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what is meant by knee level


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#1 praveen kumar

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Posted 18 October 2005 - 02:40 AM

We have panasonic varicam, in that adjusting of knee level is difficult to me please explain what is the knee level & what is the knee slope? please suggest me for taking good pictures.
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#2 Laurent Andrieux

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Posted 18 October 2005 - 02:55 AM

It has to do with how the highlights will be rendered by the camera.

You see, in video, the high levels are often a problem.

- because one is supposed not have level over 100 IRE
- because the saturated highlights don't llok good (no details, chroma problems...)
- because the way video renders signal is not as "smooth" as film does

You can see this when shooting an ITW outside for instance, if you have the sky/clouds in the frame.

One solution is to "break" the curve in the highlights, giving it a slower slope, decreasing gamma (contrast) after a certain point.

It will allow you to have details in the highlights as well as bieng able to record highlights that would be saturated otherwise.

Then, the "knee point" is the point where this break occures
the slope is the curve's new slope after this point.

When you set it, have a highlight (window, sky, clouds...) in the frame and notice the changes in the settings.

Regards,
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#3 Dimitrios Koukas

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Posted 18 October 2005 - 05:22 AM

We have panasonic varicam, in that adjusting of knee level is difficult to me please explain what is the knee level & what is the knee slope? please suggest me for taking good pictures.


Ok,
I will not get into details, I will just answer simple.
knee level up means details in the highlights.
Knee level down means no details in the highlights.

Be carefull for what you are doing, it affects the midtones too, wich will make the faces look like they have plaster on their faces.
All has to do with how u have lighted one scene, and what contrast ratio/ lighting ratio's you are using.
If you see knee on a vectorscope, it does exactly the same as an audio compressor to the signal.
Compresses the signal overall.
So it doesn't affect only the highlights.I affects everything that it's in this signal.
I would suggest to just adjust it with a grey scale normal exposed, and then just reduce some master pedestal (black level).
Dimitrios Koukas
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#4 John Sprung

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Posted 02 November 2005 - 02:43 PM

It sounds like what video people call a "knee" is what film people call a "shoulder". Even the anatomy gets confused.... ;-)



-- J.S.
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#5 G McMahon

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Posted 01 November 2007 - 09:33 AM

One solution is to "break" the curve in the highlights, giving it a slower slope, decreasing gamma (contrast) after a certain point.

[/quote]

Please correct me if I am wrong, but doesn't Dimitrios statement, "knee level up means details in the highlights", contradict yours? To me, knee level up means a steeper slope, higher gamma, less detail. Therefore, lower knee means more details in highlights. Is this correct?

While I have you, can you confirm for me, a high gamma, means a steeper incline, meaning a higher contrast image?

And why would you play with the vertical detail level as opposed to the whole detail level?

Thanks all,
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#6 Michael Nash

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Posted 03 November 2007 - 02:18 AM

Please correct me if I am wrong, but doesn't Dimitrios statement, "knee level up means details in the highlights", contradict yours? To me, knee level up means a steeper slope, higher gamma, less detail. Therefore, lower knee means more details in highlights. Is this correct?

While I have you, can you confirm for me, a high gamma, means a steeper incline, meaning a higher contrast image?

And why would you play with the vertical detail level as opposed to the whole detail level?

Thanks all,


He may have been referring to the physical switch on the side of the camera (Knee ON or OFF).

Raising the gamma simply means raising the midtones relative to exposure, resulting in a lower-contrast curve in the mids-to highlights. Lowering the gamma pushes the shadows darker, which most people associate with looking "more contrasty." Gamma is the distribution of tones throughout the scale; it's not contrast per se.

Vertical detail is detail applied in the vertical dimension only; overall detail is detail in both vertical and horizontal.

http://bssc.sel.sony...otingTips.shtml

Knee: http://bssc.sel.sony...otingTips05.pdf

Gamma: http://bssc.sel.sony...otingTips04.pdf

Detail: http://bssc.sel.sony...otingTips03.pdf
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#7 G McMahon

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Posted 06 November 2007 - 07:26 AM

Thanks
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