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Amira - Log vs 709

arri amira flat gamma rec. 709

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#1 James R Martin

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Posted 26 September 2014 - 04:51 AM

My team is about to take possession of an Amira. We’ve been renting for a while and shooting Log-C as standard.

I’m starting to question the merits of shooting Log. Typically we shoot product footage in a studio, with finely tuned and very controlled light. We really craft each shot – bread and butter shots are pretty low DR. Occasionally we go for dramatic contrast.

I’ve done a fair but of reading on the theory, pros, and cons of shooting Log, but I have to say I’m still not convinced either way. If I’m careful with clipping and try to get a healthy looking histogram/waveform, is Rec 709 just as good as Log, or in fact would it be better?


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#2 Freya Black

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Posted 26 September 2014 - 05:36 AM

My team is about to take possession of an Amira. We’ve been renting for a while and shooting Log-C as standard.

I’m starting to question the merits of shooting Log. Typically we shoot product footage in a studio, with finely tuned and very controlled light. We really craft each shot – bread and butter shots are pretty low DR. Occasionally we go for dramatic contrast.

I’ve done a fair but of reading on the theory, pros, and cons of shooting Log, but I have to say I’m still not convinced either way. If I’m careful with clipping and try to get a healthy looking histogram/waveform, is Rec 709 just as good as Log, or in fact would it be better?

 

Are you going to grade the footage in post?

If so shoot Log, if not then shoot Rec 709 and get it right on the day.

 

Freya


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#3 Freya Black

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Posted 26 September 2014 - 05:44 AM

To answer the question more bluntly, if you aren't going to be spending ages mucking about with the images in post (or for that matter someone else mucking around with the images in post but you get what I mean) then Rec 709 will always be better unless you are intending to shoot log for effect in some way.

 

Freya


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#4 James R Martin

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Posted 26 September 2014 - 05:46 AM

Yeah - I'll be grading either way.


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#5 David Mullen ASC

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Posted 26 September 2014 - 10:01 AM

If you can control your brightest highlights with careful lighting and the way it looks in Rec.709 on the monitor is good for the final look, then Log-C is probably not necessary. It's just that with a Log image, in post you have more options to control how smoothly your whites burn out and can even use luminance keys to control detail in selected hot spots, whereas if you record Rec.709, you basically have fewer stops of overexposure information to work with in post.

There is also that Low-Contrast Rec.709 option for people who want to record Rec.709 but want a slightly flatter image in post for color-correction.

Personally I find that the roll-off to white when a camera is switched to Rec.709 from Log always looks a bit video-ish when you look at things like bright lampshades but perhaps the Alexa is different, I just noticed that with the Genesis/F35.
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#6 James R Martin

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Posted 26 September 2014 - 02:12 PM

Thanks David! Is that control of highlights in post at the expense of mids and shadows? I sometimes feel like that is the case when grading low DR log footage.
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#7 David Mullen ASC

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Posted 26 September 2014 - 04:15 PM

Not if your colorist knows how to grade Log footage. If he's just adding contrast to a flat Log image as if it were just a really low-contrast Rec.709 image rather than starting with a proper Log-to-Rec.709 LUT then he may have some issues.
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#8 Bruce Greene

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Posted 27 September 2014 - 06:32 PM

Sorry, I haven't used the Amira yet...

But with the Alexa, REC709 is rather low contrast compared to "broadcast" video. There is a bit of highlight roll off built in, which you might compensate for by lighting with a high contrast. So you will need to watch that on the waveform and may even find that you still need to perform color grading to get your optimal image. Just not starting from the log curve.

Further, in LOG mode, one still may want to use the Arri LUTs to convert the image to 709 as there is still some color matrix yet to add for the "Alexa" look. It may well also be the case that you will want to use an Arri LUT to apply this matrix from Arri 709 to video 709. But I'm not sure as I've always used LOG with the Alexa.
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#9 Albion Hockney

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Posted 28 September 2014 - 12:09 AM

I dont think Log C is something to talked about as necessary or not. There is a reason that camera's of differnt technology grades look better or worse and latitude is a huge part of that reason. 

 

 

Latitude is not just shown in the way you light. in other words just because you condense your DR by lighting flat that doesnt mean you are not going to benefit from having the latitude.

your picture will have greater subtilities in contrast in LOG C.

 

 

 

the only reason I could see not to shoot log is if you were shooting for a quick turnaround with out a color grade....I can't see there being a benefit to the rec 709 curve at all.


Edited by Albion Hockney, 28 September 2014 - 12:11 AM.

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#10 James R Martin

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Posted 29 September 2014 - 04:57 AM

Thanks all. Some useful thoughts and advise there.

 

Might to do some side by side comparisons just for fun when I've got some time.


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#11 Freya Black

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Posted 29 September 2014 - 08:17 AM


the only reason I could see not to shoot log is if you were shooting for a quick turnaround with out a color grade....I can't see there being a benefit to the rec 709 curve at all.

 

A related issue other than time can be cost, although as Bruce points out you could possibly just apply a LUT or similar at a later date if you are looking for a simple alternative to a proper grade.

 

Freya


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#12 David Mullen ASC

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Posted 29 September 2014 - 10:31 AM

If you shoot a test, put a small lampshade or candle flame in the shot to see how it rolls off to white.  I've found on the older cameras that things round off more smoothly to the clip point if working from a log image to create Rec.709, the in-camera Rec.709 setting tends to truncate detail in whites more abruptly.  But as I said, I haven't tested the Alexa in that regards since I've only shot log with it.


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#13 John Miguel King

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Posted 14 October 2014 - 05:07 AM

This truly is, and I'm definitely not trying to be arrogant, a non problem. In answer to your question, 709 cannot be any better than Log.

 

If it is speed that you're after all you need is a 3d LUT in your post pipeline. All major NLEs have the capability of applying a 3d Lut, so it's just a matter of dropping the effect on the clip/sequence. What is more, the 709 that Arri provides is just their interpretation of a Log to Lin colour transform, and not a very good one at that. As Mr. Mullen says, Arri's LUT condenses the highlights just a bit too much. I'd add that it also crushes the blacks.

Never, in my DIT work, do I use Arri's LUT. When going for a "one size fits all" I either use the one created by the guys at Assimilate or work in ACES colourspace. Assimilate's is as contrasty and saturated as Arri's, but both knee and shoulder are much much softer. In all other cases, when time has been allotted to work on looks, I use the LUTs created during prep for each job.

To finish this, shooting in Log gives you the awesome opportunity of creating your very own luts and looks.

 

Log is freedom!


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