How to Use a Vectorscope


The vectorscope gives you control of your color video signal. This article will give teach you how to match colors and white balance using your vectorscope while ensuring that you don't over saturate. While the waveform monitor displays both color and brightness, a vectorscope displays color information only.

Things You'll Need

  • Vectorscope
  • Video source
  • Know that there are 2 parts to a vectorscope--the scale or graticule against which you do your measurement and the trace which represents the chrominance, or color portion of the video signal. The vectorscope's display is created by decoding the chrominance portion of the video signal into 2 components, B-Y, blue less luminance, and R-Y, red subtracting luminance. These 2 signals are then plotted horizontally and vertically on the scale. B-Y is on the horizontal axis. R-Y is on the vertical axis. Colors are displayed as vectors between them, hence the name of the instrument.

  • Calibrate your vectorscope before using it. The point in the center of the scale is the reference for centering the trace. In REF mode, you'll generate a circle with your trace that you'll match the circle of your display. NTSC color subcarrier, known as burst, should be rotated until it rests on the 9 o'clock line. Burst is the lime green 3.58 MHz color reference signal that is sent out with every line of video. If you put a professional monitor in underscan, you'll see it as a green stripe on the left side of your picture to the right of the blacker than black synch pulse.

  • Determine the relative strength of each color once your signal is calibrated. The center is reserved for black or white. The relative signal strength of each color can be readily seen by seeing its distance from the center.

  • Turn on your SMPTE color bars. With a clean signal source, the output of bars should rest within the center of all the labeled boxes. If your source is on tape, you'll detect a little jitter and see a blurred image. To match the phase or tint of 2 or more different cameras, turn each source to bars, and on program output of your switcher adjust the phase pots on the camera control units until all of the bars land in their appropriate boxes.

  • Check to see if camera white balances properly. Choose the correct filter. Light with the "white" light that you'll use. Open the iris up until the waveform monitor reaches 100 IRE. Activate white balance and see if all the vectors retreat into the center. Most cameras have auto black balance. Cap it and the same thing should happen. If the camera has a color shift, check that the filter matches the light source. If the signal doesn't shrink down to the center, your camera might need repair.

  • Protect against over saturation. Video equipment is designed to work within broadcast specs, but as the line between computers and broadcast video gear blurs, it's easy to create graphics that simply have too much color for transmitters and televisions to handle. In some cases the over saturation is easy to see. The color will extend outside the vectorscope's circle. Strictly speaking, any part of the picture with over 75% saturation is illegal for NTSC. On your vectorscope those target boxes represent the color limit.

  • Know the legal exceptions. Sometimes a highly saturated color can slip through. If you find a color that goes past 75% turn to the waveform monitor in the flat, or luminance plus color position. If your color plus luminance together is under 121 IRE, you should be able to get by with it.

Tips & Warnings

  • Make sure the signal is terminated properly at the end of the line.

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