Log and negative film stock

[Daniel Meier]

Hi there.

Just a general question that arose yesterday. As I never worked with negative film stock before.

What does negative film (35mm, 16mm) look like, when coming straigh out of the lab. Is it as flat looking as nowadays digital Log footage?

 

 

[Mark Dunn]

Out of the lab it looks like a strip of orange plastic unless you're having a workprint, in which case it hopefully looks quite a bit like the scene you've photographed.

Do you mean after scanning?

[Daniel Meier]

Sorry, I don't have that much of an idea.

 

Let's say at the point where the editors are doing their first rough cuts.

Maybe someone could post a sample frame.

 

Me and my workmate were just wondering if the flat look of a log image is just an invention of the digital age.

He said that e.g. the Canon C300 puts out images that look more similar to film stock than the S-Log2 image of a FS 700, because the C300's image is not as flat.

Edited April 5, 2016 by Daniel Meier

[Brian Drysdale]

All these log curves etc are to match film. The gamma of film neg is lower than that of a projection contrast print. This is a rough example:

 

http://www.cameraposition.com/podcast/images/CP45/TransFilmCurve.jpg

[Mark Dunn]

Oh dear. That graph is terribly misleading, not to say wrong. No units.. The response doesn't cut off like that. The reversal curve should be the other way around- density goes down with exposure, not up.

[Brian Drysdale]

True, I was more comparing shapes, it's rather simplified ,

[Tyler Purcell]

Me and my workmate were just wondering if the flat look of a log image is just an invention of the digital age.

Umm yes.. it is an invention of the digital age, specifically MPEG cameras. WHY? Because MPEG in of itself is a compressed color space format. It's designed to record REC 709 color space, no more. Plus, only a hand-full of them record 10 bit 4:2:2, which is still a format missing quite a bit of image data. So it's REC 709 mixed with 10 bit 4:2:2, which are actually the standards for broadcast and have nothing to do with cinema (12 bit 4:4:4) quality. In order to compress a fuller bandwidth signal into the REC 709 color space, MPEG based cameras have created a "FAUX" Raw format called S-Log. With that said, you will never recover the missing data unless you record in 4k and scale down to 2k, which fills in the missing color information, but doesn't change the bit depth.

 

By contrast, Red, Arri and Blackmagic, record to uncompressed AND compressed RAW formats, ranging from 12 - 16 bit, depending on which flavor. Camera RAW is very unique because it takes the imager data without the Debayer layer and records it. This allows for the debayer process to be done in software, which allows FAR more control over the color correction. This is part of the reason you see almost every feature film today using RED and ARRI cameras. As a side note, the only non-RAW codec that allows full bandwidth is Pro Res XQ, which is a 12 bit 444 codec, but does the Debayer in camera. Arri and Blackmagic have focused on using this codec as an alternative to RAW. What humors me is that RED and Sony have tried to jump on the Pro Res bandwagon, but as this writing, they use Pro Res to save space, so they only have the lower-end codec's.

 

Film negative has full dynamic range already in it. Yes, it's a bit flatter then a print for instance, but it's not like S-Log or camera RAW which can be extremely flat.

[Robin R Probyn]

More wrong info from Tyler come on really please study up n this.. you are always giving out dud info man.:).. Slog is NOT RAW. or ever claimed to be .its a log curve..as in S LOG !! in fact Slog3 is almost exactly the same as Arri LogC.. F5/55 can record 16 bit RAW..

 

It has nothing to do with MPEG..

 

"Canon C300 puts out images that look more similar to film stock than the S-Log2 image of a FS 700, because the C300's image is not as flat."

 

The canon C300 C Log is a rather compromised Log curve.. due to the 8 bit max of that camera.. its more like a hyper gamma curve from a Sony camera.. Sony Slog is more of a "true" log curve ..has more DR than C Log.. and so when un corrected appears alot more flat,un saturated than the C300 "log" footage

[Tim Tyler]

Tyler says that S-log is flatter than film negative, not that S-Log = RAW.

 

More wrong info from Tyler come on really please study up n this.. you are always giving out dud info man. :).. Slog is NOT RAW. or ever claimed to be

[David Mullen ASC]

A Cineon log scan of film negative looks very flat on a Rec.709 monitor, very similar to ARRI Log-C.

[Tyler Purcell]

Slog is NOT RAW. or ever claimed to be .its a log curve..as in S LOG !! in fact Slog3 is almost exactly the same as Arri LogC.. F5/55 can record 16 bit RAW..

That's right and nowhere did I say slog is raw. The word "faux" means fake.

 

Slog was developed specifically for cameras that don't record raw and record to rec709. If you shoot raw you don't need slog curve, it's irrelevant in fact.

 

Ohh and we've already had discussions on cameras that need special hardware to record properly. Most people won't invest unless it's necessary. In the case of the OPs question, film has no relationship to camera raw or slog.

[Satsuki Murashige]

Umm yes.. it is an invention of the digital age, specifically MPEG cameras.

 

No. Log was created as a means of capturing the full dynamic range of the negative in a film scan to the Kodak Cineon format. It is directly analogous to the film negative. Arri created Log-C for their digital cameras to emulate Cineon/DPX film scans based on experience with their film scanners, which is why the Alexa looks similar to scanned Kodak color negative.

 

Log has nothing to do with mpeg, don't know where that idea came from.

 

https://en.m.wikipedia.org/wiki/Cineon

[Adrian Sierkowski]

I thought that the Cineon stuff was Lin not Log though? Or was it just that there was an option for Lin with Cineon?

[Tyler Purcell]

Log has nothing to do with mpeg, don't know where that idea came from.

The whole reason LOG was created is to keep a certain look from scan through projection. They wanted something that mimic's film's dynamic range and color space, to create a "digital negative".

 

S-Log is designed to optimize the noise floor and tonal reproduction of the imager and compress it into a data packet which will work within the limited Rec 709 codec's.

 

S-Log is a SONY format, which took off because vendors picked up on the idea to be compatible with Sony cameras. If Sony cameras recorded RAW, there would be no reason for their own S-Log system. However, until very recently, Sony cameras didn't record RAW, so it's clear their whole intention from the get go was to solve a HUGE problem their cameras had. If you have a limited dynamic range REC 709 RECORDING format, how do you squeeze high dynamic range material into it? You simply compress the dynamic range and expand it in post. Same philosophy as analog audio tape noise reduction.

 

You will notice, S-Log is used on cameras that shoot MPEG. Cameras that DON'T shoot MPEG... Arri, RED, Blackmagic, AJA, don't have S-Log because they don't need it.

[Stuart Brereton]

Arri, RED, Blackmagic, AJA, don't have S-Log because they don't need it.

 

S Log is just Sony's name for their version of the LOG curve. Arri don't have S Log, because they have Log C, as Canon have C-Log, Blackmagic has Film Gamma and Aja has Expanded Gamma. All just different versions of the same thing, tweaked to suit the dynamic range and response of the cameras.

[Tyler Purcell]

S Log is just Sony's name for their version of the LOG curve. Arri don't have S Log, because they have Log C, as Canon have C-Log, Blackmagic has Film Gamma and Aja has Expanded Gamma. All just different versions of the same thing, tweaked to suit the dynamic range and response of the cameras.

That's one way to look at it. I see it as a compromise for the lack of a decent recording format.

[David Mullen ASC]

Log has nothing to do with MPEG compression -- after all, a 10-bit Cineon Log scan of film negative is recorded to uncompressed DPX files.

 

One could say, however, that Log is a method of more efficiently storing a wide dynamic range from a digital sensor into 10-bits, 12-bits, etc. However, if we start getting into 16-bit recording such as RAW recording for the Sony F65 or the whole ACES workflow, then it is possible to work in linear gamma without worrying so much about wasted bits.

 

But compression is a whole separate issue. The S-Log gamma has nothing to do with whether it is recorded to MPEG or not. In theory you could shoot and record 16-bit RAW on a Sony F65 and convert it in post to S-Log gamma but stored as 10-bit uncompressed DPX files.

 

You often record Log-C on an Alexa to ProRes, which is another DCT-varient similar to MPEG.

[Tyler Purcell]

Right, but again it exists because of the inferiority of the storage format.

 

If the storage medium was 24 bit RAW directly off the imager with zero processing, there would be no reason for S-Log.

 

Sony and Canon's incessant use of antiquated 8 bit 4:2:0 Rec 709 color space recording formats are EXACTLY the reason we have S-log.

[Stuart Brereton]

Sony and Canon's incessant use of antiquated 8 bit 4:2:0 Rec 709 color space recording formats are EXACTLY the reason we have S-log.

 

You seem to be using S-Log as a generic term for Log Gamma, whereas it's actually the name of Sony's own implementation of a Log Curve

[Stuart Brereton]

That's one way to look at it. I see it as a compromise for the lack of a decent recording format.

Are you saying that Pro Res 444 is NOT a decent recording format?

[Tyler Purcell]

You seem to be using S-Log as a generic term for Log Gamma, whereas it's actually the name of Sony's own implementation of a Log Curve

That's right, S-Log is it's own LOG curve, incompatible with every other system and looks nothing like real LOG, which even looks nothing like color negative.

 

Are you saying that Pro Res 444 is NOT a decent recording format?

Pro Res XQ is the best standard recording format out there today. It actually doesn't work in REC 709, it has far more dynamic range then even the standard Pro Res codec's. I use XQ all the time, mostly to color Alexa shots. Yes, we use Log - C on the Alexa material but that's only as a precaution, rather then a pre-requisite like with MPEG formats.

[David Mullen ASC]

Right, but again it exists because of the inferiority of the storage format.

 

 

 

Has nothing to do with MPEG compression though, just the limitations of 10-bit recording.

 

S-Log was not developed to deal with MPEG compression. It first appeared as a copy of Panavision Genesis' PanaLog but in the Sony F35, both of which recorded to HDCAM-SR tape in 10-bit 4:4:4 or 4:2:2 using a fairly mild MPEG compression scheme. PanaLog and S-Log were created to store dynamic range in a form closer to the 10-bit Cineon Log format that D.I. colorists were used to working with from film scans. They were fairly mild Log gamma curves because the cameras only generated about 12-stops of dynamic range (which is one reason why Canon's C-Log is also fairly mild.) You could get similar dynamic range using a different gamma curve like Hypergamma but it wouldn't have had the headroom range of Log, which puts white on an 1-step grey scale at something like 70 IRE in order to record a couple of stops of overexposure detail. Hypergamma curves didn't place white so low though you could have done that by underexposing. But the shape of the Hypergamma curve was also different than with Log.

 

S-Log is just a gamma curve, it could be recorded uncompressed, it could be recorded at 16-bits, RGB, YUV, 4:4:4, 4:2:2, whatever... it has nothing to do with MPEG compression. That's not why it exists. It exists to fall into the log workflows leftover from film's D.I. color-correction days and the colorists who are used to working with images that way. It exists to fit 12 to 15 stops of dynamic range into 10-bits, which again, has nothing to do with compression, you can have 10-bit uncompressed recording.

[Satsuki Murashige]

You will notice, S-Log is used on cameras that shoot MPEG. Cameras that DON'T shoot MPEG... Arri, RED, Blackmagic, AJA, don't have S-Log because they don't need it.

Again, no. S-Log and its successors were intended for use on cameras recording uncompressed 12-bit video like the F23 and F35. It was an improvement of the Hypergamma curves used on the F900 camcorders. As video compression became more advanced, it became feasible to add Log curves to the lower-end cameras. And people were shooting 16-bit raw on the F65 before Blackmagic and AJA had even announced that they would be entering the camera manufacturer market.

 

S-Log2 and S-Log3 are still used when transcoding F65 raw footage. Blackmagic has a low contrast 'Film' gamma on their cameras for recording Prores which serves the same function. And the AJA Cion desperately needs an actual low contrast curve that is usable. What they currently have is essentially a baked-in Rec709 gamma. They're both trying to do same thing as S-Log, only not nearly as well.

[Stuart Brereton]

That's right, S-Log is it's own LOG curve, incompatible with every other system and looks nothing like real LOG, which even looks nothing like color negative.

 

 

Pro Res XQ is the best standard recording format out there today. It actually doesn't work in REC 709, it has far more dynamic range then even the standard Pro Res codec's. I use XQ all the time, mostly to color Alexa shots. Yes, we use Log - C on the Alexa material but that's only as a precaution, rather then a pre-requisite like with MPEG formats.

 

I don't understand what you mean when you say that S-Log is 'incompatible with every other system'. These curves are proprietary, they're not designed to be used on non Sony cameras.

[Satsuki Murashige]

Sony and Canon's incessant use of antiquated 8 bit 4:2:0 Rec 709 color space recording formats...

 

Sounds to me like your real beef is with the implementation of log on the lower end camera systems. Again, S-Log/2/3 were intended for use on F23/35/65/55/5 with their 10/12/16-bit recording systems. Everything else was an unintentional bonus.