TV
Although video equipment today includes quite a bit of automatic circuitry to adjust audio and video levels, these automatic controls are programmed to maintain only rudimentary technical parameters—which may or may not be in line with your desired results. Thus, if you are to consider yourself "a pro," (i.e., a professional who can produce consistently good results) it's essential that you understand the elements of a Waveform Monitor.
The waveform monitor graphically displays and measures the brightness or luminance level of the video.
What you see will tell you a lot about video quality and give you some clues how to fix problems.
The dark areas of the video picture are represented near the bottom of the waveform scale (marked "Setup”) and white areas appear at the top (marked "100 IRE").
A scale along the side of the waveform monitor starts at about -30 (at the very bottom) and goes to about +120 (at the very top). The numbers on the waveform monitor are based on IRE units, units first established by the Institute of Radio Engineers.
Ideally, video levels (for an average picture) should be somewhat evenly distributed between 7.5 (where "black" should start) and 100 (where "white" should end)
While looking at your waveform monitor, you should adjust video level so that the “white” information averages around 100 IRE. You should adjust setup to keep the “blacks” averaging around 7.5 IRE units.
When monitoring you off-the-air signal, it is important to make sure the bottom of your “sync” level is near –40 IRE units. If it is normally around –40 IRE and you see it slowly start to rise, this is a sign the transmitter is unable to make power properly and is compressing or “clipping” sync. A large amount of clipping will result in the picture rolling on home TV sets.
The eye sees color very subjectively, so when it comes to making accurate judgments about color our eyes can easily lead us astray. Thus, we need a reliable way of judging the accuracy of color.
The device that does this is called a Vectorscope. There are six little boxes marked R, G, B, Mg, Cy and Yl on the face of the vectorscope. As you might suspect, these stand for red, green, blue, magenta, cyan and yellow, the primary and secondary colors used in color TV.
When video equipment is reproducing color bars, (shown on the left) the primary (red, green and blue) and secondary (magenta, cyan and yellow) color bars should appear in their proper boxes.
When color bars are up and the display seems to be rotated in the wrong direction, adjust chroma phase or hue to rotate it in the proper position. If they are in the proper position but do not fall into the boxes properly, adjust chroma level to move them into the boxes. If you do not have the luxury of color bars, an old engineer trick is to adjust chroma phase so when flesh tones are on the screen, they line up with the line between Yellow (YL) and Red (R) (near the “11 o’clock” position). This will give you a pleasing picture not matter how bad the video was shot.
