Category Archives: Technology

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.

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What are the benefits of ProRes Raw with the PXW-FS5?

There has been a lot of discussion recently and few videos posted that perhaps give the impression that if you shoot with S-Log2 on an FS5 and compare it to raw shot on the FS5 there is very little difference.

Many of the points raised in the videos are correct. ProRes raw won’t give you any more dynamic range. It won’t improve the cameras low light performance. There are features such as automatic lens aberration correction applied when shooting internally which isn’t applied when shooting raw.  Plus it’s true that shooting ProRes raw requires an external recorder that makes the diminutive little FS5 much more bulky.

So why in that case shoot ProRes Raw?

Frankly, if all you are doing is producing videos that will be compressed to within an inch of their life for YouTube, S-Log2 can do an excellent job when exposed well, it can be graded and can produce a nice image.

But if you are trying to produce the highest quality images possible then well shot ProRes raw will give you more data to work with in post production with fewer compression artefacts than the internal 8 bit UHD XAVC.

I was looking at some shots that I did in preparation for my recent webinar on ProRes raw earlier today and at first glance there isn’t perhaps much difference between the UHD 8 bit XAVC S-Log2 files and the ProRes raw files that were shot within seconds of each other. But look more closely and there are some important differences, especially if skin tones are important too you.

Skin tones sit half way between middle grey and white and typically span around 2 to 3 stops. So with S-Log 2 and an 8 bit recording a face would span around 24 to 34 IRE and have a somewhere between 24 and 35 code values – Yes, that’s right, maybe as few as 24 shades in each of the R, G and B channels. If you apply a basic LUT to this and then view it on a typical 8 bit monitor it will probably look OK.

But compare that to 12 bit linear raw recording and the same face with 2 to 3 stops across it will have anywhere up to 10 to 20 times as many code values ( somewhere around 250 – 500 code values depending on exactly how it’s exposed) . Apply the same LUT as for the S-Log2 and on the surface it looks pretty much the same – or does it?

Look closely and you will see more texture in the 12 bit raw. If you are lucky enough to have a 10 bit monitor the differences are even more apparent. Sure, it isn’t an in-your-face night and day difference but the 12 bit skin tones look less like plastic and much more real, they just look nicer, especially if it’s someone with a good complexion.

In addition looking at my test material I am also seeing some mpeg compression artefacts on the skin tones in the 8 bit XAVC that has a smoothing effect on the skin tones, reducing some of the subtle textures and adding to the slightly un-real, video look.

The other deal with a lack of code values and H624 compression  is banding. Take 8 bit S-Log2 and start boosting the contrast in a sky scene, perhaps to bring out some cloud details and you will start to see banding and stair stepping if you are not very careful. You will also see it across wall and other textureless surfaces. You can even see this on your grading suite waveform scopes in many cases. You won’t get this with well exposed 12 bit linear raw (for any normal grading at least).

None of these are huge deals perhaps. But what is it that makes a great picture? Take Sony’s Venice or the Arri Alexa as examples. We know these to be great cameras that produce excellent images. But what is it that makes the images so good? The short answer is that it is a combination of a wide range of factors, each done as well as is possible. Good DR, good colour, good skin tones etc. So what you want to record is whatever the sensor in your camera can deliver as well as you can. 8 bit UHD compressed to only 100Mb/s is not really that great. 12 bit raw will give you more textures in the mid range and highlights. It does have some limitations in the shadows, but that is easily overcome with a nice bright exposure and printing down in post.

And it’s not just about image quality.

Don’t forget that ProRes Raw makes shooting at 4K DCI possible. If you hope to ever release your work for cinema display, perhaps on the festival circuit, you are going to be much better off shooting in the cinema DCI 4K standard rather than the UHD TV standard. It also allows you to shoot 60fps in 4K (I’m in the middle of a very big 4K 60p project right now). Want to shoot even faster – well with ProRes Raw you can, you can shoot at up to 120fps in 4K. So there are many other benefits to the raw option on the FS5 and recording to ProRes raw on a Shogun Inferno.

There is also the acceptability of 8 bit UHD. No broadcaster that I know of will ever consider 8 bit UHD unless there is absolutely no other way to get the material. You are far more likely to be able to get them to accept 12 bit raw.

Future proofing is another consideration. I am sure that ProRes raw decoders will improve and support in other applications will eventually come. By going back to your raw sensor data with better software you may be able to gain better image quality from your footage in the future. With Log you are already somewhat limited as the bulk of the image processing has already been done and is baked into the footage.

It’s late on Friday afternoon here in the UK and I’ve promised to spend some time with the family this evening. So no videos today. But next week I’ll post some of the examples I’ve been looking at so that you can see where ProRes raw elevates the image quality possible from the FS5.

PXW-FS5 II Secret Sauce and Venice Colour Science.

At NAB 2018 a very hot topic is the launch of the FS5 II. The FS5 II is an update on the existing FS5 that includes the FS Raw output option and the HFR option as standard. So out of the box this means that this camera will be a great match to an Atomos Inferno to take advantage of the new Apple ProRes Raw codec.

Just like the FS5 the FS5 II can shoot using a range of different gamma curves including Rec-709, HLG, S-Log2  and S-Log3. So  for those more involved projects where image control is paramount you can shoot in log (or raw)  then take the footage into your favourite grading software and create whatever look you wish. You can tweak and tune your skin tones, play with the highlight roll off and create that Hollywood blockbuster look – with both the FS5 and the FS5 II. There is no change to this other than the addition of FS-Raw as standard on the FS5 II.

The big change, is to the cameras default colour science.

FS5II-1-1024x564 PXW-FS5 II Secret Sauce and Venice Colour Science.
New color science from the Sony PXW-FS5 II

Ever since I started shooting on Sony cameras, which was a very long time ago, they have always looked a certain way. If you point a Sony camera at a Rec-709 test chart you will find that the colours are actually quite accurate, the color patches on the chart lining up with the target boxes on a vector scope. All Sony cameras look this way so that if you use several different cameras on the same project they should at least look very similar, even if one of those cameras is a few years old.  But this look and standard was establish many years ago when camera and TV technology was nowhere near as advanced as it is today.

in addition, sometimes accurate isn’t pretty. Television display technology has come a long way in recent years. Digital broadcasting combined with good quality LCD and OLED displays now mean that we are able to see a wider range of colours and a larger dynamic range. Viewers expectations are changing, we all want prettier images.

When Sony launched the high end Venice digital cinema camera a bold step was taken, which was to break away from the standard Sony look and instead develop a new, modern, “pretty” look. A lot of research was done with both cinematographers and viewers trying to figure out what makes a pretty picture. Over several months I’ve watched Pablo, Sony’s colourist at the Digital Motion Picture Center at Pinewood studios develop new LUT’s with this new look for the Venice camera. It hasn’t been easy, but it looks really nice and is quite a departure from that standard Sony look.

The FS5 II includes many aspects of this new look. It isn’t just a change to the colours it is also a change to the default gamma curve that introduces a silky smooth highlight roll off that extends the dynamic range well beyond that normally possible with a conventional Rec-709 gamma curve. A lot of time was spent looking at how this new gamma behaves when shooting people and faces. In particular those troublesome highlights that you get on a nose or cheek that’s catching the light. You know – those pesky highlights that just don’t normally look nice on a video camera.

So as well as rolling off the brightness of these highlights in a smooth way, the color also subtly washes out to prevent the highlight color bloom that can be a video give away. This isn’t easy to do. Any colorist will tell you that getting bright skin tone highlights to look nice is tough. You bring down the brightness and it looks wrong because you loose too much contrast. De-saturate too much and it looks wrong as it just becomes a white blob. Finding the right balance of extended dynamic range with good contrast, plus a pleasing roll-off without a complete white-out is difficult enough to do in a grading suite where you can tweak and tune the settings for each shot. Coming up with a profile that will work over a vast range of shooting scenarios with no adjustment is even tougher. But it looks to me as though the engineers at Sony have really done a very nice job in the FS5 II.

Going forwards from here I would expect to see, or at least like to see, most of Sony’s future cameras have this new colour science. But this is a big step for Sony to break away from decades of one look and every camera looking more or less the same.  But do remember this change is primarily to the default, “standard” gamma look. It does not effect the FS5 II’s log or raw recordings. There is also going to have to be a set of LUT’s to go with this new color science so that those shooting with with a mix of the baked in look and S-log or raw can make all the footage match. In addition users of other S-Log cameras will want to be able to make their cameras match. I see no reason why this won’t be possible via a LUT or set of LUT’s, within the limitations of each cameras sensor technology.

There has been a lot of people that seem unhappy with the FS5 II. I think many people want a Sony Venice for the price of an FS5. Let’s be realistic, that isn’t going to happen. 10 bit recording in UHD would be nice, but that would need higher bit rates to avoid motion artefacts which would then need faster and more expensive media. If you want higher image quality in UHD or 4K DCI do consider an Atomos recorder and the new ProRes Raw codec. The files are barely any bigger than ProRes HQ, but offer 12 bit quality.

Given that the price of the FS5 II is going to be pretty much the same or maybe even a little lower than the regular FS5 (before you even add any options), I am not sure why so many people are complaining. The FS5-II takes a great little camera, makes it even better and costs even less.

 

ProRes Raw and Atomos Inferno and Sumo – BIG deal for the FS5 and FS7!!

proresraw-logo ProRes Raw and Atomos Inferno and Sumo - BIG deal for the FS5 and FS7!!Over the last few days there have been various rumours and posts coming from Apple about how they intend to get back to providing decent support for professional users of their computers. Apple have openly admitted that the Trash Can Mac Pro has thermal problems and as a result has become a dead end design, which is why there haven’t been any big updates to the flagship workstation from Apple. Apple have hinted that new workstations are on the way, although it would seem that we won’t see these until next year perhaps.
Another announcement came out today, a new version of FCP-X is to be released which includes support for a new ProRes codec called ProRes Raw. This is BIG!

PRORES RAW.

Raw recordings can be made from certain cameras that have bayer sensors such as the Sony FS5 and FS7. Recording the raw data from the sensor maximises your post production flexibility and normally offers the best possible image quality from the camera. Currently if you record 4K raw with these cameras using an Atomos Shogun or similar the bit rate will be close to 3Gb/s at 24p. These are huge files and the cDNG format used to record them is difficult and clunky to work with.  As a result most users take the raw output from the camera and transform it to S-Log2 or S-Log3 and record it as 10 bit ProRes on the external recorder. This is a bit of a shame as going from 12 bit linear raw to 10 bit S-log means you are not getting the full benefit of the raw output.

Enter ProRes Raw:  ProRes Raw will allow users to record the cameras raw output at a much reduced bit rate with no significant of quality. There are two versions, ProRes Raw and ProRes Raw HQ. The HQ bit rate is around 1Gb/s at 24fps. This is not significantly bigger than the ProRes HQ (880Mb/s) that most users are using now to record the raw, yet the full benefit of 12 bit linear will be retained. A 1TB SSD will hold around an hour of ProRes Raw, compare that to uncompressed raw where you only get around 20 mins and you can see that this is a big step forwards for users of the FS5 in particular.

ProRes Raw (the non HQ version) is even smaller! The files are smaller than typical ProRes HQ files. This is possible because recording raw is inherently more efficient than recording component video.

It is claimed by Apple that ProRes Raw will play back in real time on MacBook Pro’s and iMacs without any additional rendering or external graphics cards, so it obviously isn’t terribly processor intensive. This is excellent news! Within FCP-X the playback resolution can be decreased to bring improved playback performance in less powerful systems or mutistream playback.

It looks like you will be able to record from a 4K DCI  from an FS5 or FS7 at up to 60fps continuously. This breaks through the previous limits for the Shogun of 30fps. The FS7 will be able to record 2K raw at up to 240fps and the FS5 will be able to record 4K raw at 100 and 120fps for 4 seconds. Other raw cameras are also supported by the Atomos recorders at differing frame sizes and frame rates.

At the moment the only recorders listed as supporting ProRes Raw are the Atomos Shogun Inferno and the Sumo19 and it looks like it will be a free update. In addition the DJI Inspire 2 drone and Zenmuse X7 Super 35mm camera will also support ProRes Raw.

Whether you will be able to use ProRes Raw in other applications such as Resolve or Premiere is unclear at this time. I hope that you can (or at least will be able to in the near future).

SEE: Apple Press Release.

SEE: Apple ProRes Raw White Paper

SEE: ATOMOS ProRes Raw INFO PAGE.

 

 

Banding in your footage. What Causes It, is it even there?

Once again it’s time to put pen to paper or fingers to keyboard as this is a subject that just keeps coming up again and again.

People really seem to have a lot of problems with banding in footage and I don’t really fully understand why as it’s something I only ever really encounter if I’m pushing a piece of material really, really hard in post production. General the vast majority of the content I shoot does not exhibit problematic banding, even the footage I shoot with 8 bit cameras.

First things first – Don’t blame it on the bits. Even an 8 bit recording  (from a good quality camera) shouldn’t exhibit noticeable banding. An 8 bit recording can contain up to 13 million tonal values. It’s extremely rare for us to shoot luma only, but even if you do it will still have 235 shades and these steps in standard dynamic range are too small for most people to discern so you shouldn’t ever be able to see them. I think that when most people see banding they are not seeing teeny, tiny almost invisible steps what most people see is something much more noticeable – so where is it coming from?

It’s worth considering at this stage that most TV’s, monitors and computer screens are only 8 bit, sometimes less! So if you are looking at one camera and it’s banding free and then you look at another and you see banding, in both cases you are probably looking at an 8 bit image, so it can’t just be the capture bit depth that causing the problem as you cant see 10 bit steps on an 8 bit monitor.

So what could it be?

A very common cause of banding is compression. DCT based codecs such as Jpeg, MJPEG, H264 etc break the image up into small blocks of pixels called macro blocks. Then all the pixels in each block is processed in a similar manner and as a result sometimes there may be a small step between each block or between groups of blocks across a gradient. This can show up as banding. Often we see this with 8 bit codecs because typically 8 bit codecs use older technology or are more highly compressed. It’s not because there are not enough code values. Decreasing the compression ratio will normally eliminate the stepping.

Scaling between bit depths or frame sizes is another very common cause of banding. It’s absolutely vital that you ensure that your monitoring system is up to scratch. It’s very common to see banding in video footage on a computer screen as the video data levels are different to computer data levels and in addition there may also be some small gamma differences so the image has to be scaled on the fly. In addition computer desktops runs at one bit range, the HDMI output another, so all kinds of conversions are taking place that can lead to all kinds of problems when you go from a video clip, to computer levels, to HDMI levels. See this article to fully understand how important it is to get your monitoring pipeline properly sorted. http://www.xdcam-user.com/2017/06/why-you-need-to-sort-out-your-post-production-monitoring/

Look Up Tables (LUT’s) can also introduce banding. LUT’s were never really intended to be used as a quick fix grade, the intention was to use them as an on-set reference or guide, not the final output. The 3D LUT’s that we typically use for grading break the full video range into bands and each band will apply a slightly different correction to the footage than the band above or below. These bands can show up as steps in the LUT’s output, especially with the most common 17x17x17 3D LUT’s. This problem gets even worse if you apply a LUT and then grade on top – a really bad practice.

Noise reduction – In camera or postproduction noise reduction will also often introduce banding. Very often pixel averaging is used to reduce noise. If you have a bunch of pixels that are jittering up and down taking an average value for all those pixels will reduce the noise, but then you can end up with steps across a gradient as you jump from one average value to the next. If you shoot log it’s really important that you turn off any noise reduction (if you can) when you are shooting because when you grade the footage these steps will get exaggerated. Raising the ISO (gain) in a camera also makes this much worse as the cameras built in NR will be working harder, increasing the averaging to compensate the increased noise.

Coming back to 8 bit codecs again – Of course a similar quality 10 bit codec will normally give you more picture information than an 8 bit one. But we have been using 8 bits for decades, largely without any problems. So if you can shoot 10 bit you might get a better end result. But also consider all the other factors I’ve mentioned above.

 

Skills and knowledge in TV and video production are not keeping up with the technology.

TV and video production, including digital cinema is a highly technical area. Anyone that tells you otherwise is in my opinion mistaken. Many of the key jobs in the industry require an in depth knowledge of not just the artistic aspects but also the technical aspects.
Almost everyone in the camera department, almost everyone in post production and a large portion of the planning and pre-production crew need to know how the kit we use works.
A key area where there is a big knowledge gap is gamma and color. When I was starting out in this business I had a rough idea of what gamma and gamut was all about. But then 10 years or more ago you didn’t really need to know or understand it because up to then we only ever had variations on 2.2/2.4 gamma. There were very few adjustments you could make to a camera yourself and if you did fiddle, generally you would often create more problems than you solved. So those things were just best left alone.
But now it’s vital that you fully understand gamma, what it does, how it works and what happens if you have a gamma miss-match. But sadly so many camera operators (and post people) like to bury their heads in the sand using the excuse “I’m an artist – I don’t need to understand the technology”. Worse still are those that think they understand it, but in reality do not, mainly I think, due to the spread of miss-information and bad practices that become normal. As an example shooting flat seems to mean something very different today to what it meant 10 years ago. 10 years ago it meant shooting with flat lighting so the editor or color grader could adjust the contrast in post production. Now though, shooting flat is often incorrectly used to describe shooting with log gamma (shooting with log isn’t flat, it’s a gamma miss-match that might fool the operator into thinking it’s flat). The whole “shooting flat” miss-conception comes from the overuse and incorrect use of the term on the internet until it eventually became the accepted term for shooting with log.
 
As only a very small portion of film makers actually have any formal training and even fewer go back to school to learn about new techniques or technologies properly this is a situation that isn’t going to get any better. As we move into an era where, in the short term at least, we will need to start delivering multiple versions of productions in both standard dynamic range as well as several different HDR versions, additionally saving the programme master in another intermediate format. Things are only going to get more complicated and more and more mistakes will be made, technology will be applied and used incorrectly.
Most people are quite happy to spend thousands on a new camera, new recorder or new edit computer. But then they won’t spend any money on training to learn how to get the very best from it. Instead they will surf the net for information and guides of unknown quality and accuracy.
When you hire a crew member you have no idea how good their knowledge is. As it’s normal for most not to have attended any formal courses we don’t ask for certificates and we don’t expect them. But they could be very useful. Most other industries that benefit from a skilled labour force have some form of formal certification process, but our industry does not, so hiring crew, booking an editor etc becomes a bit of a lottery.
Of course it’s not all about technical skills. Creative skills are equally important. But again it’s hard to prove that you do have such skills to a new client. Showreels are all to easy to fake.
Guilds and associations are a start. But many of these can be joined simply by paying the joining or membership fee. You could be a member of one of the highly exclusive associations such as the ASC or BSC, but even that doesn’t mean you know about technology “A” or technique “Z”.
We should all take a close look at our current skill sets. What is lacking, where do I have holes, what could I do better. I’ve been in this business for 30 years and I’m still learning new stuff almost every day. It’s one of the things that keeps life interesting. Workshops and training events can be hugely beneficial and they really can lead to you getting better results. Or it may simply be that a day of training helps give you the confidence that you are doing it right. They are also great opportunities to meet other similar people and network.
Whatever you do, don’t stop learning, but beware the internet, not everything you read is right. The key is to not just read and then do, but to read, understand why, ask questions if necessary, then do. If you don’t understand why, you’ll never be able to adapt the “do” to fit your exact needs.

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. 

How can 16 bit X-OCN deliver smaller files than 10 bit XAVC-I?

Sony’s X-OCN (XOriginal 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.

Bayer-to-RGB How can 16 bit X-OCN deliver smaller files than 10 bit XAVC-I?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.

Sony Venice. Dual ISO’s, 1 stop ND’s and Grading via Metadata.

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!

METADATA GRADING.

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.

What shutter speed to use if shooting 50p or 60p for 50i/60i conversion.

An interesting question got raised on Facebook today.

What shutter speed should I use if I am shooting at 50p so that my client can later convert the 50p to 50i? Of course this would also apply to shooting at 60p for 60i conversion.

Lets first of all make sure that we all understand that what’s being asked for here is to shoot at 50(60) progressive frames per second so that the footage can later be converted to 25(30) frames per second interlace – which has 50(60) fields.

If we just consider normal 50p or 60p shooing the the shutter speed that you would chooses on many factors including what you are shooting and how much light you have and personal preference.

1/48 or 1/50th of a second is normally considered the slowest shutter speed at which motion blur in a typical frame no longer significantly softens the image. This is why old point and shoot film cameras almost always had a 1/50th shutter, it was the slowest you could get away with.

Shooting with a shutter speed that is half the duration of the cameras frame rate is also know as using a 180 degree shutter, a very necessary practice with a film movie camera due to the way the mechanical shutter must be closed while the film is physically advanced to the next frame. But it isn’t essential that you have the closed shutter period with an electronic camera as there is no film to move, so you don’t have to use a 180 degree shutter if you don’t want to.

There is no reason why you can’t use a 1/50th or 1/60th shutter when shooting at 50fps or 60fps, especially if you don’t have a lot of light to work with. 1/50(1/60) at 50fps(60fps) will give you the smoothest motion as there are no breaks in the motion between each frame. But many people like to sharpen up the image still further by using 1/100th(1/120th) to reduce motion blur.  Or they prefer the slightly steppy cadence this brings as it introduces a small jump in motion between each frame. Of course 1/100th needs twice as much light. So there is no hard and fast rule and some shots will work better at 1/50th while others may work better at 1/100th.

However if you are shooting at 50fps or 60fps so that it can be converted to 50i or 60i, with each frame becoming a field, then the “normal” shutter speed you should use will be 1/50th or 1/60th to mimic a 25fps-50i camera or 30fps-60i camera which would typically have it’s shutter running at 1/50 or 1/60th. 1/100th(120th) at 50i(60i) can look a little over sharp due to an increase in aliasing due to the way a interlace video field only has half the resolution of the full frame. Particularly with 50p converted to 50i as there is no in-camera anti-aliasing and each frame will simply have it’s resolution divided by 2 to produce the equivalent of a single field. When you shoot with a “real” 50i camera line pairs on the sensor are combined and read out together as a  single field line and this slightly softens and anti-aliases each of fields. 50i has lower vertical resolution than 25p. But with simple software conversions from 50p to 50i this anti-aliasing does not occur. If you combine that with a faster than typical shutter speed the interlaced image can start to look over sharp and may have jaggies or color moire not present in the original 50/60p footage.