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A basic video question: is there loss of data when the luma is over 100?

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Noam Osband
A basic video question: is there loss of data when the luma is over 100?
on Oct 13, 2015 at 10:32:15 pm

I know luma ranges go from 0-120. That said....is there loss of data between 100-120?


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john sharaf
Re: A basic video question: is there loss of data when the luma is over 100?
on Oct 14, 2015 at 12:02:06 am

Noam,

Yes, a basic question, that many people are afraid to ask.

Knowing some basic video fundamentals are very useful in mastering digital cinema, and how would learn what's up there above 100IRE WITHOUT asking?

In Video, you can set the camera clip at either 100 or 105IRE. Normally the "100" setting is for television and the known "gamma" of monitors on which you would be viewing; but now of course we have Tubes, LCD, OLED, Projection, cell phones, etc., each of which have their own gamma, dynamic range and color gamut characteristics. This is where you benefit from setting the "clip" higher on your video camera. You'll get a little more tonality in the highlights.

Now, in answer to your question; anything above the clip is CLIPPED, meaning gone, clear, white, nothingness! In fact Waveform Monitors used to measure the video exposure don't go above 110 IRE.

Of course we've been talking about video. If you are using a high end Digital Cinema camera, it's another story altogether. With such kit you have a sensor, electronics and recording system designed to put 14 stops between 5IRE (Black) and 105 IRE (White). With bleeding edge technology known as High Dynamic Range (HDR) features it's possible to crunch 18 stops into the recording. Alexa for example can record either 12 bit (ProRes) or 14 bit ARRIRAW (Uncompressed), this is the last step in the system that preserves many thousand shades of gray and each color.

Sometimes of course it doesn't matter that the over exposure is essentially "clear film" that the naked projector light goes right through. For example, if it's moving lights and flares it doesn't matter, and has a pronounced emotional effect which can be exploited.

YES. Loss of data. Good thing to know, but better how to use it for your creative intent. Best way of figuring that out. DO IT. TEST. INVENT.

Good luck,

JS



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Noam Osband
Re: A basic video question: is there loss of data when the luma is over 100?
on Oct 14, 2015 at 3:39:16 pm

John, super helpful response. Thanks! So, if everything over 100 is lost, why does the luma meter on FCP X go up to 120? Is there a difference between 100-120 in that context?


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