Category Archives: PXW-FS5

The great S-Log2 or S-Log3 debate.

I’ve written about this many times before, but still it comes up again and again. Which is better? Which should I use? I hear all kinds of crazy comments and a lot of incorrect information, so first of all lets dispel a few myths:

S-Log2 captures more dynamic range than S-Log3, it goes to a higher level on the waveform, S-Log3 clips the highlights sooner.

On most of Sony’s current cameras S-Log2 and S-Log3 both currently record exactly the same dynamic range as this is limited by the sensors that Sony are using. The S-log3 curve could be used in a future camera to capture up to 16 stops and in fact the new Venice camera records over 15 stops.  But as all of Sony’s other cameras sensors can only see 14 stops and the S-Log3 curve is designed to go beyond 14 stops, stop No. 14 is not recorded all the way at the top of the recording range.  S-Log2 is a 14 stop maximum curve, so the peak level is recorded right at the top of the recording range. There is no space held in reserve for anything beyond 14 stops.

In Sonys current camera range (other than Venice) the limit is 14 stops whether it’s S-Log2 or S-Log3. The chart that Sony provide showing both S-Log2 and S-Log3 is a little confusing as it shows the entire gamma curve rather than what the camera can actually “see”. In their current implementations both curves stop at +6 stops over middle grey, both capture the same dynamic range, there is no difference.

S-Log2 is brighter than S-Log3 so it must be capturing highlights better.

No, not really, see above. Playback and on screen brightness comes from the levels chosen to record something at and is dependant on the shape and range of the gamma curve. But the actual captured range is dependant on what the sensor can cope with. As we are not changing the sensor, the captured dynamic range, brightness range and shadow range does not change between S-Log2 and S-log3, both of which take the entire sensor range (they just store that same range using slightly different levels or code values). After applying a LUT or other conversion to your normal viewing gamma both S-Log2 and S-log3 will have the same brightness, same highlight and same shadow range.

S-Log3 has noisy shadows.

No, not really. Shadows appear noisy with S-Log3 as the shadow part of the curve is stored using higher code values compared to S-Log2. So when you view S-Log3 uncorrected the shadows are raised and stretched on your conventional monitor and this gives the impression of a noisy picture. In reality once you restore the levels to normal there is no additional noise. See this article for a full explanation.

S-log-levels The great S-Log2 or S-Log3 debate.
Chart showing S-Log2 and S-Log3 plotted against f-stops and code values. Note how little data there is for each of the darker stops, the best data is above middle grey. Note that current sensors only go to +6 stops over middle grey so S-Log2 and S-Log record to different peak levels.

S-Log3 is newer than S-Log2 so it must be better.

Newer, perhaps not. Better, no not really. S-Log3 is based on the industry standard Cineon log gamma curve. This curve was developed in the 1980’s to allow the digitising of film using 10 bit data. So S-Log3 matches a curve designed to work with negative film and is capable of storing more than the 14 stops that most of the current cameras sensors can see. In effect it is an old log gamma curve. As it is a curve designed for more than 14 stops, when used in a 14 stop camera some of the available recording data is empty and wasted.

S-Log2 was specifically designed by Sony to work with an electronic sensor with 14 stops of dynamic range and is optimised to match the performance characteristics of video sensors. By using a 14 stop curve with a 14 stop camera almost every bit of available data is utilised, there is no wastage. So S-Log2 makes better use of the data you have available to you,

BUT THERE ARE SOME OTHER FACTORS WE NEED TO CONSIDER.

S-Log2 and S-Gamut:

As well as the gamma curve we also have different Gamuts or color ranges. S-Log2 was originally designed for the F65 camera. The F65 sensor can capture a huge color range beyond the range that most conventional video sensors can see. So as well as S-Log2 Sony introduced S-Gamut which was matched to the very wide color range of the F65 sensor. S-Log2 is designed to be used with S-Gamut. But many of the cameras we use, like the FS7, F5, FS5 cannot see this color range (Sony’s F55 and Venice can). In addition this very large color range can be a little tricky to deal with in post production. Add to this the fact that S-Log2 is quite different to the quite common Cineon gamma curve and behaves differently to other curves in post. The end result was that in the early days of S-Log2 there were a number of complaints and comments that Sony’s S-log2 material was difficult to grade.

S-Log3 and S-Gamut3.

Because some people were struggling a bit with S-Gamut and S-Log2 in post production (Resolve and many of the other tools we have today were not as well developed 4 years ago), Sony introduced S-Gamut3 and S-log3 as well as a further Gamut called S–Gamut3.cine. S-Log3 was based on Cineon as that’s what people were familiar with. Arri’s Log-C is also based on Cineon as are many other log curves. This makes it a more “familiar” grading experience for many colorists. In addition Sony created a modified version of the super large S-Gamut to make it easier to grade.  S-Gamut3 is just as big as S-Gamut but some tweaks inside make it easier to grade (fewer color shifts). At the same time Sony realised that most users were producing content for TV, the web or digital cinema that had little use for the huge color range of S-Gamut/S-Gamut3.  So S-Gamut3.cine was developed as a smaller, more manageable version of S-Gamut3 and it incorporated a few tweaks to the color science to provide colors closer to those used by other manufacturers. S-Gamut3.cine is also a better match for cameras with sensors that cannot see the full S-Gamut range (like the FS5, FS7, F5, A7).

The end result is that in general most people prefer or find it easier to grade S-Log3/S-Gamut3.cine material than S-Log2/S-Gamut. Plus you can often use LUT’s designed for Log-C or Cineon with S-log3 material (this isn’t optimum, but it can work).

Gamuts-1024x632 The great S-Log2 or S-Log3 debate.
SGamuts Compared.

Getting the data from camera to post.

In terms of getting the data from your cameras sensor in to post production S-Log2 is the better choice (unless you have a Sony Venice which only has S-Log3). S-Log2 is optimised for the way an electronic sensor works. S-log3 is essentially a curve designed for negative film applications, not video and no matter how you look at it, these are electronic video cameras. However, if you are recording 10 bit or greater you have a lot of data whichever curve you use, so in practice it will be rare to see any difference in the final result.

So use the curve you find easiest to work with. It is true that S-Log 3 allocates a little more data to the shadows and less to the highlights than S-Log2, but don’t confuse data and code values with more range. S-Log3 has a few extra code values in it’s darkest stops, S-log2 has a few extra in the bright stops, but the dynamic range, highlight and shadow handling is governed by the sensor not the gamma curve. Overall S-Log3 has fewer code values than S-Log2, S-Log2  makes better use of the data available, but with 10 bit this really isn’t going to make a huge difference.

8 Bit Recording.

But if you are only recording with an 8 bit codec you are already at a disadvantage. When recording 8 bit you really need to maximise the way what little data you have is used. For that reason I will always recommend that S-Log2 is used when recording 8 bit on a camera like the FS5 in UHD or A7s or similar (FS5 is 10 bit in HD). By using S-Log2 you are using as many of the limited code values available as you can. This doesn’t mean you can’t use S-log3, it just wouldn’t be my choice.

The end result should be the same.

At the end of the day, if you were to use matching LUTs, S-log2 and S-log3 material should look more or less exactly the same after grading or application of the LUT, no matter what the scene you are shooting. If they do look significantly different then you are doing something wrong. So your choice of curve, other than for 8 bit recordings will most likely come down to ease of use rather than anything else.

If your camera doesn’t have LUT’s then S-Log2 can be easier to work with as it is more contrasty. This makes it a bit easier to focus and also makes it easier to gauge exposure. If your camera has LUT’s and you use them, then you may decide to use S-Log3 simply because you should find it a little easier to work with in post. Either way both curves capture the same range of picture information and both should give more or less the same end result.

There may be some very, very subtle differences due to the small differences in data distribution, but often these will be hard to really see in the final image.

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Video Tutorials for the FS5. Picture Profiles and Raw Recording.

I was recently asked by Sony to produce some videos to help users get the most from the PXW-FS5. The videos and articles can now be found on Sony’s website by following the links below. Part 1 covers the camera setup including using Picture Profiles to change the way the images look. Part 2 covers the special effects modes including S&Q, super-slow-motion, clear image zoom and the variable ND filter. Part 3 looks at the raw option for the FS5.

PXW-FS5 Shooting Tips Part 1. Camera Setup and Picture Settings.

PXW-FS5 Shooting Tips Part 2. Slow and Quick Motion, Variable ND, Clear Image Zoom.

PXW-FS5 Recording Raw and using the Raw output option (Atomos Shogun Flame and Convergent Design Odyssey 7Q used as examples).



Looking For LUT’s for the Sony S-Log2 and S-Log3 Cameras?

This website has a great feature. If you look up in the top left corner of every page you will see a small magnifying glass symbol. If you click on that it will allow you to search the entire site for information… and there’s lots and lots of hint, tips and guides going back many years.

One thing though that a lot of people keep asking about is LUT’s or Look Up Tables. I have lots and they are all (for the moment at least) provided for free. There will be some paid LUT sets coming soon. If you follow the link below you will get a single page that lists all the current LUT articles on the web site. Links to my free LUT sets will be included in these articles.

Remember that LUT’s for S-Log2 and S-Log3 can be used in any camera with S-Log2 or S-Log3. So a LUT for the FS7 can also be used in the FS5 for example.

Here’s the link: http://www.xdcam-user.com/?s=LUT%27s

PXW-FS5 Gets MPEG2 HD Option.

A little bit of news from IBC in Amsterdam is that Sony are going to allow owners of the PXW-FS5 to buy an upgrade that adds the MPEG2 HD codec to the camera. This is the same 8 bit 50Mb/s 4:2:2 codec as used for many years for broadcast HD television production (XDCAM HD422) as well as the 35Mb/s 4:2:0 found in many lower cost Sony camcorders such as the PMW-300 or EX1.

The MPEG2 HD422 codec is one of the most commonly used codecs world wide for TV and video production. It’s supported by just about every edit system and is very easy to handle. So if you need compatibility with legacy edit software such as FCP7 this could be the option you’ve been looking for. When you buy the upgrade you will receive a special activation code that allows you to go online and enter the cameras serial number to generate an unlock key for the codec option. There’s no need to send the camera in and it takes just a few minutes to activate the option.

The upgrade option is called the CBKZ-SLMP and the list price is 500 Euro’s. It’s actually the same upgrade option/key as used to add MPEG2 HD to the PXW-X70, but now as well as the X70 you can use it to upgrade an FS5.

Picture Profiles for the PXW-FS5.

Caption Picture Profiles for the PXW-FS5.
PXW-FS5 Picture Profiles

The Sony PXW-FS5 is a great little camera. It’s a camera I really enjoy shooting with as I can just grab it and go, picking up some great pictures with the minimum of effort. The built in Picture Profiles offer a wide range of different looks that can be quickly selected by pressing the P Profile button and choosing a profile. But one of the best parts is that you can tweak and adjust each profile to suit different shooting applications.

I tend to leave Picture Profile 7 alone. This is the S-Log2/S-Gamut profile that you must use when shooting raw and S-Log2 is my preferred log curve for shooting 8 bit UHD. But that leaves profiles 1 to 6 to play with and adjust, plus profiles 8 and 9 if you don’t use S-Log3. If you want to go back to the factory settings each profile can be reset individually (using “reset” within the profile settings).

Perhaps the two most challenging situations to shoot in are scenes that are high contrast and bright or low light scenes. Often you may encounter both types of scene on the same shoot, so it would be good if the pictures were at least similar. So we don’t want to use totally different color settings. But you can use different gamma settings to help better deal with the differing lighting levels and contrast ranges.

For brighter scenes I am a big fan of Sony’s “Cinegammas”. The Cinegammas differ from the standard gammas in the way they handle highlights. Basic television gamma has a very limited dynamic range, around 6 stops. Then to extend the dynamic range something called a “knee” is added to the top of the gamma curve. The point where the curve transitions from normal gamma to the knee is called the “knee point”. Everything above the knee is is compressed or squeezed. So in effect below the Knee 1 stop  is record with 1 stops worth of data, but above the knee 3 or 4 stops may be recorded in the same space.

cinegammas-1024x768 Picture Profiles for the PXW-FS5.

In practice this means anything brighter than the knee point will have very little contrast, when you have low contrast it is also hard to see any detail. So the highlights in the image look flat, lack texture and detail. If you have bright skin tones up in the knee they just look like blobs of color. Cotton wool clouds come out as white blobs in the sky and it is the knee that is largely responsible for the “video look”.

Sony’s Cinegammas are different. They do not have a knee. Instead of a hard knee point where you switch instantly from not compressed to compressed they have a slow and gradual transition from not compressed to very compressed. This is not unlike the way film behaves and is typically called a “highlight roll-off”. In practice because this transition is gradual it is less obvious. Because it is less obvious you can start the transition lower down the gamma curve which means you have more recording range for the highlights and can therefore increase the captured dynamic range. But to get the best looking recordings you want to keep faces and skin tones below the more aggressive parts of the roll off, so often you need to expose marginally darker than you would with conventional gamma.

For standard gammas it is typical to set the cameras zebras to 70% and have zebras just starting to appear on skin tones. With the Cinegammas I recommend reducing the zebras to 60%. See this article for more info on the correct exposure http://www.xdcam-user.com/2013/07/correct-exposure-levels-with-sony-hypergammas-and-cinegammas/

If you want to use the Cinegammas and are doing anything for broadcast TV that will not be graded and the video levels corrected to the 100% maximum required for broadcast then you should only ever use Cinegamma 2. All the other Cinegammas allow recording up to 109%.

All the Cinegammas record a similar extended dynamic range, Cinegamma 2 will almost always appear a little darker as it’s recording range is shrunk to ensure it does not exceed 100%., but even though it may appear a little darker, the captured dynamic range is the same.

For brighter scenes Cinegamma 1 is my go-to gamma curve on the FS5. It captures a large dynamic range. For darker scenes I will often use Cinegamma 4 as this raises shadows and the mid range. Cinegamma 4 is also useful for shooting back lit scenes.

Cinegamma 3 is a little more contrasty than Cinegamma 1 so if you want a picture with higher contrast this is the curve you should consider.

What about color?

The standard color mode is OK, but I find it a little gaudy. If you want a more film like look then the Cinema mode works quite well to give a more de-saturated look. But my favourite color mode is the Pro color mode. It’s not as vibrant or highly saturated as the standard or ITU709 color modes but it does produce very accurate colors. It’s a bit less green that the standard color mode. If you want a more vibrant image you can increase the saturation, I find Pro Color at +14 saturation gives great color straight out of the camera.

The Color Depth control is a bit of an odd control. It works by targeting a particular color, but instead of increasing/decreasing the saturation of the color it makes the luminance level of objects that are that color brighter or darker. If you make a red car darker in brightness it makes the color appear stronger relative to the brightness. A positive setting makes the luminance darker, so the color appears stronger, a negative setting makes the luminance brighter so the color appears slightly more washed out.

First the standard look (notice the blobby, flat, no texture look to the clouds from the knee):

standard-1024x576 Picture Profiles for the PXW-FS5.
PXW-FS5 Standard Settings

So, here are some suggested settings for different shooting conditions. Remember, you can mix and match the color and gamma settings, so if you like the colors from one profile you can take the color settings and use them with the contrast settings (gamma, black gamma) of another.

1: AC-GPMC – General purpose, medium contrast (good all-round profile).

Gamma: Cine3, Black Gamma Middle -7, Color Mode Pro, Saturation +16 (substitute Cine3 with Cine2 for direct to air broadcast).

ACGPMC-1024x576 Picture Profiles for the PXW-FS5.
Alister’s PXW-FS5 Profile AC-GPMC

2: AC-GPBT – General purpose for bright high contrast scenes.

Gamma: Cine1, Black Gamma Low -3, Color Mode Pro, Saturation +16 (substitute Cine1 with Cine2 for direct to air broadcast).

ACGPBT-1024x576 Picture Profiles for the PXW-FS5.
Alister’s PXW-FS5 Profile AC-GPBT

3: AC-GPGD – General purpose, looks good direct but good if going to be graded (shadows raised to help in grading)

Gamma: Cine1, Black Gamma Low +4, Color Mode Pro, Saturation 0 (substitute Cine1 with Cine2 for direct to air broadcast).

ACGPGD-1024x576 Picture Profiles for the PXW-FS5.
Alister’s PXW-FS5 profile AC-GPGD

4: AC-GPLL – General purpose profile for darker scenes (raised shadows to make grading easier).

Gamma: Cine4, Black Gamma High +7, Color Mode Pro, Saturation +6 (substitute Cine4 with Cine2 for direct to air broadcast).

ACGPLL-1024x576 Picture Profiles for the PXW-FS5.
Alister’s PXW-FS5 Picture Profile AC-GPLL

5: AC-EXLL – For use in very low light levels (is the equivalent to adding +6db gain, does increase noise).

Gamma: ITU709(800), Black Gamma Low +7, Color Mode Pro, Saturation 0.

ACEXLL-1024x576 Picture Profiles for the PXW-FS5.
Alister’s PXW-FS5 Picture Profile for very low light AC-EXLL

6: AC-ASIA1 – Vibrant colors, slight boost to reds/blues.

Gamma: Cine3, Black Gamma Middle -7, Color Mode ITU709, Saturation +10, Color Depth R+5, G-3, B+2, C+1, M0, Y-2.

ACASIA-1024x576 Picture Profiles for the PXW-FS5.
Alister’s PXW-FS5 Picture Profile AC-ASIA1. Vibrant vivid colors.

AC-FILM1 – Film like color and contrast.

Gamma Cine1, Black Gamma Middle -7, Color Mode Cinema, Saturation +8, Phase -3, Color Depth R+4, G-1, B+1, C0, M0, Y-4.

ACFILM-1024x576 Picture Profiles for the PXW-FS5.
Alister’s PXW-FS5 Picture Profile AC-FILM1, a film-like profile.

 

 

Training Videos for the PXW-FS5 and PXW-FS7

Just a reminder that the full sets of traing films for the PXW-FS5 and the PXW-FS7 are available for viewing for free on YouTube.

The FS7 videos can be found by following this playlist link.

There are 10 videos taking you from basic setup all the way through scene files, cine EI and the effects shooting modes.

There are currently 2 PXW-FS5 videos.

The first on picture profiles and picture settings is here.

The second on the advanced shooting modes is here.

I am currently working on a further video on using the FS5’s raw output and this should be available in the next couple of weeks.

Don’t forget if you have any questions I have my Webinar day coming next week.

 

Free Webinar Day – July 26th 2016.

PXW-FS5 Tutorial Videos.

I was asked to prepare two tutorial videos on the PXW-FS5 for Sony. The first video covers the advanced features of the camera including super slow mo and the variable ND filter. The second video gives an overview of the picture profile settings with some suggestions for which to use and when, including the correct exposure for S-Lo2 and S-Log3.

There should be some downloadable PDF guides to go with these videos coming shortly.

Sample clips form the FS5 in Iceland.

I’m running a workshop here in Iceland tomorrow at Nyherji. So I spent the day getting some local sample footage with my FS5.

Here’s the FS5 clip.

Shot with a stock FS5 with either the Sony 18-105mm (Geyser) kit lens or a Sigma 18-250mm Canon mount lens (Gulfoss Waterfalls). I used  S-log2 with the Pro color matrix. It was edited and graded on my laptop using Premiere CC.

 

Deeper Understanding Of Log Gamma. Experiments with a Waveform Display.

I started writing this as an explanation of why I often choose not to use log for low light. But instead it’s ended up as an experiment you can try for yourself if you have a waveform monitor that will hopefully allow you to better understand the differences between log and standard gamma. Get a waveform display hooked up to your log camera and try this for yourself.

S-Log and other log gammas are wonderful things, but they are not the be-all and end-all of video gammas. They are designed for one specific purpose and that is to give cameras using conventional YCbCr or RGB recording methods the ability to record the greatest possible dynamic range with a limited amount of data, as a result there are some compromises made when using log. Unlike conventional gammas with a knee or gammas such as hypergammas and cinegammas, log gammas do not normally have any highlight roll off, but do have a shadow roll-off. Once you get above middle grey log gammas normally record every stop with almost exactly the same amount of data, right up to the clipping point where they hard clip. Below middle grey there is a roll off of data per stop as you go down towards the black clip point (as there is naturally less information in the shadows this is expected). So in many respects log gammas are almost the reverse of standard gammas. The highlight roll off that you may believe that you see with log is often just the natural way that real world highlights roll off anyway, after all there isn’t an infinite amount of light floating around (thank goodness). Or that apparent roll off is simply a display or LUT limitation.

An experiment for you to try.

xdcam-greyscale-300x169 Deeper Understanding Of Log Gamma. Experiments with a Waveform Display.
Click on the chart to go to larger versions that you can download. Display it full screen on your computer and use it as a test chart. You may need to de-focus the camera slightly to avoid aliasing from the screens pixels.

If you have a waveform display and a grey scale chart you can actually see this behaviour. If you don’t have a chart use the grey scale posted here full screen on your computer monitor. Start with a conventional gamma, preferably REC-709. Point the camera at the chart and gradually open up the aperture. With normal gammas as you open the aperture you will see the steps between each grey bar open up and the steps spread apart until you reach the knee point, typically at 90% (assuming the knee is ON which is the default for most cameras).  Once you hit the knee all those steps rapidly squash back together again.

What you are seeing on the waveform is conventional gamma behaviour where for each stop you go up in exposure you almost double the amount of data recorded, thus capturing the real world very accurately (although only within a limited range). Once you hit the knee everything is compressed together to increase the dynamic range using only a very small recording range, leaving the shadows and all important mid range well recorded. It’s this highlight compression that gives video the “video look”, washed out highlights with no contrast that look electronic.

If you repeat the same exercise with a hypergamma or cinegamma once again in the lower and mid range you will see the steps stretch apart on the waveform as you increase the exposure. But once you get to about 65-70% they stop stretching apart and now start to squeeze together. This is the highlight roll off of the hypergamma/cinegamma doing it’s thing. Once again compressing the highlights to get a greater dynamic range but doing this in a progressive gradual manner that tends to look much nicer than the hard knee. Even though this does look better than 709 + Knee in the vast majority of cases, we are still compressing the highlights, still throwing away a lot of data or highlight picture information that can never be recovered in post production no matter what you do.

Conventional video = Protect Your Highlights.

So in the conventional video world we are taught as cameramen to “protect the highlights”. Never overexpose because it looks bad and even grading won’t help a lot. If anything we will often err on the side of caution and expose a little low to avoid highlight issues. If you are using a Hypergamma or Cinegamma you really need to be careful with skin tones to keep them below that 65-70% beginning of the highlight roll off.

Now repeat the same experiment with Slog2 or S-log3. S-log2 is best for the experiment as it shows what is going on most clearly. Before you do it though mark middle grey on your waveform display with a piece of tape or similar. Middle grey for S-log2 is 32% (41% for S-log3).

Now open up the aperture and watch those steps between the grey scale bars. Below middle grey, as with the standard gammas you will see the gap between each bar open up. But take careful note of what happens above middle grey. Once you get above middle grey and all the way to the clip point the gap between each step remains the same.

So what’s happening now?

Well this is the S-log curve recording each stop above middle grey with the same amount of data. In addition there is NO highlight roll off. Even the very brightest step just below clipping will be same size as the one just above middle grey. In practice what this means is that it doesn’t make a great deal of difference where you expose for example skin tones, provided they are above middle grey and below clipping. After grading it will look more or less the same. In addition it means that that very brightest stop contains a lot of great, useable picture information. Compare that to Rec-709 or the Cinegammas/Hypergammas where the brightest  stops are all squashed together and contain almost no contrast or picture information.

Now add in to the equation what is going on in the shadows. Log has less data in the shadows than standard gammas because you are recording a greater overall dynamic range, so each stop is recorded with overall less data.

Standard Gammas = More shadow data per stop, much less highlight data = Need to protect highlights.

Log= Less shadow data per stop, much more highlight data = Need to protect shadows.

Hopefully now you can see that with S-log we need to flip the way we shoot from protecting highlights to protecting shadows. When you shoot with conventional gammas most people expose so the mid range is OK, then take a look at the highlights to make sure they are not too bright and largely ignore whats going on in the shadows. With Log you need to do the opposite. Expose the mid range and then check the shadows to make sure they are not too dark. You can ignore the highlights.

Yes, thats’ right, when shooting log: IGNORE the highlights!

WF-Cinegamma-3-1024x576 Deeper Understanding Of Log Gamma. Experiments with a Waveform Display.
Cinegamma highlight roll off. Note how the tree branches in the highlights look strangled and ugly due to the lack of highlight data, hence “protect your highlights”.
WF-Slog-graded-1024x576 Deeper Understanding Of Log Gamma. Experiments with a Waveform Display.
Graded S-Log2. Note how nice the same tree branches look because there is a lot of data in the highlights, but the shadows are a little crunchy. Hence: protect your shadows.

For a start you monitor or viewfinder isn’t going to be able to accurately reproduce the highlights as bright as they are . So typically they will look a lot more over exposed than they really are. In addition there is a ton of data in those highlights that you will be able to extract in the grade. But most importantly if you do underexpose your mid range will suffer, it will get noisy and your shadows will look terrible because there will be no data to work with.

When I shoot with log I always over expose by at least 1 stop above the manufacturer recommended levels. If you are using S-log2 or S-log3 that can be achieved by setting zebras to 70% and then checking that you are JUST starting to see zebras on something white in your shot such as a white shirt or piece of paper. If your camera has CineEI use an EI that is half of the cameras native ISO (I use 1000 or 800 EI for my FS7 or F5).

I hope these experiments with a grey scale and waveform help you understand what is going on with you gamma curves. One thing I will add is that while controlled over exposure is beneficial it can lead to some issues with grading. That’s because most LUT’s are designed for “correct” exposure so will typically look over exposed. Another issue is that if you simply reduce the gain level in post to compensate than the graded footage looks flat and washed out. This is because you are applying a linear correction to log footage. Fo a long tome I struggled to get pleasing results from over exposed log footage. The secret is to either use LUT’s that are offset to compensate for over exposure or to de-log the footage prior to grading using an S-Curve. I’ll cover both of these in a later article.

S-log-levels Deeper Understanding Of Log Gamma. Experiments with a Waveform Display.
Chart showing S-Log2 and S-Log3 plotted against f-stops and code values.

 

 

 

 

 

 

 

 

 

What about shooting in low light?

OK, now lets imagine we are shooting a dark or low light scene. It’s dark enough that even if we open the aperture all the way the brightest parts of the scene (ignoring things like street lights) do not reach clipping (92% with S-Log3 or 109% with S-Log2). This means two things. 1: The scene has a dynamic range less than 14 stops and 2: We are not utilising all of the recording data available to us. We are wasting data.

Log exposed so that the scene fills the entire curve puts around 100 code values (or luma shades) per stop above middle grey for S-log2 and 75 code values for S-Log3 with a 10 bit codec. If your codec is only 8 bit then that becomes 25 for S-log2 and 19 code values for S-Log3. And that’s ONLY if you are recording a signal that fills the full range from black clip to white clip.

3 stops below middle grey there is very little data, about thirty 10 bit code values for S-Log2 and about 45 for S-log3. Once again if the codec is 8 bit you have much less, about 7 for S-Log2 and about 11 for S-log2. As a result the darker parts of your recorded scene will be recorded with very little data and very few shades. This impacts how much you can grade the image in post as there is very little picture information in the darker parts of the shot and noise tends to look quite coarse as it is only recorded with a limited number of steps or levels (this is particularly true of 8 bit codecs and an area where 8 bit recordings can be problematic).

So what happens if we use a standard gamma curve?

Lets say we now shoot the same scene with a standard gamma curve, perhaps REC-709. One point to note with Sony cameras like the FS5, FS7, F5/F55 etc is that the standard gammas normally have a native ISO one to two stops lower than S-Log. That’s because the standard gammas ignore the darkest couple of stops that are recorded when in log. After all there is very little really useable picture information down there in all the noise.

Now our limited dynamic range scene will be filling much more of our recording range. So straight away we have more data per stop because we are utilising a bigger portion of the recording range. In addition because our recorded levels will be higher in our recording range there will be more data per stop, typically double the data especially in the darker parts of the recorded image. This means than any noise is recorded more accurately which results in smoother looking noise. It also means there is more data available for any post production manipulation.

But what about those dark scenes with problem highlights such as street lights?

This an area where Cinegammas or Hypergammas are very useful. The problem highlights like strret lights normally only make up a very small part of your your overall scene. So unless you are shooting for HDR display it’s a huge waste to use S-log just to bring some highlights into range as you make big compromises to the rest of the image and you’ll never be able to show them accurately in the finished image anyway as they will exceed the dynamic range of the TV display.  Instead for these situations a Hypergamma or Cinegamma works well because below about 70% exposure Hypergammas and cinegammas are very similar to Rec-709 so you will have lots of data in the shadows and mid range where you really need it. The highlights will be up in the highlight roll off area where the data levels or number of recorded shades are rolled off. So the highlights still get recorded, perhaps without clipping, but you are only giving away a small amount of data to do this. The highlights possibly won’t look quite as nice as if recorded with log, but they are typically only a small part of the scene and the rest of the scene especially the shadows and mid tones will end up looking much better as the noise will be smoother and there will be more data in that all important mid-range.