Category Archives: Tips

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

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Video Feature Sony RX100 Mark II in Malta

Following from my previous post I managed to get together a clip out of the 5 dives I did

The first day was somewhat plagued by visibility a bit lower than the norm for the location but the second day was fabulous

For this trip I brought with me the Inon UWL-H100 and the red push on filter from deep roof H20 and the Inon UCL-330 as I was expecting medium size fish and nothing really small

Here is the outcome

I am quite happy how things turned out so let me share the settings with you

First I shot most of the footage in 25p AVCHD mode only some small sections are shot at 50p and actually I did not need to slow down any of the material.

For the wide shots I used steady shot in normal mode and shutter priority at 1/50th. With the filter on I had auto white balance with tint correction G2 A1. I noticed that the camera was giving red tint in some situation and so added a bit of green back. The Amber correction instead is for the RX100 itself the camera does not have vibrant yellow and is a bit blue.

Tunas
Tunas – AWB with filter

For the first time I use creative mode changing the standard contrast to -3 in order to prevent crushing of blacks.

Exposure was set all along to -1/3 and metering to multi area with AUTO ISO limited 160-800.

I think the results are so good that in fact I have performed no colour correction to any shots in ambient light.

Opening the tuna farm
Opening the tuna farm – AWB with filter

For shots with lights I set up first colour temperature to 6500K and A1 to match the lights but then in some of the far shots this resulted a bit cold so I adjusted very slightly in post the temperature.

Seahorse
Seahorse – AWB UCL330

Only 40″ are adjusted in the whole video in essence is as shot and the editing took me half hour.

In cave
In cave –  AWB no filter

I did a bit of analysis and the camera was operating for most at ISO200 with aperture around f/3.5 – f/4.0 which is really the sweet spot of the lens.

I did have some challenges using the UCL330 for some nudibranches  that really required a stronger lens so they look a bit small, there was also surge so I had to fight with focus problems but all in all very happy.

Nudibranch
Nudibranch – AWB UCL330

The longer working distance of the UCL330 (20-30 cm or 8″ to 1′) proved challenging on walls as you are too far to hang on to anything or use a stick. I will bear this in mind in the future.

For the close up shots I used steady shot active.

I also wanted to say that a few times the camera did manage to white balance properly however the results were not exciting and frankly not worth the hassle. Using the filter is just so much better with the auto white balance.

Tweaking the Sony RX100 Mark II Video Performance

I am currently in Malta for few days relaxing and I manage to squeeze in some dives. The Mediterranean sea is nothing sensational (from a pure diving point of view) but does offer clear water, and some brisk thermoclines, and a combination of algae, blue water, caves and silvery fish that is challenging on the dynamic range of our little RX100.

The purpose of this trip is mostly to refine the video settings and go more in depth in few topics. I wanted to try specifically the following:

  • Metering modes
  • Creative modes
  • Stabiliser modes
  • Tracking focus
  • Medium size fish portraits
  • White balance
  • Caves and low light

Some of my settings will be the same and I am not intending to changed them those are:

Auto ISO: 160 – 800

DRO: Auto

Starting off with metering, the first attempt was to try and use the camera on 0 exposure compensation with centred weighted average metering.

Entering Cave Fairly Bright
Entering Cave Fairly Bright

Pretty soon I realised this gave issues of banding of the blue water, this was apparent not only in backlit shots but also in normal wide angle of fish in specific cases. So after dive number 1 I changed it to the standard -0.3 from dive 2.

I set a new creative style with contrast at -3 in the hope to recover detail and seem to be working fine with the shots still having plenty of contrast.

Lowered Constrast on -3
Lowered Constrast on -3

I also tried spot metering for close up but it makes no sense the video lights are too wide and ended up with burned highlights at the edges of the frame so back to centred weighted average for close up shots.

Spot metering
Spot metering

So when it comes to metering my settings are:

Wide angle: multi area

Close up: centered weighted average

I did some tests with stabiliser in steadyshot mode, this gives back some field of view and the lens offers 100 degrees diagonal and 90 horizontal, I actually think a bit more anyway with fairly stable conditions this worked fine. At longer focal length for close up I am still using active mode.

Schooling Fish 100 fov
Schooling Fish 100 fov

I have a +3 diopter for this test as I realised in my last still trip I don’t have a lens for medium size fish, the lens worked very well and I also tried the camera tracking focus but it seems it won’t work with fireworms or similar. So either keep normal focus or manual with peaking.

Tracking focus fail
Tracking focus fail
Rock FIsh UCL 330
Rock FIsh UCL 330

White balance has been a subject of discussion, I did manage this time to white balance a few times but to be honest it was not worth the effort there is a better correction of the purple hue of the filter but this can be corrected setting Green to 1 or 2 in AWB. I also changed the AWB to include a correction with Amber 1 as per examples. Very happy with the results I think this is the final set up with this filter lacking a proper orange filter.

AWB corrected
AWB corrected

Shooting in low light was rewarding with ISO maxed out at 800. I am becoming less and less a fan of video lights in cave due to the amount of backscatter am getting. I think I will default at using the lights as dive torches instead of wide beams of even leaving them off for effect.

Backscatter
Backscatter
Cave in natural light
Cave in natural light

 

Underwater Photography Workshops – My Tips

I thought the Red Sea workshop with Alex Mustard was brilliant to I thought of writing down my notes and sharing them with you.

This final post is a general one and has my lesson learned from attending the workshop, those that follow are generic tips that I think would be beneficial to anyone wanting to attend a similar experience.

Before the Workshop

The experience actually starts before you even attend the sessions key points for me include:

  • Ask questions about the workshop and how it works
  • Know your equipment
  • Take all the gear you have
  • Be fit and self reliant
  • Set your self objectives

I did not really ask many questions before going as Dr Mustard sent a very comprehensive document however this is not standard and it is better to ask in advance about the conditions, the dives, the type of training and generally how the workshops is organized. Some have talks, other have one to one, other are just dive trips where you ask when you need. Not all types fit everyone so better to make sure you go to one that matches your need.

Sadly even this time like in every trip I have come across people using their equipment or part of their equipment for the first time. The end results is wasted dives and opportunities, I cannot stress enough that testing your rig in a pool before going allows you to familiarize with it and make any corrections you need.

Pool Conditions
Pool Practice

Also take all the possible lens, ports, parts that may be useful. Once you are there you don’t want to have regrets about something you have left home. In my case all was there but I did not know about remote strobes otherwise I would have got myself a trigger as I have 2 Z240s.

Transformer Tray
In case of doubt exceed with equipment

In most of those workshops buddy system does not really apply so make sure you are self reliant and fit as the conditions allow to avoid embarrassing or even dangerous incidents. Once there dive within your comfort limit and if you don’t really have a buddy dive with a guide.

It is useful to know before you go what your objectives are, for example what type of shots you want to work on. This means you have something to do over and above the assigned tasks.

During the workshop

Once there you need to stay focused on your performance. Those are additional points to think about:

  • Deliver the assigned tasks
  • Go off the beaten track
  • Learn from other participants
  • Take notes

Sometimes during those workshop there are challenges or set shot that are suggested, this is your opportunity to compare your work with others and therefore you should make sure you deliver those also to find out if there are limits with your equipment.
Eggs
In the Red Sea workshop were given the task of taking pictures of cardinal fish with eggs in their mouth. I realized I could not fill the frame because I lacked a mid range close up lens and my camera would not focus closer.

In addition to the suggested shots you should make changes to those and try something different even if not totally different.

Ras Katy Sunset

There are many landscape split shots but not many portrait so why not try one results can be excellent and it is easier with a small dome.

Other participants also will give a go to the same shots or have better editing skills it is worth to watch and learn.

Trucks
My buddy was setting up a remote strobe I fired a few shots (unintentionally of course) so I got my own shot!

Finally take notes of what you did right and wrong and if you missed anything.

After the workshop

After the sessions are over still there is work to do over and above going over your pictures again.

  • Write down your lessons learned
  • Look at other people images
  • Order any equipment that you missed

Well it goes without saying that I put the notes together and summarized them here.

I also found great to connect to other people and then look at their gallery for other shots that we had not discussed before.

Finally I ordered myself an Inon UCL330, funny I had this lens and sold it not realizing the real use which is fish portraits!!!

That’s all for now if you go on a workshop soon I hope you find this useful.