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Making Sony Log Cameras Behave Like Arri Cameras When Shooting Cine EI and S-Log3.

Arri have a little trick in their cameras when shooting log to ProRes that the Sony Log cameras don’t have. When you change the Exposure Index in an Arri camera they modify the position of the exposure mid point and the shape of the Log-C gamma curve. There is actually a different Log-C curve for each EI. When you take this into post it has the benefit that the brightness at each EI will appear similar. But as the curve changes for each EI a different LUT is needed for each exposure if you want something shot at say 800EI to look the same as something shot at 200EI.

With a Sony camera the same S-Log curve is used for each Exposure Index and the LUT brightness is changed so that you end up altering the mid point of the recording as well as the highlight and shadow range. In post each EI will appear to be a different brightness. You can use the same LUT for each EI provided you do an exposure correction prior to adding the LUT or you can use dedicated offset LUT’s for each exposure.

But what you need to remember is that you are always working within a restricted recording range with either system. You can’t go darker than the black recording level or brighter than the highest value the codec can record.

If you do it in camera, as Arri do and change the log curve, at a low EI you seriously constrict the recording range (at 200 EI peak only reaches around 78IRE). This happens because at a low EI you put more light on to the sensor, so to keep the mid range looking a normal brightness in post it must be recorded at a much lower level. So with all the levels now reduced you end up recording your entire capture range into a smaller recording range. In addition to avoid clipping the blacks at a low EI the shadows are rolled off so you lose some detail and textures in the shadows. You can see the different Log-C curves in this Arri White paper.

Most people choose a low EI for 2 reasons, better signal to noise ratio and improved shadow range. The Arri method gives you the better SNR but while the dynamic range is preserved it’s recorded using less data and in particular the shadow data decreases compared to shooting at the base ISO.

Shoot at a high EI, you put less light on to the sensor. So to maintain similar looking mids in post everything has to be recorded at a higher level. Now you have a problem because the highlights will extend beyond the upper limits of the recording range so  Arri have to add a highlight roll off at the top of the Log-C curve. This can present some grading challenges as the curve is now very different to regular Log-C. In addition the highlights are compressed.

Most people choose to shoot at a high EI to extend the highlight range or to work in lower light levels.

The latter is a bit of a pointless exercise with any log camera as the camera sensitivity isn’t actually any different, you are only fooling yourself into thinking it’s is more sensitive and this can result in noisy footage. If you using a high EI to extend the highlight range then really the last thing you want is the extra highlight roll off that Arri have to add at 3200 EI to fit everything in.

One thing here in Arri’s favour is that they can record 12 bit ProRes 444. 12 bits helps mitigate the compressed recording range of low EI’s provided the post workflow is managed correctly.

The beauty of the Sony method is the recording range never changes, so low EI’s and brighter recordings deliver better shadow ranges with more data in the shadows and mids and high EI’s with darker recordings deliver better highlight ranges with no additional data restrictions or additional roll-offs giving the cinematographer more control to choose the exposure mid point without compromise to the data at either end.

But it does mean that post need to be awake and that the shooter needs to communicate with post regarding the brighter/darker looking images. But to be honest if post don’t understand this and recognise what you have done either buy just looking at the footage or checking the metadata what chance is there of post actually doing a decent job of grading your content? This should be fundamental and basic stuff for a colourist/grader. For a colourist/grader to not understand this and how to work with this is like hiring a camera operator that doesn’t know what an ND filter is.

The Sony FS7/FX9/F5/F55/Venice cameras can do something similar to an Arri camera by baking in the S-Log3 LUT. Then in post the exposure will look the same at every EI. BUT you will lose some highlight range at a low EI’s and some shadow range at a high EI’s without gaining any extra range at the opposite end. As a result the total dynamic range does  reduce as you move away from the base ISO.

In addition on the Venice, FS7/F5/F55 (and I suspect in a future update the FX9) you can bake in a user LUT to the SxS recordings. If you  create a set of S-Log3 to S-Log3 LUT’s with EI offsets included in the LUT you could replicate what Arri do by having an offset and tweaked S-Log3 User LUT for each EI that you want to shoot at. You would not use the cameras EI control you would leave the camera st the base ISO. The LUT’s themselves will include the exposure offset. These will maintain the full dynamic range but just like Arri they will  need to roll off the shadows or highlights within the LUT.

But monitoring will be tricky as you won’t have the benefit of a 709 type LUT for monitoring so you you may need to use an external monitor or viewfinder that can apply a LUT to it’s image. The good news is the same LUT would be used in the monitor for every version on the offset S-Log3 LUT that you are baking in as the exposure brightness levels will be the same for each offset.

So here you are a set of 4 S-Log3/S-Gamut3.cine offset LUT’s for those Sony cameras that will take a user LUT. I have named the LUT’s – 2S Down SL3C, 1S Down SL3C,  1S UP SL3C, 2S UP SL3C.

The name means (Number of Stops) (Down or Up) (Slog3.Cine).

So if the cameras base ISO is 2000 (F5/FS7 etc) and you want to shoot at the equivalent of 1000EI, which is 1 stop down from base you would use “1S Down SL3C”.

As always (to date at least) I offer these as a free download available by clicking on the links below.  But I always appreciate a contribution if you find them useful and make use of them. I will let you pay what you feel is fair, all contributions are greatly appreciated and it really does help keep this website up and running. If you can’t afford to pay, then just download the LUT’s and enjoy using them. If in the future you should choose to use them on a paying project, please remember where you got them and come back and make a contribution. More contributions means more LUT offerings in the future.

Please feel free to share a link to this page if you wish to share these LUT’s with anyone else or anywhere else. But it’s not OK to to share or host these on other web sites etc.

Here’s the link to download my offset S-Log3 Camera LUTs

To make a contribution please use the drop down menu here, there are several contribution levels to choose from.


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pixel Making Sony Log Cameras Behave Like Arri Cameras When Shooting Cine EI and S-Log3.


Making Sony Log Cameras Behave Like Arri Cameras When Shooting Cine EI and S-Log3. was first posted on February 25, 2020 at 9:10 pm.
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Why Does S-Log Recorded Internally Look Different To S-Log Recorded On An External Recorder?

I have written about this many times before, but I’ll try to be a bit more concise here.

So – You have recorded S-Log2 or S-Log3 on your Sony camera and at the same time recorded on an external ProRes Recorder such as an Atomos, Blackmagic or other ProRes recorder. But the pictures look different and they don’t grade in the same way. It’s a common problem. Often the external recording will look more contrasty and when you add a LUT the blacks and shadow areas come out very differently.

Video signals can be recorded using a several different data ranges. S-Log2 and S-Log3 signals are always Data Range.  When you record in the camera the cameras adds information to the recording called metadata that tells your editing or grading software that the material is Data Range. This way the edit and grading software knows how to correctly handle the footage and how to apply any LUT’s.

However when you record to an external recorder the external recorder doesn’t have this extra metadata. So the recorder will record the Data Range signal that comes from the camera but it doesn’t add the metadata. The ProRes codec is normally used for Legal Range video and by default, unless there is metadata that says otherwise, edit and grading software will assume any ProRes recordings to be Legal Range.

So what happens is that your edit software takes the file, assumes it’s Legal Range and handles it as a Legal Range file when in fact the data in the file is Data Range. This results in the recording levels being transposed into incorrect levels for processing. So when you add a LUT it will look wrong, perhaps with very dark shadows or very bright over exposed looking highlights. It can also limit how much you can grade the footage.

What Can We Do About It?

Premiere CC.

You don’t need to do anything in Premiere for the internal .mp4 or MXF recordings. They are handled correctly but Premiere isn’t handling the ProRes files correctly.

My approach for this has always been to use the legacy fast color corrector filter to transform the input range to the required output range. If you apply the fast color corrector filter to a clip you can use the input and output level sliders to set the input and output range. In this case we need to set the output black level to CV16 (as that is legal range black) and we need to set output white to CV235 to match legal range white. If you do this you will then see that the external recording appears to have almost exactly the same values as the internal recording. However there is some non-linearity in the transform, it’s not quite perfect.

Screenshot-2019-03-01-at-11.04.04 Why Does S-Log Recorded Internally Look Different To S-Log Recorded On An External Recorder?
Using the legacy “fast color corrector” filter to transform the external recording to the correct range within Premiere.

Now when you apply a LUT the picture and the levels are more or less what you would expect and almost identical to the internal recordings. I say almost because there is a slight hue shift. I don’t know where the hue shift comes from. In Resolve the internal and external recordings look pretty much identical and there is no hue shift. In Premiere they are not quite the same. The hue is slightly different and I don’t know why. My recommendation – use Resolve, it’s so much better for anything that needs any form of grading or color correction.

DaVinci Resolve:

It’s very easy to tell Resolve to treat the clips as Data Range recordings. In the media bin, right click on the clip and under “clip attributes” change the input range from “auto” to “full”. If you don’t do this DaVinci Resolve will assume the ProRes file to be legal range and it will scale the clip incorrectly in the same way as Premiere does. But if you tell Resolve the clip is full range then it is handled correctly.


Why Does S-Log Recorded Internally Look Different To S-Log Recorded On An External Recorder? was first posted on January 5, 2020 at 11:40 am.
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Don’t Convert Raw to ProRes Before You Do Your recording.

This comes up again and again, hence why I am writing about it once again.
Raw should never be converted to log before recording if you want any benefit from the raw. You may as well just record the 10 bit log that most cameras are capable of internally. Or take log and output it via the cameras 10 bit output (if it has one) and record that directly on the ProRes recorder. It doesn’t matter how you do it but if you convert between different recording types you will always reduce the image quality and this is as bad a way to do it as you can get. This mainly relates to cameras like the PXW-FS7. The FS5 is different because it’s internal UHD recordings are only 8 bit, so even though the raw is still compromised by converting it to ProRes log, this can still be better than the internal 8 bit log.
S-Log like any other log is a compromise recording format. Log was developed to squash a big dynamic range into the same sized recording bucket as would normally be used for conventional low dynamic range gammas. It does this by discarding a lot of tonal and textural information from everything brighter than 1 stop above middle grey, instead of the amount of data doubling for each stop up you go in exposure, it’s held at a constant amount. Normally this is largely transparent as human vision is less acute in the highlight range, but it is still a compromise.
The idea behind Linear raw is that it should give nothing away, each stop SHOULD contain double the data as the one below. But if you only have 12 bit data that would only allow you to record 11 stops of dynamic range as you would quickly run out of code values. So Sony have to use floating point math or something very similar to reduce the size of each stop by diving down the number of code values each stop has. This has almost no impact on highlights where you start off with 100’s or 1000’s values but in the shadows where a stop may only have 8 or 16 values dividing by 4 means you now only have 2 or 4 tonal levels. So once again this is a compromise recording format. To record a big dynamic range using linear what you really need is 16 bit data.
In summary so far:
S-Log reduces the number of highlight tonal values to fit it a big DR in a normal sized bucket.
Sony’s FSRaw, 12 Bit Linear reduces the number of tonal Values across the entire range to fit it in a compact 12 bit recording bucket, but the assumption is that the recording will be at least 12 bit. The greatest impact of the reduction is in the shadows.
Convert 12 bit linear to 10 bit S-Log and now you are compromising both the highlight range and the shadow range. You have the worst of both, you have 10 bit S-Log but with much less shadow data than the S-log straight from the camera. It’s really not a good thing to do and the internally generated S-Log won’t have shadows compromised in the same way.
If you have even the tiniest bit of under exposure or you attempt to lift the shadows in any way this will accentuate the reduced shadow data and banding is highly likely as the values become stretched even further apart as you bring them up the output gamma range.
If you expose brightly and then reduce the shadows this has the effect of compressing the values closer together or pushing them further down the output curve, closing them together as they go down the output gamma range, this reduces banding. This is one of the reasons why exposing more brightly can often help both log and raw recordings. So a bit of over exposure might help, but any under exposure is really, really going to hurt. Again, you would probably be better off using the internally generated S-Log.
To make matters worse there is also often an issue with S-Log in a ProRes file.
If all that is not enough there is also a big problem in the way ProRes files record S-Log. S-Log should always be recorded as full range data. When you record an internal XAVC file the metadata in the clips tells the edit or grading software that the file is full range. Then when you apply a LUT or do your grading the correct transforms occur and all shadow textures are preserved. But ProRes files are by default treated as legal range files. So when you record full range S-Log inside a ProRes file there is a high likelihood that your edit or grading software will handle the data in the clip incorrectly and this too can lead to problems in the shadows including truncated data, clipping and banding, even though the actual recorded data may be OK. This is purely a metadata issue, grading software such as DaVinci resolve can be forced to treat the ProRes files as full range.
 
 
more on S-Log and ProRes files here: http://www.xdcam-user.com/2019/03/sonys-internal-recording-levels-are-correct/

Don’t Convert Raw to ProRes Before You Do Your recording. was first posted on December 27, 2019 at 6:33 pm.
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Shooting S-Log3 on the PXW-FX9 – Do I need to expose bright?

Having shot quite a bit of S-Log3 content on the new Sony PXW-FX9 I thought I would comment on my exposure preferences. When shooting with an FS5, FS7 or F5, which all use the same earlier generation 4K sensor I find that to get the best results I need to expose between 1 and 2 stops brighter than the 41% for middle grey that Sony recommend. This is because I find my footage to be noisier than I would like if I don’t expose brighter. So when using CineEI on these cameras I use 800EI instead of the base 2000EI

However the FX9 uses a newer state of the art back illuminated sensor. This more sensitive sensor produces less noise so with the FX9 I no longer feel it is necessary to expose more brightly than the base exposure – at either of the base ISO’s. So if I am shooting using CineEI and 800 base, I use 800EI. When shooting at 4000 base, I use 4000 EI. 

This makes life so much easier. It also means that if you are shooting in a mode where LUT’s are not available (such as 120fps HD) then you can use the included viewfinder gamma assist function instead. Viewfinder gamma assist adds the same 709(800) look to the viewfinder as you would get from using the cameras built in 709(800) LUT.  You can use the VF gamma assist to help judge your exposure just as you would with a LUT.  Basically, if it looks right in the viewfinder, it almost certainly is right.

Testing various FX9’s against my Sekonic light meter the cameras CineEI ISO ratings seem to be spot on. So I would have no concerns if using a light meter to expose.  The camera also has a waveform scope and zebras to help guide your exposure.

VF Gamma assist is available in all modes on the FX9, including playback. Just be careful that you don’t have both a LUT on and gamma assist at the same time.


Shooting S-Log3 on the PXW-FX9 – Do I need to expose bright? was first posted on December 1, 2019 at 7:19 pm.
©2018 “XDCAM-USER.COM“. Use of this feed is for personal non-commercial use only. If you are not reading this article in your feed reader, then the site is guilty of copyright infringement. Please contact me at contact@xdcam-user.com