Just a quick note to tell you that I will be co-presenting a session at the Kit Plus show in Twickenham on Tuesday the 14th of September 2021. Philip Bloom on the subject of “Buying the right camera IS important – don’t get sucked into the marketing hype”. We will be discussing how people make their purchasing decisions, what different manufacturers have to offer and debating – what does “cinematic” mean – if anything at all.
Come and join us it should be fun and it’s face to face!!
Chroma Key and Greenscreen – Should I use S-Log3 or might Rec-709 be Better?
I’ve covered this before, but as this came up again in an online discussion I thought I would write about it again. For decades when I was doing a lot of corporate video work we shot greenscreen and chroma key with analoge or 8 bit, limited dynamic range, standard definition cameras and generally got great results (it was very common to use a bluescreen as blue spill doesn’t look as bad on skin tones as green). So now when we have cameras with much greater dynamic ranges and 10 bit recording is it better to shoot for greenscreen using S-Log3 (or any other log curve for that matter) or perhaps Rec-709?
Before going further I will say that there is no yes-no, right-wrong, answer to this question. I will also add that Rec-709 gets a bad rap because people don’t really understand how gamma curves/transfer functions actually work and how modern grading software is able to re-map the aquisition transfer function to almost any other transfer function. If you use a colour managed workflow in DaVinci Resolve it is very easy to take a Rec-709 recording and map it to S-Log3 so that you can apply the same grades to the 709 as you would to material originated using S-Log3. Of course the 709 recording may not have as much dynamic range as an S-Log3 recording, but it will “look” more or less the same.
Comming back to shooting greenscreen and chromakey:
S-Log3:
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Shoot using 10 bit S-log3 and you have 791 code values available (95-886) to record 14/15 stops of dynamic range. so on average across the entire curve each stop has around 55 code values. Between Middle Grey and +2 stops there are approx 155 code values – this region is important as this is where the majority of skin tones and the key background are likely to fall.
Rec-709:
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Shoot using vanilla Rec-709 and you are using 929 code values (90-1019) to record 6/7 stops so each stop has on average across the entire curve has around 125 code values. Between Middle Grey and +2 stops there are going to be around 340 code values.
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That is not an insignificant difference, it’s not far off the difference between shooting with 10 bit or 12 bit.
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If you were to ask someone whether it is better to shoot using 10 bit or 12 bit I am quite sure the automatic answer would be 12 bit because the general concensus is – more bits is always better.
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A further consideration is that the Sony cameras operate at a lower ISO when shooting with standard gammas and as a result you will have an improved signal to noise ratio using 709 than when using S-log3 and this can also make it easier to achieve a good, clean, key.
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However you do also need to think about what it is you are shooting and how it will be used. If you are shooting greenscreen in a studio then you should have full control over your lighting and in most cases 6 or 7 stops is all you need, so Rec-709 should be able to capture everything comfortably well. If you are shooting outside with less control over the light perhaps Rec-709 won’t have sufficient range.
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If the background plates have been shot using S-Log3 then some people don’t like keying 709 into S-Log3. However a colour managed workflow can deal with this very easily. We should consider that 709 and S-Log3 in a workflow where grading is a big part should not be though of as “looks” but simply as transfer functions or maps of what brightness/saturation seen by the camera is recorded at what code value. Handle these transfer functions correctly via a colour managed workflow and both will “look” the same and both will grade the same within their respective capture limits.
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For an easy workflow you might chose to shoot the greenscreen elements using log with the same settings as the plates. There is nothing wrong with this, it works, it is a very commonly used workflow but it isn’t necessarily always going to be optimum. A lot of people will put a lot of emphasis on using raw or greater bit depths to maximise the quality of their keying, but overlook gamma choice altogether, simply because “Rec-709” is almost a dirty word these days.
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If you have more control, and want absolutely the best possible key, you might be better off using Rec-709. As you will have more data per stop which makes it easier for the keying software to identify edges and less noise. If using Rec-709 you want to chose a version of Rec-709 where you can turn off the camera’s knee as this will prevent the 709 curve from crushing the highlights which can make them difficult to grade. In a studio situation you shouldn’t need to use a heavy knee.
I suggest you experiment and test for yourself and not every situation will be the same, sometimes S-Log3 will be the right choice, other times Rec-709.
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Chroma Key and S-Cinetone
A question poped up today asking about how to expose S-Cinetone when shooting green screen.
The answer is really quite simple – no differently to how you would expose S-Cinetone anywhere else. But, having said that it is important to understand that S-Cinetone is a bit different to normal Rec-709 and this needs to be considered when shooting for chroma key or green screen.
S-Cinetone’s highlight roll off and shoulder starts much lower than most “normal” rec-709 curves. From around 73% the gamma curve changes and starts to compress the levels and reduce contrast. In the shdows there is a variable toe that increases contrast at lower brightness levels. The nominal “normal” brightness levels are also lower, all part of the contemporary film like look S-Cinetone is designed to give. A 90% reflectivity reference white card would be exposed at approx 83% instead of the more normal 90% (if you were using a light meter you should end up with a 90% white card at 83IRE). A white piece of paper will be a bit brighter than this as printer and copier paper etc is designed to look as bright as possible, typically printer paper comes out around 3 to 5% brighter than a proper white card.
The lower start to the highlight roll-off means that if you place skintones around 70% the brighter parts of a face will be affected by the rolloff and this will make them flatter. Expose skin tones at 60% and the face will be more contrasty and in my opinion look better. Although darker this would still be well with the “normal” exposure range for S-Cinetone so you will not have excessive noise and it will still key well.
S-Cinetone would be considered correctly exposed when a 90% white card is exposed between 78% and 88%. This is quite a wide window and is due to the way S-Cinetone is designed to give differening contrast levels simply by exposing a touch brighter or darker. The variable toe and shoulder mean that exposing brighter will make the image flatter and exposing darker more contrasty. Exposing as you would with normal Rec-709 levels with a white card at 90% will place skintones rather higher than “normal” and they will appear very flat. So either expose so a white card falls in the 78-88% window or use a calibrated monitor to observe how the skin tone look and be careful not to overexpose them.
Your greenscreen should be between 40IRE and 60IRE for a good clean key, I normally aim for 50IRE with S-Cinetone, but provided you don’t go below 40IRE or above 60IRE you should be good.
Nanlite Forza 300 LED Spotlight
The Nanlite Forza 300 is a LED COB spotlight normally used with a reflector to provide a 55 degree light cone.
The lamp is 300 watts and can be powered from the mains with the included power adapter or vai a pair of V-lock batteries. It is daylight balanced at 5500K and has a CRI of 95 (measured by myself). It has always resulted in very pleasing skin tone whenever I have used it.
The 300 watt LED COB emitter produces a similar amount of light to a 3000 watt tungsten lamp. This makes the Forza 300 suitable for illuminating very large areas or as a source light for a large soft box or for use with large silk diffusers. Nanlite make a very nice parabolic reflectors/soft boxes for the Forza lamps that are very quick to erect due to the use of clever quick locking support arms.
The lamphead has a standard Bowens mount so there are many light modifiers that can be used, but one that I particularly like is the Nanlite zoomable Fresnel adapter. This large fresnel lens can be adjusted to provide a very tightly controlled light beam from just 5 degrees wide to 45 degrees wide. It comes with barn doors and turns the Forza 300 into something comparable to the old Arri 2K fresnel, just without the heat and power draw.
I’m a big fan of fresnels as they give you good control of where your light is going. Make it dimmable as well and you have a very versatile lamp.
The light can be controlled via DMX as well as a couple of very cheap wireless remote control units (around £20/$30) and an app is due to be released soon.
Like many modern lights it also has a number of effects modes including strobe, storm, TV and bad bulb and these can be quickly and easily selected from the lamps control unit and power supply. The build quality is very good. The lamp head is mostly metal while the control unit is a mix of good quality plastics and metal. The whole thing weighs 4.8kg so you don’t need a particularly large light stand to support it.
with a street price of around £650/$850 this is a very affordable yet also very capable lamp. I would suggest that anyone trying to build their own versatile light kit should include at least one spot light and not just rely on LED panel lights. Having a good, bright spot light allows you to a lot more creative lighting as a spot light, especially if you add the Fresnel lens can be used with gobo’s or objects in the foreground to create interesting shadow effects.
For a recent short film shoot I used the Forza 300 to throw light through a forest of trees. The trees creating interesting shadows adding a lot of extra contrast to the shots. For another scene I used the Forza 300 as a backlight through some smoke for an interesting mystic effect. A flat panel light cannot reproduce these effects in the same way.
For this shoot I needed to power the lamp off batteries. It is worth noting that if running the lamp at is maximum output of 300 watts you will be drawing over 10 amps from each of the 2 V-Lock batteries need to run it. This is right at the limit of what many V-Locks can deliver. As a result you may find your batteries cutting off before they are fully discharged. To run a high power LED lamp like this you should consider Lithium Manganese batteries or other batteries capable of at least a 12 amp output. My own preference is to use Pag Paglink batteries as by linking two batteries together you can double the amount of power they can deliver. Using 4 Paglink batteries (2 pairs of 2) I was able to run the lamp for 90 minutes at full power.
The lamp I used for the review was supplied by Prolight Direct UK. They are very knowledgable with many years of experience with all kinds of film and television lighting, so do contact them with your lighting needs.
I highly recommend the Forza 300. It is, in my opinion, one of the best of this type of lamp on the market today and very competitively priced. Please see the video above for more information.
Hollyland Lark 150 Dual Channel wireless Mic System
In this video – live streamed on June 24th 2021 I take a look at the new Hollyland Lark 150 dual channel wireless microphone system.
The Lark 150 is a compact digital wireless microphone system that is available as a single channel or dual channel kit. If you buy the single channel kit you can add an extra transmitter pack later if you wish and pairing the units is really simple.
Each kit is supplied in a storage box that acts as a drop-in charger. To pair the transmitters to the receiver simply place them all in the storage box together and they are paired automatically, it’s as simple as that.
The transmitter units have a built in microphone and come with a clip on fluffy wind gag. But in addition a plug in lavalier microphone of pretty good quality is also included in the kit, one for each transmitter pack. There is also a mute button on each transmitter unit.
The receiver outputs a mono output or stereo output via a 3.5mm TRS socket depending on you personal preferences (connecting cables for cameras or phones are included in the kit). There is also a handy “safety mode” that outputs at full level on channel 1 and at a reduced level on channel 2. This is great for filming in environments where the audio levels can suddenly change as the lower level recording helps avoid clipping or distortion if the levels suddenly increase. There are two large control knobs on the receiver that control the levels of the two channels and allow you to switch between the different operating modes. The LCD screen clearly shows how the microphone is configured along with the audio levels. There is an additional headphone output on the receiver for headphone monitoring in case your camera doesn’t have a headphone jack.
Battery life is excellent, I got around 8 hours of use from a single charge. To charge the transmitter and receiver units just put them in the carry case and the battery built into the case will charge them back up again. The case has a USB socket to charge it.
The sound quality is very good for a low cost system. As it is entirely digital there is virtually no hiss or noise. The only downside is that the range is more limited than most much more expensive professional radio mics. This system uses the licence free 2.4Ghz band so there are no licensing issues in most countries and the digital transmissions are very secure, so you don’t need to worry about people illicitly listening in.
While you can get up to 100m/300ft range from them in perfect conditions. I found that I reliably and consistently get a range of about 100ft (30m). Operate them in this distance range and they are generally rock solid. However if the presenters body or some other substantial objects gets between the transmitter and receiver there is a small decrease in range, perhaps dropping to a reliable 50ft (15m). This is still plenty for most applications.
I really like these microphones. They won’t replace my much more expensive Sony UWP-D professional microphones, but they are great when you need something compact, ultra light and really simple to use. They are perfect for a lot of blogging applications as well as for interviews etc. At a cost of around £210/$275 for the dual channel kit these are excellent value for the money.
Fixing Hot or Bright Pixels On the Sony FX3
The FX3’s larger brothers, the FX6 and FX9 have a function called “APR” that is used to periodically inspect every pixel on the sensor and normalise or map out any out of spec pixels. With modern 4K cameras having at least 8.8 million pixels the chances of a few going out of spec or being damaged by cosmic rays from time to time is quite high. So on the FX6 and FX9 you will get a reminder to perform the APR process around once a week.
From what I understand, the Alpha series cameras and FX3 also periodically perform a similar process automatically. Because these camera have a mechanical shutter to shut out any external light there is no need for any user intervention to perform this process so you will not be aware that it’s happening. On the FX6 and FX9 the user has to place a cap over the lens or sensor, hence why the camera asks you before it can happen.
But what if you find you have some bright or hot pixels with the FX3? Perhaps you have just travelled on a plane where the high altitude reduces the atmospheres damping effect of the high energy particles from space that can damage pixels. Well you can go into the camera’s menu system and force it to run its pixel mapping process which does the same thing as APR on the other cameras.
You need to go to:
MENU: (Setup) ? [Setup Option] ? select [Pixel Mapping] and then select OK. It doesn’t take long and I would recommend that you do this after flying on a plane or prior to any shoot where you will use large amounts of gain as this is when hot pixels are most likely to show up.
Understanding Sony’s Viewfinder Display Gamma assist.
Most of sony’s cameras that support S-Log3 or Hybrid Log Gamma also have a function called Viewfinder Display Gamma Assist.
Viewfinder Display Gamma Assist allows you to monitor with the cameras built in LCD screen or viewfinder with the correct brightness and contrast range when using gamma curves that are not directly compatible with these Rec-709 screens.
Whenever you try to view a gamma curve that is not normal Rec-709 on a Rec-709 screen the brightness and contrast that you will see will be incorrect. The most common scenario is perhaps viewing S-Log3 without any form of LUT. In this case the images will look less bright and have less contrast than they should and this makes judging exposure difficult as well making it less easy to see focus errors.
With a camera like the FX6 or FX9 most people will use the cameras CineEI mode and add a LUT to the viewfinder image to convert the S-Log3 to something that looks more contrasty and on the FX6 and FX9 the default LUT is “s709”. However s709 is not the same thing as Rec-709 (Note that with the FX6, because LUTs are always available in the CineEI mode, viewfinder display gamma assist is not available in the CineEI mode of the FX6, you should instead use a LUT).
I think a lot of people think that the default s709 LUT is the same as Rec-709, it’s not, it is very different. They look very different and result in quite different brightness levels when exposed correctly. s709 when exposed correctly will put skin tones somewhere around 50-60% and white at 78%. If you expose s709 using normal Rec-709 brightness levels (70% skintones, 90% white) this is actually over exposed by just over 1 stop. As a result if you expose the s709 LUT, using Rec-709 levels, and then turn off the LUT and instead use Viewfinder Gamma Assist, the gamma assist will look wrong, it will be too bright and may look washed out and this is simply because the exposure IS wrong.
Almost always, if the viewfinder display gamma assist looks wrong, the exposure is wrong. When it looks right, the likelihood is the exposure is right.
A few things to understand:
- The viewfinder is a Rec-709 range display device only capable of showing Rec-709 range and colour.
- Feed true Rec-709 to a Rec-709 device and you will have a correct looking image with “normal” brightness, contrast and colour.
- Feed S-Log3 to a Rec-709 device and you will have an incorrect dull, flat looking image due to the gamma miss-match between the capture gamma and display gamma.
- Feed S-Log3 to a device with S-Log3 gamma and you will once again have the correct brightness and contrast as there is no longer a gamma miss-match (S-Log3 only appears to be flat due to the gamma missmatch between S-Log3 and Rec-709, use the right gamma and you will see that it is not actually flat).
Viewfinder Display Gamma Assist works by changing the gamma curve used in the Viewfinder to a gamma curve similar to S-Log3. When you view S-Log3 with a monitor with S-Log3 gamma you will have the correct contrast and brightness, so correct exposure will look correct.
But because the cameras LCD display screen can only show 6 to 7 stops you don’t get the full S-Log3 viewing range, just the central mid range part that is the direct equivalent of Rec-709. This very closely matches what you see if you use the Sony 709(800) LUT to convert the S-log3 to 709. The 709(800) LUT converts S-Log2 or S-Log3 to vanilla Rec-709 (70% skintones/90% white) with a knee that provides a slightly extended highlight range. It is broadly comparable to how most conventional Rec-709 cameras will look. So as a result viewfinder display gamma assist and Sony’s 709(800) LUT’s will look almost identical, while the s709 LUT will (and should by design) look different.
Viewfinder Display Gamma Assist is extremely useful for scenarios where you do not have a LUT option such as when shooting in CineEI in HD with the FX9. It can help you make good exposure assessments. It can make it easier to see when you are in focus. But it isn’t a LUT, so can’t be applied to the cameras outputs, only the built in viewfinder. Additionally if you use zebras, the waveform or histogram, gamma assist has no effect on these so you must remember that you are still measuring the levels of the actual recording gamma, not Rec-709 levels.
Viewfinder Gamma Assist is useful not only for shooting with S-Log but also when shooting using HLG (Hybrid Log Gamma). HLG is an HDR gamma curve and because the LCD viewfinder isn’t HDR you can’t correctly monitor HLG directly. Viewfinder Gamma Assist allows you to monitor with the correct brightness and contrast when shooting HLG making it easier to confidently get the correct exposure levels, as much like S-log3 the levels required for the correct exposure of HLG are quite different to Rec-709.
One last thing: NEVER use Viewfinder Gamma Assist with a LUT at the same time, this will result in a completely incorrect looking image and could result in very bad exposure as a result.
FX6 Firmware Update Adds 120fps Raw.
Sony have just released firmware version 1.10 for the ILME-FX6. This firmware update adds the ability to output raw at 100p and 120p to a suitable external raw recorder. The only raw recorder that can record the 100 and 120fps raw is the Atomos Ninja V+ which will be available very soon. This is a welcome update for the FX6 and it also includes some “stability fixes” so I recommend that all users update their cameras.
I’ve found the most reliable way to update the camera is to download the SD Card/CFExpress card version and place the Bodydata.dat file on an SD card. This is listed on the Sony site as “ILME-FX6 Update Guide(SD Card/CFexpress card. Put the SD card in the BOTTOM of the cameras 2 SD card slots (slot B) and then start the update from the Maintenance, Version, Version Up setting in the cameras full menu. You should insert a fully charged battery and also connect mains power when doing the update.
You will find the various firmware updaters here: https://www.sony.com/electronics/support/camcorders-and-video-cameras-interchangeable-lens-camcorders/ilme-fx6v/downloads
The Atomos Ninja V+ is an upgraded version of the Ninja V. It’s the same size and shape but has much more internal processing power. The extra processing allows it to record 4K 120fps raw or 8K 30p raw (it will be interesting to know which cameras are going to be outputting 8K raw). I really like the Ninja V, it’s small, compact and packed with useful features for not a lot of money. To record the raw from the FX6 do remember that you have to add the AtomX SDI module.
Important Firmware Update For The FX9
A few days ago Sony quietly released a new important firmware update for the PXW-FX9. Firmware version 2.10 adds the long awaited 4K 120fps raw function to the FX9 (you do still need the XDCA-FX9) but also importantly includes some change the the daylight white balance settings.
From my before and after testing it appears that a change has been made to the daylight white balance preset settings. For some time it has been apparent that if you used the white balance presets in the daylight range (4000K and higher) that the FX9 has a tendency to accentuate any green in the image. If you white balance of a white card this tendency is not there.
The new preset white balance settings now provide a much more neutral white balance with less green bias. This should also help those that were suffering from green fringing in extreme contrast shots as the reduced green bias will stop the camera from accentuating chromatic aberration as it did before. It won’t eliminate the chromatic aberration, but it won’t be nearly as obvious.
The first image was taken before doing the firmware update using a preset of 5500K. This test was done in a bit of a hurry as it was threatening to rain, but I wanted to use real daylight.
The second image, below, was taken after the firmware update (unfortunately the focus shifted slightly between the two shots, sorry). But you can clearly see that even though the white balance settings are the same and the same 5500K preset used this image is less green.
It is a subtle difference, but if you look at the wood panels you can see a difference. To help you see the difference here is a wipe between the before and after clips with the saturation boosted to make it more obvious.
As you can see this isn’t an “in your face” difference. But it is still none the less an important improvement as it makes it easier to match the FX9 to the FX6 and FX3 if you are using a preset white balance. I would still recommend white balancing off a white card for all cameras wherever possible as this will still normally provide the best results as it helps neutralise any lens or calibration differences. Whether you are shooting using S-Cinetone as in the examples here or using S-Log3, the new white balance preset provides in my opinion a much better colour response.
HOWEVER it’s important to consider that it will make cameras with version 2.10 and later look different to FX9’s with earlier firmware versions.
The firmware update can be downloaded via the link below. It took around 35 minutes for my FX9 to complete the update. The process is easy but when the camera gets to 80% complete it will appear that the update has stalled. It stays at 80% for around 10-15 minutes with no indication that the update is still continuing. So don’t turn the camera off thinking it’s stuck!!! Be patient and give it time to complete.
https://pro.sony/en_GB/support-resources/pxw-fx9/software/
Pixels and Resolution are not the same thing.
Before the large sensor resolution most professional video cameras used 3 sensors, one each for red, green and blue. And each of those sensors normally had as many pixels as the resolution of the recording format. So you had enough pixels in each colour for full resolution in each colour.
Then along came large sensor cameras where the only way to make it work was by using a single sensor (the optical prism would be too big to accomodate any existing lens system). So now you have to have all your pixels on one sensor divided up between red, green and blue.
Almost all of camera manufacturers ignored the inconvenient truth that a colour sensor with 4K of pixels won’t deliver 4K of resolution. We were sold these new 4K cameras. But the 4K doesn’t mean 4K resolution, it means 4K of pixels. To be fair to the manufactures, they didn’t claim 4K resolution, but they were also quite happy to let end users think that that’s what the 4K meant.
My reason for writing about this topic again is because I just had someone on my facebook feed discussing how wonderful it was to be shooting at 6K with a new camera as this would give lots of space for reframing for 4K.
The nature of what he wrote – “shooting at 6K” – implies shooting at 6K resolution. But he isn’t, his 6K sensor is probably delivering around 4K resolution and he won’t have any room for reframing if he wants to end up with a 4K resolution final image. Now again, in the name of fairness, shooting with 6K of pixels is going to be better than shooting with 4K of pixels if you do choose to reframe. But we really, really need to be careful about how we use terms like 4K or 6K. What do we really mean, what are we really talking about. Because the more we muddle pixels with resolution the less clear it will be what we are actually recording. Eventually no one will really understand that the two are different and the differences really do matter.