monitors designed for viewing have bright pictures. Monitors for test purposes have specially formulated phosphors that yield sharper more color-accurate, but dimmer pictures.
Physical features -
1. Screen size - As with CRTs, TV screens are listed in inches measured diagonally. Choose the larger screen sizes when possible, taking into consideration the distance between you and the screen. Don't get a screen less than 12" as the smaller picture tubes and LCD screens cannot maintain adequate sharpness. Thirteen inches to 20" are the most popular sizes for test monitors, while 19" through 31" are popular for group viewing.
2. Flat screen - If room reflections are a problem, try to get a flat screen TV as opposed to one with a rounded surface.
3. Rack mount - Professional studio video equipment is generally mounted in standard 19" wide steel racks. If you plan to use this monitor in a console or rack, buy a model with a rack mount chassis or with an optional kit for rack mounting.
4. Metal cabinet - When TV monitors are placed side-by-side or are near other electromagnetic gear, interference (faint bars, waves, or ghosts) may appear on the TV screens. Metal cabinets shield the sensitive electronics from the interference.
5. LCD vs. CRT vs. PDP - CRTs are the most accurate colorwise. LCDs are next most accurate, as long as you view from in front of them. Some exhibit a little smear when displaying fast moving images. Plasma displays (PDPs) don't smear, but are fuzzier than their LCD and CRT counterparts, and tend to "burn in" images that remain on the screen too long.
1. Multiscan - Some TV monitors can work with computer signals as well as TV signals. The common 13" multiscan monitor costs about $1335 and will scan horizontal frequencies 15-36 KHz and vertical frequencies 50-100 Hz. Television works at a horizontal frequency of 15.736 KHz, and vertically at 59.94 Hz (commonly referred to as 60 Hz). VGA computers work at twice the horizontal scan rate (around 30 KHz) as regular TV monitors.
When selecting a multiscan monitor, make sure it has the appropriate 9 or 15 pin computer input as well as a composite video input. Also, make sure it will handle the necessary screen resolution.
Although buying one multiscan monitor may save space and some money, there are times when two monitors (one computer, one video) are better than one. For instance, when trying to view computer menus and status prompts you will want to view a computer monitor. While simultaneously watching video, you'll want a standard video monitor also.
2. Input switch - Multiscan monitors can display computer or video signals. Even if all you are using is video signals, it is sometimes convenient to feed a camera, a VCR, and some other source into your monitor, selecting each with a push of a button. This can save you from buying extra monitors or connecting and disconnecting wires.
3. Multiformat inputs - Broadcast TV and home VCRs use composite video; the colors, luminance (brightness), and sync all travel together on one wire. High-end professional videographers produce and edit their pictures in component video; the colors travel on three separate wires (RGB for red/green/blue, or Y/R-Y/B-Y, or Y/I/Q for other configurations). A hybrid between the two is called Y/C (also called S for Super) whereby combined colors travel on one wire and luminance travels on another. All industrial TV monitors have composite video inputs using BNC (push and twist type) professional connectors.
Consumer gear carry their composite video signals on RCA or phono connectors like the ones found on home VCRs. The better monitors also have Y/C inputs requiring small 4-pin connectors. Super VHS and Hi8 VCRs as well as many prosumer and industrial video devices use Y/C connectors. They are preferable because the luminance and chrominance signals, being on separate wires, don't interfere with each other as they do with composite video. Keeping the signals separate avoids electronic processing which contaminates the color and detail in the TV picture.
Some TV monitors have component RGB inputs for connection to computers, character generators, and graphics cameras. A few models also have Y/R-Y/B-Y (pronounced Y, R minus Y, B minus Y) inputs for direct connection to professional digital and Betacam VCRs. To see the most accurate rendition of your picture, use the component inputs (RGB or Y/R-Y/B-Y). To ascertain what the home viewer will see, view your picture in the Y/C or composite mode. Your picture will be fuzzier but reduced to the quality Joe Couchpotato will see.
4. Cross pulse and underscan - Your home TV set overscans its picture; about 10% of the image is hidden behind the bezel of the screen. An overscanned TV monitor will give you the proper impression of what your viewers will see while alerting you when words or graphics disappear off the edge of the active part of the TV picture. There are other times, however, when you wish to see the entire TV image, right out past the edge. A TV monitor that underscans will permit you to do this. If you play a video tape through an underscanned monitor, you will see the top edge of the screen jitter back and forth (called flagwaving) due to tape tension and time base errors in the mechanism. Viewing your tape through an underscanned monitor gives you the opportunity to adjust the VCR or add additional video processing or time base correction equipment to remove this artifact. The home viewer may never see the flagwaving (it's off the top edge of their screens), but you, as a professional videographer, wish to create master tapes as perfect as possible. Other esoteric electronic details such as video head crossover noise, etc. can be viewed in the underscanned mode. Technicians would use this information to correct VCR playback anomalies.
Cross pulse monitors (also called pulse cross) slide the TV image down 1/2 picture, and to the right 1/2 picture placing the vertical and horizontal sync pulses in the center of the TV screen where they are easier to see. Cross pulse monitors also brighten the image making the dark sync pulse lighter and easier to examine. As before, a technician could diagnose video problems from aberrations in the sync pulse.
Professionals take special care to assure that the sync signal is straight, stable, and accurate. The FCC as well as other video standards committees specify in great detail how the sync pulse should look. A professional 13" monitor ($1300) will have cross pulse capability, several inputs (RGB, Y/C, composite), 750 lines of resolution and Type C phosphors (described later).
5. Bridging or looping inputs - If you wish to send your video signal through the TV monitor on the way to some other destination (say a VCR), you will need a looping or bridging input. This dual input allows the signal to enter the TV (which samples a tiny bit of it) while sending the rest of the signal on to its final destination. When using a monitor with bridging inputs, be sure you flip the monitor's impedance switch (next to the input socket) to the right position: HI Z if you are sending the signal through the monitor to another device, and 75 ohm if the monitor is the last device in the line to receive the signal.
6. Speaker - Although TV monitors are used mostly to display video, there are times when you need to hear audio, for instance, when viewing a video tape. An internal speaker saves you the hassle of finding an amplifier and speaker for your sound.
7. Blue gun - A TV monitor with a blue gun allows you to shut off all of the colors except blue. This is useful for calibrating the colors on the screen. You would send a color bar test signal to the monitor, shut off all the colors but blue, and then adjust the hue control until you saw three evenly matched, equally spaced, equally dark blue bars.
Monitors without a blue gun capability can be calibrated almost as easily with the use of a deep blue filter available from photographic stores (ask for Kodak #47b gelatin filter, costing about $10) or from Imero Fiorentino Associates (they call it a "Monitor Analyzer"). You would send color bars to the monitor, and then view the image through the blue filter while adjusting the hue control to create three similar blue bars on the screen. The blue gun is mostly a matter of convenience; you don't need to mess with a blue lens.
8. External sync - Studios using several TV cameras and other synchronized sources use TV monitors with external sync. These monitors receive their sync from the facility's master sync generator and receive the video from the various sources. If anything happens that puts one out of step with the others, the monitors with external sync will show the problem. In most other circumstances, external sync is unnecessary.
9. Degaussing switch - Stray magnetism, even from the earth's magnetic poles, can cause color tints to appear on the TV screen. Although most TV monitors degauss (demagnetize) their screens each time they are turned on, professional monitors allow additional, more thorough degaussing to completely assure that the screen displays pure untainted colors.
10. AC/DC - If you plan to use the TV monitor in the field for portable productions, you'll need an AC/DC monitor to run on batteries.
Quality issues -
1. Resolution - One of the most important ways to describe the quality of a TV monitor is its resolution. It is impossible to tell if your picture is sharp if your monitor is fuzzy. Resolution is measured in horizontal lines (not to be confused with the 525 scan lines that always make up a television picture). Lines of resolution measured horizontally are like pickets in a fence: the more pickets you can see crowded close together, the sharper the image. Small TV monitors costing under $300 each usually yield 220 lines of horizontal resolution, about the quality of a VHS tape. Broadcast television comes to your home with a maximum resolution of 330 lines. Super VHS and Hi8 VCRs can create 400 lines of resolution, requiring a 400 line monitor (preferably with a Y/C input) to view the image in all its glory. DV VCRs make up to 500 lines of horizontal resolution, DVDs up to 540. Professional studio monitors display 600 to 700 lines of resolution and generally cost $1500 to $2500. These monitors match the resolution of high end industrial $10,000 TV cameras and digital VCRs (DV, DVCPRO, DVCAM, and Digital8).
Computer users are more familiar with measuring resolution in terms of pixels. In the video world, resolution is measured in lines. The difference in the ways these numbers are calculated make it difficult to convert from one to the other directly. Multiscan monitors used for computer and video display often list their resolution both ways. For instance, the Sony GVM-1311Q 13" monitor has an RGB resolution of 900 x 560 pixels and a composite video resolution of 600 lines. Sony's GVM-2020 20" monitor has a pixel resolution of 720 x 480 and has a composite video resolution of 560 lines. In all cases, the higher the resolution the better.
2. Screen pitch - Also related to resolution is the screen dot or line pitch which is the distance in millimeters between individual phosphor dot triads or RGB stripes on a monitor screen. The smaller the dot pitch the better since it allows for more potential dots to be displayed giving you more resolution. In order to remain sharp, small TV screens require a smaller dot pitch than large screens. A dot pitch of .47mm allows a 14" monitor to yield about 300 lines of resolution. Better monitors would have a pitch of .31mm or as small as .25mm.
3. Comb filter - Composite video images from TV broadcasts or VHS VCRs have the luminance (brightness) mixed with the color aspects of the signal. The monitor must separate the two. Inexpensive monitors use notch filters or traps which lose some of the picture sharpness while separating the color from the luminance. Monitors with comb filters carefully separate the video frequencies in a way that retain picture sharpness while reducing moire, those crawling dots along the edges of saturated colors in your picture. This is one of the more valuable TV monitor features.
4. DC restorer - The bright parts of a TV picture electronically affect dark parts of the picture. TV monitor circuits with DC restoration keep the dark parts of the picture dark regardless of what the bright parts of the picture are doing, yielding a picture with better contrast and finer detail.
5. Type C phosphors - Monitors designed for audience viewing have phosphors designed for bright images with a slightly warm glow. Test monitors are slightly bluer and dimmer but their SMPTE Type C phosphors are very precise both in color reproduction and sharpness. Broadcast quality monitors which must precisely match each other use Type C phosphors.
6. Beam current feedback - As electronic circuits age, they drift causing white parts of the picture to change their colors slightly. Beam current feedback results in a more stable picture with better color balance by adjusting to the changing picture tube characteristics. This feature is important mostly to broadcast TV professionals. The Sony PVM-1340 13" professional monitor ($835) has DC restoration, SMPTE Type C phosphors, and beam current feedback.
7. Auto convergence and convergence error - Every color TV monitor must fire three electron guns in a way that creates the red, green, and blue parts of a picture. These parts must overlap precisely (converge) in order to avoid making rainbow colors around objects, especially in the corners of the screen. The error made by the monitor as it fails to overlap the color images is called is called a convergence error. The better monitors specify this convergence error. The Sony BVM-1910 19" professional monitor ($7500) with 900 lines of resolution, has convergence error of .4mm at the center of the screen and .7mm at the edge.
8. Items 6 and 7 above apply only to CRTs. LCDs don't need convergence and beam adjustments. For best results, they should be set for their NATIVE RESOLUTION, the resolution determined by the number of pixels in the screen. This number is found in the manufacturing specs, and is settable through a menu.
CRT TV monitors are converged at the factory and should occasionally be tested and reconverged by a technician to be sure that the colors properly overlap. TV monitors with auto convergence assure proper geometric alignment of the signals without the help of the technician. A cheap monitor with a sharp picture may be your computer monitor-Many of us have now invested in 19" monitors for our computers. These monitors are very sharp, compared to NTSC TV monitors. Leveraging that investment, it is possible to buy a computer circuit called a video card or frame grabber or analog-to-digital video converter card that will change NTSC video signals to computer signals that will display, in all their glory, on your hi res computer monitor. Matrox and All-in-Wonder and others sell these TV cards for about $200-300. If you already have a super sharp computer monitor, then $200 is not a big price to pay to turn it into a hi res TV monitor. Downside: You have to do your TV work near the computer.
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