Vectorscopes & Waveform Monitors

[Ken Tanaka]

Can you recommend a book for learning how to use a vectorscope display? I've read add re-read (usually brief) references to this tool in other material. I've pulled-up the v.s. display on FCP3 and studied it with varius footage. But it still has less meaning to me than an ultrasound of a rhino's belly. Is this -really- a useful tool and, if so, where does one learn to use it (short of becoming an apprentice broadcast engineer)?

[Vic Owen]

Glad to hear you say that, Ken. With the FAA, I have the opportunity to work with system analyzers, sophisticated oscilloscopes, spectrum analyzers, logic analyzers, etc. I still feel stupid when trying to figure out the vector scope -- I just thought it was the limited time I'd spent with video........maybe not? I'm ready for the 'experts' to weigh in! Surely there's some use for this puppy.....

<<<-- Originally posted by KenTanaka : Can you recommend a book for learning how to use a vectorscope display? I've read add re-read (usually brief) references to this tool in other material. I've pulled-up the v.s. display on FCP3 and studied it with varius footage. But it still has less meaning to me than an ultrasound of a rhino's belly. Is this -really- a useful tool and, if so, where does one learn to use it (short of becoming an apprentice broadcast engineer)? -->>>

Hi Ken
Sorry but, offhand, I don't know of a good reference book. I do know that most of the edit software out there (eg, Final Cut Pro) includes some form of waveform/vector scope display - a manual might be a good place to start. Here's a very BASIC description of function - waveform displays luminance info and vector scope the chroma.....colour (no spelling error - north of 49th) bars are the known reference used for calibration of both luma and chroma. If you're going to do any signal processing (TBC's, proc amps etc.) or colour correction you need to be certain your monitors are accurate. You can achieve reasonable results adjusting your monitor visually using colour bars but a waveform/vector scope is more precise.
If you want to pursue perhaps a new thread - we've digressed from back focus..

[Ozzie Alfonso]

Vic,

To answer your questiion on how to use a vectorscope and to amplify on Sweeper's reply - a vector scope is strictly for setting up color hue, chroma intensity and color burst strength. It works only as long as the bars and the subsequent material are faithful to eachother, and, I believe, it applies to NTSC only, at least at the receiver's end.

The vector scope should not be confused with the wave form monitor which is strictly used to determine video gain, black level (pedestal) and vertical interval. It is a rectangular display while the vector scope is circular. When running bars, the first thing to do is to place the small "spoke" coming off the center of the circle in the box where the color burst belongs. Doing this simply gets you to set the color burst's level and phase. Having done that, the next step is to increase, or decrease the gain of all the colors and turn the dial to place each color in it's proper box. If the color burst has been correctly set, this should be a simple turning up, or down, of the dial that controls chroma saturation. Very much like turning the hue control on a monitor.

If you've had problems reading a vectorscope it's probably because you've looked at it while a signal other than bars is being read. In that case what you see is a seemingly chaotic display that only tells you where most of the colors lie and how saturated they are. The only constant should be the placing of the color burst and the Y/C "spokes".

That's about it. We've come to ignore much of what the vectorscope does since so much is automated, especially in the DV world. But signals coming through a TBC most surely need to be adjusted. I hope this confusing little dissertation has been of help and not too off the mark. I am not a NABET member, just the DGA. ;-)

[Vic Owen]

Thanks, ozzie -- that's the best 1 minute explanation I've seen so far. I *was* trying to see more than bars on it.

[Ken Tanaka]

Thank you very much, Ozzie! I ditto Vic's remarks. A good, concise micro-tutorial that I will try this afternoon!

[Bill Ravens]

well, in short, there's a great deal to be deduced from a vectorscope and waveform monitor. the position of the central dot on the vectorscope is a good indication of the color balance of the frame being analyzed. A dot that is not centered represents a white balance not calibrated for pure white. Indeed, the color burst is an indication of correct hue, however, color corrections can be repeatably and predictably applied thru the calibrated use of the "hue" control. As far as the waveform analyzer goes....it's the final arbiter on whether the sequence is NTSC Broadcast compliant. DV, being what it is, rarely needs adjustment, however, if anyone has been fiddling with the colors, it's prudent to make sure the luma still falls between 0 and 100 IRE. Software like Synthetic Aperture's Video Finesse allows you to adjust the pedestal, knee and slope of the curve. This let's one bring an out of spec image sequence into spec without crushing the blacks or burning out the whites. All in all, still a useful tool if you know how to use it.

The drawback to software analyzers is that they carry their own internal reference values, therefore, are not a true relative measure of the signal being analyzed. The only way to get it right is with a hardware proc amp and analyzer.