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Sony Issues Official Statement on FS5 Image Quality Issues

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Sony have now officially responded in a small statement to the many concerns about the image quality issues of the FS5 camera. While the camera has just started shipping in some parts of the world (including here in India) several early users have reported seeing some macro blocking in the internally recorded 4K image, as well as some odd artifacts that resemble torn edges while shooting at higher (3200+) ISOs.

Some users also claim that these artifacts appear more when recording 4K internally to the SD card but also appear in the 4K external output and the internal HD recording as well.

Sony said in the statement

 “We are aware of this perceived issue with the PXW-FS5 performance. Sony is investigating this matter as a matter of priority and will work with users to understand the specific issue they are facing. Any actual issue will then be addressed in the most appropriate manner by our engineers.”

While Sony is choosing very carefully worded “perceived issues” to describe these concerns, it is good to see them acknowledging the concerns of users publicly.

Last week renowned British Filmmaker and Sony Independent Certified Expert also published his thoughts on the issue 

From Alistair Chapman’s blog-

 

 

Native ISO: The Sony PXW-FS5’s native ISO for the standard gammas and cinegammas is 1000 ISO. It is NOT 3200 ISO. If you shoot with standard or cinegammas at 3200 ISO then you are adding +10dB to +12dB of gain.

+10dB gain = noisy picture. If you add +10db of gain to most cameras the picture will get noisy and grainy, the FS5 is no exception to this. Adding +10db gain also means you will have a +10db noise increase (roughly 300% more noise, a significant increase) or have an increase in noise plus a significant increase in other artefacts as the cameras built in noise reduction has to work much harder. The FS5 does incorporate noise reduction processes and these do introduce a degree of smear when you add more than +6db of gain. At +12db or higher the smear and other artefacts (including a tendency towards banding) becomes quite noticeable, this is a typical artefact of this type of noise reduction and one of the reason why on more advanced cameras like the PMW-F5/F55 you are able to turn it off.

Ultra Compressed: In UHD the XAVC-L codec has a bit rate of 100Mb/s. Uncompressed UHD requires over 3.5Gb/s for decent quality, so you’re looking at a camera with a compression ratio of around 35:1. Is it really all that surprising that there are some compression artefacts? Consider that 35Mb/s is considered the minimum for broadcast quality H264 based HD work and that’s a compression ratio of only 25:1. So we are some way below the normal minimums for broadcast.

8 bit in UHD. UHD XAVC-L is an 8 bit codec. 8 bit codecs don’t deal with noise terribly well as the limited number of shades/steps mean that noise cannot be reproduced with small steps and as a result any noise or grain will often appear quite coarse. So is it any surprise that in UHD the camera exhibits a lot more artefacts than in HD where the codec is 10 bit and much less compressed?

S-log at high ISO’s. Oh come on people, please understand that S-log only does one thing well and that’s maximise dynamic range. If you can’t get a correct exposure or better still a 1 to 2 stop over exposed exposure at the native ISO you really, really shouldn’t be using log. It will be noisy, it will be grainy, it won’t look good and if you record it with XAVC-L in UHD it will look like rubbish as the excessive noise will stress the codec, introduce more artefacts and your exposure mid range will only represented by approx 17 code values or shades. you will have very little data to play with in post and noise and grain will look awful.

External Recorder. Adding an external recorder can really improve the UHD image quality. Again, this shouldn’t come as a surprise. If you use an external ProRes recorder running at 880Mb/s (ProRes HQ) compared to the 100 Mb/s of XAVC-L is it really any surprise that it’s possible to record a better quality image? The FS5 has been designed as a grab and go camera recording on to cheap media. Sure adding an external recorder can increase the image quality, but your media costs go through the roof and most of the grab and go benefits are lost.

So when you see a test of XAVC-L with a standard gamma at 3200 ISO being recorded using an 8 bit,  35:1 codec don’t be surprised to see a noisy, grainy image with compression artefacts from all the extra work the codec is having to do to deal with the noise that comes from adding +10db gain. The same for low light log footage at 6400 ISO. This is not the best way to use a camera like this. It’s not clever and anyone can make even a straight forward scene look like rubbish by shooting this way. I don’t know what people are trying to say or achieve when they post a bunch of high gain clips with headline titles like “The FS5 codec is broken” or “FS5 un-usable in UHD” without even considering what it is that they are actually looking at. AT 3200 ISO with standard gammas the camera noise reduction circuits are working overtime to try and clean up the image. This results in the introduction of other artefacts such as edge tearing or smear. Stick that into a super compressed codec and it is not going to be a perfect image. 50Mb/s HD at 60fps is also very highly compressed and will also exhibit artefacts.

As I have written in other articles, the use of ISO with video cameras appears to be miss-leading many people into thinking that a camera will produce a noise free image at all kinds of ridiculous sensitivities as they often focus on the wrong ISO rating or simply believe that it’s possible to have very high sensitivities without noise. Sadly this is not the case. I don’t think people would be surprised to see noise and grain at +10dB gain, but sadly dB’s of gain isn’t hip, cool or make you sound like a film cameraman. No, ISO is much cooler sounding, but is confusing the c**p out of people that don’t really understand how it works in relation to a video camera. Also the use of log for low light is just nuts, it’s entirely the wrong type of gamma to use, especially with a sub optimum codec.

The FS5 is not simply a shrunk down FS7. It is a very different camera. You should not be expecting FS7 performance in UHD, the UHD version of XAVC-L codec is very different to the XAVC-I available in the FS7. The image processing is also different (do remember the FS5 consumes 1/2 the power of an FS7).

It is possible that over future firmware updates Sony may be able to fine tune the codec and noise reduction circuits to work a little better. It’s also possible that we may see improvements in the decoders used to decode the codec (remember the decoder is just as important as the encoder), so possibly things may get improved a little. But don’t expect miracles. Squeezing UHD into a highly compressed 8 bit codec and recording it 100% reliably on off the shelf SD cards will always be a challenge. Even at the correct native ISO’s, at 0dB gain, there will be some artefacts. But start adding in gain and yes, you will start to see more noise and more artefacts.

The FS5 is a great little camera, I really enjoy shooting with mine and I think the results I am getting are great. I know that I can get a technically better 4K/UHD image from my FS7 or F5, but sometimes it’s not just about getting the best technical quality. The FS5 allows me to shoot more freely, it’s a breeze to carry around or travel with, I can throw it on a gimbal, on the end of a microphone boom pole, chuck it and a bunch of lenses in a small back-pack, it’s fun to use! As a result I’m getting shots that I just can’t get with the FS7 or F5.

Just how terrible is the FS5’s image quality? Take a look at my Falcon video and judge for yourself.

 

 

 


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