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-   -   Knee and black stretch (https://www.dvinfo.net/forum/jvc-gy-hd-series-camera-systems/61732-knee-black-stretch.html)

Tim Gray February 28th, 2006 08:38 AM

Knee and black stretch
Do Knee and Black Stretch actually provide more dynamic range? There seems to be one camp that says use Black Stretch 3 and a Knee 0f 80%. The other "True Color" camp has this stuff turned off. Looking at the histograms in Paolo's True Color page, it appears to me that the dynamic range of Cinewide is not extended, just compressed. There doesn't seem to be any extra highs or lows beyond what is available in the DSC calibrated scene file.

Are we just creating the illusion of more dynamic range using or are we actually creating more dynamic range?

(Creating the illusion is certainly useful for quick projects where a lot of color correction isn't going to happen.)

Tim Dashwood February 28th, 2006 09:03 AM

You should read this article. http://www.24pdigitalcinema.com/cinegamma.pdf

It specifically refers to the Panasonic Varicam, but the concept is exactly the same.

Page 1 essentially shows the difference between Paulo's setting and mine.

In a nutshell, yes knee and black stretch allow us to compress more dynamic range into the limited luminance range of the video spec. There are trade-offs, but the whole point of knee and black stretch is to use them as tools to extend the effective dynamic range (aka latitude.) You could liken it to shooting on film, but then doing a teleciné transfer to video and choosing to include more information in the highlights and blacks.

Tim Gray February 28th, 2006 09:24 AM

That's certainly what I hoped to be true... However I had my doubts of if that was the case. Paolo's histograms scared me a little bit since there was nothing above or below the headroom provided by the Cinewide settings. I guess that was just an artifact of shooting such a controlled chart.

The JVC's imaging chip operates at 10 bit, right? So Knee is essentially compression on the highs to squeeze the 10 bit signal down into 8 for tape, correct?

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