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Old January 27th, 2002, 12:26 AM   #16
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<<<-- Originally posted by zchildress : (Completely bewildered at this stuff...going through my books right now to find out what IRE means exactly. Exuse my greenness!) -->>>

No big mystery. In the analog world 0 is no signal and 100 is equal to one volt - as much as the signal can carry. Anything beyond 100 and you have breakup. If you have an old TV set (older than 10 or 15 years) and a signal over 100 (or 1 volt) comes through you're sure to get hum in the audio and maybe even get the video signal to breakup or turn negative. But that was in the old days of analog and when TV receivers were simple machines.

The digital world has changed everything because it works in a completely different realm but we still hold on to terms and concepts that are... well analogs or the analog world. Very much like we still say "dialing the phone" when we haven't actually dialed a phone in years. A hangover from the analog phone days.

Broadcasters are very picky with having signals adhere to rigid standards mainly because signals are processed a great deal more now than ever before. A signal is compressed and decompressed a number of times before it reaches your receiver. Any minor deviation from the standard is magnified. Up until a few years ago NBC wasn't accepting any compressed material for this reason. Fortunately they've gotten over it by now.
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Last edited by Ozzie Alfonso; January 27th, 2002 at 01:20 AM.
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Old January 27th, 2002, 12:37 AM   #17
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Thanks, Ozzie.

I was just searching through the "American Cinematographer Video Manual 3rd Ed." looking for an explanation of IRE...and shaking my head. Lots of techno-jargon that's way over the head of a greenhorn like me. Your explanation makes it understandable.
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Old January 27th, 2002, 08:23 AM   #18
 
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Z.....

yeah, I can understand your confusion. The broadcast industry seems to have been pretty fickle in its standards.....and now they're moving to HDTV which will be backwards compatible with NTSC, but, different...LOL.

Anyway, Tektronics has a pretty good technical website describing how to use a vectorscope and set up to NTSC standards. There's so much info it's a little daunting, but, their website is at :

http://www.tek.com/Measurement/cgi-bin/framed.pl?Document=/Measurement/video_audio/index/prodindex_video.html?wt=255&link=/Measurement/video_audio/index/prodindex_video.html&FrameSet=television

There's also a good explanation of the NTSC standards as relating to IRE and the old RGB values we all know and love at :

http://www.dv.com/magazine/2000/0400/luminanceranges0400.html

This is a good starting place, I think.

I believe FCP also has a software vectorscope and signal analyzer built in. In MediaStudio Pro, the vectorscope and signal analyzer acts as a filter to adjust the various chroma and luma values of your avi clip while displaying the readings on a software"oscilloscope". You then adjust these values to get things withing the IRE values of 7.5-100. Ideally, this adjustment is done by the camera because all post processing will re-render the video(with a small loss). The problem with having IRE values below 7.5 is that it begins to interfere with the sync signal, which is "hidden" in the blacks below IRE 0.

Hope this helps some.

Bill

Last edited by Bill Ravens; January 27th, 2002 at 08:35 AM.
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Old January 28th, 2002, 03:15 AM   #19
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Bill...????? Go easy on us rookie's in here!!!!
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Old January 28th, 2002, 04:18 AM   #20
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Someone asked where to set Black level on the XL1S. It's
in the custom preset submenu, called setup level.

Good luck
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Old January 28th, 2002, 08:12 AM   #21
 
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Zimvg304...

errr....sorry
I really like the DV format...it just takes a little extra care to use....and I get a little carried away with the techie stuff. Don't mean to be obnoxious.

BTW, Ozzie...

My XL1s checks out like Chris' at ASA 160. I ran a black level test thru the signal analyzer. On my cam it turns out that the factory nominal setting of black level falls right on 7.5 IRE.

Last edited by Bill Ravens; January 28th, 2002 at 08:23 AM.
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Old January 28th, 2002, 10:17 AM   #22
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Bill that's ok,just giving you a hard time.I'm glad there are people in here who know what's going on. Even if I don't know what they are talking about!!!! But it gives me alot of stuff to look up.
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Old January 28th, 2002, 11:37 AM   #23
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re: 90 IRE zebras

I tested my cam (live) and feel that when shooting a white textured wall, I get good detail until the zebras hit 90+. Therefore if I shoot higher than 90 I feel I'm getting less detail than I should be.

So to me, anything (slightly) over 90 is just white.

Again in the Zone system: I'm placing a tone (with little to no texture) on a (white) zone.
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Old January 28th, 2002, 11:46 AM   #24
 
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Thanx JoPhoto, I reset my zebra to 90, gonna give it a try.
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