What is the Film 'Look' Gamma Curve?

[Undead Sega]

Its been awhile since i have posted, and again abit rusty to know if this is the right place to post this but quick and simple question, what is the Film Gamma Curve?

i have looked around and there are so many, i dont know which one is which, and basically i just want THE curve that emulates how light is captured on 35mm film.

[hanfrunz]

THE curve does not exist.

[Undead Sega]

what do you mean???

[Alex_ander]

Film itself gives (almost) linear responce (has gamma close to 1.0) except for extremely overexposed or underexposed cases. Telecine devices (as any TV system) use internal gamma correctors mainly to compensate for non-linearity of 'standard' display devices (the correction amplifies lower signal range with a factor of about 4).

[Sagekilla]

The only "curve" that exists is that film tapers off very gently when being overexposed. Unlike a digital sensor, you still get highlights in massively exposed areas. It's pointless to try to emulate this though, since it should only be done at the point of capture, if at all.

Interestingly, Canon and Nikon do something like this already on some cameras: They play around with the curves of how everything is amplified and you get a few extra stops at the highlights at the cost of your shadows. Not perfect, but useful sometimes and interesting.

[Undead Sega]

doesnt film have a more 'S'-curve when video has a linear line in the gamma adjustments?

[Sagekilla]

Yes, it does have an S-curve. But that's only at the highlights and shadows. In the middle of it, it behaves fairly linearly. CCD and CMOS sensors suffer from being linear throughout the whole range, and blowout quickly. It would be very difficult to simulate a film like curve if you don't do it the moment you capture the video.

[Undead Sega]

when recording, it is essential to not over expose areas in the first place, but as i said video records with a linear or straight line in the gamma curve, whereas film is an S-curve, which is how 35mm captures light, and i am wanting to know what is the film curve of that?

[Sagekilla]

I'm confused here. You're saying 35 mm film has a nonlinear response that looks like an S-curve (correct). What are you asking for?


i am wanting to know what is the film curve of that?


film curve of.. film? Like I said it's just a nonlinear curve that overexposes gently instead of blowing out completely on a digital sensor.

[Undead Sega]

yes, the non-linear response that looks like an S-curve, to which i am looking for, or how to set.

[Sagekilla]

As I said earlier the best time to do it would be right as the sensor is capturing the light. Doing so on a video you already have is pointless since you'd just be playing around with contrast, which you can do with a certain function whose name eludes me (Giocou?).

To do that properly you'd need to be able to tell how film actually reacts to light from 0 - 100% brightness.

[tin3tin]

Heres a curve for the Cine look for the DVX100a camera: http://www.kino-eye.com/ (http://www.kino-eye.com/archives/downloads/DVX100AGammaCurve_v2.pdf)(a pdf)

[zee944]

yes, the non-linear response that looks like an S-curve, to which i am looking for, or how to set.

Perhaps you should try playing with 'gradation curves' filter for VirtualDub by BBugsBunny. You can also feed the curve from AviSynth with GiCoCu.

Try look here:
http://forum.doom9.org/showthread.php?t=87791&highlight=filmlook

[Mug Funky]

bear in mind that when we're talking about "film look", there's a lot to digest.

original camera neg is fairly linear (though obviously not perfect because kodak and fuji look different in more than just highlight and shadow).

however, actual film prints are a different story. there's intermediate films involved - sometimes a few generations of copies in the analog domain before it gets on the screen, and each generation adds it's own extra peculiarities.

a release print can be approximated by an s-curve. you'll need to play around a lot though. there is no "THE" curve, because even intermediate stocks vary quite a bit (and in cases like saving private ryan the intermediates are processed differently which causes drastically different looks like the "bleach bypass" look).

if you want a rule of thumb, try apply an s-curve to a low contrast original (on video, underexpose a bit), bias the highlight in this curve rather than the blacks (which you'll flatten right at the floor, but lift quickly after that), and desaturate the highlights

[FlimsyFeet]

Applying an 's-curve' is pretty much what my little script HERE (http://avisynth.org/mediawiki/FlimsYlevels) does. It's not meant to approximate any thing in particular, it was just a bit of a fun effect, try playing with the strenght of the effect and see what difference it makes.