PANASONIC GH5 my underwater still rigs

The Panasonic GH5 is well known to be a great camera for video and I can confirm that see my latest videos

Clearly the camera is fantastic and with the right set up that I will cover in future posts it takes amazing video.

I wanted to start however from photography as the GH5 also takes great still images.

First and foremost macro. In general terms the lens choice of other micro four third also applies to the GH5 so my favourite lens is the Olympus 60mm. Alternatively if you don’t have that lens and you don’t have extremely small subjects you can get good results with a zoom lens I use the Pana 14/42 MKII but other work well too.

In terms of arms strobes nothing changes so my current rig is based on a Nauticam NA-GH5 housing and two Inon Z240. I have each arm set with 1x 8″ and 1x 5″ arm segments you will notice that the longer arms is closer to the camera this because in macro you will usually shoot above the sand so this makes it easier.

For wide angle the situation changes slightly as I use a 12″ arm segment as in the rig below.

GH5 with WWL-1 wet lens and 8+12 arm segments

For wide angle the arms return to a standard situation with shorter segment close to the housing. The same configuration applies if you shoot the 8mm fisheye.

In terms of floatation the GH5 housing is heavy with the 35 macro port is 720 grams and with the fisheye 620 grams. For macro I like my set up to be negative so less floats . For wide angle in case you take slow shutter speed shots I also use the tripod kit for the NA-GH5 this is not as good as a complete tripod but works well in wrecks

In the next posts I will talk about video as here there is a question about diopters and which ones do I use. Lights is also a topic of contention and will discuss few options there too

As always please ask questions if you wish

How to choose the best close-up lens for your underwater MFT rig

How many times you see practically new close up lenses being sold on eBay after sitting for years in a cupboard? Have you ever experienced the frustration of buying a close-up lens to find out it did not add anything to your set up?

There is a lot of confusion in terms of what is that you are really getting when you buy an underwater close-up lens. In most cases lenses are specified in diopters, in some other cases with a magnification factor, in few cases with the focal length.

The focal length is probably the most useful of those specification because in a traditional diopter the following formula is valid if you approximate the lens to converge in the rear element:

Working distance ≤ Focal length – physical length of the close-up lens

For example for a Subsee +5 diopter the focal length is 1000/5=200mm the lens is 32mm therefore the working distance is less than 168mm.

Now on its own this means very little. Depending on the camera we use a distance of 168mm may be a great improvement or no improvement at all.

To understand why we need to look on our camera and find the little symbol that indicates the focus distance reference mark.

While for DSLR the shooting distance is typically calculated from the front on the lens for micro four third you need to use this obscure symbol.

IMG_1394
P1055540

Once we locate the reference mark we need to identify the corresponding reference on the housing we can use the other dials as starting point. In this case the mark is approximately in the middle of the cold shoe.

When we put the camera in the housing we can then look up the specifications of the lens and calculate the minimum shooting distance. For example for an Olympus 60mm this value is 19cm.

P1055541

We take note of this point and then measure the distance between the glass and the minimum working distance on land.

P1055543

This works out to be around 9cm. We now need to consider that once immersed in water this distance will be multiplied by 1.33 to become 12cm.

It follows that any diopter with a focal length close to 12cm or longer is not going to be effective for our camera and lens combination. More likely we need something that can focus substantially closer or the benefit will be minimal. Assuming we half the physical working distance between the port and the subject we need something around 60-80mm focal length which considering the length of the lens itself could mean getting 2cm away from the subject.

Continue reading How to choose the best close-up lens for your underwater MFT rig

Panasonic GH5 Demystifying Movie recording settings

 

There are a lot of videos on YouTube that suggest that there is not much difference among the various recording settings of the GH5 for UHD.

To recap we have 4 settings for UHD (I will refer to PAL system because it is easier but all applies equally to 24p, the 30p/60p format will be the same with worse results)

  1. 100 Mbps 420 8 Bits Long GOP 25p
  2. 150 Mbps 420 8 Bits Long GOP 50p
  3. 150 Mbps 422 10 Bits Long GOP 25p
  4. 400 Mbps 422 10 Bits All-Intra 25p

The difference between Long GOP and All Intra is that in the Long GOP what is encoded is a group of pictures (GOP) and not separate individual pictures. In this article I will use ProRes as a proxy to AVC-Intra as, in the GH5 implementation, they have very similar logic and performance you can find some posts on the internet of people trying to discern the two but there really is not difference as essentially this is just image compression. 

Within a Group of Pictures there are different type of frames:

  • I (Intra coded) frames containing a full picture
  • P (Predictive coded) frames containing  motion interpolated picture based on a prediction from previous frames
  • B (bi-predictive coded) frames containing a prediction from previous or future frames

It is important to note that frames are not stored sequentially in a GOP and therefore the GOP needs to be decoded and the frames reordered to be played, this requires processing power.

The reason why H264 is very efficient is that within a group of picture there is only one full frame and the rest are predictions clearly if the prediction algorithm is accurate the level of perceived quality of long GOP is very high and similar to All-Intra clips.

This is the reason why comparing All Intra and Long Gop using static scenes or scenes with repetitive movement that can be predicted very accurately by the codec is a fundamental error.

Incorrect example here:

The scene is composed of static predictable objects with no motion and after YouTube compression the (wrong) conclusion is that there is no absolute difference between the codecs. Instead what this shows is the effectiveness of Long GOP when the prediction is accurate which is exactly the point of the codec plus the fact that YouTube flattens differences due to heavy compression and use of Long GOP.

Another example is a bit better as it uses a fountain which is a good representation of unpredictable motion

In the 300% crop you can see how All_Intra performs better than Long GOP in terms of prediction despite the YouTube compression, but generally those tests are unreliable if you see the last section of the video where there is a semi-static scene you cannot really take the three examples apart.

So why is that and is there any point selecting different settings on your Panasonic GH5?

In order to understand the workings we need to dig deeper into the structure of the GOP but before doing so let’s evaluate the All-Intra codec.

AVC All-Intra explanation

This codec records at 400 Mbps so with 25 fps this means circa 16 Mbits per frame or  1.9 MB per frame and there is no motion interpolation so each frame is independent from the others. The implementation of All-Intra of the GH5 does not make use of CABAC entropy encoding as Panasonic does not believe this is beneficial at higher bit-rates making this AVC-Intra implementation very close to ProRes as both are based on Discrete Cosine Transform.

If you consider a Jpeg image of your 3840×2160 frame on the GH5 you see that it stores around 4.8 MB per image because there is no chroma sub-sampling so if you wanted to have exactly the same result you would need to use ProRes 4444 to get a comparable quality (this not even taking into account that Jpeg are 8 bits images).

Video uses chroma sub-sampling so only part of the frame contain colours at a given time. Apple in their ProRes white paper declare that both ProRes 422 and 422 HQ are adequate to process 10 bit colour depth and 422 sub-sampling however they show some quality differences and different headroom for editing. If you count 50% for 4.2:0 sub-sampling and 67% for 422 you get around 2.34 MB and 3.5 MB frame sizes that correspond to ProRes 422 and ProRes 422 HQ individual frame sizes.

In simple terms All Intra 400 Mbps would fall short of Apple recommended bit-rate for 422 10 bit colour for circa 92 Mbps is like saying you are missing 0.44 MB from your ProRes 422 frame and 1.6 MB from ProRes 422 HQ and you have 0.3 MB more than ProRes LT however I do not have the full technical details of ProRes to evaluate directly.

The real benefit of such codec is that it can be processed with modest hardware without conversion as the AVC Intra codec is edit ready and each frame is captured individually without any motion artefacts and therefore the computer does not have to do a great deal of work to decode and render the clips.

In order to record All-Intra in your memory card you need a V60 or higher specs card which in terms of $ per GB costs you more than an SSD drive however you no longer need a recorder.

Coming back to the other recording quality option we still need to evaluate how the various long GOP codecs compare relative to each other.

In order to fully understand a codec we need to decompose the GOP into the individual frames and evaluate the information recorded. If you look on Wikipedia it will tell you that P frames are approximately half the size of an I frame and B frame are 25%. I have analysed the Panasonic GH5 clips using ffprobe a component of ffmpeg that tells you what is exactly in each frame to see if this explains some of the people claims that there is no difference between the settings.

Link to Panasonic documentation

 

100 Mbps 420 8 Bits Long Gop 25p Deep Dive

An analysis with ffprobe shows a GOP structure with N=12 and M=3 where N is the length in frames of the group of pictures and M is the distance between I or P frames.

So each Group of Picture is made like this

IBBPBBPBBPBBP before it repeats again.

A size analysis shows that B frames are in average 14% of the I frame and P frames are around 44% of the I frame.

I B B P B B P B B P B B
Size 1648326 247334 237891 728777 231947 228048 721242 228347 227544 713771 236866 232148
Ratio to I frame 100% 15.01% 14.43% 44.21% 14.07% 13.84% 43.76% 13.85% 13.80% 43.30% 14.37% 14.08%

With an average video bit-rate of 94 Mbps each GOP has 45.3 Mbps which means an I Frame has around 13.1 Mbits or 1.57 MB per frame and an equivalent All-Intra bit-rate of approximately 328 Mbps however this codec is using CABAC entropy encoding that Panasonic states is 20-30% more efficient than CAVLC used in All-Intra so net of motion artefacts this codec is pretty strong.

150 Mbps 420 8 Bits Long GOP 50p Deep Dive

An analysis with ffprobe shows a GOP structure with N=24 and M=3 where N is the length in frames of the group of pictures and M is the distance between I or P frames.

So each Group of Pictures is made like this

IBBPBBPBBPBBPBBPBBPBBPBB before it repeats again.

A size analysis shows that B frames are in average 13.4% of the I frame and P frames are around 41% of the I frame. With an average bit-rate of 142.7 Mbps each GOP has 68.5 Mbits which means an I Frame has around 11.3 Mbits or 1.35 MB per frame and an equivalent all Intra bit-rate of approximately 566 Mbps. Again this uses CABAC entropy encoding so the equivalent All-Intra is higher.

One very important aspect of the 150 Mbps codec is that as the GOP is double the length of the single frame rate 100 Mbps codec there are the same number of key frames per second and therefore it is NOT true that this codec is better at predicting motion. In fact it is exactly the same so if you had acquired a 100 Mbps codec at 25 fps and then slowed down the footage to half speed asking your editor to interpolate intermediate frames it would come to the same result although with some more processing required.

150Mbps 422 10 Bits Long Gop 25 fps

An analysis with ffprobe shows a GOP structure with N=12 and M=1 which means this codec does not use B frames but just I and P frames so the GOP structure is as follows:

IPPPPPPPPPPP before it repeats again.

A size analysis shows that P frames are on average 53% of I frames so this codec is in fact less compressed however this has also some consequences.

With an average bitrate of 150 Mbps each GOP has 72 Mbits which means an I Frame has around 10.5 Mbits or 1.25 MB per frame and an equivalent all Intra bitrate of approximately 262 Mbps. So this codec in terms of compression efficiency this is actually the worst and this is due to the lack of B frames.

We can only think that the Panasonic GH5 processing is not strong enough to capture 10 bit and then write 422 Long GOP with IPB structure.

Codec Ranking for Static Image Quality UHD

So in terms of absolute image quality and not taking into account other factors the Panasonic GH5 Movie recording settings ranked by codec quality are as follows:

  1. 400 Mbps 422 10 Bit All intra 25 fps (1.9 MB per frame)
  2. 100 Mbps 420 8 Bit Long Gop 25 fps (1.57 MB per frame)
  3. 150 Mbps 420 8 Bit Long Gop 50 fps (1.35 MB per frame)
  4. 150 Mbps 422 10 Bit Long Gop 25 fps (1.25 MB per frame)

The 100 Mbps  and 400 Mbps codec are marginally different (21% larger frame size) with the 422 10 Bits long GOP really far away.

Conclusion

If you want to record your footage to the internal memory card you are really left with two choices:

  1. Use the 100 Mbps Long Gop codec it is very efficient in the compression and the perceived quality is very good. It does however require you to convert to ProRes or similar during editing if you don’t want to overload your computer as the codec is really heavy on H264 features. You need to get the exposure and white balance right in camera as the clips may not withstand extensive corrections. There is a risk with footage with a lot of motion of some errors in motion interpolation that can generate artefacts.
  2. Buy a V60 or V90 memory card and use 400 All intra at single frame rate. This will give you edit ready footage of higher quality without motion artefacts, You still need to get exposure and white balance right in camera as the headroom is not so large to allow extensive corrections. The bit-rate and frame size is not sufficient to really give you all the benefits of 422 sampling and 10 bit colour but it will be a good stepping stone to produce good quality rec709 420 8 bit footage.

Generally there appears to be no benefit using the internal 422 10 Bit codec nor the 420 8 bit double frame rate due to the limitations of the GOP structure, here Panasonic has created a few options that to be honest appear more a marketing effort than anything else.

There may be some use to the 150 Mbps double frame rate if you intend to slow down the footage after the conversion to ProRes or similar but the extremely long GOP does not make this codec particularly robust to scenes with a lot of motion and in any case not more robust than the 100 Mbps codec.

A final thought if you are interested in 10 bit colour is that the FHD All Intra 200 Mbps codec has enough quality and headroom to allow manipulation. This is in fact the only codec that has bit-rate higher than ProRes HQ at least at 24 and 25 fps so if you want to check the real range of colours and dynamic range the camera is capable of you should try this codec.

Note: I have removed some comments on ProRes and external recorders as there are plenty of people that believe that the intra codec does better than ProRes HQ on the Atomos

Panasonic GH5 settings for underwater video

In the previous post I described the HDR settings especially relevant if you have an external recorder. However there is quite a lot of discussion if it is worth shooting HDR underwater video with the Panasonic GH5 at all. This follows the discussions about using VLOG L underwater versus studio production: many people that start using VLOG L revert to a more normal setting something using standard profiles and not even Cine profiles because the workflow is just too much work.

In general there are 3 characteristics that are important to underwater footage but more in general to any footage: colour , contrast and noise. This is the reason why when you look at DXOMark you have some measures of those 3 characteristics.

GH5DXOMARKSCORES

What DxOMark is telling us is that looking at a RAW image produced from the GH5 the colour depth is at best 23.9 bits, the dynamic range is at best 13 Evs and the Low-light ISO that still gives some decent colour depth and dynamic range is 807 ISO.

Let’s have some interpretation of those measures colour depth of 23.9 bits means 15.6 millions colours, this is actually less than true colour of an sRGB display. Considering the RGB scale the 23.9 bits per colour really mean 8 bit colour. OK so why does the camera have a 10 bit colour (equivalent to 30 bits per pixel no camera reaches that even full frame) option at all? We will talk about it in a minute…

Dynamic range for a RAW image is 13 Evs however Panasonic says VLOG L offers 12 stops compared to 10 stops of professional SDR footage. Now 12 stops require a display with a contrast ratio of 4000:1 which is beyond all commercial computer monitor and in the range of HDR devices. The new VESA DisplayHDR standard HDR600 is a minimum requirement to display this level of contrast ratio.

Finally the Low-light ISO of 807 (corresponding to 1600 on your GH5 as ISO values are always incorrect and geared towards higher values for marketing reasons) means that unless you are at the surface pretty soon there won’t be any colour or dynamic range to show (low-light ISO requires 18 bit colour depth 9 Ev Dynamic range and 30 dB SNR).

WHAT ABOUT THE GH5S?

The GH5s will give you 1.5 stops more of low-light performance and therefore your footage will look good until ISO 2400 or ISO 4800 looking at the camera settings which is quite a bump.

OK now coming to the main point of the post having seen those limitations why would I bother shooting in VLOG or HLOG?

First consideration: Noise

As we have seen both dynamic range and colour depth drop considerably when ISO goes up. In short unless you have abundance of natural light or you are shooting macro with a lot of artificial light is unlikely you will see any benefit shooting VLOG or HLG.

Considering that compression brings additional noise here we see why shooting with an external recorder at higher bitrate really helps fighting noise even if you don’t shoot log because you reduce the compression artifacts. If you don’t have a recorder consider setting a max ISO limit quite low around 1600 on your GH5 or you will see a lot of grain.

Second consideration: color depth

If the camera cannot even resolve 10 bits per pixel RGB why would you shoot 10 bits? When you shoot VLOG or HLG you are not operating in the REC709 colour space which is limited to 8 bits so it is possible that the colour that the sensor is capturing are not all the 16.7 millions of the RGB palette but some of them are outside in the Dci-P3 or even REC.2020 colour space. Clearly if you do not have a 10 bit screen (and almost all computer screens are 8 bits) or 8 bits with FRC to simulate 10 bits, this is a total waste of time and you won’t see those colours and nobody on a computer working in sRGB will see them either. So unless you have a proper screen to watch your clips there is no point working in 10 bits. When it comes to grading again if you can’t display those colours it won’t be possible to do your work properly so don’t waste your time and shoot in 8 bits.

You now understand why you can’t see any difference in all those youtube comparison that by the way have been encoded 8 bits!

A lot of people records in VLOG 10 bit to then produce in REC709 that has 8 bit colour and the reason is that they have proper grading monitors to see what they are doing.

Just to give you an example laptops with exception of some recent MacBook Pro and others like the Dell XPS can’t display 10 bit colour. An iMac displays 10 bit colour and some screens that support DCI-P3 also are capable any other RGB screen won’t work.

Conclusion don’t waste your time with 10 bit if you don’t have a decent screen and if you only produce for youtube.

Third consideration: Dynamic range

VLOG and HLG start at base ISO 400 (that really is 200) and this is where you have your 12 stops. Once you get to ISO 1600 (nominal 3200 on your GH5) you still have 9.5 stops but the colours are gone. Generally it does make sense to shoot LOG however the issue may well be that your editing display is not HDR600 and therefore you can’t really see what you are shooting accurately. Having a screen that can correctly display HDR is even harder than finding one that can display 10 bit colours. What you need to consider though that unless you are capturing a sunburst or a backlit scene or you are shooting the surface you will not have more than 10 stops in your scene anyway.

Conclusion

The settings you can shoot really depend on your editing and display devices.

If you have a laptop or just an 8 bit computer screen and no external recorder you can shoot at 100 mbps 8 bit colour with the picture profile of your choice, standard, natural, cine like whatever you like as you won’t be able to tell the difference at any point in the process from any other formats 10 bits logs etc.

If you have a DCI-P3 display or better for editing shoot 10 bit colour. Examples are iMac and MacBook Pro or some Philips or Acer screens on the market.

If you have an HDR display for editing and an HDR Tv set shoot HLG.

If you have an external recorder shoot in PRORES HQ (as the GH5 does not support camera RAW). Some of those recorders like the Atomos Shogun Inferno support HDR and can also be used for editing with some adapters so shoot in HLG to get the best results.

Generally VLOG L requires a lot of work and is best suited to studio production so if you don’t have a good grading set up don’t waste your time with it.

If you are one of those shooters that after a lot of trial and error ended up shooting 8 bits colour because you don’t have a recorder or shooting natural or cine-like because you don’t have a proper grading HDR monitor now you know why you are doing what you are doing….

Setting up your GH5 for HLG HDR capture

We got our GH5 ready for HDR capture in the previous post so how do we make the most of it?

If you have an external recorder or monitor that supports HDR it is easy! Also if you do you probably have a fair bit of money and you are not reading this blog…

Currently Atomos recorders that can be housed all support HDR including HLG

DSC_9783_2c838594-1601-42d1-b145-40821cd34bb2_1024x1024
Nauticam Atomos Flame

The Nauticam Atomos Flame available at list price of $3,650 will house the Shogun Inferno, Shogun Flame, Ninja Inferno and Ninja Flame

On the Atomos website you can see that for the GH5 the products recommended are the Ninja and Shogun Inferno there first is priced at $995 and the second at $1,295.

There is a difference of $300 between the Shogun  and the Ninja  however the Shogun  provides an SDI video port that may turn out quite useful in grading phase. So if you got to the point of spending $3,650 for the housing I would definitely invest the extra $300 needed for the Shogun Inferno.

Once you get a recorder you can set up the GH5 to output 4Kp50/60 at 10 bit and be happy. The HDR screen of the Atomos device will provide the real time monitoring you need to expose footage properly in HLG. It is not my intention to start a debate about log vs HLG there is plenty of material out there.

A very good video is here

If you don’t have a recorder you are left to the GH5 screen that does not support HDR so how are you going to expose correctly? You have a couple of tools available.

The first one is Zebra Patterns that can be accessed in the Monitor subsection of the menu.

There is a great tutorial on YouTube

Now if you are working in HLG you will notice that the maximum value that can be set is 95% this is because luminance in HLG is limited to 64-940.

If you look on ITU website you can see that white ranges between 69 and 87 in HLG so using Zebra we can still attempt at exposing properly without an HDR monitor.

If you do have a reference white balance card you should set the Zebra to 75% as this is the reference for white if you are in the field without a reference your value should be set to max 90% to ensure you don’t blow highlights. Now you will find some website that tell you 95% is fine too but you do want to leave a bit of headroom. If you want you can set Zebra 1 to 75% and Zebra 2 to 95% so you cover all eventualities.

So once you have set the Zebra the next step is to decide if you want to use HLG View Assist or not. Here you have three options:

  1. Off
  2. Mode 1
  3. Mode 2

Off leaves the display in REC709

Mode 1 gives priority to background areas for example the sky

Mode 2 gives priority to the main subject

The 3 modes are really a progression of brightness, when Off the image looks completely desaturated and Log like. In Mode 1 the image appears to have a preference to show shadows in Mode 2 the image looks the brighter and the most punchy making it easy to work on the foreground but crashes the black and shadows quite a bit.

No matter what you select the Zebra value remain unchanged.

The final setting that can be useful is the Waveform monitor which is accessible in the creative video menu. As the Zebra this gives you a real time display of the image within a diagram that on the horizontal axis represent the image left to right and on the vertical has the signal. This is practically a spacial representation of your image and has the same intensity of the Zebra from 0 to 100. So anything too dark on the bottom won’t be visible and things above max will be clipped.

There are several tutorials available on YouTube

So in essence you could try to expose correctly using Zebra and waveform monitors on the GH5 LCD display but let’s face it the screen is tiny and underwater you won’t be really able to use it effectively. If you have an external monitor or recorder this becomes more useful and something to effectively try.

If you are using the camera meter to expose remember that the GH5 as most cameras has only three settings for metering: multi area, center weighted and spot those influence how the camera calculates the average exposure, this is true also if you use manual mode the reading on the meter will change depending on the metering mode. However for what we have said here if your objective is simply not to clip highlights you have a long way to go before reaching 90% IRE with HLG.

In short you have three options to set exposure on your GH5:

1. Super lazy option trust your camera meter as this was a still image, most likely you will be exposing to the right and without further checks there is a chance to have dark area or clipped highlights.

2. Use Zebra and manual exposure in combination with the camera meter to ensure you stay within safe limits.

3. Use waveform monitor and completely ignore the other parameters as this gives you full control of what you are shooting and removes any dependency on having or not an HDR monitor

As a final note it is important to remember that performing a white balance adjustment is essential in order to expose correctly it is not just to get the colour right as the IRE values on what is white actually change and the camera makes assumptions on what is white to calculate the rest. This is especially true for environment in difficult light conditions.

Getting yourself familiar with waveform monitoring is essential for editing as majority of people will not have the possibility to grade on an HDR screen. In the next post I will explain how to get the lowest possible cost HDR screen that supports HLG.

 

Panasonic GH5 the gateway to 4K HDR Video

It has been a while I have been busy with some personal stuff and to be frank not much has been happening the Underwater Video or Still scene that was of interest to me until pretty much September 2017 when Panasonic released the 2.0 version of the DC-GH5 firmware.

The link to the firmware updates is here and here is link to the full PDF

The section we are interested is this one

4K HDR video recording

– [HLG] (Hybrid Log Gamma) is added to [Photo Style]. HDR (High Dynamic Range) is a mode to reproduce both bright part and dark part in an image, making it look just as human eyes see. The camera records video with a designated gamma curve compatible with ITU-R BT.2100, and you can now choose Hybrid Log Gamma (HLG) in [Photo Style].
– A low-bit-rate recording mode 4K HEVC for HLG was added. This enables playback on AV equipment compatible with the HEVC compression format, such as Panasonic 4K HDR TVs.

 

In the PDF we read this additional information

Recording of HDR (High Dynamic Range) motion pictures in HLG (Hybrid Log Gamma) format is now supported. With this format, you can record bright images susceptible to overexposure with more natural colors than is possible with conventional formats.
• “HLG” is a standardized HDR video format that converts and expands the dynamic range of

compressed high-luminance image data on a supported device.
• The monitor and viewfinder of the camera are not capable of displaying images in HLG format. • HDR images appear darker on devices that do not support the HLG format.

If you have headache to understand what is HLG and how it differs from other HDR formats search on the internet the following short document from BBC may help.

 

Why does HDR matter and what can I do to record HDR?

HDR matters because the human eye is more sensible to contrast and colours than resolution. In majority of cases if you do a blind test of UHD 4K footage to anyone sitting at the recommended seating distance for cinema at home (look up SMPTE seating distance) nobody can actually see differences between HD and UHD and this is because the ability of the human eye to resolve pixels is limited by our visual acuity. So why does a YouTube video in 4K looks better than HD? Simply because the bitrate is higher and this means the quality is higher but if you look at your own 4K footage at home and scale it down to HD with good quality you are not able to tell the difference.

However try now some HDR material if you have Amazon or Netflix or even on YouTube and have a compatible Tv set the difference to normal content is staggering. This is because a normal REC709 (the standard for HDTV) display has 6 stops of dynamic range. There are no official figures of how many stops is REC2020 for HDR but good Tv sets are capable of around 10 stops. Now that is a big difference especially on the bright part of the image which is where the HDR displays really excel.

So HDR does matter more than 4K UHD in fact Sony has just produced an HD set HDR capable not sure there will be many of those but this gives an idea.

So how do I record HDR and why there are no HDR certified cameras but only certified displays? The answer is pretty easy you need a camera that offers more than 10 stops dynamic range in video and that is where our Panasonic DC-GH5 comes into the picture.

The camera is capable of 13 stops dynamic range but what is more important it can produce around 8 eV even at ISO 12800 so in essence the camera is well above what is required for REC709 and it can get to around ISO 3200 and still produce nearly 10 stops which is great. So if you have a Panasonic GH5 you have a sensor that is capable of producing the required dynamic range.

However this is not sufficient the camera needs to be able to product at least 10 bit colour depth, an image resolution of 3840×2160 and a colour palette aligned to BT.2020 specifications (wide colour gamut) and finally have the appropriate transfer function to deliver the signal. Majority of commercial cameras are not capable to deliver 10 bit colour depth and do not have a compatible transfer function. The GH4 predecessor of the GH5 was already capable of delivering 10 bit colour to an external recorder using the HDMI output now the GH5 makes this available in camera for recording on SD card at bit rate of 150 mbps IPB and 400 mbps all intra H.264.

HLG vs VLOG and why it matters

Before the firmware 2.0 the only way to produce HDR out of the GH5 was to buy the VLOG upgrade and then attempt to use the recording feature of the camera or an external recorder with Prores 422 or 422 HQ and then take a trip into grading. The reality is that once you crammed the VLOG dynamic range into a REC709 format you essentially limit yourself to 6 stops and therefore waste majority of your effort. So in order to extract real dynamic range you need to output in HDR that is possible but not so easy to do. In practical terms unless you are producing a documentary you will soon give up using vlog underwater because it is just too much work. Here now comes HLG so what is good about HLG and why this can make a real difference here my list:

  1. It is free you don’t need to pay for an upgrade
  2. It is backward compatible with standard dynamic range
  3. Requires a less intensive workflow compared to Vlog
  4. You can produce a decent file recording in camera without external recorders
  5. If you do have an HDR capable external recorder than it shows things are they are and not the washed out version of vlog

This is just my personal list of reasons there may be more.

How to set the Panasonic GH5 to record in HLG and UHD

There are 3 settings that give you the possibility to record HLG HDR compatible files, two are available in MP4 (LPCM) and MOV and one in MP4 (HEVC).

MP4 (LPCM) and MOV

P1040940
400 mbps ALL Intra

P1040941
150 Mbps LongGOP

There are not many cards that can work at 400 mbps and they are expensive. In any case do not assume that 400 mbps ALL-intra is better than longGOP as longGOP is fairly efficient and if you look into the various YouTube videos you will see it is very hard to see any difference unless you do pixel peeping.

MP4 (HEVC)

There is also a convenient low bit rate format available that uses HEVC in camera you can access it selecting MP4 (HEVC) in the REC FORMAT menu

P1040942

You then have this option available

P1040943

Tests show that when done real time HEVC produces files 50% of H.264 so the bitrate makes sense however unless you want to play the files directly on your Tv this is not such a good choice as the files are too hard to edit with any computer as there are no H265 hardware accelerated display widely available.

So the format of choice is as follows:

REC FORMAT: MP4 (LPCM)

REC QUALITY 422/10 bit/LongGOP 150 mbps

Please note the format at 50/60p does not give HLG in camera only the HDMI output is HLG compatible this is because the output is 10 bit as required by HLG. 8 bit colour does NOT qualify for UHD HDR so if you use this format in camera the HLG photo style will be greyed out.

How to convert 150 mbps HLG LongGOP files

At time of writing only programs like VLC play the H264 10 bit files produced by the GH5 and on my computer they play badly. So when you will go and edit those files your NLE program will most likely convert them into a format that is easier to digest and still supports 422 10 bit colour, this format is Apple Prores.

Unfortunately unless you have a paid software the files will only be unreadable if you use DaVinci Resolve or iMovie. However you can use a command line encoder like ffmpeg and convert all those files for free.

The command once you have the executable and you have the files in the right directory is something like this:

ffmpeg -i GH5file.mp4  -c:v prores -c:a copy GH5file.mov

This tells ffmpeg to transcode the video to prores 422 and to just copy the file as is (prores uses linear PCM for audio) here you notice that the source file has mp4 and the destination mov that is the default for prores and the reason to set your GH5 to record mp4 and not mov.

I have developed an automator script that is able to convert all selected files in the memory card and place them in a location of choice on the hard disk or else.

automator

Ffmpeg will convert using prores 422 that in my case bumped the files from 150mps to 474 mbps as prores is an all intra codec this is reasonable and there is no reason to use higher version like 422 HQ starting from a 150 mbps longGOP. Obviously if you use an external recorder feel free to use the higher bitrate available.

How to produce your HDR video clip for free

DaVinci Resolve is able to use your prores files converted from the GH5 and produce HDR compatible files.

You need to go into project settings and select colour management and change your settings as shown here

DaVinciProjectSettings

Colour Space Rec.2020 and Gamma Rec.2100 HLG will produce a file that on a compatible Tv will trigger HDR.

Now the bad news if you don’t have an HDR monitor it is very hard to grade properly on a standard monitor although you can look at luminance curves and chroma curves to see if you have situation of bad exposure or saturation this can be tricky with underwater footage so the trick is to try and get it right in camera.

Of particular interest is the HLG View Assist setting on the GH5: as the screen of the camera is not HDR this should help exposing the scene properly but I have to yet determine what is the setting that I prefer.

Well that is all for now…!

 

4K with the Sony RX100 in Egypt

 

 

It was time to go for a second trip with the RX100 Mark IV

I decided last minute to use the UWL-H100 LD however I managed to forget the M67-LD converter so ended up taking footage holding the wet lens with my left hand.

This created some flare issues in some scenes anyway judge for yourself.

I used the Picture Profile PP6 modified with some small changes around color matrix (I used the Pro setting) and some increased saturation.

As always the RX100 cannot white balance underwater so I used a filter (deeproof), this gives a magenta tinge and sometime the water looked a bit purple.
I have two versions of this clip the first one uncorrected and the second where I tried to remove the purple water. Look for yourself which one is best.

First version with minimal to no editing is here

 

The second version has some colour correction mostly to remove the cast but I have also done some minimal correction in some scenes at the surface shot without filter.

The other settings were shutter speed 1/50 fixed, Auto ISO with max ISO set to 800, auto white balance.

Generally I am very happy with the RX100 however the snorkeling footage was affected by one episode of fogging of the glass port. This was during a dolphin trip so very disappointing. The camera got extremely hot and I think the fact I was holding my hand close to the port to hold the wetlens created the problem as this had never occurred before.

Upon reflection I think I will go back to the UWL-100 M67 type two as the colours I get with the magic filter were superior in my opinion and more natural.

For those wondering about the dugong dugong it was dark as I was free-diving to 12 meters with the camera and the wet lens hand held so not the easiest job.

Let me know which version of the video you prefer!

Getting the best underwater colours for your 4K Sony RX100 Mark IV

It is not a mystery that even the new Mark IV version has issues with custom white balance.

The ergonomics have not changed and you need to go into photo mode to set custom white balance but generally underwater results are poor. Using filters is therefore a necessity also on the new 4K version.

RX100 Mark IV Video Behavior

The RX100 offers now a 4K 100 mbps mode and can use picture profiles.

I have used a modified version of PP6 that use the cine2 gamma curve, I have however changed the colour to the Pro mode and changed a number of other settings in my last video in Puerto Galera.

The water was green and murky but this gives you an idea of what you can get.

Filter Options and Wide Angle

Although the Nauticam WWL-1 is the best lens for the RX100 it does not take filters and therefore is not adequate for video.

In this review clip you can see the options available on the market.

In terms of wide angle you have two options for 4K:

  1. Inon UWL-H100
  2. Inon UWL-100

Both lenses work fine in 4K however the older UWL-100 achromat does vignette in photo mode.

The UWL-H100 offers a very wide field of view also in HD mode with no vignette and accepts the mangrove/deeproof filter.

This filters is loaded with magenta so I suggest adjusting the tint in the auto white balance mode to +2 green.

The UWL-100 works fine in 4K and is wider than the UWL-H100 however has only the M67 mount. If you have one of those lenses you can use the Ikelite 6442 filter. This filter required you to remove the rubber ring on the lens and does work quite well except has a yellow cast to it you can reduce by changing the tint to +2 blue and increasing also magenta to +1.

For flexibility purposes probably the UWL-H100 is better as it takes the bayonet but the UWL-100 is really wide and has a little less fringing. Some people do like the UR/PRO filters better.

I hope you find this post useful and good luck with getting the best colours from your Sony RX100 Mark IV

What does UHD Premium specification mean to 4K

The UHD alliance is a working group that includes a number of well known brands.

In the board are directors of the following major players:

  • Fox
  • Sony
  • Netflix
  • Panasonic
  • Dolby
  • Technicolor
  • Samsung
  • LG
  • Universal
  • Warner Bros
  • Walt Disney
  • Direct Tv

The members include companies like Sky, Amazon, Intel, Thx, Dts and others.

The key purpose is specifications mostly for high end use and the key pillars are:

  • High dynamic range video (SMPTE ST2084 EOTF)
  • Wide colour gamut (BT.2020)
  • 4K resolution
  •  10 bit colour depth

This is obviously a large improvement compared to the current specification of HD Video:

  • BT.709 colour
  • 1920×1080 Resolution
  • 8 bit colour

Probably the most interesting feature is high dynamic range video as the human eye is more sensitive to contrast than it is to colour and resolution although surely the 10bit colour depth will make a difference.

Currently all professional recorders that manage 4K use 10 bit colour but none uses the BT.2020 colour gamut and the dynamic range is left to the sensor quality and has no minimum specifications.

So what will UHD premium mean to us? Well currently not much!

The key is that UHD alliance has also stayed clear from the major issue for distribution that are the video codecs.

Currently HEVC or H.265 has got royalty challenges but is the most  efficient codec on the market and the widest in terms of diffusion in hardware.

To give an idea two minutes of 100 Mbps H.264 become 76.5 Mbps once you push the H.264 to the limit but the corresponding H.265 is only 13.6 Mbps only 18% of the size.

Google does not support HEVC and are distributing 4K using VP9 and H.264. From my tests VP9 is not as efficient as HEVC the same file came at 17 Mbps. The key issue of VP9 is playback that does not even work on a powerful home computer although some new Android TV have accelerated VP9 and so has the new Nvidia box.

Whilst this gets worked out it is likely that cameras will continue to record in H.264 and the key here is higher bitrate as H.264 is clearly inefficient with 4K.

If you are in the 4K space and you want to produce semipro or pro footage you need to have an external recorder working in Prores HQ or your device needs to be able to record higher than 100 Mbps.

Sony has just introduced the XQD memory cards that write 800 Mbps

http://pro.sony.com/bbsc/ssr/mkt-recmedia/mkt-recmediaxqd/product-QDM128/

This is potentially a way forward for higher bitrate recording as UHS 3 is limited to 240 Mbps and would only work with compressed footage.

Another thing to consider is that you need a pretty big Tv to notice UHD at the normal viewing distances we tend to watch.

http://s3.carltonbale.com/resolution_chart.html

Carlton Bale was on the scene few years ago when HD came about and the conclusion was you need 55″ or more at 8 feet to ‘see’ HD as your eyes can’t resolve more.

This distance becomes 120″ at 8 feet which is essentially the size of a projector screen.

Essentially UHD seems to be more for computer freaks watching clips very close to the screen that for the average user.

I did several test on my Tv with clips I had produced in 4K downscaled to HD and at my normal viewing distance I could not see any difference what so ever!

Essentially I have determined that 50 Mbps XAVC from the RX100 Mark IV looks actually better than 4K on my Tv.

I guess we will have to wait for HDR to see some real benefits meanwhile the clips from you tube look better simply because they have more information. There is a factor of 6x for UHD compared to HD and this shows a higher quality clip.

I don’t see a large future for UHD in TV broadcast it could die as 3D just did.

 

The painful quest of 4K Video

2015 has probably been the first year where consumer devices have taken the journey to 4K as even iPhones now can record at Ultra High Definition.

However there is still a very long way to get us to the level of standardisation of HD video and the war of the codecs has still to determine a winner.

As of January 2016 if we consider only digital cameras only three manufacturers produce 4K capable devices that can be housed for underwater use and those are Canon, Sony and Panasonic.

Specifically we have two compact cameras with fixed lenses, the Sony RX100 Mark IV and the Panasonic LX100, two micro four thirds the Panasonic GH4 and GX8 and three DSLR the Sony A7IIR and A7IIS and the Canon EOS-1D C that was in fact the first camera to record 4K video in 2013.

From a consumer point of view we are interested in a 4K device that can operate with wet lenses across the focal range and that is under the $5,000 mark including the housing so I will focus on the Micro Four Thirds and fixed lens compacts and exclude immediately the Panasonic LX100 that requires a port system to operate we are now left with 3 devices that today are the real options for 4K underwater video.

4K Digital Cameras for Underwater Use

  1. Panasonic GH4 with Panasonic 14-42mm II Mega OIS
  2. Panasonic GX8 with Panasonic 12-32mm Mega OIS
  3. Sony RX100 Mark IV

I have added the lenses of choice of each camera for convenience.

In 35mm terms the focal lengths offered by the 3 devices are:

Panasonic GH4 with 14-42mm : 35-105mm

Panasonic GX8 with 12-32mm: 31.2-83.2mm

Sony RX100 IV: 28-80mm

Wet lenses

Both Panasonic cameras revert to a traditional 35mm cameras when the 4K crop is applied. The wet lens of choice is therefore the old Inon UWL-100 with M67 thread. This is a lens with a magnification of 0.57077 that with the 14-42mm II Mega OIS and Macro Port 35 or the 12-32mm and Macro Port 29 performs very well without vignetting and offers zoom through the whole focal range. The same lens appears to work fine also with the Sony RX100 Mark IV but is almost border line in terms of vignetting and I will need to conduct further experiments for now we will refer to the Inon UWL-H100

Focal range with Inon UWL-100 / UWL-H100* (Sony)

Panasonic GH4+14-42 : 20-60mm

Panasonic GX8+12-32 : 18-48mm

Sony RX100 Mark IV : 17-48mm

You can see that the GX8 and the RX100 are virtually equivalent and the same holds true for macro with the GX8 and the RX100 offering same working distance and magnification. The GH4 is superior in this area due to the longer focal length after crop of 105mm. For me the most versatile wet lenses for macro remain the Inon UCL-165 despite the various Nauticam and Subsee options because you can cover all the working distances from 16cm to 8cm which is the sweet spot for macro work.

Unfortunately the level of magnification obtainable with the GX8 and RX100 is not great and really small subject will still look tiny in the frame. Obviously the use of the 14-42mm lens on the GX8 resolves all problems except the field of view with wet lens at wide end is now 21mm anyway not a huge issue.

I am still waiting for a proper review of the GX8 but in terms of 4K resolution I have been impressed with the Sony RX100 Mark IV that appears to be sharper than the GH4 and even the A7IIR.

4K formats

In terms of 4K recording all devices on the market use some form of H264 100 Mb/s codec Sony uses what they call XAVC S while Panasonic uses a standard Mp4 compatible wrapper. Sony codecs do not use B frames in their H264 implementation but this does not seem to affect quality that much.

So now that you have your 4K footage what do you do with it?

The first consideration is that all cameras record internally at 8 bit with 4:2:0 subsampling this means that colours are only recorded for 50% of the pixels and then interpolated. The implication is that color grading opporunites are limited and heavy manipulation should be avoided to avoid undesired effects such as banding.

This means custom white balance better with a filter is still very much needed for 4K.

In the Mac camp there are many consumer options for 4K editing including iMovie, Final Cut Pro X, Adobe Premiere Pro and for Windows you also add Sony Vegas, Avid composer and many more

S-logs or V-log are also not meaningful at 8 bits without external recording capabilities as grading will ruin the footage.

Workflow for Consumer Use on Mac

For the average home user on a Mac iMovie offers now decent functionality and imports and edits in native format all the clips produced by our selected cameras. iMovie also exports in Prores 422 which is ideal for storing your master copy after editing.

Unless you edit on a laptop or a machine with poor hardware there is no need to convert the footage in intermediate formats as most of GPU have H264 acceleration so your 4K workflow will look like this:

  1. Import into your 4k editor
  2. cut and edit sequence
  3. Perform minimal corrections to exposure and color
  4. Add some transitions
  5. Add music of voice over
  6. Export to Prores 422 or 422 HQ if available
  7. Compress with 3rd party software or plug in

Compression Headaches

Step 6 is particularly important as none of the above mentioned editors has good native export capabilities so you want to do that with another program. If we take for good what apple says Prores HQ is very rarely fooled by 4K footage at 737 Mb/s for 25p. Consindering that our footage was 4:2:0 to start with this means we need only 75% of that bandwidth or 552 Mb/s. As Prores 422 records at 492 Mb/s which is only 11% less than the required bandwidth so iMovie with the Prores export option is pretty good.

We now have our 492 Mb/s video with most likely an AAC audio what are we going to do with it?

This is where it gets really painful. If you have a 4K Tv you definitely want to watch your footage on it, today UHD Tv support the HEVC codec and more recently also the VP9 codec that google uses in YouTube however both those codecs have limited options for encoding and do not have any hardware acceleration support in your computer that will be used to compress the footage.

To make matters worse if you then share your footage online on YouTube this will be heavily re-compressed. I have done some analysis on some clips that I watch to find that 4K bandwidth is between 17 and 20 Mb/s in H264 and the files are not even encoded with CABAC to ensure they can be played on devices with limited hardware capabilities. In terms of web browser many now supports VP9 however hardware acceleration is lacking so it is likely that you will be watching H264 4K footage at 18 Mb/s when you connect to YouTube on your computer.

It is likely that the mp4 files that you can produce with handbrake or other tools are easily coded at 60-70 Mb/s so YouTube, as it does with HD footage, will introduce significant issues to your 4K videos.

Interestingly the 4K bandwidth is higher in terms of Bits/(Pixel*Frame):

  • 0.090 for 4K
  • 0.076 for 2K
  • 0.055 for HD

This would suggest that 4K videos are less compressed but on the other hand the compression is less efficient. 2K appears an interesting mix that still uses Cabac and 3 reference frames but is really a computer only option.

For who has access to an x264 encoder  this is a suggestion for 4K  encoding that does not kill your computer

Preset slower – modified

cabac=1 / ref=5 / deblock=1:0:0 / analyse=0x3:0x113 / me=umh / subme=9 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=2 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=3 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=2 / b_bias=0 / direct=3 / weightb=1 / open_gop=0 / weightp=2 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=60 / rc=crf / mbtree=1 / crf=18.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00

The options that differ are ref=5 otherwise we break the limit of level 5.1 and the decoder may have issues, and crf=18 from 23 to increase quality.

This H264 encoding can easily produce files around 1.4 Gb for just 3 minutes and will require playback on the device or USB disk attached or a good cat 5 ethernet network or solid wireless at at least 100 Mb/s effective speed.

It follows that H264 really is not the way forward at 32 Mb/s HEVC two pass or crf=23 in single pass you get files that are 20% or less of the size and work well if you have a 4K HEVC accelerated player like I do. At this bitrate is also very easy to stream over your wireless LAN even at mediocre quality. Unfortunately YouTube will reject your HEVC files and require H264 or VP9.

Google plot for 4K world domination

Google did not want to incur more royalties so they pushed out HEVC to use the open source VP9 as they did years ago with Vp8.

VP9 is at least in the Mac version very slow and seems fairly amateurish. They have been succesful with Android Tvs that have YouTube as a prime source of 4K content because the YouTube app does not work in 4k on Tv sets unless it can decode VP9. This is clearly only a commercial plot as all TVs can play H264 and YouTube wants to reach as many people as possible with 4K therefore keeping bandwidth below 20 Mb/s and accessible to the higher end of DSL connections not just fiber so that they can push their ads to the masses, however it also means that your video will look pretty pathetic on YouTube unless  you use a VP9 capable browser or Tv set or android to box to watch it.

At time of writing the only android box that can decode Vp9 is the Nvidia Shield Tv so if you want to watch YouTube 4K videos at 18 Mb/s Vp9 there is at least one choice.

http://shield.nvidia.com/android-tv

Also the Roku and Kindle fire Tv support YouTube 4K but don’t have Kodi so I would not consider them

 

 

 

 

 

 

 

 

 

 

Tips to make the most of underwater time