FS5: FS5: Shooting slog in 8-bit on the FS5

starcentral

starcentral

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With the FS5 around the corner some folks considering the camera might be fretting the fact the 4K is only available in 8-bit 420, especially when the word on the street is that you should really avoid shooting slog in 8-bit or else something devastating might happen. :shocked:

Ok it is true that 8-bit only offers 256 levels of information which might not be enough considering you need to de-log the footage later and then possibly color/grade, etc.. and yes for sure I think more bits are better but I also wanted to share that I've had some moderate success shooting slog in 8-bit to the Sony F3 back in the day when I owned one.

Below is a frame from a project I worked on shot on the Sony F3, XDCAM codec, 8-bit 420 to internal SXS cards. This was "normalized" and lightly color corrected using the built-in color tools in FCP X.

You might not like my colouring job so here is a DPX frame extract which can be downloaded and played around at your leisure.

Download DPX here

slog:
toishi-8-bit-slog1-sonyF3-slog_zpsrr7bzpjh.jpg


graded/cc:
22628967947_e9e6c09cc2.jpg


22628967947_e9e6c09cc2_c.jpg


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Dennis, Slog2 and Slog3 are 14 stops instead of 12 (Slog1), meaning there are even less data numbers for recording...
 
Why did you choose to record internally? I've done it a few times but that is only because my recorder hadn't yet arrived, I can't imagine now shooting without the external recorder once I've got it!
 
Let's add to the discussion that the old xdcam in the F3 was weaker than XAVC-S on modern a7 cameras.
I haven't tested the L flavour yet, but so far XAVC-S has given me decent results as long as I don't push the image too far.
Anyway I shoot mostly with cine4 since I still think that the slog-2 curve is tricky.
 
Actually the internal codec on the F3 is suprisingly good even for slog. I did a bunch of tests where I compared the same frame in internal and prores hq, both with a LUT and without. For 90% of the frames they were extremely close.
 
Couple o points.

8 bit refers to 8 bit YUV, not RGB. So when you think of steps in colours it doesn't quite work like that because the YUV is converted to RGB for display, if that conversion is done in a higher space then you don't see quite the same type of banding you would in RGB space.

Slogs are containers that can store an absolute maximum amount of range. Each camera may fill that container to a different level. Slog2 is around 12 and SLog2 has a couple more (i can't recall the exact figures)

If the camera is outputting log correctly then you may not fill all that space. If you don't fill that space in 8 bit you are loosing tonality.

As an example the A7sII has Slog3, the camera does not have enough range to fill that container, it gets to about 90%. That means 10% of that 8 bit potential is wasted on empty space. Conversely log curves have raised blacks, so that a % of the bottom of the container is not used.

So it is important to match the camera to the log curve, there's no point having the A7sII in Slog3. It's too early to know with the FS5 as well.

That's the theory.

The reality is that sony tweak the output. Sometimes they lower the black point to make better use of space, the A7s camera have lowered black points. Also they may apply a small curve to the source data or scale the data to fit the curve. This means the image is no longer scene linear but you do get more image in there.

I believe Sony tweaked the Slog2 curve for the A7s series, it has lower black point and the camera can fill that curve.

It's good that they tweak it.

But here's the thing. A lot of folk like using LUTs, either to translate log into linear or to add a look to an image. Each LUT expects data in a set range, any LUT which is SLog2 expects black at point X. If you give it data below that point it gets clipped (crushed blacks). So beware.

Also some LUTs have banding issues because each not is not built the same way. I've seen commercial look luts produce terrible banding. So be careful again. In the top image there's a magenta section on the wall, sometimes banding looks like that - i'm not saying this is banding because it may well be there in the scene.

cheers
Paul
 
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