Tag Archives: S-log2

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.

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/

Sony’s Internal Recording Levels Are Correct.

There is a video on YouTube right now where the author claims that the Sony Alpha cameras don’t record correctly internally when shooting S-Log2 or S-Log3. The information contained in this video is highly miss-leading and the conclusion that the problem is with the way Sony record internally is incorrect. There really isn’t anything wrong with the way Sony do their recordings. Neither is there anything wrong with the HDMI output. While centered around the Alpha cameras the information below is also important for anyone that records S-Log2 or S-log3 externally with any other camera.

Some background: Within the video world there are 2 primary ranges that can be used to record a video signal.

Legal Range uses code value 16 for black and code value 235 for white (anything above CV235 is classed as a super-white and these can still be recorded but considered to be beyond 100%).

Full or Data Range uses code value 0 for black and code value 255 for white or 100%.

Most cameras and most video systems are based on legal range. ProRes recordings are almost always legal range. Most Sony cameras use legal range and do include super-whites for some of the curves such as Cinegammas or Hypergammas to gain a bit more dynamic range. The vast majority of video recordings use legal range. So most software defaults to legal range.

But very, very importantly – S-log2 and S-log is always full/data range.

Most of the time this doesn’t cause any issues. When you record internally in the camera the internal recordings have metadata that tells the playback, editing or grading software that the S-Log files have been recorded using full range. Because of this metadata the software will play the files back and process them at the correct levels. However if you record the S-Log with an external recorder the recorder doesn’t always know that what it is getting is full range and not legal range, it just records it, as it is, exactly as it comes out of the camera. That then causes a problem later on because the externally recorded file doesn’t have the right metadata to ensure that the full range S-Log material is handled correctly and most software will default to legal range if it knows no different.

Lets have a look at what happens when you import an internally recorded S-Log2 .mp4 file from a Sony A7S into Adobe Premiere:

Screenshot-2019-03-01-at-10.04.22 Sony's Internal Recording Levels Are Correct.
Internal S-Log2 in Premiere.

A few things to note here. One is Adobe’s somewhat funky scopes where the 8 bit code values don’t line up with the normally used IRE values used for video productions. Normally 8 bit code value 235 would be 100IRE or 100%, but for some reason Adobe have code value 255 lined up with 100%. My suspicion is that the scope % scale is not video % or IRE but instead RGB%. This is really confusing. A further complication is that Adobe have code value 0 as black, again, I think, but am not sure that this is RGB code value 0. In the world of video Black should be code value 16. But the scopes appear to work such that 0 is black and that 100 is full scale video out. Anything above 100 and below 0 will be clipped in any file you render out.

Looking at the scopes in the screen grab above, the top step on the grey scale chart is around code value 252. That is the code value you would expect it to be, that lines up just nicely with where the peak of an S-Log2 recording should be. This all looks correct, nothing goes above 100 or below 0 so nothing will be clipped.

So now lets look at an external ProRes recording, recorded at exactly the same time as the internal recording and see what Premier does with that:

Screenshot-2019-03-01-at-10.05.32 Sony's Internal Recording Levels Are Correct.
External ProRes in Adobe Premiere

OK, so we can see straight away something isn’t quite right here. In an 8 bit recording it should be impossible to have a code value higher that 255, but the scopes are suggesting that the recording has a peak code value of something around CV275. That is impossible, so alarm bells should be ringing. Something is not quite right here. In addition the S-Log2 appears to be going above 100, so that means if I were to simply export this as a new file, the top of the recording will be clipped and it won’t match the original. This is very clearly not right.

Now lets take a look at what happens in Adobe Premiere when you apply Sony’s standard S-Log2 to Rec-709 LUT to a correctly exposed internal recording:

Screenshot-2019-03-01-at-10.10.05 Sony's Internal Recording Levels Are Correct.
Internal S-Log2 with 709 LUT applied.

This all looks good and as expected. Blacks are sitting down just above the 0 line (which I think we can safely assume is black) and the whites of the picture are around code value 230 or 90, whatever that means. But they are certainly nice and bright and are not in the range that will be clipped. So I can believe this as being more or less correct and as expected.

So next I’m going to add the same standard LUT to the external recording to see what happens.

Screenshot-2019-03-01-at-10.11.24 Sony's Internal Recording Levels Are Correct.
External S-Log2 with standard 709 LUT applied.

OK, this is clearly not right. Our blacks now go below the 0 line and they look clipped. The highlights don’t look totally out of place, but clearly there is something going very, very wrong when we this normal LUT to this correctly exposed external recording. There is no way our blacks should be going below zero and they look crushed/clipped. The internal recording didn’t behave like this. So what is going on with the external recording?

To try and figure this out lets take a look at the same files in DaVinci Resolve. For a start I trust the scopes in Resolve much more and it is a far better programme for managing different types of files. First we will look at the internal S-Log2 recording:

Screenshot-2019-03-01-at-10.21.17-1 Sony's Internal Recording Levels Are Correct.
Internal S-Log2, all looks good.

Once again the levels of the internal S-Log2 recordings look absolutely fine. Our peak is around code value 1010 which would be 252 in 8 bit. Right where the brightest bits of an S-log2 file should be. Now lets take a look at the external recording.

Screenshot-2019-03-01-at-10.22.51 Sony's Internal Recording Levels Are Correct.
External ProRes S-Log2 (Full Range)

If you compare the two screen grabs above you can see that the levels are exactly the same. Our peak level is around CV1010/CV252, just where it should be and the blacks look the same also. The internal and external recordings have the same levels and look the same. There is no difference (other then perhaps less compression and fewer artefacts in the ProRes file). There is nothing wrong with either of these recordings and certainly nothing wrong with the way Sony record S-Log2 internally. This is absolutely what I expect to see.

BUT – I’ve been a little bit sneaky here. As I knew that the external recording was a full range recording I told DaVinci Resolve to treat it as a full range recording. In the media bin I right clicked on the clip and under “clip attributes” I changed 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.

This is what it looks like if you allow Resolve to guess at what range the S-Log2 full range clip is by leaving the input range setting to “auto”:

Screenshot-2019-03-01-at-10.24.46 Sony's Internal Recording Levels Are Correct.
External ProRes S-Log2 Auto Range

In the above image we can see how in Resolve the clip becomes clipped because in a legal range recording anything over CV235/CV940 would be an illegal super white. Resolve is scaling the clip and pushing anything in the original file that was above CV235/CV940 off the top of the scale. The scaling is incorrect because Resolve doesn’t know the clip is supposed to be full range and therefore not scaled. If we compare this to what Premiere did with the external recording it’s actually very similar. Premiere also scaled the clip, only Premiere will show all those “illegal” levels above it’s 100 line instead of clipping then as Resolve does. That’s why Premiere can have those “impossible” 8 bit code values going up to CV275.

Just to be complete here, I did also test the internal .mp4 recordings in Resolve switching between “auto” and “full” range and in both cases the levels stayed exactly the same. This shows that Resolve is correctly handling the internally record full range S-Log as full range.

What about if you add a LUT? Well you MUST tell Resolve to treat the S-Log2 ProRes clip as a full range clip otherwise the LUT will not be right, if your footage is S-Log3 you also have to tell Resolve that it is full range:

Screenshot-2019-03-01-at-13.09.16 Sony's Internal Recording Levels Are Correct.
Resolve: Internal recording with the standard 709 LUT applied, all is exactly as expected. Deep shadows and white right at the top of the range.
Screenshot-2019-03-01-at-13.10.10 Sony's Internal Recording Levels Are Correct.
Resolve: External recording with the standard 709 LUT applied, clip input range set to “full”. Everything is once again as you would expect. Deep shadows and white at the top of the range. Also not that it is near perfect match to the internal recording. No hue or color shift (Premiere introduces a color shift, more on that later).
Screenshot-2019-03-01-at-13.14.02 Sony's Internal Recording Levels Are Correct.
Resolve: External recording with the standard 709 LUT applied, clip input range set to “auto”. This is clearly not right. The highlights are clipped and the blacks are crushed and clipped. It is so important to get the input range right when working with LUT’s!!

CONCLUSIONS:

Both the internal and external recordings are actually exactly the same. Both have the same levels, both use FULL range. There is absolutely nothing wrong with Sony’s internal recordings. The problem stems from the way most software will assume that the ProRes files are legal range. But if it’s an S-Log2 or S-Log3 recording it will in fact be full (data) range. Handling a full range clip as legal range means that highlights will be too high/bright or clipped and blacks will be crushed. So it’s really important that your software handles the footage correctly. If you are shooting using S-Log3 this problem is harder to spot as S-Log3 has a peak recording level that is well with the legal range, so you often won’t realise it’s being scaled incorrectly as it won’t necessarily look clip. If you use LUT’s and your ProRes clips look crushed or highlights look clipped you need to check that the input scaling is correct. It’s really important to get this right.

Why is there no difference between the levels when you shoot with a Cinegamma? Well when you shoot with a cinegamma the internal recordings are legal range so the internal recordings get treated as legal range and so do the external recordings, so they don’t appear to be different (In the YouTube video that led to this post the author discovers that if you record with a normal profile first and then switch to a log profile while recording the internal and external files will match. But this is because now the internal recording has the incorrect metadata, so it too gets scaled incorrectly, so both the internal and external files are now wrong – but the the same).

Once again: There is nothing wrong with the internal recordings. The problem is with the way the external recordings are being handled. The external recordings haven’t been recorded incorrectly, they have been recorded as they should be. The problem is the edit software is incorrectly interpreting the external recordings. The external recordings don’t have the necessary metadata to mark the files as full range because the recorder is external to the camera and doesn’t know what it’s being sent by the camera. This is a common problem when using external recorders.

What can we do in Premiere to make Premiere work right with these files?

You don’t need to do anything in Premiere for the internal .mp4 recordings. They are handled correctly but Premiere isn’t handling the full/data range 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. So if anyone knows of a better way to do this do please let me know.

Screenshot-2019-03-01-at-11.04.04 Sony's Internal Recording Levels Are Correct.
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.

Atomos Ninja V, the arctic and the Northern Lights.

I’m sitting here in the UK, Its February and it almost 20c (68f). Very nice indeed for the UK this time of year. Just a couple of weeks ago I was in Northern Norway, up above the arctic circle running one of my annual Northern Lights adventure tours. The weather there was very different. At no time did the temperature get above -15c(5f) and for most of the trip it was around -24c(-11f) both during the day and during the night.

Now, you might consider me a sadist when I say this, but for my Northern Lights trips I normally want it to be -20c or colder. The reason being that when it’s very cold like this we normally get beautifully clear skies. And we need clear skies to see the Aurora.

DSC_0249 Atomos Ninja V, the arctic and the Northern Lights.
Everyone all wrapped up for the hour long ride by snow scooter and sledge to the cabins that we stay at.

After many years of taking a full size video camera up to Norway I decided to go light this year and just take my trusty A7S and A6300 cameras. We get around on snow scooters and on sledges towed behind the snow scooters. This can make lugging around a larger camera tricky and there are times when you just can’t take a big camera. But in order to get the very best from these cameras I also decided to take an Atomos Ninja V.

DSC_0253 Atomos Ninja V, the arctic and the Northern Lights.
Out and about on the snow scooter. It really is a very beautiful place in the winter.

The Ninja V is the first of a new generation of recorders and monitors from Atomos. It’s much smaller than the Shogun range of recorders making it a better size and weight match for smaller cameras and DSLR’s. It has a very, very nice 5″ screen with a maximum brightness of 1000 Nits. The 1000 Nit output and Atomos’s clever way of driving it means it can display both SDR and HDR images depending on how it is set up. A key difference between the Shogun and the Ninja devices is that the Shoguns have both SDI inputs and HDMI inputs while the Ninja only has an HDMI input. But if your using this with a DSLR than only has an HDMI output, as I was, the lack of SDI connectors is not a problem.

DSC_0281 Atomos Ninja V, the arctic and the Northern Lights.
Shooting a sunset with the Ninja V on my A6300. We were way up on the Finnmarksvidda when this image was taken, absolutely in the middle of nowhere and it was -27c!

The build quality of the Ninja V is really good. Most of the body is made of aluminium. The rear part where the slots for the SSD and battery are is made from plastic, but it appears to be a good high quality and tough plastic. A new feature is an “AtomX” expansion port tucked inside the battery compartment. The expansion port allow different modules to be attached to the Ninja V to add functionality such a video over IP (ethernet) using the Newtek NDI protocol for live streaming or to turn the Ninja V into an IP connected monitor. There is also an AtomX sync module that allows you to wirelessly synchronise timecode and control multiple Ninja V”s on a single network and to use Bluetooth remote control. You can find out more about the AtomX modules here https://www.atomos.com/AtomX

Anyway – back to Norway. We were very lucky with the weather, and with the Northern Lights. On the first night at the cabins we stay at the Aurora put on a pretty good display. I was shooting with my Sony A7S with a Sigma Art 20mm f1.4 lens. I was shooting a mix of time-lapse, in which case I simply record the raw frames in the camera on it’s internal SD cards as well as real time video.

DSC09536-small Atomos Ninja V, the arctic and the Northern Lights.
The Aurora put on a great display for us on several nights.

The Northern Lights are only rarely very bright. Most of the time they are fairly dim. So I was using the Sigma lens wide open, shooting at 24fps and with the shutter at 1/24th. The adjusting the cameras ISO to get a nice bright image. At times this did mean I was using some very high ISO’s with a lot of gain. Shooting like this is going to put a lot of strain on any codec. But the Long GOP XAVC-S codec used in the A7S is going to be very hard pushed to not introduce a lot of additional artefacts. In addition my older original A7S can only record HD internally.

By using the Ninja V I was able to record video of the Northern Lights in 4K using the ProRes codec. I used ProRes HQ and ProResHQ uses much less compression than XAVC-S. So even though both the internal recordings and the external recordings are limited to 8 bit (due to the cameras HDMI output limitations rather than any limitation of the Ninja) the ProRes recordings are far more robust and will noise reduce in post much better than the XAVC-S.

DSC_0278-crop Atomos Ninja V, the arctic and the Northern Lights.
Just to prove it really was -27c!!

When you’re working outside for extended periods and it’s -27c(-17f) it’s tough on the gear and tough on you. When shooting the Aurora my camera are outside all night, exposed to the cold. Typical problems include frost and ice on the front element of the lens. The moisture from your own body can easily freeze onto the lens if you stand close to the camera. If you look at the lens to check it for frost and breath out you will leave it coated in ice.

Wires and cables that are soft and flexible in normal temperatures become as stiff as steel rods and can crack and fracture if you try to bend them. All batteries will loose some of their capacity. Very small batteries are worst affected. Larger batteries tend to fair a bit better, but there is a tremendous difference between the way most cheap budget batteries behave in the cold to good quality brand name batteries. For this reason I power my complete setup from a single PAG PAGLink V-Mount battery. The PAGlink batteries are great for all sorts of different applications, but for these trips a big benefit is that a small plug type charger can be used to charge many PAGlink batteries by stacking the batteries together. Then to power multiple devices I use the clip-on PAG Power hub plate to provide 5V for the camera battery adapters that I use, 12V for the lens heaters I use and another 12V feed for the Ninja V.

DSC_0311 Atomos Ninja V, the arctic and the Northern Lights.
This is what the kit looks like when you bring it into the warm after many hours out in the cold. The thing with the yellow strap on the lens is a lens heater to prevent frost from building up on the lens. The lens is a sigma 20mm f1.4, the camera is an A7S and the recorder is the Atomos Ninja V.

After more than a few minutes outside the camera kit itself will have become extremely cold. If you then take that kit inside into a nice warm cabin the warm moist air in the cabin will condense onto the cold camera body. Because the camera body will be extremely cold this will then freeze. Before you know it the camera kit is covered in ice. What you can’t see is that it’s likely that there will also be some ice and moisture inside the camera. It can take hours to warm the camera back up again and get it dried out properly. Bagging the camera before you take it indoors can help, but taking the camera in and out many times over the coarse of a shoot like this can cause a lot of damage. So I prefer to leave all the camera kit outside for the duration of the trip.

DSC_0314 Atomos Ninja V, the arctic and the Northern Lights.
Another view of the frozen Ninja V after a night shooting the Aurora. Don’t worry, the screen isn’t damaged, that’s just frost and ice on the screens surface.

This means that when you come to fire it up you are often trying to switch on an absolutely frozen camera. In the past I have had problems with cold recorders that wouldn’t start up. But I’m pleased to report that the Ninja V always came to life no matter how cold it was. Whenever I pressed the record button it went into record. Operating the touch screen in the cold was not an issue. In fact using touch screen gloves, the Ninja was really easy to use. Pressing small fiddly buttons isn’t easy, even with thin gloves, but the touch screen turned out really easy to work with.

A big change on the Ninja V over previous models is the operating system. The new operating system looks really good and is quite logically laid out. Gone is the old AtomHDR slider that changes the brightness of the screen when in HDR. This is replaced with dedicated viewing modes for Native, 709, PQ HDR and HLG HDR and viewing via a LUT. I prefer the new fixed HDR modes over the Atom HDR slider modes as it eliminates the uncertainty that can sometimes creep in when you use a slider to change the brightness of the display. In my case, when shooting during the day using S-Log2 I would simply select S-Log2 as the source and then use PQ to display an HDR image on the screen. At night when shooting the Aurora I used Rec-709.

DSC_0283 Atomos Ninja V, the arctic and the Northern Lights.
You can see how the normal size 2.5″ SSD sticks out a bit from the side of the Ninja V. The SSDMini’s don’t stick out in the same way. Also note that even though I am shooting using S-Log2 on the A6300 the Ninja V is showing a nice contrasty image thanks to the PQ HDR display option.

The Ninja V can take the same size 2.5″ SSD caddies as the current Shogun recorders. So I was able to use the SSD’s that I already own. However to keep the size of the recorder down it has been designed around a new slightly shorty SSD form factor called SSDMini. When you use a standard size 2.5″ SSD it does stick out from the side of the recorder by about 25mm. If you use an SSDMini it doesn’t stick out at all. SSDMini’s are currently being manufactured by Angelbird and Sony. They have the same sata connector as regular 2.5″ SSD’s and the SSDMini’s can also be used on the larger Atomos Shoguns.

DSC_0286 Atomos Ninja V, the arctic and the Northern Lights.
A basic lightweight but effective setup. Atomos Ninja V, Sony A6300, Miller Compass 15 head and Solo tripod.

By the time we were ready to leave Norway we had seen the Northern Lights on 3 different nights. By day we had seen some beautiful sunrises as well as other optical effects like sun dogs caused by the light from the sun being refracted by ice crystals in the air. The Atomos Ninja V had impressed me hugely. It just worked perfectly despite the extreme cold. It allowed me to record at higher quality than would have been possible without it and turned out to be easy to operate. What more can you want really?

Fancy joining me on one of these trips? Follow the link to find out more: http://www.xdcam-user.com/northern-lights-expeditions-to-norway/

Noise, ISO, Gain, S-Log2 v S-Log3 and exposure.

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: http://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.

New Venice Look LUT’s Version 3. Includes minus green LUTs. For FS5, FS7, F55, A7S, A7R.

I released my first version of the Venice Look LUT’s a few weeks ago and they have been a big hit. Overall most people seem to like them and get some great results. I’ve seen quite a few good looking videos produced using them.

I have received some feedback though that some people feel that the LUT’s may be crushing the blacks a bit too much for them, personally I think the deep shadows gives quite a film like look. However in response to that feedback I created an additional LUT set that keeps the blacks slightly higher. This can make grading a little easier, especially in FCP-X. You will find these new version 3 LUT’s here in the packages below – but please read on…..

While I was at it I also created another set of LUTs with a minus green offset. The idea behind these was that they can be used for material shot under lights with a green tint such as many LED or fluorescent light fixtures. Playing with these “-G1” LUT’s I have decided that I really like the slightly warmer and even less “Sony” look that these versions of the LUT’s give when shooting under “normal” lighting. So do please give them a try for a warmer look for skin tones both with LED/Fluorescent lighting and also with full spectrum lighting such as tungsten and sunlight.

Taking that a step further I have also included an even stronger minus green offset in a further -G2 set of LUT’s. So between the 3 sets of LUT’s offered in this download you should be able to find a set for most types of lighting with a variety of skin tone renditions.

Included in the LUT sets are LUTs for grading (with exposure offsets), LUT’s for Small HD monitors and the Zacuto Gratical. The grading LUT’s can also be used in other monitors and devices such as the Atomos recorder/monitors.

As always (to date at least) I offer these as a free download available by clicking on the links below. However a lot of work goes into creating and hosting these. I feel that this LUT set is worth $25.00 and would really appreciate that being paid if you find the LUT’s useful. But 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. I’m currently working on a couple of different film stock emulations based combined with the Venice look highlight rendition.

Please feel free to share a link to this page if you wish to share these LUT’s with anyone else or anywhere else.

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


Your choice:



pixel New Venice Look LUT's Version 3. Includes minus green LUTs. For FS5, FS7, F55, A7S, A7R.

There are two different LUT sets. One set is for S-Log3 and S-Gamut3.cine. The other set is for S-Log2 and SGamut. Please only download what you need to save my bandwidth!

Typically if you are shooting with 8 bit, for example with an FS5 in UHD or an A7S, A7R etc, then I recommend you use S-Log2 with SGamut. For most other cameras that have 10 bit recording then I recommend S-Log3 and SGamut3.cine.

Here are the links to my Venice Look Version 3 LUT’s. Including the minus green offset LUTs. Make sure you choose the right version and once you have downloaded them please read the README file included within the package.

Alister V-Look V3 LUT’s S-Log2/SGamut

Alister V-Look V3 LUT’s S-Log3/SGamut3.cine

I got a request for a set of Rec-709 Venice Look LUT’s – So here they are. I’m not expecting miracles from these, you will be starting with a much reduced dynamic range by shooting with Rec-709, but try them if you wish. I make no promises as to how well they will or will not work!

Alister Venice Look for Rec709

 

 

Why is the white balance limited to 3 presets when using S-Log2, S-Log3 or raw?

This seems to be a source of frustration for many people shooting  raw or using S-Log2 or S-Log3 on a Sony camera. When shooting log and raw you should also be using a matching S-Gamut colour gamut if you want to get the best from the camera and this ties you into one of 3 preset white balances.

With a PXW-FS7, PMW-F5 or F55 it is possible to use custom mode to select a different colour space to mix with S-Log2 or S-Log3 and then have a variable white balance. With the Alpha cameras, PXW cameras such as the FS5 you can choose any Gamut you want in the picture profiles, but I don’t recommend this. For a start, if you don’t use one of the S-Gamuts you will be limited to Rec-709 Gamut, so you won’t be recording  the cameras full colour range. Also in custom mode there are some other things like noise reduction that you really don’t want when shooting S-log2/3 (it can cause banding).

So why is the S-Gamut white balance fixed to the 3 presets for daylight, fluorescent and tungsten? The main reason is to ensure you get the cameras full dynamic range in each colour. White balance is a gain function, it adjusts the gain of the red, green and blue channels so that white objects appear white under differing light sources. So if the light source lacks blue light – making the pictures look excessively warm – you add extra gain to the blue channel to compensate.

But the problem with this is that gain affects dynamic range. When shooting log (or raw) the camera needs to operate the sensor at the optimum gain level to squeeze the highest possible dynamic range from the it. Changing the gain in just one colour channel to shift the white balance could result in a reduction of dynamic range in the channel. This could manifest itself as colours in one channel that clip sooner than the others. This can be really hard to deal with in post production and can show up as things like bright clouds with a colour cast that isn’t in the rest of the picture.

Another potential issue is that because of the way silicon sensors work the blue channel is almost always noisier than the red and green. So you want to keep the gain in the blue channel as low as possible to prevent the pictures getting too noisy. This is particularly important when shooting log as you won’t see your end result until after the images have been graded. So manually shifting the gain of the blue channel in camera to correct the white balance could lead to footage that ends up noisier than you would expect.

So – Sony chose to fix the white balance to 3 carefully tuned presets designed to avoid this situation and maximise the dynamic range. After all, when shooting log or raw it is expected that the footage will be graded anyway, so the white balance will normally be adjusted as part of the post production process.

There are some people that advocate adjusting the FS5’s white balance via the picture profile settings, personally I don’t recommend this or feel that it’s necessary. But yes, you can do this, but just keep a very close eye on your highlights and if you can use monitor with RGB parade to make sure you have equal recording levels for your whites without one colour channel clipping ahead of the others. Also apply a LUT in the monitor that is close to your desired output so that you can keep an eye on the noise levels.

In summary – the white balance is preset to ensure you don’t encounter problems later on. You should be able to fully adjust and fine tune your white balance in post production to a far greater degree than is possible in camera anyway, so don’t worry if the WB is a touch off when shooting.

The only exception to this is the new Sony Venice. Venice has enough dynamic range and enough internal processing power to allow you to make a wide range of white balance adjustments in camera. Hopefully we will see some of this flexibility trickle down to the next generations of lower cost Sony digital cinema cameras.

Why are Sony’s ISO’s different between standard gammas and log?

With Sony’s log capable cameras (and most other manufacturers) when you switch between the standard gamma curves and log gamma there is a change in the cameras ISO rating. For example the FS7 is rated at 800 ISO in rec709 but rated at 2000 ISO in log. Why does this change occur and how does it effect the pictures you shoot?

As 709 etc has a limited DR (between around 6 and 10 stops depending on the knee settings) while the sensor itself has a 14 stop range, you only need to take a small part of the sensors full range to produce that smaller range 709 or hypergamma image. That gives the camera manufacturer some freedom to pick the sweetest part of the sensors range. his also gives some leeway as to where you place the base ISO.

I suspect Sony chose 800 ISO for the FS7 and F5 etc as that’s the sensors sweet spot, I certainly don’t think it was an accidental choice.

What is ISO on an electronic camera? ISO is the equivalent sensitivity rating. It isn’t a measure of the cameras actual sensitivity, it is the ISO rating you need to enter into a light meter if you were using an external light meter to get the correct exposure settings. It is the equivalent sensitivity. Remember we can’t change the sensor in these cameras so we can’t actually change the cameras real sensitivity, all we can do is use different amounts of gain or signal amplification to make the pictures brighter or darker.

When you go switch the camera to log you have no choice other than to take everything the sensor offers. It’s a 14 stop sensor and if you want to record 14 stops, then you have to take 100% of the sensors output. The camera manufacturer then chooses what they believe is the best exposure mid point point where they feel there is an acceptable compromise between noise, highlight and lowlight response. From that the manufacture will get an ISO equivalent exposure rating.

If you have an F5, FS7 or other Sony log camera, look at what happens when you switch from rec709 to S-Log2 but you keep your exposure constant.

Middle grey stays more or less where it is, the highlights come down. White will drop from 90% to around 73%. But the ISO rating given by the camera increases from 800ISO to 2000ISO. This increased ISO number implies that the sensor became more sensitive – This is not the case and a little missleading. If you set the camera up to display gain in dB and switch between rec709 (std gamma) and S-Log the camera stays at 0dB, this should be telling you that there is no change to the cameras gain, no change to it’s sensitivity. Yet the ISO rating changes – why?

The only reason the ISO number increases is to force us to underexpose the sensor by 1.3 stops (relative to standard gammas such as rec709 and almost every other gamma) so we can squeeze a bit more out of the highlights. If you were using an external light meter to set your exposure if you change the ISO setting on the light meter from 800 ISO to 2000 ISO  the light meter will tell you to close the aperture by 1.3 stops. So that’s what we do on the camera, we close the aperture down a bit to gain some extra highlight range.

But all this comes at the expense of the shadows and mid range. Because you are putting less light on the sensor if you use 2000 ISO as your base setting the shadows and mids are now not as good as they would be  in 709 or with the other standard gammas.

This is part of the reason why I recommend that you shoot with log between 1 and 2 stops brighter than the base levels given by Sony. If you shoot 1 stop brighter that is the equivalent to shooting at 1000 ISO and this is closer to the 800 ISO that Sony rate the camera at in standard gamma.  Shooting that bit brighter gives you a much better mid range that grades much better.

 

Why is exposing log brightly beneficial?

I have been asked whether you should still expose log a bit brighter than the recommended base levels on the Sony PXW-FS5 now that Sony have released new firmware that gives it a slightly lower base ISO. In this article I take a look at why it might be a good idea to expose log (with any camera) a bit brighter than perhaps the manufacturer recommends.

There are a couple of reasons to expose log nice and bright, not just noise. Exposing log brighter makes no difference to the dynamic range. That’s determined by the sensor and the gain point at which the sensor is working. You want the camera to be at it’s native sensitivity or 0dB gain to get that maximum dynamic range.

Exposing brighter or darker doesn’t change the dynamic range but it does move the mid point of the exposure range up and down.  Exposing brighter increases the under exposure range but decreases the over exposure range. Exposing darker decreases the under exposure range but increases the over exposure range.

Something that’s important when thinking about dynamic range and big dynamic ranges in particular is that dynamic range isn’t just about the highlights it’s also about the shadows, it isn’t just over exposure, it’s under exposure too, it’s RANGE.

So why is a little bit of extra light often beneficial? You might call it “over exposure” but that’s not a term I like to use as it implies “too much exposure”. I prefer to use “brighter exposure”.

It’s actually quite simple, it’s about putting a bit more light on to the sensor. Most sensors perform better when you put a little extra light on them. One thing you can be absolutely sure of – if you don’t put enough light on the sensor you won’t get the best pictures.

Slide01 Why is exposing log brightly beneficial?

Put more light on to the sensor and the shadows come up out of the sensors noise floor. So you will see further into the shadows. I’ve had people comment that “why would I ever want to use the shadows, they are always noisy and grainy”? But that’s the whole point – expose a bit brighter and the shadows will be much less noisy, they will come up out of the noise. Expose 1 stop brighter and you halve the shadow noise (for the same shadows at the previous exposure).  Shadows are are only ever noise ridden if you have under exposed them.

This is particularly relevant in controlled lighting. Say you light a scene for 9 stops. So you have 9 stops of dynamic range but a 14 stop sensor. Open up the aperture, put more light on the sensor, you get a better signal to noise ratio, less noisy shadows but no compromise of any type to the highlights because if the scene is 9 stops and you have 14 to play with, you can bring the exposure up by a couple of stops comfortably within the 14 stop capture range.

S-log-levels Why is exposing log brightly beneficial?
Chart showing S-Log2 and S-Log3 plotted against f-stops and code values. Note how little data there is for each of the darker stops, the best data is above middle grey. Note that current sensor only go to +6 stops ove middle grey so S-Log2 and S-Log record to different peak levels.

Look at the above diagram of Sony’s S-Log2 and S-Log3 curves. The vertical 0 line in the middle is middle grey. Note how above middle grey the log curves are more or less straight lines. That’s because above the nominal middle grey exposure level each stop is recorded with the same amount of data, this you get a straight line when you plot the curve against exposure stops. So that means that it makes very little difference where you expose the brighter parts of the image. Expose skin tones at stop + 1 or stop +3 and they will have a very similar amount of code values (I’m not considering the way dynamic range expands in the scene you shoot as you increase the light in the scene in this discussion). So it makes little difference whether you expose those skin tones at stop +1 or +3, after grading they will look the same.

Looking at the S-Log curve plots again note what happens below the “0” middle grey line. The curves roll off into the shadows. Each stop you go down has less data than the one before, roughly half as much. This mimics the way the light in a real scene behaves, but it also means there is less data for each stop. This is one of the key reasons why you never, ever want to be under exposed as if you are underexposed you mid range ends up in this roll off and will lack data making it not only noisy but also hard to grade as it will lack contrast and tonal information.

Open up by 1 additional stop and each of those darker stops is raised higher up the recording curve by one stop and every stop that was previously below middle grey doubles the amount of tonal values compared to before, so that’s 8 stops that will have 2x more data than before. This gives you a nice fat (lots of data) mid range that grades much better, not just because it has less noise but because you have a lot more data where you really need it – in the mid range.

Note: Skin tones can cover a wide exposure range, but typically the mid point is around 1 to 1.5 stops above middle grey. In a high contrast lighting situation skin tones will start just under middle grey and extend to about 2 stops over. If you accidentally under expose by 1 stop or perhaps don’t have enough light for the correct exposure you will seriously degrade the quality of your skin tones as half of your skin tones will be well below middle grey and in the data roll-off.

Now of course you do have to remember that if your scene does have a very large dynamic range opening up an extra stop might mean that some of the very brightest highlights might end up clipped. But I’d happily give up a couple of specular highlights for a richer more detailed mid range because when it comes to highlights – A: you can’t show them properly anyway because we don’t have 14 stop TV screens and B: because highlights are the least important part of our visual range.

A further consideration when we think about the highlights is that with log there is no highlight roll-off. Most conventional gamma curves incorporate a highlight roll-off to help increase the highlight range. These traditional highlight roll-offs reduce the contrast in the highlights as the levels are squeezed together and as a result the highlights contain very little tonal information. So even after grading they never look good, no matter what you do. But log has no highlight roll-off. So even the very brightest stop, the one right on the edge of clipping contains just as much tonal information as each of the other brighter than middle grey stops. As a result there is an amazingly large amount of detail than can be pulled out of these very bright stops, much more than you would ever be able to pull from most conventional gammas.

Compare log to standard gammas for a moment. Log has a shadow roll-off but no highlight roll-off. Most standard gammas have a strong highlight roll-off. Log is the opposite of standard gammas. With standard gammas, because of the highlight roll-off, we normally avoid over exposure because it doesn’t look good. With Log we need to avoid under exposure because of the shadow roll-off, it is the opposite to shooting with standard gammas.

As a result I strongly recommend you never, ever under expose log. I normally like to shoot log between 1 and 2 stops brighter than the manufacturers base recommendation.

Next week: Why is a Sony camera like the FS7,F5 800 ISO with standard gamma but 2000 ISO in log and how does that impact the image?

 

Beware Exposing To The Right With Log.

That may seem like quite a sensational headline – beware exposing to the right with log – but let me explain.

First of all, I’m not saying you can’t or shouldn’t expose to the right, all I am saying is beware – understand the implications.

First of all what is normally meant by exposing to the right? Well it’s a term that comes from the world of photography where you would use the cameras histogram to measure the exposure levels. Exposing to the right would normally mean setting the shutter speed and aperture so that the levels shown on the histogram are as far to the right as you can get them without going beyond the right side of the histogram. This would ensure a nice bright exposure with lots of light falling on the sensor, something that is normally highly desirable as you get a nice low noise picture once you have adjusted and processed it in your photo editing software.

You can expose to the right with a video camera too. However when shooting with Rec-709 or conventional gammas this can often result in nasty looking highlights thanks to the default knee settings, so it’s not normally a good idea for 709 and standard gammas.

With log or raw as there is no highlight roll off you can expose to the right and it should give you a nice bright exposure… or will it?????

The problem with exposing to the right is that you are exposing for the highlights in the scene. If shooting a low contrast or low dynamic range scene this isn’t going to cause any problems as exposing to the right will mean that everything in the scene is nice and bright.

But if shooting a high dynamic range scene, say an outdoor scene with bright clouds in the sky but large areas of shadow, the exposure will be optimised for the highlights. The mid range and shadows may end up too dark. On a sunny day if shooting a person with their back to the sun the sky could easily be 6 or 7 stops brighter than the skin tones. If you expose for the sky/highlights the skin tones will be 1 or 2 stops darker than the basic exposure level recommended for most  log curves.

(S-log2/3 has 14 stops. At the base exposure you have 6 stops above middle grey and 8 below. Skin tones are normally between 1 and 2 stops above middle grey. So if the sky/highlights are 6 stops above the skin tones, then exposing for the highlights will put the skin tones where middle grey should be, which is 1 stop under exposed and 2 stops below where I would normally like to see skin tones when shooting with log or raw).

The first thing a viewer will notice when they look at a scene with faces or people will be the skin tones. If these have been under exposed they will be grainy and less than ideal. The viewer will notice noise and grain and poor shadows long before they look at the brightest highlights. Shooting log and protecting the highlights or exposing to the right will often compromise the all important mid tones because you are exposing for the highlights, not the midrange. In addition exposing for highlights with a high dynamic range scene can often push the shadows down in level and they will end up noisy and grainy. The biggest issue with exposing to the right is that it’s extremely difficult to estimate how many stops there are between your mid tones and the highlights, so you never know quite where your mid tones are falling.

(Midtones – generally a white piece of paper or a 90% reflectivity white card would be considered to be the top end of the mid tones. Go down about 2.5 stops from white and you hit middle grey  (18% grey card). This range between middle grey and white is where skin tones, plants, most animals etc will be and it probably the most important part of most images).

An important consideration with log and raw is that there is no highlight roll off. Standard gammas (with the default knee found on almost every camera) , cinegammas, hypergammas etc all roll off the highlights. That is to say that as you approach the peak recording level the contrast is reduced as the highlights are squeezed together to try to extend the dynamic range. This reduction in contrast means that it is very difficult, if not impossible, to recover any nice, useable picture information out of anything close to the peak recording level. As a result with conventional gammas we tend to avoid over exposure at all costs as it looks nasty. This highlight roll off is one of the things that gives video the video look.

Log and raw don’t have this same kind of highlight roll off. The image gets brighter and brighter until it clips. With log the stop immediately below clipping contains just as much picture information as any other stop brighter than middle grey. With linear raw the stop just below clipping has more information than any other stop. As a result in post production there is a very large amount of data that can be pulled out of these highlights, even if they are a little clipped! So don’t worry about a few clipped highlights when shooting log. The other thing to remember is there is no TV or monitor that can show these highlights as they really are, so they will never look perfect anyway.

Another thing that happens when exposing to the right is that grading becomes harder than it needs to be. Because the separation between the mid tones and highlights will vary greatly depending on things like whether you are shooting into or away from the sun, when you expose to the right you mid tone brightness will be up and down all over the place. So in post production as well as adding the look that you want to your footage, you are also going to have to spend a lot of time matching the mid range exposure to balance skin tones etc from shot to shot.

Rather than exposing to the right what I recommend is exposing for the mid range. After all this is the important part of the image. To do this you need to use a diffuse reflective shade. The most commonly used shades are a 90% white card and/or an 18% reflectivity grey card – middle grey. Get the mid range right and in most cases the highlights will take care of themselves. Getting the mid range right might mean exposing the mid range  brighter than the recommended levels. But it’s the mid range we need to measure, not the highlights, this is the important part of the image.

90% white is an incredibly important level in the world of film and video. A typical piece of office paper reflects about 92-94% of the light falling on it. Office paper often uses brighteners and special chemicals to make it look bright and white. This white is the brightest diffuse surface you will likely ever see.  Anything brighter than this is normally going to be an actual source of light. The sky perhaps or a direct bounced reflection off a shiny, reflective surface such as the bodywork of a car. So anything brighter than 90% white would normally be considered to be a highlight and to us humans, highlights are visually less important than the mid range. This is why the knee on most video cameras kicks in at around 90%. Anything brighter than 90% is a highlight so the knee only effects highlights and leaves the all important mid range alone.

Middle grey is also very important because it’s a shade of grey that to most people looks to be half way between black and white. Skin tones fall roughly half way between middle grey and white. In addition if you average all the brightness levels within a typical scene the end result is typically very close to middle grey.  Light meters are calibrated to middle grey. The relationship between middle grey and white is fixed. White reflects 90%, middle grey 18%, no matter how bright the actual light source. So whether you are indoors, outside. Whether it’s sunny or overcast, white and middle grey will always be close to 2.5 stops apart. They are extremely useful fixed reference levels.

There are many ways to measure the brightness of a white or grey card. My preferred method is with a waveform display. But you could also use zebras (use a narrow zebra window if you can).  You can also use false colour. Unfortunately it’s very difficult to use a histogram to measure the brightness of a specific target. The histogram is a great measuring tool for photography, but less than ideal for video. If you can’t get a white/grey card out in front of the camera you could consider using a light meter. It’s also worth noting that skin tones sit just a little over half way between middle grey and white, so if you have no other reference you could simply place your skin tones a touch brighter than half way between the values you are targetting for middle grey and white.

Just to be clear: I do still recommend exposing Sony’s S-log2, S-log3 and raw between 1 and 2 stops brighter than the Sony base levels. But the key take-away is that it’s the mid range you need to measure and expose at this level. Exposing to the right using a histogram or waveform and just looking at the peaks and brightest parts of the image does not tell you what is happening in he mid range. Measure the mid range, not the peak brightness.