Cine gamma settings in the EX1

[Les Wilson]

Originally Posted by Alister Chapman

...If you shoot using a CG and you have your skin tones at the traditional 70 ire (which is rubbish anyway as everyones face is different) then those skin tones are in the compressed part of the gamma curve and no amount of grading will ever make them look as good as they should. You must keep skin tones and natural textures at a lower level when using the CG's to avoid this compression. When using CG's you need to modify the way you expose to get the most out of them.

Rats. Just when I thought I understood what to use. I've been using Cine3 and 4 setting the skin highlights to 60-70 using false colors. Alister, for caucasian skin in a studio with black background, what ire would you use for skin highlights?

[Piotr Wozniacki]

I'm exposing faces up to 65, and I'm good with it.

But that's just me,,, Alister?

[Brian Tori]

Here is a good article by Adam Wilt on the effect of Cinegamma on images.

ProVideo Coalition.com: Camera Log by Adam Wilt | Founder | Pro Cameras, HDV Camera, HD Camera, Sony, Panasonic, JVC, RED, Video Camera Reviews

[Dominik Krol]

Originally Posted by Alister Chapman

Cinegammas are designed to be graded. They are not designed to be used in the same way as you would with a standard gamma and you need to adjust where you put your skin tones accordingly.

Yes I realize that, but it does not change the fact that you OVEREXPOSE your bright background quicker (If exposing for Caucasian skin tones at 75%) when using cinegamma 1.. Even beyond 109%, then you cant grade yourself out of that.

[Doug Jensen]

Originally Posted by Piotr Wozniacki

I'm exposing faces up to 65, and I'm good with it.

Wow, I didn't realize everyone in Poland had the same shade of skin. In my country, we have whites, blacks, latinos, asians, and all different kinds of skintones to deal with. 65% on one guy might be fine, but totally wrong for the next guy. No matter how you slice it, using zebra on skintones just comes down to guessing because every face is different. Sure, an experienced shooter can still guess right most of the time, but it's still just guessing. I can do that without zebra. Zebra is one of the most important functions on a pro video camera, but it is only correct if you know the value of WHAT you are measuring -- and usually that should be white card, gray card, or chip chart. Anything else is just guessing.

[Piotr Wozniacki]

Originally Posted by Doug Jensen

Wow, I didn't realize everyone in Poland had the same shade of skin. .

Ha, ha :) Actually yes, Doug - 99.9% of this nation is of the same race, and similar skin color.

I just wanted to stress that - in spite of the common "recipe" for the Caucasian skin tone to be exposed with zebra at 70-75% - after some experimenting, I settled with 65% as being safer from decolorization due to highlight compression.

[Doug Jensen]

Piotr,
Well, one of these days I'm going to get over there to Poland and see the faces for myself! I've traveled all over the rest of Europe better never made it to Poland. It's on my list.

[Alister Chapman]

Either I don't understand you Dominik or I believe you are wrong.

The standard gammas (without knee) will give you about 2.5 stops of head room above 70IRE while the cinegammas give you around 5.5, stops of headroom. Total DR for standard gamma with no knee is about 7.5 stops and cinegammas is 12. A well set knee will extend the standard gammas out to around 10-10.5 stops giving you about 5 above 75IRE. If you take a look at the plots prepared by Serena earlier in this thread, or the published curves you can clearly see the extra headroom the cinegammas give you. But the key principle when using the cinegammas is that you should lower your midtone levels to keep them in the more linear part of the curve so that you can make use of the gradually compressed highlights. Taking something that with a standard gamma you would have exposed at say 75ire and now exposing that at 60ire gives you around an extra 1.5 stops of useable headroom. Then in the grade you sort out you contrast range to give the tonal range that you want.
You don't want to do this with a standard gamma plus knee because the knee area is either compressed or not, there is nothing in between and due to the sharp onset of the knee you don't want the knee point set too too low, so to get good dynamic range you end up using just the range from 85ire to 100 (109)ire for the knee (15-19% of recorded data) for 4 to 4.5 stops which is a lot of compression. As a result if you try to grade this it will look bad as you have not really used sufficient data to enable you to extract useable picture information.
Cinegammas on the other hand start the compression at around 30ire with it steadily increasing especially above 65ire. As a result the same highlight range that with the knee is squashed into just 15 to 19% of the available data is now spread over 35%-39% of the recorded data so you have much more data to work with so the information recorded can be manipulated in post without so much degradation, thus making this useful information that you can do something with. In addition the gentle increase in compression means that more data is allocated to the areas that are most important, gradually decreasing as you approach overexposure and clipping.

[Dominik Krol]

Alister

Apparently you don't want to understand me because I never mentioned Standard gammas.. I'm sure you are a experienced guy, but try to read my post for once before you begin taking it apart.

I will repeat for you once more. CINE gamma 3 and 4, will give you more headroom to the bright sky, if you are exposing for a caucasian skin tone.

Even when grading, you would appreciate that the second most important subject in your shot (the sky in this example) laying closely exposed to your first (the person in front of it). Otherwise you are just "fixing" in post what you did wrong in the field.

If thats what you like to do. ok. It still doesn't make it optimal.

And I repeat. No mention of Standard gammas in this post.


----
Im sorry for sounding arrogant, but it annoys me endlessly when people pick apart my arguments, and making me sound stupid, with fancy "I know it all" answers that don't even relate to what I wrote in the first place.

[Alister Chapman]

Ok Dominik, I've re-read your post and I apologise for bringing standard gammas into my reply, but I still don't believe you understand the way the Cinegammas are supposed to work.

Originally Posted by Dominik Krol

I don't know how you guys derived at the "conclusion" that Cine gamma 1 is for bright/outdoor scenes, and Cine gamma 3/4 are for dark/indoor.

My tests have shown the following.

If you expose for skin tones at 70-75% in Cine 1, you will overexpose the white background/bright sky much faster, than you would in Cine 3 and 4.

If you set zebra 1 to 75 and enable zebra 2 which is at 100, you will expose the color chart "Caucasian" square at the same time. So 75% skin = 100% white at same exposure in Cine 1

Set the gamma to Cine 3, the white square will be sitting at 97% with the skin square is at 75%

Go down to Cine 4, and the white square will sit comfortable at 95%

Your treating the CG's as you would standard gammas in your tests and thats not how they are supposed to be used. For starters straight shooting with CG's without grading will lead to a flat, un-natural image on a monitor due to the large miss-match between the cameras cinegamma curve and the monitors gamma curve (rec-709 for an HD monitor).
The reason why CG's 3 and 4 work better for darker scenes is not to do with the top end of the curve but the middle and bottom end. CG3 and CG4 lift dark and mid range parts of the image, improving shadow areas and dark areas and giving you more to work with in post in these darker scenes. Exposure is not just about highlights and skin tones. As an option when shooting a dark scene this would allow you to have skin tones and mid tones at a lower ire level and still get a good looking image after grading as by reducing the exposure a little you will not be compromising you shadow and dark areas as much as with CG1.
Trying to fix skin tone exposure at 70-75ire (which is too high even for standard gammas IMHO) is not the way to use Cinegammas or Hypergammas. Not only do faces vary from person to person, but the brightness of faces will change from scene to scene. On a bright sunny day a face would typically be bright and well illuminated and should be exposed as such, in a dark scene the face might well be much darker and should be exposed darker to keep the mood of the scene.

Originally Posted by Dominik Krol

Finally you can use Cine 2 for scenes which could introduce banding in the 8bit colorspace. Since Cine gamma 2 compresses the image to 100% white clipping (which btw can be changed back to 109 if you set the gamma level to -5), You will effectively have a better "dynamic range resolution" pr stop.

That's not correct. Cine 2 is recording 12 stops into the standard 100 % range that uses bits 16 to 235. The other cinegammas record the same exposure range but now using the full 109% recording range (same stops- more range) that includes the extra bits above 235, so now your using bits 16 to 255. So MORE bits are being used by CG's 1,3 and 4 for the same range, not less, that's why they are allowed to go to 109.

Originally Posted by Dominik Krol

Same goes for all of you who use -3 DB gain.. If you set any of the Cine Gammas to -4 (cine gamma 2 to -9) You can maintain the dynamic range at 109%

On the majority of cameras using -3db gain reduces the dynamic range of the camera by -3db (half a stop), EX1/EX3 included. It can however bring a -3db noise improvement. Using -3db gain and then adding that gain back in again buy adjusting the curve level is pretty pointless as you will also increase the noise again, you may as well just stick to 0db. Adjusting the curve level adjusts the gain level of the curve and thus noise levels as well.

[Alister Chapman]

Originally Posted by Les Wilson

Alister, for caucasian skin in a studio with black background, what ire would you use for skin highlights?

In a studio, where I have control over the lighting, for a shoot for television, I would try to use standard gamma 3 with no knee and use the lightning to keep everything within the standard Rec-709 range that standard 3 gives. This should give the end viewer the best result as the contrast range displayed by the TV should match that of what you have captured. You won't get any gamma compression on skin highlights and it should look very natural. In this case for a typical caucasian person you would be looking at 65 to 70ire. If your struggling with specular highlights and reflections blowing out then you could introduce some knee with a fixed point at 85 to 90, but as highlight go into the knee the usual inevitable knee color shift gets introduced giving that nasty yellow hue to over exposed skin tones.

If you are shooting for a higher dynamic range output, or plan to grade then I would switch to Cinegamma 1 unless it's a low key scene in which case I would most likely use CG4. I would want to keep any skin tones below the more highly compressed part of the curve, so below 65ire, typically around 60ire depending on the shoot. This will look a touch under exposed when shooting. That way you keep any highlights in the more linear part of the curve so they will look more natural once you've done your grade, overexposed cinegamma faces don't look good.

[Doug Jensen]

Originally Posted by Les Wilson

Alister, for caucasian skin in a studio with black background, what ire would you use for skin highlights?

Hey, do you mind if I take a shot at answering this question, too?

The term "caucasian" skin has no meaning. Show me two white people, and I'll show you two different skin tones. 65% might be great for one, and over-exposed on the next. By using zebras, I would set my exposure based on either a white card or gray card of known reflectance value. And in this example, the background is irrelevant. The face should be exposed the same whether the background is white, black, pink, yellow, or a green screen. The face is the subject, and that is what matters.

[Les Wilson]

Thanks Doug. I mentioned the black background because I want the blacks to crush. I mentioned Caucasian because I expected the technique for judging exposure based on highlights to be different in the Caucasian range than dark skinned. And so I was wanting to draw out that technique as I was shooting that today and would adjust the technique I use.

What I've been doing is lightIng the scene using a mannequin so as to get the relative intensity between fixtures as I want them. I then adjust the iris using false colors so that the highlights on the face have no yellows indicating under 70 (I use the Marshall 7" monitor). If my iris is in the desired range, i'm done. Otherwise I adjust the lighting or nd so I can get the iris where I want it.

When the talent shows up, I adjust the iris to achieve he same false color reading on their actual skin (no yellow). So with this technique I think I'm dialing the same level on the highlight Thus compensating for skin to es (wihin a range at least) and letting the relative intensity of the fixtures handle the rest.

[Doug Jensen]

Unless I misunderstand how you are describing your technique, it sounds like you are saying everyone's skin tone should result in the same false color display. Is that what you are saying? Because, if so, you are wrong. If false color works on a fair-skinned white guy, it can't also be correct for a darker skinned latino, someone with a good tan, or a black person. Your technique does not take into account different shades of skin. False color and/or zebra on skin tone tells you nothing about the proper exposure because you don't know the reflectance of the subject's skin. Ultimately, you're just guessing at the exposure.

Proper exposure is more complicated than just not blowing out the highlights. If you applied that same logic to sound, then recording a whisper and someone shouting should both be just under the redline on a VU meter. Obviously that would not sound right. And exposing everyone's skin tones at the same zebra or false-color level (no matter what the level is) is wrong too. A darker person should look darker than a lighter person, and if you exposue them both to the same IRE, at least one is going to be wrong.

[Michael B. McGee]

And what about adjusting the Gamma Level? I remember once reading that (+) darkens mid-tones and (-) lightens mid-tones, yet the opposite appears to be true when looking at my camera's LCD.