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Exposure

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Randy Strome
Exposure
on Jan 26, 2008 at 6:06:17 pm

Brightness-level indictor:

Displays a percentage, but I am unsure of what is being sampled. No mention of note in the manual. Is this a spot reading, full image?


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Don Greening
Re: Exposure
on Jan 26, 2008 at 7:08:53 pm

I don't know if the indicator is spot or for the overall picture but I trust the zebra bars and my eyes. I use the dual zebra bars with one set at 80% for faces and the other set at 100% to see what would be blown out if I pressed the record button. The exposure latitude of this camera is such that there is still detail in highlights that are covered by the 100% bars. I think detail doesn't disappear completely until the highlights hit 108% if that makes sense.

- Don


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Sean Donnelly
Re: Exposure
on Jan 26, 2008 at 9:16:49 pm

There is a marker option that seems to be a 1% center spot directly next to the brightness level indicator, and it seems like it is at least weighted to that area. I'll do some more thorough testing this afternoon to try and confirm that. Personally I think a combination of zebras and histogram is the best way to judge exposure.

-Sean





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Randy Strome
Re: Exposure
on Jan 26, 2008 at 9:18:35 pm

Thanks for that Dan.

I have set the zebra at 95 and 100 as I am finding 95 useful the cine gamma curves that have some knee built in. I would love to know for sure what the 108% is about on Zebra 1.

My guess on the Brightness would be an average pixel brighness reading, but that is a guess. Unlike the Zebra 1, this seems to be limited to 100%.


Any other thoughts?



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john sharaf
Re: Exposure
on Jan 26, 2008 at 9:36:04 pm

You'll find considerable discussion of zebras in the archives of this and/or the Varicam forums, but basically in HD the convention is to set faces at 50-60 IRE or percent as the case may be vs. the more common 70 ire setting in SD. This is to allow more room in the higher exposure to let the cine gamma's do their work. The 108 ire setting is the common level for "clip" above which all picture is clipped to white, where no detail in the image remains. It's a convention that prevents overexposure from interfering with the audio in broadcast.

Video is commonly criticized for making the faces too bright, thus the reduction of exposure to the 50 ire setting for Hd, thus a more filmic look. This is also enhanced by crushing (or lowering) the gamma, which represents the middle grey from it's nominal setting of .45 to .50 or even .55. Again the adds to what you might call the filmic look. It would be a good idea to do your own tests of exposure and gamma, along the lines of what I've suggested, so that you make up your own mind about these things, rather than take what I say as gospel. It's a good process to become familiar with and will result in discovering your own look and technique.

JS



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Randy Strome
Re: Exposure
on Jan 27, 2008 at 2:41:16 pm

[john sharaf] "The 108 ire setting is the common level for "clip" above which all picture is clipped to white, where no detail in the image remains."

Thanks so much John, a real schooling for me. The utility of the Brightness indicator has come clear and I think it will be very useful once I do some testing. So I understand, is the right boundary of the histogram based on a 108 reading or 100? Maybe simpler, what relevance does an IRE of 100 have if 108 is the level of clipping?

Thanks to all for putting up with what are obviously very basic questions for many here.

Randy



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john sharaf
Re: Exposure
on Jan 27, 2008 at 6:37:00 pm

Not being familiar with histograms, but rather scopes, I would suspect that it ends at 100. In digital, with balack being at zero instead of 7.5 ire, the range from 0-100 equals 100%. The white clip is always adjustable in professional cameras, I'm not sure of what your EX-1 does, but you might just set it at 100 instead of 108. See if you can tell the difference on overexposed areas on your shot.

JS



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Randy Strome
Re: Exposure
on Jan 27, 2008 at 7:04:52 pm

The Histograms in digital photography are based on a zero to 255 scale.

I am confused by the center reading which is shown as a percentage reading but goes to 108%. If 100% is blown, what is 108%?

I am getting more comfortable with making zebras and the histogram work for me regardless of the numbers behind them, but it would be nice to really get it.



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Randy Strome
Re: Exposure
on Jan 26, 2008 at 10:15:06 pm

Whoops,
Let me check that. The brightness reading does seem to be a center spot reading and goes to 108 as well. Apologies.



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Sean Donnelly
Re: Exposure
on Jan 27, 2008 at 1:51:56 am

This is confirmed by the brochure as well (page 8). It is a center spot average (sampling only what is inside the center mark and averaging that data).





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Randy Strome
Re: Exposure
on Jan 27, 2008 at 2:04:34 pm

Thanks for that confirmation. We may need to modify the typical to RTFB :)



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