zeebra bars...so bad! or so what?
 

I was on a shoot this weekend and the director didn't care about the zeebra bars because he couldn't see any problem in his monitor. I had them set at 100, so the XL2 was telling me that those portions of the shot were definitely over exposed (and they were relatively large areas). In the monitor, those areas were bright, but I thought you could see details.

I thought that the video in those parts of the screen would be completely white and contain no real video information that could be retrieved.

Could someone enlighten me?

Thanks,

Kelly

Personally I think 100 IRE for zebras is kinda high... my own preference is down around 80 or 85. If you backed off on the exposure until the bars went away, then you should have been fine, but again I think 100 is a bit too high. That's just me though.

Though it wasn't asked on the quiz, I've read (and amazingly remember) that a zebra setting of 85% is supposed to indicate the beginning of over-exposure of caucasian skin. The XL2 provides controls to normalize that for other skin tones in the Skin Detail menu, but I don't know if changing skin detail settings will alter zebra feedback.

Thanks Chris,

Maybe I am misunderstanding the zebra bars settings. I thought the setting was a threshhold before you were told there was overexposure.

For instance, if you start to see zebra bars at 80 IRE, you might not actually have overexposure...it is just telling you that you are getting close. And if you start to see zebra bars at 100 IRE, you are absolutely getting overexposure because the threshhold is set at the limit.

Am I understanding the zebra bar settings incorrectly?

Oh, and what does "IRE" stand for?

Thanks,

Kelly

Kelly,
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!?!

IRE = Institute of Radio Engineers

(Wait, what do they know about video? Well, video broadcast, or television, came from radio... when my mom was a kid, on VJ-Day in August 1945 she asked her father, "now can we get a moving picture radio?" because before he'd told her they'd have to wait until the war was over).

Overexposure is not absolute, it's actually somewhat relative. When the zebra appears, then you're overexposed; back off on the iris until they go away -- only then are you not blowing out that portion of the image.

My grandparents didn't buy that TV until 1955.

So just to verify I understand, can someone confirm the following:

1. The zebra setting only sets the threshhold at which you are told there is overexposure. The higher the setting, the hotter you can shoot without being told there is a problem.

2. At 100 IRE, you aren't necessarily losing video information (where the picture is so bright that the color information is lost and the pixels will be white and can't be recovered in post). In other words, 100 IRE is just a broadcast standard and not a point of "digital clipping."

Thanks,

Kelly

1. Right!

2. Hmm, I think you risk clipping at 100 IRE.

Hey everyone,

My professional suggestion is to set the zebras to 80%. With controlled interview type lighting you should set your exposure so that you see zebra indicators on the cheeks and forehead. You should then have perfect exposure. However, I have been forced to "blow-out" the background in some situations, (sometimes to the point of almost losing all detail of the background) to get good exposure on the subject. Your director probably understood that the shot was fine even with the large areas of overexposure.

Most video transmission venues have the white clip set to 110 IRE. At that range you will see "clipping" of the image.

Man.... I've got to stop reading these posts and get some work done!

Sinceres,

Stephanie

Thank you all for your responses and insight.

Another clarification: I see Stephanie talking about zebras and "%" instead of IRE. Stephanie also talks about the ability to see clipping at 110 IRE. Patrick also talks about monitors that read IRE above 100.

This confuses me a bit.

110 IRE is 110% of what? If 100 IRE is 100% exposure, doesn't that mean that clipping starts at 100 IRE?

If that is the case, how can you even hit 110 IRE? How can you get any higher than 100% exposed?

Is this just a mistake? Is IRE NOT actually % of exposure and just some other scale?

Thanks,

Kelly

I could stand to learn more about this topic myself. Sorry I don't have time to research this at present, but I did a quick search and found this lengthy thread that appears to at least be somewhat related and worth a read:

http://www.dvinfo.net/conf/showthread.php?t=35336

"1. The zebra setting only sets the threshhold at which you are told there is overexposure. The higher the setting, the hotter you can shoot without being told there is a problem." quote from Kelly

Hi Kelly,

Sorry that I didn't have the time to read the post that Pete so graciously found for us. Look forward to reading it tomorrow. Hopefully it has answered your question much better than I can. However... I'm just so damn proud of the little knowledge that I possess that I can't help but share.

The zebra setting doesn't actually "set" anything in the camera nor does it affect how it's shooting. It is an arbitrary VIEWFINDER ONLY setting that the camera person chooses based on his/her preference. It is set to indicate when the exposure you choose is attained. As I said in my last post, I was taught to set the zebras at 80 (% or IRE?) and look for zebras on the cheeks and forehead. If your zebras are set at 100 than zebras on the same face would indicate your exposure is 20 more (IRE?) than my exposure. This is again purely based on how we have individually set our zebra settings for the viewfinder.

I know plenty of photogs that don't even use zebras. They prefer to gauge their aperture by the detail they see. This requires a very close relationship with your camera, lens and viewfinder. I've been shooting for over 20 years and I still use zebras. And I still ask for directions when lost.

But then I'm just a girl, ya know....

Sincerely,

Stephanie

Brilliant. Great reply. Thanks Stephanie!

Thank you Chris,

I have never ever felt "brilliant" in my entire life, but now thanks to you I will go to sleep feeling a "little bit of a smarty pants".... Thanks so much for that.

Video production is all I've ever done and at 49 years of age, with 22 years of experience in the biz, this is all I know....

It has been such a pleasure to help the youngsters as a result of your forum.. It has also allowed me to learn so much about what I didn't know from those genius engineer types who also enjoy your forum.

Many many thanks to you, Mister Chris

Sincerely,

Stephanie

When I am directing, I dont use Zebras, especially if I am using the XL2 and have an external monitor. If you set the knee to low, it can help with highlights and reflections.



ash =o)

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

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

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.

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