Converting ProRes 4444 material to ProRes 422 (HQ)

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Converting ProRes 4444 material to ProRes 422 (HQ)

Hi all-

I have a question that hopefully someone on here can answer. One of my company's clients is requesting that we shift to ProRes 4444 for mastering their features. Our workflow, for various reasons I dont want to get into on here, will be to capture the material from HDCAM-SR to ProRes 4444 and use that file as our top level master. I then will need to deliver a ProRes 422 HQ file to some of their vendors. An obvious workaround would be to do a second capture of this tape as 422HQ, but i would rather not tie up the machine for two captures.

The problem I am having is this, I cannot get ProRes 4444 to convert successfully to ProRes 422 HQ. For my tests I captured a set of 444 SMPTE bars as ProRes 4444. When i view this material on my scope it decodes properly, white is at 700mv and black is at 0mv. Additionally, the pluge is intact so I know that the system is not clipping any sub-blacks. All colors fall into place on the vectorscope as well.

I then take the 4444 material and export a QT file from the timeline (or compressor) to ProRes 422 HQ. The resulting material looks fine to the eye, but when you put it out to a scope the white values have dropped from 700mv down to around 650mv and the blacks have been raised from 0mv to around 50mv. Additionally, this conversion also effects the chroma values in the color bars. So it seems to me that there is some sort of strange gamma shift happening in the file conversion process and I cannot for the life of me figure out where to compensate for this. I messed with a number of settings in compressor but ultimately nothing worked. I searched through the forum and I couldnt find anything other than "you shouldnt be using 4444" because the source material was of lesser quality. I unfortunately have to use this codec and I am working from HDCAM-SR tapes recorded as 444 from film transfers or DI, so hopefully someone has a solution.

Thanks-

Holter

Final Cut Studio '09

Posted on May 19, 2011 5:15 PM

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Answer 1

Jim Cookman

Level 7

23,447 points

May 19, 2011 5:30 PM in response to Holter31007

Well... keep in mind that you are going from a stunning color space to a lesser one. I've not done this but common sense tells me that you'd be best off starting with the appropriate Advanced conversion in compressor.

Export a clip of about a minute-- bars and china girl or somesuch and start messing around with parameters, just like you have been doing. If you drill down you can find all the gamma corrections etc. Once you've got it the best you can get it, save the parameters as a preset.

I hope a better mind than mine will chime in here.

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Answer 2

Holter31007 Author

Level 1

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May 20, 2011 2:42 PM in response to Jim Cookman

Jim-

I spent the past two days on and off in between jobs running a section of bars through compressor to try to get the colorspace conversion to work but as of yet i have had no luck.

I know that I am dealing with a colorspace conversion, so there will be an effect on the final image, so a small chroma shift can be acceptable (although i would prefer no change). However, the crushing of the whites and lifting the blacks is where I draw the line of acceptability. I figured I would post on here to see if anyone else had any experience with this before I submitted anything to Apple. I was told this would work, and I know in some form it will be possible. For example, you can output a 422 format convert signal from an HDCAM-SR deck set to 444 and maintain 100% accurate color bars. I should be able to do this in software as well.

Thanks for your response, its appreciated.

Holter

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Answer 3

Meis

Level 1

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Jun 17, 2011 7:44 AM in response to Holter31007

I am having the same troubles. I have made several attempts at exporting from many different methods. (Export from Compressor, timeline, QT conversion, QT current settings switched to 422 HQ with automatic on & off...etc..). I always get the same color space change. Machine side is the only way to correctly change spaces. So far that is. Not given up.

Any takers?

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