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Old August 10th, 2006, 11:26 PM   #1
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Another zebra stripes question

I'm trying to understand how to use the zebra stripes. I have read several places on what it's for, but never seen what I'm supposed to do about it.

For example on my XL2, the stripes are on 85. If I was shooting video of someone in my apartment sitting on a couch near a lamp, obviously the wall behind them is going to be over exposed and have the stripes all on it. But what am I supposed to do about it? Am I supposed to make adjustments with the iris to make the stripes minimal, or make them go away? It seems the only way to make the stripes go away is to almost close the iris, but then the picture is too dark.

I don't get it. What am I supposed to be looking for or doing about it? I'm guessing this is the reason for having "light kits" to make everything even and soft?

Sorry for the stupid question, but I have to learn some how.
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Old August 11th, 2006, 02:24 AM   #2
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Hi Adam. I hope this link helps.
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Old August 11th, 2006, 06:35 PM   #3
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I've seen that site. It does not explain much. It seems to pretty much just say "If you see stripes, the area is overexposed". I got that much. But it does not explain what I'm supposed to do. Is there supposed to be no stripes? minimal stripes? What adjustments am I supposed to make to counter overexposed areas? When I see stripes, what's the first thing to do? Adjust the iris? Adjust the lighting? What if you can't adjust the lighting, such as in the example of the mountain scene on that page.
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Old August 11th, 2006, 07:04 PM   #4
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Most scenes will contain more exposure latitude than your camera can record. So whatever exposure you set, you will lose some information in the shadows or highlights.

There are some different approaches as to which exposure is correct.
A- Do what looks good.
B- Always have flesh tone between particular IRE / brightness / exposure levels. (This may not be very popular now.)
C- Rule of thumb: Protect your highlights, since you can't get the detail back after clipping. Of course you lose information in the shadows. But blown-out highlights can be more noticeable.
D- Rule of thumb: Adjust exposure just to the point where the important details blow out / zebra, and then back off. Let specular reflections and the background blow out. You will lose information there, but that's ok since we don't care about the background or specular reflections.

It gets slightly more complicated if you take into account:
1- Knee and gamma settings. These will affect the appearance of your image.
2- Color grading in post... this will also affect the appearance of your image (and you may want this). With DV especially, certain things can bring out noise in the image... so there's only so far you can go with color grading.

Some related information:

But to simplify:
Doing what looks best is probably what you're after, although this is entirely subjective and as a result may give inconsistent results. But if you have a (portable) broadcast monitor, just sit there and fiddle with the iris and see what you like. Better yet, bring it into your NLE and color grade it and play with the camera settings too. Doing your own test would be the most enlightening.

If you want a simple easy answer, then do approaches B, C or D (I personally lean towards D). There is no "right" answer, and the zebras are merely a tool to aid you in setting exposure.
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Old August 11th, 2006, 07:22 PM   #5
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I tend to keep things as simple as posible. I shoot outdoor segments for current affairs type program which is broadcast here. If I'm oudoors I set the Zebra to 100 and if the sky is zebra and a few highlights also I just shoot. If I'm shooting a close up or mcu interview I expose so there is no zebra stripes on the face. If I'm indoors doing an interview I set the zebra at 85 and try to expose with no zebra on the face, and if there is a odd patch of zebra floating about in the distance. I just shoot it anyway.

Now I know a lot of experts will probably throw up their hands in horror. Experiment as much as you can to get a feel for it.
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Old August 14th, 2006, 10:34 AM   #6
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Adam, basically zebra stripes just tell you when you are hitting a pre-determined IRE level. With the Canon XL2, the zebra stripes can be adjusted to show 80, 85, 90, 95 or 100 IRE. For general shooting, some people will set the zebra level to 100 IRE, so that it just indicates any area that is over-exposed. For an interview shot, you want the person's face to be exposed at about 70 IRE. So in this case, you would increase your exposure until you saw the zebra pattern on the subjects face, then decrease the exposure just enough so that the zebra pattern disappears. When you're using the zebra bars set at a level lower then 100 IRE, remember that it doesn't tell you HOW MUCH you are over. So if you set the camera at 80 IRE, areas of the frame that have zebra bars will be over 80 IRE, but could also be over 100 IRE, causing them to be over-exposed in the shot. This is why a lot people use just the 100 IRE setting, so they simply know what is over and what is not.
If you see zebra bars indicating over exposure your options are:
-close down your iris, increase your shutter speed, or reduce the amount of light hitting the subject.
-If some parts of your scene are just way too bright, while others are too dark, then your CONTRAST RATIO is too high, meaning the difference from the brighest to the darkest part of your scene is greater than the camera can handle. You need to try and even the light out as best as you can, so that the bright spots and dark spots fall into a range that your camera can handle, while still keeping you main subject lit as desired. You're right, this is what lights are used for and is the beginings of cinematography.
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Old August 14th, 2006, 12:07 PM   #7
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I was 'instructed' to use the zebras like this...

Everytime you set up a shot, hit it with 100 zebra setting and make sure you don't have any, anywhere.

If you can set your zebra to 70, do so and make sure your talent's face is free from zebra (here's the tricky part) unless you're going for that look.

I didn't understand crushing, clipping and over exposure until I saw examples of them in a Waveform scope. Then again I'm a visual guy.

I've attached a jpg of a still photo we took on location and the Waveform scope for it. If I looked at this same set up with 100 zebra, this whole area would be 'zebra-ing'.

Like Glenn and others are telling you, if you clip highlights and crush blacks, that's it, you've lost that part of your shot. No amount of fudging in post will recover those areas.

I think lighting is a way to paint your frames with light and shadow not to make everything even and soft. You want your talent (read that as actors) to stand out from the wall so you light the wall behind them and you light the actor from behind.

Hope this helps.
Attached Thumbnails
Another zebra stripes question-clipped.jpg  
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Old August 15th, 2006, 08:21 PM   #8
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thanks guys, that's some good info
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