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    A7s: S-log2 too noisy? Then underexpose cine4
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    Senior Member macgregor's Avatar
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    Given that with my tests I get the following results, showing that cine4 has the same ammount of DR than S-Log2...



    ... I said today, what if I underexpose the cine4 by 1 2/3 stops (which is quite a lot actually) so that I get the dynamic range allocated in the same way the Slog2 profile does (more highligths, less shadows)? Maybe I will be able to get less noise since I can use a much lower base ISO setting (200ISO in cine4) and also, I won't need to use ultra heavy ND filters anytime I want to shoot with this camera.

    I did tweak the black levels and gamma on cine4 all the way up and the footage so that it fills about the same histogram bucket that the Slog2 profile does.

    Some grading in Davinci and here you go:





    Don't ask me which is which because it's hard to tell. They have the same DR so the differences are very subtle. Saturation in the highlights changes a bit here and there but wow, not a bad match!




    So which one is which then?
    Lets zoom in 400x:







    Noisy pics --> Slog 3200ISO.
    So what's the catch then? Donno. None so far. But I've only been playing with this for a couple hours.
    Will the footage be more prone to posterization? Mayyybe. BUt at the same time, it fills the histogram the same way Slog does. So it could just be the noise in the Slog helps avoiding posterization in the compression. I need to test this with an external recorder to see if its the codec or the internal processing.
    But the best thing is that the camera could now be rated to a much more decent 640ISO and while keeping the same amount of DR in the highlights, it shows less noise. Win win situation?
    Last edited by macgregor; 08-30-2014 at 05:52 PM.


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    Looks pretty good. The slight posterization on the last image could probably be helped with a little monochromatic noise in post, which should look better than the colored noise from slog2. For low light I've been shooting with stock PP5. Also had good results with stock PP6 (16-235 vs. full 0-255 for PP5).


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    I dunno, it's hard to tell on these pictures - to me, on the bottom pic, the black square looks noisy on the right but the grey card and the seat cushion on the left look very noisy. Yet everything else the right side is noisy. Right side on the chair looking out the window the highlights outside are a lot clearer and the color of the grey card on the counter seems more pleasing...

    I guess my point is that there's clearly more noise in the right side blow up pics except for the last one, yet in the non-blown up pics, the right side overall looks better to me. So I'm confused a bit.


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    #4
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    Macgregor what gamma did you use? And what did you change the black the level too?


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    Senior Member macgregor's Avatar
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    Black level +15
    black gamma wide and all the way up too.
    I haven't played with the knee yet.
    Pro color.
    Give it a try if you can, so that we can all get an idea of what the best settings are.


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    I think you're on to something. I did a quick comparison with my non-log, go-to setting so far: gamma - cine1, black level - 0, black gamma - wide at -7, exposed properly, and there's about an extra stop of highlight detail with your setting, slightly better shadow detail, with almost no added noise.


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    Senior Member starcentral's Avatar
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    @macgregor - how did you end up matching the slog2 footage to cine4 in post?
    Dennis Hingsberg


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    We ended up doing something similar with the C100. Found 320iso is so much less noisy than log at 850, it was often worth using WDR and tweaking settings for more latitude (as needed - folks, you don't always need 12 stops!!!!) and the noise in blacks is much better. With the C100, always black balance when you can with ISO changes.


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    PS, that grey building on the bottom A/B looks dreadful. I can see why you've begun this experiment.


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    #10
    Senior Member starcentral's Avatar
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    It makes sense to have more apparent noise at higher ISO's in general, so if you want a cleaner slog you can rate the camera at 1000ISO over exposing everything by one stop and then lowering it one stop in post for an approximate 6db improvement. It eats into you highlights but 1-2 stops is not necessarily going to be a big deal. Especially if in fact the A7s is capable of 14 stops as some other tests have shown.
    Dennis Hingsberg


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