Zebra on ProRes

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Peter Östlund

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Zebra on ProRes

PostSat Apr 06, 2013 8:32 pm

I just shot a lot documentary stuff and chose to go ProRes for the first time. When searching for Zebra I got the feeling that the 100% level is much over what ProRes can handle. My suspicion is that zebra levels always only can be used when shooting RAW.
Can anybody confirm this?

Thanks


Peter
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adamroberts

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Re: Zebra on ProRes

PostSat Apr 06, 2013 8:39 pm

This has been discussed at length in a few threads already.

The zebras are based on the RAW sensor data. So if you have the zebras set to 100% and you see them onscreen you know that the area where you see the zebras is actually clipping at the sensor level.

How I understand it is that ProRes data is created from the RAW sensor data. A curve is applied to that data based on your ISO settings and then the LUT (Film or Video) is applied to it before writing to the file. So if your zebras are showing it will clip that data in the ProRes file as it was clipped at the sensor level.

From my testing and shooting I've found this to be the case.
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Re: Zebra on ProRes

PostSat Apr 06, 2013 9:34 pm

adamroberts wrote:This has been discussed at length in a few threads already.

The zebras are based on the RAW sensor data. So if you have the zebras set to 100% and you see them onscreen you know that the area where you see the zebras is actually clipping at the sensor level.

How I understand it is that ProRes data is created from the RAW sensor data. A curve is applied to that data based on your ISO settings and then the LUT (Film or Video) is applied to it before writing to the file. So if your zebras are showing it will clip that data in the ProRes file as it was clipped at the sensor level.

From my testing and shooting I've found this to be the case.



can you explain the clipping part... i am new to editing and how can 100% zebra be helpful in shooting prores?
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adamroberts

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Re: Zebra on ProRes

PostSat Apr 06, 2013 9:53 pm

When the sensor clips it records no colour info. As in the light falling on the sensor is beyond the sensors capabilities. You can't fix that in post because there is no data to recover.

So when the camera writes data to a ProRes file (or DNxHD) it uses the RAW data from the sensor. If you have clipped the highlights they can't be recovered recovered as there is no data to write to the file.

If there is a bright highlight in your scene like a light, the sun or speculation highlights they will probably clip and show you zebras. In most cases that is just fine as you don't want that detail, you want the detail of you scene. However if some area in your scene (highlight on the skin for instance) that you do want to capture is clipping you need to fix that before its recorded.

Exposure with this camera is that simple. Keep areas you want in you image free of zebras.
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CptZero

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Re: Zebra on ProRes

PostSun Apr 07, 2013 3:12 am

so making it 100% determine that it is really unrecoverable in prores shot? how about the 75%? so i should stay away on zebra popping out especially in skin areas and areas i want a lot of details?
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Re: Zebra on ProRes

PostSun Apr 07, 2013 9:38 am

Exposing with this camera is really simple. It's been explain over and over by many who use the camera including award winning cinematographers like John Brawley who has the most experience with the camera.

Set the camera to 100% Zebras and Expose to the right. In other words open up the exposure as much as possible until you see your zebras appear on areas you want exposed properly. Back off your exposure so those zebras disappear and you are set.

This method will give you the cleanest image with the least noise in the shadows.

It's been tried and tested. Works in ProRes and RAW. If exposed like this you footage is correctly exposed.

May have said they are over exposing in RAW. This is not true even tho the RAW DNGs might appear over exposed on your computer they are not. The data is there it just needs to be processed correctly.
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Peter Östlund

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Re: Zebra on ProRes

PostSun Apr 07, 2013 3:04 pm

Interesting.
My experience is that 100% zebra in ProRes is over the top.
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adamroberts

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Re: Zebra on ProRes

PostSun Apr 07, 2013 3:09 pm

Where you highlights clipped in the ProRes file?
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Randy Walters

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Re: Zebra on ProRes

PostSun Apr 07, 2013 3:14 pm

I have to confess to feeling a certain level of frustration at seeing this ground out over and over again.

It's almost indecent how easy this camera is to use, and to get beautiful, exquisitely exposed results. Perhaps it's just very hard to believe that shooting can be so simple and bulletproof.

Every time I use the camera, all I do is give the sensor as much light as I possibly can without clipping.

IGNORE HOW THE IMAGE LOOKS ON THE MONITOR. IT JUST DOESN'T MATTER. This may be the core notion people are having difficulty accepting. All you need to worry about are the zebras. If there are strong lights or highlights in the scene, I allow them to break into the 100% zebra zone.

And every time I get home and open the footage in Resolve, it's a joy to pull down the exposure, and BAM - there everything is; incredible dynamic range, velvety noise-free shadows, beautiful detail and saturated colors... it knocks me out every time.

Here are a couple images I posted back in February - first, the image as it appeared when shot:

whiteout.jpg
whiteout.jpg (52.99 KiB) Viewed 12421 times


And here it is, after adjustment in Resolve: (full-size link: http://memepuffs.com/temple.jpg )

temple-50.jpg
temple-50.jpg (182.49 KiB) Viewed 12421 times
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Peter Östlund

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Re: Zebra on ProRes

PostSun Apr 07, 2013 3:57 pm

Ok, relax Randy.
I am on location so I dont have access to Resolve at the moment. But the qt-files look a bit blown out in the parts where the zebra is.

Do you mean that your still from the roof is from an ungraded qt-movie or is it from RAW?

I know how to handle RAW, but I was sloppy and did not do enough tests with ProRes before I went.
My mistake.

Peter
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Theodore Prentice

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Re: Zebra on ProRes

PostSun Apr 07, 2013 4:18 pm

Peter Östlund wrote:I know how to handle RAW, but I was sloppy and did not do enough tests with ProRes before I went.
My mistake.

Peter


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Peter J. DeCrescenzo

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Re: Zebra on ProRes

PostSun Apr 07, 2013 4:22 pm

Peter Östlund wrote:... the qt-files look a bit blown out in the parts where the zebra is. ...


With the BMCC's zebras set at 100% (a good technique), anything that has zebras is gone, clipped, unrecoverable. No color, no detail, nothing. On the BMCC, zebras represent sensor clipping.

While shooting RAW, or compressed "Film" mode, set the zebras at 100% and adjust exposure so no zebras are displayed on the highlights in which you want to retain detail/color. Highlights with 100% zebras are clipped.

Compressed "Video" mode has slightly less latitude than Film mode, so you might need to be a bit more conservative protecting highlights. For example, when shooting compressed Video mode, you might use zebras set at 95% or less.
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adamroberts

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Re: Zebra on ProRes

PostSun Apr 07, 2013 5:12 pm

Peter Östlund wrote:But the qt-files look a bit blown out in the parts where the zebra is.


As Peter J. DeCrescenzo said, if the Zebras (at 100%) are showing then you have lost that data. It's gone. In RAW and ProRes.

Have you looked at the footage in you NLE with you waveform monitor turned on? Is the wave form clipped?
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Peter Östlund

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Re: Zebra on ProRes

PostSun Apr 07, 2013 5:58 pm

Yes I know the info is gone at 100% but my feeling (as the other Peter said) is really that when shooting ProRes you cannot use the 100% zebra as a safe reference.
That is why I started this thread, to get that confirmed and I guess Peter J confirmed this.
Thanks for the discussion.

Peter (Ö)
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Re: Zebra on ProRes

PostSun Apr 07, 2013 6:17 pm

This thread is really helpful. I think that there is logic in 95 zebra setting. It is really important to know how to handle the compressed mode.
Cheers guys!
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Peter Östlund

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Re: Zebra on ProRes

PostMon Apr 08, 2013 9:30 am

Ok Guys (where are the women?).

Lets test and report here what zebra level is corresponding to clipping when shooting Prores.
That would be useful for us all.

Peter
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Peter Östlund

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Re: Zebra on ProRes

PostTue Apr 09, 2013 9:17 am

My first quick test of zebra versus clipping gives the result that zebra cannot be used at all shooting ProRes. Even when adjusting the level to the lowest setting (75%) the zebra areas are clipped.
I did not use a waveform monitor, only the iris button.
In next upgrade it would be good to have the zebra level adjusted to work with the codec used.

Peter
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Peter Östlund

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Re: Zebra on ProRes

PostFri Apr 12, 2013 11:44 am

So I am updating this thread just to get it more in focus.
I still believe this is an important issue.
I know it is very sexy with all the new cameras but....

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Peter J. DeCrescenzo

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Re: Zebra on ProRes

PostFri Apr 12, 2013 2:18 pm

My understanding is that with the BMCC, "zebras = sensor clipping". Regardless of what value zebras are set to.

If you don't want an area of the frame that's currently showing zebras to clip, slightly reduce exposure until the zebras disappear.

Is this not what you're seeing there?

(Unfortunately, I don't currently have a BMCC to test with.)
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Peter Östlund

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Re: Zebra on ProRes

PostFri Apr 12, 2013 2:38 pm

The clipping would only occur when setting zebra at 100% otherwise it would useless.
My beliefe is that it is useless when shooting ProRes anyway but trust it will be fixed in an upgrade.
100% should be clipping in all settings, RAW, ProRes, DNxHD, thankyouverymuch.

P
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rick.lang

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Re: Zebra on ProRes

PostFri Apr 12, 2013 5:23 pm

Peter Östlund wrote:My first quick test of zebra versus clipping gives the result that zebra cannot be used at all shooting ProRes. Even when adjusting the level to the lowest setting (75%) the zebra areas are clipped.
I did not use a waveform monitor, only the iris button.

Peter


I wonder if that is the key when you said there appeared to be clipping whether zebras were set to 100% or 75%? The IRIS button adjusts the iris so no sensor clipping occurs. Therefore it is going to use the same actual iris no matter where you set the sensor. The zebra display technique Peter suggested of setting zebras at 95% assumes you are manually adjusting the iris until the lower threshhold zebras disappear (at the cost of some dynamic range). Would be good if BMD can clarify if there is any difference in actual exposure if the ISIS button is used with lower threshold zebra settings.

Rick Lang
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Peter Östlund

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Re: Zebra on ProRes

PostFri Apr 12, 2013 10:24 pm

What I am saying is that all zebra-levels are above the brightest part of the image after pressing the iris-button. Therefore the zebra is useless when shooting ProRes.
But I hope this will be taken care of in next update.
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sean mclennan

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Re: Zebra on ProRes

PostSat Apr 13, 2013 1:13 am

Peter Östlund wrote:I am on location so I dont have access to Resolve at the moment. But the qt-files look a bit blown out in the parts where the zebra is.


If you're recording shots where zebras are showing on the monitor...and they're set at 100%...those areas are going to be clipped/blown out.
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Re: Zebra on ProRes

PostSat Apr 13, 2013 2:06 am

Ok, I've been using pretty much only ProRes, and I somewhat understand what Peter might be saying. Maybe I'm misunderstanding though....

From my shooting experience, getting every ounce of light into the sensor (before the zebras pop up and the sensor begins to clip) works for the majority of shots, however there are times I've noticed the camera's image gets a little soft, and the highlights have less roll-off. At first I thought I might be just too open on my lens, but that seems to not be the case.

I would say 98% of my footage looks awesome with the 100% Zebra rule, just sometimes I get some of results....maybe it's an operator error haha

Also, how's everyone bringing back their footage? (Prores) I've been tending to lower the highlights first, then the shadows, and then the mids for contrast, with a little gamma.
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sean mclennan

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Re: Zebra on ProRes

PostSat Apr 13, 2013 5:33 am

setting your zebras to 100% isn't a rule, just a guide. You still have to use your knowledge and preference to determine what's right for each lighting setup...
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Peter Östlund

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Re: Zebra on ProRes

PostSat Apr 13, 2013 6:44 am

Well then there is something wrong with my camera. I cannot rely on zebra at 100% not even at 75%, it is just blow out.
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adamroberts

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Re: Zebra on ProRes

PostSat Apr 13, 2013 6:56 am

Peter Östlund wrote:Well then there is something wrong with my camera. I cannot rely on zebra at 100% not even at 75%, it is just blow out.


Out of interest what ISO are you shooting?

I'm assuming you are exposing so that no Zebras appear on screen at all??
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Peter Östlund

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Re: Zebra on ProRes

PostSat Apr 13, 2013 7:29 am

I have shot both 800 and 1600. No I am much lover than zebra-level, except from open lamps and reflections. I am shooting video mode.
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adamroberts

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Re: Zebra on ProRes

PostSat Apr 13, 2013 7:32 am

Ah... ok. i don't shoot anything in Video mode. I find the images too crushed to do much with in post.

Have you tried shooting Film mode and then applying a REC.709 LUT in post?
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Peter Östlund

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Re: Zebra on ProRes

PostSat Apr 13, 2013 7:42 am

The reason for me shooting video mode is that the people getting the material don't have access to Resolve or other professional grading systems.
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John Brawley

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Re: Zebra on ProRes

PostSat Apr 13, 2013 2:35 pm

rick.lang wrote:
Peter Östlund wrote:My first quick test of zebra versus clipping gives the result that zebra cannot be used at all shooting ProRes. Even when adjusting the level to the lowest setting (75%) the zebra areas are clipped.
I did not use a waveform monitor, only the iris button.

Peter


I wonder if that is the key when you said there appeared to be clipping whether zebras were set to 100% or 75%? The IRIS button adjusts the iris so no sensor clipping occurs. Therefore it is going to use the same actual iris no matter where you set the sensor. The zebra display technique Peter suggested of setting zebras at 95% assumes you are manually adjusting the iris until the lower threshhold zebras disappear (at the cost of some dynamic range). Would be good if BMD can clarify if there is any difference in actual exposure if the ISIS button is used with lower threshold zebra settings.
T
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In VIDEO mode the IRIS button does NOT work this way. It "centers" the exposure ( more like regular auto exposure ) and may let some areas clip.

In FILM mode the iris button will set the exposure so nothing clips.

The iris button CHANGES depending on the mode of recording.

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rick.lang

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Re: Zebra on ProRes

PostSat Apr 13, 2013 3:44 pm

John Brawley wrote:In VIDEO mode the IRIS button does NOT work this way. It "centers" the exposure ( more like regular auto exposure ) and may let some areas clip.

In FILM mode the iris button will set the exposure so nothing clips.

The iris button CHANGES depending on the mode of recording.

JB.


Face slap myself! That would appear to explain how some clipping can occur in the ProRes files shooting Video and relying on the Iris button. Thanks again, John.

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Peter J. DeCrescenzo

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Re: Zebra on ProRes

PostSat Apr 13, 2013 5:50 pm

I believe that information is in the BMCC user manual ...
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sean mclennan

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Re: Zebra on ProRes

PostSat Apr 13, 2013 7:32 pm

Come on Peter....no one read the manual! :mrgreen:
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Peter Östlund

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Re: Zebra on ProRes

PostSat Apr 13, 2013 8:37 pm

Thanks John.
Finally the sky cleared and the sun reached my zebra striped cheek.

Peter Ö
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rick.lang

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Re: Zebra on ProRes

PostSat Apr 13, 2013 10:28 pm

sean mclennan wrote:Come on Peter....no one read the manual! :mrgreen:


That why I slapped myself, I read it last August and forgot that little tidbit.

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Bill Rich

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Re: Zebra on ProRes

PostThu Apr 18, 2013 2:39 am

I just completed my first shoot in ProRes film log..
A few weeks ago on the first day of a b-roll shoot, I was setting exposure for what looked good in the LCD.. much like on a DSLR.. and it did look quite good.. but today when finishing up the 2nd unit type shots and an interview.. I set my zebras on 95% and adjusted the exposure until the zebras were gone.. and while it looked a bit overexposed on the LCD.. the final result after a bit of CC looks simply amazing! While the previous b-roll will still look great.. I wish I had used the same exposure as today and it would have looked that much better..
So from now on when shooting ProRes Film log I'm using the 95% zebra exposure!!!
I know folks are saying to set the zebras to 100%.. but I didn't want to experiment with that on this shoot.. I'll do that another time.. :mrgreen:

Also. my Sigma 30mm F1.4 is just brilliant on the BMCC!!
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Re: Zebra on ProRes

PostThu Apr 18, 2013 3:16 am

Bill I totally agree with you using 95%. I've been doing this for 30yrs. Yikes, I'm showing my age. On cameras in the past where I've had multiple options that I could change with a button, I always used 75% mode for exposure to skin tones and 95% for everything else. General rule of thumb for all digital is you can always go up in post, but once over, it's TOAST!

warmly,
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Peter Östlund

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Re: Zebra on ProRes

PostThu Apr 18, 2013 7:51 am

Have you tried the 95% shooting video mode?
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Dominik Gehring

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Re: Zebra on ProRes

PostThu Jul 18, 2013 12:27 pm

hi peter

i had the same issues with zebras in prores/video settings.
utrascope shows clearly that everything is still clipping (above 100IRE) long after the zebra is gone.
doesnt matter if its set Zebra at 75 or 100%.
the zebra in video mode is only usable if you set the ISO to 200ASA. then it works fine as in film mode.

hope this helps.

kind regards - dom
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Re: Zebra on ProRes

PostSat Sep 12, 2015 12:42 pm

Sorry to resurrect an old thread, but as someone completely new to the world of Cinema Cameras I found the whole thread really engaging and learnt a lot from it.

My only question is whether this all applies to the Pocket Cinema Camera as well as that is all my budget will stretch to for now :-( If anyone has a view on this I would be very interested to read it - thank you!

My camera is due to arrive in about a week so I'm trying to get up to speed as quickly as possible :-)
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rick.lang

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Re: Zebra on ProRes

PostTue Sep 15, 2015 5:16 am

Iain, I hope as part of your familiarization tasks you do your own series of tests and make your own conclusions. It could well be that the old thread is 'dated' and you may have no problems with a new camera after you ensure you are on the latest firmware upgrade for that camera.



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Norbert von der Heidt

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Re: Zebra on ProRes

PostSun Sep 20, 2015 2:11 pm

I spent many of my 35+ years in the biz as a CCU operator back in Canada on multiple 4 camera OB's and as a setup tech in a production house. If the camera allowed access to zebra settings (and sometimes even when it didn't), I've always set them at 95-98% (depending on adjustment increments available). This is done so that you have a bit of artistic margin between bright parts of the image – that you would like to keep very white – and specular highlights, like reflections on metal – which are supposed to be clipped.

In those analogue days, we always set camera output or OB proc amp master clip at 105%, so there was always a bit of headroom before you flat-topped the signal. In digital, I don't think there is quite that much leeway so I think it's a much better trade off to have the zebra at 95% for whites/highlights and then bump up the level a few more units (IRE) in post if required, when you are in a proper HQ monitoring environment.

I absolutely hated Sony's invention of the 75% zebra which was supposed to equate to average Caucasian skin tone, which made no sense to me ..... what if you are shooting black actors or landscapes where there's not a white person on screen. IMHO, that was just done so that Sony could sell the cameras as idiot proof and so simple that anybody could be a cameraman.
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Denny Smith

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Re: Zebra on ProRes

PostSun Sep 20, 2015 5:11 pm

I have the Pocket camera, and have my Zebras set at 95-percent. I close down the iris, until only highlights/ white areas show zebra, and get very close to correct exposure, no unintentional clipping. The camera has a little latitude in exposure, even in ProRes, that can be corrected in post to get the "look" you want, correcting unclipped values as required.
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rick.lang

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Re: Zebra on ProRes

PostMon Sep 21, 2015 1:40 am

Norbert and Denny, when the BMCC cameras first came out, the advice was to ETTR. Setting zebras at 95% seems like you are exposing ProRes to get as much light as you feel is safe for your highlights. That's pretty much ETTR. But beginning this year, there have been other threads that concluded ETTR is the best approach when shooting raw, but when shooting ProRes it is better to expose for the scene and perhaps opening the iris a stop or so from that (slight ETTR). Exposing for ProRes requires more care and consideration of the exposure levels in the scene because you are not opening the iris up as much to light the shadows.

Have we now swung back to recommending ETTR for both raw and ProRes Film mode? I assume ProRes Video mode would always expose for the scene average or skin with maybe a half stop extra light.


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Denny Smith

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Re: Zebra on ProRes

PostMon Sep 21, 2015 1:54 am

You are right Rick, but ETTR is more based on using 100-percent zebra to get no clipping. Using 95-percent, you are exposing more for the shadows in ProRes, in video mode I go with 90-percent on an average scene to get the needed shadow detail, and try to get a balance, based on the scene. If a person is my subject, then it is back to 70-percent to get get skin exposure correct (closing down until zebra drops from skin). I also use a meter to get ballpark grey card reading.

The best bet, is to shoot some tests of different typical situation you shoot in, and seem what works best for you.
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John Simatos

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Re: Zebra on ProRes

PostMon Sep 21, 2015 5:52 am

Just a question, is there a reason why my zebras completely disappear above 90% zebra level?

I'm shooting 400 iso, 25fps, 180degree shutter on an URSA 4K v2 at firmware 2.6. This seems to occur in raw and raw 3:1 at any frame rate I haven't checked prores but I don't intend to shoot prores.

When I have the zebras set to 90% I can see zebras but at 95 or 100 they completely disappear. The highlights are obviously clipping, but the zebras don't seem to show up at all.


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Nickvecher

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Re: Zebra on ProRes

PostMon Sep 21, 2015 6:38 am

John Simatos wrote:Just a question, is there a reason why my zebras completely disappear above 90% zebra level?

I'm shooting 400 iso, 25fps, 180degree shutter on an URSA 4K v2 at firmware 2.6. This seems to occur in raw and raw 3:1 at any frame rate I haven't checked prores but I don't intend to shoot prores.

When I have the zebras set to 90% I can see zebras but at 95 or 100 they completely disappear. The highlights are obviously clipping, but the zebras don't seem to show up at all.


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Checked it at bmpc, looks like the same. I see that whites are clipping, but zebra don't appear. The sensor issue?
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John Simatos

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Re: Zebra on ProRes

PostMon Sep 21, 2015 6:41 am

Nickvecher wrote:Checked it at bmpc, looks like the same. I see that whites are clipping, but zebra don't appear. The sensor issue?


Weird, was thinking it might have been a v2 ursa sensor issue.


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Nickvecher

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Re: Zebra on ProRes

PostMon Sep 21, 2015 7:05 am

John Simatos wrote:
Nickvecher wrote:Checked it at bmpc, looks like the same. I see that whites are clipping, but zebra don't appear. The sensor issue?


Weird, was thinking it might have been a v2 ursa sensor issue.


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I doubt the v1 & v2 sensors are the same, just another cooling sys etc. Am I right? So nothing weird.
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