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Joe Huggins
resolve render compressions
on Mar 21, 2012 at 3:02:02 pm

Resolve gurus,

If I am coloring an Avid 175 file, and render a color grade out in 175. Does that technically get 'recompressed' or does it pass through with the current compression with just a new color grade?

In FCP you could output 'using current settings' and not 'recompress' an edited piece. Is that similar in a color grade workflow. So the digital file is not 'loosing generations' each time a color grade is changed?

Thanks, Film Joe


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Mike Most
Re: resolve render compressions
on Mar 21, 2012 at 4:05:28 pm

Any image processing must of necessity take place on an uncompressed RGB frame. You can't perform transforms and other manipulations on compressed data because there's no real image information to use when it's in that form. So the short answer to your question is yes, everything that goes through Resolve - or any other grading system, VFX compositing software, or any effects creation (and that would include a simple dissolve in any editing software) gets decompressed, transformed, and then recompressed on output. The only way to do a "pass through," as you describe in Final Cut, is to do nothing to the image other than trim it. This eliminates the need to decompress because you're not manipulating any of the image information. That's also why a mixdown on an Avid can be done so quickly, because it's basically just rewrapping the already compressed information. But as I said, as soon as you want to do anything to the image itself that goes out the window.


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Joe Huggins
Re: resolve render compressions
on Mar 21, 2012 at 4:21:15 pm

Mike,

Thanks for the explaination. In your opinion, is there any significant or noticiable image degredation when color correction on Resolve is done to a 175x image? I assume it is nothing like an analog generational loss, but to decompress into RGB, and then export as 175x is that descernable to the eye or just to a detailed technical scope for instance? I guess most network TV shows work from Arri ProRes or Avid 175x camera originals; edit, then color before an air date. No networks complain about that recompression loss do they?

Thanks, Film Joe


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Juan Salvo
Re: resolve render compressions
on Mar 21, 2012 at 4:21:09 pm

As Mike said it does recompress. And I find when rendering out a color grade it does pay to export into a 10bit codec. Even of your source is 8bit. I'd recommend 220x.



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Mike Most
Re: resolve render compressions
on Mar 21, 2012 at 4:28:28 pm

220X is only for 60i material. 175X is the same level of compression for 24p material.

There are network shows that shall remain nameless that are posting, coloring, and delivering using DNxHD115, so if you think 175X has problems, consider that fact. I certainly don't recommend using something as heavily compressed as 115 for mastering, and I certainly don't recommend it for color correction purposes, but it's being done anyway, appalling though it may be. And on some very major projects. The race to the bottom continues....


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Joe Huggins
Re: resolve render compressions
on Mar 21, 2012 at 4:48:11 pm

Mike,
So I take it that 175x to 175x is not a quality issue. It would have to go through several compress and recompress stages (multiple color corrections) to be detectable? This material will be used for movie trailers and TV ads at some point. But I only make a daily grade, somoeone else may cut and do a final grade before it airs.

Thoughts?

Thanks, Film Joe


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Juan Salvo
Re: resolve render compressions
on Mar 21, 2012 at 5:03:05 pm

I'm aware. But resolve refers to it as 220.

Joe, 220x or 175x is a perfectly adequate mastering format for broadcast work. And would require several recompression cycles to show significant degradation of the image,



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Joe Huggins
Re: resolve render compressions
on Mar 21, 2012 at 5:51:50 pm

Thanks for the confirmation. That was my assumption but I wanted my techs to know for sure. Yes 175x is the 24p and 220x is 1080i, but the same compression format I would assume.

Thanks, Film Joe


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Joseph Owens
Re: resolve render compressions
on Mar 22, 2012 at 8:19:54 pm

[Mike Most] "There are network shows that shall remain nameless that are posting, coloring, and delivering using "

H264.

And what do you think a PVR is doing to it?

jPo

You mean "Old Ben"? Ben Kenobi?


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Mike Most
Re: resolve render compressions
on Mar 22, 2012 at 8:24:44 pm

I didn't say they were using H.264. I said they are using DNxHD 115. That's quite different.

As far as PVR goes, a PVR doesn't really do anything to the image. Ir records the off air compressed data and plays it back, in most cases.


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Lauri Laidna
Re: resolve render compressions
on Mar 22, 2012 at 9:54:27 pm

If you are interested in testing codec "quality" you can do multiple decode-encode cycles and stack the video files on top of each other and apply difference layer mode. Then boost exposure to see the difference better.

IMHO this is best way to analyze the codecs and see what they are doing to the picture and where.

Avid Media Composer | Adobe After Effects | DaVinci Resolve


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Joe Huggins
Re: resolve render compressions
on Mar 22, 2012 at 10:01:29 pm

Thanks for all the input. We will do. Best.

Thanks, Film Joe


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