Tag Archives: 4k

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So, if I can hack an F5 for 4K, can I also get the F55’s color gamut?

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So, we have seen that it is possible to trick an F5 into thinking its an F55 by altering an all file from the F5 and adding some F55 4K settings. This enables 4K internal recording and 4K output over HDMI on the F5. Internal 4K is one of the key differences between the lower cost F5 and the much more expensive F55. Another major difference is that the F55 has a global shutter so no CMOS image skew or other rolling shutter artefacts and the F55 has a larger colour gamut allowing better colour rendition and capture.

A question that has been asked is: Well if we can get 4K, can we also enable the larger colour gamut? One thing we do know is that the sensor used in the F55 is different to the sensor in the F5 as the sensor is replaced if you upgrade your F5 to an F55.

A cameras gamut is determined more by the sensors colour filters than the recording gamut. The recording gamut is like a bucket, the sensor a scoop. If the scoop isn’t big enough you won’t fill the bucket.

The color filters on the F55 are very different to those in the F5, so the F55 can capture a much greater gamut than the F5.

If you think about it, if you hold a red gel up infront of your eyes you will only see an extremely narrow colour gamut, just a single narrow part of the red spectrum. Imagine if you have a red, green and blue filter, you will now see a bit of red, a bit of green and a bit of blue. But you might only see a very narrow part of the full blue spectrum or a very narrow part of red or of green, you won’t see the full spectrum or a large gamut, just narrow slithers of it. The trick is to make filters that are wide enough and with the righ charcteristics to pass all of the R, G and B spectrum but sharply cut off unwanted colors, infra-red or UV at the exactly the right point. This is very hard to do. So the quality and accuracy of the color filters determines both the gamut and the precision of the colors that the camera can capture.

In practice it can be hard to see this difference as none of the monitors available today can show the full gamut that the F55 can capture so you can’t directly see it. But it does make a difference in post as the F55 is able to separate subtle hues more accurately and capture an extended tonal range, for example very subtle differences in skin tones that may be lost on a camera with poorer filters. This means when grading you are able to draw more tonal information out of the image when you transform the color space in to Rec 709 or DCI-P3 and it results in a more natural looking image.

The F5’s sensor gamut is probably somewhere around the size of DCI P3, maybe a bit bigger, but it’s clearly not as big as the F55’s. In addition the colour precision is not as great so some subtle tones are lost. It’s not a massive difference and the F5 does a great job. It’s not something that can be changed with software, it’s all down to the sensor hardware. The F5 just can’t fill the S-Gamut recording bucket so by using S-Gamut your wasting a lot of data. By using a smaller recording gamut like S-Gamut3.cine you can more effectively fill the bucket and make better use of the data available to you.

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Hack to get internal 4K on the Sony PMW-F5 CAUTION THERE MAY BE ISSUES!!!!

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STOP PRESS: It’s been found that this modification is also changing the exposure and dynamic range! See bottom of post.

Well, Paul Ream over at http://extrashot.co.uk/ has worked out how to make the F5 record 4K internally. It’s actually pretty straight forward. The camera can save a file called an “All File” on an SD card to memorise the way it’s set up. By mdifying this file you can trick the F5 to go into 4K or UHD frame size instead of the usual HD or 2K. First you have to modify line 15o of an existing All File (they are simple text files) where the frame rate and frame size are saved using a text editor, putting in the frame size you want. Then delete line 1 where the files MD5 checksum is stored. Save the file. Next determine the checksum of the file, then add the new checksum to line 1 and finally save the file to the SD card and read it in to the camera. By loading this modified (hacked???) all file in to the camera you can enable 4K and UHD recording to the SxS cards.

It’s certainly created a stir. Many F55 owners think they have been short changed because of this hack and of course most F5 are very happy. It will be interesting to see if any other F55 features can be unlocked on the F5 such as 4K output or 4K playback. Right now the hack is a little limited as you can’t even playback files to see if they are OK. Full details over on Extrashot in the latest podcast…. if you can grind your way through the bit on shoes and iphones without nodding off first.

UPDATE: So, now a few people have tried this, there have been a couple of reports of the dynamic range of image clipping and some other issues. I’ve had a quick look on an F5 (not mine, I’m travelling) and there is most definitely something odd going on as the pictures are darker and clip earlier in 4K XAVC compared to HD and 2K. I need to test this further to see what’s going on, but it’s not quite as perfect as perhaps hoped.

What we know: The hack tricks the camera into behaving like a PMW-F55. We know the F5 and F55 have different sensors with very different behaviour, different colour filters and different sensitivity, so the processing must be different for these two cameras.

My very quick test, shooting the same scene in 4K and in normal HD XAVC shows the 4K to be darker. Others are reporting that the 4K clips appear to over-exposure more readily than the HD.

SPECULATION: If the hack is doing more than just turning on 4K recording, if it is making the camera use the F55’s processing, then there will be a miss-match between the sensor and the processing and this might cause issues with dynamic range, gain and colour.

As soon as I get a chance (should be tomorrow) I will do some more involved testing to see exactly what is going on.

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PXW-X70 Teaser Video.

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Here’s a short clip to keep you going until later in the week when I will upload the full length version of my video “Dancers on the line” shot with the new Sony PXW-X70 camcorder. As well as the film there will be a behind the scenes video with some insight into what the camera is like to shoot with and how the images look. It’s all good stuff, this is a great little compact handycam and a pretty big step up from the AX100.

Frame grab from the PXW-X70.
Frame grab from the PXW-X70.

It has a nice big 1″ size sensor, built in ND filters and a nice power zoom lens. It records XAVC long GOP 10bit 422 at 50Mbps at up to 60fps. Also has AVCHD and standard definition DV. The ergonomics are brilliant, clearly Sony have done a lot of works on this area and it a delight to operate run and gun or when your pressed for time. You get great battery life and the pictures are pretty amazing for a compact handycam. You can even dial in your own picture profiles for a custom look. Dual SD card slots allow for relay recording or dual card recording, there’s an full size SDI and HDMI out too. LAst thing for now… it’s 4K ready. There will be a paid upgrade to 4K option in the first half of next year. More details to come as the week progresses.

Here’s the press release from Sony.

Basingstoke, July 29, 2014: Sony has today launched the 4K-ready PXW-X70, the first compact XDCAM professional camcorder ever produced. Expanding the popular file-based XDCAM family to a new smaller form factor and lower price point, Sony has combined stunning picture quality, speed of shooting and robust performance into a package which is ideal for a wide range of applications from news gathering and documentary to events work.??

The PXW-X70 features a 1.0 type Exmor® R CMOS Sensor with a resolution of 20 megapixels. The sensor, which is even larger than the Super 16mm film frame, delivers high resolution and fantastic low light performance, as well as offering more depth of field control as demanded by today’s diverse shooting requirements. The new camcorder has the ability to record High Definition in XAVC Long GOP, enabling 422 10-bit sampling at 50 Mbit/s. This in-turn supports a broadcast-quality workflow, increasingly adopted by productions in many different professional applications.

This addition to the expanding next generation XDCAM family follows the recently announced PXW-X180 and PXW-X160 and builds upon Sony’s successful heritage of compact professional camcorders. The PXW-X70 is the first professional compact camcorder from Sony to include Wi-Fi-enabled control via Smart Phone or Tablet using the Content Browser Mobile application. An upcoming release will also provide customers with the ability to upgrade the PXW-X70 to record in 4K Ultra High Definition, with file transferring, and live video streaming capabilities.

“This first compact member of the XDCAM family brings the performance and workflow benefits associated with XAVC to an even wider range of shooting scenarios,” said Robbie Fleming, Product Marketing Manager, at Sony Professional Solutions Europe. “Over the past couple of years we’ve seen the broadcast industry really embrace the picture quality benefits associated with large sensors; the one-inch sensor at the heart of the PXW-X70 sets a new standard for colour, depth and texture in a professional compact camcorder. Coupled with the ability to upgrade to 4K, this represents a multipurpose, future-proof option for customers looking for a tough camcorder which doesn’t compromise on image.”

Key features of the PXW-X70

• 1.0 type Exmor® R CMOS Sensor and Carl Zeiss Vario Sonnar T* lens for stunning picture quality. High sensitivity and fantastic resolution with 14.2 million effective pixels delivers striking detail and colours, even in low light conditions. The lens offers a 12x Optical Zoom, which can be increased to 24x with Clear Image Zoom while retaining full resolution thanks to Super Resolution Technology. Zoom performance can be doubled at any point with a Digital Extender by up to 48x.

• Compact, lightweight XDCAM camcorder packed with adaptable professional functions. The PXW-X70 weighs less than 1.4kg, including the XLR handle unit, battery (NP-FV70), lens hood and large eye-cup. It offers professional interfaces such as 3G-SDI and HDMI output connectors plus an XLR x 2 handle unit with zoom lever. Other professional features include a manual lens ring that can intuitively control zoom and focus, ergonomic palm grip with large zoom lever, two SD memory card slots for backup, simultaneous and relay recording, and a three-level switchable ND filter.

• Breadth of recording format capabilities. Provides multiple choices depending on application required, including XAVC, AVCHD and DV® file-based recording. When recording in XAVC, the PXW-X70 uses the MXF file format, efficiently compressing full HD (1920 x 1080) resolution using the MPEG-4 AVC/H.264 CODEC. Image sampling is 4:2:2 10-bit with high-efficiency Long-GOP compression at 50 Mbps, 35 Mbps or 25 Mbps.

• Built-in Wi-Fi control functionality for monitoring and remote control versatility. Near Field Communication functions enable easy, one-touch wireless LAN connection to a smartphone or tablet, while the Content Browser Mobile application allows confirmation of shot angles and operation of the camcorder by remote, including field angle setting, spot focus and iris adjustment.

• Upcoming announcements to add even greater, future-proof functionality. Sony is set to make upgrades to 4K and file transfer and streaming by Wi-Fi function available for the PXW-X70 in the coming months.

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How big a compromise is using a DSLR zoom on a 4K camera?

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This came up as a question in response to the post about my prototype lens adapter. The adapter is based around an electronic Canon EF mount and the question was, what do I think about DSLR zooms?

There is a lot of variation between lenses when it comes to sharpness, contrast and distortions. A zoom will always be a compromise compared to a prime lens. DSLR lenses are designed to work with 24MP sensors. A 4K camera only has around 9MP, so your working well within the design limits of the lens even at 4K. While a dedicated PL mount zoom like an Angenieux Optimo will most likely out perform a similar DSLR zoom. The difference at like for like apertures will not be huge when using smaller zoom ratios (say 4x). But 10x and 14x zooms make more compromises in image quality, perhaps a bit of corner softness or more CA and these imperfections will be better or worse at different focal lengths and apertures. At the end of the day zooms are compromises but for many shoots it may simply be that it is only by accepting some small compromises that you will get the shots you want. Take my storm chasing shoots. I could use primes and get better image quality, but when you only have 90 seconds to get a shot there simply isn’t time to swap lenses, so if you end up with a wide on the camera when a long lens is what is really needed, your just not going to get the shot. Using a zoom means I will get the shot. It might not be the very best quality possible but it will look good. It is going to be better than I could get with an HD camera and a very slightly compromised shot is better than no shot at all.
If the budget would allow I would have a couple of cameras with different prime lenses ready to go. Or I would use a big, heavy and expensive PL zoom and have an assistant or team tasked solely with getting the tripod set up and ready asap. But my budget isn’t that big. I could spend weeks out storm chasing before I get a decent shot, so anything I can do to minimise costs is important.
It’s all about checks and balances. It is a compromise, but a necessary one. It’s not a huge compromise as I suspect the end viewer is not going to look at the shot and say “why is that so soft” unless they have a side by side, like for like shot to compare. DSLR zooms are not that bad! So yes, using a DSLR zoom is not going to deliver quality to match that of a similar dedicated PL zoom in most cases, but the difference is likely to be so small that the end viewer will never notice and thats a compromise I’m prepared to accept in order to get a portable camera that shoots 4K with a 14x zoom lens.

What about DSLR primes and why have I chosen the Canon Mount?

This is where the image performance gap gets even narrower. A high quality DSLR prime can perform just as well as many much more expensive PL mount lenses. The difference here is more about the usability of the lens. Some DSLR lenses can be tiny and this makes them fiddly to use. They are all All sorts of sizes, so swapping lenses may mean swapping Matte boxes or follow focus positions etc. Talking of focus, very often the focus travel on a DSLR lens is very, very short so focussing is fiddly. If the lens has an aperture ring it will probably have click stops making smooth aperture changes mid shot difficult. My prime lenses are de-clicked or never had clicks in the first place (like the Samyang Cine Primes). It’s not so much the issue of requiring a finer step than the one stop click, but more the ability to pull aperture during the shot. It’s not something I need to do often, but if I suddenly find I need to do it, I want a smooth aperture change. That being said, one of the issues with using Canon EF lenses with their electronic iris is that they operate in 1/8th stop steps and this is visible in any footage. Ultimately I am still committed to using the Canon mount lenses simply because there are so many to choose from and they focus in the right direction unlike Nikon lenses which focus back to front. For primes I’m using the excellent and fully manual Samyang T1.5 Cine Primes. I really like these lenses and they produce beautiful images at a fraction of the price of a PL mount lens. My zoom selection is a bit of a mish-mash. One thing about having a Canon mount on the camera is that I can still use Nikon lenses if I fit the lens with a low cost Nikon to Canon adapter ring. If you do this you can only use lenses with an actual iris ring, so generally these are slightly older lenses, but for example I have a nice Sigma 24-70mm f2.8 with a manual iris ring (and it focusses the RIGHT way, like most Sigmas but unlike most Nikon mount lenses). In addition I have a 70-300mm f4 Nikon mount Sigma as well as an Old Tokina 28-70mm f2.6 (lovely lens, a little soft but very nice warm colour). One thing I have found is that most of the Nikon to Canon adapter rings are little bit on the thin side. This prevents any zooms from being Parfocal as it puts the back focus out. Most of the adpaters are made in two parts and it’s quite easy to take the front and back parts apart and add shims made out of of thin plastic sheet or even card between the two halves to correct the back focus distance.

So there you have it. Overall DSLR lenses are not a huge compromise. Of course I would love to own a flight case full of good quality PL mount, 4K ready, glass. Perhaps one day I will, but it’s a serious investment. Currently I use DSLR lenses for my own projects and then hire in better glass where the budget will allow. For any commercials or features this normally means renting in a set of Ultra Primes or similar.  I am keeping a close eye on the developments from Zunow. I like their 16-28mm f2.8 and the prototype PL primes I saw at NAB look very good. I also like the look of the Zeiss 15.5 to 45 light weight zoom. Then of course there is the excellent Fujinon 19-90mm Cabrio servo zoom, but these are all big bucks. Hopefully I’ll get some nice big projects to work on this year that will allow me to invest in some top end lenses.

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The practicalities of fast run and gun shooting with a large sensor camera.

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Supercell-panoramaWell I’ve just returned home from NAB and a week of Tornado Chasing in the USA. For the Tornado chasing I was shooting in 4K using my Sony F5. I’ve shot run and gun with my F3 and FS700 in the past when shooting air-shows and similar events. But this was very different. Tornado chasing is potentially dangerous. You often only have seconds  to grab a shot which involves leaping out of a car, quickly setting up a tripod and camera and then framing and exposing the shot. You often only have time for one 30 second shot before you have to jump back into the car and move on out ahead of the storm. All of this my be happening in very strong winds and rain. The storms I chased last week had inflow winds rushing into them at 50+ MPH.

The key to shooting any thing fast moving, like this, is having whatever camera kit your using well configured. You need to be able to find the crucial controls for exposure and focus quickly and easily. You need to have a way of measuring and judging exposure and focus accurately. In addition you need a zoom lens that will allow you to get the kinds of shots you need, there’s no time to swap lenses!

For my storm chasing shoot I used the Sony F5 with R5 recorder. This was fitted with a Micron bridge plate as well as a Micron top cheese plate and “Manhandle”. Instead of the Sony viewfinder I used an Alphatron viewfinder as this has a waveform display for exposure. My general purpose lens was a Sigma 18-200mm f3.5-f6.5 stabilised lens with a Canon mount. To control the iris I used a MTF Effect iris control box. For weather protection a CamRade F5/F55 Wetsuit. The tripod I used for this shoot was a Miller 15 head with a set of Carbon Fibre Solo legs.

Storm chasing with a PMW-F5
Storm chasing with a PMW-F5

Overall I was pleased with the way this setup worked. The F5’s ergonomics really help as the logical layout makes it simple to use. The 18-200mm lens is OK. I wish it was faster for shooting in low light but for the daytime and dusk shots, f3.5 (at the wide end) is OK. The F5 is so sensitive that it copes well even with this slow lens. The CamRade wetsuit is excellent. Plenty of clear windows so you can see the camera controls and a well tailored yet loose fit that allows you to get easy access to the camera controls. I’ve used Miller Solo legs before and when you need portability they can’t be beaten. The are not quite as stable as twin tube legged tripods, but for this role they are an excellent fit. The Miller 15 head was also just right. Not too big and bulky, not too small. The fluid motion of the head is really smooth.

Storm Chasing in the USA with the PMW-F5
Storm Chasing in the USA with the PMW-F5

So what didn’t work? Well I used the Element Technica Micron bridge plate. I really like the Micron bridge plate as it allows you to re-balance the camera on the tripod very quickly. But it’s not really designed for quick release, it’s a little tricky to line up the bridge plate with the dovetail so I ended up removing and re-fitting the camera via the tripod plate which again is not ideal. The Micron Bridge plate is not really designed for this type of application, when I go back storm chasing in May I’ll be using a  baseplate that locks into a VCT-14 quick release plate, not sure which one yet, so I have some investigating to do.  The VCT-14 is not nearly as stable or as solid as the Micron, but for this application speed is of the essence and I’m prepared to sacrifice a little bit of stability. The Micron bridge plate is better suited to film style shooting and in that role is fantastic, it’s just not the right tool for this job.

Rainbow under a severe thunderstorm.
Rainbow under a severe thunderstorm.

The MTF-Effect unit is needed to control the aperture of the Canon mount lens, it also powers the optical image stabiliser. But it’s a large square box. I had it mounted on the top of the camera, not in the best place. I need to look at where to mount the box. I’m actually considering re-housing the unit in a custom made hand grip so I can use it to hold the camera with my left hand and have iris control via a thumbwheel. I also want to power it from one of the camera’s auxiliary outputs rather than using the AA batteries internally. The other option is the more expensive Optitek lens mount which I’m hoping to try out soon.  I’m also getting a different lens. The Sigma was fine, but I’m going to get a Sigma 18-250mm (15x) f3.5-f6.5 for a bit more telephoto reach. The other option I could have used is my MTF B4 adapter and a 2/3″ broadcast zoom, but for 4K the Tamron will have better resolution than an HD lens. If I was just shooting HD then the broadcast lens would probably be the best option. After dark I swapped to my Sigma 24-70mm f2.8 for general purpose shooting and this worked well in low light but with the loss of telephoto reach, I need to look into a fast long lens but these tend to be expensive. If you have deep enough pockets the lens to get would probably be the Fujinon Cabrio 19-90 T2.9, but sadly at the moment my budget is blown and my pockets are just not that deep. The Cabrio is very similar to an ENG broadcast lens in that it has a servo zoom, but it’s PL mount and very high resolution. Another lens option would be the Canon CN-E30-105mm T2.8, but overall there isn’t a great deal of choice when it comes down to getting a big zoom range and large aperture at the same time, in a hand-held package. If I was working with a full crew then I would consider using a much larger lens like the Arri Alura 18-80 or Angenieux Optimo 24-290, but then this is no longer what I would consider run and gun and would require an assistant to set up the tripod while I bring out the camera.

A Supercell thunderstorm looking like a flying saucer.
A Supercell thunderstorm looking like a flying saucer.

From an operating point of view one thing I had to do was to keep reminding myself to double check focus. If you think focus is critical in HD, then it’s super critical for 4K. Thunderstorms are horrid things to try and focus on as they are low contrast and soft looking. I had to use a lot of peaking as well as the 1:1 pixel function of the Alphatron viewfinder, one of the neat things about the Alphatron is that peaking continues to work even in the 1:1 zoom mode. As I was shooting raw and using the cameras Cine EI mode to make exposure simpler I turned on the Look Up Tables on the HDSDI outputs and used the P1 LUT. I then exposed using the waveform monitor keeping my highlights (for example the brighter clouds) at or lower than 100%. On checking the raw footage back this looks to have worked well. Quite a few shots needed grading down by 1 to 1.5 stops, but this is not an issue as there is so much dynamic range that the highlights are still fine and you get a cleaner, less noisy image. When shooting raw with the F5 and F55 cameras I’d rather grade down than up. These cameras behave much more like  film cameras due to the massive dynamic range and raw recording, so a little bit of overexposure doesn’t hurt the images as it would when shooting with standard gammas or even log. Grading down (bringing levels down) results in lower noise and a cleaner image.

Frame grab from the F5 of a Supercell storm with a grey funnel cloud beneath.
Frame grab from the F5 of a Supercell storm with a grey funnel cloud beneath.

So you can run and gun in an intense fast moving environment with a large sensor camera. It’s not as easy as with a 2/3″ or 1/2″ camera. You have to take a little more time double checking your focus. The F5 is so sensitive that using a F3.5-F6.5 lens is not a huge  problem. A typical 1/2″ camera (EX1, PMW-200) is rated at about 300 ISO and has an f1.8 lens. The F5 in Cine EI mode is 2000 ISO, almost 3 stops more sensitive. So when you put an f3.5 lens on, the F5 ends up performing better in low light, even at f6.5 it’s only effectively one stop less sensitive. For this kind of subject matter you don’t want to be at f1.8 – f2.8 with a super 35mm sensor anyway as the storm scenes and shots involved work better with a deep focus range rather than a shallow one.

Having watched the footage from the shoot back in HD on a large screen monitor I am delighted with the quality of the footage. Even in HD it has better clarity than I have seen in any of my previous storm footage. This is I believe down to the use of a 4K sensor and the very low noise levels. I’d love to see the 4K material on a 4K monitor. It certainly looks good on my Mac’s retina display. Hopefully I’ll get back out on the plains and prairies of Tornado Alley later in May for some more storm chasing. Anyone want to join me?

 

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Convergent Design Odyssey 7Q To Work With FS700 Raw!

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Waveform and measurement options on the Convergent Design Odyssey7Q
Waveform and measurement options on the Convergent Design Odyssey7Q

Hot off the press from NAB is the announcement that the Convergent Design Odyssey 7Q will be able to work directly with the FS700 to record  4K and 2K with from the FS700 with 2K raw going up to 240fps. This is really great news. I’ll be posting a video blog about this later in the week. for now here is an extract from the official press release

LAS VEGAS, NAB Booth C11001, April 8, 2013 — Sony is announcing that its affordable 4K production camcorder, the NEX-FS700, will support a direct connection to Convergent Design’s new Odyssey7Q. The combination will allow recording of 2K RAW at up to 240 frames per second, with 4K video enabled via a single 3G connection.

The NEX-FS700 can achieve a high frame rate of up to 240 fps recording in 2K RAW while recording to the Odyssey 7Q. The 240 content fps is recording continuously, without windowing the imager or line doubling the signal. This assures full resolution at all times without windowing artifacts.
The direct connection to Convergent Design’s new Odyssey 7Q complements Sony’s own newly announced recording solution using the AXS-R5 RAW recorder and the new HXR-IFR5 interface unit. Now professional users have even more flexibility in choosing a workflow that meets their needs for today’s diverse client requirements.

“The addition of RAW and 4K recording unleashes the full power of the FS700’s state of the art 4K imager, vastly increasing the potential applications for the camcorder and resulting in tremendous flexibility in post-production,” said Peter Crithary, marketing manager for large sensor technology at Sony Electronics. “Now, interoperability with the exciting Odyssey 7Q in addition to our own recording technology gives users a wide range of cost effective choices when working with diverse workflows.”

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Sony PMW-F55 raw samples for download.

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I have uploaded a couple of short F55 raw sample for you to play with. The exposure was deliberately pushed to it’s limits on these clips so you can have a go at grading them. Resolve Lite (free) can be used with the footage.
https://www.alisterchapman.com/samples/f55-raw-samples.zip

If you find the footage useful please make a small donation to go towards the cost of hosting the files or buy me a coffee. All donations no matter how small gratefully received.

 

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When is 4k really 4k, Bayer Sensors and resolution.

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When is 4k really 4k, Bayer Sensors and resolution.

First lets clarify a couple of term. Resolution can be expressed two ways. It can be expressed as pixel resolution, ie how many individual pixels are there on the sensor. Or as TV lines or TVL/ph, or how many individual lines can I see. If you point a camera at a resolution chart, what you talking about is at what point can I no longer discern one black line from the next. TVL/ph is also the resolution normalised for the picture height, so aspect ratio does not confuse the equation. TVL/ph is a measure of the actual resolution of the camera system.  With video cameras TVL/ph is the normally quoted term, while  pixel resolution or pixel count is often quoted for film replacement cameras. I believe the TVL/ph term to be prefferable as it is a true measure of the visible resolution of the camera.
The term 4k started in film with the use af 4k digital intermediate files for post production and compositing. The exposed film is scanned using a single row scanner that is 4,096 pixels wide. Each line of the film is scanned 3 times, once each through a red, green and blue filter, so each line is made up of three 4K pixel scans, a total of just under 12k per line. Then the next line is scanned in the same manner all the way to the bottom of the frame. For a 35mm 1.33 aspect ratio film frame (4×3) that equates to roughly 4K x 3K. So the end result is that each 35mm film frame is sampled using 3 (RGB) x 4k x 3k, or 36 million samples. That is what 4k originally meant, a 4k x 3k x3 intermediate file.
Putting that into Red One perspective, it has a sensor with 8 Million pixels, so the highest possible sample size would be 8 million samples. Red Epic 13.8 million. But it doesn’t stop there because Red (like the F3) use a Bayer sensor where the pixels have to sample the 3 primary colours. As the human eye is most sensitive to resolution in the middle of the colour spectrum, twice as many of these pixel are used for green compared to red and blue. So you have an array made up of blocks of 4 pixels, BG above GR.
Now all video cameras (at least all correctly designed ones) include a low pass filter in the optical path, right in front of the sensor. This is there to prevent moire that would be created by the fixed pattern of the pixels or samples. To work correctly and completely eliminate moire and aliasing you have to reduce the resolution of the image falling on the sensor below that of the pixel sample rate. You don’t want fine details that the sensor cannot resolve falling on to the sensor, because the missing picture information will create strange patterns called moire and aliasing.
It is impossible to produce an Optical Low Pass Filter that has an instant cut off point and we don’t want any picture detail that cannot be resolved falling on the sensor, so the filter cut-off must start below the sensor resolution. Next we have to consider that a 4k bayer sensor is in effect a 2K horizontal pixel Green sensor combined with a 1K Red and 1K Blue sensor, so where do you put the low pass cut-off? As information from the four pixels in the bayer patter is interpolated, left/right/up/down there is some room to have the low pass cut off above the 2k pixel of the green channel but this can lead to problems when shooting objects that contain lots of primary colours.  If you set the low pass filter to satisfy the Green channel you will get strong aliasing in the R and B channels. If you put it so there would be no aliasing in the R and B channels the image would be very soft indeed. So camera manufacturers will put the low pass cut-off somewhere between the two leading to trade offs in resolution and aliasing. This is why with bayer cameras you often see those little coloured blue and red sparkles around edges in highly saturated parts of the image. It’s aliasing in the R and B channels. This problem is governed by the laws of physics and optics and there is very little that the camera manufacturers can do about it.
In the real world this means that a 4k bayer sensor cannot resolve more than about 1.5k to 1.8k TVL/ph without serious aliasing issues. Compare this with a 3 chip design with separate RGB sensors. With a three 1920×1080 pixel sensors, even with a sharp cut-off  low pass filter to eliminate any aliasing in all the channels you should still get at 1k TVL/ph. That’s one reason why bayer sensors despite being around since the 70s and being cheaper to manufacture than 3 chip designs (with their own issues created by big thick prisms) have struggled to make serious inroads into professional equipment. This is starting to change now as it becomes cheaper to make high quality, high pixel count sensors allowing you to add ever more pixels to get higher resolution, like the F35 with it’s (non bayer) 14.4 million pixels.
This is a simplified look at whats going on with these sensors, but it highlights the fact that 4k does not mean 4k, in fact it doesn’t even mean 2k TVL/ph, the laws of physics prevent that. In reality even the very best 4k pixels bayer sensor should NOT be resolving more than 2.5k TVL/ph. If it is it will have serious aliasing issues.
After all that, those that I have not lost yet are probably thinking: well hang on a minute, what about that film scan, why doesn’t that alias as there is no low pass filter there? Well two things are going on. One is that the dynamic structure of all those particles used to create a film image, which is different from frame to frame reduces the fixed pattern effects of the sampling, which causes the aliasing to be totally different from frame to frame so it is far less noticeable. The other is that those particles are of a finite size so the film itself acts as the low pass filter, because it’s resolution is typically lower than that of the 4k scanner.