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kyah

Working with ProRes 4444 from Alexa

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Hey everyone,

 

I have footage that I'm being asked to key, from an Alexa I'm told and the files are ProRes 4444.

 

When I import the files into after effects, no matter the bit depth in the project settings, I can't get a good key from this footage.

 

Whats weird to me is that when I put levels on and look at the histogram, its only using about 1/4 of the available range. This is true even for when the project is in 8 bit.

 

After doing a bunch of googling before asking here, it looks like there is a special quicktime thing available on their site, but I need a camera serial in order to download it?? Is there something I am missing here?

 

The footage appears as 'prores 4444 - trillions of colors', which I thought meant 16 or 32 bit. But no matter how I try to set the project or interpret the footage, keying this is horrible. Perhaps worse and harder than with minidv.

 

I received footage from those guys before but it went through a davinci before it got to me, as dpx files which was fine. This time, its media managed from fcp without transcoding, so I assume its straight from the camera.

 

I feel like there is some mystery codec or something I can't find that makes everything work how I imagine it to, but either can't find it, or found it on their website but it requires having a serial number to download it from the site. I can't see how restricting it to camera owners could possibly be the case.

 

By the way, I also found on a forum elsewhere that I am supposed to use the Apply LUT filter and load a file of some kind? But there is no such file provided and I'm just getting a blank stare when asking for it.

 

Quicktime is up to date, I can't find a log C codec and presume it just works with regular quicktime.

 

Thanks for any help with this.

 

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Your Alexa footage is probably in Log-c you should learn about what it is.

My guess is use lut buddy with a lut from Arri's website.

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Whats weird to me is that when I put levels on and look at the histogram, its only using about 1/4 of the available range. This is true even for when the project is in 8 bit.

 

 

 

It's mapping it's 14.7 stops of latitude to the bounds of video space. So unless your shot has something almost near the sun and a deep shadow underneath a car in the same shot, your data will look like it's using only part of the space avail. This is normal. You can mess with luts if you want. But just stick levels on it, Put the gamma to around .6 or .7 (to drop the gamma to closer to linear) and set the black and white points to where the used data is touching the bottom and top of the output range. Pre-comp this result then pull the key from that.

 

And DEFINITELY make sure you are working in at least 16 bit space. Stretching out that compressed data in 8 bit would destroy it. The only way that LogC / ProRes system works fairly well is that it needs a high bit depth to compress the full sensor latitude into an integer based format. Unlike RAW which is a floating point format.

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Thanks.

 

I initially tried pinching levels in 32 and 16 bit before asking here but it didn't make matters too much better. It helped, but I was still pulling my hair out. I will have to try out the rest of your suggestions, chris. I didn't precomp it, just stacked the keyer on top of that. And I didn't fiddle with the gamma either.

 

Using the LUT generator and guessing at the settings within it, I was able to get a much better key. I used video as the output, not linear. Went to rec 709. The files in the zip didn't seem to have any difference. I assumed that they were for different ISO settings or something, but they didn't look any different from eachother. I will have to load the footage up again and try linear to see what happens.

 

There were teals, aqua blues, and yellows in the shot that were causing headaches. Using Apply LUT with the .cube files from the Alexa site resolved all of that. I will have to read up on logC more thoroughly in between jobs to get a more comprehensive understanding of it because while those .cube files helped the key, it made the footage look horrible. Didn't matter for my use anyway, but I'd still like to know for in the future.

 

If receiving alexa footage in the future, should I request .cube files from them based on their camera settings, kinda like how RED works?

Edited by kyah

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You should also check how after effects handle your footage, 'interpretation' and color management or whatever it's called.

Some DP sometimes make a custom lut for the client monitor if they want something to go in a certain direction you can use them no prob.

 

 

A lut can contain any color transformations but you have to specify what colorspace is in and out.

You can download a trial for nuke and see how it should look. Put your footage in alexa colorspace grab a vectorfield node, and maybe an inverse gamma correction of .45 depending on your lut.

 

With this format it's not always easy to see it how it was intendedly shot.

Hopefully someday this will become popular for round tripping between applications

http://opencolorio.org/CompatibleSoftware.html

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