V1/FX7 Zebra and superwhite at DVinfo.net

Robert Altman · July 8th, 2008, 10:08 AM

I am taping in a very contrasty situation with a darker interior and large windows. Two questions came to mind --

Does the 100% zebra on the FX7 represent 100% of NTSC video or HDV superwhite?

If it is calibrated to NTSC might I eek out a little more video range by allowing more areas of zebra that I can pull back down in Final Cut Pro with the 3 way color corrector by decreasing the Whites?

Obviously if the zebras represent the max of superwhite then no data will be extractable in these blown areas.

Thanks.

--Robert Altman

Seth Bloombaum · July 8th, 2008, 10:48 AM

My understanding is 100% of 100 ire (NTSC), full NTSC white.

Which should mean that you can shoot with zebras at 100, see them across a bright area, and find some detail in post. It isn't clear from the V1 manual if the 100 zebras are displayed at 100-105 (as are the 70 zebras, and the zebras in many other cameras), or whether anything over 100 gets zebraed. That could mean that something at 115 would display the 100 zebra, which is trouble.

As you've hinted, DV and HDV codecs are capable of showing detail up to 110 IRE.

Seems worth testing, YMMV.

BTW, the histogram function of the V1 makes understanding what's happening with overexposure and underexposure a snap. I love it. Looks like you have it on the FX7 - check it out.

Generally, if you have a slope on the histogram that trails down on the right to a very low value, you have detail. If it peaks to the right that indicates severe overexposure - no detail.

Robert Altman · July 8th, 2008, 02:28 PM

I do use the histogram to set my exposure. I have been trying to limit anything beyond the 100% mark on the histogram--it sounds like I can use the fact that HDV will record beyond this to get a little more exposure range.

I will try your concept of checking for a downsloping tail in the histogram. Often there are a bunch of pixels in the mid/low range which slope down, then a spike up at the end where the windows are blowing out. I guess it is the nature of video to have to compromise in this situation (unless you can gel the windows down or add in HMI fill inside, which I can't do).

Steve Mullen · July 8th, 2008, 03:10 PM

Quote:

Originally Posted by Robert Altman

it sounds like I can use the fact that HDV will record beyond this to get a little more exposure range.

Some NLE's simply clip the digital data at what is 100IRE so you can't assume you can actually make any use of the extra 8IRE.

FCP allows you to enable Superwhite mode that uses the extra range. But, awhile back I think someone posted that not all FX actually supported it. CC did which means the idea is you can use CC to bring the range to 100IRE under your control.

Any use of an RGB-based FX is limited to 100IRE because 255 is defined as 100IRE. Which is why NLE's like Premiere that are RGB based, simply clip everything. I suspect CineForm supports Superwhite under Premiere.

Don't know about EDIUS and Vegas is simply bizarre with several settings to make. I suspect the issue with Vegas is that it was an all RGB NLE that Sony has grafted on some extra YUV support.

Seth Bloombaum · July 8th, 2008, 07:27 PM

Steve makes a good point - YMMV on any particular NLE.

I'll repeat - test, test, test through your workflow before depending on detail above 100.

The point I'm trying to make about the histogram - if there is significant reading right against the right-hand edge you can be pretty sure there's clipping. Likewise on the low end.

There are various ways to "compress" the range in-camera, then you would later expand via levels or cc in post. There were quite a few posts on this subject over in the JVC HD100 forum, as the HD100 (now HD110) had quite a few ways to set up picture profiles. It's worth a look.

Did I mention I love the histogram function? I'd be hard-pressed to shoot without it now.

Stephan Stryhanyn · July 9th, 2008, 09:37 AM

EDIUS will let you recover what's between 100-108 IRE (and btw I thought Adobe Premiere went YUV since it was renamed to Premiere Pro), I was able to recover detail in some otherwise overblown white surface. However there's a catch... This is part of the luminance range where the knee will ordinarily compress the highlights, so if you just pull luminance downwards it'll still have that 'video look' of crushed highlights, only slightly darker. And as those 8 IRE only translate into so few actual distinct 8-bit values, you can gamma-correct the highlights ('decompress' to recover detail) only as much as won't create banding or posterizing - which unfortunately shows up soon very clearly on the waveform.

So yes there's potential to recover detail, but maybe more in the way of salvaging footage than a repeatable shooting technique. I wouldn't rely on it for paid work.

Side note about 100% zebras: did you notice how they can appear on saturated colored surfaces, whereas 100 IRE means white? Like they would appear wherever one of the 3 color channels would start clipping (not just luma), with some particular color bleaching out as a result. So with smarter CC (not just gamma), maybe sometimes there's even greater potential than those 8 IRE, but I haven't tried that though.

July 8th, 2008, 10:08 AM	#1
Robert Altman Regular Crew Join Date: Jun 2007 Location: New York Posts: 28	V1/FX7 Zebra and superwhite I am taping in a very contrasty situation with a darker interior and large windows. Two questions came to mind -- Does the 100% zebra on the FX7 represent 100% of NTSC video or HDV superwhite? If it is calibrated to NTSC might I eek out a little more video range by allowing more areas of zebra that I can pull back down in Final Cut Pro with the 3 way color corrector by decreasing the Whites? Obviously if the zebras represent the max of superwhite then no data will be extractable in these blown areas. Thanks. --Robert Altman

July 8th, 2008, 10:48 AM	#2
Seth Bloombaum Inner Circle Join Date: Sep 2003 Location: Portland, Oregon Posts: 3,420	My understanding is 100% of 100 ire (NTSC), full NTSC white. Which should mean that you can shoot with zebras at 100, see them across a bright area, and find some detail in post. It isn't clear from the V1 manual if the 100 zebras are displayed at 100-105 (as are the 70 zebras, and the zebras in many other cameras), or whether anything over 100 gets zebraed. That could mean that something at 115 would display the 100 zebra, which is trouble. As you've hinted, DV and HDV codecs are capable of showing detail up to 110 IRE. Seems worth testing, YMMV. BTW, the histogram function of the V1 makes understanding what's happening with overexposure and underexposure a snap. I love it. Looks like you have it on the FX7 - check it out. Generally, if you have a slope on the histogram that trails down on the right to a very low value, you have detail. If it peaks to the right that indicates severe overexposure - no detail.

July 8th, 2008, 02:28 PM	#3
Robert Altman Regular Crew Join Date: Jun 2007 Location: New York Posts: 28	I do use the histogram to set my exposure. I have been trying to limit anything beyond the 100% mark on the histogram--it sounds like I can use the fact that HDV will record beyond this to get a little more exposure range. I will try your concept of checking for a downsloping tail in the histogram. Often there are a bunch of pixels in the mid/low range which slope down, then a spike up at the end where the windows are blowing out. I guess it is the nature of video to have to compromise in this situation (unless you can gel the windows down or add in HMI fill inside, which I can't do).

July 8th, 2008, 07:27 PM	#5
Seth Bloombaum Inner Circle Join Date: Sep 2003 Location: Portland, Oregon Posts: 3,420	Steve makes a good point - YMMV on any particular NLE. I'll repeat - test, test, test through your workflow before depending on detail above 100. The point I'm trying to make about the histogram - if there is significant reading right against the right-hand edge you can be pretty sure there's clipping. Likewise on the low end. There are various ways to "compress" the range in-camera, then you would later expand via levels or cc in post. There were quite a few posts on this subject over in the JVC HD100 forum, as the HD100 (now HD110) had quite a few ways to set up picture profiles. It's worth a look. Did I mention I love the histogram function? I'd be hard-pressed to shoot without it now.

July 9th, 2008, 09:37 AM	#6
Stephan Stryhanyn Regular Crew Join Date: Dec 2006 Location: France Posts: 48	EDIUS will let you recover what's between 100-108 IRE (and btw I thought Adobe Premiere went YUV since it was renamed to Premiere Pro), I was able to recover detail in some otherwise overblown white surface. However there's a catch... This is part of the luminance range where the knee will ordinarily compress the highlights, so if you just pull luminance downwards it'll still have that 'video look' of crushed highlights, only slightly darker. And as those 8 IRE only translate into so few actual distinct 8-bit values, you can gamma-correct the highlights ('decompress' to recover detail) only as much as won't create banding or posterizing - which unfortunately shows up soon very clearly on the waveform. So yes there's potential to recover detail, but maybe more in the way of salvaging footage than a repeatable shooting technique. I wouldn't rely on it for paid work. Side note about 100% zebras: did you notice how they can appear on saturated colored surfaces, whereas 100 IRE means white? Like they would appear wherever one of the 3 color channels would start clipping (not just luma), with some particular color bleaching out as a result. So with smarter CC (not just gamma), maybe sometimes there's even greater potential than those 8 IRE, but I haven't tried that though.