Sony FX6 - Why is in Slog3 the High ISO Base 12800 ASA?

[Erik Krambeck]

Hi, 

I own since 4 years the FS-5 & Atomos Inferno for gimbal work, but mostly I work with ARRI Cameras on bigger projects. Last weekend I did a FX6 Test (from a rental company) and I think its a huge step forward to the FS-5, a very interesting camera ! But I was wondering why the High ISO Base in Slog3 is 12800 ASA?

I watched the Slog3 material (12800ASA) in 4K via HDMI on a 43Inch LG UHD Monitor and you could see the grain "dancing". 

In the Custom Mode in Cinetone with 12800 ASA (Base) but set to 5000 ASA, it looks much better, hardly any visible grain. I think in most cases 5000 - 6400 ASA (in Slog3) would be quite sufficient, and easier to work with because you don't have to use noise reduction in post.

I think in the High ISO Base 12800 ASA in Slog3 is to much electronic "Reinforcement", that causes grain. I would wish that Sony would "downgrade" the High Iso Base to 5000 ASA or 6400 ASA in a further firmware update. Similar to the FS-5, which had a slog base ISO of an absurdly grainy 3200 ASA when it shipped, which was changed to 2000 ASA in firmware 4.0.

Who thinks similarly?

Or is there a reason why Sony did this? Marketing or to take advantage of the full dynamic range? 

[Satsuki Murashige]

Were you looking at S-Log3 or did you have a Rec.709 LUT applied? Log will always appear noisy, since the shadows are raised to maximize the captured dynamic range. You will normally crush them back down in color grading for viewing, either with a LUT or manually with grading tools. 

From what I understand with the FX6 (haven’t used it myself yet), the High Base is only 12,800 ISO in CineEI mode. With S-Cinetone in Custom mode, the High Base is 5000 ISO. Since S-Cinetone is basically Rec.709, the blacks are already crushed for you, hiding the noise in the shadows.

If you don’t need the exposure, then you can stay in the High Base, dial the EI back down to 6400 or 3200, and use the internal ND to compensate. This will give you less noise in the High Base, at the cost of some highlight range and it will be less noisy than using the Low Base of 800 ISO and pushing the EI up to 3200 or 6400. Of course, if you do need the exposure, then 12,800 is very useful. So you get the best of both worlds. 

It’s also possible to turn on the in-camera noise reduction setting if you want to reduce the appearance of noise in the High Base, at the cost of some blurring and smearing artifacts. Really though, noise reduction is best done in post as once it’s baked into the image, it can’t be undone.

[Erik Krambeck]

Hi Satsuki Murashige!

Thanks for your reply!

The noise in 12800 ASA slog was visible, even in with a Rec709 LUT applied. But it depends on the resolution and size of the monitor - my example with a 43 inch UHD is certainly extreme. 

I have the impression that Slog3 12800 ASA (with a LUT) absolutely needs noise reduction in post-production, otherwise the later compression for streaming or YT looks terrible because the compression logarithms can't cope with the noise. 

Hence the desire to reduce the High BASE ISO to 5000 or 6400 in order to be able to do without noise reduction in post-production. 

With my older MacPro computer, the grading can be played out in 4K at 12 fps and the noise reduction at 0.5 fps. 
For me, noise reduction is "pain in the ...".

Greetings Erik

[Satsuki Murashige]

Noise tolerance is certainly a personal preference, so if you’re finding the High Base ISO too noisy then I can see why it’s a problem for you. 

That said, have you tried lowering the EI in High Base to 3200-6400 EI and increasing exposure to compensate?

Also, have you tried the in-camera noise reduction setting to see if it is sufficient for YouTube projects?

I can sympathize about the slow rendering time of Neat Video in post, it is painfully slow for long clips. Can’t argue with the results though. 

[Ben Scott]

My reading so far with my FX6 is at 12800 is the noise is fine if the footage is not underexposed.