Correct Exposure with Cinegammas and Hypergammas.

workshops-275 Correct Exposure with Cinegammas and Hypergammas.

When an engineer designs a gamma curve for a camera he/she will be looking to achieve certain things. With Sony’s Hypergammas and Cinegammas one of the key aims is to capture a greater dynamic range than is possible with normal gamma curves as well as providing a pleasing highlight roll off that looks less electronic and more natural or film like. To achieve these things though, sometimes compromises have to be made. The problem being that our recording “bucket” where we store our picture information is the same size whether we are using a standard gamma or advanced gamma curve. If you want to squeeze more range into that same sized bucket then you need to use some form of compression. Compression almost always requires that you throw away some of your picture information and Hypergamma’s and Cinegamma’a are no different. To get the extra dynamic range, the highlights are compressed.

exposure2-300x195 Correct Exposure with Cinegammas and Hypergammas.
Compression point with Hypergamma/Cinegamma.

To get a greater dynamic range than normally provided by standard gammas the compression has to be more aggressive and start earlier. The earlier (less bright) point at which the highlight compression starts means you really need to watch your exposure. It’s ironic, but although you have a greater dynamic range i.e. the range between the darkest shadows and the brightest highlights that the camera can record is greater, your exposure latitude is actually smaller, getting your exposure just right with hypergamma’s and cinegamma’s is very important, especially with faces and skin tones. If you overexpose a face when using these advanced gammas (and S-log and S-log2 are the same) then you start to place those all important skin tones in the compressed part of the gamma curve. It might not be obvious in your footage, it might look OK. But it won’t look as good as it should and it might be hard to grade. It’s often not until you compare a correctly exposed shot with a slightly over shot that you see how the skin tones are becoming flattened out by the gamma compression.

But what exactly is the correct exposure level? Well I have always exposed Hypergammas and Cinegammas about a half to 1 stop under where I would expose with a conventional gamma curve. So if faces are sitting around 70% with a standard gamma, then with HG/CG I expose that same face at 60%. This has worked well for me although sometimes the footage might need a slight brightness or contrast tweak in post the get the very best results. On the Sony F5 and F55 cameras Sony present some extra information about the gamma curves. Hypergamma 3 is described as HG3 3259G40 and Hypergamma 4 is HG4 4609G33.
What do these numbers mean? lets look at HG3 3259G40
The first 3 numbers 325 is the dynamic range in percent compared to a standard gamma curve, so in this case we have 325% more dynamic range, roughly 2.5 stops more dynamic range. The 4th number which is either a 0 or a 9 is the maximum recording level, 0 being 100% and 9 being 109%. By the way, 109% is fine for digital broadcasting and equates to bit 255 in an 8 bit codec. 100% may be necessary for some analog broadcasters. Finally the last bit, G40 is where middle grey is supposed to sit. With a standard gamma, if you point the camera at a grey card and expose correctly middle grey will be around 45%. So as you can see these Hypergammas are designed to be exposed a little darker. Why? Simple, to keep skin tones away from the compressed part of the curve.

Here are the numbers for the 4 primary Sony Hypergammas:

HG1 3250G36, HG2 4600G30, HG3 3259G40, HG4 4609G33.

Cinegamma 1 is the same as Hypergamma 4 and Cinegamma 2 is the same as Hypergamma 2.

All of the Hypergammas and Cinegammas are designed to exposed a little lower that with a standard gamma.


8 thoughts on “Correct Exposure with Cinegammas and Hypergammas.”

  1. Thank’s, very helpful. About to order a PXW-FS7 and guess your your advice of how to expose are the same for this camera and slog3?

  2. Thanks for very useful post. I got FS7 and didn’t know about how HG works. And what these number means. So this post helped me a lot.
    With HG,I think I going to use Zebra for expose face 60%. I will set zebra 1 60%. But could you give me advice that zebra aperture must be how many present? 5% is too wide? Maybe 3 percent or something?

    And I have one more question. HG has G40 and G33 as you mentioned. Could I expose 60% to face with both G40 and G33? In my understand, I have to change percentage between G40 and G33. 60% is for G40? And how many percent with G33?

    I’m sorry for my English.

    1. Different curves require slightly different exposure levels. G40 puts skin tones around 60-65% and G33 at around 55-60%. A 5% window is fine, zebras are a guide only, skin tones vary hugely so no two faces will ever have exactly the same exposure.

  3. I shot with my SONY FS7 in HG4 – 4609G33 day exterior for the first time. I tried to expose the shot with a gray card at 33 IRE and the image was way under exposed. Flesh tones down at 45 IRE. I just went with my gut reaction and exposed them at 55 to 60 IRE. The Gray card was over exposed based on the 33 IRE. The exposure looked good but the whole image was washed out and de-satured. Almost like I was shooting SLog. What’s going on? I thought it would be closer to the final image.

    1. Exposure is NOT brightness. Exposure is letting the right amount of light fall on the sensor. Hypergammas are different to the gamma curve used in most monitors, so the image will look a bit flat and washed out until you grade the footage.

  4. Is it fair to say that a difference in IRE of 10% is equivalent to one F stop? From what you’re saying here, to get a good exposure for light skin tones, it sounds like you just get a normal exposure, then back off a stop or less.

    1. 1 stop is about 10% in the mid range. More in the upper range, less in the lower range. Depends on what you mean by “normal” exposure. Skin tone should be around 60% with Hypergammas.

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