Tag Archives: log

What Benefits Do I Gain By Using CineEI?

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.

For more information on CineEI see:

Using CineEI with the FX6  
 
 

Raw Myths. You Can’t Change The white Balance Of the Camera Or ISO in Post.

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.

Shooting S-Log3 on the PXW-FX9 – Do I need to expose bright?

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

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

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

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

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

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.

ProRes Raw Over Exposure Magic Tricks – It’s all smoke and mirrors!

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.

Log and Raw Don’t have highlight a highlight roll off.

This just keeps coming up over and over. Almost all log gamma curves and the majority of raw recording formats don’t have a highlight roll-off. Any roll off that you might see is probably in the LUT’s that you are using.

The whole point of log and raw is to capture as much information about the scene that you are shooing as you can. Log normally achieves this by recording every stop above middle grey with a constant amount of data, so even the very brightest stop has the same amount of recording data as the ones below it – there is no roll off.

In conventional limited range recordings such as Rec-709, hypergamma, cinegamma etc, highlight roll-offs work by reducing the contrast in the highlights to make the amount of data needed to record the very brightest stops much smaller than used for the rest of the image. This allows 2 or 3 stops to be squeezed into a very small recording range, keeping most of the recording data available for a nice bright high contrast image. The reduction in contrast in the extreme highlights helps hide any highlight handling problems and makes it appear as though the sensors clipping point is reach in a more pleasing soft manner.

But you don’t want this in a log or raw recording as it makes grading much harder as the footage will contain different contrast ranges, each needing it’s own grading adjustments. Also by reducing contrast in the highlights you are reducing the data. It would be very difficult to un-pick a highlight roll off and if you did want to expand the data back out you will get issues such as banding.

S-log-levels Log and Raw Don't have highlight a highlight roll off.
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 and there is no highlight roll-off. Note that current sensor only go to +6 stops over middle grey so S-Log2 and S-Log record to different peak levels.

S-Log2 and S-Log3 like almost all log gammas have no highlight roll-off. The only roll off is from middle grey and down. So if you underexpose you will start to roll away the data in your scenes mid range and that’s not good. Expose for the mid range, this is the most important part of any image. If your highlights are a bit clipped don’t worry about this too much. In post production you can add a roll off in the grade that will make any clipped highlights roll away gently. Adding a bit of highlight diffusion in post will also nicely mask any clipped highlights and make them look natural.

Shooting Flat – No it’s not!

I know that many of my readers like to shoot log. One of the most common terms used around shooting log is “shooting flat”. Lets take a look at that term and think about what it actually means.

One description of a flat image might be – “An image with low contrast”. Certainly an image with low contrast can be considered flat.

Once upon a time shooting flat meant lighting a scene so that there was very little contrast. The background in an interview might be quite well  lit. You would avoid deep shadows or strong highlights. This was done because cameras had very limited dynamic ranges. These flat images of low contrast scenes could then have the contrast boosted in post production to make them look better.

8 years ago, with the advent of DSLR cameras that could shoot with film like depths of field it became fashionable to shoot flat because digital film cameras  when shooting using log produced an image that looks flat when viewed on a conventional TV or monitor.

But lets think about that for a moment. A typical digital cinema camera can capture 14 stops of dynamic range. A scene with 14 stops of dynamic range contains a huge contrast range, perhaps a brilliant bright sky and deep shadows, you can possibly describe the capture a scene with 14 stops of dynamic range as “flat”?

The answer is you can’t – or at least you shouldn’t because the recording  isn’t flat. The dynamic range that most digital cinema cameras can capture is not flat, not at all.

The problem is that a normal TV or video monitor can’t show a very big dynamic range. A conventional TV can only show around 6 stops. If you take a log video signal with a 14 stop image and try to show that on a 6 stop screen you will be squashing the highlights and shadows closer together, so the highlight that was at +14 stops in the scene and is recorded at 100%, gets pushed closer to the deepest shadow in the scene that is recorded at 1%.

On a normal 6 stop TV the 100% recording level is shown at +6 stops while the deepest shadow will be at 1%, so now the 14 stop recording is being shown with only 6 stops between the deepest black and the brightest highlight. Instead of the highlight being dazzlingly bright it’s now just a bright white and not all that much brighter than the shadows. As a result the image on the screen looks all wrong, nothing like what you recorded and it appears to be “flat”.

BUT THE DATA IN THE FILE IS NOT FLAT – that recording contains a high contrast, 14 stop image – it’s the inability of the TV or monitor to show it correctly that makes it look wrong, not that you have shot flat.

In the early days of DSLR shooting many DSLR shooters decided to mimic the way the image from a digital cinema camera looks flat on a normal TV, perhaps in the miss-guided belief that a flat image must always have a greater dynamic range. This definitely isn’t always the case. I can take any regular dynamic range image and make it look flat by reducing the contrast, raising the blacks a bit, shifting the gamma perhaps, that’s easy. But that doesn’t increase the dynamic range that is captured. Changing the capture range of a camera typically requires fundamental changes to the way it operates rather than simple tweaks to the basic picture settings.

So we went through a period where shooting a flat looking image with a DSLR was the trendy way to shoot because on a normal TV or monitor the image recorded is reminiscent of the image from a true digital cinema camera shooting log, even though in practice the “flat look”  was often damaging the image rather than improving it.

Now there are many digital cinema cameras that can capture a very big dynamic range using log encoding and these images look washed out and flat on a normal monitor or TV because of the miss-match between the camera and the monitor, not because the captured scene is flat. But we still call this shooting flat (wrong)!

Why? In many cases people like to leave the image this way as they like this “incorrect” look. Flat is trendy, it’s fashionable, at least to those inside the TV and Video production world. I’m not sure that the wider general audience really understands why their pictures look washed out.

If you have a monitor with high dynamic range display capabilities such as a Atomos Shogun Flame or Inferno, that can show a large dynamic range then you’ll know that if you feed it log and set the display range to HDR and choose the right gamma curve, the picture on the screen is no longer flat, it’s bright and contrasty. This isn’t a LUT or any other cheat. The monitor is simply showing the image with a range much closer to the capture range and now it looks right again.

storm-PQ-14stop-1024x577 Shooting Flat - No it's not!
This is a high dynamic range image. View it on an HDR TV set to HDR10 and it will be brilliantly bright, highly colorfull and full of contrast. On a regular TV or monitor it looks flat and washed out because the regular TV can’t show it properly.

So next time you use the term “shooting Flat” think very carefully about what it actually means and whether you are really shooting flat or whether it’s simply a case of using the wrong monitor. Using words or terms like this incorrectly causes all kinds of problems. For example most people think that log footage is flat and that that’s how it’s supposed to look. But it isn’t flat and it’s not supposed to look flat, we are just using the wrong monitors!

Should I shoot 8 bit UHD or 10 bit HD?

This comes up so many times, probably because the answer is rarely clear cut.

First lets look at exactly what the difference between an 8 bit and a 10 bit recording is.
Both will have the same dynamic range. Both will have the same contrast. Both will have the same color range. One does not  necessarily have more color or contrast than the other. The only thing you can be sure of is the difference in the number of code values. An 8 bit video recording has a maximum of 235 code values per channel giving 13 million possible tonal values. 10 bit recording has up to 970 code values per channel giving up to 912 million tonal values.
 
There is a lot of talk of 8 bit recordings resulting in banding because there are only 235 luma shades. This is a bit of a half truth. It is true that if you have a monochrome image there would only be 235 steps. But we are normally making colour images so we are typically dealing with 13 million tonal values, not simply 235 luma shades. In addition it is worth remembering that the bulk of our current video distribution and display technologies are 8 bit – 8 bit H264, 8 bit screens etc. There are more and more 10 bit codecs coming along as well as more 10 bit screens, but the vast majority are still 8 bit.
Compression artefacts cause far more banding problems than too few steps in the recording codec. Most codecs use some form of noise reduction to help reduce the amount of data that needs to be encoded and this can result in banding. Many codecs divide the image data into blocks and  the edges of these small blocks can lead to banding and stepping.
 
Of course 10 bit can give you more shades. But then 4K gives you more shades too. So an 8 bit UHD recording can sometimes have more shades than a 10 bit HD recording. How is this possible? If you think about it, in UHD each color object in the scene is sampled with twice as many pixels. Imagine a gradient that spans 4 pixels. In 4K you will have 4 samples and 4 steps. In HD you will only have 2 samples and 2 steps, so the HD image might show a single big step while the 4K may have 4 smaller steps. It all depends on how steep the gradient is and how it falls relative to the pixels. It then also depends on how you will handle the footage in post production.
 
So it is not as clear cut as often made out. For some shots with lots of textures 4K 8 bit might actually give more data for grading than 10 bit HD. In other scenes 10 bit HD might be better.
 
Anyone that is getting “muddy” results in 4K compared to HD is doing something wrong. Going from 8 bit 4K to 10 bit HD should not change the image contrast, brightness or color range. The images shouldn’t really look significantly different. Sure the 10 bit HD recording might show some subtle textures a little better, but then the 8 bit 4K might have more texture resolution.
 
My experience is that both work and both have pro’s and con’s. I started shooting 8 bit S-log when the Sony PMW-F3 was introduced 7 years ago and have always been able to get great results provided you expose well. 10 bit UHD would be preferable, I’m not suggesting otherwise (at least 10 GOOD bits are always preferable), but 8 bit works too. 

Using LUT’s for exposure – choosing the right LUT.

If using a LUT to judge the exposure of a camera shooting log or raw it’s really important that you fully understand how that LUT works.

When a LUT is created it will expect a specific input range and convert that input range to a very specific output range. If you change the input range then the output will range will be different and it may not be correct. As an example a LUT designed and created for use with S-Log2 should not be used with S-Log3 material as the the higher middle grey level used by S-Log3 would mean that the mid range of the LUT’s output would be much brighter than it should be.

Another consideration comes when you start offsetting your exposure levels, perhaps to achieve a brighter log exposure so that after grading the footage will have less noise.

Lets look at a version of Sony’s 709(800) LUT designed to be used with S-Log3 for a moment. This LUT expects middle grey to come in at 41% and it will output middle grey at 43%. It will expect a white card to be at 61% and it will output that same shade of white at a little over 85%. Anything on the S-Log3 side brighter than 61% (white) is considered a highlight and the LUT will compress the highlight range (almost 4 stops) into the output range between 85% and 109% resulting in flat looking highlights. This is all perfectly fine if you expose at the levels suggested by Sony. But what happens if you do expose brighter and try to use the same LUT either in camera or in post production?

Well if you expose 1.5 stops brighter on the log side middle grey becomes around 54% and white becomes around 74%. Skin tones which sit half way between middle grey and white will be around 64% on the LUT’s input. That’s going to cause a problem! The LUT considers anything brighter than 61% on it’s input to be a highlight and it will compresses anything brighter than 61%. As a result on the output of your LUT your skin tones will not only be bright, but they will be compressed and flat looking. This makes them hard to grade. This is why if you are shooting a bit brighter it is much, much easier to grade your footage if your LUT’s have offsets to allow for this over exposure.

If the camera has an EI mode (like the FS7, F5, F55 etc) the EI mode offsets the LUT’s input so you don’t see this problem in camera but there are other problems you can encounter if you are not careful like unintentional over exposure when using the Sony LC709 series of LUTs.

Sony’s  709(800) LUT closely matches the gamma of most normal monitors and viewfinders, so 709(800) will deliver the correct contrast ie. contrast that matches the scene you are shooting plus it will give conventional TV brightness levels when viewed on standard monitors or viewfinders.

If you use any of the LC709 LUT’s you will have a miss-match between the LUT’s gamma and the monitors gamma so the images will show lower contrast and the levels will be lower than conventional TV levels when exposed correctly. LC709 stands for low contrast gamma with 709 color primaries, it is not 709 gamma!

Sony’s LC709 Type A LUT is very popular as it mimics the way an Arri Alexa might look. That’s fine but you also need to be aware that the correct exposure levels for this non-standard LC gamma are middle grey at around 41% and white at 70%.

An easy trap to fall into is to set the camera to a low EI to gain a brighter log exposure and then to use one of the LC709 LUT’s and try to eyeball the exposure. Because the LC709 LUT’s are darker and flatter it’s harder to eyeball the exposure and often people will expose them as you would regular 709. This then results in a double over exposure. Bright because of the intentional use of the lower EI but even brighter because the LUT has been exposed at or close to conventional 709 brightness. If you were to mistakenly expose the LC709TypeA LUT with skin tones at 70%, white at 90% etc then that will add almost 2 stops to the log exposure on top of any EI offset.

Above middle grey with 709(800) a 1 stop exposure change results in an a 20% change in brightness, with LC709TypeA the same exposure change only gives a just over 10% change, as a result over or under exposure is much less obvious and harder to measure or judge by eye with LC709. The cameras default zebra settings for example have a 10% window. So with LC709 you could easily be a whole stop out, while with 709(800) only half a stop.

Personally when shooting I don’t really care too much about how the image looks in terms of brightness and contrast. I’m more interested in using the built in LUT’s to ensure my exposure is where I want it to be. So for exposure assessment I prefer to use the LUT that is going to show the biggest change when my exposure is not where it should be. For the “look” I will feed a separate monitor and apply any stylised looks there. To understand how my highlights and shadows, above and below the LUT’s range are being captured I use the Hi/Low Key function.

If you are someone that creates your own LUT’s an important consideration is to ensure that if you are shooting test shots, then grading these test shots to produce a LUT it’s really, really important that the test shots are very accurately exposed.

You have 2 choices here. You can either expose at the levels recommended by Sony and then use EI to add any offsets or you can offset the exposure in camera and not use EI but instead rely on the offset that will end up in the LUT. What is never a good idea is to add an EI offset to a LUT that was also offset.