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Old June 17th, 2009, 03:52 AM   #1
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What are 108% white ?

Hi :)

when calibrating my light meter I found that the built-in spot meter of the EX1 shows 108% when completely white. 108% not 100%.

Further I found, that when importing EX1 clips to the Adobe Premiere timeline I also get more than a 100% on the waveform monitor. A pure white is normally 100% there.

But even better:
There is real information in that misterious 8%. I had a shot whith snow-covered mountains that showed clearly more information than when I limit the footage to 100%.

My next problem is how to keep that information. As soon as it's rendered out it clips to 100% :(
But that's probably for a Premiere Pro forum.

So: Is there more than the usual 8-Bit. Maybe 8.5 :)

Thanks for and ideas!

Peter
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Old June 17th, 2009, 04:32 AM   #2
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Broadcast legal is 16-235, or 100% in analogue in most countries. The EX can use the full 255 for 109% which now works for some HD delivery formats.
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Old June 17th, 2009, 08:47 AM   #3
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Are You sure ?

I can switch my Matrox Card to broadcastsafe and that reduces the whites from 100% to something little below. Or better to say from 1 to 0.95 or so.

So I would assume that 255 white = 100% or the Value 1.
Which it clearly is when I switch back from Broadcastsafe to "Post Production", which means full Range 0-255.

BUT the EX1 is above that 1.
But it's probably a interpretation thing.
I am of course aware, that it cannot be more than 8-Bit.

Anyone any more ideas ?

Thanks!

Peter
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Old June 17th, 2009, 09:39 AM   #4
 
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hmmm...not sure why there is a mystery. Most HDV cams, these days, record superwhites(white to 109% IRE). The issue is how to handle these superwhites within the NLE because delivery NTSC and PAL displays limit the range to RGB16-235. Computer monitors can display full range 0-255, but, unless your delivery medium is the web, these values will be clipped to RGB16-235 by the delivery display unless you deal with this during color correction.

One way to deal with it is to just ignore the fact that values outside RGB16-235 will be clipped. A better way to deal with it is do apply a knee to the "levels curve" that smoothly blends the illegal values back into the RGB16-235 range. Note that some NLE's will automatically remap the color mapping to broadcast levels when you import your footage, so, you'll never know that your cam was recording 109% IRE. Each NLE has a different way for dealing with this issue, altho' the actual techniques are to either clip or blend with a knee.
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Old June 17th, 2009, 09:43 AM   #5
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Going to 108% simply means more of the range of digital values are used. For certain it can get clipped down the track however it's simple enough to use a curve to map the 100% to 108% values into the legal range.
Some of the Cine gamma curves in the EX produce 108% at 480%. What that means I'm pretty sure is that if you set exposure so that 100% white (e.g. white card) = 100% then clipping will occur for something 480% brighter than the white card e.g. a specular highlight. You can decide to clip that off or retain the superwhite or make use of it during compositing.
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