log is often a poor choice for low light.

XDCAM-sliding-system-v2 log is often a poor choice for low light.

UPDATE: Following much debate and discussion in the comments section and on my Facebook feed I think one thing that has become clear is an important factor in this subject is the required end contrast. If you take S-Log3 which has a raised shadow range and shoot with it in low light you will gain a low contrast image. If you choose to keep the image low contrast then there is no accentuation of the recorded noise in post and this can bring an acceptable and useable result. However if you need to grade the S-log3 to gain the same contrast as a dedicated high contrast gamma such as 709, then the lack of recorded data can make the image become coarser than it would be if recorded by a narrow range gamma. Furthermore many other factors come into play such as how noisy the camera is, the codec used, bit depth etc. So at the end of the day my recommendation is to not assume log will be better, but to test both log and standard gammas in similar conditions to those you will be shooting in.

Log gamma curves are designed for one thing and one thing only, to extend the dynamic range that can be recorded. In order to be able to record that greater dynamic range all kinds of compromises are being made.

Lets look at a few facts.

Amount of picture information:
The amount of picture information that you can record, i.e. the amount of image samples, shades or data points is not determined by the gamma curve. It is determined by the recording format or recording codec. For example a 10 bit codec can store up to 1023 shades or code values while an 8 bit codec can record up to 255 shades or code values (in practice this is a maximum of 235 shades as 16 are used for sync). It doesn’t matter which gamma curve you use, the 10 bit codec will contain more usable picture information than the 8 bit codec. The 10 bit picture will have over 1000 shades while the 8 bit one less than 255. For low light more “bits” is always going to be better than less as noise can be recorded more faithfully. If noise is recorded with only a few shades or code values it will look coarse and ugly compared to noise recorded with lots more levels which will look smoother.

Bottom line though is that no matter what gamma curve, the  maximum amount of picture information is determined by the codec or recording format. It’s a bit of a myth that log gives you more data for post, it does not, it gives you a broader range.

Log extends the dynamic range: This is the one thing that log is best know for. Extending the dynamic range, but this does not mean we have more picture information, all it means is we have a broader range. So instead of say a 6 or 7 stop range we have a 14 stop range. That range increase is not just an increase in highlight range but also a corresponding increase in shadow range. A typical rec-709 camera can “see” about 3 or 4 stops below middle grey before the image is deemed to be too noisy and any shades or tone blend into one. An S-log2 or S-log3 camera can see about 8 stops below middle grey before there is nothing else to see but noise. However the lower 2 or 3 stops of this extended range really are very noisy and it’s questionable as to how useful they really are.

Imagine you are shooting a row of buildings (each building representing a few stops of dynamic range). Think of standard gammas as a standard 50mm lens. It will give you a great image but it won’t be very wide, you might only get one or two buildings into the shot, but you will have a ton of detail of those buildings.

Hong-Kong-50mm log is often a poor choice for low light.
Shot of buildings taken with standard lens, think “standard gamma”

Think of a wide dynamic range gamma such as S-log as a wide angle lens. It will give you a much wider image taking in several buildings and assuming the lens is of similar quality to the 50mm lens, the captured pictures will appear to be of similar quality. But although you have a wider view the level of detail for each building will be reduced. You have a wider range, but each individual building has less detail

Hong-Kong-20mm log is often a poor choice for low light.
Buildings shot with 20 mm wide lens. Think “wide gamma” or log gamma.

But what if in your final scene you are only going to show one or two buildings and they need to fill the frame? If you shoot with the wide lens you will need to blow the image up in post to the show just the buildings you want. Blowing an image up like this results in a lower quality image. The standard lens image however won’t need to be blown up, so it will look better. Log is just the same. While you do start off with a wider range (which may indeed be highly beneficial) each element or range of shades within that range has less data than if we had shot with a narrower gamma.

Hong-Kong-20mm-cropped log is often a poor choice for low light.
Wide lens (think wide gamma) cropped to match standard lens (think standard gamma). Note the loss of quality compared to starting with standard.

Using log in low light is the equivalent of using a wide angle lens to shoot a row of buildings where you can actually only see a few of the buildings, the others being invisible and then blowing up that image to fill the frame. The reality is you would be better off using the standard lens and filing the frame with the few visible building, thus saving the need to blow up the image.

Hong-Kong-50mm-wasted-data log is often a poor choice for low light.
Shooting a scene where most of it is dark with wide lens (wide gamma/log) wastes a lot of data.
Hong-Kong-50mm-dark2 log is often a poor choice for low light.
Using a narrower lens (narrow or standard gamma) wastes less data and the information that is captured is of higher quality.

S-Log2/3 has a higher base ISO: On a Sony camera this higher ISO value is actually very miss-leading because the camera isn’t actually any more sensitive in log. The camera is still at 0dB gain, even though it is being rated at a higher ISO. The higher ISO rating is there to offset an external light meter to give you the darker recording levels normally used for log. Remember a white card is recorded at 90% with standard gammas, but only 60% with log. When you change the ISO setting upwards on a light meter it will tell you to close down the aperture on the camera, that then results in the correct darker log exposure.

S-Log3 may appear at first brighter than standard gammas when you switch to it. This is because it raises the very bottom of the log curve and puts more data into the shadows. But the brighter parts of the image will be no brighter than with a camera with standard gammas at 0db gain. This extra shadow data may be beneficial for some low light situations, so if  you are going to use log in low light S-Log3 is superior to S-Log2.

If you can’t get the correct exposure with log, don’t use it! Basically if you can’t get the correct exposure without adding gain or increasing the ISO don’t use log. If you can’t get your midrange up where it’s supposed to be then you are wasting data. You are not filling your codec or recording format so a lot of data available for picture information is being wasted. Also consider that because each stop is recorded with less data with log not only is the picture information a bit coarser but so too is any noise. If you really are struggling for light, your image is likely to be a bit dark and thus have a lot of noisy and coarse noise is not nice. Log has very little data allocated to the shadows in order to free up data for the highlights because one of the key features of log is the excellent way it handles highlights as a result an under exposed log image is going to lack even more data. So never under expose log.

S-log-levels log is often a poor choice for low light.
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.

Think of log as the opposite of standard gammas. With standard gammas you always try never to over expose and often being very slightly under exposed is good. But log must never be under exposed, there is not enough data in the shadows to cope with under exposure. Meanwhile log has more data in the highlights, so is very happy to be a little over exposed.

My rule of thumb is quite simple. If I can’t fully expose log at the base sensitivity I don’t use it. I will drop down to a cinegamma or hypergamma. If I can’t correctly expose the hypergamma or cinegamma then I drop down to standard gamma, rec-709.

25 thoughts on “log is often a poor choice for low light.”

  1. Hi Alister. Maybe Sony would consider commissioning you to pull all this very helpful advice and guidance together into a manual that could be provided with their high end cameras. Sony provide the technical facilities but it is you who seems to provide the most accurate English information on how to use them. Sony do not do this and I think that they are missing a trick. In the meantime, thank you! Bob.

    1. It is happening. Finally after many years, Sony are working on some really good things for the end users. I can’t say to much as some of the finer details are still being worked out, but you can expect to see a big increase in the information that’s going to be available.

      1. Good news.. I paid a fortune by todays camera costs for a digibeta years ago and about half of the English manual made no sense what so ever..

  2. Thank Alistair, really Great analogy with the buildings.
    I’m a post production specialist and used to working with SLOG and CLOG. It’s great for careful shot by shot grading using curves, masks and colour wheels. But most of my producer clients are working on corporates and don’t want me spending hours finnessing 100s of shots. Most of the time they just want it looking ‘normal’ by just sticking a standard LUT on it. Okay it’s very cool to shoot with a filmic range, it often helps me put richer detail back into the sky and mid tones, but a well exposed shot using a standard gamma is far quicker to tweak, often gives less noise to clean and looks very similar to a graded LOG shot. The real question is……….does the end corporate client care? Appreciate the extra work? And willing to pay extra for it?

    1. I think people get carried away by all the hype. I’ve got log and I’m gonna use it no matter what because someone somewhere said log is cool.

      It’s just a tool in the tool box. Just as using a mallet to hammer in a tiny nail is crazy, so to is using log when there isn’t the time or budget to spend on the post side.

  3. Great article.. so if you bake in a REC709 orientated, non LC type LUT.. in Cine EI slog3.cine mode 2000 ISO.. is the LUT acting as a “gamma curve”.. “over” the slog curve.. are you then shoot with a way narrower DR but in 2000 ISO.. giving you more noise.. but with a color space /image you like..
    Hope this makes sense !

  4. ah .. but your not exposing at Slog levels so maybe not.. maybe a better question..
    What does a LUT really do.. when burnt in over a Slog curve.. I know it “re maps” levels .. but how.. its not gamma curve .. whats the difference to shooting REC709..STD5 or shooting Cine EI and burning in a LUT exactly matching the custom REC 709.. just the different colour space.. ?

    Thanks..

    1. If you bake in a LUT you are back down to the colorspace etc of the LUT, many of the log benefits are gone and depending on the LUT you may be back down to 709 color too. Inside the Sony cameras the LUT’s are not actually applied over the log, they are applied directly to the signal from the sensor, but result in the same image as if applied on top of the log.

      Log, gamma, LUT’s are all simply mathematical processes in a digital camera. The benefit of baking in a LUT is the range of different looks and styles you can create is greater than the limited range of fixed gamma curves that you have in custom mode.

  5. Great that you’re using lens focal lenght tot open up a lot of peoples eyes. Hopefully one can understand things better, and stop worshipping Slog in every condition. In grading sessions i see a lot of mistakes in exposure but “it’s s-log” so you can fix it, right?”
    Thanks for your contribution!

  6. Sony’s marketing department is actually too good. Sometimes they are so effective at using buzzwords and impressive specs to sell a product that they create unrealistic expectations. The Playstation 3, the first generation of A7 cameras, and now the FS5, are good examples of this.
    It seems that this is a particular problem for them with the video “prosumer” market segment. Many of the people who are buying the A7Sii and the FS5 are more technically literate than the average consumer but still aren’t as fluent as long time professionals, in other words, they know just enough to get themselves in trouble. They understand the potential benefits of things such as SLOG but don’t understand how and when to use it and Sony is completely unhelpful in this regard. So while an expert like yourself may be able to look at the FS5 spec sheet and think, “SLOG3 and 8-bit UHD with a low bit rate is a recipe for disaster”, most people will only think “SLOG3, 4K and the ability to use SD cards? Awesome!”. Then, after they have spent over $6000, which is a lot of money for many of us, they slowly begin to realize that the camera isn’t as capable as they had assumed.
    Coming from still photography, where even the most basic dSLR can shoot 14-bit RAW stills, I never appreciated just how much video image quality is constrained by throughout and storage limitations. It was an ugly surprise when I realized that I couldn’t just recover highlights or open up the shadows in post like I could with RAW still files in Lightroom.
    I think that your very thorough Vocas video on the FS5 enlightened many people, probably more than you realize (I count myself among them). Before that, I had assumed that SLOG was kind of just a “set it and forget it” thing, kind of like RAW in still photography. In the last two months I have given myself a crash course in videography and I am now much more confident in my technical understanding. Thanks for the knowledge!

      1. A rare thing, to be able to film and teach with such clarity. Thank you, the vocas seminar was a real eye opener and the reason that I bought the fs5. I shoot trailers for theatre plays mostly. Lighting shifts rapidly and hard spotlights often means dark backgrounds. Not sure that slog would help, so far I’ve only used cinegammas. Have not had time to play with different color spaces yet. This is truly a learning experience for me. Thank you!

  7. I found it interesting that in the heading you used the word ‘Often’. Unless I read over it, I am curious to hear in what situations log could be a better choice than Standard or Hypergamma’s in low light.
    There will always be more noise so I assume you mean for stylizing purposes?

    1. This post has led to a lot of discussion and one thing that plays an important part is contrast. For certain low light, low contrast scenes S-log3 may actually work quite well as it has a raised shadow range. If you can keep the entire scene in that raised shadow range then it can work quite well. Other factors include how the camera applies noise reduction and the quality of the recording codec. More research and testing is required and will be done in the coming weeks.

  8. As much as I understand your argument my experience with the FS5 is different. I’m usually not shooting S-Log since I try to achieve the general look in camera. Ideally with room to play, so I go for a rather flat image that I can tweak in post. I avoid S-Log except for really high-contrast scenes because it creates more work in postproduction and because the image tends to suffer more with a weak (high compression rate) codec. Exactly your point.

    But shooting in low-light the standard gammas on the FS5 apply a much more aggressive noise reduction than the S-Log settings. Regardless of the actual ISO or gain settings and regardless of the different base ISOs I can simply achieve a much nicer 4K image in low-light with S-Log. There is noise, of course, but the noise is nicer and much more organic than the blotching I get using the other profiles.

    I don’t want to use S-Log in low-light but the camera at the moment doesn’t give me a better option. And thats purely from looking a the results. All the theories and math (in which a totally agree) put aside.

    1. Have you actually tested this with like for like contrast in the final image? This is a simple test that I just did with my FS5 that illustrates some interesting things. https://www.youtube.com/edit?o=U&video_id=4oxT00Ha8lUA
      It clearly shows S-log3 to be particularly noisy in low light due to the raised shadow range, this isn’t a big surprise as it is expected in post that you would take this raised shadow range down to restore the images contrast. At first glance the S-log3 appears to have a small advantage at 0dB over the Cinegamma at 0dB. But it is worth considering that the brighter parts of both images are at almost exactly the same brightness levels, the exposure difference is contrast.
      So with a very low contrast scene, if you don’t mind keeping the final image very low contrast, then maybe the S-log has some benefits if you can live with the extra noise, so on the one hand I agree, but on the other disagree as it’s going to depend on contrast.

      Now when I add just 6dB of gain to the cinegamma we have a much brighter image, the whites are now at 70% compared to S-logs 50% (this means the S-log is about 1.5 stops under exposed). The cinegamma image has less noise than the S-log3 image and more contrast but we do see some more noise reduction artefacts in the image. Which is the better image? I’m not sure? Really I need to repeat the test with skin tones because I think the skin tones are going to be much more pleasing with the right contrast rather than flat.

  9. Allister, if you would be offered two camera choices (Canon 70D 8bits 4.2.0 or Sony PMW F3 with Odyssey 7Q recording 10 bits RGB 444 ProResHQ) using same Rokinon prime lenses and were asked to shoot a super low budget film with interior scenes using available lighting in offices with just a few small Fresnel to give some accent, fill some dark corners, shots pointing to tv monitors with news footage, etc, because is part of the story and almost not exteriors..Some shots ambient around the 1980’s…..would you choose the F3 and shoot standard gamma at 444 (ProResHQ)? or S Log? I could even shoot DPX. I know it depends but I am hoping you can tell me what do you think. I am also not clear about if it is OK or not to use other LUTs besides the Sony slog1 R709 when recording from the F3 into the Odyssey 7Q or I could use any LUTs I want? (Like I did here on ProResHQ 422 using an ARRI EE R709 LUT

    and spent no time by simply dropping the Arri LUT on top of clip in Avid MC 8…unfortunately I added those BorisFx between shots but on the raw footage you could see I had to really push the contrast to get raid of some noise in his right shoulder in one of the takes where my reflector wasn’t behind him). I understand about how S Log is overblown but if I use S LOG am I limited to slog1 only? How about SLog2 or 3? Arri, canon, etc.? can I use 3D LUTs? or is it OK to do what I did in this sample using a LUT that was not intended for the F3? I am worry that if I do that and in post editor realized the LUT does not work well then my exposure is now off because I exposed for the ARRI LUT. Is recording standard Gamma R709 at 444 is best for this type of low budget films? I could record a PP I like on this case. Or without PP. The film will be edited in A. Premiere P and DaVinci for CC. My apologies if my questions are a little too confusing or basics. Thanks for your help as always!

    1. I really think you need to go back to basics.

      First the F3 cannot deliver raw, it can only output standard gamma and slog1, so that’s what you are limited to. LUT’s are designed for specific log curves, while you can add any LUT to any gamma the results will be unpredictable at best. You should really use LUT’s designed for the curves you are using, if you don’t exposure will be off and you may have clipped highlights or blacks.

  10. Need help: Hi Alister, I recently got my Fs5 and while not being very pro at it i discovered that all my wide shots (in focus) are not at all clean and sharp while all close shots are nearly clean and sharp! What could i be missing/doing wrong for the not so clean wide shots? Settings i use are: PP6, Cine 2, ISO1000 (Full HD mode)

  11. If a stop of light in the scene you shoot gets unusable in slog because it’s too noisy, it will probably be even more unusable in baked-in rec 709, because you won’t be in the middle/high contrast part of the curve, you’ll be in the toe of each curves.
    So sure the data recorded in slog won’t be of decent quality, but the data recorded in rec will be inexistant all together.
    An other way of putting it would be : if you’re recording decent shadows in rec709 it means you’re not completely in its toe, if you’re not in its toe you won’t be in the toe of slog either.
    Plus I don’t know how it works for Sony, but for other manufacturers the rec709 curves (either the lut or the baked in files) are created from log data.
    For the alexa for example the math is : linear=>log(los of data)=>rec709(2nd loss of data)

    1. The math in most video cameras is done as a single DSP process. Add a LUT to log in a Sony camera and the final output is generated directly from the sensor output in a single step that combines the two mathematical calculations into one single process. It is not converted to log then converted to 709, it goes directly from the sensor output to 709. Even if it was done in multiple stages it should be virtually lossless as the DSP runs at a significantly greater bit depth and with greater precision than the final output and no compression is involved. Arri’s internal image processing is 16 bit so plenty of precision for virtually loss less 10 or 12 bit output, even if they do split the processing (which I very much doubt).

      The signal to noise ratio of a camera is determined by the sensor and how much light you put on the sensor. The darkest useable signal depends on the sensors noise floor. These things don’t change whether you are shooting log or 709. But at 0db, with no added gain shoot a scene where you can only just hit white at 60% in log and white will hit over 70% in 709, the 709 image will have more data. The 709 will have a more data in the brighter parts of the image which would normally be where the all important skin tones etc are.

      I am not saying that you can’t use log for low light. You just need to understand what is actually going on inside the camera. For example the the miss conception that many have, that the camera is more sensitive in log compared to 709. A miss conception that comes from a higher ISO number for log that’s given to force you to push the exposure down if you are using a light meter, to extend the high end latitude at the expense of an extra stop of noise.

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