zeebra bars...so bad! or so what? - Page 2 at DVinfo.net

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Canon XL and GL Series DV Camcorders
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Old July 21st, 2005, 10:53 AM   #16
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I am very new at this, but when I experimented with the zebra bars and where I wanted them set, I did notice one thing that may or may not be correct.

They are much more applicable in controled lighting situations. If you are inside and have your scene lighted as you want it and you blow areas out, adjust accordinging, but, you can still have areas that seem blownout, but may not really be necessary to adjust for. Some would be white papers or very white or light painted surfaces in the scene. Adjusting down for them may actually put you too low.

Outside, you may have areas that blow out just from the same type of situations as above.

These areas basically have no detail in them anyway, even to the human eye!

Does this make any sense?

Thanks

Mike
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Old July 21st, 2005, 03:09 PM   #17
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Sort of ????

What percentage do you have your zebras set at; 100, 85, 80?

Yes, you will lose detail if the whites are above peak; i.e. 110 IRE.

Sincerely,

Stephanie
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Old July 21st, 2005, 05:52 PM   #18
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I sort of like to use the zebras as an EXCESSIVE CONTRAST IN SCENE alarm so that I will either get the highlights down, or bring the shadows up to even out the overall exposure by manipulating the lighting, or the objects in the scene.

Another little nifty trick I discovered on the old XL1 using the color vf was to adjust exposure until zebras appeared in specular reflectiions. This proved to be a focusing aid because if the object wasn't in focus, the softness would blur the specular hightlight and the zebra would go away. Kind of like using the peaking control on the b/w viewfinder.

--->Someone here might come along and correct me, but digital video will produce more latitude (higher highs and lower lows) than what is "broadcast legal". I think that the Master Pedestal setting lets you move the floor from the default 0 IRE up to the broadcast standard of 7.5 IRE. I don't know what setting, if any, lets you limit the upper setting to 100 IRE. I do know I've seen greater than 100 IRE indications on my waveform monitor in Vegas. I think that if I sent that video to the TV station for on-air broadcast, their equipment would have to "press" the upper threshold back to a max of 100 IRE to be legal for transmission. I think!?! <---

The importance of keeping the video between certain levels in analog NTSC transmission is because the video and blanking pulses are amplitude modulated. When you amplitude modulate a carrier wave beyond 100%, you not only distort the waveform of the modulation envelope, you generate 'spurious harmonics' which would have your transmitted signal showing up on other frequencies and causing interference. A big no-no if you want to keep the FCC off your back!

Higher levels of white will modulate the carrier to greater amplitude until at some point, the minimum portion of the wave would be beyond the zero centerline of the carrier wave and distorting it. The black levels of the video can only be a certain minimum modulation so that there is room for the blanking and sync pulses 'beyond the black level'

After we transition over to all digital ATSC transmission here in the US, these broadcast legal requirements may become obsolete.
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Old July 21st, 2005, 09:39 PM   #19
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Quote:
Originally Posted by Stephanie Wilson
Sort of ????

What percentage do you have your zebras set at; 100, 85, 80?

Yes, you will lose detail if the whites are above peak; i.e. 110 IRE.

Stephanie
Stephanie,

Sorry to be late getting back. I experimented between 90 and 100. Finally decided to use 100, and just look at what is blown out at that range. In other words, worry about it only if it has detail to begin with, like I said, ignore total whites that may be blown out, if I can see no detail to begin with. Just experimenting, as I don't know crap to begin with.

Thanks,

Mike
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