Sony’s X-OCN (X–Original Camera Negative) is a new type of codec from Sony. Currently it is only available via the R7 recorder which can be attached to a Sony PMW-F5, F55 or the new Venice cinema camera.
It is a truly remarkable codec that brings the kind of flexibility normally only available with 16 bit linear raw files but with a files size that is smaller than many conventional high end video formats.
Currently there are two variations of X-OCN.
X-OCN ST is the standard version and then X-OCN LT is the “light” version. Both are 16 bit and both contain 16 bit data based directly on what comes off the cameras sensor. The LT version is barely distinguishable for a 16 bit linear raw recording and the ST version “visually lossless”. Having that sensor data in post production allows you to manipulate the footage over a far greater range than is possible with tradition video files. Traditional video files will already have some form of gamma curve as well as a colour space and white balance baked in. This limits the scope of how far the material can be adjusted and reduces the amount of picture information you have (relative to what comes directly off the sensor) .
Furthermore most traditional video files are 10 bit with a maximum of 1024 code values or levels within the recording. There are some 12 bit codecs but these are still quite rare in video cameras. X-OCN is 16 bit which means that you can have up to 65,536 code values or levels within the recording. That’s a colossal increase in tonal values over traditional recording codecs.
But the thing is that X-OCN LT files are a similar size to Sony’s own XAVC-I (class 480) codec, which is already highly efficient. X-OCN LT is around half the size of the popular 10 bit Apple ProRes HQ codec but offers comparable quality. Even the high quality ST version of X-OCN is smaller than ProRes HQ. So you can have image quality and data levels comparable to Sony’s 16 bit linear raw but in a lightweight, easy to handle 16 bit file that’s smaller than the most commonly used 10 bit version of ProRes.
But how is this even possible? Surely such an amazing 16 bit file should be bigger!
The key to all of this is that the data contained within an X-OCN file is based on the sensors output rather than traditional video. The cameras that produce the X-OCN material all use bayer sensors. In a traditional video workflow the data from a bayer sensor is first converted from the luminance values that the sensor produces into a YCbCr or RGB signal.
So if the camera has a 4096×2160 bayer sensor in a traditional workflow this pixel level data gets converted to 4096×2160 of Green plus 4096×2160 of Red, plus 4096×2160 of Green (or the same of Y, Cb and Cr). In total you end up with 26 million data points which then need to be compressed using a video codec.
However if we bypass the conversion to a video signal and just store the data that comes directly from the sensor we only need to record a single set of 4096×2160 data points – 8.8 million. This means we only need to store 1/3rd as much data as in a traditional video workflow and it is this huge data saving that is the main reason why it is possible for X-OCN to be smaller than traditional video files while retaining amazing image quality. It’s simply a far more efficient way of recording the data from a bayer camera.
Of course this does mean that the edit or playback computer has to do some extra work because as well as decoding the X-OCN file it has to be converted to a video file, but Sony developed X-OCN to be easy to work with – which it is. Even a modest modern workstation will have no problem working with X-OCN. But the fact that you have that sensor data in the grading suite means you have an amazing degree of flexibility. You can even adjust the way the file is decoded to tailor whether you want more highlight or shadow information in the video file that will created after the X-OCN is decoded.
Why isn’t 16 bit much bigger than 10 bit? Normally a 16 bit file will be bigger than a 10 bit file. But with a video image there are often areas of information that are very similar. Video compression algorithms take advantage of this and instead of recording a value for every pixel will record a single value that represents all of the similar pixels. When you go from 10 bit to 16 bit, while yes, you do have more bits of data to record a greater percentage of the code values will be the same or similar and as a result the codec becomes more efficient. So the files size does increase a bit, but not as much as you might expect.
So, X-OCN, out of the gate, only needs to store 1/3rd of the data points of a similar traditional RGB or YCbCr codec. Increasing the bit depth from the typical 10 bit bit depth of a regular codec to the 16 bits of X-OCN does then increase the amount of data needed to record it. But the use of a clever algorithm to minimise the data needed for those 16 bits means that the end result is a 16 bit file only a bit bigger than XAVC-I but still smaller than ProRes HQ even at it’s highest quality level.
With the first of the production Venice cameras now starting to find their way to some very lucky owners it’s time to take a look at some features that are not always well understood, or that perhaps no one has told you about yet.
Dual Native ISO’s: What does this mean?
An electronic camera uses a piece of silicon to convert photons of light into electrons of electricity. The efficiency at doing this is determined by the material used. Then the amount of light that can be captured and thus the sensitivity is determined by the size of the pixels. So, unless you physically change the sensor for one with different sized pixels (which will in the future be possible with Venice) you can’t change the true sensitivity of the camera. All you can do is adjust the electronic parameters.
With most video cameras the ISO is changed by increasing the amount of amplification applied to the signal coming off the sensor. Adding more gain or increasing the amplification will result in a brighter picture. But if you add more amplification/gain then the noise from the sensor is also amplified by the same amount. Make the picture twice as bright and normally the noise doubles.
In addition there is normally an optimum amount of gain where the full range of the signal coming from the sensor will be matched perfectly with the full recording range of the chosen gamma curve. This optimum gain level is what we normally call the “Native ISO”. If you add too much gain the brightest signal from the sensor would be amplified too much and exceed the recording range of the gamma curve. Apply too little gain and your recordings will never reach the optimum level and darker parts of the image may be too dark to be seen.
As a result the Native ISO is where you have the best match of sensor output to gain. Not too much, not too little and hopefully low noise. This is typically also referred to as 0dB gain in an electronic camera and normally there is only 1 gain level where this perfect harmony between sensor, gain and recording range is achieved, this becoming the native ISO.
Side Note: On an electronic camera ISO is an exposure rating, not a sensitivity measurement. Enter the cameras ISO rating into a light meter and you will get the correct exposure. But it doesn’t really tell you how sensitive the camera is as ISO has no allowance for increasing noise levels which will limit the darkest thing a camera can see.
Tweaking the sensor.
However, there are some things we can tweak on the sensor that effect how big the signal coming from the sensor is. The sensors pixels are analog devices. A photon of electricity hits the silicone photo receptor (pixel) and it gets converted into an electron of electricity which is then stored within the structure of the pixel as an analog signal until the pixel is read out by a circuit that converts the analog signal to a digital one, at the same time adding a degree of noise reduction. It’s possible to shift the range that the A to D converter operates over and the amount of noise reduction applied to obtain a different readout range from the sensor. By doing this (and/or other similar techniques, Venice may use some other method) it’s possible to produce a single sensor with more than one native ISO.
A camera with dual ISO’s will have two different operating ranges. One tuned for higher light levels and one tuned for lower light levels. Venice will have two exposure ratings: 500 ISO for brighter scenes and 2500 ISO for shooting when you have less light. With a conventional camera, to go from 500 ISO to 2500 ISO you would need to add just over 12dB of gain and this would increase the noise by a factor of more than 4. However with Venice and it’s dual ISO’s, as we are not adding gain but instead altering the way the sensor is operating the noise difference between 500 ISO and 2500 ISO will be very small.
You will have the same dynamic range at both ISO’s. But you can choose whether to shoot at 500 ISO for super clean images at a sensitivity not that dissimilar to traditional film stocks. This low ISO makes it easy to run lenses at wide apertures for the greatest control over the depth of field. Or you can choose to shoot at the equivalent of 2500 ISO without incurring a big noise penalty.
One of Venice’s key features is that it’s designed to work with Anamorphic lenses. Often Anamorphic lenses are typically not as fast as their spherical counterparts. Furthermore some Anamorphic lenses (particularly vintage lenses) need to be stopped down a little to prevent excessive softness at the edges. So having a second higher ISO rating will make it easier to work with slower lenses or in lower light ranges.
COMBINING DUAL ISO WITH 1 STOP ND’s.
Next it’s worth thinking about how you might want to use the cameras ND filters. Film cameras don’t have built in ND filters. An Arri Alexa does not have built in ND’s. So most cinematographers will work on the basis of a cinema camera having a single recording sensitivity.
The ND filters in Venice provide uniform, full spectrum light attenuation. Sony are incredibly fussy over the materials they use for their ND filters and you can be sure that the filters in Venice do not degrade the image. I was present for the pre-shoot tests for the European demo film and a lot of time was spent testing them. We couldn’t find any issues. If you introduce 1 stop of ND, the camera becomes 1 stop less sensitive to light. In practice this is no different to having a camera with a sensor 1 stop less sensitive. So the built in ND filters, can if you choose, be used to modify the base sensitivity of the camera in 1 stop increments, up to 8 stops lower.
So with the dual ISO’s and the ND’s combined you have a camera that you can setup to operate at the equivalent of 2 ISO all the way up to 2500 ISO in 1 stop steps (by using 2500 ISO and 500 together you can have approximately half stops steps between 10 ISO and 650 ISO). That’s an impressive range and at no stage are you adding extra gain. There is no other camera on the market that can do this.
On top of all this we do of course still have the ability to alter the Exposure Index of the cameras LUT’s to offset the exposure to move the exposure mid point up and down within the dynamic range. Talking of LUT’s I hope to have some very interesting news about the LUT’s for Venice. I’ve seen a glimpse of the future and I have to say it looks really good!
The raw and X-OCN material from a Venice camera (and from a PMW-F55 or F5 with the R7 recorder) contains a lot of dynamic metadata. This metadata tells the decoder in your grading software exactly how to handle the linear sensor data stored in the files. It tells your software where in the recorded data range the shadows start and finish, where the mid range sits and where the highlights start and finish. It also informs the software how to decode the colors you have recorded.
I recently spent some time with Sony Europe’s color grading guru Pablo Garcia at the Digital Motion Picture Center in Pinewood. He showed me how you can manipulate this metadata to alter the way the X-OCN is decoded to change the look of the images you bring into the grading suite. Using a beta version of Black Magic’s DaVinci Resolve software, Pablo was able to go into the clips metadata in real time and simply by scrubbing over the metadata settings adjust the shadows, mids and highlights BEFORE the X-OCN was decoded. It was really incredible to see the amount of data that Venice captures in the highlights and shadows. By adjusting the metadata you are tailoring the the way the file is being decoded to suit your own needs and getting the very best video information for the grade. Need more highlight data – you got it. Want to boost the shadows, you can, at the file data level before it’s converted to a traditional video signal.
It’s impressive stuff as you are manipulating the way the 16 bit linear sensor data is decoded rather than a traditional workflow which is to decode the footage to a generic intermediate file and then adjust that. This is just one of the many features that X-OCN from the Sony Venice offers. It’s even more incredible when you consider that a 16 bit linear X-OCN LT file is similar in size to 10 bit XAVC-I(class 480) and around half the size of Apples 10 bit ProRes HQ. X-OCN LT looks fantastic and in my opinion grades better than XAVC S-Log. Of course for a high end production you will probably use the regular X-OCN ST codec rather than the LT version, but ST is still smaller than ProRes HQ. What’s more X-OCN is not particularly processor intensive, it’s certainly much easier to work with X-OCN than cDNG. It’s a truly remarkable technology from Sony.
Next week I will be shooting some more test with a Venice camera as we explore the limits of what it can do. I’ll try and get some files for you to play with.
Here are some scene files for the PXW-FS7-II and original PXW-FS7. The first 5 scene files I published a couple of years ago but never got around to converting them over to the PXW-FS7-II. You can download the files in their correct folder structure to put on to an SD card so you can load them directly in to an FS7 or FS7-II. Or you can manually copy the settings from here. If copying the settings in manually I recommend you start by going to the “Files” section of the cameras menu and “Scene File” and import a “standard” default scene file from the cameras internal memory first to ensure you paint settings are at the original factory defaults prior to entering the settings by hand. The easiest way is to load the files linked at the bottom of the page onto an SD card and then go to the files section of the menu to load the scene files into the camera from the SD card.
If you find these useful, please consider buying me a coffee or other drink. It’s always appreciated!
Most computer screens run at 60Hz and very often this rate can’t be changed. 25p shown on most computer screens requires 15 frames to be shown twice and 10 frames to be shown 3 times to create a total of 60 frames every second. This creates an uneven cadence and it’s not something you can control as the actual structure of the cadence depends on the video subsystem of the computer the end user is using.
Every now and again I get asked how to adjust the color matrix in a video camera. Back in 2009 I made a video on how to adjust the color matrix in the Sony’s EX series of cameras. This video is just as relevant today as it was then. The basic principles have not changed.
The exact menu settings and menu layout may be a little different in the latest cameras, but the adjustment of the matrix setting (R-G, G-R etc) have exactly the same effect in the latest camera that provide matrix adjustments (FS7, F5, F55 and most of the shoulder mount and other broadcast cameras). So if you want a better understanding of how these settings and adjustment works, take a look at the video.
I’ll warn you now that adjusting the color matrix is not easy as each setting interacts with the others. So creating a specific look via the matrix is not easy and requires a fair bit of patience and a lot of fiddling and testing to get it just right.
This came up on facebook the other day, how long do SD cards last?
First of all – I have found SD cards to be pretty reliable overall. Not as reliable as SxS cards or XQD cards, but pretty good generally. The physical construction of SD cards has let me down a few times, the little plastic fins between the contacts breaking off. I’ve had a couple of cards that have just died, but I didn’t loose any content as the camera wouldn’t let me record to them. Plus I have also had SD cards that have given me a lot of trouble getting content and files off them. But compared to tape, I’ve had far fewer problems with solid state media.
But something that I don’t think most people realise is that a lot of solid state media ages the more you use it. In effect it wears out.
There are a couple of different types of memory cell that can be used in solid state media. High end professional media will often use single level memory cells that are either on or off. These cells can only store a single value, but they tend to be fast and extremely reliable due to their simplicity. But you need a lot of them in a big memory card. The other type of cell found in most lower cost media is a multi-level cell. Each multi-level cell stores a voltage and the level of the voltage in that cell represents many different values. As a result each cell can store more than one single value. The memory cells are insulated to prevent the voltage charge leaking away. However each time you write to the cell the insulation can be eroded. Over time this can result in the cell becoming leaky and this allows the voltage in the cell to change slightly resulting in a change to the data that it holds. This can lead to data corruption.
So multi level cards that get used a lot, may develop leaky cells. But if the card is read reasonably soon after it was written to (days, weeks, a month perhaps) then it is unlikely that the user will experience any problems. The cards include circuitry designed to detect problem cells and then avoid them. But over time the card can reach a point where it no longer has enough memory to keep mapping out damaged cells, or the cells loose there charge quickly and as a result the data becomes corrupt.
Raspberry Pi computers that use SD cards as memory can kill SD cards in a matter of days because of the extremely high number of times that the card may be written to.
With a video camera it will depend on how often you use the cards. If you only have one or 2 cards and you shoot a lot I would recommend replacing the cards yearly. If you have lots of cards either use one or two and replace them regularly or try to cycle through all the cards you have to extend their life and avoid any one card from excessive use which might make it less reliable than the rest.
One thing regular SD cards are not good for is long term storage (more than a year and never more than 5 years) as the charge in the cells will leak away over time. There are special write once SD cards designed for archival purposes where each cell is permanently fused to either On or Off. Most standard SD cards, no matter how many times they have been used won’t hold data reliably beyond 5 years.
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.
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.
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?
I was recently asked by Sony to write a user guide for the PXW-FS7 and FS7M2. Well it’s now complete and available for free download from Sony. The guide does not replace the manual but should act as a useful point of reference for those unfamiliar with the cameras. It should also help guide you through the use of the CineEI mode or change the various gammas settings in custom mode to suit different types of scene.
There are sections on exposure tools and controls, the variable ND filter, exposure tools and controls. Custom mode paint settings, Cine EI and LUT’s and additional information on the various shooting modes and functions.
There are two versions of the guide. One is an ePub book that can be displayed and read by may book reader programs such as iBooks and the other is an interactive PDF formatted for use on a mobile phone or tablet.
Both versions of the guide can be downloaded from the resources section this page on the Sony site..
While we wait for Sony to re-release the version 4 firmware for the FS5 I thought I would briefly take a look at what HLG is and what it’s designed to do as there seems to be a lot of confusion.
HLG stands for Hybrid Log Gamma. It is one of the gamma curves used for DISTRIBUTION of HDR content to HDR TV’s that support the HLG standard. It was never meant to be used for capture, it was specifically designed for delivery.
As the name suggests HLG is a hybrid gamma curve. It is a hybrid of Rec-709 and Log. But before you get all excited by the log part, the log used by HLG is only a small part of the curve and it is very agressive – it crams a very big dynamic range into a very small space – This means that if you take it into post production and start to fiddle around with it there is a very high probability of problems with banding and other similar artefacts becoming apparent.
The version of HLG in the FS5 firmware follows the BBC HLG standard (there is another NHK standard). From black to around 70% the curve is very similar to Rec 709, so from 0 to 70% you get quite reasonable contrast. Around 70% the curve transitions to a log type gamma allowing a dynamic range much greater than 709 to be squeezed into a conventional codec. The benefit this brings is that on a conventional Rec-709 TV the picture doesn’t look wrong. It looks like a very slightly darker than normal, only slightly flat mid range, but the highlights are quite flat and washed out. For the average home TV viewer watching on a 709 TV the picture looks OK, maybe not the best image ever seen, but certainly acceptable.
However feed this same signal to an HDR TV that supports HLG and the magic starts to happen. IF the TV supports HLG (and currently only a fairly small proportion of HDR TV’s support HLG. Most use PQ/ST2084) then the HLG capable HDR TV will take the compressed log highlight range and stretch it out to give a greater dynamic range display. The fact that the signal gets stretched out means that the quality of the codec used is critical. HLG was designed for 10 bit distribution using HEVC, it was never meant to be used with 8 bit codecs, so be very, very careful if using it in UHD with the FS5 as this is only 8 bit.
So, HLG’s big party trick is that it produces an acceptable looking image on a Rec-709 TV, but also gives an HDR image on an HDR TV. So one signal can be used for both HDR and SDR giving what might be called backwards compatibility with regular SDR TV’s. But it is worth noting that on a 709 TV HLG images don’t look as good as images specifically shot or graded for 709. It is a bit of a compromise.
What about the dynamic range? High end HDR TV’s can currently show about 10 stops. Lower cost HDR TV’s may only be able to show 8 stops (compared to the 6 stops of a 709 TV). There is no point in feeding a 14 stop signal to a 10 stop TV, it won’t look the best. From what I’ve seen of the HLG curves in the FS5 they allow for a maximum of around 10 to 11 stops, about the same as the cinegammas. HLG can be used for much greater ranges, but as yet there are no TV’s that can take advantage of this and it will be a long tome before there are. So for now, the recorded range is a deliberately limited so you don’t see stuff in the viewfinder that will never be seen on todays HDR TV’s. As a result the curves don’t use the full recording range of the camera. This means they are not using the recording data in a particularly efficient way, a lot of data is unused and wasted. But this is necessary to make the curves directly compatible with an HLG display.
What about grading them? My advice – don’t try to grade HLG footage. There are three problems. The first is that the gamma is very different in the low/mid range compared to the highlights. This means that in post the shadows and mid range will respond to corrections and adjustments very differently to the high range. That makes grading tricky as you need to apply separate correction to the midrange and highlights.
The second problem is that the is a very large highlight range squeezed into a very small recording range. It should look OK when viewed directly with no adjustment. But if you try stretching that out to make the highlights brighter (remember they never reach 100% as recorded) or to make them more contrasty, there is a higher probability of seeing banding artefacts than with any other gamma in the camera.
The third issue is simply that the limited recording range means you have fewer code values per stop than regular Rec-709, the cinegammas or S-Log2. HLG is the least best choice for grading in the FS5.
Next problem is color. Most HDR TV’s want Rec-2020 color. Most conventional monitors want Rec-709 color. Feed Rec-2020 into a 709 monitor and the colors look flat and the hues are all over the place, especially skin tones. Some highly saturated colors on the edge of the color gamut may pop out more than others and this looks odd.
Feed 709 into a 2020 TV and it will look super saturated and once again the color hues will be wrong. Also don’t fool yourself into thinking that by recording Rec2020 you are actually capturing more. The FS5 sensor is designed for 709. The color filters on the sensor do work a little beyond 709, but nowhere near what’s needed to actually “see” the full 2020 color space. So if you set the FS5 to 2020 what you are capturing is only marginally greater than 709. All you really have is the 709 with the hues shifted and saturation reduced so color looks right on a 2020 monitor or TV.
So really, unless you are actually feeding an Rec 2100 (HLG + 2020) TV, there is no point in using 2020 color as this require you to grade the footage to get the colors to look right on most normal TV’s and monitors. As already discussed, HLG is far from ideal for grading, so better to shot 709 if that’s what your audience will be using.
Don’t let the hype and fanfares that have surrounded this update cloud your vision. HLG is certainly very useful if you plan to directly feed HDR to a TV that supports HLG. But if you plan on creating HDR content that will be viewed on both HLG TV’s and the more common PQ/ST2084 TV’s then HLG is NOT what you want. You would be far – far better off shooting with S-Log and then grading your footage to these two very different HDR standards. If you try to convert HLG to PQ it is not going to look nearly as good as if you start with S-Log.
Exposure levels: If you want to get footage that works both with an HLG HDR TV and a SDR 709 TV then you need to expose carefully. A small bit of over exposure wont hurt the image when you view it on a 709 TV or monitor, so it will look OK in the viewfinder. But on an HDR TV any over exposure could result in skin tones that look much too bright and an image that is unpleasantly bright. As a guide you should expose diffuse 90% white (a white card or white piece of paper) at no more than 75%. Skin tones should be around 55 to 60%. You should not expose HLG as brightly as you do Rec-709.
Sure you can shoot with HLG for non HDR applications. You will get some slightly flat looking footage with rolled off highlights. If that’s the image you want then I’m not going to stop you shooting that way. If that’s what you want I suggest you consider the Cinegamma as these capture a similar DR also have a nice highlight roll off (when exposed correctly) and do use the full recording range.
Whatever you do make sure you understand what HLG was designed for. Make sure you understand the post production limitations and above all else understand that it absolutely is not a substitute for S-log.