Jerome Glick (MBHS Magnet '12) | Television Display Calibration
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~Television Display Calibration Page~
Looks as good as new!
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Know how to get the most out of any old TV set, and make it look even better than those new "flatties"!
      The sad fact is that many hard-working reliable television sets across the country (and the world) are being frowned upon by viewers who demand more in picture quality and who are told by the salesmen that their flawless sets are "old". Just because cathode ray tube (CRT) televisions may not look like the slickest thing on the market today, it doesn't mean they should be banished if they can still operate to a quality standard. Besides, the picture quality of CRT TVs are in many ways superior to that of any new pixel-based digital LCD or plasma TV, as explained in this article from Aerials and TV (ATV). The problem is that there is a common misunderstanding of the five basic television picture adjustment controls and how to properly set them to an internationally-recognized quality picture standard. Frequent maladjustment renders these TVs displaying pictures so bright that black is only seen when the TV is off and white patches swell obtrusively while skin tones are unnaturally red or even green. Don't blame the TV set for being "old"! It just needs a few minutes of proper adjustment and the pictures will look as good as new.
      You will need a source from which to feed standardized video test patterns to your television set, whether it be a broadcast station, VHS/DVD player, or professional pattern generator (harder to get your hands on). It is ideal to use a pattern from the medium which you will most frequently be watching (i.e. broadcast TV). Unfortunately, test patterns are rarely broadcast nowadays as informercials and 24-hour programming keep the TV busy day and night. For a calibration DVD instead, I recommend Digital Video Essentials from Joe Kane Productions. The only pattern you really need is the ubiquitous SMPTE Color Bars, though it may be easier to use the larger grayscale bars on the PLUGE (picture line-up generation equipment) test pattern to calibrate luminance. You will also need a blue filter, a piece of transparent material (usually a film or lens) which allows only blue light to pass through. (Do not use the color bars displayed by clicking on the link above. Digital image formats do not store sub-black luminance information and therefore cannot be used as accurate test pattern sources.)

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  1. First, clean the screen with a damp cloth. The electrostatic behavior of cathode ray tubes attracts dust over time which collects on the screen and dulls the picture you see. You will be suprised at how much dust there is and how much brighter your picture may appear after a simple cleaning. After cleaning our TV screen for the first time in a decade, the dust that came off looked as thick and black as the carbon from a car tire!

  2. Next, have your set on for at least a half-hour to allow all electronic components to stabilize. Turn off or disable all picture and color "enhancement" settings, such as "flesh tone" or "color correction/temperature". These usually add extraneous information to the video signal and don't correspond to the broadcaster's original intentions.

  3. Every color television has at least the following five basic picture adjustment controls: Brightness (black level), Contrast (white level), Color (saturation), Tint (gamut), and Sharpness. A monochrome television lacks the Color, Tint, and Sharpness controls. These five controls are put in place to correct for deviations in the properties of a video signal caused either by the environmental effects on or the aging of the electronics, or by distortions introduced while in transmission from the broadcast site. We'll focus on these one at a time in order in this tutorial. To begin, turn the Color and Sharpness controls all the way down and set the Contrast control to its middle setting.

  4. Brightness:(☼) Due to their interactivity, the brightness and contrast controls are frequently confused and referred to interchangebly. However, they are very distinct and control only the luminance (monochrome) part of the video signal. Brightness refers to the level of black in the video signal. More specifically, changing the brightness will actually change the absolute intensity of all monochrome shades on-screen, including full black and full white. Technically speaking, this changes the luminance signal's DC component or normalization. Think of Brightness as the "volume knob" for light intensity (a video signal's normalization is analogous to an audio signal's amplitude). Only one setting is appropriate, because all others would not be an accurate portrayal of reality. Brightness is often set too high, making black areas of the picture appear gray.
          Turn the Brightness control all the way up. Observe the three adjacent narrow bars in the lower right of the SMPTE Color Bars test pattern. The left bar is electronically encoded as "blacker-than-black", which means it should never stand out against normal black. Reduce the Brightness until the "blacker-than-black" bar is no longer visible against the middle black bar. The right gray bar should still be visible. If it is not, increase Brightness until it is just barely visible.

  5. Contrast:(◑) Frequently confused with Brightness, Contrast is sometimes labeled as "Picture" on TV sets. Contrast refers to the level of white in the video signal. Adjusting the contrast will change the level of white relative to the signal's black level (technically speaking, the amplitude) and thereby increase the difference in light output between the brightest and the darkest spots in a picture. Think of Contrast as the "dynamic range" knob (if one existed) for light intensity. Contrast is also often set too high, causing bright spots of the picture to swell or "bloom". Excessively intense whites can also burn the picture tube's phosphors in the long run.
          Observe the white square in the lower left of the SMPTE Color Bars test pattern. Gradually increase Contrast until either this square starts to bloom or any vertical lines in the pattern start to bend. Once either of these distortions occur, the Contrast setting is too high and must be reduced. Since Contrast and Brightness are interactive, you may find that the three narrow bars used for the Brightness setting have been altered. Alternate between setting the Brightness and Contrast controls until they are both correct.

  6. Color: The Color control adjusts the intensity of the color information on-screen. Technically speaking, this is the amplitude of the chrominance signal. Turning it all the way down will produce a monochrome (colorless) image. When set improperly, this can make skin tones glow an unnatural red or orange.
          Now it's time to take out your blue filter and look through it. You should only see blue. Focus on the extreme left and right bars. Adjust the Color control until these bars are the same shade of blue. You may also use each bar's lower sub-bar as a reference.

  7. Tint: Sometimes labeled as "Hue", Tint adjusts the color balance in the video signal, ranging from green to magenta. Technically speaking, this is a relative phase adjustment to the chrominance signal.
          Still looking through the blue filter, focus on the third and fifth bars. Adjust the Tint control until these bars are the same shade of blue. You may also use each bar's lower sub-bar as a reference. Repeatedly adjust the Color and Tint controls until all four sets of blue bars are of equal intensity and shade.

  8. Sharpness: Sometimes called "Detail", this is the most often maladjusted control. Your instinct questions what couldn't be good about the sharpest, most detailed picture possible out of your set, but don't be fooled. This setting actually adds a bit of processed information to the video signal, outlining dark objects in white. This is harsh and artificial; definitely nothing that the broadcaster intended. It was originally added to color TVs because the early models lost a bit of highly-detailed (high frequency) picture luminance information while demultiplexing the chrominance signal.
          Gradually increase Sharpness until just below the point at which distortion or a white outline begins to form along the edges of the bars. This is the ideal Sharpness setting for your display.

  9. Now your TV picture should be properly calibrated. Just to be sure, observe some flesh tones on-screen. If necessary, make further adjustments to the Color and Tint controls to optimize the picture's depiction of reality.

  10. In the end you will enjoy a cleaner, warmer, more natural picture from your television set. It may take some getting used to, but your new pictures will be more representative of reality. Even after properly calibrating your TV set to NTSC standards, you may find that you have to make readjustments now and then, particularly with the Color control. As it turns out, standards can deviate from station to station while the quality of signal reception and your distance to the transmitter also plays a role. So even after over a half-century of television innovation, standardization still hasn't quite been perfected, but with a bit more care, it will get there.

Bonus: Oscilloscope-Based Video Monitor
Introduction/Background: Oscilloscope Basics
      Besides duct tape, an engineer's other best friends are the multimeter and the oscilloscope. While a multimeter provides a quantitative reading of the electrical voltage or current in a wire, an oscilloscope provides a qualitative display, projecting the actual shape of the signal's waveform on-screen. An oscilloscope is a device (usually found in laboratories and in ham radio shacks) used to observe the waveforms of an electrical signal on a wire. To see what the oscilloscope can do, a novice user can plug the audio output from a headphone jack into the oscilloscope's "vertical input" jack (grounded, of course). It's screen will then display the shape of the sound waves (waveforms) in time with the music. High-pitched sounds will appear as narrow waves (high frequency) and low-pitched sounds will appear as wide waves (low frequency). Loud sounds will make tall waves (high amplitude) and quiet sounds will make short waves (low amplitude). Silence will make the oscilloscope display just a horizontal line with zero amplitude. If you consider the display as a coordinate graph, the vertical axis is the amplitude of the wave and the horizontal axis is time.

      You can adjust the relative amplification of the signal (how tall the tallest waves appear on-screen) with the vertical sensitivity knob. This is typically calibrated in millivolts per division (a unit on the graticule) with a continuously-variable knob concentrically stacked in the middle. On older units, the knob may be labeled as an uncalibrated ratio, such as 1:1 or 100:1. You can also adjust the rate at which the oscilloscope "paints" the waveform (from left to right) with the timebase knob, typically calibrated in milliseconds per division. Older units have the "frequency" knob calibrated in horizontal sweeps per second (hertz), or "cycles", the unit for frequency used before 1960. These make up the basic controls on an oscilloscope. All words specifically referring to oscilloscope controls will be in bold.

      An oscilloscope is helpful in many scenarios dealing with the testing and troubleshooting of electronic circuits. Looking at the shape of a signal can tell you a lot about the kind of circuit you're working with or the causes of its possible malfunction. For example, an oscilloscope can show you the quality of the circuitry in a cell phone's MP3 player compared to that of a PC's sound card. If you use an oscilloscope to "read" a sawtooth wave (example of a test signal which can tend to challenge or stress electronic circuitry) played by the PC and by the cell phone, the one from the cell phone will look ragged (distorted signal), whereas the one from the PC will look like an actual sawtooth wave. The differences are too subtle to detect by ear with speakers. Given a test signal, the oscilloscope can also show you the impact of distortion on the original audio signal caused by speaker impedance loading.
      Furthermore, you can use an oscilloscope to track the changes in a signal as it passes through the components of a circuit. In practice, no "perfect" undistorted signal exists. But we can get it as close to perfect as possible by isolating the sources of distortion and making suitable adjustments.
      The oscilloscope's X-Y mode graphs two signals against each other (parametrically), most commonly used to compare phase differences between them. A common application is to graph the left and right channels of an audio signal against each other to determine the amount (if any) of stereo separation present in the audio. A mono signal would produce a line with a slope of 1. A signal in which the two channels are 180░ out of phase would produce a line with a slope of -1. A signal in which the two channels are 90░ out of phase would produce a circle (for sine waves), a square (for square waves), a double triangle (for sawtooth waves), etc. A variety of Lissajous curves can be produced by graphing a wave against its harmonics. The X-Y mode can also make the oscilloscope behave in a vectorscope fashion to analyze video signals before they reach their display monitors.

Video (.mov): Sine Waves - Continuous Phase Shift Sawtooth Waves - Continuous Phase Shift Square Waves - Continuous Phase Shift Lissajous Curves - 4:1 to 1:4 Phase Sweep
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Advanced: Video Display Technique
      For all its contributions to the dry analysis of electronic circuitry, the oscilloscope can also behave like a common form of twentieth-century entertainment, the television. I have discovered a rarely-known but logical technique for displaying a composite video signal on any basic oscilloscope (provided it has an external trigger/sync input and a sweep rate of up to 15.7 kHz), effectively turning it into a video monitor. The method lies in a fundamental understanding of how television monitors work. There are three world standards for video signals and displays: NTSC, PAL, and SECAM. North America uses only the NTSC (National Television System Commitee) protocol. Television pictures are displayed in a raster format, which means that a rectangular "canvas" is created on which to "paint" a picture. A television "paints" a picture by starting in the upper left corner, going one line at a time from left to right and down the screen, until all 525 of them are scanned, forming one still picture frame. Then the whole process repeats for the next picture frame, and so on. This all happens so fast that our eyes see a moving image on the screen.

      Normally an oscilloscope's CRT uses a vector scan (i.e. it draws a circle like you would on a sheet of paper without picking up your pencil). However, in order to display a video signal it must employ a raster-scan technique. (By analogy, imagine drawing many close light parallel lines on a paper, only darkening your stroke on the points which represent a circle.) How exactly does one go about creating this raster on an oscilloscope? Well, the NTSC standard calls for a horizontal refresh rate of about 15,734.267 Hz (15.75 kHz ¸ 1.001) and a vertical refresh rate of about 59.94 Hz (60 Hz ¸ 1.001). The horizontal refresh rate describes how fast the beam of electrons travels from left to right and the vertical refresh rate describes how fast it travels from top to bottom to cover the screen with a raster. Setting the horizontal sweep is relatively simple with the timebase knob. But setting the vertical sweep is a bit trickier because there is no "vertical timebase knob"; a vertical timebase signal must be input. This is where a quality signal generator comes in handy, or if you haven't got one, use the free software program, Audacity, with your computer's sound card. You need to generate a wave of 59.94 hertz for the oscilloscope's vertical input. But what kind of a wave must it be? Think about the way a raster is scanned vertically over time. The electron beam starts at the top of the screen and smoothly (linearly) makes its way down to the bottom, then instantly jumps back to the top for the next picture frame. This kind of a pattern traces an inverse sawtooth wave. This technique won't work unless your signal generator is good at generating true sawtooth waves. Just to be sure, observe the wave itself before proceeding. If it looks like a sawtooth wave (no curves), you're good to go. (You could salvage a vertical sweep generator from an old NTSC TV if you're lucky. Better yet, if you have the time and the know-how you could even build a circuit specifically for this purpose.) Essentially, the oscilloscope's internal timebase component serves as the video monitor's horizontal sweep circuit, while the external signal generator (or computer sound card) serves as its vertical sweep circuit. This is the purpose of "vertical hold" and "horizontal hold" controls on a TV. If your picture rolls up or down, it means that the TV's vertical scanning frequency got knocked off a bit from 59.94 Hz and should be readjusted.

      Next we must figure out a way to vary the brightness of each spot on the raster in order to form a picture. The oscilloscope circuitry takes on quite a complicated procedure to accomplish this, and even I don't quite know how it works, but through experimentation I know that the following method does work. After the vertical and horizontal input jacks, the only remaining jack on my basic oscilloscope is for the external trigger, sometimes labeled "Ext. Sync.," "Ext. Input," or "Z-Axis Input". (This jack might be on the back of the oscilloscope.) Normally this is used to steady the display of waveforms rather than having them uncontrollably roll across the screen. (The oscilloscope detects spikes (steep slopes of relatively large amplitude) in the external synchronization signal to trigger the scan of each cycle of the vertical input signal across the screen.) But we're in luck because somehow it works just as well for a composite video signal! Actually, the video signal must first be inverted, otherwise the picture's luminance gets inverted (black becomes white and white becomes black). This is accomplished by switching the connections between the external trigger input and its respective ground input. So, just connect your video signal to the external trigger jack and, voila, you have a picture on the oscilloscope screen! What a thrill! Well, it is an ugly dim monochromatic black-and-green picture on a tiny screen rife with chroma dots, but it's an oscilloscope! Stare at the screen in amazement for a moment before moving on to the relatively easy task of calibration.

      Say hello to your new tabletop TV! The oscilloscope's controls now have new names. "Intensity" becomes "brightness", "focus" is still "focus" (or what I like to call "actual sharpness"), "vertical sensitivity" becomes "vertical size", "horizontal sensitivity" becomes "horizontal size", "frequency/timebase" becomes "horizontal hold", and the horizontal/vertical position knobs still do their usual jobs. Here's a convenient recap of the six (or seven) steps required to set up your oscilloscope as a video monitor:
  • Materials: oscilloscope, signal generator (preferably digital)(or computer with Audacity and a quality sound card, or iPhone running the free app FreqGen), video source (i.e. TV/DTV tuner (demodulator only), VHS/DVD player, closed-circuit video, computer, etc.), necessary cables, wires, and connectors
  1. Turn on the oscilloscope and ensure that it is working properly. Center the beam on-screen. Keep the beam intensity low so as not to "burn" the CRT's phosphor coating.

  2. Set coupling to external trigger/synchronization.

  3. Horizontal Sweep Circuit: Adjust the timebase or "frequency" control as close as possible to 15,734.266 Hz. This equates to 6.356 microseconds per division (if there are ten horizontal graticule divisions). (In practice, you'll most likely have to fish around that number; 5.39 Ás recently worked best on a Tektronix scope.) If you want to be really precise, feed a 15,734.266 Hz sawtooth wave from your signal generator to the vertical input and adjust the scope's unsynchronized timebase until one cycle remains steady on screen. If this is too hard to do (due to sensitive wide-range variable controls), wait until a later stage to readjust the horizontal scan.

  4. Vertical Sweep Circuit: Feed a 59.94 Hz inverted sawtooth wave from your signal generator or computer to the vertical input. (It has to be inverted, otherwise the picture will be upside-down!) If your oscilloscope has BNC jacks, use a male-BNC-to-female-RCA adapter to make it compatable with audio patch cables. (If your oscilloscope has binding posts, use a double-male-banana-jack-to-female-BNC adapter in line with the male-BNC-to-female-RCA adapter.) If you're using a computer, unplug your speakers first, otherwise you'll get an annoyingly loud buzz. Connect a cable from the "audio out" jack on your sound card to the oscilloscope's vertical input jack. Turn your computer's volume control all the way up so as to get the highest definition sawtooth wave on-screen. Adjust the vertical sensitivity so that the entire wave, from peak to trough, is visible on-screen.

  5. Video Signal: Connect an inverted composite (single-cable, unmodulated) video signal to the external trigger input, using the necessary adapters mentioned in step 3 to comply with a male RCA phono jack. The inversion can be accomplished by plugging a double banana jack adapter upside down. This connects signal to ground and vice versa. The signal can be supplied by any device which outputs an NTSC composite video signal, such as a TV/DTV tuner, cable/satellite tuner, VHS/DVD player, video camera, computer, iPhone, etc. (The entire experiment can be executed for PAL signals by adjusting the timebase frequencies accordingly. However, this method will never work for SECAM signals, as they are frequency-modulated.)

  6. Display Calibration: There are seven picture controls available on the oscilloscope: horizontal & vertical size and position, brightness, focus, and horizontal hold. Display a variety of common video test patterns (i.e. Indian Head Test Pattern, Philips PM5540, and BBC Test Card F) to aid in precise calibration. Adjust the horizontal size (sensitivity) such that the sides of the picture are just beyond the edges of the screen. Adjust the vertical size (sensitivity) such that circles appear as circles (using a ruler can help). Adjust these in tandem with the horizontal and vertical position controls to center the picture. Adjust the horizontal hold (timebase) such that the picture is horizontally aligned and not slanted. The brightness control (intensity) should be adjusted such that none of the green phosphor is lit in the black regions of the picture. Although you may be tempted to set the brightness control higher than the standardized setting, this won't necessarily improve the picture's clarity. Some oscilloscopes may include an external sync amplitude knob to serve as a "contrast control." Since most don't have this, however, the ideal scenario would be to amplify the video signal before it goes in the oscilloscope to increase the contrast (difference between light and dark areas of the picture) and therefore make the picture easier to view. But for now, just darken the room. Adjust the focus (actual sharpness) such that the finest lines in the picture appear sharp and clear.

  7. Miscellaneous Troubleshooting: If your picture's top half is swapped with its bottom half, but not rolling up or down, your instinct may tell you to adjust the vertical hold control, which in this case represents the frequency from the signal generator. However, the stability of the picture tells you that the generator is spot-on 59.94 Hz and doesn't really need an adjustment. The problem is that the vertical scan is out of phase with the video signal's vertical blanking interval. Sometimes the vertical alignment of the picture may jump around erratically. These "blips" can happen more often with lower-quality computer sound cards which periodically disturb the phase, and your picture. The only solution is to get a better vertical sweep generator circuit. If you already are using a quality signal generator, a misaligned picture tells you that you just happened to start the vertical scan signal out of phase with the video signal. Simply restart the signal with hopes that the phases will line up correctly by chance, or, if your generator's frequency is continuously variable, simply nudge the frequency control until the picture is aligned again. A digital signal generator with discrete frequency increments is recommended because you will find it nearly impossible to lock the picture in place by nailing 59.94 Hz spot-on with an analog signal generator. You will find the picture shifting vertically every minute at best, requiring you to constantly readjust the frequency. With a digital generator, simply start the signal and change frequency to 59.92 Hz until the picture is vertically aligned, then return to 59.94 Hz to lock the picture in place.
Below is a circuit diagram of an idealized adapter box built for the specific function of neatly interfacing any oscilloscope to either a VHF/UHF modulated or unmodulated NTSC video signal. The orange components are used to momentarily adjust the phase relationship of the vertical/horizontal sweep signals with respect to the blanking intervals of the video signal. The color subcarrier filter attempts to prevent "chroma dot" artifacts from appearing on a monochrome-only display.
Oscilloscope Screen Video (.mp4):
Cold Start (tubes take a while to warm up) Warm Start Brief Cartoon Animation Brief ION Life Program Turn-off (has a nice effect)

      And that's all there is to it! Realize that a TV is just a refined oscilloscope with its vertical and horizontal controls locked and hidden inside. Also realize that an oscilloscope is just a more flexible, more versatile kind of TV (like a low-level programming language, for computer geeks). So the next time your television quits on you, turn to your trusty oscilloscope to catch that emergency weather report, or the latest episode of Jeopardy! If anyone knows the mathematics behind how the external trigger magically varies the brightness of each spot on the screen, please explain it to me!

Note: As far as I know, this technique will not work on any digital sample-based oscilloscopes, as the persistance of phosphor CRTs is a necessary ingredient. A digital scope will instead display a raster of widely-spaced pixels and is not capable of varying its beam intensity as a function of the external trigger signal.
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Double Bonus: Waveform Monitor

      A waveform monitor is as much a friend to the video engineer as the oscilloscope is to electrical engineers in general. This device was made for graphically monitoring the luminance of video signals and is designed for use in tandem with the SMPTE Color Bars to calibrate a video source. A waveform monitor displays the actual waveform of the video signal in a special manner. The x-axis corresponds to the horizontal positioning of objects in the video and the y-axis corresponds to the brightness of said objects. The vertical position of said objects cannot be distinguished on a waveform monitor as all horizontal lines are superimposed. For example, if there is a bright window in the left side of your video, it will appear as a peak in the left portion of the waveform on the waveform monitor. Technicians use a waveform monitor to ensure that on average the brightest components of a video signal do not surpass a level of 100 IRE (1 volt, full white) and the darkest components do not go below 7.5 IRE (0.339 volts, full black). 0 IRE (0.285 volts) is used as a blanking interval to switch off the electron beam as it sweeps back to start scanning a new line and -40 IRE (0 volts) is used as a sync pulse to signal the start of a new line or frame. (The IRE is the unit of brightness in composite video; it appears in a marked scale on the waveform monitor.)

      Since professional waveform monitors were originally derived from oscilloscopes, you can make any oscilloscope behave like a waveform monitor (in "line mode") by simply connecting a composite video signal source to the vertical input of the scope and setting the horizontal timebase to as close as possible to 15,734.266 Hz, the NTSC horizontal scan frequency. The oscilloscope is painting the waveforms that represent each of the 525 lines of the image, one at a time in sequence, each for only 1/15,734.266 of a second. Because this is too fast for the human eye to detect and because of the persistance of the CRT phosphor, we perceive this as a display of all 525 lines continuously superimposed. Furthermore, 54.94 of those superimposed "frame signals" must pass by our eyes each second. The resolution of the displayed waveform is dependent on the bandwidth of your oscilloscope. For example, since my economy-grade Heathkit oscilloscope was made in 1960, its bandwidth is only 200 kHz. The vertical amplifier cannot react properly to frequencies above this limit and therefore such waveforms are rounded off.

      To make the oscilloscope function in "field mode," set the horizontal timebase to 59.94 Hz, the NTSC vertical scan frequency. In this case, the brightness of all 525 lines are not superimposed, but adjacently positioned such that the left side of the scan corresponds to intensity at the top of the image and the right side corresponds to intensity at the bottom of the image. To magnify the waveform, simply increase the horizontal timebase as desired. This will cause the waveform to "stretch" horizontally. Of course, the effectiveness of this capability is dependent on the bandwidth of your oscilloscope.
[IMG:SMPTE Color Bars on Scope.jpg]
[IMG:Waveform Monitor.jpg]

Last Updated: September 10, 2013. Created with Notepad++. ©2013 Jerome Glick
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