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Multi-gamma function


Prasad Kumar
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I was reading about Panasonic Varicam Camera. In that, it specified “master-quality, full-resolution 10-bit 4:2:2 AVC-Intra 100 recording; variable frame rates in one-frame increments; HD-SDI output of 23.98PsF/24PsF; and a multi-gamma function including Film-Rec for the prized VariCam look closely matching the color and response of film stocks".

What is multi-gamma function in the layman term? (Google search mostly talks about Gamma camera, I believe that is different from this).

 

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Hi Kumar, Perhaps this will be helpful. https://pro-av.panasonic.net/manual/html/VARICAM_LT(VQT5M58A-8(E))/chapter04_04.htm

I own a Varicam LT and find the camera amazing to work with in almost all regards. All cameras demand some flexibility and adaptation by the user but to me the Varicam is quite good. A very well-rounded tool. The work flow is very easy; the link above may help answer your question regarding multi-gamma.

- Guy

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Hello Mr. Mastrion:

Thank you for your reply.

I looked into the link you gave me. It says how to do the setup in the camera, but I am looking for the meaning of multi-gamma.

PS: Please forgive me if this is a basic question. I am a beginner, and I am just learning about the camera and the cinematography concepts.

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Hi Kumar, here is a link with more detail about the various gamma of the Varicam https://pro-av.panasonic.net/manual/html/VARICAM_LT(VQT5M58A-8(E))/chapter04_04_04.htm

the gamma settings in the most basic sense are color spaces the camera will record the image; from V-log which is the most expansive dynamic range and is a recording format that requires additional work to complete the color grading either live on-set or in post.... to 709 which is considered standard broadcast color space in the U.S. and can be viewed right out of the camera.  It has less dynamic range than v-log but if fast work flow is required and you are releasing right to broadcast or the web you can record files to this space.  Varicam has options in between. Importantly the camera will preserve the original V-log footage, while also allowing recording to 709 or other.

Additionally, you can apply 709 to the view finder and/or SDI out to a monitor if you have a need to  show basic color on set. You can also load in a custom color profile or LUT.  The V-log space will deliver a relatively flat look to the images so 709 is often applied to the monitors for quick reference. Much more specialized and sophisticated color can be applied via custom LUTs ( Look Up Tables) or via live grading during your shoot.

the camera is essentially always recoding in v-log and will create the 709 files from the log footage. 

here is a link to a video that goes into great detail on the camera menus. It’s a few years old but you may find it informative. https://youtu.be/QluloJUu0H4

here is a deep look at gamma; https://poynton.ca/notes/colour_and_gamma/GammaFAQ.html

I hope this is helpful. 

 

 

 

 

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Gamma in this case means exponential function like x squared (x^2) or the square root of x (x^1/2). If you don't know the difference between linear and gamma corrected signals you should research it online.  Your sensor records linear data and applies a gamma correction which is an exponential function.  So every pixel is receiving a function like if x = pixel brightness, new pixel brightness = square root of x.  Square rooting all the pixel values between zero and one makes the brightness and contrast of the image closer to the human eye.  I think when they say multi gamma, I think its just a fancy way of saying contrast curve.  I might be wrong, but the formulas for s-curves  for contrast can be considered multi gamma because how the code works is usually if the pixel value is above .5 then apply a positive exponential function and if its below .5 apply a negative exponential function, so there are "two" gamma curves being applied.  All in all its probably just marketing and wont change anything fundamentally that you do with the camera. 

 

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I am not sure but I think a log can also be a multi gamma function. Brands modify the shoulder and knee regions in log gamma to squeeze more and more details . However, a gamma is not color space or equation ,it is the power in the equation. In a CRT input output response is denoted by something like I=V^y (think 'y' as gamma,I don't have greek letters in my keyboard) . 

For the time being you can refer to this article that I found recently ,it is very informative and easy to grasp:

https://www.thebroadcastbridge.com/content/entry/5246/looking-deeper-into-log-gamma

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If I'm not mistaken, "multi-gamma function" is just a marketing term referring to different output displays the camera can record in. REC709 has its own gamma, vLog has its own gamma, etc. Choosing from multiple gammas means choosing to record in multiple outputs.

If you're shooting for cinema and a color grade, then vLog captures the entire dynamic range of the camera and gives you the choice in post of how to apply the gamma.

If you're shooting for broadcast, then you need to pick the gamma that matches your broadcast means.

Please correct me if I'm wrong! 🙂

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On 1/23/2021 at 4:37 PM, Prasad Kumar said:

I was reading about Panasonic Varicam Camera. In that, it specified “master-quality, full-resolution 10-bit 4:2:2 AVC-Intra 100 recording; variable frame rates in one-frame increments; HD-SDI output of 23.98PsF/24PsF; and a multi-gamma function including Film-Rec for the prized VariCam look closely matching the color and response of film stocks".

What is multi-gamma function in the layman term? (Google search mostly talks about Gamma camera, I believe that is different from this).

 

I believe this describes an older, video style Varicam.

FilmRec mode allowed a choice of 4 or 5 different gamma corrections, based upon a gamma 2.2 base.

The choices for gamma were given in percentages. 200% through 500 or 600%. The highest number recorded the entire dynamic range of the camera, but not in a log curve.

 

Adding a correction curve during color grading was done to create the look and contrast desired.

As it’s not a log recording, 10 bit or higher recording was necessary to avoid banding on color corrected footage.

 

When these cameras were current, they recorded the highest dynamic range of the early digital cinema cameras.

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