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Cine Gamma Exposure

COW Forums : Sony XDCAM - EX & Related

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Ajit PatelCine Gamma Exposure
by on Aug 8, 2012 at 5:55:20 am

Hi,

I just got a new EX1R and loaded Alister Chapmans Cine Gamma 1 settings in the picture profile. But I noticed that the exposure goes darker by about 1-1.5 stops than when the PP is on OFF. So do I attempt to correct the exposure on camera visually and using zebras or do I leave it and correct it in post? The cine gamma 1 is supposed to control the highlights so do I risk to negate its function if I correct the exposure in camera?
Thanks--Ajit


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Don GreeningRe: Cine Gamma Exposure
by on Aug 10, 2012 at 8:37:57 pm

Make sure you've copied Alister's settings exactly. I don't know what part of his web site you got the profile from but check out his 'how to' YouTube video about the 4 kinds of gamma curves that come pre-programmed with the EX cameras as well as when to use them.

http://www.xdcam-user.com/how-to-videos/

It's the second one down.

- Don

Don Greening
A Vancouver Video Production Company
Reeltime Videoworks
http://www.reeltimevideoworks.com


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Dean LongfieldRe: Cine Gamma Exposure
by on Aug 13, 2012 at 8:19:54 pm

I always adjust the zebra stripes. I'd rather have an underexposed image than an overexposed image,
as it's more possible to correct in post.

Regarding settings I kind of use a combination of Doug Jensen's suggestions and Alister Chapman's I suppose, in that I like DJ's suggested settings of:

Matrix: Turned ON and set to HIGH SAT
Detail Level: -10
Master Black: -3
Black Gamma: -2

But i tend to use: (more like AC)

Cine Gamma 1: for outdoor, Daylight shooting
Cine Gamma 3; For indoor shooting
Cine Gamma 4; (sometimes) for indoor when it's very dark and I want to increase brightness of the entire frame.

i believe DJ uses Cine Gamma 4 most of the time, (indoors or outdoors).
Note that even the Cine Gamma 4 is a little darker than the Default settings.

So that's what's working best for me right now. Hope that helps.


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Bob ColeRe: Cine Gamma Exposure
by on Aug 15, 2012 at 2:06:43 am

[Dean Longfield] "I always adjust the zebra stripes. I'd rather have an underexposed image than an overexposed image,
as it's more possible to correct in post. "


Zebras set to what? Back in the day, I used 70, but I've read that some people use 60 and even lower.

And, how does the gamma setting (i.e.,using CineGamma) affect the desired zebras?


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Michael PalmerRe: Cine Gamma and Exposure
by on Aug 15, 2012 at 5:26:54 am

Cine Gammas are a fixed advanced feature set for those that either don't have a vector scope and/or haven't learned how to adjust other advanced features on the camera.

I believe zebras should be set to 95-100 so you know what is clipping, thats all they are good for.

I only use the cine gammas for a quick fix because you can dial in the same (or better) look using other features including the Knee, Slope and Black Gamma in combination with the many Matrix setting to find what I believe are even better looks. Its a way to open the lower stop range from what is being suppressed by the Cine Gammas.

I use the vector scope to dial in not only my picture profile look but also help me to set my exposure.
If you have a vector scope as a feature on your field monitor you might want to spend some time working with your pp's. This will definitely expand your dynamic range, it just takes time between each shot and/or setup.

Good Luck
Michael Palmer


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Bob ColeRe: Cine Gamma and Exposure
by on Aug 16, 2012 at 4:21:30 am

I'd like to take a course from you, Michael. I tend to stick to Cine Gamma and to avoid deviating from the "tried and true" mainly out of concern about producing a usable image. But from what you're saying, there are some real possibilities that I'm ignoring. Food for thought. Thanks.


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Alister ChapmanRe: Cine Gamma and Exposure
by on Oct 20, 2012 at 9:46:39 am

While you can adjust the slope (gain), black gamma and knee of the standard gammas these are still very different to the way the cinegammas work. The key difference is that the highlight compression applied by the cinegammas starts very gently around 50% and the progressively increases as you go up the exposure range. If you try to use the knee to get a similar amount of highlight compression you have to use either a very low knee point or a steep slope or maybe even both. The problem with the knee is that it is either on or off, your highlights are either compressed or not, there is no middle ground. The more compression you add to any part of an image, the less well it tends to grade.

Where you have controlled lighting or a restricted dynamic range then standard gammas with minimal knee work very well and would be my recommendation. But where you have less control over the lighting or are dealing with a high dynamic range scene then the cinegammas tend to deal with overexposure in a much more natural way than the knee. A typical knee artefact would be an ugly highlight on a face that suddenly overexposes and looks wrong because you go from normal exposure below the knee to compressed range for the overexposure almost instantly. A cinegamma will handle the overexposure in a more progressive manner.

If your worried about loss of shadow detail with the cinegammas you can use black gamma with the cinegammas, just as you would with a standard gamma, so by using a cinegamma combined with black gamma you gain the benefits of progressive overexposure control with adjustable shadow and mid range control.

Middle grey with the Cinegammas should be around 42-44%. Exposure with cinegammas should be alittle lower than with 709 as you want to avoid putting faces etc too high up the exposure range to keep them in the more linear part of the curve. It should be remembered that if your using a monitor or TV with Rec-709 or similar then whenever you use a camera gamma that doesn't match that display gamma you will have a miss-match so you are moving away from the optimum settings for 1:1 reproduction of the scene. The further away you go from the display gamma the bigger the discrepancy. Sometimes this is desirable and helps create a "look", but sometimes as with a cinegamma or any other gamma that captures a greater range than the display gamma was designed to show it will result in a flat looking image that may then need grading. Cinegammas were designed to maximise dynamic range to offer maximum flexibility in post, they are not really optimum for "direct to air" type productions.

Alister Chapman
http://www.xdcam-user.com


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