S-Log for dummies?

[Jay Birch]

Can someone explain, in simple terms... how S-log works? (shooting and post)

I have read through various PDFs on the subject, but can't quite get my head around it.

Thanks in advance, Jay.

[lexicon]

Can someone explain, in simple terms... how S-log works? (shooting and post)

I have read through various PDFs on the subject, but can't quite get my head around it.

Thanks in advance, Jay.

This is an introduction to the basic notion of s-log and gamma curves in general (though no info about the details of camera operation and post). Just in case.

http://www.dvxuser.com/V6/showthread.php?230753-Understanding-Gamma-Cinegamma-Hypergamma-and-S-Log-%28Alister-Chapman%29

[Everts]

The video in this (http://www.dvxuser.com/V6/showthread.php?235918-Overview-of-F3-by-Sony-s-Peter-Crithary-(Rule-Boston-Camera)) thread talks about it but this iswhat I understand:

Its Sony's version of shooting RAW !
Basically the s-log files will be files that are untouched, not a baked in look. S-log looks very flat.
There are no contrast, brightness,color etc values applied to the image that has been recorded . It's not compressed like xdcam, avchd or hdv for that matter. It' s as uncompressed as one get nowadays:).The files are going to be huge !
It will, from what I've read, retain a good amount of detail in the highlights and shadows
This works great if you want to do colograding and VFX work.
S-log wont be necassary for every production but seems like a good option for Big budget productions.
Hope this helps !

Add: Feel free to correct me where Ive said something incorrect ...just to get the ball rolling !

[Jay Birch]

Thanks guys...

I have used RED One, so I guess it will work in a similar way (nail your exposure, in camera... do the rest in post)? I really like working in RAW, so if it is similar, that would be great.

I really love the look of the F3 and it hits my budget, as I take the step up from my tired HVX and DSLRs. It sounds like a system that I can get more involved with as I add to it and learn more with each project.

[mmm]

It's not compressed like xdcam, avchd or hdv for that matter. It' s as uncompressed as one get nowadays:).The files are going to be huge !


RAW, S-Log and compression are all different things. You can compress both S-Log and RAW data and almost all cameras do.

S-Log is a gamma curve that stretches blacks and compresses highlights so that you can manipulate the image extensively in post. It can theoretically be recorded to any codec although it really needs a high end codec (10 bit and moderate compression) due to the heavy manipulation that HAS to be done in the grade. Native S-Log looks flat and horrible.

[Joe Walker]

Here's what I think would really help this out, because I'm still a tad bit hazy on this myself, it'd be sweet if they would publish a sort of white paper detailing a beginning to end scenario of how to get the s-log material into an editor like FCP. Like what kind of transcoding software/hardware is needed/supported, what kind of support is there/workflow for the material in Apple Color, or DaVinci Resolve, etc. I mean a thoroughly detailed from beginning to end kind of instruction manual. We all know WHAT S-log is, what I want is a white paper that tells HOW we get it into FCP and work with if from there.

[G.P.]

My understanding is that Slog is an extreme gamma curve and nothing more. This is visual, and will not need anything special in post. Just like using a cine gamma, the curve is allowing a greater dynamic range to be captured. This is "burned in" the footage. Slog can then be graded to look like how you want.

This is how it was explained to me at least.

[Steve Castle]

Sony likes to call S-log "digital negative" because it captures the entire tonal range of the sensor. Confusing because Adobe's RAW standard DNG is also refereed to as a "digital negative". RAW itself is also bit of marketing speak, as some RAW (even on stills) also have NR applied and are compressed. A/D conversion is also done in different locations (on and off the sensor) in CCDs and CMOS so data 'off the sensor' can also be misleading.

The meanings we associate with 'raw' are gastronomic; usually something more primal like meats. That there needs to be a process that happens before we reach our final product we can consume. I suppose we could apply those meat terms to images as well, 'rare', 'medium-rare", "well-done", etc to the amount of compression, grading, debayering, etc., but then again any amount of 'cooking' by definition is no longer 'raw' (even a rare steak isn't raw). Which is why its all a misnomer if you aren't referring to uncompressed images off the sensor, but there really is also no point in being pedantic with the semantics.

Its a layer of marketing abstraction. What really matters is what you can do with the product as well as what you don't need to do. In the case of S-log it gives you a large latitude in grading but it won't give you options with demosaicing and you'll be working with 1080p rather than the effective resolution of the sensor (which is suppose to be ~3.4k). Sony's perspective is that they want to remove the unnecessary busy-work, your time is money, and that some things are better handled within the camera rather than off. You can argue both sides of this, and there are both up-sides and down-sides associated with each perspective.


There are whitepapers on S-log for those interested:

PDF:
http://www.sony.co.uk/res/attachment/file/66/1237476953066.pdf
http://pro.sony.com/bbsccms/assets/files/mkt/cinema/solutions/slog_manual.pdf

[Nate Weaver]

Yay for concise, egghead free explanations. Thanks Steve. It is my feeling as well that Sony is trying to find the sweet spot in time/expense/flexibility, and quietly say as much, rather than speak in hyperbole and extremes.

[powervideo]

What non-linear editors can interpret the S-log files? I'm particularly interested in integration with Premiere and After Effects CS5, and FCP. I can't find much info around in regard to posting S-log.

[powervideo]

Just checked. You can use the Cineon convertor utility in Premiere CS5 to convert S-log to linear, but I don't have an S-log clips so experimentation will have to wait... but it looks promising!

[Nate Weaver]

S-Log isn't a very aggressive log curve. As read somewhere else, most colorists just work with it as is without applying a LUT, and from what I've seen of S-Log I'd do the same in my Davinci. You can do the same with levels and gamma filters in any NLE.

A true Log encoded file, like a log DPX, or LogC from an Alexa is a bit more extreme and you're probably better off finding a LUT to decode.

[Joe Walker]

So basically, if I'm reading everyone correctly here, I can take either the XDCAM EX files from the SxS cards or (for example) the Pro Res clips from a Ki Pro Mini with S-Log as the already applied gamma curve into my editor of choice (FCP), and start editing and grading to my heart's content right away...correct? They'll already look nice and flat and grey and dull and then I just go in there and start messing with them in the grading app of my choice? IF this is the case, this makes me very happy :)

[CinemaElectronika]

Joe,

I have read at another forum that it is not possible...

Quote-

"No, that's not possible. The S-Log signal feeds out of the Dual HD-SDI ports and is 4:4:4 RGB. The Ki Pro, Nanoflash, and similar devices can only record 4:2:2, and should appropriately be attached to the single SDI spigot on the top right rear of the camera. That port is designed to be used for onset monitoring during S-Log recording, so the LUT can either be displayed or turned off, but the recorded result is baked in.

To use S-Log you would need to purchase the firmware upgrade, rent or buy an appropriate recorder, and then, (after any SxS offline editing) move to a suitable online edit suite.

I suspect if you only occasionally have use for S-Log that renting a recorder may be the most economical option."

Unquote-

http://www.dvinfo.net/forum/sony-xdcam-f3-cinealta/490530-s-log-cheap-n-easy.html#post1610185

Cheers!

[mmm]

...I can take either the XDCAM EX files from the SxS cards or (for example) the Pro Res clips from a Ki Pro Mini with S-Log as the already applied gamma curve into my editor of choice (FCP)

XDCAM EX is not ideal for S-Log anyway as it is only 8 bit and heavily compressed so it would likely fall apart during the extensive grading dictated by S-Log. Prores 4:4:4 would be better but would require a Dual Link recorder. I believe S-Log will only be available to those who purchase the Dual Link upgrade. Sony are hoping people will use their solid state HDCAM SR recorder and have suggested that the files generated will be able to be imported into FCP. My guess is they will be MXF files that need rewrapping to .movs.

Anyhow, once you manage to record to a suitable codec, yes you can take it straight into FCP or Colour. I'm not sure how the LUT files will interface with FCP, I'm not sure if Sony have clarified that yet.

EDIT:
As suggested below an offline-online is an option but I see no reason why a direct online is not possible on a modern, fast system.

[Joe Walker]

XDCAMSony are hoping people will use their solid state HDCAM SR recorder and have suggested that the files generated will be able to be imported into FCP. My guess is they will be MXF files that need rewrapping to .movs.

Anyhow, once you manage to record to a suitable codec, yes you can take it straight into FCP or Colour.


That makes sense, thanks for that clarification and that is good news that it's directly ingestible through L&T in FCP. This is good news, I've been privately telling myself that the workflow for this S-Log stuff CANNOT be more complex than RED's workflow or people would immediately discount it.

[Nate Weaver]

So basically, if I'm reading everyone correctly here, I can take either the XDCAM EX files from the SxS cards or (for example) the Pro Res clips from a Ki Pro Mini with S-Log as the already applied gamma curve into my editor of choice (FCP), and start editing and grading to my heart's content right away...correct? They'll already look nice and flat and grey and dull and then I just go in there and start messing with them in the grading app of my choice? IF this is the case, this makes me very happy :)

Yes. Except you can't get S-Log onto SxS cards, the firmware won't let you. And there's little point anyway.

But S-Log from AJA Ki will be VERY easy to deal with. And you'll be able to make it look like something even in your NLE.

[Viddovation]

My understanding was that the firmware would let you (when in S-Log mode) record to SxS either with the LUT applied, or with the washed out Slog look. Of course, either way, it's only intended for use as an offline edit.

[Nate Weaver]

My understanding was that the firmware would let you (when in S-Log mode) record to SxS either with the LUT applied, or with the washed out Slog look. Of course, either way, it's only intended for use as an offline edit.

I hope you're right, because even though I said it's of little use above, there are times when you need a flat look regardless, and S-Log would be the best way to get it.

It's only a problem if/when you shoot S-Log 8-bit, and you need to make it look normal or high-contrast. Then you'd be in trouble stretching that flat 8-bit image out.

[Viddovation]

In the Rule Boston presentation Peter Crithary indicated that when in S-log mode (which requires the paid firmware update), you can use the regular SDI output for a producer/director monitor, and you can preview with or without the LUT displayed. My understanding is that this signal could be recorded with an Aja or Nanoflash recorder. I'm not sure if the camera will permit you to use just one side of the dual link as a dedicated 10bit 4:2:2 HD-SDI out Slog for this purpose. (Meaning, if not - and recording to an Aja Ki Pro Mini, you owuld be forced to only preview the flat look while recording)

He also stated that the SxS can record either the flat look or the baked LUT look. Either way - it's XDCAM-EX compressed of course.

What I'm not certain of - is whether those are separate switches, or just one switch for both SxS and the 4:2:2 HD-SDI output. I have a suspicion just one switch flips all monitoring and recording, with the exception of the Dual link output.

[G.P.]

So as stated before, you can only use S-log once you paid the price for the upgrade. I could be wrong but I don't remember any talk at all about the 8bit having an Slog ability. They said it burns in the LUT on the 8bit while simultaneously recording the 4:4:4.

I have a 1 on 1 meeting with Sony tomorrow, I'll try to get clarification on all this. I'll have the camera in my hands as well, and should be able to take some close up photos for those of you who are still interested in the "almost production" models mounting hole positions.

[Viddovation]

Giuseppe,

I don't think 8bit is practical for Slog - I'm just repeating what I understood to be said in Rule Boston - which is that you can record the washed out look to SxS in XDCAM-EX (with paid upgrade). Not high enough fidelity to actually use for anything but the offline edit.

But hey - I'm talking out of my rear, just parroting what i'm hearing. So, I welcome any *real* information you have.

Can't wait. I'm feeling like it's going to be week 2 of February.

[Razz16mm]

RAW formats record the individual sensor photosite data values to a clip file, even if there is gain, noise reduction or compression of one kind or another applied. The demosaic and encoding to a standard image format take place in post camera processing.

Encoded video formats, however processed, record fully defined RGB or YCbCr pixels to a clip file. The demosaic or matrix processing and encoding take place in camera regardless of whether it is a single chip or 3-chip camera system. S-log is a gamma curve applied in camera then recorded to the encoded video file of whatever format. At the high end this would be at least a full 10 bit 4:4:4 format with minimal compression for maximum flexibility in post. With Sony this would be like HDCAMSR or whatever solid state file format Sony is creating for their new recorder and the F3. In FCP, Quicktime Prores 4444 would be the highest quality followed by Prores 422HQ. Theoretically if you ingest or transcode a video file, the recorded gamma curve should be preserved unchanged. Unfortunately this is not always the case. Quicktime has known gamma issues that hopefully will be corrected with the next update.

[Andrew Stone]

So as stated before, you can only use S-log once you paid the price for the upgrade. I could be wrong but I don't remember any talk at all about the 8bit having an Slog ability. They said it burns in the LUT on the 8bit while simultaneously recording the 4:4:4.

Yes, I have heard that several times in the recorded sessions from Sony marketing people. Slog is meant to be used in the 10bit 444 material. The logic behind the LUTs being burned into the 35mBit material is one is supposed to be using this material for proxies and, of course, the material couldn't handle the stretch in post so it is applied in a one-pass burn in before it is dithered down to 8bit 422.

Looking forward to your report.

BTW I heard, the cameras are supposed to be in the distribution channel in Canada on the 29th so you being in NYC could get your hands on a shipping demo unit tomorrow.

[Noel Evans]

The workflows for S-LOG on the F3 already exist. Apart from the S-Log whitepaper why not checkout the F35 user manual http://ws.sel.sony.com/PIPWebServices/RetrievePublicAsset/StepID/SEL-asset-152645/original/F35_OPERATION_MANUALAUG09REV04.pdf

open the PDF and search S-LOG. Will help fill some blanks for new users.

FWIW S-Log can be utilised through standard HD-SDI @ 10 bit. The dual link function enables 12bit 444 recording. Im not sure where / how these processes will effect overall DR. Need to wait and see the F3 for that.

[Duke M.]

Hypergamma with 4.2.2 should be mighty nice too. And very usable for 98% of all purposes.

[Noel Evans]

So now we know the camera will operate in S-log exactly the same as the F35, not sure why I thought it wouldnt, but wondered if there'd be a dumbed down version.

SO you need -

SLOG to REC.709 LUT applied for onset monitoring.
HDCAMSR deck or similar to capture

The beauty is in the ability to use the SXS cards to capture simultaneously for an offline edit.

So to use S-LOG you will need

Upgrade (any word on price?) by my estimates most likely 5-7K
HDCAM SR DECK around 10K

So on the base price of 13K for body you're looking around the $30k mark (without lenses) to be S-LOG ready. That's a huge reduction on what it cost previously to purchase an S-Log camera system. When released Im going to be looking for a rental to give it a run.

[Viddovation]

Rumors float with the camera upgrade price as low as $1k. Which really wouldn't suprise me horribly - it looks like we'll all be able to download the firmware update, but then you need a license key. This suggests the camera already has the capability, it's just turned off. If Sony doesn't make the license fairly affordable, I would assume there might be an independent effort to crack the license or the firmware entirely.

The lower the upgrade cost, the less incentive for those enterprising souls...

[Nate Weaver]

So now we know the camera will operate in S-log exactly the same as the F35, not sure why I thought it wouldnt, but wondered if there'd be a dumbed down version.

SO you need -

SLOG to REC.709 LUT applied for onset monitoring.
HDCAMSR deck or similar to capture

The beauty is in the ability to use the SXS cards to capture simultaneously for an offline edit.

So to use S-LOG you will need

Upgrade (any word on price?) by my estimates most likely 5-7K
HDCAM SR DECK around 10K

So on the base price of 13K for body you're looking around the $30k mark (without lenses) to be S-LOG ready. That's a huge reduction on what it cost previously to purchase an S-Log camera system. When released Im going to be looking for a rental to give it a run.

You can get the dynanamic range S-Log affords by recording to a Ki Mini. Lot less than $10K

[Noel Evans]

You can get the dynanamic range S-Log affords by recording to a Ki Mini. Lot less than $10K

No you cant. Anything recorded to the ki pro mini will have the applied LUT baked in. The RAW function is gone.

[Nate Weaver]

You would record with the LUT off.

[Razz16mm]

No you cant. Anything recorded to the ki pro mini will have the applied LUT baked in. The RAW function is gone.

Slog is still just a gamma curve applied to encoded video. It is not in any sense of the word raw. It is just better for grading for film transfer or digital cinema when recorded to a high end video format like HDCAM-SR.

[Noel Evans]

You would record with the LUT off.

Technically speaking S Log Gamma can be turned on like any other gamma setting and then recorded to the ki pro, yes, and thats a great function for an offline. But it defeats the purpose of what S Log is designed for.

[Noel Evans]

It is just better for grading for film transfer or digital cinema when recorded to a high end video format like HDCAM-SR.

Which is essentially my point as this is where you'd get all the benefits of S Log and its DR.

[Nate Weaver]

Technically speaking S Log Gamma can be turned on like any other gamma setting and then recorded to the ki pro, yes, and thats a great function for an offline. But it defeats the purpose of what S Log is designed for.

What is it designed for? Benefits of S-Log have nothing to do with 4:4:4, or HDCAM SR. I understand clearly that Sony would have you believe it's an all-or-nothing proposition with 4:4:4 and HDCAM SR, but if you really understand what's going on technically, S-Log by itself is very valuable.

As long as you record S-Log to a 10bit codec, in any fashion, you get it's benefits.

Lots of F35 and Genesis users do S-Log to 4:2:2 HDCAM SR mode. Been doing it for a while now...4:4:4 is usually saved for effects shots in my experience. Same with Alexa users, doing LogC to ProRes 4:2:2

[Nate Weaver]

Slog is still just a gamma curve applied to encoded video. It is not in any sense of the word raw.

As it's been told to me by one of the Sony Japanese project managers, it bypasses the detail processing block, and the color matrix block. So closer to RAW than just a gamma curve applied, but...

But generally, yes, I agree it's not RAW and it shouldn't be called such.

[Fohdeesha]

What is it designed for? Benefits of S-Log have nothing to do with 4:4:4, or HDCAM SR. I understand clearly that Sony would have you believe it's an all-or-nothing proposition with 4:4:4 and HDCAM SR, but if you really understand what's going on technically, S-Log by itself is very valuable.

As long as you record S-Log to a 10bit codec, in any fashion, you get it's benefits.

Lots of F35 and Genesis users do S-Log to 4:2:2 HDCAM SR mode. Been doing it for a while now...4:4:4 is usually saved for effects shots in my experience. Same with Alexa users, doing LogC to ProRes 4:2:2


Yeah, this guy. I've been trying to explain that logarithmic gamma curves have nothing to do with chroma subsampling for a while now. Bit depth is far, far more important when dealing with log output. 444 is saved for very very heavy post work, or if the output is going to be scaled up by a large percentage. 422 is visually indistinguishable from 444 unless you're dealing with a source outputting very very hard per-pixel contrast such as computer generated output with very small font. A digital cinema imaging sensor will not provide that much per-pixel contrast to push 422 to the point of plain visual distinction. An argument that can be made for 444 is that it is providing, indirectly, when converted from ycbcr to an rgb color space, 1:1 rgb output which would allow you to an extent adjust white balance in post. But you are still dealing with the already exposed r g and b channels as you are with 422, and in my experience an rgb offset adjustment holds up just as solidly on a 422 DI as a 444. (Unless of course your source is dealing with under and over exposure information, such as a cineon or DPX sequence). 444 is not a magical format that allows you to fix things you got wrong the first time around, save that kind of thing for formats dealing with raw sensor output and over/under information. And even then, you still only have a little leeway.


Here's a nice comparison (albeit grainy), you're going to have to save it and zoom way in to see any difference. The source was a 12 bit RGB scan of 65mm TODD-AO


http://img217.imageshack.us/img217/3186/chromasamplingmethods.png



All that said and done, from sony's whitepaper it still seems they are not allowing s-log output out of a single HDSDI port. I don't want to sound like a conspiracy theorist, but it honestly sounds like they are protecting their market infrastructure, and don't want you taking advantage of something as high-end as logarithmic output without spending more money on an HDCAM deck first. I dunno though, could be several reasons! We'll find out for sure when the firmware release comes out.

[Viddovation]

From the Rule Boston presentation, it was stated that once you have the S-Log upgrade you could turn on or off LUT for monitoring purposes. This would imply that With the LUT off it should be possible to record 10bit 4:2:2 out of the "monitoring" HD-SDI port. If this is indeed true, Aja Ki Pro Mini should do the trick.

Also, the brochure says you'll be able to select either Dual Link or 3G SDI. And there's no requirement to use a Sony recorder. For studio or narrative work one might be able to get away with a $1000 decklink Extreme HD 3D card in a Mac Pro. If Sony's offering is priced over $10k, people will get the Cinedeck Extreme instead, which is $10k, records to off the shelf laptop harddrives, and has a monitor built in.

[Nate Weaver]

I have 10 dollars that says when the S-Log update hits the ground, it will have an option to make that Dual Link A channel output just a straight 4:2:2 10 bit output. People need to be able to step that down to keep compatibility on F35 shoots, plenty of which shoot 4:2:2. Tethered, no less.

[Andrew Stone]

Makes sense Nate. Hope you are correct. One thing to keep in mind about the Cinedeck, as amazing a piece of technology as it is, the unit is known to be a bit unstable in a production environment. Reports of having to reboot the unit on the set are known to happen and it can put things on pause for 10 minutes while the thing gets back up and running again. You can be pretty sure the Sony recorder will just work.

[powervideo]

It would be great to hook up a Ki Pro Mini. It's been recently reported that it will support 25P in 60Hz tape Varicams so I am very interested in addition to how it can work with S-log in 4:2:2 on the F3. AJA has been deathly quiet about the Ki Pro as to when it's shipping. It's been in the trade mags for months. I would buy it tomorrow if it was available.

[Nate Weaver]

BTW, here is an S-Log image taken from a white-paper test of the F35 by Alfonso Parra:

http://www.alfonsoparra.com/php/baul/F35TestEV.pdf

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There's nothing exotic or extreme about it, the gamma curve is gentle, and you could easily edit without modification or a LUT.

In fact, the gamma modification is so mild in fact, I'd probably elect not to use LUTs for it in my Davinci. It's just more simple and direct, and I can see immediately how much shadow/highlight detail I have to work with rather than what a LUT gives me, which always requires some screwing around to find out what's really in the image.

Not to mention, anybody who's colored flat Red transcodes in 10bit will be at home as well, I'd think.

Compare to Alexa Log-C:

http://vimeo.com/18316283 (I colored this test, didn't shoot it)

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Not completely apparent here, but Log-C is really kinda out there. You'd probably want to use a LUT with it...attempting to bring things close to normal with the lift, gamma, and gain wheels gets it close but not 100% right. It needs a more careful curve.

By the way, it's the Alexa tests that I did with my friend, that let me in on something I never guessed: a quality, low-noise 10-bit image can be just as good or better than Red RAW, which for the prior 2 years is all I've worked with. We did Alexa at 10bits Prores 4:2:2, and 12bit Prores 4:4:4 in LogC for both, and the difference was very, very minor. And that's after putting some really extreme looks on the footage.

Which has led me to this camera.

[CinemaElectronika]

It would be great to hook up a Ki Pro Mini. It's been recently reported that it will support 25P in 60Hz tape Varicams so I am very interested in addition to how it can work with S-log in 4:2:2 on the F3. AJA has been deathly quiet about the Ki Pro as to when it's shipping. It's been in the trade mags for months. I would buy it tomorrow if it was available.

AJA Ships Ki Pro Mini Portable Flash Disk Recorder

http://www.aja.com/news/index_article.php?id=137

[lexicon]

Mitch Gross from AbelCine shot this video illustrating the differences between recording in standard gamma (such as REC709) versus LOG recording:

http://blog.abelcine.com/2011/02/03/why-shoot-in-log/

[Yak]

here is some more helpful info on s-log
http://www.xdcam-user.com/?s=s-log

[Noel Evans]

In fact the uncorrected image is so flat and washed out that it can make judging the optimum exposure difficult and crews using S-Log will often use traditional light meters to set the exposure rather than a monitor or rely on zebras and known references such as grey cards. For on set monitoring with S-Log you need to apply a LUT (look Up Table) to the cameras output. A LUT is in effect a reverse gamma curve that cancels out the S-Log curve so that the image you see on the monitor is closer to a standard gamma image or your desired final pictures. The problem with this though is that the monitor is now no longer showing the full contrast range being captured and recorded so accurate exposure assessment can be tricky as you may want to bias your exposure range towards light or dark depending on how you will grade the final production. In addition because you absolutely must adjust the image in post production quite heavily to get an acceptable and pleasing image it is vital that the recording method is up to the job. Highly compressed 8 bit codecs are not good enough for S-Log. That’s why S-Log is normally recorded using 10 bit 4:4:4 with very low compression ratios. Any compression artefacts can become exaggerated when the image is manipulated and pushed and pulled in the grade to give a pleasing image. You could use 4:2:2 10 bit at a push, but the chroma sub sampling may lead to banding in highly saturated areas, really Hypergammas and Cinegammas are better suited to 4:2:2 and S-Log is best reserved for 4:4:4.


From the xdcam user article. This is the point Ive been trying to make. Can you do it in 4:2:2, sure. But it you dont have the chroma stretch of 444.

At the end of the day I think hypergamma will be more than enough for most applications.

[Fohdeesha]

Dude, there is no "chroma stretch" in 4:2:2. You get banding from from stretching a low bit depth image, such as 8 bit, not from chroma subsampling. Unless it's way way down, like 4:2:0. But even then, you run into reduced bit depth artifacts way before chroma subsampling artifacts. Either way this is irrelevant, as gamma is a function of luma, not chroma. The "stretching" going on natively when working with log is in the luma domain.

F35, Genesis, and Viper users record 4:2:2 log curves ALL the time, and those cameras log curves are much more aggressive, and require much further "stretching" to get a "normal" looking image than sony's s-log will. And they rarely run into artifacts. It almost seems like you don't want people using s-log. It's very sad to see someone as intelligent and respected as Alister Chapman say something like "S-Log is best reserved for 4:4:4." What everyone seems to be forgetting is that gamma is a function of LUMA. 4:2:2 compresses (very efficiently) CHROMA. All your luma information is still there, to be pushed or pulled into or out of a linearized looking fashion.

So I'll say it one last time - Due to the specification of dual link sdi - whether sony allows s-log out of a single port SDI or not - it won't matter. When s-log is operating in dual link, the first link is a valid 4:2:2 10 bit feed, that can easily be sent to a ki pro and recorded in s-log. And it will be beautiful. And you will not run into banding. And it will be visually indistinguishable from 4:4:4, unless you're zoomed in or scaled up around 200%. When you're working with 4:2:2, the internal engine of whatever program you're using has plenty of information when it interpolates to 444 rgb internally, and the interpolation is almost spot on. The artifacts people run into when doing hard color correction is 95% of the time reduced bit depth.

[Duke M.]

Meh. Its a new camera with new (to most people) outputs. There is bound to be some misinformation until we can all get our hands on them. Its happened with all the new cameras.

I'm betting the 8bit Nano files will be perfect for hypergammas, but might not fair as well with the s-log. I'll reserve that for actual testing though.

[Fohdeesha]

Yeah, the nano should be great for the hypergammas. However s-log will not hold up in an 8 bit space, with only 256 values per channel available to assign the sensors entire range of output.

[Noel Evans]

First off, my bad on terminology - I should have said "reach" not stretch.

Secondly, Im not attacking you personally here. I just happen to agree with the article. Now weather I do or not, does not have any effect on you or anyone else, or their ability to shoot on an F3 and make stunning images - I think we are going to see many of those as the camera is released.


Dude, there is no "chroma stretch" in 4:2:2. You get banding from from stretching a low bit depth image, such as 8 bit, not from chroma subsampling. Unless it's way way down, like 4:2:0. But even then, you run into reduced bit depth artifacts way before chroma subsampling artifacts. Either way this is irrelevant, as gamma is a function of luma, not chroma. The "stretching" going on natively when working with log is in the luma domain.

F35, Genesis, and Viper users record 4:2:2 log curves ALL the time, and those cameras log curves are much more aggressive, and require much further "stretching" to get a "normal" looking image than sony's s-log will. And they rarely run into artifacts. It almost seems like you don't want people using s-log. It's very sad to see someone as intelligent and respected as Alister Chapman say something like "S-Log is best reserved for 4:4:4." What everyone seems to be forgetting is that gamma is a function of LUMA. 4:2:2 compresses (very efficiently) CHROMA. All your luma information is still there, to be pushed or pulled into or out of a linearized looking fashion.

So I'll say it one last time - Due to the specification of dual link sdi - whether sony allows s-log out of a single port SDI or not - it won't matter. When s-log is operating in dual link, the first link is a valid 4:2:2 10 bit feed, that can easily be sent to a ki pro and recorded in s-log. And it will be beautiful. And you will not run into banding. And it will be visually indistinguishable from 4:4:4, unless you're zoomed in or scaled up around 200%. When you're working with 4:2:2, the internal engine of whatever program you're using has plenty of information when it interpolates to 444 rgb internally, and the interpolation is almost spot on. The artifacts people run into when doing hard color correction is 95% of the time reduced bit depth. This should all be common knowledge for someone advertising a grading suite in his signature. Sorry if this sounds harsh, but I'm just appalled at all the misinformation being thrown around here with the advent of this latest crop of cameras. I'd be happy to link you to some 4:2:2 log video, and you can see for yourself

[Fohdeesha]

Understandable. Sorry about how harsh my post came off as, I'm not a morning person :) I just wanted to clarify that technically, 4:2:2 chroma subsampling does not have a waywardly adverse effect on log curves, and that stating it is "best reserved for 4:4:4" is very technically misleading, and I feel that article could stop people from experimenting with s-log and reaping it's glorious benefits. with 4:2:2, all your full raster luma information is still there, and this is what log curves deal with. This is why DIT's have been shooting 4:2:2 log on f35's, vipers, genesis, and alexas for some time now, and the results are beautiful with tons of latitude. Here's a couple Prores 4:2:2 LogC files shot on an Alexa for you to play with, if you're curious: (I dare you to find artifacts :) )

http://www.cinematography.net/Alexa/Interior/Int_PR422HQ_LogC.mov

http://www.cinematography.net/Alexa/Exterior/Ext_PR422HQ_LogC.mov

[Nate Weaver]

There is so much confusion out there about what chroma subsampling and what it is. And moreover how when it's bad, how it affects making good images. Chroma subsampling doesn't cause banding. Nor does it cause limitations in how far you can alter gamma/exposure. It causes blurring/aliasing on edges comprised of saturated colors. That's it. Oh, and it compromises chroma keying. Because that saturated green edge has less resolution than the details of the wispy hair you're trying to key...as an example.

In color correction, it matters if say you have a red ball on a blue sky that's relatively unsaturated...and you want to crank the saturation. Do that on a 4:2:0 image, and the apparent sharpness will go down. If it's a picture with lots of fine, fine detail in that unsaturated color and you go CRANK that color up, the fine detail will get nasty and aliased. Which is hard to see clearly in an HD image. It just starts looking nasty in a subtle way that's hard to describe. That's my definition of an image "falling apart".

I've been coloring video professionally for a number of years now, and it's importance definitely takes a backseat to things like bit-deph, compression ratio/codec efficiency, and camera noise level.

[Fohdeesha]

Bingo! :)

[nomad-3]

I'd say there is also some more chroma noise introduced by subsampling, since you are averaging out neighboring colors to do it (similar to quantization noise when your bit depth is limited). So, in a soft transition between strong colors you may see some more chroma noise after massive manipulations. But I believe you rarely need such massive manipulation that it will show in 4:2:2 vs. 4:4:4 (I can see it in quite a few situations on 4:2:0, though).

[tom.wong]

I'd say there is also some more chroma noise introduced by subsampling, since you are averaging out neighboring colors to do it (similar to quantization noise when your bit depth is limited). So, in a soft transition between strong colors you may see some more chroma noise after massive manipulations. But I believe you rarely need such massive manipulation that it will show in 4:2:2 vs. 4:4:4 (I can see it in quite a few situations on 4:2:0, though).

wouldn't say rare, just situation dependent.