So this came up on social media. Someone had been playing with some sample raw footage provided by a camera manufacturer and he/she was concerned because he felt that this manufacturer supplied footage graded much better than his/her own Sony XAVC-I footage.
There is a lot to a situation like this, but very often the issue isn’t that the other footage was raw while his/her own footage was XAVC-I S-Log. Raw doesn’t normally have more colour or more DR than log. The colour range and the shadow range won’t be significantly different as that tends to be limited by the cameras sensor rather than the recording codec. But what you might have if the raw is 12 bit or greater is a larger bit depth or less compression. Perhaps a bit of both and that can sometimes give some extra precision or finer gradations as well as a bit less noise (although compression can reduce noise). This may come into play when you really start to push and pull the footage very hard in the grade, but generally, if you can’t get the image you want out of 10 bit XAVC-I, 12 bit raw isn’t going to help you. Raw might make it a bit quicker to get to where you want to be and I do love working with the 16 bit X-OCN (raw) from Venice and Burano, but I have never really felt that XAVC S-Log3 is lacking. Even a deeper bit depth might not be all it seems. The sensors in most video cameras under $20K only have 12 bit analog to digital converters and that tends to be the main image quality bottleneck (and this where Venice really shines with its 14 bit A2D).
Sony’s XAVC-I S-log3 grades really well, really, really well. A big issue however is the reliance on LUTs. 3D LUTs divide the image up into 33x or 65x adjustment bands and then it is down to the grading software to interpolate between each band. This can introduce artefacts into the image.
Some people simply skip doing a proper colourspace transform altogether and this may introduce twists into the gamma and colourspace which then makes it hard to get the colours or contrast they really want as it can be hard to bend the colours in a pleasing way without them going “weird”.
Colour managed workflows help to maintain the full range of the original content within the correct output colourspace without any unwanted twists and are often the best way to full realise the potential of the content you have shot.
Plus not all grading software is created equal. I was an Adobe Premiere user for years until I needed to do a lot more grading. When DaVinci Resolve became affordable I switched to Resolve for grading and have never looked back – after all it is a proper grading tool, not edit software with a bunch of plugins bolted on.
But as always the real key is how it was shot. Manufacturer supplied sample content is likely to have been shot very well and highly optimised, after all they want it to make their camera look as good as possible. When comparing footage from different sources you really do need to consider whether just how well it was shot. Was the most appropriate exposure index used for the type of scene. Was it shot at the best possible time of day for the best sun positioning. How much attention went in to things like the careful choice of the colours in the scene to provide pleasing colour contrast. How much time was spent with negative fill to bring down the shadow areas etc, what filtration was used to bleed off highlights or polarise the sky or windows. What lenses were used. All these things will have a massive impact on how gradeable the footage will be.
I’ve written about this before, but the way Adobe have changed the way they manage colourspaces has changed, it hasn’t been well documented, and it’s causing a lot of confusion.
When importing Log footage into the latest versions of Adobe Premiere instead of the log footage looking flat and washed out as it used to, now it looks contrasty and well saturated. If it has been exposed correctly (according to the manufacturers specifications) then it will look like normal Rec-709 footage rather than the flat look that most people associate with log. This is confusing people, many assume Adbe is now adding a LUT to the footage by default, it isn’t. What is happening isd a fundamental change to the way Premiere handles different colorspaces.
NOT ADDING A LUT.
Premiere is NOT adding a LUT. It is transforming between the captured colorspace and the display colorspace so that the footage looks correct with the right contrast, colour and brightness on your display. Your footage remains in its native colorspace at all times (unless you force it into an alternate and possibly wrong colorspace by using the interpret footage function).
Your display could be 709, HDR10, HLG, SGamut3/S-log3 and in each case the footage would, within the limitations of the displays format have the same basic contrast and colour etc, the footage would look the same whether viewing in SDR, HDR or Log because Premiere maps it to the correct levels for the output colorspace you are using to view your content.
OLD BROKEN WORKFLOWS.
The issue is that previously we have been using very broken workflows that are normally incapable of showing capture colorspaces other than Rec-709 correctly. This has made people believe that log formats are supposed to look flat – They are not! When viewed correctly they should have the same contrast as 709 etc. Log is not flat, but we have been viewing it incorrectly because most workflows have been incapable of mapping different source colorspaces to our chosen working/viewing colorspace.
LUTs ARE A QUICK FIX – WITH LIMITATIONS.
Up to now to fix these broken workflows we have added LUT’s to convert our beautiful, high dynamic range, vast colorspace source formats into restricted, reduced dynamic range display formats. Once you add that 709 LUT to you S-Log3 footage it is no longer SGamut3/Slog3 it is now Rec-709 with all the restrictions that 709 has such as limited dynamic range, limited colorspace etc and that may limit what you can do with it in the grade. Plus it limits you to only ever outputting in SDR 709.
But what we have now in a colour managed workflow is our big range log being displayed correctly on a 709 display or any other type of display, including HDR or DCI-P3 etc. Because the footage is still in its native colorspace you will have much greater grading latitude, there’s no knee added to the highlights, no shadow roll off, no artificial restriction to the source colorspace. So you can more easily push and pull the material far further during adjustment and grading (raw workflows have always been color managed out of necessity as the raw footage can’t be viewed correctly without first being converted into a viewable colorspace).
HERE’s THE RUB!
But the rub is – you are not now adding someone else’s carefully crafted LUT, which is a combination of creative and artistic corrections that give a pleasing look combined with the Log to Rec 709 conversion.
So – you’re going to have to learn how to grade for yourself – but you will have a much bigger colour and contrast range to work with as your footage will remain in it’s full native capture range.
And – if you need to deliver in multiple formats, which you will need to start doing very soon if you are not already, it is all so much easier as in a colour managed workflow all you do is switch the output format to change from 709 to HDR10 or HLG or DCI-P3 to get whatever format you want without having to re-grade everything or use different LUT’s for each format.
HOW LONG CAN YOU STAY JUST IN REC-709?
And when you consider that almost all new TV’s, the majority of new Phones and Tablets all have HDR screens and this is all now supported on YouTube and Vimeo etc how much longer do you think you will be able to cling on to only delivering in SDR Rec-709 using off-the-shelf SDR LUTs? If you ever want to do stuff for Netflix, Amazon etc you will need to figure out how to work in both SDR and HDR.
IT’S HERE TO STAY
Adobe have done a shockingly bad job of documenting and explaining this new workflow, but it is the future and once you learn how to use it properly it should improve the quality of what you deliver and at the same time expand the range of what you can deliver.
I have to deliver both SDR and HDR for most of my clients and I’ve been using colour managed workflows for around 6 years now (mostly ACES in Resolve). I could not go back to the restrictions of a workflow that doesn’t allow you to output in multiple colorspaces or requires you to perform completely separate grades for SDR and HDR. The great thing about ACES is that it is a standardised and well documented workflow so you can use ACES LUT’s designed for the ACES workflow if you wish. But until Adobe better document their own colour managed workflow it is difficult to design LUT’s for use in the Adobe workflow. Plus LUT’s that work with the Adobe workflow, probably won’t work elsewhere. So – it’s never been a better time to learn how to grade properly or think about what workflow you will use to do your grading.
The bottom line is the days of using LUT’s that add both an artistic look and convert your footage from its source colorspace to a single delivery colorspace are numbered. Color managed offer far greater flexibility for multi format delivery. Plus they retain the full range and quality of your source material, no matter what colorspace you shot it in or work in.
CineEI is different to conventional Shooting and you will need to think differently.
Shooting using CineEI is a very different process to conventional shooting. The first thing to understand about CineEI and Log is that the number one objective is to get the best possible image quality with the greatest possible dynamic range and this can only be achieved by recording at the cameras base sensitivity. If you add in camera gain you add noise and reduce the dynamic range that can be recorded, so ideally you always need to record at the cameras base sensitivity for the best possible captured image.
Sony call their system CineEI. On an Arri camera the only way to shoot log or raw is using Exposure Indexes and it’s the same with Red, Canon and almost every other digital cinema camera when shooting log. You always record at the cameras base sensitivity because this will deliver the greatest dynamic range.
Post Production.
A key part of any log workflow is the post production. Without a really good post production workflow you will never see the best possible results from shooting Log. An important part of the post production workflow will be correcting for any exposure offsets used when shooting. If something has been exposed very brightly, then in post you will bring that exposure down to a normal level. Bringing the levels down in post will decrease noise. The flip side to this is that if the exposure is very dark then you will need to raise the levels in post and this will make then more noisy
Exposure and Light Levels.
It is assumed that when using CineEI and shooting with log that you will control the light levels in your shots and use levels suitable for the recording ISO (base ISO) of the camera using combinations of aperture, ND and shutter speed, again it’s all about getting the best possible image quality. If lighting a scene you will light for the base ISO of the camera you are using.
Here’s the bit that’s different:
Changing the EI (Exposure Index) allows you to tailor where the middle of your exposure range is. It allows you to alter the balance between more highlight range with less shadows or less highlight range with more shadow information in the captured image. On a bright high contrast exterior you might want more highlight range, while for a dark moody night scene you might want more shadow range. Exposing brighter puts more light on to the sensor. More light on the sensor will extend the shadow range but decrease the highlight range. Exposing darker will decrease the shadow range but also allow brighter highlights to be captured without clipping.
IMPORTANT: EI is NOT the same as ISO.
ISO is a measure of a film stock or camera sensors SENSITIVITY to light. It is the measure of how strongly the cameras sensor responds to light.
Exposure Index is a camera setting that determines how bright the image will become for a given EXPOSURE. While it is related to sensitivity it is NOT the same thing and should always be kept distinct from sensitivity.
ISO= Sensitivity and a measure of the sensors response to light.
EI =Exposure Index – how bright the image seen in the viewfinder will be.
The important bit to understand is that EI is an exposure rating, not a sensitivity rating. The EI is the number you would put into a light meter for the optimum EXPOSURE for the type of scene you are shooting. The EI that you use depends on your desired shadow and highlight ranges as well as how much noise you feel is acceptable.
What Actually happens when I change the EI value on a Sony camera?
On a Sony camera the only things that change when you alter the EI value are the brightness of any Look Up Tables (LUTs) being used, the EI value indicated in the viewfinder and the EI value recorded in the metadata that is attached to your clip.
Importantly – To actually see a change in the viewfinder image or the image on an external monitor you must be viewing your images via a LUT as the EI changes the LUT brightness, changing the EI does not on it’s own change the way the S-Log3 is recorded or the sensitivity of the camera. If you are not viewing via a LUT you won’t see any changes when you change the EI values, so for CineEI to work, you must be monitoring via a LUT.
Raising and Lowering the EI value:
When you raise the EI value the LUT will become brighter. When you lower the EI value the LUT will become darker.
If we were to take a camera with a base ISO of 800 then a nominal “normal” exposure would result from using 800 EI. When the base ISO value and the EI value are matched, then we can expect to get a “normal” exposure.
The S-Log3 levels that you will get when exposed correctly and the EI value matches the cameras base ISO value. Note you will have 6 stops of range above middle grey and 8+ stops below middle grey.
Let’s now look at what happens when we use EI values higher or lower than the base ISO value.
(Note: One extra stop of exposure is the equivalent of doubling the ISO or EI. One less stop of exposure is the equivalent of halving the ISO or EI. So if double 800 EI so you get to 1600 EI this would be considered 1 stop higher. If you double 1600 EI so you are at 3200 EI this is one further stop higher. So 800 EI to 3200 EI is 2 stops higher)
If you were to use a higher EI, let’s say 3200 EI, two stops higher than the base 800 EI, then the LUT will become 2 stops brighter.
If you were using a light meter you would enter 3200 into the light meter.
When looking at this now 2 stops brighter viewfinder image you would be inclined to close the aperture by 2 stops (or add ND/shorter shutter) to bring the brightness of the viewfinder image back to normal. The light meter would also recommend an exposure that is 2 stops darker.
Because the recording sensitivity or base ISO remains the same no matter what the EI, the fact that you have reduced your exposure by 2 stops means that the sensor is now receiving 2 stops less light, however the recording sensitivity has not changed.
Shooting like this, using a higher EI than the base ISO will result in less light hitting the sensor which will result in images with less shadow range and more noise but at the same time a greater highlight range.
The S-Log3 levels that you will get when the EI value is 2 stops higher than the cameras base ISO value and you have exposed 2 stops darker to compensate for the brighter viewfinder image. Note how you now have 8 stops above middle grey and 6+ stops below. The final image will also have more noise.
A very important thing to consider here is that this is not what you normally want when shooting darker scenes, you normally want less noise, more shadow range. So with CineEI, you would normally try to shoot a darker, moody scene with an EI lower than the base ISO.
In this chart we can see how at 800 EI there is 6 stops of over exposure range and 9 stops of under. At 1600 EI there will be 7 stops of over range and 8 stops of under and the image will also be twice as noisy. At 400 EI there are 5 stops over and 10 stops under and the noise will be halved.
This goes completely against most peoples conventional exposure thinking.
For a darker scene or a scene with large shadow areas you actually want to use a low EI value. So if the base ISO is 800 then you might want to consider using 400 EI. 400 EI will make the LUT 1 stop darker. Enter 400 EI into a light meter and compared to 800 the light meter will recommend an exposure that is 1 stop brighter. When seeing an image in the viewfinder that is 1 stop darker you will be inclined to open the aperture or reduce the ND to bring the brightness back to a normal level.
This now brighter exposure means you are putting more light on to the sensor, more light on the sensor means less noise in the final image and an increased shadow range. But, that comes at the loss of some of the highlight range.
The S-Log3 levels that you will get when the EI value is 2 stops lower than the cameras base ISO value and you have exposed more brightly to compensate for the darker viewfinder image. Note how you now have 4 stops above middle grey and 10+ stops below. The final image will have less noise.
Need to think differently.
The CineEI mode and log are not the same as conventional “what you see is what you get” shooting methods. CineEI requires a completely different approach if you really want to achieve the best possible results.
If you find the images are too dark when the EI value matches the recording base ISO, then you need to open the aperture, add light or use a faster lens. Raising the EI to compensate for a dark scene is likely to create more problems than it will fix. It might brighten the image in the viewfinder, making you think all is OK, but on your small viewfinder screen you won’t see the extra noise and grain that will be in the final images once you have raised your levels in post production. Using a higher EI and not paying attention could result in you stopping down a touch to protect some blown out highlight or to tweak the exposure when this is probably the last thing you actually want to do.
I’ve lost count of the number of times I have seen people cranking up the EI to a high value thinking this is how you should shoot a darker scene only to discover they can’t then make it look good in post production. The CineEI mode on these cameras is deliberately kept separate from the conventional “custom” or “SDR” mode to help people understand that this is something different. And it really does need to be treated differently and you really do need to re-learn how you think about exposure.
For dark scenes you almost never want to use an EI value higher than the base ISO value and often it is better it use a lower EI value as this will help ensure you expose any shadow areas sufficiently brightly.
The CineEI mode in some regards emulates how you would shoot with a film camera. You have a single film stock with a fixed sensitivity (the base ISO). Then you have the option to expose that stock brighter (using a lower EI) for less grain, more shadow detail, less highlight range or expose darker (using a higher EI) more grain, less shadow detail, more highlight range. Just as you would do with a film camera.
Sony’s CineEI mode is not significantly different from the way you shoot log or raw with an Arri camera. Nor is it significantly different to how you shoot raw on a Red camera – the camera shoots at a fixed sensitivity and any changes to the ISO value you make in camera are only actually changing the monitoring brightness and the clips metadata.
Exposing more brightly on purpose to achieve a better end result is not “over exposure”. It is simply brighter exposure. Over exposure is generally considered to be a mistake or undesirable, but exposing more brightly on purpose is not a mistake.
This keeps cropping up more and more as users of Adobe Premiere Pro upgrade to the 2022 version.
What people are finding is that when they place S-Log3 (or almost any other log format such as Panasonic V-Log or Canon C-Log) into a project, instead of looking flat and washed as it would have done in previus versions of Premiere, the log footage looks more like Rec-709 with normal looking contrast and normal looking color. Then when they apply their favorite LUT to the S-Log3 it looks completely wrong, or at least very different to the way it looked in previous versions.
So, what’s going on?
This isn’t a bug, this is a deliberate change. Rec-709 is no longer the only colourspace that people need to work inand more and more new computers and monitors support other colourspaces such as P3 or Rec2020. The Macbook Pro I am writing this on has a wonderful HDR screen that supports Rec2020 or DCI P3 and it looks wonderful when working with HDR content!
Color Management and Colorspace Transforms.
Premiere 2022 isn’t adding a LUT to the log footage, it is doing a colorspace transform so that the footage you shot in one colorspace (S-Log3/SGamut3.cine/V-Log/C-Log/Log-C etc) gets displayed correctly in the colorspace you are working in.
S-Log3 is NOT flat.
A common misconception is that S-log3 is flat or washed out. This is not true. S-log3 has normal contrast and normal colour.
The only reason it appears flat is because more often than not people use it in a miss matched color space and the miss match that you get when you display material shot using the S-log3/SGamut3 colorspace using the Rec-709 colorspace causes it to be displayed incorrectly and the result is images that appear to be flat, lack contrast and colour when in fact your S-Log3 footage isn’t flat, it has lots of contrast and lots of colour. You are just viewing it incorrectly in the incorrect colorspace.
So, what is Premiere 2022 doing to my log footage?
What is now happening in Premiere is that Premiere 2022 reads the clips metadata to determine its native colorspace and it then adds a colorspace transform to convert it to the display colourspace determined by your project settings.
The footage is still S-Log3, but now you are seeing it as it is actually supposed to look, albeit within the limitations of the display gamma. S-log3 isn’t flat, it just that previously you were viewing it incorrectly, but now with the correct colorspace being added to match the project settings and the type of monitor you are using the S-Log3 is being displayed correctly having been transformed fro S-Log3/SGamut3 to Rec-709 or whatever your project is set to.
If your project is an HDR project, perhaps HDR10 to be compatible with most HDR TV’s or for a Netflix commission then the S-log3 would be transformed to HDR10 and would be seen as HDR on an HDR screen without any grading being necessary. If you then changed you project settings to DCI-P3 then everything in your project will be transformed to P3 and will look correct without grading on a P3 screen. Then change to Rec709 and again it all looks correct without grading – the S-Log3 doesn’t look flat, because in fact it isn’t.
Color Managed Workflows will be the new “normal”.
Colour managed workflows such as this are now normal in most high end edit and grading applications and it is something we need to get used to because Rec709 is no longer the only colorspace that people need to deliver in. It won’t be long before delivery in HDR (which may mean one of several different gamma and gamut combinations) becomes normal. This isn’t a bug, this is Premiere catching up and getting ready for a future that won’t be stuck in SDR Rec-709.
A color managed workflow means that you no longer need to use LUT’s to convert your Log footage to Rec-709, you simply grade you clips within the colorspace you will be delivering in. A big benefit of this comes when working with multiple sources. For example S-Log3 and Rec-709 material in the same project will now look very similar. If you mix log footage from different cameras they will all look quite similar and you won’t need separate LUT’s for each type of footage or for each final output colorspace.
The workaround if you don’t want to change.
If you don’t want to adapt to this new more flexible way of working then you can force Premiere to ignore the clips metadata by right clicking on your clips and going to “Modify” and “Interpret Footage” and then selecting “Colorspace Override” and setting this to Rec-709. When you use the interpret footage function on an S-Log3 clip to set the colorspace to Rec709 what you are doing is forcing Premiere to ignore the clips metadata and to treat the S-Log3 as though it is a standard dynamic range Rec-709 clip. In a Rec-709 project his re-introduces the gamut miss-match that most are used to and results in the S-Log3 appearing flat and washed out. You can then apply your favourite LUTs to the S-Log3 and the LUT then transforms the S-Log3 to the projects Rec-709 colorspace and you are back to where you were previously.
This is fine, but you do need to consider that it is likely that at some point you will need to learn how to work across multiple colorspaces and using LUTs as colorspace transforms is very inefficient as you will need separate LUTs and separate grades for every colorspace and every different type of source material that you wish to work in. Colour managed workflows such as this new one in Premiere or ACES etc are the way forwards as LUTs are no longer needed for colorspace transforms, the edit and grading software looks after this for you. Arri Log-C will look like S-Log3 which will look like V-Log and then the same grade can be applied no matter what camera or colorspace was used. It will greatly simplify workflows once you understand what is happening under the hood and allows you to output both SDR and HDR versions without having to completely re-grade everything.
Unfortunately I don’t think the way Adobe are implementing their version of a colour managed workflow is very clear. There are too many automatic assumptions about what you want to do and how you want to handle your footage. On top of this there are insufficient controls for the user to force everything into a known set of settings. Instead different things are in different places and it’s not always obvious exactly what is going on under the hood. The color management tools are all small addons here and there and there is no single place where you can go for an overview of the start to finish pipeline and settings as there is in DaVinci Resolve for example. This makes it quite confusing at times and it’s easy to make mistakes or get an unexpected result. There is more information about what Premiere 2022 is doing here: https://community.adobe.com/t5/premiere-pro-discussions/faq-premiere-pro-2022-color-management-for-log-raw-media/
This is a question that comes up a lot. Especially from those migrating to a camera with a CineEI mode from a camera without one. It perhaps isn’t obvious why you would want to use a shooting mode that has no way of adding gain to the recordings.
If using the CineEI mode shooting S-log3 at the base ISO, with no offsets or anything else then there is very little difference between what you record in Custom mode at the base ISO and CineEI at the base EI.
But we have to think about what the CineEI mode is all about. It’s all about image quality. You would normally chose to shoot S-Log3 when you want to get the highest possible quality image and CineEI is all about quality.
The CineEI mode allows you to view via your footage via a LUT so that you can get an appreciation of how the footage will look after grading. Also when monitoring and exposing via the LUT because the dynamic range of the LUT is narrower, your exposure will be more accurate and consistent because bad exposure looks more obviously bad. This makes grading easier. One of the keys to easy grading is consistent footage, footage where the exposure is shifting or the colours changing (don’t use ATW with Log!!) can be very hard to grade.
Then once you are comfortable exposing via a LUT you can start to think about using EI offsets to make the LUT brighter or darker. When the LUT is darker you open the aperture or reduce the ND to return the LUT to a normal looking image and vice versa with a brighter LUT. This then changes the brightness of the S-log3 recordings and you use this offsetting process to shift the highlight/shadow range as well as noise levels to suit the types of scenes you are shooting. Using a low EI (which makes the LUT darker) plus correct LUT exposure (the darker LUT will make you open the aperture to compensate) will result in a brighter recording which will improve the shadow details and textures that are recorded and thus can be seen in the shadow areas. At the same time however that brighter exposure will reduce the highlight range by a similar amount to the increase in the shadow range. And no matter what the offset, you always record at the cameras full dynamic range.
I think what people misunderstand about CineEI is that it’s there to allow you to get the best possible, highly controlled images from the camera. Getting the best out of any camera requires appropriate and sufficient light levels. CineEI is not designed or intended to be a replacement for adding gain or shooting at high recording ISOs where the images will be already compromised by noise and lowered dynamic range.
CineEI exists so that when you have enough light to really make the camera perform well you can make those decisions over noise v highlights v shadows to get the absolute best “negative” with consistent and accurate exposure to take into post production. It is also the only possible way you can shoot when using raw as raw recordings are straight from the sensor and never have extra gain added in camera.
Getting that noise/shadow/highlight balance exactly right, along with good exposure is far more important than the use of external recorders or fatter codecs. You will only ever really benefit fully from higher quality codecs if what you are recording is as good as it can be to start with. The limits as to what you can do in post production are tied to image noise no matter what codec or recording format you use. So get that bit right and everything else gets much easier and the end result much better. And that’s what CineEI gives you great control over.
When using CineEI or S-Log3 in general you need to stop thinking “video camera – slap in a load if gain if its dark” and think “film camera – if its too dark I need more light”. The whole point of using log is to get the best possible image quality, not shooting with insufficient light and a load of gain and noise. It requires a different approach and completely different way of thinking, much more in line with the way someone shooting on film would work.
What surprises me is the eagerness to adopt shutter angles and ISO ratings for electronic video cameras because they sound cool but less desire to adopt a film style approach to exposure based on getting the very best from the sensor. In reality a video sensor is the equivalent of a single sensitivity film stock. When a camera has dual ISO then it is like having a camera that takes two different film stocks. Adding gain or raising the ISO away from the base sensitivity in custom mode is a big compromise that can never be undone. It adds noise and decreases the dynamic range. Sometimes it is necessary, but don’t confuse that necessity with getting the very best that you can from the camera.
It’s amazing how often people will tell you how easy it is to change the white balance or adjust the ISO of raw footage in post. But can you, is it really true and is it somehow different to changing the ISO or white balance of Log footage?
Let’s start with ISO. If ISO is sensitivity, or the equivalent of sensitivity how on earth can you change the sensitivity of the camera once you get into post production. The answer is you can’t.
But then we have to consider how ISO works on an electronic camera. You can’t change the sensor in a video camera so in reality you can’t change how sensitive an electronic camera is (I’m ignoring cameras with dual ISO for a moment). All you can do is adjust the gain or amplification applied to the signal from the sensor. You can add gain in post production too. So, when you adjust the exposure or using the ISO slider for your raw footage in post all you are doing is adjusting how much gain you are adding. But you can do the same with log or any other gamma.
One thing that makes a difference with raw is that the gain is applied in such a way that what you see looks like an actual sensitivity change no matter what gamma you are transforming the raw to. This makes it a little easier to make changes to the final brightness in a pleasing way. But you can do exactly the same thing with log footage. Anything you do in post must be altering the recorded file, it can never actually change what you captured.
Changing the white balance in post: White Balance is no different to ISO, you can’t change in post what the camera captured. All you can do is modify it through the addition or subtraction of gain.
Think about it. A sensor must have a certain response to light and the colours it sees depending on the material it’s made from and the colour filters used. There has to be a natural fixed white balance or a colour temperature that it works best at.
The Silicon that video sensors are made from is almost always more sensitive at the red end of the spectrum than the blue end. So as a result almost all sensors tend to produce the best results with light that has a lot of blue (to make up for the lack of blue sensitivity) and not too much red. So most cameras naturally perform best with daylight and as a result most sensors are considered daylight balanced.
If a camera produces a great image under daylight how can you possibly get a great image under tungsten light without adjusting something? Somehow you need to adjust the gain of the red and blue channels.
Do it in camera and what you record is optimised for your choice of colour temperature at the time of shooting. But you can always undo or change this in post by subtracting or adding to whatever was added in the camera.
If the camera does not move away from its native response then if you want anything other than the native response you will have to do it in post and you will be recording at the cameras native white balance. If you want a different colour temp then you need to add or subtract gain to the R & B channels in post to alter it.
Either way what you record has a nominal white balance and anything you do in post is skewing what you have recorded using gain. There is no such thing as a camera with no native white balance, all cameras will favour one particular colour temperature. So even if a manufacturer claims that the white balance isn’t baked in what they mean is they don’t offer the ability to make any adjustments to the recorded signal. If you want the very best image quality, the best method is to adjust at the time of recording. So, as a result a lot of camera manufacturers will skew the gain of the red and blue channels of the sensor in the camera when shooting raw as this optimises what you are recording. You can then skew it again in post should you want a different balance.
With either method if you want to change the white balance from what was captured you are altering the gain of the red and blue channels. Raw doesn’t magically not have a white balance, so shooting with the wrong white balance and correcting it in post is not something you want to do. Often you can’t correct badly balanced raw any better than you can correct incorrectly balanced log.
How far you can adjust or correct raw depends on how it’s been compressed (or not), the bit depth, whether it’s log or linear and how noisy it is. Just like a log recording really, it all depends on the quality of the recording.
The big benefit raw can have is that the amount of data that needs to be recorded is considerably reduced compared conventional component or RGB video recordings. As a result it’s often possible to record using a greater bit depth or with much less compression. It is the greater bit depth or reduced compression that really makes a difference. 16 bit data can have up to 65,536 luma gradations, compare that to the 4096 of 12 bit or 1024 of 10 bit and you can see how a 16 bit recording can have so much more information than a 10 bit one. And that makes a difference. But 10 bit log v 10 bit raw, well it depends on the compression, but well compressed 10 bit log will likely outperform 10 bit raw as the all important colour processing will have been done in the camera at a much higher bit depth than 10 bit.
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.
Last week I did an almost 2 hour long Webinar with Visual Impact on Gamma and gamma curves. The webinar was recorded and you can view the full session by following the link below.
Even though I have written about these many times before the message still just doesn’t seem to be getting through to people.
Since the dawn of photography and video the only way to really change the signal to noise ratio and ultimately how noisy the pictures are is by changing how much light you put onto the sensor.
Gain, gamma, log, raw, etc etc only have a minimal effect on the signal to noise ratio. Modern cameras do admittedly employ a lot of noise reduction processes to help combat high noise levels, but these come at a price. Typically they soften the image or introduce artefacts such as banding, smear or edge tearing. So you always want to start off with the best possible image from the sensor with the least possible noise and the only way to achieve that is through good exposure – putting the optimum amount of light onto the sensor.
ISO is so confusing:
But just to confuse things the use of ISO to rate an electronic cameras sensitivity has become normal. But the problem is that most people have no clue about what this really means. On an electronic camera ISO is NOT a sensitivity measurement, it is nothing more than a number that you can put into an external light meter to allow you to use that light meter to obtain settings for the shutter speed and aperture that will give you the camera manufacturers suggest optimum exposure. That’s it – and that is very different to sensitivity.
Lets take Sony’s FS7 as an example (most other cameras behave in a very similar way).
If you set the FS7 up at 0dB gain, rec-709, it will have an exposure rating of 800 ISO. Use a light meter to expose with the meters ISO dial set to 800. Lets say the light meter says set the aperture to f8. When you do this the image is correctly exposed, looks good (well as good as 709 gets at least) and for most people has a perfectly acceptable amount of noise.
Now switch the camera to S-Log2 or S-Log3. With the camera still set to 0dB the ISO rating changes to 2000 which give the impression that the camera may have become more sensitive. But did we change the sensor? No. Have we added any more gain? No, we have not, the camera is still at 0dB. But if you now expose at the recommended levels, after you have done your grading and you grade to levels similar to 709 the pictures will look quite a lot noisier than pictures shot using Rec-709.
So what’s going on?
If you now go back to the light meter to expose the very same scene, you turn the ISO dial on the light meter from 800 to 2000 ISO and the light meter will tell you to now set the aperture to f13 (approx). So starting at the f8 you had for 800 ISO, you close the aperture on the camera by 1.3 stops to f13 and you will have the “correct” exposure.
BUT: now you are putting 1.3 stops less light on to the sensor so the signal coming from the sensor is reduced by 9dB and as a result the sensor noise that is always there and never really changes is much more noticeable. As a result compared to 709 the graded S-Log looks noisy and it looks noisier by the equivalent of 9dB. This is not because you have changed the cameras sensitivity or changed because you have changed the amount of camera gain but because compared to when you shoot in 709 the sensor is being under exposed and as a result it is outputting a signal 9dB lower. So in post production when you grade or add a LUT you have to add 9dB of gain to get the same brightness as the original direct rec-709 recording and as well as making the desirable image brighter it also makes the noise 9dB higher (unless you do some very fancy noise reduction work in post).
So what do you do?
It’s common simply to open the aperture back up again, typically by 1.5 stops so that after post production grading the S-log looks no more noisy than the 709 from the FS7 – Because in reality the FS7’s sensor works best for most people when rated at the equivalent of 800 ISO rather than 2000 – probably because it’s real sensitivity is 800 ISO.
When you think about it, when you shoot with Rec-709 or some other gamma that won’t be graded it’s important that it looks good right out of the camera. So the camera manufacturer will ensure that the rec-709 noise and grain v sensitivity settings are optimum – so this is probably the optimum ISO rating for the camera in terms of noise, grain and sensitivity.
So don’t be fooled into thinking that the FS7 is more sensitive when shooting with log, because it isn’t. The only reason the ISO rating goes up as it does is so that if you were using a light meter it would make you put less light onto the sensor which then allows the sensor to handle a brighter highlight range. But of course if you put less light onto the sensor the sensor won’t be able to see so far into the shadows and the picture may be noisy which limits still further the use of any shadow information. So it’s a trade-off, more highlights but less shadows and more noise. But the sensitivity is actually the same. Its’s an exposure change not a sensitivity change.
So then we get into the S-Log2 or S-Log3 debate.
First of all lets just be absolutely clear that both have exactly the same highlight and shadow ranges. Both go to +6 stops and -8 stops, there is no difference in that regard. Period.
And lets also be very clear that both have exactly the same signal to noise ratios. S-log3 is NOT noisier than S-log2. S-log 3 records some of the mid range using higher code values than S-Log2 and before you grade it that can sometimes make it appear like it’s noisier, but the reality is, it is not noisier. Just like the differing ISO ratings for different gamma curves, this isn’t a sensitivity change, it’s just different code values being used. See this article if you want the hard proof: https://www.xdcam-user.com/2014/03/understanding-sonys-slog3-it-isnt-really-noisy/
Don’t forget when you shoot with log you will be grading the image. So you will be adjusting the brightness of the image. If you grade S-Log2 and S-Log3 to the same brightness levels the cumulative gain (the gain added in camera and the gain added in post) ends up the same. So it doesn’t matter which you use in low light the final image, assuming a like for like grade will have the same amount of noise.
For 8 bit records S-Log2 has different benefits.
S-Log2 was designed from the outset for recording 14 stops with an electronic video camera. So it makes use of the cameras full recording range. S-Log3 is based on an old film log curve (cineon) designed to transfer 16 stops or more to a digital intermediate. So when the camera only has a 14 stop sensor you waste a large part of the available recording range. On a 10 bit camera this doesn’t make much difference. But on a 8 bit camera where you are already very limited with the number of tonal values you can record it isn’t ideal and as a result S-Log2 is often a better choice.
But if I shoot raw it’s all going to be so much better – isn’t it?
Yes, no, maybe…. For a start there are lot’s of different types of raw. There is linear raw, log raw, 10 bit log raw, 12 bit linear, 16 bit linear and they are all quite different.
But they are all limited by what the sensor can see and how noisy the sensor is. So raw won’t give you less noise (it might give different looking noise). Raw won’t give you a bigger dynamic range so it won’t allow you to capture deeper or brighter highlights.
But what raw does normally is to give you more data and normally less compression than the cameras internal recordings. In the case of Sony’s FS5 the internal UHD recordings are 8 bit and highly compressed while the raw output is 12 bit, that’s a 4 fold increase in the amount of tonal values. You can record the 12bit raw using uncompressed cDNG or Apples new ProResRaw codec which doesn’t introduce any appreciable compression artefacts and as a result the footage is much more flexible in post production. Go up to the Sony Venice, F5 or F55 cameras and you have 16 bit raw and X-OCN (which behaves exactly like raw) which has an absolutely incredible range of tonal values and is a real pleasure to work with in post production. But even with the Venice camera the raw does not have more dynamic range than the log. However because there are far more tonal values in the raw and X-OCN you can do more with it and it will hold up much better to aggressive grading.
It’s all about how you expose.
At the end of the day with all of these camera and formats how you expose is the limiting factor. A badly exposed Sony Venice probably won’t end up looking anywhere near as good as a well exposed FS7. A badly exposed FS7 won’t look as good as a well exposed FS5. No camera looks good when it isn’t exposed well.
Exposure isn’t brightness. You can add gain to make a picture brighter, you can also change the gamma curve to change how bright it is. But these are not exposure changes. Exposure is all about putting the optimum amount of light onto the sensor. Enough light to produce a signal from the sensor that will overcome the sensors noise. But also not so much light that the sensor overloads. That’s what good exposure is. Fiddling around with gamma curves and gain settings will only every make a relatively small difference to noise levels compared to good exposure. There’s just no substitute for faster lenses, reflectors or actually adding light if you want clean images.
And don’t be fooled by ISO ratings. They don’t tell you how noisy the picture is going to be, they don’t tell you what the sensitivity is or even if it’s actually changing. All it tells you is what to set a light meter to.
There are a lot of videos circulating on the web right now showing what appears to be some kind of magic trick where someone has shot over exposed, recorded the over exposed images using ProRes Raw and then as if by magic made some adjustments to the footage and it goes from being almost nothing but a white out of over exposure to a perfectly exposed image.
This isn’t magic, this isn’t raw suddenly giving you more over exposure range than you have with log, this is nothing more than a quirk of the way FCP-X handles ProRes Raw material.
Before going any further – this isn’t a put-down of raw or ProRes raw. It’s really great to be able to take raw sensor data and record that with only minimal processing. There are a lot of benefits to shooting with raw (see my earlier post showing all the extra data that 12 bit raw can give). But a magic ability to let you over expose by seemingly crazy amounts isn’t something raw does any better than log.
Currently to work with ProRes Raw you have to go through FCP-X. FCP-X applies a default sequence of transforms to the Raw footage to get it from raw data to a viewable image. These all expect the footage to be exposed exactly as per the camera manufacturers recommendations, with no leeway. Inside FCP-X it’s either exposed exactly right, or it isn’t.
The default decode settings include a heavy highlight roll-off. Apple call it “Tone Mapping”. Fancy words used to make it sound special but it’s really no different to a LUT or the transforms and processes that take place in other raw decoders. Like a LUT it maps very specific values in the raw data to very specific output brightness values. So if you shoot just a bit bright – as you would often do with log to improve the signal to noise ratio – The ProRes raw appears to be heavily over exposed. This is because anything bright ends up crushed into nothing but flat white by the default highlight roll off that is applied by default.
In reality the material is probably only marginally over exposed, maybe just one to 2 stops which is something we have become used to doing with log. When you view brightly exposed log, the log itself doesn’t look over exposed, but if you apply a narrow high contrast 709 LUT to it, it then the footage looks over exposed until you grade it or add an exposure compensated LUT. This is what is happening by default inside FCP-X, a transform is being applied that makes brightly exposed footage look very bright and possibly over exposed – because thats the way it was shot!
This is why in FCP-X it is typical to change the color library to WCG (Wide Color Gamut) as this changes the way FCP-X processes the raw, changing the Tone Mapping and most importantly getting rid of the highlight roll off. With no roll-off, highlights and any even slight over exposure will still blow out as you can’t show 14 stops on a conventional 6 stop TV or monitor. Anything beyond the first 6 stops will be lost, the image will look over exposed until you grade or adjust the material to control the brighter parts of the image and bring them back into a viewable range. When you are in WCG mode in FCP-X the there is no longer a highlight roll off crushing the highlights and now because they are not crushed they can be recovered, but there isn’t any more highlight range than you would have if you shot with log on the same camera!
None of this is some kind of Raw over exposure magic trick as is often portrayed. It’s simply not really understanding how the workflow works and appreciating that if you shoot bright – well it’s going to look bright – until you normalise it in post. We do this all the time with log via LUT’s and grading too! It can be a little more straight forward to recover highlights from Linear Raw footage as comes form an FS5 or FS7 compared to log. That’s because of the way log maintains a constant data level in each highlight stop and often normal grading and colour correction tools don’t deal with this correctly. The highlight range is there, but it can be tricky to normalise the log without log grading tools such as the log controls in DaVinci Resolve.
Another problem is the common use of LUT’s on log footage. The vast majority of LUT’s add a highlight roll off, if you try to grade the highlights after adding a LUT with a highlight roll off it’s going to be next to impossible to recover the highlights. You must do the highlight recovery before the LUT is added or use a LUT that has compensation for any over exposure. All of these things can give the impression that log has less highlight range than the raw from the same camera. This is not normally the case, both will be the same as it’s the sensor that limits the range.
The difference in the highlight behaviour is in the workflows and very often both log and raw workflows are miss-understood. This can lead to owners and users of these cameras thinking that one process has more than the other, when in reality there is no difference, it’s appears to be different because the workflow works in a different way.
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