Everythign you ever wanted to know about sLog but was afraid to ask...

[Timur Civan]

This is all covered on my Blog as well, with a bit more detail.
T.STOPS: Sony F3 - sLog Testing

I got sLog yesterday, and i finally have had a chance to test it out a bit.

Below you will see, sLog raw Tiffs, and graded Tiffs. Feel free to DL and grade. For reference, i shot the skin tones at about 35 IRE to Uncompressed Quicktime - 3G 444 sLog, @ 0dB F16, with a 2k Par with double diffusion, and in the shot is a 40w Compact fluorescent. no Fill.

The skin tone is metered at a T16, with the highlight +1 stop, and the fluorescent bulb itself is +9 stops, and the top of the puppy's head is +3 stops over key.

I am flabbergasted that i can own a camera that has this much imaging power.


Uncompressed TIFF http://www.timurcivan.com/downloads/me_log_1.1.3.tif

Quickly graded on a Davinci Resolve to put some contrast and secondaries in the image so you can see what its supposed to look like.


Uncompressed TIFF http://www.timurcivan.com/downloads/me_delog_1.1.2.tif



By the way..... 444 IS everything its cracked up to be.

Some extreme lowlight grain testing...

This was lit with 1 single candle. Cooke Panchros @T2.8 @ 0dB on The Sony F3 with sLog.

MIND YOU: when in sLog your sensitvity doubles. So 0dB, is now 1600 ISO, 6dB is 3200 ISO etc.... 18dB is 12,800ISO

They do get grainy, but its REMARKABLY clean considering the ISO.

sLog Raw Out of camera (DL the 1080p TIFF)

TIFF: http://www.timurcivan.com/downloads/0dblog_1.1.1.tif

0dB Graded

http://www.timurcivan.com/downloads/0dbdelog_1.1.3.tif

6dB

6dB Delogged TIFF http://www.timurcivan.com/downloads/6dbdelog_1.2.2.tif
6dB RAW LOG TIFF http://www.timurcivan.com/downloads/6dblog_1.2.1.tif

12dB

12dB delogged TIFF http://www.timurcivan.com/downloads/12dbdelog_1.3.2.tif
12dB RAW LOG TIFF http://www.timurcivan.com/downloads/12dblog_1.3.3.tif

18dB

18dB deLogged TIFF http://www.timurcivan.com/downloads/18dbdelog_1.4.2.tif
18dB RAW LOG TIFF http://www.timurcivan.com/downloads/18dblog_1.4.1.tif


Also, just for kicks we recorded log to xdcam, to see if we could grade it. Did not work one bit. Log has to go offboard. Too bad.

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Todays Test:

Sony F3 - sLog Test - on Vimeo

1 Sony F3 w/ sLog update
1 Ki Pro Mini
1 set Cooke iPanchros
1 DaVinci Resolve

Objective, to discover where sLog should be exposed, How it should be treated in post, and what the difference between 709 standard Gammas and sLog in post, and acqusition.

From previous testing the F3 w/ sLog clips to white @ 6 stops over key. Using this information i metered the brightest highlights in each scene to +6 stops, JUST touching the clip point ( or what i thought was the clip point). The dark end of the scale fell to where it fell.

The goal being to see how far down you can drag up the image, and how conservative i have to be with using fill light to maintain an image in the black section of the scene.

OK, So here's the skinny. You have to expose just as carefully as you would with any other medium. The sLog w/ Offboard capture gives you incredible room to adjust and manipulate later, however like every camera, the closer you get to perfect in camera, exposure wise, the more Oomph your image will have after delogging. That said, 10bit 422 ( and especially 444 capture) gives you and INSANE amount of room to fudge.

For kicks we recorded the REC709 180% LUT as well and tried to match them to see if matching was possible. The Footage can be massaged into a similar looking image, but the highlight quality, grain structure, and shadow retention goes out the window. If you need a very high dynaic range shot with and F3 and dont have sLog, if you at least have a KI Mini, you can get SOMETHING.... it wont be as pretty, but it'll be there.

These compositions are boring, very boring, but they are carefully chosen. to reflect situations i've run in to the last few years, on various shots that have always bothered me and made me wish i had the "Infinite Dynamic Range" as MacGregor so eloquently put it. Well, for the most part, we have that now, at an indie price point. Yes, the Alexa is better.... by about a stop. (when you hit the 13.5+ zone 1 stop actually becomes a lot) but at 1/3 the price, this is terrifying performance. And the fact that i own it, and its paid it self off in 3 months, and i dont have a 70k mill stone around my neck is simply phenomenal.

The thing when shooting sLog thats tricky; it goes against every instinct you have as a DP. You have to under expose, so far down that you think "Theres NOTHIGN THERE!!!!! WHAT THE #$%^ I'M DOOING!?!?!?!?" but use your exposure tools, use your false color, use your wave form. Skin tones stay at 35IRE, High lights on skin @ 40-45 IRE. Dont worry, its ALLLLL there.... The trick is to use spot meter to see how many stops you are from one point to another in the scene. Get a Grey card, light your set, get your highlights to about +6 stops over key, then set the Grey card @ 35IRE with the waveform. You should be set.

The truth is i dont know why, but for some reason, color information, because of the sLog, is more accurate, pleasing, and is retained all the way up to the clipping point. Even 10bit capture on regular 709 doesnt have the same amount of detail in highlights. Its just not retained in the same way. Pay attention to the highlights in the forearms in the "dramatic" lighting shots.

I highly reccomend downloaing the 2gig low compression version to really see in full resolution whats going on, and how Frigging sharp the F3 really is.

[Alister Chapman]

Sorry Timur, but I don't agree with your exposure methodology.
Trying to set skin tones at a fixed level of 35IRE and skin highlights at 45IRE or any other fixed level is a throw back to conventional video where you had limited grading latitude. The whole point of high dynamic range capture followed by a grade to restore/shift levels is that being consistent with things like skin tones from shot to shot is much less relevant and this gives you the freedom to over expose or under expose depending on whether you want to preserve shadows or highlights. As you say accurate exposure is still important and you do still need to think about what your end shot will look like. If you want a dark moody shot you want to expose and light accordingly possibly completely going against convention and bringing shadows up in brightness so you don't run into clipping issues in deep shadows during the grade (as in your first example). In this scenario you may end up with skin tones much higher than 35IRE. For a very bright scene you may need to go the other way.

Skin tones at 35IRE is a sure fire way to introduce a lot of additional noise to those areas of the picture as bring them up to the more traditional 65IRE in post will nearly double the grain in those areas, so I would really want my skin tones at a higher level than this, it will also help the colourist separate faces etc from the general background more easily during the grade.

S-Log does give you a lot more latitude, but latitude is not just highlight handling, it is the ability to handle a broad range from dark to light. Having more latitude does not automatically mean you should under expose every shot. One of the nice things with S-Log is that while highlights will still clip if overexposed, the roll off into clipping tends to be a lot more film-like due to the increased DR, so overexposure (like the lamp in you first example) is much less stark and thus something that we don't need to be quite so afraid of.

[Timur Civan]

I am more of the opinion that keeping it all the same, maintains your consistency of exposure and grain structure through the scene. In Log, middle grey is 30IRE, This is a clean safe point to work from in post.

Yes of course there is room for variation, but in general for the average portrait shot found in an interview, or standard coverage in a narrative scene, 35-45 is where its gotta be. Tha'ts just how log works, same with Alexa and Genesis. If you place the subject any higher when the image is deLogged, they will seem over exposed. Setting skin @ 35IRE isnt under exposing. That's how you expose for a LOG image. This is not simply put "more Dynamic Range", its a method of capturing that information in an image that looks unnatural till deLogged. The F3 is is relatively grainless, thus pushing up the mids really gives no noise penalty. The shot where the subject, Tom, walks from the shadow of the trees into the sun, is a prime example of why you HAVE to keep it at 35. The central midpoint in the exposure range is right at 35IRE. 7.5 stops below, and 6 stops above. I set him @ 30 IRE. The standard exposure for the scene was T8 (skin would have been @ 35 IRE), i had Tom @ T5.6(30IRE), and when he was in the sun he would have been a T22 (75 IRE). I kept him a stop under to maintain the natural look of being in a shadow, while leaving head room for the move into the sun.

If you prefer to leave the Log image as is, and shoot with that look, then yes the 35IRE will seem dark, but this is why we have 709 LUT;s in place.

[Doug Jensen]

Timur, if I am reading your comments correctly it seems that you are saying "In Log, middle grey is 35IRE" and you are also saying that skintones should be exposed around 35IRE. How can that be? 18% gray is a lot darker than your average skintone. How can they both be 35IRE? If I put skintones around 35IRE, then that means 18% gray is going to be more like 25IRE. Defintately underexposed.

I agree totally with Alister. I think your method underexposes needlessly by about 2 stops. I don't know how log works on other cameras, but on the F3, if middle gray is exposed at 35IRE, then that puts bright white at only 80-82IRE. There's no way I need that much headroom. Log or no log, exposing close to the correct level is still the best way -- as long as you don't blow out the whites. That is the key -- don't blow out the whites. I prefer to shoot with middle gray at about 50% and I still have plenty of headroom.

I don't mean to be critical of your footage, but all your de-logged examples look flat, dull, and lifeless to me. I'm sorry if that sounds harsh, because I don't mean to be unnecessarily negative. However, I know without a doubt that I could have done better in some of those situations with my normal custom Picture Profile, no S-LOG, no external recorder, and no time spent grading.

[Timur Civan]

These shots are simply Delogged, meaning white approaches 100, and black touches 0. There is no grade to speak of, and they are exposed to maintain the maximum the scene can muster. Naturally anything can be exposed where ever you want, but thats not the purpose of what im doing here.

I'm learning this new gamma curve.... ( no pun intended). IT seems skintones like to be a touch darker, because its the middle point of the exposure scale. The F3 holds 7.5 below and 6 above. The signal is so clean there is no noise penalty for boosting it. Scouts honor. Try it out..

Its how i like to expose, and since the camera is so quiet i have the luxury to buy an incredible amount of highlight detail back.

As far as making "prettier" images, that was not the exercise. In post, after delogging, you can reapply an aggressive curve that gives the image lots of punch, and color. But you have the luxury of choosing where white and black encroach on the image.

Also having lights, and the right time of day helps too. Shooting between 11am and 4pm isnt exactly the best time to shoot, but it is the most challenging for digital. Thats why we did it.

cheers

[Timur Civan]

Also Doug you are right, Skin is a stop over middle grey, i ment to type 18% is 30 IRE. 35 being skin tone. ( in log the stops are closer together towards the bottom of the scale)

I corrected the post above.

However, i was taught this method on alexa and from several friends who worked with PanaLog. The F3 may be a different curve. This is the point of all this testing to learn how to do it right. :)

[Alister Chapman]

Originally Posted by Timur Civan

( in log the stops are closer together towards the bottom of the scale)

You have to be a little careful with that statement. If the scale is Log then the stops are evenly spaced across the exposure range. If it's linear then it is true, BUT up to about 50IRE or the first 3.5 to 4 stops there is almost no difference between Sony S-Log and Rec-709 so if you expose skin at 35IRE you are notably underexposing faces and that forces a significant push in post with the associated noise penalty that will incur. Also taking references like setting middle grey to a specific exposure is a throw back to film where you had no choice but to rely on a light meter. With video we can see instantly exactly what we are capturing. Film and video behave in very different ways and applying film techniques directly to video is not always a good way to go as it often ties your hands unnecessarily.

Here's my take on the situation:
A couple of caveat's first: Most of my F3 S-Log work has been in indoor situations as I have been tied to recording to various less than portable 10 bit recording solutions, so very often using a restricted contrast range. I've only owned S-Log for my F3's for a short while now, so many of my earlier tests were on 3rd party cameras, some of these were beta cameras.

I have not fully tied down my workflow. I'm still investigating external recorders, everything from the Ninja, Ki-Pro, Sound Devices and of course Gemini. I'm leaning very heavily towards the Gemini as I do a lot of 3D and the Gemini LCD makes for a fantastic monitor.

Back to exposure, this is obviously going to be a slightly contentious area as there is no real "correct way to do it". While I might not agree with pinning skin tones or anything else for that matter to one particular brightness range, that does not mean I'm right and anyone else is wrong, it is just a different approach and methodology. At the end of the day, if it works for you and gets the results you want, then that will be the way you should go, these things are not black and white, right or wrong.

A very un-scientific test that a did a while back was an eye opener for me. I was exploring the finite latitude of S-Log compared to the F3's cinegammas. I did a couple of very quick shots, you will find them here: PMW-F3 S-Log and Cinegamma quick look. | XDCAM-USER.COM

When I filmed these two examples I was looking at dynamic range, I exposed in both cases with the bright whites of the back wall behind the girl just going into clipping so I could then see how far into the shadows I could still see useable detail. I was not concerned about getting the skin tone exposure correct. When you look at the raw S-Log it really looks pretty shocking and even I wasn't sure how much I would recover from the highlights and the girl is a good stop overexposed. However after a very simple grade using only the colour corrector in FCP, I was able to extract a pretty good looking image and it's amazing how much detail was actually retained in what looked like over exposed high lights. The Girl's skin tones which I've measured at over 85IRE came down very nicely without any issue. A proper grade in a grading suite would I'm sure improve them still further.

What this very crude test told me was that you have incredible flexibility over where you put skin tones, you can comfortably move them up and down in post by a quite significant margin. Also seemingly overexposed S-Log highlights will contain surprisingly large amounts of fully recoverable detail. In the same test I graded the Cinegamma material to try to recover the shadow detail that was lost by due to the reduced latitude. This involved attempting to pull up the shadow areas. While this was somewhat successful, what became very apparent was the way the noise increased quite dramatically, this is something I have been aware of since I started using Cinegammas many years ago, pulling levels up will increase noise.

So… when I expose with Cinegammas (as I have done for many years) I have always been very conscious of the noticeable effect on noise that trying to lift underexposed parts of the image has. Very often in the grade the limiting factor as to how far you can push the image has been down to the noise floor and noise effects. This has mainly been with Sony EX's which have a 54db noise floor.

Now with the F3 with have a dilemma! S-Log gives us another +1.5ish stops of dynamic range, but at the expense of a +6db increase in noise due to the +1 stop increase in sensitivity associated with S-Log.

Lets say for example that we shoot a shot with a person and we under expose the face by one stop (one stop = 6db).

If we do this with with the Cinegammas and then grade the shot bringing the face up one stop then the noise will increase by 6db from the base noise figure of 63db giving a final noise figure of approx 57db (in the case of signal to noise, a lower number is worse).

If we do this with S-Log and then grade the shot bringing up the face by one stop then the noise will increase by 6db from the base of 57db giving a final noise figure of approx 51db, noticeably noisier than a correctly exposed EX1.

So the S-Log image becomes twice as noisy as the cinegamma material and therefore depending on the footage, it is quite possible that you would actually be able to push mid ranges and shadows further with Cinegammas than S-log in an underexposed situation due to noise issues. The S-Log and Cinegamma curves are almost identical up to over 50IRE, so latitude performance under 50IRE is essentially the same. See the charts on this page: S-Log. A Further In Depth Look. | XDCAM-USER.COM

If I get some time at IBC I might see if I can set up some tests to show this in practice.

Now given that I have seen for myself how with S-Log skin tones can be pushed down just as much as up in post, I tend to try to evaluate the entire scene and consider how it will be treated in post before choosing how to expose. In particular I don't want to expose so that the entire scene will end up being lifted by a significant amount, as noise will become a concern. This isn't always going to be possible as there are many shots where highlights have to be protected, but I don't believe that you have to set skins etc at any particular narrow brightness range, I tend to let skin ride somewhere between 45IRE and 70IRE depending on the overall scene.

If I can fit the contrast range of the scene into the 11.5 stops of a cinegamma then I will often use the cinegammas over S-Log because of the noise improvement. S-Log comes into it's own where you have an extreme contrast range that needs to be captured. However at the end of the day you do still have to remember that the end display device is unlikely to be able to display more than 7 stops with any accuracy!

One tool I have found very useful is the BlackMagic HDLink box. I often use this to connect to a monitor as it has the ability to apply LUT's very quickly. If you have a PC connected to the HDLink you can go in an modify the LUT curve in real time and in effect do an on-set grade. The HDLink is only $499 USD.

[Timur Civan]

Hmmmm.... Look where middle grey falls.....

OK this is gonna take some additional testing.

[Charles Papert]

Gents:

Very slightly off-topic but I am investigating F3 with S-log for an upcoming series, where the simplification of post workflow has to be taken into consideration. Need to deliver dailies to network (so REC709) but want to retain some control via shooting log, while keeping files manageable in size. I understand that one can record 10 bit 422 out of the camera as well as 444, but can I also record a 709 proxy at the same time? and do I understand correctly that working in 422 will eliminate the possibility of monitoring in 709 out of the camera? (can't be feeding a raw image to the director). Is 444 my only option in this scenario? Adding Gemini's to the rental package will start to move it towards Alexa territory price-wise and I fear that I will get forced to shoot non-log as a result.

Thanks for suggestions on this.

[Timur Civan]

well, you can get a cheap recorder, like this:

http://www.bhphotovideo.com/c/product/625609-REG/Panasonic_AG_HMR10_AG_HMR10_AVCCAM_Memory_Card.html
And after you use the Black Magic LUT box that Alister suggeted record the LUT image that goes out to video village.

Basically it will go something liek this, LOG SDI -> KI PRO/PIX -> Onboard monitor -> LUT BOX -> AVC recorder -> Video Village. You have ot run all this through the DIT anyway, so its really just a box in the video village path. it will record by self through timecode, and you just seliver AVC for the mto view dalies. i think it even plays back...

[Alister Chapman]

In standard gamma video video terms middle grey (or at least the value that to our eyes appears halfway between light and dark) is approx 42 - 45IRE.

An 18% Grey card is a card that most people would perceive as being half way between a pure white card and a completely black card. Caucasian faces are typically 1.5 stops brighter than middle grey.

So subjectively an 18% middle grey card should give you an exposure of around 42-45IRE. But in reality true middle grey is not 18%, ANSI middle grey is actually 12%, there was a lot of research done about this long before Kodak introduced their 18% grey cards, but as our eyes have a hard job distinguishing between subtle variations in dark tones compared to light tones most people would have a hard time telling any difference between 12% and 18%.

The use of grey cards for exposure is a highly contentious area for many reasons. Yes, for film it had it's uses, you needed some kind of starting point, but for video or digital stills it is of little use IMHO. A grey card will not tell you anything about the contrast range of your scene in particular what's going on in shadows or shade. While there is consistently a 2.3 stop difference between middle 18% grey and the total diffuse light reflected from a scene it tells us nothing about whats going on in shadow areas, direct light sources including the sky or lamps or specular highlights and it tends to be these areas that make or break a shot, not whether mid grey is 42IRE or not. At the end of the day a waveform monitor or monitor are much better tools for judging exposure than using a grey card and fixing it at 42 IRE with spot metering.

[Chris Medico]

Originally Posted by Charles Papert

Gents:

Very slightly off-topic but I am investigating F3 with S-log for an upcoming series, where the simplification of post workflow has to be taken into consideration. Need to deliver dailies to network (so REC709) but want to retain some control via shooting log, while keeping files manageable in size. I understand that one can record 10 bit 422 out of the camera as well as 444, but can I also record a 709 proxy at the same time? and do I understand correctly that working in 422 will eliminate the possibility of monitoring in 709 out of the camera? (can't be feeding a raw image to the director). Is 444 my only option in this scenario? Adding Gemini's to the rental package will start to move it towards Alexa territory price-wise and I fear that I will get forced to shoot non-log as a result.

Thanks for suggestions on this.

Charles you can apply a 709 LUT to the monitor output while recording LOG on SDI outputs A and B. You would be able to record the 709 signal and/or display it as a viewfinder/directors monitor. All the SDI outputs are 10bit.

Depending on the contrast range of your scene you may not need to go LOG at all. Just go with the 10bit external recorder with one of the built in gama curves.

I'm personally going the 422/10bit route using the Sound Devices PIX240. Uncompressed sounds nice till you see what that does to your media requirements and post workflows. I'm not interested in that headache.

On the fence buying LOG for my personal F3. I've not had a lot of call for it yet.

[Charles Papert]

Yeah, I've been tracking my colleague's work on TV shows with the Alexa and seeing some varying approaches. Arrirraw is of course the preference but over at "Community", they are outputting 709 and recording to XDCAM disk, which is a workflow they have maintained since the beginning. That show is mostly on stage so easy enough to control values. Mine is going to be all on location and I'd like the flexibility of raw/log recording to give me more flexibility in day exteriors, interiors with hot windows etc.

[Chris Medico]

Also meant to add that the monitor LUT selected is recorded to the SXS cards.

I hope the PIX240 recorders are available soon.